What physics says about time travel

The concept of time travel has captivated readers and moviegoers for many decades now. But while people have been fascinated by the idea, no one has managed to make the notion of time travel any more of a reality than before. It seems like a dream that's just a bit too far from reach. But in an age where science continues to push the boundaries of what's possible, do we even know—in theory—what the physics of time travel might involve?

Curious? Click on to discover what we know so far about the prospect of journeying through time.

How time works

It might surprise you to learn that exactly how time works is still a bit of a mystery to physicists. For now, travel into the future seems possible (as we hurtle toward it each day).

Theory of relativity

For Einstein, time was relative. A key outcome of relativity is that the flow of time isn't constant. Time can speed up or slow down, depending on the circumstances.

Time is relative

The fact that it can speed up or slow down is where the concept of time travel enters as a possibility, with real-world repercussions.

Gravitational pull

Likewise, time passes more slowly in an intense gravitational field, for example in a black hole.

GPS satellites

For us, day-to-day, the relativistic effects of time are too subtle to notice. But they actually do affect the satellites used for global positioning system (GPS).

Future travel

Relativity means it's possible to travel into the future. Whether traveling at the speed of light or spending time in an intense gravitational field, you would experience a relatively short amount of subjective time.

Backwards travel

Relativity does open some doors for backwards time travel, but right now these haven't evolved past the theoretical stage.

Closed-circle loop theory

However, a major problem with this theory is that there is no existing closed-circle loop anywhere in the universe. It's pure theory.

Cosmic strings

In 1991, a physicist named Richard Gott put forward the theory that such a closed-circle loop would be possible if there were two "cosmic strings" that moved past each other in opposite directions.

Wormholes

Another phenomenon that's seemingly allowed by relativity is wormholes. Theoretically, it's possible for space-time to be folded like a piece of paper, allowing a tunnel to be punched through to create a shortcut between two widely-separated points, AKA a wormhole.

Intense gravitational field

If wormholes did exist, they wouldn't have a very long lifespan. In fact, if they are two black holes that have joined together as is theorized, their intense gravitational field would collapse under its own gravity.

Negative energy

In order to solve the size and gravity problems, a large amount of negative energy would be required inside the atom. The energy of the atom field must have more positive energy overall, however, so even if tiny pockets of negative energy expanded inside, it's not a very realistic proposal.

Non-locality

Strange observations have emerged from quantum mechanics, notably non-locality. This is where a change in a particle's state in one location can instantaneously influence another "entangled" particle somewhere else.

This is because in order for the effect to be instantaneous, the information would have to move faster than the speed of light. This is supposed to be impossible.

Retrocausality

If this is the case, our linear concept of time isn't necessarily correct. In fact, it means information from the future is always spiraling back to influence the past. It's worth bearing in mind that this theory is not universally accepted either, with some seeing it as more outrageous than non-locality.