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Why Super-Small Black Holes Haven’t Destroyed the Universe

And probably won’t

Artist’s view of a black hole — the normal sized kind, mini black holes would be cuter. (Alain r via Wikimedia Commons (CC BY-SA 2.5))
smithsonian.com

When the largest machine on the planet, the Large Hadron Collider, first fired up, people got a little concerned that the high-energy particle collisions scientists would produce might create mini black holes that would gobble up the Earth. That didn’t happen, and researchers soothed the feathers of a nervous public. But now theorists posit that a chain reaction involving mini black holes could trigger a universe collapse, reports Adrian Cho for Science.

Of course, the Sun, this planet and humans are all still here, as is the rest of the universe, so this hasn’t happened. The question intriguing physicists is: Why not?

The whole issue got more complicated with the discovery of the Higgs boson, an elementary particle which provides a way for other particles to have mass. The discovery of the Higgs boson means that the Higgs field probably exists — an invisible energy field spread throughout the universe. (The Higgs boson is actually a manifestation of that field.)

But given the mass of the Higgs boson researchers measured in 2012, and assuming that the current standard model of physics is correct, the Higgs field might not be stable. It could be in a higher energy state. If something triggers it to fall to the lowest energy state, it could cause the vacuum of space to collapse. No, you did not misread — if the Higgs field falls to its lowest energy state, the universe could simply disappear. (Those intrigued or puzzled by this can check out an explanation of this vacuum decay by Sabine Hossenfelder at Medium.)

Fortunately, that would require a lot of energy. As theoretical astrophysicist Katie Mack of the University of Melbourne explains for The World Science Festival’s blog, if such a phenomenon could happen, it probably would have already.

New calculations from theorists in the United Kingdom show that mini black holes, which may exist, could trigger a bubble of space that does fall to that lower-energy vacuum state. That bubble would ripple out and consume the universe. The black holes would have to be small, Cho reports, but it could still happen.

There’s another wrinkle in the question of why black holes haven’t already laid waste to the entire universe — the mere fact of humans’ existence. Physicists may need to find some new physics to explain the mystery of why tiny black holes haven't triggered this vacuum decay, researchers argue in their paper for Physical Review Letters. After all, something must be stabilizing the vacuum. 

Theorists will debate whether this new argument is persuasive or not, but in the meantime, there's no need to fear your abrupt end at the hands of a very small black hole. After all, fretting probably won't be enough to stop the collapse of an entire universe.

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