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Special Relativity
Newton's laws of motion give us a complete description of the behavior moving objects at low speeds. The laws are different at speeds reached by the particles at SLAC.
Einstein's Special Theory of Relativity describes the motion of particles moving at close to the speed of light. In fact, it gives the correct laws of motion for any particle. This doesn't mean Newton was wrong, his equations are contained within the relativistic equations. Newton's "laws" provide a very good approximate form, valid when v is much less than c. For particles moving at slow speeds (very much less than the speed of light), the differences between Einstein's laws of motion and those derived by Newton are tiny. That's why relativity doesn't play a large role in everyday life. Einstein's theory supercedes Newton's, but Newton's theory provides a very good approximation for objects moving at everyday speeds.
Einstein's theory is now very well established as the correct description of motion of relativistic objects, that is those traveling at a significant fraction of the speed of light.
Because most of us have little experience with objects moving at speeds near the speed of light, Einstein's predictions may seem strange. However, many years of high energy physics experiments have thoroughly tested Einstein's theory and shown that it fits all results to date.
t1theory.gif (1444 bytes)
Theoretical Basis for Special Relativity
Einstein's theory of special relativity results from two statements -- the two basic postulates of special relativity:
1. The speed of light is the same for all observers, no matter what their relative speeds.
2. The laws of physics are the same in any inertial (that is, non-accelerated) frame of reference. This means that the laws of physics observed by a hypothetical observer traveling with a relativistic particle must be the same as those observed by an observer who is stationary in the laboratory.
Given these two statements, Einstein showed how definitions of momentum and energy must be refined and how quantities such as length and time must change from one observer to another in order to get consistent results for physical quantities such as particle half-life. To decide whether his postulates are a correct theory of nature, physicists test whether the predictions of Einstein's theory match observations. Indeed many such tests have been made -- and the answers Einstein gave are right every time!
theory-bullet.gif (1023 bytes)The Speed of Light is the same for all observers.
The first postulate -- the speed of light will be seen to be the same relative to any observer, independent of the motion of the observer -- is the crucial idea that led Einstein to formulate his theory. It means we can define a quantity c, the speed of light, which is a fundamental constant of nature.
Note that this is quite different from the motion of ordinary, massive objects. If I am driving down the freeway at 50 miles per hour relative to the road, a car traveling in the same direction at 55 mph has a speed of only 5 mph relative to me, while a car coming in the opposite direction at 55 mph approaches me at a rate of 105 mph. Their speed relative to me depends on my motion as well as on theirs.
theory-bullet.gif (1023 bytes)Physics is the same for all inertial observers.
This second postulate is really a basic though unspoken assumption in all of science -- the idea that we can formulate rules of nature which do not depend on our particular observing situation. This does not mean that things behave in the same way on the earth and in space, e.g. an observer at the surface of the earth is affected by the earth's gravity, but it does mean that the effect of a force on an object is the same independent of what causes the force and also of where the object is or what its speed is.
Einstein developed a theory of motion that could consistently contain both the same speed of light for any observer and the familiar addition of velocities described above for slow-moving objects. This is called the special theory of relativity, since it deals with the relative motions of objects.
Note that Einstein's General Theory of Relativity is a separate theory about a very different topic -- the effects of gravity.
t1theory.gif (1444 bytes)
Relativistic Definitions
Physicists call particles with v/c comparable to 1 "relativistic" particles. Particles with v/c << 1 (very much less than one) are "non-relativistic." At SLAC, we are almost always dealing with relativistic particles. Below we catalogue some essential differences between the relativistic quantities the more familiar non-relativistic or low-speed approximate definitions and behaviors.
theory-bullet.gif (1023 bytes)Gamma (Gamma Symbol)
The measurable effects of relativity are based on gamma. Gamma depends only on the speed of a particle and is always larger than 1. By definition:
Equation relating speed of light, speed of object and constant, gamma c is the speed of light
v is the speed of the object in question
For example, when an electronGlossary Term has traveled ten feet along the acceleratorGlossary Term is has a speed of 0.99c, and the value of gamma at that speed is 7.09. When the electron reaches the end of the linac, its speed is 0.99999999995c where gamma equals 100,000.
What do these gamma values tell us about the relativistic effects detected at SLAC? Notice that when the speed of the object is very much less than the speed of light (v << c), gamma is approximately equal to 1. This is a non-relativistic situation (Newtonian).
theory-bullet.gif (1023 bytes)Momentum
For non-relativistic objects Newton defined momentum, given the symbol p, as the product of mass and velocity -- p = m v. When speed becomes relativistic, we have to modify this definition -- p = gamma (mv)
Notice that this equation tells you that for any particle with a non-zero mass, the momentum gets larger and larger as the speed gets closer to the speed of light. Such a particle would have infinite momentum if it could reach the speed of light. Since it would take an infinite amount of force (or a finite force acting over an infinite amount of time) to accelerate a particle to infinite momentum, we are forced to conclude that a massive particle always travels at speeds less than the speed of light.
Some text books will introduce the definition m0 for the mass of an object at rest, calling this the "rest mass" and define the quantity (M = gamma m0) as the mass of the moving object. This makes Newton's definition of momentum still true provided you choose the correct mass. In particle physics, when we talk about mass we always mean mass of an object at rest and we write it as m and keep the factor of gamma explicit in the equations.
theory-bullet.gif (1023 bytes)Energy
Probably the most famous scientific equation of all time, first derived by Einstein is the relationship E = mc2.
This tells us the energy corresponding to a mass m at rest. What this means is that when mass disappears, for example in a nuclear fission process, this amount of energy must appear in some other form. It also tells us the total energy of a particle of mass m sitting at rest.
Einstein also showed that the correct relativistic expression for the energy of a particle of mass m with momentum p is E2 = m2c4 + p2c2. This is a key equation for any real particle, giving the relationship between its energy (E), momentum ( p), and its rest mass (m).
If we substitute the equation for p into the equation for E above, with a little algebra, we get E = gamma mc2, so energy is gamma times rest energy. (Notice again that if we call the quantity M =gamma m the mass of the particle then E = Mc2 applies for any particle, but remember, particle physicists don't do that.)
Let's do a calculation. The rest energy of an electron is 0.511 MeV. As we saw earlier, when an electron has gone about 10 feet along the SLAC linac, it has a speed of 0.99c and a gamma of 7.09. Therefore, using the equation E = gamma x the rest energy, we can see that the electron's energy after ten feet of travel is 7.09 x 0.511 MeV = 3.62 MeV. At the end of the linac, where gamma = 100,000, the energy of the electron is 100,000 x 0.511 MeV = 51.1 GeV.
The energy E is the total energy of a freely moving particle. We can define it to be the rest energy plus kinetic energy (E = KE + mc2) which then defines a relativistic form for kinetic energy. Just as the equation for momentum has to be altered, so does the low-speed equation for kinetic energy (KE = (1/2)mv2). Let's make a guess based on what we saw for momentum and energy and say that relativistically KE = gamma(1/2)mv2. A good guess, perhaps, but it's wrong.
Now here is an exercise for the interested reader. Calculate the quantity KE = E - mc2 for the case of v very much smaller than c, and show that it is the usual expression for kinetic energy (1/2 mv2) plus corrections that are proportional to (v/c)2 and higher powers of (v/c). The complicated result of this exercise points out why it is not useful to separate the energy of a relativistic particle into a sum of two terms, so when particle physicists say "the energy of a moving particle" they mean the total energy, not the kinetic energy.
Another interesting fact about the expression that relates E and p above (E2 = m2c4 + p2c2), is that it is also true for the case where a particle has no mass (m=0). In this case, the particle always travels at a speed c, the speed of light. You can regard this equation as a definition of momentum for such a mass-less particle. Photons have kinetic energy and momentum, but no mass!
In fact Einstein's relationship tells us more, it says Energy and mass are interchangeable. Or, better said, rest mass is just one form of energy. For a compound object, the mass of the composite is not just the sum of the masses of the constituents but the sum of their energies, including kinetic, potential, and mass energy. The equation E=mc2 shows how to convert between energy units and mass units. Even a small mass corresponds to a significant amount of energy.
* In the case of an atomic explosion, mass energy is released as kinetic energy of the resulting material, which has slightly less mass than the original material.
* In any particle decayGlossary Term process, some of the initial mass energy becomes kinetic energy of the products.
Even in chemical processes there are tiny changes in mass which correspond to the energy released or absorbed in a process. When chemists talk about conservation of mass, they mean that the sum of the masses of the atoms involved does not change. However, the masses of molecules are slightly smaller than the sum of the masses of the atoms they contain (which is why molecules do not just fall apart into atoms). If we look at the actual molecular masses, we find tiny mass changes do occur in any chemical reaction.
At SLAC, and in any particle physics facility, we also see the reverse effect -- energy producing new matter. In the presence of charged particles a photon (which only has kinetic energy) can change into a massive particle and its matching massive antiparticle. The extra charged particle has to be there to absorb a little energy and more momentum, otherwise such a process could not conserve both energy and momentum. This process is one more confirmation of Einstein's special theory of relativity. It also is the process by which antimatterGlossary Term (for example the positrons accelerated at SLAC) is produced.
t1theory.gif (1444 bytes)
Units of Mass, Energy, and Momentum
Instead of using kilograms to measure mass, physicists use a unit of energy -- the electron volt. It is the energy gained by one electron when it moves through a potential difference of one volt. By definition, one electron volt (eVGlossary Term) is equivalent to 1.6 x 10-19 joules.
Lets look at an example of how this energy unit works. The rest mass of an electron is 9.11 x 10-31 kg. Using E = mc2 and a calculator we get:
E = 9.11 x 10-31 kg x (3 x 108 m/s)2 = 8.199 x 10-14 joules
This gives us the energy equivalent of one electron. So, whether we say we have 9.11 x 10-31 kg or 8.199 x 10-14 joules, we really talking about the same thing -- an electron. Physicists go one stage further and convert the joules to electron volts. This gives the mass of an electron as 0.511 MeV (about half a million eV).
So if you ask a high energy physicist what the mass of an electron is, you'll be told the answer in units of energy. You can blame Einstein for that!
Eagle-eyed readers will notice that if you solve E=mc2 for m, you get m=E/c2, so the unit of energy should be eV/c2. What happened to the c2? It's very simple, particle physicists choose units of length so that the speed of light = 1! How can we do that? Quite easily, as long as everyone understands the system. All we have to do is use a conversion factor to get back the "real" (i.e. everyday) units, if we want them.
Not only are mass and energy measured in eV, so is momentum. It makes life so much easier than dividing by c2 or c all the time.
There is more information available on units in relativistic physics.
t1theory.gif (1444 bytes)
Peculiar Relativistic Effects
theory-bullet.gif (1023 bytes) Length Contraction and Time Dilation
One of the strangest parts of special relativity is the conclusion that two observers who are moving relative to one another, will get different measurements of the length of a particular object or the time that passes between two eventsGlossary Term.
Consider two observers, each in a space-ship laboratory containing clocks and meter sticks. The space ships are moving relative to each other at a speed close to the speed of light. Using Einstein's theory:
* Each observer will see the meter stick of the other as shorter than their own, by the same factor gamma (gamma- defined above). This is called length contraction.
* Each observer will see the clocks in the other laboratory as ticking more slowly than the clocks in his/her own, by a factor gamma. This is called time dilation.
In particle acceleratorsGlossary Term, particles are moving very close to the speed of light where the length and time effects are large. This has allowed us to clearly verify that length contraction and time dilation do occur.
theory-bullet.gif (1023 bytes) Time Dilation for Particles
Particle processes have an intrinsic clock that determines the half-life of a decay process. However, the rate at which the clock ticks in a moving frame, as observed by a static observer, is slower than the rate of a static clock. Therefore, the half-life of a moving particles appears, to the static observer, to be increased by the factor gamma.
For example, let's look at a particle sometimes created at SLAC known as a tau. In the frame of reference where the tau particle is at rest, its lifetime is known to be approximately 3.05 x 10-13 s. To calculate how far it travels before decaying, we could try to use the familiar equation distance equals speed times time. It travels so close to the speed of light that we can use c = 3x108 m/sec for the speed of the particle. (As we will see below, the speed of light in a vacuum is the highest speed attainable.) If you do the calculation you find the distance traveled should be 9.15 x 10-5 meters.
d = v t
d = (3 x 108 m/sec)( 3.05 x 10-13 s) = 9.15 x 10-5 m
Here comes the weird part - we measure the tau particle to travel further than this!
Pause to think about that for a moment. This result is totally contradictory to everyday experience. If you are not puzzled by it, either you already know all about relativity or you have not been reading carefully.
What is the resolution of this apparent paradox? The answer lies in time dilation. In our laboratory, the tau particle is moving. The decay time of the tau can be seen as a moving clock. According to relativity, moving clocks tick more slowly than static clocks.
We use this fact to multiply the time of travel in the taus moving frame by gamma, this gives the time that we will measure. Then this time times c, the approximate speed of the tau, will give us the distance we expect a high energy tau to travel.
What is gamma in this case? It depends on the tau's energy. A typical SLAC tau particle has a gamma = 20. Therefore, we detect the tau to decay in an average distance of 20 x (9.15 x 10-5 m) = 1.8 x 10-3 m or approximately 1.8 millimeters. This is 20 times further than we expect it to go if we use classical rather than relativistic physics. (Of course, we actually observe a spread of decay times according to the exponential decay law and a corresponding spread of distances. In fact, we use the measured distribution of distances to find the tau half-life.)
Observations particles with a variety of velocities have shown that time dilation is a real effect. In fact the only reason cosmic ray muons ever reach the surface of the earth before decaying is the time dilation effect.
theory-bullet.gif (1023 bytes) Length Contraction
Instead of analyzing the motion of the tau from our frame of reference, we could ask what the tau would see in its reference frame. Its half-life in its reference frame is 3.05 x 10-13 s. This does not change. The tau goes nowhere in this frame.
How far would an observer, sitting in the tau rest frame, see an observer in our laboratory frame move while the tau lives?
We just calculated that the tau would travel 1.8 mm in our frame of reference. Surely we would expect the observer in the tau frame to see us move the same distance relative to the tau particle. Not so says the tau-frame observer -- you only moved 1.8 mm/gamma = 0.09 mm relative to me. This is length contraction.
How long did the tau particle live according to the observer in the tau frame? We can rearrange d = v x t to read t = d/v. Here we use the same speed, Because the speed of the observer in the lab relative to the tau is just equal to (but in the opposite direction) of the speed of the tau relative to the observer in the lab, so we can use the same speed. So time = 0.09 x 10-3 m/(3 x 108)m/sec = 3.0 x 10-13 sec. This is the half-life of the tau as seen in its rest frame, just as it should be!
ha!
Special Relativity
Newton's laws of motion give us a complete description of the behavior moving objects at low speeds. The laws are different at speeds reached by the particles at SLAC.
Einstein's Special Theory of Relativity describes the motion of particles moving at close to the speed of light. In fact, it gives the correct laws of motion for any particle. This doesn't mean Newton was wrong, his equations are contained within the relativistic equations. Newton's "laws" provide a very good approximate form, valid when v is much less than c. For particles moving at slow speeds (very much less than the speed of light), the differences between Einstein's laws of motion and those derived by Newton are tiny. That's why relativity doesn't play a large role in everyday life. Einstein's theory supercedes Newton's, but Newton's theory provides a very good approximation for objects moving at everyday speeds.
Einstein's theory is now very well established as the correct description of motion of relativistic objects, that is those traveling at a significant fraction of the speed of light.
Because most of us have little experience with objects moving at speeds near the speed of light, Einstein's predictions may seem strange. However, many years of high energy physics experiments have thoroughly tested Einstein's theory and shown that it fits all results to date.
t1theory.gif (1444 bytes)
Theoretical Basis for Special Relativity
Einstein's theory of special relativity results from two statements -- the two basic postulates of special relativity:
1. The speed of light is the same for all observers, no matter what their relative speeds.
2. The laws of physics are the same in any inertial (that is, non-accelerated) frame of reference. This means that the laws of physics observed by a hypothetical observer traveling with a relativistic particle must be the same as those observed by an observer who is stationary in the laboratory.
Given these two statements, Einstein showed how definitions of momentum and energy must be refined and how quantities such as length and time must change from one observer to another in order to get consistent results for physical quantities such as particle half-life. To decide whether his postulates are a correct theory of nature, physicists test whether the predictions of Einstein's theory match observations. Indeed many such tests have been made -- and the answers Einstein gave are right every time!
theory-bullet.gif (1023 bytes)The Speed of Light is the same for all observers.
The first postulate -- the speed of light will be seen to be the same relative to any observer, independent of the motion of the observer -- is the crucial idea that led Einstein to formulate his theory. It means we can define a quantity c, the speed of light, which is a fundamental constant of nature.
Note that this is quite different from the motion of ordinary, massive objects. If I am driving down the freeway at 50 miles per hour relative to the road, a car traveling in the same direction at 55 mph has a speed of only 5 mph relative to me, while a car coming in the opposite direction at 55 mph approaches me at a rate of 105 mph. Their speed relative to me depends on my motion as well as on theirs.
theory-bullet.gif (1023 bytes)Physics is the same for all inertial observers.
