Scientists have shown how a ring-shaped black hole could cause Einstein's general theory of relativity, a foundation of modern physics, to break down - assuming the universe contains at least five dimensions. The researchers, from the University of Cambridge and Queen Mary University of London, have successfully simulated a black hole shaped like a very thin ring, which gives rise to a series of 'bulges' connected by strings that become thinner over time.
These strings eventually become so thin that they pinch off into a series of miniature black holes - similar to how a thin stream of water from a tap breaks up into droplets. This bizarrely shaped black hole could cause Einstein's general theory of relativity, a foundation of modern physics, to break down. However, such an object could only exist in a universe with five or more dimensions, say the researchers from University of Cambridge and Queen Mary University of London. Ring-shaped black holes were discovered by theoretical physicists in 2002 but this is the first time that their dynamics have been successfully simulated using supercomputers. Should this type of black hole form, it would lead to the appearance of a naked singularity, which would cause the equations behind general relativity to break down.
A singularity is a point where gravity is so intense that space, time, and the laws of physics, break down. General relativity predicts that singularities exist at the center of black holes, and that they are surrounded by an event horizon the point of no return where the gravitational pull becomes so strong that escape is impossible, meaning that they cannot be observed from the outside.
As long as singularities stay hidden behind an event horizon, they do not cause trouble and general relativity holds the cosmic censorship conjecture says that this is always the case, explained study co-author Markus Kunesch from Cambridge's Department of Applied Mathematics and Theoretical Physics (DAMTP).
But what if a singularity existed outside of an event horizon?
If it did, not only would it be visible from the outside, but it would represent an object that has collapsed to an infinite density, a state which causes the laws of physics to break down. Theoretical physicists have hypothesised that such a thing, called a naked singularity might exist in higher dimensions. "If naked singularities exist, general relativity breaks down," added Saran Tunyasuvunakool, a PhD student from DAMTP. "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", Tunyasuvunakool noted in a paper appeared in the journal Physical Review Letters.
We think of the universe as existing in three dimensions, plus the fourth dimension of time, which together are referred to as spacetime. Since humans can only directly perceive three dimensions, the existence of extra dimensions can only be inferred through very high energy experiments, such as those conducted at the Large Hadron Collider. "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," explained Tunyasuvunakool. "But if cosmic censorship doesn't hold in higher dimensions, then maybe we need to look at what's so special about a four-dimensional universe that means it does hold," the authors noted.
Here is a video of a very thin black ring. Now, there is clear evidence of the black ring starting to break up into little droplets. In this process a naked singularity is created and weak cosmic censorship is violated. Credit: Pau Figueras, Markus Kunesch, and Saran Tunyasuvunakool.