ATG wrote:
IMatter never goes away it just changes form.
Keep in mind though, matter can change into energy (the basic principle of the atomic bomb), but it takes a truck load of energy to transform back into matter. Given the universe's basically moves from a highly ordered state to a low order (all to do with entropy
http://en.wikipedia.org/wiki/Entropy ), it is unlikely that once you transform into an energy state, you are going to be able to change back.
As for aliens out there, almost certainly "Yes". Although either answer is a remarkable one.
Have they visited us? Extremely unlikely. The universe has been around for about 13 billion years, but there really has only been a reasonable short time where life could develop into intelligence capable of interstellar travel. Just travelling would have taken far too long, and the odds of them finding another system with life on it would have been extremely small. So they would have had to decide where they wanted to go before leaving rather than just jaunting around and hope for the best. That means they would have had to decide to come here long before we even invented radio, or steam engines, or probably even the wheel come to think of it. There would have been nothing remarkable about this planet for them to make the call to come here. If we develop interstellar travel, we would have to pick a star that gave some clue to life, but the most likely scenario if we got there would be that the civilisation would have died out by the time we got there (keeping in mind it would have taken many years fore the signal just to reach us, and an even longer time for us to trace it and follow it back to the source).
Also, no government in the world today, even totally oppressive ones would have been able to keep it a secret.
As for transportation devices, you would have to know where every single atom is in order to successfully duplicate whatever you were transporting and Heisenberg's uncertainty principle precludes that from ever happening. They may have transported a sub atomic particle, but that is a long way off from transporting an organic being, with memories. It ain't gonna happen folks. Shame really, I hate sitting in a plane for 10 hours just to get somewhere.