This second postulate is really a basic though unspoken assumption in all of science -- the idea that we can formulate rules of nature which do not depend on our particular observing situation. This does not mean that things behave in the same way on the earth and in space, e.g. an observer at the surface of the earth is affected by the earth's gravity, but it does mean that the effect of a force on an object is the same independent of what causes the force and also of where the object is or what its speed is.
Einstein developed a theory of motion that could consistently contain both the same speed of light for any observer and the familiar addition of velocities described above for slow-moving objects. This is called the special theory of relativity, since it deals with the relative motions of objects.
Note that Einstein's General Theory of Relativity is a separate theory about a very different topic -- the effects of gravity.
t1theory.gif (1444 bytes)
Relativistic Definitions
Physicists call particles with v/c comparable to 1 "relativistic" particles. Particles with v/c << 1 (very much less than one) are "non-relativistic." At SLAC, we are almost always dealing with relativistic particles. Below we catalogue some essential differences between the relativistic quantities the more familiar non-relativistic or low-speed approximate definitions and behaviors.
theory-bullet.gif (1023 bytes)Gamma (Gamma Symbol)
The measurable effects of relativity are based on gamma. Gamma depends only on the speed of a particle and is always larger than 1. By definition:
Equation relating speed of light, speed of object and constant, gamma c is the speed of light
v is the speed of the object in question
For example, when an electronGlossary Term has traveled ten feet along the acceleratorGlossary Term is has a speed of 0.99c, and the value of gamma at that speed is 7.09. When the electron reaches the end of the linac, its speed is 0.99999999995c where gamma equals 100,000.
What do these gamma values tell us about the relativistic effects detected at SLAC? Notice that when the speed of the object is very much less than the speed of light (v << c), gamma is approximately equal to 1. This is a non-relativistic situation (Newtonian).
theory-bullet.gif (1023 bytes)Momentum
For non-relativistic objects Newton defined momentum, given the symbol p, as the product of mass and velocity -- p = m v. When speed becomes relativistic, we have to modify this definition -- p = gamma (mv)
Notice that this equation tells you that for any particle with a non-zero mass, the momentum gets larger and larger as the speed gets closer to the speed of light. Such a particle would have infinite momentum if it could reach the speed of light. Since it would take an infinite amount of force (or a finite force acting over an infinite amount of time) to accelerate a particle to infinite momentum, we are forced to conclude that a massive particle always travels at speeds less than the speed of light.
Some text books will introduce the definition m0 for the mass of an object at rest, calling this the "rest mass" and define the quantity (M = gamma m0) as the mass of the moving object. This makes Newton's definition of momentum still true provided you choose the correct mass. In particle physics, when we talk about mass we always mean mass of an object at rest and we write it as m and keep the factor of gamma explicit in the equations.
theory-bullet.gif (1023 bytes)Energy
Probably the most famous scientific equation of all time, first derived by Einstein is the relationship E = mc2.
This tells us the energy corresponding to a mass m at rest. What this means is that when mass disappears, for example in a nuclear fission process, this amount of energy must appear in some other form. It also tells us the total energy of a particle of mass m sitting at rest.
Einstein also showed that the correct relativistic expression for the energy of a particle of mass m with momentum p is E2 = m2c4 + p2c2. This is a key equation for any real particle, giving the relationship between its energy (E), momentum ( p), and its rest mass (m).
If we substitute the equation for p into the equation for E above, with a little algebra, we get E = gamma mc2, so energy is gamma times rest energy. (Notice again that if we call the quantity M =gamma m the mass of the particle then E = Mc2 applies for any particle, but remember, particle physicists don't do that.)
Let's do a calculation. The rest energy of an electron is 0.511 MeV. As we saw earlier, when an electron has gone about 10 feet along the SLAC linac, it has a speed of 0.99c and a gamma of 7.09. Therefore, using the equation E = gamma x the rest energy, we can see that the electron's energy after ten feet of travel is 7.09 x 0.511 MeV = 3.62 MeV. At the end of the linac, where gamma = 100,000, the energy of the electron is 100,000 x 0.511 MeV = 51.1 GeV.
The energy E is the total energy of a freely moving particle. We can define it to be the rest energy plus kinetic energy (E = KE + mc2) which then defines a relativistic form for kinetic energy. Just as the equation for momentum has to be altered, so does the low-speed equation for kinetic energy (KE = (1/2)mv2). Let's make a guess based on what we saw for momentum and energy and say that relativistically KE = gamma(1/2)mv2. A good guess, perhaps, but it's wrong.
Now here is an exercise for the interested reader. Calculate the quantity KE = E - mc2 for the case of v very much smaller than c, and show that it is the usual expression for kinetic energy (1/2 mv2) plus corrections that are proportional to (v/c)2 and higher powers of (v/c). The complicated result of this exercise points out why it is not useful to separate the energy of a relativistic particle into a sum of two terms, so when particle physicists say "the energy of a moving particle" they mean the total energy, not the kinetic energy.
Another interesting fact about the expression that relates E and p above (E2 = m2c4 + p2c2), is that it is also true for the case where a particle has no mass (m=0). In this case, the particle always travels at a speed c, the speed of light. You can regard this equation as a definition of momentum for such a mass-less particle. Photons have kinetic energy and momentum, but no mass!
In fact Einstein's relationship tells us more, it says Energy and mass are interchangeable. Or, better said, rest mass is just one form of energy. For a compound object, the mass of the composite is not just the sum of the masses of the constituents but the sum of their energies, including kinetic, potential, and mass energy. The equation E=mc2 shows how to convert between energy units and mass units. Even a small mass corresponds to a significant amount of energy.
* In the case of an atomic explosion, mass energy is released as kinetic energy of the resulting material, which has slightly less mass than the original material.
* In any particle decayGlossary Term process, some of the initial mass energy becomes kinetic energy of the products.
Even in chemical processes there are tiny changes in mass which correspond to the energy released or absorbed in a process. When chemists talk about conservation of mass, they mean that the sum of the masses of the atoms involved does not change. However, the masses of molecules are slightly smaller than the sum of the masses of the atoms they contain (which is why molecules do not just fall apart into atoms). If we look at the actual molecular masses, we find tiny mass changes do occur in any chemical reaction.
At SLAC, and in any particle physics facility, we also see the reverse effect -- energy producing new matter. In the presence of charged particles a photon (which only has kinetic energy) can change into a massive particle and its matching massive antiparticle. The extra charged particle has to be there to absorb a little energy and more momentum, otherwise such a process could not conserve both energy and momentum. This process is one more confirmation of Einstein's special theory of relativity. It also is the process by which antimatterGlossary Term (for example the positrons accelerated at SLAC) is produced.
t1theory.gif (1444 bytes)
Units of Mass, Energy, and Momentum
Instead of using kilograms to measure mass, physicists use a unit of energy -- the electron volt. It is the energy gained by one electron when it moves through a potential difference of one volt. By definition, one electron volt (eVGlossary Term) is equivalent to 1.6 x 10-19 joules.
Lets look at an example of how this energy unit works. The rest mass of an electron is 9.11 x 10-31 kg. Using E = mc2 and a calculator we get:
E = 9.11 x 10-31 kg x (3 x 108 m/s)2 = 8.199 x 10-14 joules
This gives us the energy equivalent of one electron. So, whether we say we have 9.11 x 10-31 kg or 8.199 x 10-14 joules, we really talking about the same thing -- an electron. Physicists go one stage further and convert the joules to electron volts. This gives the mass of an electron as 0.511 MeV (about half a million eV).
So if you ask a high energy physicist what the mass of an electron is, you'll be told the answer in units of energy. You can blame Einstein for that!
Eagle-eyed readers will notice that if you solve E=mc2 for m, you get m=E/c2, so the unit of energy should be eV/c2. What happened to the c2? It's very simple, particle physicists choose units of length so that the speed of light = 1! How can we do that? Quite easily, as long as everyone understands the system. All we have to do is use a conversion factor to get back the "real" (i.e. everyday) units, if we want them.
Not only are mass and energy measured in eV, so is momentum. It makes life so much easier than dividing by c2 or c all the time.
There is more information available on units in relativistic physics.
t1theory.gif (1444 bytes)
Peculiar Relativistic Effects
theory-bullet.gif (1023 bytes) Length Contraction and Time Dilation
One of the strangest parts of special relativity is the conclusion that two observers who are moving relative to one another, will get different measurements of the length of a particular object or the time that passes between two eventsGlossary Term.
Consider two observers, each in a space-ship laboratory containing clocks and meter sticks. The space ships are moving relative to each other at a speed close to the speed of light. Using Einstein's theory:
* Each observer will see the meter stick of the other as shorter than their own, by the same factor gamma (gamma- defined above). This is called length contraction.
* Each observer will see the clocks in the other laboratory as ticking more slowly than the clocks in his/her own, by a factor gamma. This is called time dilation.
In particle acceleratorsGlossary Term, particles are moving very close to the speed of light where the length and time effects are large. This has allowed us to clearly verify that length contraction and time dilation do occur.
theory-bullet.gif (1023 bytes) Time Dilation for Particles
Particle processes have an intrinsic clock that determines the half-life of a decay process. However, the rate at which the clock ticks in a moving frame, as observed by a static observer, is slower than the rate of a static clock. Therefore, the half-life of a moving particles appears, to the static observer, to be increased by the factor gamma.
For example, let's look at a particle sometimes created at SLAC known as a tau. In the frame of reference where the tau particle is at rest, its lifetime is known to be approximately 3.05 x 10-13 s. To calculate how far it travels before decaying, we could try to use the familiar equation distance equals speed times time. It travels so close to the speed of light that we can use c = 3x108 m/sec for the speed of the particle. (As we will see below, the speed of light in a vacuum is the highest speed attainable.) If you do the calculation you find the distance traveled should be 9.15 x 10-5 meters.
d = v t
d = (3 x 108 m/sec)( 3.05 x 10-13 s) = 9.15 x 10-5 m
Here comes the weird part - we measure the tau particle to travel further than this!
Pause to think about that for a moment. This result is totally contradictory to everyday experience. If you are not puzzled by it, either you already know all about relativity or you have not been reading carefully.
What is the resolution of this apparent paradox? The answer lies in time dilation. In our laboratory, the tau particle is moving. The decay time of the tau can be seen as a moving clock. According to relativity, moving clocks tick more slowly than static clocks.
We use this fact to multiply the time of travel in the taus moving frame by gamma, this gives the time that we will measure. Then this time times c, the approximate speed of the tau, will give us the distance we expect a high energy tau to travel.
What is gamma in this case? It depends on the tau's energy. A typical SLAC tau particle has a gamma = 20. Therefore, we detect the tau to decay in an average distance of 20 x (9.15 x 10-5 m) = 1.8 x 10-3 m or approximately 1.8 millimeters. This is 20 times further than we expect it to go if we use classical rather than relativistic physics. (Of course, we actually observe a spread of decay times according to the exponential decay law and a corresponding spread of distances. In fact, we use the measured distribution of distances to find the tau half-life.)
Observations particles with a variety of velocities have shown that time dilation is a real effect. In fact the only reason cosmic ray muons ever reach the surface of the earth before decaying is the time dilation effect.
theory-bullet.gif (1023 bytes) Length Contraction
Instead of analyzing the motion of the tau from our frame of reference, we could ask what the tau would see in its reference frame. Its half-life in its reference frame is 3.05 x 10-13 s. This does not change. The tau goes nowhere in this frame.
How far would an observer, sitting in the tau rest frame, see an observer in our laboratory frame move while the tau lives?
We just calculated that the tau would travel 1.8 mm in our frame of reference. Surely we would expect the observer in the tau frame to see us move the same distance relative to the tau particle. Not so says the tau-frame observer -- you only moved 1.8 mm/gamma = 0.09 mm relative to me. This is length contraction.
How long did the tau particle live according to the observer in the tau frame? We can rearrange d = v x t to read t = d/v. Here we use the same speed, Because the speed of the observer in the lab relative to the tau is just equal to (but in the opposite direction) of the speed of the tau relative to the observer in the lab, so we can use the same speed. So time = 0.09 x 10-3 m/(3 x 108)m/sec = 3.0 x 10-13 sec. This is the half-life of the tau as seen in its rest frame, just as it should be!
ha!
NandP
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Deepening the quantum mysteries
The "central mystery" of quantum physics just got more mysterious. Experimenters from the United States and Austria have got together to provide a new demonstration of how light going through a "double slit" experiment seems to know before it sets out in its journey exactly what kind of traps have been set for it along the way.
This is a variation on the Young's slit experiment, familiar from school laboratory demonstrations of the wave nature of light. When a beam of monochromatic light is shone through two narrow holes in a screen, the light spreading out from the two holes interferes, just like ripples interfering on the surface of a pond, to produce a characteristic pattern on a second screen.
The mystery is that light can also be described as a stream of particles, called photons. The light source in a Young's slit experiment can be turned down to the point where it consists of individual photons going through the experiment, one after the other. If the spots of light made by individual photons arriving at the second screen (actually a photoelectric detector) are added together, they still form an interference pattern, as if each photon goes through both holes and interferes with itself on the way through the experiment. It was Richard Feynman who described this as "the central mystery" of quantum theory, and then corrected himself, saying that in fact it is "the only mystery". If you understood this, you would understand quantum physics -- but as Feynman also said, "nobody understands quantum mechanics" (The Character of Physical Law, BBC Publications, 1965).
The new demonstration of how incomprehensible the quantum world is has been made by Raymond Chiao, of the University of California, Berkeley, Paul Kwiat, of the University of Innsbruck, and Aephraim Steinberg, of the US National Institute of Standards and Technology, in Maryland. Their results were presented at a meeting in Nathiagali, Pakistan.
In fact, the team has carried out several tests of the stranger predictions of quantum theory, but the most dramatic is what they call the "quantum eraser". In this variation on the Young's slit theme, the experiment is first set up in the usual way, and run to produce interference. Quantum theory says that the reason why interference can occur, even if light is a stream of photons, is that there is no way to find out, even in principle, which photon went through which slit. The "indeterminacy" allows fringes to appear.
But then Chiao and his colleagues ran the same experiment with polarising filters in front of each of the two slits. Any photon going one way would become "labelled" with left-handed circular polarization, while any photon going through the other slit is labelled with right-handed circular polarization. In this version of the experiment, it is possible in principle to tell which slit any particular photon arriving at the second screen went through. Sure enough, the interference pattern vanishes -- even though nobody ever actually looks to see which photon went through which slit.
Now comes the new trick -- the eraser. A third polarising filter is placed between the two slits and the second screen, to scramble up (or erase) the information about which photon went through which hole. Now, once again, it is impossible to tell which path any particular photon arriving at the second screen took through the experiment. And, sure enough, the interference pattern reappears!
The strange thing is that interference depends on "single photons" going through both slits "at once", but undetected. So how does a single photon arriving at the first screen know how it ought to behave in order to match the presence or absence of the erasing filter on the other side of the slits?
All of these experiments were carried out using beams of individual photons, and there is no way in which the results can be explained by using classical physics. They lay bare the mysteriousness of quantum mechanics in all its glory, and in particular demonstrate its "non local" nature -- the way in which a photon starting out on its journey behaves in a different way for each experimental setup, as if it knew in advance what kind of experiment it was about to go through.
Don't worry if you don't understand this. Richard Feynman didn't, and he warned "do not keep saying to yourself, if you can possibly avoid it, 'But how can it be like that?' because you will go 'down the drain' into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that."
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More atoms that communicate faster than light
PHYSICISTS still struggling to come to terms with experiments which show instantaneous communication between quantum particles under special circumstances are now faced with another puzzle. Correcting a mistake made by Enrico Fermi more than sixty years ago, Gerhard Hegerfeldt, of the University of Gttingen, has shown that in theory any pair of atoms can communicate faster than light.
The now-familiar puzzle of what are called "non local" interactions develops from theoretical work by John Bell, of CERN, in the 1960s and experiments by Alain Aspect in Paris in the 1980s. Together, these show that a pair of photons ejected in opposite directions from an atom remain somehow entangled, as if they were one particle. Measuring the state of one of the photons instantaneously affects the state of the other one, wherever it may be. Now, it seems that even atoms which have never come into contact (from the perspective of classical Newtonian physics) are entangled in a similar way.
The calculation Fermi carried out in 1932, in the early days of quantum mechanics, concerned the response of one atom to radiation emitted by another atom of the same kind, some distance away. If the second atom is in an excited state, sooner or later it will emit radiation, falling back to its ground state. This radiation will have exactly the right frequency to excite the second atom (this is one of the principles underlying the way atoms are "pumped" into an excited state to make a laser).
Common sense tells us that the first atom cannot be excited until a finite time after the second atom decays -- until there has been time for radiation travelling at the speed of light to cross the gap. That is the result Fermi found. But it now turns out that he made a mistake in his calculation. Probably because the mistaken conclusion matched common sense, it took a long time for this to come to light. But Hegerfeldt's correct version of the calculation now makes it clear that there is a small chance that the first atom will be excited as soon as the second atom decays (Physical Review Letters, vol 72 p 596). As with all such quantum puzzles, this is only the beginning of the story; now, the experts have to explain what this mathematical result means. The best interpretation of the evidence so far seems to be that we should not think of any object, not even a single atom, as an "isolated system".
Because particles must also be considered as waves (one of the basic tenets of quantum mechanics), the individual particles in the atom are spread out, and there is a finite (though small) chance of finding them anywhere in the Universe. So the wave functions of the electrons in the first atom overlap with those of the electrons in the second atom. They are entangled, like the two photons produced in the Aspect experiment, and when an electron in one atom jumps down an energy level that can instantaneously make its counterpart in the other atom jump up by the same amount.
