Science & Technology

# Want to Time Travel? You'll Probably Need a Wormhole

Some of the greatest sci-fi shows and movies center on the concept of time travel. It's no wonder — who wouldn't want to pop over to the distant future to see how their life turned out or shuffle back to the past to kill Hitler? The possibility of time travel, especially to the past, is vanishingly unlikely. But if it is possible, your best bet is via another unlikely concept: a wormhole.

## Blast From the Past?

You can take a deep dive into the concept of wormholes in our recent article on the topic, but in the most basic terms, a wormhole is a passageway that connects two points in space as if there's no space between them at all.

Say you had a balloon, which would represent spacetime, with a dot on either side, which would represent the two mouths of a wormhole. The wormhole itself, then, would be the incredibly short path you made if you pushed the two dots inward toward each other and connected them. You could get from one side of the balloon-universe to the other by moving through hardly any space. That makes wormholes a tantalizing option for faster-than-light travel since you could effectively travel from one point to another faster than light without actually breaking that cosmic speed limit.

But here's where things get really interesting: The wormholes don't have to be fixed in space. The two ends are quantum linked in such a way that one or both could be moving at pretty much any velocity and they'd still get you from one end to the other. And when you've got moving objects — especially fast-moving objects — you've got the exciting principles of special relativity at play.

Special relativity says that the faster you travel through space, the slower you travel through time. If you had some way to build a wormhole so that you could put the ends anywhere you wanted, you could put one end on the Earth and one end on a spaceship. Say you flew that spaceship at close to the speed of light for, say, six hours, then returned to Earth the way you came. During the 12 hours you were traveling, 10 years would have passed on Earth. Whoa.

But wait! Don't mourn all the Netflix you missed out on: You've got one end of a wormhole in your spaceship, remember? Because the other end stayed put on Earth where it's still 10 years ago, you could theoretically walk through the wormhole and travel 10 years in the past. Even better, people in the past could also walk through the wormhole and end up in the future. Just no "Game of Thrones" spoilers, okay?

## An Einstein-Rosen Bridge Too Far

Of course, this all comes with a big helping of caveats. There's no proof that wormholes exist and a lot of the math that suggests they could says they'd be smaller than an atom and might only stay open for a fleeting moment in time.

Other theories say they'd require a black hole on at least one end, which would most likely kill you before you got to see who wins "American Idol 2037." And in almost all of these scenarios, the wormhole staying open requires a bunch of theoretical stuff with negative energy called "exotic matter," which is very unlikely to exist. That's all before you get to the sticking points of time travel, like entropy (which says time can't go backward) and the grandfather paradox (which asks what would happen if you went to a time before you were born and killed your grandfather).

In the end, time travel through a wormhole is an improbability turducken: an unlikely possibility wrapped in an unlikely possibility. But that doesn't mean it's impossible. Just get your DVR ready, that's all we're saying.

For more mind-blowing theories about traveling through space and time, check out "The Science of Interstellar" by physicist and wormhole expert Kip Thorne. The audiobook is free with a 30-day trial of Audible. We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.

Ashley Hamer