How a 5-Dimensional Black Hole Could Break Down General Relativity

Space physics doesn't get freakier than this.

University of Cambridge

We don’t live in a world that’s pinning the survival of humanity on Matthew McConaughey’s shoulders, but if it turns out the plot of the 2014 film Interstellar is true, then we live in a world with at least five dimensions. And that would mean that a ring-shaped black hole would, as scientists recently demonstrated, “break down” Einstein’s general theory of relativity. (And to think, the man was just coming off a phenomenal week.)

In a study published in Physical Review Letters, researchers from the UK simulated a black hole in a “5D” universe shaped like a thin ring (which were first posited by theoretical physicists in 2002). In this universe, the black hole would bulge strangely, with stringy connections that become thinner as time passes. Eventually, those strings pinch off like budding bacteria or water drops off a stream and form miniature black holes of their own.

This is wicked weird stuff, but we haven’t even touched on the most bizarre part. A black hole like this leads to what physicists call a “naked singularity,” where the equations that support general relativity — a foundational block of modern physics — stop making sense.

That’s a pretty exhilarating thought. Our entire understanding of gravity is derived from general relativity. But the single biggest limitation behind the century-old school of physics has to do with singularities: points in gravity that are incredibly intense, the laws of physics as we understand them break down. They’re anomalies — inexplicable and aggravating — yet general relativity predicts they exist at the center of black holes, where gravity is strong enough to suck all matter and light.

None of this really matters inside a black hole’s event horizon — where the gravitational pull is so strong you cannot observe anything. But outside an event horizon, singularities are thorny. Like, thorny enough to throw physics into complete chaos.

Concept art for a black hole with an accretion disk.


Which gives rise to the idea of naked singularity — where singularities can occur outside of an event horizon, but only in higher dimensions.

“If naked singularities exist, general relativity breaks down,” study coauthor Saran Tunyasuvunakool said in a news release. “And if general relativity breaks down, it would throw everything upside down, because it would no longer have any predictive power — it could no longer be considered as a standalone theory to explain the universe.”

Are five dimensions or more possible? If you’re a string theory enthusiast, then sure — as many as 11 dimensions are possible. But humans can’t observe the world beyond three dimensions, except perhaps through high energy particle experiments.

This new simulation at least provides support for the idea that a naked singularity could exist. And in return, we can perhaps pull some of lessons back and test them in our own world to better understand the 3D world we live in right now.

“The better we get at simulating Einstein’s theory of gravity in higher dimensions, the easier it will be for us to help with advancing new computational techniques — we’re pushing the limits of what you can do on a computer when it comes to Einstein’s theory,” Tunyasuvunakool said.

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