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Solving the quantum mysteries
John Gribbin
For seventy years, physicists have worried about what quantum mechanics means. They can use quantum physics, to be sure; witness the successful designs of lasers and computer microchips, and the understanding of molecules that makes genetic engineering possible. But the equations that are a routine part of this kind of work contain one embarrassing feature. The say, according to the standard interpretation (the Copenhagen interpretation), that nothing is real unless you look at it, that an electron (say) exists only as a wave of probability, called a wave function, which collapses into reality when it is measured, and promptly dissolves into unreality when you stop looking at it. We are no further advanced philosophically, on this picture, than the image of the tree in the quad which disappears when nobody is looking at it.
In fact, few physicists worry about such things. Most of them prefer to ignore them, in the hope they will go away. But now there is another interpretation, which solves all of the quantum mysteries. The snag is, those physicists may not like this one, either, because it involves signals that travel backwards in time.
The archetypal example of the quantum mysteries is the "experiment with two holes", where the measured position of a single electron that passes through two holes in a screen can only be explained in terms of the wave function travelling through both holes at once and interfering with itself. But perhaps you've heard that one already, so here is a rather sideways look at the whole business of collapsing wave functions, a thought experiment which says that the lack of an observation can make the wave function of a system collapse. This wonderful example of the strangeness of the quantum world dates back to the early 1950s, and is known as "Renninger's negative- result experiment", after the German physicist Mauritius Renninger who first thought of it. It is one of the easiest examples of quantum strangeness to understand -- but not to explain.
Imagine that we have a source which will emit a single quantum particle in a random direction (ordinary radioactive nuclei do exactly this, so there is nothing special about the source). This source is in the middle of a large hollow sphere, and the inner surface of the sphere is lined with material that will give a flash at the point where the particle hits it. The accepted quantum description of what happens when the source emits a particle is that a quantum probability wave spreads out evenly in all directions around the source, since there is an equal probability for the particle being emitted in any direction. When the probability wave reaches the inner surface of the spherical shell, there is just one flash of light as the wave collapses to a single point. The particle is only "real" when it is being observed -- when it makes the flash of light -- not while it is travelling from the source to the sphere.
So far, simple enough. But now imagine that half way between the source and the sphere there is a hemispherical shield, which blocks off exactly half of the outer sphere from the field of view of the source. Like the outer sphere, this inner hemispherical shell is lined with scintillating material that will flash when it is struck by a particle from the source. Now what happens when the source emits a particle? We are not interested in exactly where on the outer or inner spheres the particle makes a flash of light, only in which of the two spheres it strikes. Either the particle strikes the inner sphere and makes it flash, or it strikes the outer sphere and makes it flash. There is an equal probability of either outcome of the experiment. Now, suppose that the source is once again triggered into emitting a particle. Once again, standard quantum theory describes this as an expanding spherical shell of probability, moving out evenly in all directions. We wait for a time longer than the time needed for it to reach the inner hemisphere, but too short for it to have reached the outer sphere, and see no flash on the inner sphere. So we know that the final state of the experiment will involve a flash on the outer sphere -- the particle must have been emitted in the wrong direction to strike the inner hemisphere. From a 50:50 probability of the flash occurring either on the hemisphere or on the outer sphere, the quantum wave function has collapsed into a 100 per cent certainty that the flash will occur on the outer sphere. But this has happened without the observer actually "observing" anything at all! It is purely a result of a change in the observer's knowledge about what is going on in the experiment. It requires an observer intelligent enough to infer what is happening, and what would have happened if the particle had been heading towards the inner hemisphere (so a cat, for example, clearly would not be intelligent enough to cause this particular collapse of a wave function). Under these circumstances, the absence of an observation can collapse the quantum wave function as effectively as an actual observation can. At least, so says the Copenhagen interpretation.
This central role for the observer -- not just any observer, but an intelligent observer -- lies at the heart of the standard Copenhagen interpretation of quantum mechanics.
But a giant leap in what might be called quantum philosophy has recently been taken by the American physicist John Cramer. He has taken a new look at the wave equations of quantum mechanics -- the famous Schrdinger equation, and the equations describing the probability waves, which travel, like photons, at the speed of light. What Cramer has pointed out is that the equations actually have two sets of solutions, one equivalent to a positive wave flowing into the future (a "********" wave), and the other describing a negative wave flowing into the past (an "advanced" wave). As all physicists learn at university (and most promptly forget) the full version of the wave equation has two sets of solutions -- one corresponding to the familiar simple Schrdinger equation, and the other to a kind of mirror image Schrdinger equation describing the flow of negative energy into the past.
The proper mathematical description of the wave function actually includes a mixture of both ordinary ("real") numbers and imaginary numbers -- those numbers involving i, the square root of minus one. Such a mixture is called a complex variable, for obvious reasons; it is written down as a real part plus (or minus) an imaginary part. The probability calculations needed to work out the chance of finding an electron (say) in a particular place at a particular time actually depend on calculating the square of the complex number corresponding to that particular state of the electron.
But calculating the square of a complex variable does not simply mean multiplying it by itself. Instead, you have to make another variable, a mirror image version called the complex conjugate, by changing the sign in front of the imaginary part -- if it was + it becomes -, and vice versa. The two complex numbers are then multiplied together to give the probability. For equations that describe how a system changes as time passes, this process of changing the sign of the imaginary part and finding the complex conjugate is equivalent to reversing the direction of time!
The basic probability equation, developed by Max Born back in 1926, itself contains an explicit reference to the nature of time, and to the possibility of two kinds of Schrdinger equations, one describing waves that move forward in time and the other representing waves that move backward in time.
The remarkable implication is that ever since 1926, every time a physicist has taken the complex conjugate of the simple Schrdinger equation and combined it with this equation to calculate a quantum probability, he or she has actually been taking account of the influence of waves that travel backwards in time, without knowing it. There is no problem at all with the mathematics of Cramer's interpretation of quantum mechanics, because the mathematics, right down to Schrdinger's equation, is exactly the same as in the standard Copenhagen interpretation. The difference is, literally, only in the interpretation -- Cramer accepts that the wave flowing backward in time is real, and should be taken seriously, not ignored. The way Cramer describes a typical quantum "transaction" is in terms of a particle "shaking hands" with another particle somewhere else in space and time. One of the difficulties with any such description in ordinary language is how to treat interactions that are going both ways in time simultaneously, and are therefore occurring instantaneously as far as clocks in the everyday world are concerned. Cramer does this by effectively standing outside of time, and using the semantic device of a description in terms of some kind of pseudotime. This is no more than a semantic device -- but it certainly helps to get the picture straight.
It works like this. When an electron vibrates, on this picture, it attempts to radiate by producing a field which is a time-symmetric mixture of a ******** wave propagating into the future and an advanced wave propagating into the past. As a first step in getting a picture of what happens, ignore the advanced wave and follow the story of the ******** wave. This heads off into the future until it encounters an electron which can absorb the energy being carried by the field. The process of absorption involves making the electron that is doing the absorbing vibrate, and this vibration produces a new ******** field which exactly cancels out the first ******** field. So in the future of the absorber, the net effect is that there is no ******** field. But the absorber also produces a negative energy advanced wave travelling backwards in time to the emitter, down the track of the original ******** wave. At the emitter, this advanced wave is absorbed, making the original electron recoil in such a way that it radiates a second advanced wave back into the past. This "new" advanced wave exactly cancels out the "original" advanced wave, so that there is no effective radiation going back in the past before the moment when the original emission occurred. All that is left is a double wave linking the emitter and the absorber, made up half of a ******** wave carrying positive energy into the future and half of an advanced wave carrying negative energy into the past (in the direction of negative time). Because two negatives make a positive, this advanced wave adds to the original ******** wave as if it too were a ******** wave travelling from the emitter to the absorber. In Cramer's words:
The emitter can be considered to produce an "offer" wave which travels to the absorber. The absorber then returns a "confirmation" wave to the emitter, and the transaction is completed with a "handshake" across spacetime.
But this is only the sequence of events from the point of view of pseudotime. In reality, the process is atemporal; it happens all at once. This is because, as Einstein explained with his special theory of relativity, signals that travel at the speed of light take no time at all to complete any journey -- in effect, for light signals every point in the Universe is next door to every other point in the Universe. Whether the signals are travelling backwards or forwards in time doesn't matter, since they take zero time (in their own frame of reference), and +0 is the same as -0 -- and all the quantum probability waves do travel at the speed of light.
The situation is more complicated in three dimensions, but the conclusions are exactly the same. This interpretation makes no predictions that are different from those of conventional quantum mechanics, but it provides a conceptual model which helps many people to think clearly about what is going on in the quantum world. It means that when an electron is faced with a choice of two holes to go through, the offer goes through both but the handshake only comes back through one, so it knows where to go; and in Renninger's experiment, the particle setting out from the radioactive nucleus has already made its handshake and knows which hemisphere it will end up on. There is no more mystery about the quantum mysteries at all -- provided you can live with waves that go backwards in time.
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Photons faster than light
Nothing can travel faster than light -- unless it is a quantum particle "tunneling" through a barrier that, according to good old Newtonian physics, it should not be able to penetrate at all. Physicists have puzzled for decades over how long this mysterious tunneling process takes, but they need puzzle now longer, for it has been measured. And, sure enough, it takes place faster than light.
Quantum tunneling is of more than just esoteric interest. The phenomenon is related to quantum uncertainty, and to wave-particle duality. When two quantum particles, such as two protons, come close to one another, but do not actually touch, the uncertainty in their positions allows their quantum waves to overlap to some extent. As a result, they may "tunnel through" the gap between them, and interact. This is exactly what happens inside the Sun and stars -- protons which are kept at a distance from one another by the repulsion of their positive charge can still fuse together because of tunneling. And that nuclear fusion is what keeps the interior of the Sun hot, and makes its surface shine. Without tunneling, we would not be here.
Raymond Chaio, of the University of California, Berkeley, and his colleagues have actually been measuring a different, but related, kind of tunneling. They have devised an experiment in which two photons (particles of light) are produced simultaneously in a source, and travel on parallel paths. One photon goes straight to a detector; the other is confronted by a barrier which would reflect the light of the photons obeyed the laws of classical, "Newtonian" physics. But according to quantum theory there is a high probability that some of the photons arriving at the mirror will tunnel straight through, and go on their way to the detector.
Sure enough, that is what happens. The barrier is 1.1 micrometers thick, so anything travelling through it at the speed of light would take 3.6 femtoseconds (3.6 thousand million millionths of a second) on the journey. But the new experiment is so sophisticated that it can compare the arrival times of pairs of photons, one of which has gone past the barrier and one through it, and shows that the one which goes through the barrier arrives first. It tunnelled through the barrier faster than the speed of light, in less than 3.6 femtoseconds. As the researchers put it, "it is as though the particle 'skipped' the bulk of the barrier". But don't ask them, or anyone else, what it means -- in the words of Richard Feynman, "nobody understands quantum mechanics".
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Uncertainty rules in the quantum world
IN SCENES reminiscent of the great debates between Niels Bohr and Albert Einstein in the 1930s, fundamental quantum physics has been tested in a series of new "thought experiments", and has passed those tests with flying colours.
The standard interpretation of quantum physics, known as the Copenhagen Interpretation, was established largely through the efforts of Bohr at the beginning of the 1930s. The strange features of the quantum world are founded on what Bohr dubbed complementarity -- the way an entity such as an electron can behave either as a wave or as a particle -- and on Werner Heisenberg's principle of uncertainty, which says that a quantum entity such as an electron does not possess both a position and a momentum simultaneously.
As Richard Feynman was fond of pointing out, the strangeness of the quantum world is encapsulated in "the experiment with two holes". If electrons (or photons, the "particles of light") are fired one at a time through a standard Young's double slit type of experiment and arrive at a detector screen on the other side, they leave the "gun" on one side of the experiment as particles, and arrive at the screen on the other side of the two slits as particles, each making a single spot on the screen. But somehow they pass through the two slits in between as waves, interfering with one another (even though they pass through one at a time!) so that the pattern built up on the screen by the accumulation of spots is an interference pattern.
This wave-particle duality is linked with the uncertainty principle. "Waviness" is a property associated with momentum -- a typical wave is spread out, so it has no definite location in space, but it does have a direction in which it is going. By contrast, a particle can have a precisely defined position. Heisenberg found that the quantum equations imply a strict tradeoff between the two complementary properties. If the position of a quantum entity is precisely defined (for example, when it hits a detector screen), its waviness is suppressed; but if it is allowed to give full expression to its wave nature, the particle aspect vanishes.
In practical terms, this means that we can never measure both momentum and position precisely, at the same time, for any particle. Einstein argued that this was simply a reflection of our clumsiness. Measuring the position of an electron, say, would involve bouncing light off it, and the very act of bouncing light off the electron would make it recoil, changing its momentum (and, indeed, its position). He thought that there were real little particles, like tiny billiard balls, involved in quantum interactions, and that the appearance of fuzziness and interference in experiments was a result of the deficiencies of the experiments.
Bohr argued that the fuzziness was an intrinsic feature of the quantum world, and that within the limits set by Heisenberg's uncertainty principle an electron itself does not "know" both where it is and where it is going. Over several years, beginning at the end of the 1920s, Einstein tried to dream up idealised thought experiments which could in principle measure both the position and the momentum of a particle such as an electron at the same time, thereby refuting Heisenberg. Each time, Bohr found a flaw in Einstein's argument, proving that the experiment could not work as Einstein had thought, even in principle. Bohr's success in this debate with Einstein was a major reason why the Copenhagen Interpretation became the established way of thinking about the quantum world. For sixty years, it seemed there was nothing to add to the debate. Then, in 1991 Marlan Scully, of the University of New Mexico, and colleagues claimed that they had found a way to carry out the kind of measurement Einstein had sought for in vain (Nature, vol 351 p 111). The essence of their argument (see Jim Baggott, "Beating the uncertainty principle", New Scientist, 15 February 1992) was that atoms could be sent through a double slit experiment in an excited state. Behind each slot there would be a detector known as a micromaser cavity, and the experiment would be timed so that each atom emitted a photon as it passed through the appropriate cavity. This would "switch on" one of the detectors, showing which slit the atom passed through, but would leave the atom free to carry on and make its mark on the final detector screen.
In such experiments without the cavities, atoms have been shown to behave like waves when passing through the two slits, creating an interference pattern. But if it is possible to detect which slit each atom passes through, without disturbing the flight of the atom, it would surely be impossible to produce interference. That requires something going through both slits at once. The presence of the cavities would make the interference pattern vanish, as if by magic, demonstrating the absurdity of the Copenhagen Interpretation. But now it seems that things are not that simple. Pippa Storey and colleagues at the University of Auckland have shown that even in this kind of idealised experiment that atoms are disturbed by the presence of the cavities, and in just the right way to "wash out" the interference pattern. They point out (Nature, vol 367 p 626) that although the ejection of a photon by the excited atom need not affect its forward momentum through the slit(s), there is always some uncertainty in the amount of sideways momentum imparted to the atom by the kick of the departing photon.
The situation is complicated by the prediction, in line with quantum uncertainty, that instead of a single photon being emitted cleanly from the atom, the atom can be involved in interactions with "virtual" photons, which emerge briefly from the vacuum (out of "nothing at all") before disappearing. But the conclusion is that provided the cavities are narrower than the separation between the two slits in the experiment (which they have to be if they are to tell us which slit each atom passes through), the interference pattern is destroyed. And the washing out of the interference pattern can even be understood by treating the atoms as waves. Interference can only occur if the waves passing through the two slits remain in phase, but "Because the atom's motion is primarily longitudinal," say the New Zealand team, "a transverse momentum kick will simply change its direction slightly . . . the displacement . . . is effectively the familiar phenomenon of refraction: a position-dependent change in the phase of a wave results in a change in the direction of propagation". The loss of interference from a double slit in the presence of cavity detectors is caused by momentum kicks, which are themselves of a size determined by the uncertainty principle. Einstein, no doubt, would have taken this as philosophically (if unbelievingly) as he took his other setbacks; but the ghosts of Bohr and Heisenberg must be smiling.
Molecules make quantum waves
THE WEIRDNESS of the quantum world has taken another step towards the everyday world as a result of experiments which show iodine molecules behaving as waves in interference experiments. This brings properties often regarded as unique to subatomic particles out into the open on much larger scales.
It is a fundamental feature of quantum mechanics that entities described by the quantum equations are not simply particles or waves, but exhibit a mixture of wave and particle properties. Light, for example, will behave as a wave in interference experiments, with two sets of waves interacting with one another to form a new pattern, just as ripples on a pond (or in your bath) interact with one another. On the other hand, in other experiments light will behave as a stream of tiny particles, called photons.
Wave-particle duality was first discovered to be a feature of light in the early part of this century (Albert Einstein's Nobel Prize was awarded for his proof that photons exist). In the 1920s, researchers found that electrons, traditionally regarded as particles, could behave as waves in experiments where an electron beam is diffracted from a crystal lattice -- indeed, in one of the nicest examples of wave- particle duality, the physicist J. J. Thomson {ED: NB always "J J", never referred to by name} received a Nobel Prize for discovering that the electron is a particle, while his son George received a Nobel Prize for proving that the electron is a wave.
