Humans must continue exploring space, if only for the romance of it, and time travel should be possible, but engineers will have to figure out a way to warp space-time to be sure, famed physicist Stephen Hawking says. 

On paper, time travel should also be in cards because of Albert Einstein's general theory of relativity, which allows for the potential to warp space-time so much that a traveler could leave Earth in a rocket and return home before he or she ever departed, Hawking said. Of course, that means you have to be able to warp space-time, which is pretty tricky. 

He compared humanity's view of the universe to that of a goldfish looking out of its bowl, saying that we can't be sure our view is the "correct" one. We might be in a giant goldfish bowl, for there is no single, absolute picture of reality, he added.

In an April episode of his TV series "Into the Universe with Stephen Hawking," the physicist warned humanity not to be so rapturously eager to find extraterrestrial life. Advanced spacefaring civilizations could be on the prowl for resources, he said on the show. They may be interested only in conquering and strip-mining the Earth, not getting to know us.

"Because there is a law such as gravity, the universe can and will create itself from nothing," he wrote. "Spontaneous creation is the reason there is something rather than nothing, why the universe exists, why we exist. It is not necessary to invoke God to light the blue touch paper and set the universe going."