July 30, 2021

Stephen Hawking's latest study: "Black holes have soft hair" | Science

Stephen Hawking's latest study: "Black holes have soft hair" | Science



Until days before his death, Stephen Hawking worked on solving one of the biggest problems in physics. Now the results of these investigations are published, which constitute the latest study signed by the famous British scientist.

The work focuses on the so-called paradox of information. In 1974, Hawking defended the idea that any object that falls into a black hole disappears forever and none of the information that may exist in its atoms survives. In recent years Hawking realized he was wrong. The problem of lost information could have a solution. Along with Andrew Strominger, of Harvard University, and his colleagues at the University of Cambridge, Sasha Haco and Malcolm Perry, Hawking began working on a solution in 2015. "We were working 18 months in this study. He could not write anymore, but he offered us his intuition, we made the numbers, we read them and he guided us, "explains Haco, who started working with Hawking three years ago. The study maintains that in the event horizon, the point beyond which there is no possibility of escaping the attraction of the black hole's gravity, there are some particles that function as a recorder and retain information about the objects that are swallowed by these bodies.

"The laws of quantum mechanics determine that the information can never disappear, if you burn a book, even if the text has disappeared, using the laws of quantum mechanics could get to recompose it from the ashes," explains Haco. This study is the third in a series in which the team has tried to "find a weak point in the theory of information loss". In this third study "we explain how you can retrieve information about the entropy of a black hole, which is a measure of the information it contains, something like the number of bits that make up a computer or, in this case, a black hole" , explains Haco.

Einstein's theory of relativity predicts the existence of black holes and assumes that only three things can be known about them: their mass, their charge and their sense of rotation. The theory of Hawking and his colleagues is that those particles in the vicinity of the event horizon store other information, that is, there are more things that survive a black hole. That information would be stored in certain particles. "We call them soft particles, or we say that black holes have soft hair [soft hair, en inglés]"Strominger explains, referring to John Wheeler's quote that said" black holes do not have hair ", which means that only the three characteristics predicted by relativity can be measured and the rest of the information simply disappears. In soft English it means light and also soft.

[Hawking] I was convinced that we already had all the pieces of the puzzle and that we would be able to solve the problem

"In one of the two previous studies we postulated that the particles that retain the information are photons [una partícula que no tiene masa] and in the latter we explore that they are gravitones [una partícula teórica encargada de producir gravedad en el mundo cuántico de las partículas elementales]"Says Strominger. "For now we do not know if this really happens but we have provided important theoretical proof that it can happen. This problem is connected with a much larger one, because solving it would allow to unite gravity, quantum mechanics and thermodynamics, the unification of modern physics. If you do not solve this problem, the laws of physics are inconsistent, it is as if we had a huge black hole in our knowledge of the universe, "he says.

Detect gravitons and other soft particles in black holes is too difficult for current instruments, says the American physicist, but there are other experiments that could detect them if they pass close to Earth, for example the LIGO laser interferometer, in USA

Strominger and Haco recall that Hawking remained involved in the work until the week before his death, in March of this year. "I was convinced that we already had all the pieces of the puzzle and that we were going to be able to solve the problem. I am a bit more cautious, I think we will achieve it in a decade and we are still going to publish more studies on this subject, although this is the last one that will be signed by Stephen ", concludes Strominger.

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