Moving up the mass scale, first neutrons (each nearly 2,000 times the mass of an electron) and then beams of atoms and molecules were shown to diffract like waves when passed through small apertures. Over the past ten years or so, the wave-particle duality has been demonstrated ever more clearly. Not just diffraction (in which one beam, or wave, bends as it passes an obstruction) but interference (in which two beams or waves interact with one another) has been demonstrated both for electrons and atoms. Now, a team of researchers at the University of Paris-North, at Villetaneuse in France, has done the trick with molecules.
In the traditional version of the interference experiment with light, two beams of light are generated by passing light from a single source through two slits in a screen. Then, the two beams are allowed to interfere, producing a characteristic stripey pattern of light and shade. The new experiment is conceptually similar, but instead of passing through holes in a screen the iodine molecules (I2, which each have a mass about 254 times that of a neutron) interact with laser beams. The first interaction, with a pair of laser beams, puts each molecule into what is known as a "superposition of states", effectively two wave packets marching side by side. A second pair of laser beams recombines the wave packets to make "particles". At least, that is the theory. What happens in practice? After they have passed through the laser beams, the iodine molecules arrive at a detector. The distribution of the molecules arriving at the detector does not resemble the pattern you would expect if they were a stream of particles travelling through the experiment, but exactly matches the stripey pattern of peaks and troughs corresponding to interference by waves (Physics Letters A, vol 188 p 187). These are the heaviest "particles" which have ever demonstrated their wave "character" directly in experiments.
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The "central mystery" of quantum physics just got more mysterious. Experimenters from the United States and Austria have got together to provide a new demonstration of how light going through a "double slit" experiment seems to know before it sets out in its journey exactly what kind of traps have been set for it along the way.
This is a variation on the Young's slit experiment, familiar from school laboratory demonstrations of the wave nature of light. When a beam of monochromatic light is shone through two narrow holes in a screen, the light spreading out from the two holes interferes, just like ripples interfering on the surface of a pond, to produce a characteristic pattern on a second screen.
The mystery is that light can also be described as a stream of particles, called photons. The light source in a Young's slit experiment can be turned down to the point where it consists of individual photons going through the experiment, one after the other. If the spots of light made by individual photons arriving at the second screen (actually a photoelectric detector) are added together, they still form an interference pattern, as if each photon goes through both holes and interferes with itself on the way through the experiment. It was Richard Feynman who described this as "the central mystery" of quantum theory, and then corrected himself, saying that in fact it is "the only mystery". If you understood this, you would understand quantum physics -- but as Feynman also said, "nobody understands quantum mechanics" (The Character of Physical Law, BBC Publications, 1965).
The new demonstration of how incomprehensible the quantum world is has been made by Raymond Chiao, of the University of California, Berkeley, Paul Kwiat, of the University of Innsbruck, and Aephraim Steinberg, of the US National Institute of Standards and Technology, in Maryland. Their results were presented at a meeting in Nathiagali, Pakistan.
In fact, the team has carried out several tests of the stranger predictions of quantum theory, but the most dramatic is what they call the "quantum eraser". In this variation on the Young's slit theme, the experiment is first set up in the usual way, and run to produce interference. Quantum theory says that the reason why interference can occur, even if light is a stream of photons, is that there is no way to find out, even in principle, which photon went through which slit. The "indeterminacy" allows fringes to appear.
But then Chiao and his colleagues ran the same experiment with polarising filters in front of each of the two slits. Any photon going one way would become "labelled" with left-handed circular polarization, while any photon going through the other slit is labelled with right-handed circular polarization. In this version of the experiment, it is possible in principle to tell which slit any particular photon arriving at the second screen went through. Sure enough, the interference pattern vanishes -- even though nobody ever actually looks to see which photon went through which slit.
Now comes the new trick -- the eraser. A third polarising filter is placed between the two slits and the second screen, to scramble up (or erase) the information about which photon went through which hole. Now, once again, it is impossible to tell which path any particular photon arriving at the second screen took through the experiment. And, sure enough, the interference pattern reappears!
The strange thing is that interference depends on "single photons" going through both slits "at once", but undetected. So how does a single photon arriving at the first screen know how it ought to behave in order to match the presence or absence of the erasing filter on the other side of the slits?
All of these experiments were carried out using beams of individual photons, and there is no way in which the results can be explained by using classical physics. They lay bare the mysteriousness of quantum mechanics in all its glory, and in particular demonstrate its "non local" nature -- the way in which a photon starting out on its journey behaves in a different way for each experimental setup, as if it knew in advance what kind of experiment it was about to go through.
Don't worry if you don't understand this. Richard Feynman didn't, and he warned "do not keep saying to yourself, if you can possibly avoid it, 'But how can it be like that?' because you will go 'down the drain' into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that."
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More atoms that communicate faster than light
PHYSICISTS still struggling to come to terms with experiments which show instantaneous communication between quantum particles under special circumstances are now faced with another puzzle. Correcting a mistake made by Enrico Fermi more than sixty years ago, Gerhard Hegerfeldt, of the University of Gttingen, has shown that in theory any pair of atoms can communicate faster than light.
The now-familiar puzzle of what are called "non local" interactions develops from theoretical work by John Bell, of CERN, in the 1960s and experiments by Alain Aspect in Paris in the 1980s. Together, these show that a pair of photons ejected in opposite directions from an atom remain somehow entangled, as if they were one particle. Measuring the state of one of the photons instantaneously affects the state of the other one, wherever it may be. Now, it seems that even atoms which have never come into contact (from the perspective of classical Newtonian physics) are entangled in a similar way.
The calculation Fermi carried out in 1932, in the early days of quantum mechanics, concerned the response of one atom to radiation emitted by another atom of the same kind, some distance away. If the second atom is in an excited state, sooner or later it will emit radiation, falling back to its ground state. This radiation will have exactly the right frequency to excite the second atom (this is one of the principles underlying the way atoms are "pumped" into an excited state to make a laser).
Common sense tells us that the first atom cannot be excited until a finite time after the second atom decays -- until there has been time for radiation travelling at the speed of light to cross the gap. That is the result Fermi found. But it now turns out that he made a mistake in his calculation. Probably because the mistaken conclusion matched common sense, it took a long time for this to come to light. But Hegerfeldt's correct version of the calculation now makes it clear that there is a small chance that the first atom will be excited as soon as the second atom decays (Physical Review Letters, vol 72 p 596). As with all such quantum puzzles, this is only the beginning of the story; now, the experts have to explain what this mathematical result means. The best interpretation of the evidence so far seems to be that we should not think of any object, not even a single atom, as an "isolated system".
Because particles must also be considered as waves (one of the basic tenets of quantum mechanics), the individual particles in the atom are spread out, and there is a finite (though small) chance of finding them anywhere in the Universe. So the wave functions of the electrons in the first atom overlap with those of the electrons in the second atom. They are entangled, like the two photons produced in the Aspect experiment, and when an electron in one atom jumps down an energy level that can instantaneously make its counterpart in the other atom jump up by the same amount.
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Solving the quantum mysteries
John Gribbin
For seventy years, physicists have worried about what quantum mechanics means. They can use quantum physics, to be sure; witness the successful designs of lasers and computer microchips, and the understanding of molecules that makes genetic engineering possible. But the equations that are a routine part of this kind of work contain one embarrassing feature. The say, according to the standard interpretation (the Copenhagen interpretation), that nothing is real unless you look at it, that an electron (say) exists only as a wave of probability, called a wave function, which collapses into reality when it is measured, and promptly dissolves into unreality when you stop looking at it. We are no further advanced philosophically, on this picture, than the image of the tree in the quad which disappears when nobody is looking at it.
In fact, few physicists worry about such things. Most of them prefer to ignore them, in the hope they will go away. But now there is another interpretation, which solves all of the quantum mysteries. The snag is, those physicists may not like this one, either, because it involves signals that travel backwards in time.
The archetypal example of the quantum mysteries is the "experiment with two holes", where the measured position of a single electron that passes through two holes in a screen can only be explained in terms of the wave function travelling through both holes at once and interfering with itself. But perhaps you've heard that one already, so here is a rather sideways look at the whole business of collapsing wave functions, a thought experiment which says that the lack of an observation can make the wave function of a system collapse. This wonderful example of the strangeness of the quantum world dates back to the early 1950s, and is known as "Renninger's negative- result experiment", after the German physicist Mauritius Renninger who first thought of it. It is one of the easiest examples of quantum strangeness to understand -- but not to explain.
Imagine that we have a source which will emit a single quantum particle in a random direction (ordinary radioactive nuclei do exactly this, so there is nothing special about the source). This source is in the middle of a large hollow sphere, and the inner surface of the sphere is lined with material that will give a flash at the point where the particle hits it. The accepted quantum description of what happens when the source emits a particle is that a quantum probability wave spreads out evenly in all directions around the source, since there is an equal probability for the particle being emitted in any direction. When the probability wave reaches the inner surface of the spherical shell, there is just one flash of light as the wave collapses to a single point. The particle is only "real" when it is being observed -- when it makes the flash of light -- not while it is travelling from the source to the sphere.
So far, simple enough. But now imagine that half way between the source and the sphere there is a hemispherical shield, which blocks off exactly half of the outer sphere from the field of view of the source. Like the outer sphere, this inner hemispherical shell is lined with scintillating material that will flash when it is struck by a particle from the source. Now what happens when the source emits a particle? We are not interested in exactly where on the outer or inner spheres the particle makes a flash of light, only in which of the two spheres it strikes. Either the particle strikes the inner sphere and makes it flash, or it strikes the outer sphere and makes it flash. There is an equal probability of either outcome of the experiment. Now, suppose that the source is once again triggered into emitting a particle. Once again, standard quantum theory describes this as an expanding spherical shell of probability, moving out evenly in all directions. We wait for a time longer than the time needed for it to reach the inner hemisphere, but too short for it to have reached the outer sphere, and see no flash on the inner sphere. So we know that the final state of the experiment will involve a flash on the outer sphere -- the particle must have been emitted in the wrong direction to strike the inner hemisphere. From a 50:50 probability of the flash occurring either on the hemisphere or on the outer sphere, the quantum wave function has collapsed into a 100 per cent certainty that the flash will occur on the outer sphere. But this has happened without the observer actually "observing" anything at all! It is purely a result of a change in the observer's knowledge about what is going on in the experiment. It requires an observer intelligent enough to infer what is happening, and what would have happened if the particle had been heading towards the inner hemisphere (so a cat, for example, clearly would not be intelligent enough to cause this particular collapse of a wave function). Under these circumstances, the absence of an observation can collapse the quantum wave function as effectively as an actual observation can. At least, so says the Copenhagen interpretation.
This central role for the observer -- not just any observer, but an intelligent observer -- lies at the heart of the standard Copenhagen interpretation of quantum mechanics.
But a giant leap in what might be called quantum philosophy has recently been taken by the American physicist John Cramer. He has taken a new look at the wave equations of quantum mechanics -- the famous Schrdinger equation, and the equations describing the probability waves, which travel, like photons, at the speed of light. What Cramer has pointed out is that the equations actually have two sets of solutions, one equivalent to a positive wave flowing into the future (a "********" wave), and the other describing a negative wave flowing into the past (an "advanced" wave). As all physicists learn at university (and most promptly forget) the full version of the wave equation has two sets of solutions -- one corresponding to the familiar simple Schrdinger equation, and the other to a kind of mirror image Schrdinger equation describing the flow of negative energy into the past.
The proper mathematical description of the wave function actually includes a mixture of both ordinary ("real") numbers and imaginary numbers -- those numbers involving i, the square root of minus one. Such a mixture is called a complex variable, for obvious reasons; it is written down as a real part plus (or minus) an imaginary part. The probability calculations needed to work out the chance of finding an electron (say) in a particular place at a particular time actually depend on calculating the square of the complex number corresponding to that particular state of the electron.
But calculating the square of a complex variable does not simply mean multiplying it by itself. Instead, you have to make another variable, a mirror image version called the complex conjugate, by changing the sign in front of the imaginary part -- if it was + it becomes -, and vice versa. The two complex numbers are then multiplied together to give the probability. For equations that describe how a system changes as time passes, this process of changing the sign of the imaginary part and finding the complex conjugate is equivalent to reversing the direction of time!
The basic probability equation, developed by Max Born back in 1926, itself contains an explicit reference to the nature of time, and to the possibility of two kinds of Schrdinger equations, one describing waves that move forward in time and the other representing waves that move backward in time.
The remarkable implication is that ever since 1926, every time a physicist has taken the complex conjugate of the simple Schrdinger equation and combined it with this equation to calculate a quantum probability, he or she has actually been taking account of the influence of waves that travel backwards in time, without knowing it. There is no problem at all with the mathematics of Cramer's interpretation of quantum mechanics, because the mathematics, right down to Schrdinger's equation, is exactly the same as in the standard Copenhagen interpretation. The difference is, literally, only in the interpretation -- Cramer accepts that the wave flowing backward in time is real, and should be taken seriously, not ignored. The way Cramer describes a typical quantum "transaction" is in terms of a particle "shaking hands" with another particle somewhere else in space and time. One of the difficulties with any such description in ordinary language is how to treat interactions that are going both ways in time simultaneously, and are therefore occurring instantaneously as far as clocks in the everyday world are concerned. Cramer does this by effectively standing outside of time, and using the semantic device of a description in terms of some kind of pseudotime. This is no more than a semantic device -- but it certainly helps to get the picture straight.
It works like this. When an electron vibrates, on this picture, it attempts to radiate by producing a field which is a time-symmetric mixture of a ******** wave propagating into the future and an advanced wave propagating into the past. As a first step in getting a picture of what happens, ignore the advanced wave and follow the story of the ******** wave. This heads off into the future until it encounters an electron which can absorb the energy being carried by the field. The process of absorption involves making the electron that is doing the absorbing vibrate, and this vibration produces a new ******** field which exactly cancels out the first ******** field. So in the future of the absorber, the net effect is that there is no ******** field. But the absorber also produces a negative energy advanced wave travelling backwards in time to the emitter, down the track of the original ******** wave. At the emitter, this advanced wave is absorbed, making the original electron recoil in such a way that it radiates a second advanced wave back into the past. This "new" advanced wave exactly cancels out the "original" advanced wave, so that there is no effective radiation going back in the past before the moment when the original emission occurred. All that is left is a double wave linking the emitter and the absorber, made up half of a ******** wave carrying positive energy into the future and half of an advanced wave carrying negative energy into the past (in the direction of negative time). Because two negatives make a positive, this advanced wave adds to the original ******** wave as if it too were a ******** wave travelling from the emitter to the absorber. In Cramer's words:
The emitter can be considered to produce an "offer" wave which travels to the absorber. The absorber then returns a "confirmation" wave to the emitter, and the transaction is completed with a "handshake" across spacetime.
But this is only the sequence of events from the point of view of pseudotime. In reality, the process is atemporal; it happens all at once. This is because, as Einstein explained with his special theory of relativity, signals that travel at the speed of light take no time at all to complete any journey -- in effect, for light signals every point in the Universe is next door to every other point in the Universe. Whether the signals are travelling backwards or forwards in time doesn't matter, since they take zero time (in their own frame of reference), and +0 is the same as -0 -- and all the quantum probability waves do travel at the speed of light.
The situation is more complicated in three dimensions, but the conclusions are exactly the same. This interpretation makes no predictions that are different from those of conventional quantum mechanics, but it provides a conceptual model which helps many people to think clearly about what is going on in the quantum world. It means that when an electron is faced with a choice of two holes to go through, the offer goes through both but the handshake only comes back through one, so it knows where to go; and in Renninger's experiment, the particle setting out from the radioactive nucleus has already made its handshake and knows which hemisphere it will end up on. There is no more mystery about the quantum mysteries at all -- provided you can live with waves that go backwards in time.
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Photons faster than light
Nothing can travel faster than light -- unless it is a quantum particle "tunneling" through a barrier that, according to good old Newtonian physics, it should not be able to penetrate at all. Physicists have puzzled for decades over how long this mysterious tunneling process takes, but they need puzzle now longer, for it has been measured. And, sure enough, it takes place faster than light.
Quantum tunneling is of more than just esoteric interest. The phenomenon is related to quantum uncertainty, and to wave-particle duality. When two quantum particles, such as two protons, come close to one another, but do not actually touch, the uncertainty in their positions allows their quantum waves to overlap to some extent. As a result, they may "tunnel through" the gap between them, and interact. This is exactly what happens inside the Sun and stars -- protons which are kept at a distance from one another by the repulsion of their positive charge can still fuse together because of tunneling. And that nuclear fusion is what keeps the interior of the Sun hot, and makes its surface shine. Without tunneling, we would not be here.
Raymond Chaio, of the University of California, Berkeley, and his colleagues have actually been measuring a different, but related, kind of tunneling. They have devised an experiment in which two photons (particles of light) are produced simultaneously in a source, and travel on parallel paths. One photon goes straight to a detector; the other is confronted by a barrier which would reflect the light of the photons obeyed the laws of classical, "Newtonian" physics. But according to quantum theory there is a high probability that some of the photons arriving at the mirror will tunnel straight through, and go on their way to the detector.
