##### Physicists have long thought that the singularities associated with gravity (like the inside of a black hole) should vanish in a quantum theory of gravity.

It now appears that this may indeed be the case. Researchers in Uruguay and Louisiana have just published a description of a quantum black hole using loop quantum gravity in which the predictions of physics-ending singularities vanish, and are replaced by bridges to another universe.

Singularities, such as the infinitely strong crushing forces at the center of a black hole, in a physical theory are bad. What they tell you is that your description of the universe fails miserably to explain what happens as you approach the singularity. Tricks can sometimes resolve what appears to be singular behavior, but essential singularities are signs of a failure of the physical description itself.

General relativity has been summed up by the late John Wheeler’s phrase: “Spacetime tells matter how to move, matter tells spacetime how to curve.” Relativity is riddled with essential singularities, because gravity is both attractive and nonlinear – curvature in the presence of mass tends to lead to more curvature, eventually leading to trouble.

The result is rather similar to a PA system on the verge of producing a feedback whistle. If you whisper into the microphone (small gravitational fields) the positive feedback isn’t enough to send the PA into oscillation, but talking at a normal volume (larger gravitational fields) produces that horrible howl. Whispering is the comparable to the familiar actions of gravity that keep the planets and stars in their courses. The howl is the process that eventually leads to a singularity as the end result of gravitational collapse.

Let’s follow this analogy a bit further. On a PA system, the volume of the feedback is limited by the power capacity of the amplifier, so it can’t reach truly destructive levels (other than to our eardrums.) However, gravity as described by general relativity doesn’t have such a limit. Since gravity is always attractive, and eventually becomes stronger than all the (known) forces that normally give volume to matter, there is nothing to keep gravitational collapse from proceeding until the curvature of the spacetime tends toward infinity – i.e. a singularity.

Remember that this is the prediction of the classical theory of gravity, general relativity. Classical physical theories contain no fundamental limitation on mass-energy density or on the size of spacetime curvature. While this may be (and probably is) incorrect, we rarely run into a problem caused by this error, so have largely ignored the problem for centuries.

Then along came gravitational collapse and black holes. First proposed by geologist John Mitchell in 1783, a black hole is a region of spacetime from which gravity prevents anything, even light, from escaping.

##### The Latest on: Quantum black hole

- Canberra Times Letters to the Editor: Black holes exist, but theoretical understanding is not complete on October 22, 2017 at 8:22 am
a quantum theory of gravity. Mr Thornhill confuses a mathematical model with the real thing. Black holes exist, but our theoretical understanding of them is not complete. He goes on to suggest the recent observations of colliding black holes by the LIGO ... […]

- Physics & Astronomy Colloquium - Prof. Subir Sachdev, Harvard on October 19, 2017 at 9:23 pm
I will describe the simplest known quantum many-body models without quasiparticle excitations. Some of these models have a dual description as black holes in a curved spacetime with an emergent spatial direction, and the black hole connection has proved ... […]

- The long road to the 2017 Nobel Prize in physics on October 19, 2017 at 5:23 am
He similarly became a leading proponent of gravitational physics and black holes, which were finally discovered in ... of the Sciences physics professor and the author of “The Quantum Labyrinth: How Richard Feynman and John Wheeler Revolutionized Time ... […]

- Tale of two physicists on October 19, 2017 at 1:00 am
From Wheeler and his other collaborators came black holes and wormholes (terms he popularized), quantum “many worlds” and the foundations of quantum information theory encapsulated in the mantra “It From Bit”. Between them, the two physicists built ... […]

- What Are Black Holes in String Theory? on October 18, 2017 at 5:05 pm
Work led by Demetrios Christodoulou, Werner Israel, Richard Price, Brandon Carter, Roy Ken, David Robinson, Stephen Hawking, and Roger Penrose examined how black holes operate with quantum mechanics, and many interesting findings such as the no-hair ... […]

- Knowing the Mind of God: Einstein’s unfinished symphony, Hawking’s partial unification, and the quest for quantum gravity on October 17, 2017 at 11:54 am
I was an undergraduate astronomy major studying the physics of the “Schwarzschild Black Holes” when I decided to study the laws of the quantum field theory in a black hole’s curved spacetime to round up my education. I really like that it is trying ... […]

- Gravitational waves just showed us something even cooler than black holes on October 16, 2017 at 3:54 pm
Unlike black holes, neutron stars create a visible spectacle when they ... That may give us a clue for how to bring general relativity and quantum theory together in an uber-theory, a theory of everything.”) In the meantime, here are a few of the ... […]

- Steven S. Gubser & Frans Pretorius: The Little Book of Black Holes on October 13, 2017 at 4:37 pm
Hawking showed that quantum effects cause black holes to radiate very faintly. That radiation is linked with quantum fluctuations inside the black hole. But it’s a matter of ongoing debate whether these fluctuations are a key to resolving the puzzle of ... […]

- New faculty to advance quantum matter research on October 10, 2017 at 3:49 am
Yoshida studied and worked at MIT, and Caltech before coming to Perimeter in 2015. A specialist in quantum information theory, condensed matter, and black holes, his current work focuses on topological orders and quantum chaos. For Yoshida, the transition ... […]

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