Stephen Hawking’s famous black hole paradox may finally be solved

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Stephen Hawking’s work has influenced many fields, in particular cosmology: quantum gravity and black holes in particular. He was the first to point out that the behavior of black holes contradicts each other between two fundamental theories – relativity and quantum mechanics. This paradox has puzzled scientists for half a century and led some to question the fundamental laws of physics. Scientists recently say they may have solved this problem by relying in part on the fact that black holes have a property they have called “gravity’s quantum hair.” This would be a huge step forward in theoretical physics.

Black holes are cosmic objects that we don’t fully understand yet. Thus, in astrophysics, a black hole is defined as an object so compact that the strength of its gravitational field prevents any form of matter or radiation from escaping from it. In other words, their gravity warps space-time so much that nothing can reach the speed needed to escape. Such objects can neither emit nor scatter light, so they are black, which in astrophysics means they are “optically invisible”.

Similarly, information cannot escape from it, and Einstein’s general theory of relativity suggests that information about what enters a black hole, therefore, cannot leave it, i.e. say we can’t define what, a posteriorientered the black hole. But quantum mechanics says this is impossible. This is an informational paradox noted by Stephen Hawking in 1976.

An international quartet of physicists, including a professor and a research student from the University of Sussex, have co-authored two papers that could revolutionize our understanding of black holes and claim to solve a problem that has baffled scientists for almost 10 years. , half a century. Research is published accordingly in journals Physical Review Letters as well as Physics letters B.

Black holes and the information paradox

First, let’s get back to the information paradox. Hawking realized that black holes radiate in a unique way. Their curvature of space-time would change the wave nature of the surrounding quantum fields, so that a form of thermal radiation would emerge. This means that the black hole must slowly evaporate, emitting its energy photon after photon into the Universe. By radiating, a black hole loses energy and, consequently, mass. In fact, general relativity suggests that information can disappear into a black hole after this one evaporates. Conversely, the laws of quantum physics state that information is stored in black holes. Here is the informational paradox.

Many solutions have been proposed, including the “wall of fire theory” in which information was supposed to burn up before it entered the black hole, “fuzzy darkino ball theory” in which black holes are assumed to have fuzzy boundaries. But most of these proposals required a rewriting of the laws of quantum mechanics or Einstein’s theory of gravity, two pillars of modern physics.

quantum hair

All theories that assume the permanence of information actually describe these remaining connections to the universe as “hair”. This is why Xavier Calmet and his collaborators suggest that when matter collapses into a black hole, it leaves a faint imprint in its gravitational field. The authors called it the “quantum hair of gravity” because their theory replaces an earlier idea called the “no hair theorem” developed in the 1960s. This “bald black hole theory”, based on classical physics, claims that the latter can be seen as surprisingly simple objects, defined only by their mass, their electric charge, and their angular momentum, related to their rotation speed.

Instead of simple objects, the authors argue that black holes are much more complex. They believe that their quantum hair theory provides a mechanism for preserving information during the collapse of a black hole. This new solution applies quantum thinking to gravity in the form of theoretical particles called gravitons. These hypothetical elementary particles transmit gravity in most quantum gravity systems, much like the photon is associated with the electromagnetic force. Through a series of logical steps showing how gravitons could potentially behave under certain energy conditions, the team demonstrated their model of how information inside a black hole can remain connected to the surrounding space.

In particular, the researchers compared the gravitational fields of two stars with the same total mass and radius but different compositions. In classical physics, two stars have the same gravitational potential, but at the quantum level, the potential depends on the composition of the star. When stars collapse into black holes, their gravitational fields retain the memory of the stellar composition and lead to the conclusion that black holes have hair. Information about the material that fell into the black hole would leave a trace of its passage, theoretically giving us access to the composition of the black hole.

exclaimed Professor Xavier Calmette of the University of Sussex, especially for BBC news : “ The problem was solved! Our solution does not require speculative ideas; instead, our study demonstrates that both theories can be used to perform consistent black hole calculations and explain how to store information without the need for radically new physics. “.

However, there is no obvious way to test the theory with astronomical observations, gravitational fluctuations would be too small to be measured. As a theory, it is interesting, based on a solid framework. But this requires careful study by the scientific community.

Professor Calmet concludes his discovery in a press release: ” It will take time for people to accept it. One consequence of Hawking’s paradox was the incompatibility of general relativity and quantum mechanics. We find that they are fully compatible. Thus, it will take time for people to accept that there is no need for a radical solution to solve the problem. “.

Source: Physical Review Letters.

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