Keegan from Normal, IL wants to know:
“I have heard a few theories about using wormholes in space to travel from one place to another almost instantly, and I have heard that by doing that you can also travel through time in a similar way. In theory, how does time travel with wormholes work?”
It goes like this: Light travels at a finite speed, just like sound does (as you’ll know if you’ve ever counted the seconds between when you see a lightning strike and the boom of thunder that follows). But because even light has a finite speed, that lightning strike actually happens a few instants before you even see it—as a result, two people different distances from the lightning would disagree on how long ago it happened. This is called the relativity of simultaneity—the idea that, depending on your reference point, the same set of events can seem to happen in a different order.
Now, since nothing moves faster than light, it’s impossible to see the same flash of lightning twice. If you COULD travel faster than light, however—and this is where the wormholes come in, allowing you to travel between distant points in less time than it would take moving at the speed of light), you’d be able to witness events that happened in the past—if your wormhole deposited you five light-years from Earth and you turned a telescope toward our planet, you’d see the events of five years ago.
Of course, there’s always the other type of time travel, the eminently more possible forward time travel. When you’re moving at relativistic velocities—those approaching the speed of light—time seems to slow down for you, relative to a stationary observer. This is called time dilation, and it’s a very intriguing concept that results from the math of Einstein’s relativity. If you have a set of identical twins and one leaves for a five-year excursion in a rocket traveling 99.5% the speed of light while the other stays here on Earth, time will pass slower for the traveling twin. When they return to Earth, the traveler will find that their twin—and the rest of the world with them—has aged fifty years in the five years that the trip seemed to take—effectively enabling the possibility of traveling to the future! Unfortunately, we’re a long way off from being able to utilize this technique, and there’s no corresponding way to turn back the clock.
Hope this helps—and keep the questions coming!