If we formulate the fundamental theory of nature in a timeless language, we have then the problem of recovering the familiar notion of time. - Carlo Rovelli

[I]n a fundamental description of nature we must "forget time"... this can be done in the classical and in the quantum theory.

What makes the difference is the mass. ...[T]he earth is a big mass and it slows down time. If you go to a bigger mass, like Jupiter, it's stronger. If you go near a big star it's stronger. If you're near a black hole... it's even more strong, so strong that if you go very near... time essentially stops down. It goes very, very, very slowly.

If we had a starship, we could move near a black hole, stay there for a half hour and then come out. Outside hundreds of years could have gone. So we could... come away from the black hole into the far future easily.