Physics

# What Would Happen If You Stopped Time?

Though it's not as popular a trope as traveling back in time or moving at super speed, stopping time is a well-worn tradition in science fiction. The Marvel superhero Dr. Strange can do it, Flash Man from Mega Man 2 can do it, and Hiro Nakamura from the early 2000s TV show "Heroes" can do it. But what would happen if you stopped time in real life? It turns out that the real-world effects wouldn't be all that practical — but they sure are a fun way to learn about physics.

## Freeze Frame

First things first, we have to define what we mean when we say "stop time." If you had the power to stop time, period, you obviously wouldn't get much use out of it because you'd be frozen in place. So let's assume we mean "stop time for everything but you." That's precisely what happens in Nicholson Baker's 1995 novel "The Fermata," where the protagonist Arno Strine has the ability to stop time and move through the paused world unencumbered (though it's to do things that make us advise against sharing this book with children).

Even then, we need to make some allowances. As physicist Sean Carroll writes in "From Eternity to Here," you'd have to account for every molecule of fluid and air inside and outside of Arno Strine's body. If he can move around freely, then we can assume the molecules within him can, too. "But if the air in the rest of the room has truly stopped experiencing time, each molecule must remain suspended precisely in its location; consequently, Arno would be unable to move, trapped in a prison of rigidly stationary air molecules," Carroll writes.

That definitely doesn't work. So let's imagine that time keeps flowing normally for the molecules within a certain distance of Strine's body. Beyond that, time stands still. At that point, could he do what he wants in this time-frozen scene? Unfortunately, the answer is still no.

## Do the (Micro)Wave

Our generous allowances for Arno Strine's superpowers haven't yet accounted for every particle in play. As you read this, particles of light called photons are traveling at the speed of light (to state the obvious) from your screen into your eyeballs. Likewise, the sounds you hear travel at the speed of sound (professional science writer right here) through the air as pressure waves that eventually reach your ears to vibrate your eardrums. If you stopped time, all light and sound would stop, too. In some interpretations, this would leave Strine instantly deaf and blind in his frozen scene.

In a video for Play Noggin about the time-stopping video game Superhot, Julian Huguet comes to a similar conclusion, although he thinks it would take a little longer. "Photons traveling at the speed of light get their own special rules," he says. "They experience no time or distance as far as they know; they just get emitted and absorbed." In Huguet's interpretation, this means that any photons that had already been emitted by a lightbulb, a device's screen, or the sun would keep on traveling while the world around them stopped. Depending on the light source (and whether you were inside or outside), you could get a grace period of anywhere from a fraction of a second to a full eight minutes where you could still see. You'd still hear silence, but that's generally how these time-stopping sequences play out, anyway.

But we want unlimited time, so let's make one more tweak to this frozen-time scenario. What if instead of stopping time, you just slowed time to a crawl? That also wouldn't work. When you slow down electromagnetic waves (light) and pressure waves (sound), you get waves of a lower frequency. We all know what happens to sound at a lower frequency: The tone drops, in this case to a frequency that's likely below the range of human hearing. Light at a lower frequency redshifts — that is, it moves into the longer-wavelength end of the electromagnetic spectrum, down into the infrared, microwave, and radio-wave realm. So while light would have a chance to reach you, it would likely be invisible to your eyes.

Carroll has an ingenious solution to this, though: Just shine light of a faster wavelength on the stuff you want to see. "Perhaps X-rays would be redshifted down to visible wavelengths," he writes, "but X-ray flashlights are hard to come by." Shooting X-rays and gamma rays all over the place also isn't all that healthy for the people around you.

In the end, maybe the ability to stop time is one of those superpowers in the "careful what you wish for" category, like reading thoughts and turning everything you touch into gold. If you do happen to possess such a gift, we've just got one piece of advice: Get an X-ray flashlight and a good lawyer.

Ashley Hamer