Yes, as logically, it is a statical certainty that they exist purely due to the size of our universe and indeed the multiverse.
Most UFO sightings, I believe, are foo fighters.
Foo fighters started appearing during World War II. Allied pilots regularly reported seeing bright objects following them, changing direction extremely quickly and accelerating away at great speed.
The Ministry of Defence felt that these foo fighters were almost certainly Nazi technology; indeed, the Nazis were investigating some odd stuff...
That's a structure nicknamed the Flytrap. It is made out of reinforced concrete and has heavy cabling in each arch, apparently powered by a nearby power plant. The Nazis built it during the war as part of a research project surrounding a device known as the "Bell device".
It's antigravity, based on Einstein's theories.
The project was reportedly quite advanced and was labelled as "war-decisive"; it was the only project to be labelled as such - not even the atomic projects were as important.
As the allies advanced, a man called Hans Kammler, an SS General, head of research, destroyed the experiment as best he could and shot many of the researchers in an effort to keep the technology from allied hands.
The powerplant, basic infrastructure and the flytrap remain. The mines in which the bell device was researched is now flooded and inaccessible; rumours suggest that many of the scientists are still down there.
More detail
here on me temp' website (it will look better real soon, honest!)
Rich::