Einstein's Theory Allows Time Travel, But There's a Catch

Even Albert Einstein realized in 1949 that his own equations allow you to go backward in time.

If the universe were to rotate, for example, and you went with the flow,

you could go around the universe as it rotates, and you could come back into the past.

So simply walk, looking around a circle. You would come back not where you left,

but you would come back yesterday. Thus, even Einstein realized that his own equations

allow for time travel. In his memoirs, of course, Einstein had to address the question,

is time travel possible? And he said, "Aha, I have found a loophole." That is,

the universe expands. It doesn't rotate. So it means that if the universe rotated,