A model outlining the microscopic origin of black hole entropy

Black holes are fascinating astronomical objects that have such a strong gravitational pull that they prevent any object and even light from escaping. While black holes have been the subject of many astrophysical studies, their origin and underlying physics remain largely a mystery.

Researchers from the University of Pennsylvania and Centro Atómico Bariloche recently presented a new model of black hole microstates regarding the origin of entropy (ie, the degree of disorder) in black holes.

This model, presented in an article published in Physical inspection lettersprovides an alternative view of black holes that could inform future astrophysical research.

“The Bekenstein-Hawking entropy formula, which describes the thermodynamics of black holes, was discovered in the 1970s,” Vijay Balasubramanian, co-author of the paper, told Phys.org. “This formula suggests that black holes have entropy proportional to the area of ​​their horizons.

“According to statistical physics, as developed by Boltzmann and Gibbs in the late 19th century, the entropy of a system is related to the number of microscopic configurations that have the same macroscopic description.

“In a quantum mechanical world like ours, entropy arises from quantum superpositions of ‘microstates,’ i.e., microscopic components that yield the same observable features on large scales.”

Physicists have been trying for decades to provide a plausible description of the entropy of black holes. In the 1990s, Andrew Strominger and Cumrun Vafa used a hypothetical property known as “supersymmetry” to devise a method for counting the microstates of a special class of black holes, whose mass is equal to the electromagnetic charge, in universes with additional dimensions and diverse species. electric and magnetic fields.

To explain the origin of black hole entropy in universes like ours, Balasubramanian and his colleagues had to create a new theoretical framework.

“Despite previous attempts, there is no description yet that applies to the kinds of black holes that form from collapsing stars in our world,” Balasubramanian said. “Our goal was to provide such an account.”

The primary contribution of this recent work was the introduction of a new model of black hole microstates, which can be described as collapsing dust shells inside a black hole. In addition, the researchers devised a technique to calculate ways to superimpose these microstates quantum mechanically.

“A key finding of our work is that very different spacetime geometries corresponding to apparently different microstates can mix with each other due to the subtle effects of quantum mechanical ‘wormholes’ that connect distant regions of the universe,” said Balasubramanian.

“After accounting for the effects of these wormholes, our results showed that for any universe containing gravity and matter, the entropy of a black hole is directly proportional to the area of ​​its event horizon, as proposed by Bekenstein and Hawking.”

Recent work by Balasubramanian and his colleagues presents a new way of thinking about the microstates of black holes. Specifically, their model describes them as quantum superpositions of simple objects that are well described by classical physical theories of matter and the geometry of spacetime.

“This is very surprising because the community expected that a microscopic explanation of black hole entropy would require the full apparatus of quantum gravity theory, such as string theory,” Balasubramanian said.

“We also show that universes that differ from each other on macroscopic, even cosmic scales can sometimes be understood as quantum superpositions of other, macroscopically different universes. This is a manifestation of quantum mechanics on the scale of the entire universe, which is surprising given that that we usually associate quantum mechanics with phenomena on a small scale.”

The newly introduced theoretical framework could pave the way for further theoretical work aimed at explaining the thermodynamics of black holes. In the meantime, scientists plan to expand and enrich their description of the microstates of black holes.

“We are now studying to what extent and under what circumstances an observer outside the event horizon can determine which microstate a black hole is in,” Balasubramanian added.

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