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Einstein’s theory
of general relativity predicted that once an object falls inside an event
horizon, it ends up at the center of the black hole called a
singularity where it is completely crushed. At this point of singularity,
gravitational attraction is infinite and all known laws of physics break down
including Einstein’s theory. Theoretical physicists have been questioning if
singularities really exist through complex mathematical equations over the past
several decades with little success until now.

LSU Department of
Physics & Astronomy Associate Professor Parampreet Singh and collaborators
LSU Postdoctoral Researcher Javier Olmedo and Abhay Ashtekar, the Eberly
Professor of Physics at Penn State developed new mathematical equations that go
beyond Einstein’s theory of general relativity overcoming its key
limitation—the central singularity of black holes. This research was published
recently in Physical Review Letters and Physical Review D and was highlighted
by the editors of the American Physical Society.

Artist depiction of loop quantum gravity effects in a black hole. The bottom half of the image depicts the black hole which, according to general relativity, traps everything including light. Loop quantum gravity, a theory that extends Einstein’s general relativity using quantum mechanics, overcomes this tremendous pull and liberates everything shown in the top half of image, thus solving the fundamental problem of black hole singularity.

Photo Credit: A. Corichi and J. P. Ruiz.

Photo Credit: A. Corichi and J. P. Ruiz.

Theoretical
physicists developed a theory called loop quantum gravity in the 1990s that
marries the laws of microscopic physics, or quantum mechanics, with gravity,
which explains the dynamics of space and time. Ashtekar, Olmedos and Singh’s
new equations describe black holes in loop quantum gravity and showed that
black hole singularity does not exist.

“In Einstein’s theory, space-time is a fabric that can be divided as small as we want. This is essentially the cause of the singularity where the gravitational field becomes infinite. In loop quantum gravity, the fabric of space-time has a tile-like structure, which cannot be divided beyond the smallest tile. My colleagues and I have shown that this is the case inside black holes and therefore there is no singularity,” Singh said.

Instead of
singularity, loop quantum gravity predicts a funnel to another branch of the
space-time.

“These tile-like units of geometry—called ‘quantum excitations’— which resolve the singularity problem are orders of magnitude smaller than we can detect with today’s technology, but we have precise mathematical equations that predict their behavior,” said Ashtekar, who is one of the founding fathers of loop quantum gravity.

Einstein’s theory
fails not only at the center of the black holes but also to explain how the
universe was created from the Big Bang singularity. Therefore, a
decade ago, Ashtekar, Singh and collaborators began to extend physics beyond
the Big Bang and make new predictions using loop quantum gravity.

“At LSU, we have been developing state-of-the-art computational techniques to extract physical consequences of these physical equations using supercomputers, bringing us closer to reliably test quantum gravity,” Singh said.

Using the
mathematical equations and computational techniques of loop quantum gravity,
they showed that the Big Bang is replaced by the “Big Bounce.” But, the problem
of overcoming black hole singularity is exceptionally complex.

“The fate of black holes in a quantum theory of gravity is, in my view, the most important problem in theoretical physics,” said Jorge Pullin, the Horace Hearne professor of theoretical physics at LSU, who was not part of this study.

The research was
supported by the U.S. National Science Foundation, the Urania Stott Fund of the
Pittsburgh Foundation, the Penn State Eberly College of Science and the Ministry
of Economy and Competitiveness, or MINECO, in Spain.

Publications:

- Quantum Transfiguration of
Kruskal Black Holes, Physical Review Letters:
**https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.241301** - Quantum extension of the
Kruskal spacetime, Physical Review D:
**https://journals.aps.org/prd/abstract/10.1103/PhysRevD.98.126003**

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