Sure enough, that is what happens. The barrier is 1.1 micrometers thick, so anything travelling through it at the speed of light would take 3.6 femtoseconds (3.6 thousand million millionths of a second) on the journey. But the new experiment is so sophisticated that it can compare the arrival times of pairs of photons, one of which has gone past the barrier and one through it, and shows that the one which goes through the barrier arrives first. It tunnelled through the barrier faster than the speed of light, in less than 3.6 femtoseconds. As the researchers put it, "it is as though the particle 'skipped' the bulk of the barrier". But don't ask them, or anyone else, what it means -- in the words of Richard Feynman, "nobody understands quantum mechanics".
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Uncertainty rules in the quantum world
IN SCENES reminiscent of the great debates between Niels Bohr and Albert Einstein in the 1930s, fundamental quantum physics has been tested in a series of new "thought experiments", and has passed those tests with flying colours.
The standard interpretation of quantum physics, known as the Copenhagen Interpretation, was established largely through the efforts of Bohr at the beginning of the 1930s. The strange features of the quantum world are founded on what Bohr dubbed complementarity -- the way an entity such as an electron can behave either as a wave or as a particle -- and on Werner Heisenberg's principle of uncertainty, which says that a quantum entity such as an electron does not possess both a position and a momentum simultaneously.
As Richard Feynman was fond of pointing out, the strangeness of the quantum world is encapsulated in "the experiment with two holes". If electrons (or photons, the "particles of light") are fired one at a time through a standard Young's double slit type of experiment and arrive at a detector screen on the other side, they leave the "gun" on one side of the experiment as particles, and arrive at the screen on the other side of the two slits as particles, each making a single spot on the screen. But somehow they pass through the two slits in between as waves, interfering with one another (even though they pass through one at a time!) so that the pattern built up on the screen by the accumulation of spots is an interference pattern.
This wave-particle duality is linked with the uncertainty principle. "Waviness" is a property associated with momentum -- a typical wave is spread out, so it has no definite location in space, but it does have a direction in which it is going. By contrast, a particle can have a precisely defined position. Heisenberg found that the quantum equations imply a strict tradeoff between the two complementary properties. If the position of a quantum entity is precisely defined (for example, when it hits a detector screen), its waviness is suppressed; but if it is allowed to give full expression to its wave nature, the particle aspect vanishes.
In practical terms, this means that we can never measure both momentum and position precisely, at the same time, for any particle. Einstein argued that this was simply a reflection of our clumsiness. Measuring the position of an electron, say, would involve bouncing light off it, and the very act of bouncing light off the electron would make it recoil, changing its momentum (and, indeed, its position). He thought that there were real little particles, like tiny billiard balls, involved in quantum interactions, and that the appearance of fuzziness and interference in experiments was a result of the deficiencies of the experiments.
Bohr argued that the fuzziness was an intrinsic feature of the quantum world, and that within the limits set by Heisenberg's uncertainty principle an electron itself does not "know" both where it is and where it is going. Over several years, beginning at the end of the 1920s, Einstein tried to dream up idealised thought experiments which could in principle measure both the position and the momentum of a particle such as an electron at the same time, thereby refuting Heisenberg. Each time, Bohr found a flaw in Einstein's argument, proving that the experiment could not work as Einstein had thought, even in principle. Bohr's success in this debate with Einstein was a major reason why the Copenhagen Interpretation became the established way of thinking about the quantum world. For sixty years, it seemed there was nothing to add to the debate. Then, in 1991 Marlan Scully, of the University of New Mexico, and colleagues claimed that they had found a way to carry out the kind of measurement Einstein had sought for in vain (Nature, vol 351 p 111). The essence of their argument (see Jim Baggott, "Beating the uncertainty principle", New Scientist, 15 February 1992) was that atoms could be sent through a double slit experiment in an excited state. Behind each slot there would be a detector known as a micromaser cavity, and the experiment would be timed so that each atom emitted a photon as it passed through the appropriate cavity. This would "switch on" one of the detectors, showing which slit the atom passed through, but would leave the atom free to carry on and make its mark on the final detector screen.
In such experiments without the cavities, atoms have been shown to behave like waves when passing through the two slits, creating an interference pattern. But if it is possible to detect which slit each atom passes through, without disturbing the flight of the atom, it would surely be impossible to produce interference. That requires something going through both slits at once. The presence of the cavities would make the interference pattern vanish, as if by magic, demonstrating the absurdity of the Copenhagen Interpretation. But now it seems that things are not that simple. Pippa Storey and colleagues at the University of Auckland have shown that even in this kind of idealised experiment that atoms are disturbed by the presence of the cavities, and in just the right way to "wash out" the interference pattern. They point out (Nature, vol 367 p 626) that although the ejection of a photon by the excited atom need not affect its forward momentum through the slit(s), there is always some uncertainty in the amount of sideways momentum imparted to the atom by the kick of the departing photon.
The situation is complicated by the prediction, in line with quantum uncertainty, that instead of a single photon being emitted cleanly from the atom, the atom can be involved in interactions with "virtual" photons, which emerge briefly from the vacuum (out of "nothing at all") before disappearing. But the conclusion is that provided the cavities are narrower than the separation between the two slits in the experiment (which they have to be if they are to tell us which slit each atom passes through), the interference pattern is destroyed. And the washing out of the interference pattern can even be understood by treating the atoms as waves. Interference can only occur if the waves passing through the two slits remain in phase, but "Because the atom's motion is primarily longitudinal," say the New Zealand team, "a transverse momentum kick will simply change its direction slightly . . . the displacement . . . is effectively the familiar phenomenon of refraction: a position-dependent change in the phase of a wave results in a change in the direction of propagation". The loss of interference from a double slit in the presence of cavity detectors is caused by momentum kicks, which are themselves of a size determined by the uncertainty principle. Einstein, no doubt, would have taken this as philosophically (if unbelievingly) as he took his other setbacks; but the ghosts of Bohr and Heisenberg must be smiling.
Molecules make quantum waves
THE WEIRDNESS of the quantum world has taken another step towards the everyday world as a result of experiments which show iodine molecules behaving as waves in interference experiments. This brings properties often regarded as unique to subatomic particles out into the open on much larger scales.
It is a fundamental feature of quantum mechanics that entities described by the quantum equations are not simply particles or waves, but exhibit a mixture of wave and particle properties. Light, for example, will behave as a wave in interference experiments, with two sets of waves interacting with one another to form a new pattern, just as ripples on a pond (or in your bath) interact with one another. On the other hand, in other experiments light will behave as a stream of tiny particles, called photons.
Wave-particle duality was first discovered to be a feature of light in the early part of this century (Albert Einstein's Nobel Prize was awarded for his proof that photons exist). In the 1920s, researchers found that electrons, traditionally regarded as particles, could behave as waves in experiments where an electron beam is diffracted from a crystal lattice -- indeed, in one of the nicest examples of wave- particle duality, the physicist J. J. Thomson {ED: NB always "J J", never referred to by name} received a Nobel Prize for discovering that the electron is a particle, while his son George received a Nobel Prize for proving that the electron is a wave.
Moving up the mass scale, first neutrons (each nearly 2,000 times the mass of an electron) and then beams of atoms and molecules were shown to diffract like waves when passed through small apertures. Over the past ten years or so, the wave-particle duality has been demonstrated ever more clearly. Not just diffraction (in which one beam, or wave, bends as it passes an obstruction) but interference (in which two beams or waves interact with one another) has been demonstrated both for electrons and atoms. Now, a team of researchers at the University of Paris-North, at Villetaneuse in France, has done the trick with molecules.
In the traditional version of the interference experiment with light, two beams of light are generated by passing light from a single source through two slits in a screen. Then, the two beams are allowed to interfere, producing a characteristic stripey pattern of light and shade. The new experiment is conceptually similar, but instead of passing through holes in a screen the iodine molecules (I2, which each have a mass about 254 times that of a neutron) interact with laser beams. The first interaction, with a pair of laser beams, puts each molecule into what is known as a "superposition of states", effectively two wave packets marching side by side. A second pair of laser beams recombines the wave packets to make "particles". At least, that is the theory. What happens in practice? After they have passed through the laser beams, the iodine molecules arrive at a detector. The distribution of the molecules arriving at the detector does not resemble the pattern you would expect if they were a stream of particles travelling through the experiment, but exactly matches the stripey pattern of peaks and troughs corresponding to interference by waves (Physics Letters A, vol 188 p 187). These are the heaviest "particles" which have ever demonstrated their wave "character" directly in experiments.
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minniepumpernickel
<font color=FF66FF>DIS Veteran<br><font color=0099
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N&P I think that is really interesting, LOL! 
Okay boring....I have so much laundry to do! I am going away this weekend and I need to pack. I have to water the plants too....
Okay boring....I have so much laundry to do! I am going away this weekend and I need to pack. I have to water the plants too....
yeartolate
My toaster can pop more toast per hour than your t
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The history of hemorrhoids.
Chapter one - the Neandrothol years.....
Chapter one - the Neandrothol years.....
Scullyrules1013
<font color=purple>Off Kilter + Frisbees = Perfect
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Hey, who wants to hear all about how awesome I think Off Kilter is???
Sparx
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ok, this is the research that I am doing over a paper for science. I am copying all of my finds into this folder so I can read up on the subject before I attempt to type a four page paper over it.
Leprosy Research
Cause
Leprosy is a chronic disease caused by a bacillus, Mycobacterium leprae;
M. leprae multiplies very slowly and the incubation period of the disease is about five years. Symptoms can take as long as 20 years to appear;
Leprosy is not highly infectious. It is transmitted via droplets, from the nose and mouth, during close and frequent contacts with untreated cases.
Symptoms
Leprosy mainly affects the skin and nerves;
If untreated, there can be progressive and permanent damage to the skin, nerves, limbs and eyes;
Paucibacillary (PB) leprosy results in one to five numb skin patches;
Multibacillary (MB) leprosy results in more than five numb skin patches.
History
Leprosy was recognized in the ancient civilizations of China, Egypt and India;
The first known written mention of leprosy is dated 600 BC;
Throughout history, the afflicted have often been ostracized by their communities and families.
Treatment today
Leprosy is a curable disease and treatment provided in the early stages averts disability;
With minimal training, leprosy can be easily diagnosed on clinical signs alone;
A World Health Organization (WHO) Study Group recommended multidrug therapy (MDT) in 1981. MDT consists of three drugs: dapsone, rifampicin and clofazimine. This drug combination kills the pathogen and cures the patient;
MDT is safe, effective and easily administered under field conditions. MDT is available in convenient monthly calendar blister packs to all patients;
Novartis and the Novartis Foundation for Sustainable Development have made MDT available free of charge to all leprosy patients in the world. Through WHO, this MDT is provided to countries in sufficient supply to treat all people diagnosed with the disease.
High effectiveness of multidrug therapy
PB patients treated with MDT are cured within six months;
MB patients treated with MDT are cured within 12 months;
Patients are no longer infectious to others after the first dose of MDT. In other words, transmission of leprosy is interrupted;
There are virtually no relapses, i.e. recurrences of the disease after treatment is completed;
No resistance of the bacillus to MDT has been detected;
WHO estimates that early detection and treatment with MDT has prevented about three to four million people from being disabled. This suggests great cost-effectiveness of MDT as a health intervention, considering the economic and social loss averted.
History of treatment
The first breakthrough occurred in the 1940s with the development of the drug dapsone, which arrested the disease. But the duration of the treatment of leprosy was many years, even a lifetime, making it difficult for patients to follow;
In the 1960s, M. leprae started to develop resistance to dapsone, the worlds only known anti-leprosy drug at that time;
Rifampicin and clofazimine, the other two components of MDT, were discovered in the early 1960s.
The elimination of leprosy as a public health problem
Elimination of leprosy as a public health problem is defined as a prevalence rate on the global level of less than one case per 10 000 persons;
The widespread use of MDT has reduced the disease burden dramatically;
Over the past 20 years, more than 12 million leprosy patients have been cured. The prevalence rate of the disease has dropped by 90% and leprosy has been eliminated from 108 countries out of 122 countries where leprosy was considered as a public health problem in 1985.
Figures on the current leprosy situation
Approximately 755 000 new cases of leprosy were detected during 2001. At the beginning of 2002, 650 000 cases were registered and were undergoing treatment;
In 14 countries in Africa, Asia and Latin America leprosy is still considered a public health problem;
According to the latest available information, intensive efforts are still needed to reach the leprosy elimination target in six countries: Brazil, India, Madagascar, Mozambique, Myanmar, and Nepal. Taken all together, these countries account for 90% of the prevalence of the disease in the world in early 2002;
At the start of 2002, about 70% of the worlds registered leprosy patients are in India.
Actions and resources required
Political commitment needs to be strengthened in countries where leprosy remains a public health problem;
In order to reach all patients, treatment of leprosy needs to be fully integrated into general health services. This is a key to successful elimination of the disease. Strong leadership by ministries of health is absolutely necessary, especially in some of the major endemic countries;
Partners in leprosy elimination need to further accelerate activities and ensure that human and financial resources are made available for the elimination of leprosy;
The age-old stigma associated with the disease remains an obstacle to self-reporting and early treatment. The image of leprosy has to be changed at the global, national and local levels. A new environment, in which patients will not hesitate to come forward for diagnosis and treatment at any health facility, must be created.
The strategy for leprosy elimination
The following actions are part of the ongoing leprosy elimination campaign:
Ensuring accessible and uninterrupted MDT services available to all patients through flexible and patient-friendly drug delivery systems;
Ensuring the sustainability of MDT services by building the ability of general health workers to treat leprosy;
Encouraging self-reporting and early treatment by promoting community awareness and changing the image of leprosy;
Monitoring the performance of MDT services, the quality of patients care and the progress being made towards elimination through national disease surveillance systems.
To promote political commitment, leadership by ministries of health in endemic countries and partners support for leprosy elimination, the Global Alliance for Elimination of Leprosy (GAEL) was created in November 1999. Core members of the Alliance are governments of leprosy endemic countries, the Nippon Foundation, Novartis and WHO. The Alliance is co-operating closely with other national and international organizations, including the Danish International Development Agency (DANIDA), Handicap International, MORHAN, Pastoral da Criancia and the World Bank.
Definition of Leprosy
Leprosy is a chronic infectious disease which attacks the skin, peripheral nerves and mucous membranes (eyes, respiratory tract). Leprosy is also known as Hansen's disease because the bacillus which causes it was discovered by G.A. Hansen in 1873. It is most common in warm, wet areas in the tropics and subtropics.
Treatment of Leprosy
As of 1940, a treatment using dapsone is currently being used to suppress leprosy. Seldom is leprosy completely removed from the body; it can only be halted using a multi-drug treatment. Of the approximately two million cases (and half a million more each year), only one million are being treated in this way.
In addition, patients are taught to take care of themselves using a kind of visual check if they have significant nerve damage. Without the sensations of pain to identify cuts and bruises, patients must watch themselves constantly or be subject to dangerous infection.
What Leprosy Looks Like
Leprosy is characterized by multiple lesions accompanied by sensory loss in the affected areas. Usually, sensory loss begins in the extremities (toes, fingertips). In many advanced cases, gangrene sets in, causing parts of the body to "die" (necrosis) and become deformed.
Social Effects
Leprosy in all ages has been considered one of the more despicable diseases, and victims have been despised throughout history and kept in separate places (leper colonies, sanitariums). Even today, most people with leprosy are shunned by their neighbors and are held at arms length.
In the medieval period, leper colonies sprung up where victims of this then-untreatable disease would go to slowly die from the illness.
Leprosy throughout the Ages
by Eleanor E. Storrs
Until the coming of AIDS, leprosy was the most feared of infectious diseases. Even today, it warps the lives of millions of people; mostly in South America, Africa, and the Orient. The Black Death that swept though Europe in the last half of the 14th century, killing one third of the people, was more violent in its ravages. But it came and went quickly, like a great earthquake, followed by a series of after shocks.
Leprosy has tormented humans since the dawn of history; leaving lasting imprints on religion, literature, and art. It is a deep rooted part of the human psyche, with both mystical and physical meanings. Asians and Africans call it "the big disease" in many tongues because of the damage done to soul and body of those cursed with it.
We know nothing certain about the origins of leprosy, except that it is old, very old. An account of a disease that could be leprosy appears in an Egyptian papyrus inscribed about 1552-1350 B.C. But this is an imaginative guess, made by modern scholars that could be wrong.
Indian writings dated at 600 B.C, describe a disease that most experts agree was leprosy. It does not appear in the records of ancient Greece until the army of Alexander the Great came back from India in 326 B.C. In Rome, the first mention coincides with the return of Pompey's troops from Asia Minor in 62 B.C. Thus Asia could be the cradle of infection.
A Biblical Curse
The Bible often mentions a disease called leprosy. The words leprous or leprosy appear 54 times. It is from these accounts that the disease became linked to corruption of both spirit and body. The Book of Leviticus paints a chilling image of these ancient fears.
And the leper in whom the plague is, his clothes shall be rent, and the hair of his head shall go loose, and he shall cover his upper lip, and shall cry, unclean, unclean. And all the days wherein the plague is in him he shall be unclean; he is unclean: he shall dwell alone; without the camp shall his dwelling be.
The Bible equated this sickness with sin. It was a punishment by God for transgression. Thus Uzziah, King of Judah, wanted to burn incense in the temple of Jehovah, a ceremony reserved for priests. The priests opposed him, and Uzziah became angry. God struck him with leprosy.
