OPTION 5: Take a wormhole shortcut

According to General Relativity, time flows at different rates in different gravity. So to create a time machine, we just need to connect two such regions and travel between them.

Imagine one place on Earth where time passes at the normal rate and another place near a black hole, where time flows more slowly thanks to the intense gravity. If two identical clocks begin ticking on Monday – one on Earth and one at the black hole – by the time it’s Friday on Earth, it would only be Wednesday at the black hole. So, if you could travel instantaneously from Earth to the black hole, you could go from Friday back to Wednesday. Theoretical physicists Michael Morris and Kip Thorne proposed such a method using a wormhole.

A wormhole is a shortcut through spacetime, predicted by Einstein. Imagine two points, A and B, on a piece of paper. If the paper is folded in two, A and B are now much closer. If they could be connected somehow you could travel between them more quickly than if you had to go across the paper. This is a shortcut analogous to a wormhole. If the Earth and the black hole are connected by such a wormhole, we have a time machine. The problem with wormholes is they snap shut in the blink of an eye and would have to be propped open by something with repulsive gravity for us to travel through them. Actually, most of the stuff in the Universe – dark energy – does have such repulsive gravity. The problem is it’s too weak to keep a wormhole open. Also, in order to prop open a wormhole big enough for a person to crawl through, we’d require energy equivalent to that radiated by many of the stars in our Galaxy over their entire lives.

Wormholes offer a way to travel through space to a region where time flows differently. The problem is keeping the wormhole open.