Theories of the Ufo phenomenon

the ancient astronaut theory
This theory suggests that at the beginning of human history an alien race visited Earth for some reason, and interacted with the species on the planet. There are several sub theories involved here such as aliens genetically engineered mankind, etc .

the inter dimensional theory
This theory suggests UFO's are piloted by a race capable of travelling through dimensional gaps to visit our world, in fact they may even have come from Earth themselves in a different dimension.

the time travel theory
This theory suggests that in the future man has developed the means of time travel, which is actually possible according to Einstein. They have come back to study us as archaeologists sift through the soil today, looking for our past. Or they could be coming back to try and prevent an event that will happen in our future (their past) that drastically effected them and will us too.

the extra-terrestrial hypothesis
This is the famous theory which everybody thinks of when the topic of UFO's comes up.

the human theory
Technology is at present advancing at a dramatic rate, the computer you are reading this off now will, no doubt be obsolete in 2 years time at the most, probably 1!

This theory suggests that mankind has already developed the means for anti gravity flight and free energy and the like, but the governments are keeping it top secret to prevent economic collapse. There is quite a bit of evidence that during WWII Hitler has actually developed Saucer shaped craft that could seriously out-manoeuvre Allied craft at the time!!! It is said that if Hitler had delayed the end of the war anymore then the Nazi's would have had a totally different means of air combat which would have probably reversed the outcome of the war totally!

the earth theory
What if there was another species on Earth that equalled man's intelligence, or even excelled it (not hard, some may say!).

What if this race lived underground, or deep in the oceans away from mans influence. Why not??? Man doesn't know everything, well not yet, or for a long time yet!!! There are many a cases of UFO's rising or diving into/ out of the deep oceans, and there are plenty of places to hide!