And Uzziah the King was a leper unto the day of his death, and dwelt in a separate house, being a leper; for he was cut off from the house of Jehovah . .
The priests did not drive Uzziah into the wilderness like lesser sinners, but stripped him of power and denied him burial in the cemetery of kings.
The New Testament treats lepers more kindly, but even so, sets them apart from other sufferers. Jesus healed the blind and deaf but cleansed the lepers, implying a moral stigma. And then came a leper to him, beseeching him, and kneeling down to him, and saying unto him, "If thou wilt thou cans't make me clean." And Jesus, moved with compassion, put forth his hand and touched him, and saith unto him, "I will; be thou clean." And as soon as he had spoken, immediately the leprosy departed from him and he was clean.
During the early years of Christianity, healers looked at lepers with revulsion, and priests considered them depraved. Aretaeus of Cappadocia, a physician of the early 2nd century wrote:
When in such a state who would not flee- who would not turn away from them, even a father, a son, or a brother? There is danger also from communication of the ailment.
The Church ordered regulations against lepers at the Council of Ancyra in 314 A.D., defining them as unclean persons, bodily and morally. People classified as lepers included heretics.
Medieval Myths
By the Middle Ages, priests and savants accused lepers of a host of sins: they angered easily, suspected others of wanting to hurt them, had grievous dreams, and were schemers and deceivers. Medical writers of the era thought they threatened society; not only through infection, but by evil behavior.
Most of them warned that they burn with carnal desire, branding leprosy as a venereal disease. Priests sometimes gave them mock funerals before thrusting them out of society.
Within the church let a black cloth . . . be set upon two trestles at some distance apart before the altar, and let the sick man take his place on bended knees beneath it between the trestles, after the manner of a man dead . . . and in this posture let him devoutly hear mass . . . The priest then with the spade cast earth on each of his feet saying: "Be thou dead to the world, but live again unto God."
The priest then led him into an open field and forbad him to enter churches or houses; wash his hands or clothes in springs or streams; wear anything but a leper's cloak; touch anything he wanted to buy; enter taverns to buy wine; or to lie with any woman but his wife. The priest told him never to talk to people unless down wind from them; never touch railings without gloves; never touch children or give them gifts; and never eat and drink with people other than lepers.
He must always wear the grey or black mantle of a leper, and not use the dishes and spoons of others. He must warn people of his miserable presence with horn, clapper or bell; and beg for alms with a bag tied to the end of a long stick.
These were the rules imposed on lepers. Of course, they also had to obey the commandments of Moses. The medieval church left them a legacy of shame, degradation and rejection.
Leprosy Strikes Britain
We do not know when leprosy came to Britain, but by the 11th century it was a grievous plague. The first Norman Archbishop of Canterbury, Lanfranc, founded a leprosy hospice at Harbledown, near the cathedral, sometime between his arrival in England in 1070 and death in 1089.
Queen Matilda, daughter-in-law of William the Conqueror, endowed a hospice for leprosy victims outside the gates of London in 1101, and dedicated it to St. Giles, the patron saint of outcasts. At her behest, the lepers gave a "Cup of Charity" to condemned prisoners as they passed the door of the hospice chapel on their way to the gallows at Tyburn.
Many other hospices, sometimes called lazar houses, were founded before the end of the 11th century. When the Black Death swept through the land, there were 200 in Britain alone and as many as 20,000 in Europe. But the number of patients in each was small, ranging from one to a hundred. An extreme case was St. Giles in Norwich- it had one master, eight chaplains, two clerks, seven choristers, two nuns and eight lepers- a classic case of featherbedding.
Even with this proliferation of hospices, there were probably no more than two thousand lepers living in them out of a population of three million. But I suspect that these were only for the well-to-do. Poor villagers ravaged by leprosy probably fled to fens and forests, as happened in Louisiana in recent times.
If lepers were moral outcasts why were some of them provided for so abundantly? The attitudes of priests, nobles and kings differed with place and time; so treatment ranged from good to bad, with bad prevailing. Some priests thought the disease was a gift of God, because He chose lepers to bear one of the heaviest burdens of man. Others saw in leprous skin the brand of spiritual rot. Thus lepers were seen as both holy and sinful. God gave them special grace, or punished them for their sins.
Royal Attitudes, Royal Victims
Some kings loathed lepers. Philip V of France and Henry II of England had them burned at the stake without religious rites. Edward I, Henry's great grandson, was more charitable. He allowed them ritual funerals. Afterward, he had them carted to cemeteries and buried alive.
Other kings were compassionate. Henry III, father of Edward and son of John of Magna Carta fame, authorized the lepers of Bridgenorth to gather one horse-load of wood daily from the royal forest. Eight years later he made the same donation to the lepers of Shrewsbury.
Why these differences in outlook? They were probably reflections of personal traits. Henry II was an empire builder who abetted the murder of his archbishop, Thomas Becket. Edward I was a fearsome fighter who crushed the Scots at Dunbar and Falkirk. History remembers Henry III and his father John for their weaknesses. They may have felt they needed God's aid, and sought the prayers of anyone who could help them get it, even the leper's.
Yet Henry II had mixed feelings about lepers. He gave 40 marks to Harbledown hospital while on a pilgrimage to Canterbury to do penitence for the murder of the Archbishop. He may not have done this entirely from remorse. In 1158, during a visit to Paris, he made gifts to lepers and the poor, 12 years before Becket's murder.
Some kin of these kings were lepers. These include Henry II's daughter-in-law, Constance of Brittany, and his cousin Baldwin IV, the "Leper King" of Jerusalem. The disease blinded Baldwin; so he appointed regents. This led to power struggles among the nobles. He finally had to yield his throne to a five year old nephew.
Henry IV, the first Lancastrian King of England, died of an ailment that many people thought was leprosy. A skin disease ravaged his face so badly that he was repulsive to behold. There is no proof he had leprosy. But he had usurped the throne of his cousin Richard and possibly murdered him. In the eyes of his enemies, this crime and his mottled face equated him with a leper.
Robert the Bruce
The case of Robert the Bruce of Scotland is puzzling. We saw his bones displayed at a leprosy congress in Norway, where they were on loan from a Danish museum to show how leprosy causes bone damage. We were curious to learn how the remains of Scotland's greatest hero, the victor of Bannockburn, wound up in a foreign museum. We tried to visit the museum while in Copenhagen, but it was closed when we arrived.
We picked up the trail again in Scotland. Bruce died in 1329 of a mysterious ailment called the " great malady." He was ill for only two years, and his physicians did not quarantine him. No one mentioned leprosy until a generation later. Yet many reference books give it as the cause of his death.
He was buried at Dunfermline Abbey, and the site of his tomb forgotten. It was rediscovered in 1812. His skull was pitted and the upper jaw and nose eroded by disease. The people we talked to claimed he died of syphilis instead of leprosy. Physicians often confused these diseases in the middle Ages.
A cast of his skull is in the Anatomy Department of University of Edinburgh. The mysterious bones we saw in Norway were those of a man ravaged by leprosy, but are unlikely to be Bruce's.
We can add a curious postscript to this story. In a film called Braveheart Robert the Bruce, the eighth of his name, is portrayed as a clear skinned warrior. However, Hollywood showed his father, Robert the seventh, as a horribly disfigured leper. This old legend simply will not die.
The Stigma
What was this medieval leprosy that preyed on kings and commoners? Was it the disease we know today? In the minds of many, leprosy is not just a disfiguring disease: it is a disgracing disease. But its victims have done nothing to merit disgrace.
To ease their lot many caring people have looked for ways to soften the impact of the dreaded word. Some want to abolish it altogether and substitute Hansen's disease, after the discoverer of the leprosy bacillus. Others have sought to cleanse the word by showing that the aura of evil attached to it arose from accidents of history. They base their arguments on word origins, descriptions of disease and old works of art.
Most medieval savants thought that leprosy was the Biblical disease tzaraat, a Hebrew word used to describe ritual impurity associated with a skin ailment. When the scholars of Alexandria translated the Old Testament into Greek, they rendered tzaraat as lepra. The Greek lepra, meaning scaly, was a skin disease that is now unknown, but was not leprosy. About 300 B.C., physicians of Alexandria described a type of leprosy that they called elephas. In some way, the symptoms of elephas became associated with lepra that had acquired overtones of evil from tzaraat. Thus, the mystique of medieval leprosy may have resulted from fusion of three nuclei. The Greeks gave a name and the Hebrews an aura of evil to a disease described by Egyptians.
Most physicians do not think that Biblical leprosy was the disease we know today. Symptoms of tzaraat appear in many patients, but not in the same combinations mentioned in the Bible. It is likely that tzaraat was a state of ritual impurity associated with several skin diseases. Leprosy might have been one of them.
Paintings of Biblical and historic characters preserve the medieval image of leprosy. Among these are Miriam, Naaman and Emperor Constantine. But artists of the time often pictured the disease in a stylized way that lacks interpretive value. Typically, they showed the victim with bright red spots of the same size distributed uniformly over his body.
European artists used this convention from the 9th through the 15 centuries. By the 16th century, paintings began to show deformities of face and limbs. Leprosy in the late middle Ages was the same disease we know today.
Decline in Europe
The disease began to wane in Western Europe at the close of the middle Ages. Once rampant in Britain, by the 18th century it lingered only in the Shetland Islands. It reached a late peak in Norway during the 19th century, but the last leprosy hospital there closed in the 1950s. Physical disease receded, but reverberations of moral corruption linger in our language. Thus William Cowper wrote:
When nations are to perish in their sins,
tis in the church the leprosy begins.
In the 19th century, Tennyson associated leprosy with morality in his phrase:
A moral leper, I,
to whom none spoke.
Clearly, the words leper and leprosy carry overtones of evil.
Association of leprosy with sin is not unique to Western culture. Chinese and Hindu attitudes were similar, although for different reasons. Mohammedans claim they were more tolerant. Yet in 1253, Saracens killed all the lepers living in the hospice of the Order Hospitalier St. Lazare de Jerusalem.
Medical science did not vanquish leprosy in Europe. The reasons for its recession are still debated, and are still unknown. While it faded in Europe, it is still a major problem in Africa and the Orient. Explorers and settlers spread it throughout South America and the languid isles of the South Seas.
The stigma associated with leprosy perished for all time with the discovery that the disease occurs naturally in wild armadillos. Before then, many believed that leprosy was a unique punishment inflicted by God on humans for their sins. Now it must be looked upon as a bacterial infection devoid of religious significance. The mystique surrounding leprosy had started to collapse in Hawaii a century before.
Pestilence in Paradise
Hawaiians, long isolated from the rest of the world, were highly susceptible to white men's diseases. When leprosy struck, the authorities rounded them up and dumped them like trash on the shores of the island of Molokai. There they lived like starving animals stripped of humanity.
This time their exile could not be blamed on ancient priests or medieval kings, but on our own people; descendants of New England missionaries who had settled there only 50 years earlier. Father Damien, a Catholic priest of Belgian birth, heard of their plight and hastened to Hawaii to help them. He wrote:
For ten years past this scourge has spread itself in our archipelago in so frightful a manner that the government deemed itself obliged to exclude from the society of other islanders all those infected with it. Now these unfortunates, confined to a corner of the island of Molokai, hemmed in by impassable mountains and the seashore, are in perpetual exile. Of more than 2,000 conveyed here, 800 are still living . . .
We visited Molokai in 1984. A rim of cliffs towering to 4,000 feet bounds the north shore. Crouched beneath them lies a peninsula, two to three miles wide at cliff base, that juts two miles into the sea. A baby volcano burped up this sliver of land millions of years after monstrous bursts of lava flung Molokai above the water. Now it's little more than a green mound, its crater filled with grasses and scrub.
Calm beaches rim the west shore where the leprosarium now stands. But ragged volcanic rocks, flanked by stubs of black basalt, their tops rounded by pounding surf, guard it in the east. This was the rugged site of Kalawao, the final destiny of many exiles.
From anchored ships, sailors heaved supplies and cattle overboard to be hauled in by the few able bodied men of the colony. Then they rowed the newcomers to shore in longboats, to join the maimed hosts that preceded them. Food was poor, shelter scanty, the community lawless. There was no way out by land or sea.
When Father Damien came to Molokai, he found a small chapel dedicated to St. Philomena, but little else. For awhile he slept under a tree, but with the help of gifts from Honolulu, built a small house. From there he wrote of his charges:
These spots (caused by leprosy) cover the whole body, and sores appear on the feet and on the hands. The flesh decays and yields an infectious odor. The breath of the lepers poisons the air . . . I sometimes experience a feeling of repugnance. I am quite puzzled how to administer extreme unction when the hands and feet are but one sore. It is the sign of approaching death.
Damien choked down his repugnance, and strove to fill the needs of his flock. He bettered food supplies, built shanties and taught order to a lawless community. He always prayed with the dying, no matter how foul their sores.
With the help of those who could work, he built a road to the west shore of the peninsula, Kalaupapa, where St. Francis' church and the leprosy hospital now stand. There the shore is sandy and the surf mild. Eleven years into his self-imposed exile, Damien found he had leprosy. He had long been in the habit of beginning his sermons with "We lepers . . . "
Now it was true. His plight stirred sympathy throughout the world for Damien and his cause. Help came to Kalawao. Brother Joseph Dutton, an American Civil War Veteran, came to share Damien's burdens. Mother Marianne and her group of Catholic Sisters opened a school for girls, children of leprosy victims, at Kalaupapa, the" clean" coast of the peninsula.
Martyr of Molokai
Sympathizers throughout the world mourned Damien's death. Robert Louis Stevenson, then a journalist, visited Hawaii to write the story of the "Martyr of Molokai." It was well he did, since Damien had enemies, even after death.
One of them, Dr. Hyde, a Presbyterian minister from Honolulu, wrote a letter to a newspaper saying Damien was coarse, bigoted and immoral. Stevenson wrote a thundering reply that shook the conscience of the Protestant world. Point by point, he ripped Hyde to shreds:
"Damien was coarse" . . . you make us sorry for the lepers who had only a coarse old peasant for their friend and father . . . "headstrong" . . . I thank God for his strong head and heart! "Damien was bigoted" . . . in him his bigotry, his intense and narrow faith, wrought potently for good, and strengthened him to become one of the world's heroes and exemplars.
Damien's martyrdom, magnified by Hyde's stupidity and Stevenson's eloquence, marked a turning point on how the world looks at lepers. People finally realized they were victims of disease, not depraved monsters.
In 1936, Belgium moved Damien's body from Molokai to Louvain with all the panoply the nation could muster. Left behind were the remains of his helpers and followers, Brother Dutton and Mother Marianne. It would have been better to have left Damien to rest with them.
When we visited Molokai, the hospital had ceased taking new patients. The Medical Director, Dr. Oliver Hasselbladt, told us the grounds would become a National Monument when the last old leprosy patient died. "If the church ever canonizes Damien," he said, "these grounds will become as holy as Lourdes.
Cajun Country
Leprosy is still endemic in Hawaii and six mainland states, including Louisiana. Early settlers or slaves from Africa might have brought it there during French and Spanish colonial days.
Or French Canadians could have carried it when the British expelled them from Acadie in the 18th century. Physicians found leprosy in their homeland, New Brunswick, in 1817. It must have been there much earlier.
Longfellow told the story of their exile in his epic poem about Evangeline and her lover Gabriel. In real life, his heroine was Emmeline LaBiche. She landed at St. Martinsville, a town on Bayou Tech, about 12 miles north of my home in New Iberia, to find that Gabriel, in real life, Louis Arceneaux, had married another woman.
These Acadians, now called Cajuns, fanned out along the southwest coast of Louisiana, and are the dominant ethnic group in a 22 parish region known as Acadiana. During my life there, I heard many tales about local people with leprosy.
A family named Landry had two children with the disease, people said. They lived in an attic to hide from health officials. A nurse with long experience in the area told me that many leprosy victims had taken refuge in remote parts of the Atchafalaya Basin; a vast wilderness of slow waters hemmed in by levees. A great flood drove more than 40 of them to high ground, where people saw them wandering in nearby hamlets.
Denis Comeaux caught many armadillos for me, but I never met him. He had a corroding skin disease and shunned outsiders. All my contacts with him were through his family. One day I went to his house to collect animals. His wife said he had died. I will never know for sure if Denis had leprosy.
Much later I learned that people who handle armadillos can get leprosy from them. I also found many wild armadillos with leprosy in the area where Denis lived.
Leprosy was part of New Iberia folklore and had a long history in Louisiana. We know the disease occurred in New Orleans in colonial days, since a hospice called La Terre de Lepreax stood near the city then. But in 1804, New Orleans physicians claimed they were unable to find it among local residents.
There the question rested until 1872, when Dr. W.G. Kibbe of Abbeville, about 20 miles west of New Iberia, sent Felecien Ourblanc to New Orleans for examination by Dr. Joseph Jones. Felecien had leprosy.
The Road to Carville
During the next few years, physicians found other cases near Abbeville. They made additional surveys in New Orleans and rural Louisiana. By 1892, they concluded that leprosy, formerly thought to occur only in people of foreign birth, was endemic in Louisiana, mostly among whites.
