Science & Technology

Wormholes Might Cast a Visible Shadow

Like artificial gravity and anything quantum, wormholes are one of those cheap writing tools that seem to make any sci-fi plot point possible. However, they're also objects predicted by real scientific theories that real scientists are searching for. But before you go searching for something, you need to know what it looks like. According to a recent paper, to find a wormhole, you just have to spot its shadow.

Bridge to Nowhere

The concept of a wormhole was first conceived by Albert Einstein and Nathan Rosen. Einstein's general theory of relativity says it's possible to compress mass into a point so small that density and gravity reach infinity. That space is called a singularity, and it was a problem for Einstein since infinities aren't exactly clean on paper. In a 1935 paper, Einstein and Rosen argued that you could avoid a singularity by extending it to a second location. That would create a tube-shaped path between two points by wrinkling the fabric of spacetime as if you pinched together the two sides of a balloon. This "Einstein-Rosen bridge" is what most people call a wormhole.

Wormholes are different from black holes, but they're related. Some concepts of wormholes require a black hole at one end. Both black holes and wormholes have an intense gravitational pull that warps the fabric of spacetime and bends the path that light takes around them. But not all light — some unlucky light particles fall in, producing a dark void scientists call a shadow.

In fact, as we speak, scientists are combing through the first batch of data collected by the Event Horizon Telescope, which they hope will result in a visible observation of a black hole. But black holes are confirmed to exist; the existence of wormholes is much less airtight. One glaring issue is that if they do exist, we don't know how to keep one from collapsing instantly; to solve that, scientists came up with a theoretical material with negative pressure called "exotic matter" to keep the tunnel open. Of course, we don't know what, if anything, exotic matter really is. But just because you don't know if something exists doesn't mean you can't go looking for it — and Rajibul Shaikh, a physicist at the Tata Institute of Fundamental Research in Mumbai, has an idea of what to keep an eye out for.

If a Wormhole Sees Its Shadow...

In a paper released ahead of peer review in the preprint journal arXiv back in March, Shaikh concluded that a particular type of object called a Teo class rotating wormhole would cast a larger, more distorted shadow than one cast by a black hole. While your garden-variety wormhole is static and round, a Teo-class wormhole is rotating and asymmetrical. That's thought to keep the exotic matter moving around enough to avoid hitting any would-be interstellar travelers, which is what we hope to be someday.

It may surprise you to learn that scientists have already calculated a rotating wormhole's shadow, but according to Shaikh, they neglected to take the "throat," or tunnel, into account. But with this new analysis, scientists have a better shot at identifying a wormhole if they see one — but only if it's this asymmetrical, rotating class of wormhole.

Chances of spotting any wormhole are slim, of course. "It's highly unlikely that macroscopic wormholes exist," John Friedman, a physicist at the University of Wisconsin-Milwaukee, told Live Science. "If they do, the unknown nature of the matter supporting the wormhole makes it impossible to predict the shadow." That's because to know the shape of the shadow requires knowing the geometry of the wormhole, and knowing the geometry of the wormhole requires knowing the nature of the exotic matter within it. And that, we're sad to say, is a long way off.

Fascinated by wormholes? Definitely 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.

What Are Wormholes? Connecting Two Points in Spacetime

Written by Ashley Hamer June 15, 2018

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