I have a belief aka Theory that "Aliens" as we seem to perceive them are actually us (Humans) from some point in our future. Like way in the future, 1000's or tens of 1000's of years. They are a more evolved and completely different species than us. But they came from us. I believe that they are here because of a continuous loop of evolution. They seeded our planet with their DNA many tens of 1000's of years ago only for us to evolve into them and we will do the same once we are them. The way I see it we Humans have 3 stages of evolution in a cycle that has been going on since the formation of our universe. The earth is but one single planet involved in this never ending cycle of Seeding, Natural selection and evolving. We are in the middle stage now and will some day (10000+ years) be in the third and final stage and then seed a new planet ourselves. The reason for it is that once we are at the end of the third cycle we loose our ability to reproduce, even though we are living for 100's or even 1000's of years at that point. We would eventually die out if we didn't re seed a new planet and start the evolutionary cycle over again. So the "Aliens" we see watching over us studying us and tampering with our Nuclear programs, are simply future, evolved humanoids watching over and tending to their infants. Keeping us out of trouble and making sure we don't destroy ourselves. Just as we do with our own infants/offspring to ensure our own self preservation. They are simple preserving themselves. This is just my opinion. I welcome anyone else opinion in favor of or against mine. Thank you for taking the time to read my rants lol.
The only reason we cannot, is because the universe is expanding outwards from the center and time is linear. Therefore we follow a linear time pattern. If the universe stopped expanding we could travel in either direction at will. That is the basic idea anyway.