The state selected a smallpox hospital in New Orleans, managed by Dr. J. C. Beard and his son, for care of patients. The hospital got little attention until 1893. A reporter from the Daily Picayune wrote a story about a girl from New Iberia with leprosy. She was shipped to New Orleans in a boxcar labeled freight, and lodged in Dr. Beard's "Pest House." The reporter visited her, and in his article claimed neglect and possible starvation.
This scandal forced the legislature to set up a State Board of Control. Health officers suggested many sites for a home for lepers near New Orleans, but property owners opposed them. Finally, the state leased Indian Camp Plantation on a bend of the Mississippi, about 85 miles up river. Physicians thought this would be temporary and hoped to find a site closer to Charity Hospital. But property owners fought all attempts to relocate in the city. Finally, the state bought Indian Camp Plantation, and gave it a new name - Louisiana State Home for Lepers.
The home was isolated and run down, and there was no resident physician most of the time it was under state control. On January 3, 1921, the Federal Government annexed the property and patients. It became the first and only U.S. Public Health Service Hospital devoted exclusively to leprosy. Most people know it as Carville.
In March of 1968, I went to Carville to propose use of the armadillo as an animal model for leprosy research. This visit was the first step in an agonizing collaboration with U. S. Public Health Service that would endure for four years.
Cajun Country
Leprosy is still endemic in Hawaii and six mainland states, including Louisiana. Early settlers or slaves from Africa might have brought it there during French and Spanish colonial days.
Or French Canadians could have carried it when the British expelled them from Acadie in the 18th century. Physicians found leprosy in their homeland, New Brunswick, in 1817. It must have been there much earlier.
Longfellow told the story of their exile in his epic poem about Evangeline and her lover Gabriel. In real life, his heroine was Emmeline LaBiche. She landed at St. Martinsville, a town on Bayou Tech, about 12 miles north of my home in New Iberia, to find that Gabriel, in real life, Louis Arceneaux, had married another woman.
These Acadians, now called Cajuns, fanned out along the southwest coast of Louisiana, and are the dominant ethnic group in a 22 parish region known as Acadiana. During my life there, I heard many tales about local people with leprosy.
A family named Landry had two children with the disease, people said. They lived in an attic to hide from health officials. A nurse with long experience in the area told me that many leprosy victims had taken refuge in remote parts of the Atchafalaya Basin; a vast wilderness of slow waters hemmed in by levees. A great flood drove more than 40 of them to high ground, where people saw them wandering in nearby hamlets.
Denis Comeaux caught many armadillos for me, but I never met him. He had a corroding skin disease and shunned outsiders. All my contacts with him were through his family. One day I went to his house to collect animals. His wife said he had died. I will never know for sure if Denis had leprosy.
Much later I learned that people who handle armadillos can get leprosy from them. I also found many wild armadillos with leprosy in the area where Denis lived.
Leprosy was part of New Iberia folklore and had a long history in Louisiana. We know the disease occurred in New Orleans in colonial days, since a hospice called La Terre de Lepreax stood near the city then. But in 1804, New Orleans physicians claimed they were unable to find it among local residents.
There the question rested until 1872, when Dr. W.G. Kibbe of Abbeville, about 20 miles west of New Iberia, sent Felecien Ourblanc to New Orleans for examination by Dr. Joseph Jones. Felecien had leprosy.
The Road to Carville
During the next few years, physicians found other cases near Abbeville. They made additional surveys in New Orleans and rural Louisiana. By 1892, they concluded that leprosy, formerly thought to occur only in people of foreign birth, was endemic in Louisiana, mostly among whites.
The state selected a smallpox hospital in New Orleans, managed by Dr. J. C. Beard and his son, for care of patients. The hospital got little attention until 1893. A reporter from the Daily Picayune wrote a story about a girl from New Iberia with leprosy. She was shipped to New Orleans in a boxcar labeled freight, and lodged in Dr. Beard's "Pest House." The reporter visited her, and in his article claimed neglect and possible starvation.
This scandal forced the legislature to set up a State Board of Control. Health officers suggested many sites for a home for lepers near New Orleans, but property owners opposed them. Finally, the state leased Indian Camp Plantation on a bend of the Mississippi, about 85 miles up river. Physicians thought this would be temporary and hoped to find a site closer to Charity Hospital. But property owners fought all attempts to relocate in the city. Finally, the state bought Indian Camp Plantation, and gave it a new name - Louisiana State Home for Lepers.
The home was isolated and run down, and there was no resident physician most of the time it was under state control. On January 3, 1921, the Federal Government annexed the property and patients. It became the first and only U.S. Public Health Service Hospital devoted exclusively to leprosy. Most people know it as Carville.
In March of 1968, I went to Carville to propose use of the armadillo as an animal model for leprosy research. This visit was the first step in an agonizing collaboration with U. S. Public Health Service that would endure for four years.
Leprosy Research
Cause
Leprosy is a chronic disease caused by a bacillus, Mycobacterium leprae;
M. leprae multiplies very slowly and the incubation period of the disease is about five years. Symptoms can take as long as 20 years to appear;
Leprosy is not highly infectious. It is transmitted via droplets, from the nose and mouth, during close and frequent contacts with untreated cases.
Symptoms
Leprosy mainly affects the skin and nerves;
If untreated, there can be progressive and permanent damage to the skin, nerves, limbs and eyes;
Paucibacillary (PB) leprosy results in one to five numb skin patches;
Multibacillary (MB) leprosy results in more than five numb skin patches.
History
Leprosy was recognized in the ancient civilizations of China, Egypt and India;
The first known written mention of leprosy is dated 600 BC;
Throughout history, the afflicted have often been ostracized by their communities and families.
Treatment today
Leprosy is a curable disease and treatment provided in the early stages averts disability;
With minimal training, leprosy can be easily diagnosed on clinical signs alone;
A World Health Organization (WHO) Study Group recommended multidrug therapy (MDT) in 1981. MDT consists of three drugs: dapsone, rifampicin and clofazimine. This drug combination kills the pathogen and cures the patient;
MDT is safe, effective and easily administered under field conditions. MDT is available in convenient monthly calendar blister packs to all patients;
Novartis and the Novartis Foundation for Sustainable Development have made MDT available free of charge to all leprosy patients in the world. Through WHO, this MDT is provided to countries in sufficient supply to treat all people diagnosed with the disease.
High effectiveness of multidrug therapy
PB patients treated with MDT are cured within six months;
MB patients treated with MDT are cured within 12 months;
Patients are no longer infectious to others after the first dose of MDT. In other words, transmission of leprosy is interrupted;
There are virtually no relapses, i.e. recurrences of the disease after treatment is completed;
No resistance of the bacillus to MDT has been detected;
WHO estimates that early detection and treatment with MDT has prevented about three to four million people from being disabled. This suggests great cost-effectiveness of MDT as a health intervention, considering the economic and social loss averted.
History of treatment
The first breakthrough occurred in the 1940s with the development of the drug dapsone, which arrested the disease. But the duration of the treatment of leprosy was many years, even a lifetime, making it difficult for patients to follow;
In the 1960s, M. leprae started to develop resistance to dapsone, the worlds only known anti-leprosy drug at that time;
Rifampicin and clofazimine, the other two components of MDT, were discovered in the early 1960s.
The elimination of leprosy as a public health problem
Elimination of leprosy as a public health problem is defined as a prevalence rate on the global level of less than one case per 10 000 persons;
The widespread use of MDT has reduced the disease burden dramatically;
Over the past 20 years, more than 12 million leprosy patients have been cured. The prevalence rate of the disease has dropped by 90% and leprosy has been eliminated from 108 countries out of 122 countries where leprosy was considered as a public health problem in 1985.
Figures on the current leprosy situation
Approximately 755 000 new cases of leprosy were detected during 2001. At the beginning of 2002, 650 000 cases were registered and were undergoing treatment;
In 14 countries in Africa, Asia and Latin America leprosy is still considered a public health problem;
According to the latest available information, intensive efforts are still needed to reach the leprosy elimination target in six countries: Brazil, India, Madagascar, Mozambique, Myanmar, and Nepal. Taken all together, these countries account for 90% of the prevalence of the disease in the world in early 2002;
At the start of 2002, about 70% of the worlds registered leprosy patients are in India.
Actions and resources required
Political commitment needs to be strengthened in countries where leprosy remains a public health problem;
In order to reach all patients, treatment of leprosy needs to be fully integrated into general health services. This is a key to successful elimination of the disease. Strong leadership by ministries of health is absolutely necessary, especially in some of the major endemic countries;
Partners in leprosy elimination need to further accelerate activities and ensure that human and financial resources are made available for the elimination of leprosy;
The age-old stigma associated with the disease remains an obstacle to self-reporting and early treatment. The image of leprosy has to be changed at the global, national and local levels. A new environment, in which patients will not hesitate to come forward for diagnosis and treatment at any health facility, must be created.
The strategy for leprosy elimination
The following actions are part of the ongoing leprosy elimination campaign:
Ensuring accessible and uninterrupted MDT services available to all patients through flexible and patient-friendly drug delivery systems;
Ensuring the sustainability of MDT services by building the ability of general health workers to treat leprosy;
Encouraging self-reporting and early treatment by promoting community awareness and changing the image of leprosy;
Monitoring the performance of MDT services, the quality of patients care and the progress being made towards elimination through national disease surveillance systems.
To promote political commitment, leadership by ministries of health in endemic countries and partners support for leprosy elimination, the Global Alliance for Elimination of Leprosy (GAEL) was created in November 1999. Core members of the Alliance are governments of leprosy endemic countries, the Nippon Foundation, Novartis and WHO. The Alliance is co-operating closely with other national and international organizations, including the Danish International Development Agency (DANIDA), Handicap International, MORHAN, Pastoral da Criancia and the World Bank.
Definition of Leprosy
Leprosy is a chronic infectious disease which attacks the skin, peripheral nerves and mucous membranes (eyes, respiratory tract). Leprosy is also known as Hansen's disease because the bacillus which causes it was discovered by G.A. Hansen in 1873. It is most common in warm, wet areas in the tropics and subtropics.
Treatment of Leprosy
As of 1940, a treatment using dapsone is currently being used to suppress leprosy. Seldom is leprosy completely removed from the body; it can only be halted using a multi-drug treatment. Of the approximately two million cases (and half a million more each year), only one million are being treated in this way.
In addition, patients are taught to take care of themselves using a kind of visual check if they have significant nerve damage. Without the sensations of pain to identify cuts and bruises, patients must watch themselves constantly or be subject to dangerous infection.
What Leprosy Looks Like
Leprosy is characterized by multiple lesions accompanied by sensory loss in the affected areas. Usually, sensory loss begins in the extremities (toes, fingertips). In many advanced cases, gangrene sets in, causing parts of the body to "die" (necrosis) and become deformed.
Social Effects
Leprosy in all ages has been considered one of the more despicable diseases, and victims have been despised throughout history and kept in separate places (leper colonies, sanitariums). Even today, most people with leprosy are shunned by their neighbors and are held at arms length.
In the medieval period, leper colonies sprung up where victims of this then-untreatable disease would go to slowly die from the illness.
Leprosy throughout the Ages
by Eleanor E. Storrs
Until the coming of AIDS, leprosy was the most feared of infectious diseases. Even today, it warps the lives of millions of people; mostly in South America, Africa, and the Orient. The Black Death that swept though Europe in the last half of the 14th century, killing one third of the people, was more violent in its ravages. But it came and went quickly, like a great earthquake, followed by a series of after shocks.
Leprosy has tormented humans since the dawn of history; leaving lasting imprints on religion, literature, and art. It is a deep rooted part of the human psyche, with both mystical and physical meanings. Asians and Africans call it "the big disease" in many tongues because of the damage done to soul and body of those cursed with it.
We know nothing certain about the origins of leprosy, except that it is old, very old. An account of a disease that could be leprosy appears in an Egyptian papyrus inscribed about 1552-1350 B.C. But this is an imaginative guess, made by modern scholars that could be wrong.
Indian writings dated at 600 B.C, describe a disease that most experts agree was leprosy. It does not appear in the records of ancient Greece until the army of Alexander the Great came back from India in 326 B.C. In Rome, the first mention coincides with the return of Pompey's troops from Asia Minor in 62 B.C. Thus Asia could be the cradle of infection.
A Biblical Curse
The Bible often mentions a disease called leprosy. The words leprous or leprosy appear 54 times. It is from these accounts that the disease became linked to corruption of both spirit and body. The Book of Leviticus paints a chilling image of these ancient fears.
And the leper in whom the plague is, his clothes shall be rent, and the hair of his head shall go loose, and he shall cover his upper lip, and shall cry, unclean, unclean. And all the days wherein the plague is in him he shall be unclean; he is unclean: he shall dwell alone; without the camp shall his dwelling be.
The Bible equated this sickness with sin. It was a punishment by God for transgression. Thus Uzziah, King of Judah, wanted to burn incense in the temple of Jehovah, a ceremony reserved for priests. The priests opposed him, and Uzziah became angry. God struck him with leprosy.
And Uzziah the King was a leper unto the day of his death, and dwelt in a separate house, being a leper; for he was cut off from the house of Jehovah . .
The priests did not drive Uzziah into the wilderness like lesser sinners, but stripped him of power and denied him burial in the cemetery of kings.
The New Testament treats lepers more kindly, but even so, sets them apart from other sufferers. Jesus healed the blind and deaf but cleansed the lepers, implying a moral stigma. And then came a leper to him, beseeching him, and kneeling down to him, and saying unto him, "If thou wilt thou cans't make me clean." And Jesus, moved with compassion, put forth his hand and touched him, and saith unto him, "I will; be thou clean." And as soon as he had spoken, immediately the leprosy departed from him and he was clean.
During the early years of Christianity, healers looked at lepers with revulsion, and priests considered them depraved. Aretaeus of Cappadocia, a physician of the early 2nd century wrote:
When in such a state who would not flee- who would not turn away from them, even a father, a son, or a brother? There is danger also from communication of the ailment.
The Church ordered regulations against lepers at the Council of Ancyra in 314 A.D., defining them as unclean persons, bodily and morally. People classified as lepers included heretics.
Medieval Myths
By the Middle Ages, priests and savants accused lepers of a host of sins: they angered easily, suspected others of wanting to hurt them, had grievous dreams, and were schemers and deceivers. Medical writers of the era thought they threatened society; not only through infection, but by evil behavior.
Most of them warned that they burn with carnal desire, branding leprosy as a venereal disease. Priests sometimes gave them mock funerals before thrusting them out of society.
Within the church let a black cloth . . . be set upon two trestles at some distance apart before the altar, and let the sick man take his place on bended knees beneath it between the trestles, after the manner of a man dead . . . and in this posture let him devoutly hear mass . . . The priest then with the spade cast earth on each of his feet saying: "Be thou dead to the world, but live again unto God."
The priest then led him into an open field and forbad him to enter churches or houses; wash his hands or clothes in springs or streams; wear anything but a leper's cloak; touch anything he wanted to buy; enter taverns to buy wine; or to lie with any woman but his wife. The priest told him never to talk to people unless down wind from them; never touch railings without gloves; never touch children or give them gifts; and never eat and drink with people other than lepers.
He must always wear the grey or black mantle of a leper, and not use the dishes and spoons of others. He must warn people of his miserable presence with horn, clapper or bell; and beg for alms with a bag tied to the end of a long stick.
These were the rules imposed on lepers. Of course, they also had to obey the commandments of Moses. The medieval church left them a legacy of shame, degradation and rejection.
Leprosy Strikes Britain
We do not know when leprosy came to Britain, but by the 11th century it was a grievous plague. The first Norman Archbishop of Canterbury, Lanfranc, founded a leprosy hospice at Harbledown, near the cathedral, sometime between his arrival in England in 1070 and death in 1089.
Queen Matilda, daughter-in-law of William the Conqueror, endowed a hospice for leprosy victims outside the gates of London in 1101, and dedicated it to St. Giles, the patron saint of outcasts. At her behest, the lepers gave a "Cup of Charity" to condemned prisoners as they passed the door of the hospice chapel on their way to the gallows at Tyburn.
Many other hospices, sometimes called lazar houses, were founded before the end of the 11th century. When the Black Death swept through the land, there were 200 in Britain alone and as many as 20,000 in Europe. But the number of patients in each was small, ranging from one to a hundred. An extreme case was St. Giles in Norwich- it had one master, eight chaplains, two clerks, seven choristers, two nuns and eight lepers- a classic case of featherbedding.
Even with this proliferation of hospices, there were probably no more than two thousand lepers living in them out of a population of three million. But I suspect that these were only for the well-to-do. Poor villagers ravaged by leprosy probably fled to fens and forests, as happened in Louisiana in recent times.
If lepers were moral outcasts why were some of them provided for so abundantly? The attitudes of priests, nobles and kings differed with place and time; so treatment ranged from good to bad, with bad prevailing. Some priests thought the disease was a gift of God, because He chose lepers to bear one of the heaviest burdens of man. Others saw in leprous skin the brand of spiritual rot. Thus lepers were seen as both holy and sinful. God gave them special grace, or punished them for their sins.
Royal Attitudes, Royal Victims
Some kings loathed lepers. Philip V of France and Henry II of England had them burned at the stake without religious rites. Edward I, Henry's great grandson, was more charitable. He allowed them ritual funerals. Afterward, he had them carted to cemeteries and buried alive.
Other kings were compassionate. Henry III, father of Edward and son of John of Magna Carta fame, authorized the lepers of Bridgenorth to gather one horse-load of wood daily from the royal forest. Eight years later he made the same donation to the lepers of Shrewsbury.
