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Black Holes Must Have Singularities, Says Einstein’s Relativity

“The thing is, there’s a speed limit to how fast these force-carriers can go: the speed of light. If you want an interaction to work by having an interior particle exert an outward force on an exterior particle, there needs to be some way for a particle to travel along that outward path. If the spacetime containing your particles is below the density threshold necessary to create a black hole, that’s no problem: moving at the speed of light will allow you to take that outward trajectory.

But what if your spacetime crosses that threshold? What if you create an event horizon, and have a region of space where gravity is so intense that even if you moved at the speed of light, you couldn’t escape?”

Usually, when physicists first start teaching about black holes, the attitude they’re met with is skepticism. People can accept that as you compress a large mass into a smaller and smaller volume, it gets harder to escape its gravitational pull. As you go from a star to a white dwarf to a neutron star, you have to move closer to the speed of light to leave it’s surface. If you go even denser, you’ll create an event horizon: a region of space where the gravitational pull is so strong that nothing, not even light can escape. People are okay with that, but when you go to the next step and declare that anything that crosses the event horizon eventually falls into a central singularity, suddenly they’re not okay. Why, they reason, couldn’t there be some denser, exotic, degenerate form of matter than what we presently know? Why couldn’t that lie inside a black hole, rather than a singular point or ring? It’s a good question and an interesting bit of intuition, but there’s an answer for that.

If you wanted to hold anything up against collapse to a singularity inside a black hole, the force-carriers governing the interaction would have to travel faster than light, which is a no-go. Find out the full story on why black holes must have singularities!