![]() After those initial moments, "somewhere along the away, the universe becomes large and 'well-behaved' enough so that a continuum space-time approximation becomes a good description and GR can take over to reproduce what we see," Bento said. Under causal set theory, space-time is not a smooth continuum, as it is in GR, but rather made up of discrete chunks, named "space-time atoms." Since nothing can be smaller than one of these "atoms", singularities are impossible,Bruno Bento, a physicist studying this topic at the University of Liverpool in England, told Live Science.īento and his collaborators are attempting to replace the earliest moments of the Big Bang using causal set theory. One possible resolution to the Big Bang singularity is causal set theory. Though the Big Bang theory is enormously successful at describing the history of the cosmos since that moment, just as with black holes, the presence of the singularity is telling scientists that the theory - again, GR - is incomplete, and needs to be updated. Physicists know that this conclusion is incorrect. In the distant past, about 13.77 billion years ago, according to the Big Bang theory, the entire universe was compressed into an infinitely tiny point. The Big Bang theory, which assumes general relativity to be true, is the modern cosmological model of the history of the universe. (Image credit: Shutterstock) (opens in new tab) To date, all these ideas are hypothetical, and a true answer must await a quantum theory of gravity. Hypotheses that modify or replace general relativity to give us a replacement of the black hole singularity include Planck stars (a highly-compressed exotic form of matter), gravastars (a thin shell of matter supported by exotic gravity), and dark energy stars (an exotic state of vacuum energy that behaves like a black hole). Specifically, we need a quantum theory of gravity, one that can describe the behavior of strong gravity at very tiny scales, according to Physics of the Universe (opens in new tab). To understand it, we need a theory of gravity beyond GR. ![]() What's really at the center of a black hole?īecause they are mathematical singularities, nobody knows what's really at the center of a black hole. Whether such exposed singularities exist continues to be a subject of considerable debate. A naked singularity would be just that: a singularity without an event horizon, fully observable from the outside universe. However, computer simulations and theoretical work have raised the possibility of exposed (or "naked") singularities. Physicists long thought that in GR, all singularities like this are surrounded by event horizons, and this concept was known as the Cosmic Censorship Hypothesis - so named because it was surmised that some process in the universe prevented (or "censored") singularities from being viewable. The event horizon "protects" the singularity, preventing outside observers from seeing it unless they traverse the event horizon, according to Quanta Magazine (opens in new tab). These are what we call the black holes: a point of infinite density, surrounded by an event horizon located at the Schwarzschild radius. Where do gravitational singularities happen? A change in coordinate systems removes the singularity, saving GR and allowing it to still make valid predictions, astrophysicist Ethan Siegel writes in Forbes (opens in new tab). ![]() It was soon discovered that the singularity at the Schwarzschild radius was a coordinate singularity. All physicists needed was for GR to predict the gravitational influence outside the mass, according to San Jose State University (opens in new tab).īut what would happen if an object were squeezed below its own Schwarzschild radius? Then that singularity would be outside the mass, and it would mean that GR is breaking down in a region that it shouldn't. For many years, physicists thought that both singularities signaled breakdowns in the theory, but it didn't matter as long as the radius of the spherical mass was larger than the Schwarzschild radius. ![]() He found that the solution contained two singularities, one in the very center and one at a certain distance from the center, known today as the Schwarzschild radius. For example, the physicist Karl Schwarzschild applied general relativity to the simple system of a spherical mass, such as a star. ![]()
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