Why these differences in outlook? They were probably reflections of personal traits. Henry II was an empire builder who abetted the murder of his archbishop, Thomas Becket. Edward I was a fearsome fighter who crushed the Scots at Dunbar and Falkirk. History remembers Henry III and his father John for their weaknesses. They may have felt they needed God's aid, and sought the prayers of anyone who could help them get it, even the leper's.
Yet Henry II had mixed feelings about lepers. He gave 40 marks to Harbledown hospital while on a pilgrimage to Canterbury to do penitence for the murder of the Archbishop. He may not have done this entirely from remorse. In 1158, during a visit to Paris, he made gifts to lepers and the poor, 12 years before Becket's murder.
Some kin of these kings were lepers. These include Henry II's daughter-in-law, Constance of Brittany, and his cousin Baldwin IV, the "Leper King" of Jerusalem. The disease blinded Baldwin; so he appointed regents. This led to power struggles among the nobles. He finally had to yield his throne to a five year old nephew.
Henry IV, the first Lancastrian King of England, died of an ailment that many people thought was leprosy. A skin disease ravaged his face so badly that he was repulsive to behold. There is no proof he had leprosy. But he had usurped the throne of his cousin Richard and possibly murdered him. In the eyes of his enemies, this crime and his mottled face equated him with a leper.
Robert the Bruce
The case of Robert the Bruce of Scotland is puzzling. We saw his bones displayed at a leprosy congress in Norway, where they were on loan from a Danish museum to show how leprosy causes bone damage. We were curious to learn how the remains of Scotland's greatest hero, the victor of Bannockburn, wound up in a foreign museum. We tried to visit the museum while in Copenhagen, but it was closed when we arrived.
We picked up the trail again in Scotland. Bruce died in 1329 of a mysterious ailment called the " great malady." He was ill for only two years, and his physicians did not quarantine him. No one mentioned leprosy until a generation later. Yet many reference books give it as the cause of his death.
He was buried at Dunfermline Abbey, and the site of his tomb forgotten. It was rediscovered in 1812. His skull was pitted and the upper jaw and nose eroded by disease. The people we talked to claimed he died of syphilis instead of leprosy. Physicians often confused these diseases in the middle Ages.
A cast of his skull is in the Anatomy Department of University of Edinburgh. The mysterious bones we saw in Norway were those of a man ravaged by leprosy, but are unlikely to be Bruce's.
We can add a curious postscript to this story. In a film called Braveheart Robert the Bruce, the eighth of his name, is portrayed as a clear skinned warrior. However, Hollywood showed his father, Robert the seventh, as a horribly disfigured leper. This old legend simply will not die.
The Stigma
What was this medieval leprosy that preyed on kings and commoners? Was it the disease we know today? In the minds of many, leprosy is not just a disfiguring disease: it is a disgracing disease. But its victims have done nothing to merit disgrace.
To ease their lot many caring people have looked for ways to soften the impact of the dreaded word. Some want to abolish it altogether and substitute Hansen's disease, after the discoverer of the leprosy bacillus. Others have sought to cleanse the word by showing that the aura of evil attached to it arose from accidents of history. They base their arguments on word origins, descriptions of disease and old works of art.
Most medieval savants thought that leprosy was the Biblical disease tzaraat, a Hebrew word used to describe ritual impurity associated with a skin ailment. When the scholars of Alexandria translated the Old Testament into Greek, they rendered tzaraat as lepra. The Greek lepra, meaning scaly, was a skin disease that is now unknown, but was not leprosy. About 300 B.C., physicians of Alexandria described a type of leprosy that they called elephas. In some way, the symptoms of elephas became associated with lepra that had acquired overtones of evil from tzaraat. Thus, the mystique of medieval leprosy may have resulted from fusion of three nuclei. The Greeks gave a name and the Hebrews an aura of evil to a disease described by Egyptians.
Most physicians do not think that Biblical leprosy was the disease we know today. Symptoms of tzaraat appear in many patients, but not in the same combinations mentioned in the Bible. It is likely that tzaraat was a state of ritual impurity associated with several skin diseases. Leprosy might have been one of them.
Paintings of Biblical and historic characters preserve the medieval image of leprosy. Among these are Miriam, Naaman and Emperor Constantine. But artists of the time often pictured the disease in a stylized way that lacks interpretive value. Typically, they showed the victim with bright red spots of the same size distributed uniformly over his body.
European artists used this convention from the 9th through the 15 centuries. By the 16th century, paintings began to show deformities of face and limbs. Leprosy in the late middle Ages was the same disease we know today.
Decline in Europe
The disease began to wane in Western Europe at the close of the middle Ages. Once rampant in Britain, by the 18th century it lingered only in the Shetland Islands. It reached a late peak in Norway during the 19th century, but the last leprosy hospital there closed in the 1950s. Physical disease receded, but reverberations of moral corruption linger in our language. Thus William Cowper wrote:
When nations are to perish in their sins,
tis in the church the leprosy begins.
In the 19th century, Tennyson associated leprosy with morality in his phrase:
A moral leper, I,
to whom none spoke.
Clearly, the words leper and leprosy carry overtones of evil.
Association of leprosy with sin is not unique to Western culture. Chinese and Hindu attitudes were similar, although for different reasons. Mohammedans claim they were more tolerant. Yet in 1253, Saracens killed all the lepers living in the hospice of the Order Hospitalier St. Lazare de Jerusalem.
Medical science did not vanquish leprosy in Europe. The reasons for its recession are still debated, and are still unknown. While it faded in Europe, it is still a major problem in Africa and the Orient. Explorers and settlers spread it throughout South America and the languid isles of the South Seas.
The stigma associated with leprosy perished for all time with the discovery that the disease occurs naturally in wild armadillos. Before then, many believed that leprosy was a unique punishment inflicted by God on humans for their sins. Now it must be looked upon as a bacterial infection devoid of religious significance. The mystique surrounding leprosy had started to collapse in Hawaii a century before.
Pestilence in Paradise
Hawaiians, long isolated from the rest of the world, were highly susceptible to white men's diseases. When leprosy struck, the authorities rounded them up and dumped them like trash on the shores of the island of Molokai. There they lived like starving animals stripped of humanity.
This time their exile could not be blamed on ancient priests or medieval kings, but on our own people; descendants of New England missionaries who had settled there only 50 years earlier. Father Damien, a Catholic priest of Belgian birth, heard of their plight and hastened to Hawaii to help them. He wrote:
For ten years past this scourge has spread itself in our archipelago in so frightful a manner that the government deemed itself obliged to exclude from the society of other islanders all those infected with it. Now these unfortunates, confined to a corner of the island of Molokai, hemmed in by impassable mountains and the seashore, are in perpetual exile. Of more than 2,000 conveyed here, 800 are still living . . .
We visited Molokai in 1984. A rim of cliffs towering to 4,000 feet bounds the north shore. Crouched beneath them lies a peninsula, two to three miles wide at cliff base, that juts two miles into the sea. A baby volcano burped up this sliver of land millions of years after monstrous bursts of lava flung Molokai above the water. Now it's little more than a green mound, its crater filled with grasses and scrub.
Calm beaches rim the west shore where the leprosarium now stands. But ragged volcanic rocks, flanked by stubs of black basalt, their tops rounded by pounding surf, guard it in the east. This was the rugged site of Kalawao, the final destiny of many exiles.
From anchored ships, sailors heaved supplies and cattle overboard to be hauled in by the few able bodied men of the colony. Then they rowed the newcomers to shore in longboats, to join the maimed hosts that preceded them. Food was poor, shelter scanty, the community lawless. There was no way out by land or sea.
When Father Damien came to Molokai, he found a small chapel dedicated to St. Philomena, but little else. For awhile he slept under a tree, but with the help of gifts from Honolulu, built a small house. From there he wrote of his charges:
These spots (caused by leprosy) cover the whole body, and sores appear on the feet and on the hands. The flesh decays and yields an infectious odor. The breath of the lepers poisons the air . . . I sometimes experience a feeling of repugnance. I am quite puzzled how to administer extreme unction when the hands and feet are but one sore. It is the sign of approaching death.
Damien choked down his repugnance, and strove to fill the needs of his flock. He bettered food supplies, built shanties and taught order to a lawless community. He always prayed with the dying, no matter how foul their sores.
With the help of those who could work, he built a road to the west shore of the peninsula, Kalaupapa, where St. Francis' church and the leprosy hospital now stand. There the shore is sandy and the surf mild. Eleven years into his self-imposed exile, Damien found he had leprosy. He had long been in the habit of beginning his sermons with "We lepers . . . "
Now it was true. His plight stirred sympathy throughout the world for Damien and his cause. Help came to Kalawao. Brother Joseph Dutton, an American Civil War Veteran, came to share Damien's burdens. Mother Marianne and her group of Catholic Sisters opened a school for girls, children of leprosy victims, at Kalaupapa, the" clean" coast of the peninsula.
Martyr of Molokai
Sympathizers throughout the world mourned Damien's death. Robert Louis Stevenson, then a journalist, visited Hawaii to write the story of the "Martyr of Molokai." It was well he did, since Damien had enemies, even after death.
One of them, Dr. Hyde, a Presbyterian minister from Honolulu, wrote a letter to a newspaper saying Damien was coarse, bigoted and immoral. Stevenson wrote a thundering reply that shook the conscience of the Protestant world. Point by point, he ripped Hyde to shreds:
"Damien was coarse" . . . you make us sorry for the lepers who had only a coarse old peasant for their friend and father . . . "headstrong" . . . I thank God for his strong head and heart! "Damien was bigoted" . . . in him his bigotry, his intense and narrow faith, wrought potently for good, and strengthened him to become one of the world's heroes and exemplars.
Damien's martyrdom, magnified by Hyde's stupidity and Stevenson's eloquence, marked a turning point on how the world looks at lepers. People finally realized they were victims of disease, not depraved monsters.
In 1936, Belgium moved Damien's body from Molokai to Louvain with all the panoply the nation could muster. Left behind were the remains of his helpers and followers, Brother Dutton and Mother Marianne. It would have been better to have left Damien to rest with them.
When we visited Molokai, the hospital had ceased taking new patients. The Medical Director, Dr. Oliver Hasselbladt, told us the grounds would become a National Monument when the last old leprosy patient died. "If the church ever canonizes Damien," he said, "these grounds will become as holy as Lourdes.
Cajun Country
Leprosy is still endemic in Hawaii and six mainland states, including Louisiana. Early settlers or slaves from Africa might have brought it there during French and Spanish colonial days.
Or French Canadians could have carried it when the British expelled them from Acadie in the 18th century. Physicians found leprosy in their homeland, New Brunswick, in 1817. It must have been there much earlier.
Longfellow told the story of their exile in his epic poem about Evangeline and her lover Gabriel. In real life, his heroine was Emmeline LaBiche. She landed at St. Martinsville, a town on Bayou Tech, about 12 miles north of my home in New Iberia, to find that Gabriel, in real life, Louis Arceneaux, had married another woman.
These Acadians, now called Cajuns, fanned out along the southwest coast of Louisiana, and are the dominant ethnic group in a 22 parish region known as Acadiana. During my life there, I heard many tales about local people with leprosy.
A family named Landry had two children with the disease, people said. They lived in an attic to hide from health officials. A nurse with long experience in the area told me that many leprosy victims had taken refuge in remote parts of the Atchafalaya Basin; a vast wilderness of slow waters hemmed in by levees. A great flood drove more than 40 of them to high ground, where people saw them wandering in nearby hamlets.
Denis Comeaux caught many armadillos for me, but I never met him. He had a corroding skin disease and shunned outsiders. All my contacts with him were through his family. One day I went to his house to collect animals. His wife said he had died. I will never know for sure if Denis had leprosy.
Much later I learned that people who handle armadillos can get leprosy from them. I also found many wild armadillos with leprosy in the area where Denis lived.
Leprosy was part of New Iberia folklore and had a long history in Louisiana. We know the disease occurred in New Orleans in colonial days, since a hospice called La Terre de Lepreax stood near the city then. But in 1804, New Orleans physicians claimed they were unable to find it among local residents.
There the question rested until 1872, when Dr. W.G. Kibbe of Abbeville, about 20 miles west of New Iberia, sent Felecien Ourblanc to New Orleans for examination by Dr. Joseph Jones. Felecien had leprosy.
The Road to Carville
During the next few years, physicians found other cases near Abbeville. They made additional surveys in New Orleans and rural Louisiana. By 1892, they concluded that leprosy, formerly thought to occur only in people of foreign birth, was endemic in Louisiana, mostly among whites.
The state selected a smallpox hospital in New Orleans, managed by Dr. J. C. Beard and his son, for care of patients. The hospital got little attention until 1893. A reporter from the Daily Picayune wrote a story about a girl from New Iberia with leprosy. She was shipped to New Orleans in a boxcar labeled freight, and lodged in Dr. Beard's "Pest House." The reporter visited her, and in his article claimed neglect and possible starvation.
This scandal forced the legislature to set up a State Board of Control. Health officers suggested many sites for a home for lepers near New Orleans, but property owners opposed them. Finally, the state leased Indian Camp Plantation on a bend of the Mississippi, about 85 miles up river. Physicians thought this would be temporary and hoped to find a site closer to Charity Hospital. But property owners fought all attempts to relocate in the city. Finally, the state bought Indian Camp Plantation, and gave it a new name - Louisiana State Home for Lepers.
The home was isolated and run down, and there was no resident physician most of the time it was under state control. On January 3, 1921, the Federal Government annexed the property and patients. It became the first and only U.S. Public Health Service Hospital devoted exclusively to leprosy. Most people know it as Carville.
In March of 1968, I went to Carville to propose use of the armadillo as an animal model for leprosy research. This visit was the first step in an agonizing collaboration with U. S. Public Health Service that would endure for four years.
Cajun Country
Leprosy is still endemic in Hawaii and six mainland states, including Louisiana. Early settlers or slaves from Africa might have brought it there during French and Spanish colonial days.
Or French Canadians could have carried it when the British expelled them from Acadie in the 18th century. Physicians found leprosy in their homeland, New Brunswick, in 1817. It must have been there much earlier.
Longfellow told the story of their exile in his epic poem about Evangeline and her lover Gabriel. In real life, his heroine was Emmeline LaBiche. She landed at St. Martinsville, a town on Bayou Tech, about 12 miles north of my home in New Iberia, to find that Gabriel, in real life, Louis Arceneaux, had married another woman.
These Acadians, now called Cajuns, fanned out along the southwest coast of Louisiana, and are the dominant ethnic group in a 22 parish region known as Acadiana. During my life there, I heard many tales about local people with leprosy.
A family named Landry had two children with the disease, people said. They lived in an attic to hide from health officials. A nurse with long experience in the area told me that many leprosy victims had taken refuge in remote parts of the Atchafalaya Basin; a vast wilderness of slow waters hemmed in by levees. A great flood drove more than 40 of them to high ground, where people saw them wandering in nearby hamlets.
Denis Comeaux caught many armadillos for me, but I never met him. He had a corroding skin disease and shunned outsiders. All my contacts with him were through his family. One day I went to his house to collect animals. His wife said he had died. I will never know for sure if Denis had leprosy.
Much later I learned that people who handle armadillos can get leprosy from them. I also found many wild armadillos with leprosy in the area where Denis lived.
Leprosy was part of New Iberia folklore and had a long history in Louisiana. We know the disease occurred in New Orleans in colonial days, since a hospice called La Terre de Lepreax stood near the city then. But in 1804, New Orleans physicians claimed they were unable to find it among local residents.
There the question rested until 1872, when Dr. W.G. Kibbe of Abbeville, about 20 miles west of New Iberia, sent Felecien Ourblanc to New Orleans for examination by Dr. Joseph Jones. Felecien had leprosy.
The Road to Carville
During the next few years, physicians found other cases near Abbeville. They made additional surveys in New Orleans and rural Louisiana. By 1892, they concluded that leprosy, formerly thought to occur only in people of foreign birth, was endemic in Louisiana, mostly among whites.
The state selected a smallpox hospital in New Orleans, managed by Dr. J. C. Beard and his son, for care of patients. The hospital got little attention until 1893. A reporter from the Daily Picayune wrote a story about a girl from New Iberia with leprosy. She was shipped to New Orleans in a boxcar labeled freight, and lodged in Dr. Beard's "Pest House." The reporter visited her, and in his article claimed neglect and possible starvation.
This scandal forced the legislature to set up a State Board of Control. Health officers suggested many sites for a home for lepers near New Orleans, but property owners opposed them. Finally, the state leased Indian Camp Plantation on a bend of the Mississippi, about 85 miles up river. Physicians thought this would be temporary and hoped to find a site closer to Charity Hospital. But property owners fought all attempts to relocate in the city. Finally, the state bought Indian Camp Plantation, and gave it a new name - Louisiana State Home for Lepers.
The home was isolated and run down, and there was no resident physician most of the time it was under state control. On January 3, 1921, the Federal Government annexed the property and patients. It became the first and only U.S. Public Health Service Hospital devoted exclusively to leprosy. Most people know it as Carville.
In March of 1968, I went to Carville to propose use of the armadillo as an animal model for leprosy research. This visit was the first step in an agonizing collaboration with U. S. Public Health Service that would endure for four years.
HomeSweetDisney
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