Well; depends on what you mean. If you think of stuff that throws off gasses at the opposite of moving direction, an ufo-like thing would be beliveable.I think they have had the technology to create flying saucers for a long time now.
I mean; if you had a gyroscope(my thought.. dunno if there is anything better) to stabilize it and then had another power to keep it above the ground, it would be possible.
Using the gyroscope would even mean that you barely need any computer power (at all) (you could also have more throttles and then calculate wich one to give more power to stay stablized. that would require computers!)
About the time and light-speed problems:
My biggest problem is not to believe we will get to other stars or if anyone has been to visit us here, my problem is to believe that we can communicate. The fastest way of communicating (the ONLY WAY!) is radiowaves. They travel at the speed of light, and nothing can go faster (then there is this theory that particles can communicate faster between each other, however its just a theory). So if we travel 10 lightyears, the radio communication will take 10 years. And we talk millions of lightyears...
my second largest problem is that nothing can travel faster than the light, unless the theory about communication is correct. But then again, i dont know how much faster it will be... It IS a problem...
Time travelling;
Well. how??? what should store information about the past, why would anything have information about the future?
its frustrating!




