Quantum gravity would be hidden in black holes

Astronomers in the UK have discovered that black holes can become the gateway to quantum gravity, considered the holy grail of New Physics.

They have verified that black holes are more complex thermodynamic systems than previously thought: they not only emit thermal radiation, but also a pressure on the environment that emanates from the quantum gravity hidden inside them.

This finding would confirm that black holes are the ideal place to solve one of the most persistent problems in Physics: how the Big Bang arose, the great cosmic moment that gave rise to the entire universe.

Neither Quantum Theory nor Relativity have been sufficient to describe what happened then, due to a difficulty intrinsic to both bodies of knowledge.

While the General Theory of Relativity describes gravity and, consequently, the world of objects, planets and galaxies, Quantum Physics describes the paradoxical world of atoms and elementary particles. Until now, these two worlds remain theoretically irreconcilable with each other.

Merits of the question

Both theories are coherent within their own fields, but, when we analyze cosmic processes at extreme scales, whether they are infinitely small or large, we have not managed to articulate a theory that encompasses both approaches, capable of explaining, for example, how the Big occurred. Bang.

According to Einstein’s theory of General Relativity, the gravity of a black hole is so intense that nothing can escape from its interior. But explaining what happens inside a black hole using quantum theory is something much more complex.

In the seventies of the last century, Stephen Hawking tried to describe the matter in and around black holes using quantum theory, but he stumbled on gravity: he could only describe it with Einstein’s classical theory.

If we want to get to the bottom of how the universe came to be, we need to consider gravity as a quantum phenomenon, but the prospects of testing it directly are slim: we would need a Milky Way-sized particle accelerator to get there … or access the interior of a black hole .

Something doesn’t fit

This is where the discovery of British astronomers is valued. It took place last December when Xavier Calmet and Folkert Kuipers, both from the University of Sussex in the UK, examined equations that determined the energy available to black holes.

Then they realized that something was wrong: there was a factor in the equation that could only correspond to the pressure coming from a black hole.

According to the researchers, calculations of the influence of quantum mechanics on gravity at the periphery of black holes indicate that these regions could be subjected to this quantum pressure.

That means that the black hole not only emits thermal radiation, as Hawking had suggested, but also exerts associated pressure on its surroundings, all as a result of quantum processes happening inside it.

Calmet highlights in this regard in a statement that, inside black holes, dominated by gravity, there may be a singularity in which the laws of physics are diluted.

Quantum Gravity Hideout

That is the moment when gravity and quantum dynamics apparently coexist in harmony: quantum gravity would be hidden deep inside black holes and would exert pressure on their environment.

For this reason, both researchers believe that black holes are ideal for studying the unification of the theory of gravity, general relativity and quantum physics, and even for determining the theory of quantum gravity, according to which space is composed. by atoms still unknown.

A fundamental problem with all approaches to Quantum Gravity lies in reconciling the scales of atomic space with the dimensions of the Universe.

The challenge is to describe how the space of the Universe evolves from elementary particles. The new research suggests that black holes can perhaps unravel that mystery for us.

Steps forward

In this line, work is already being done from different fronts, with the aim of reaching a quantum theory of gravitation that does not contradict the relativity of macroscopic objects, nor the quantum behaviors of elementary particles.

The starting point is certain quantum effects associated with black holes, which indicate an analogy between the laws of thermodynamics and some of the properties of these mysterious regions of space.

One of the hypotheses with which we have been working for at least a decade is that, both gravity and space-time itself, can arise from quantum entanglement, that strange property of elementary particles that allows them to share information instantaneously, even if they are widely separated from each other.

Stanford University professor Monika Schleier-Smith hopes to produce in her Palo Alto lab, thanks to quantum entanglement, something that looks and acts like the spacetime predicted by Albert Einstein’s theory of General Relativity, reports Quanta.

Last frontier?

The purpose of it is to build a quantum simulator made of laser-cooled atoms to simulate what happens to quantum information inside black holes and eventually discover the hiding place of quantum gravity.

His work may also become the door to test another assumption that haunts physicists: that space-time is not the ultimate level of nature, but arises from some underlying mechanism that is neither spatial nor temporal, from which black holes might hold the answer … in a lab.


Quantum gravitational corrections to the entropy of a Schwarzschild black hole. Xavier Calmet and Folkert Kuipers. Phys. Rev. D 104, 066012, 9 September 2021. DOI: https: //doi.org/10.1103/PhysRevD.104.066012

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