One of Stephen Hawking’s most famous theorems has been proven correct using waves in spacetime caused by the merging of two distant black holes.

The black hole theorem, which Hawking derived from Einstein’s general theory of relativity in 1971, states that it is impossible for the surface area of a black hole to decrease over time. This rule interests physicists because it is closely related to another rule that seems to set time in a certain direction: the second law of thermodynamics, which says that the entropy or disorder of a closed system must always increase. Since the entropy of a black hole is proportional to its surface, both must always increase.

According to the new study, the researchers’ confirmation of the law of area seems to imply that the properties of black holes are important clues to the hidden laws of the universe. Oddly enough, the law of area seems to contradict another of the famous physicist’s proven theorems: that black holes should evaporate over an extremely long period of time, so identifying the source of the contradiction between the two theories could reveal new physics.

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“The surface of a black hole cannot be reduced, which corresponds to the second law of thermodynamics. It also has a conservation of mass because you cannot reduce its mass, so this is analogous to the conservation of energy,” first author Maximiliano Isi, astrophysicist at the Massachusetts Institute of Technology told Live Science. “At first people thought, ‘Wow, that’s a cool parallel,’ but we soon realized that it was fundamental. Black holes have an entropy that is proportional to their area. This is not just a funny coincidence, but a profound fact about the world they reveal. “The surface of a black hole is bounded by a spherical border, the event horizon – beyond this point nothing, not even light, can escape its strong attraction. According to Hawking’s interpretation of general relativity, the surface of a black hole increases with its mass and since no object thrown into it can escape, its surface cannot decrease. But the surface of a black hole also shrinks the more it rotates. Therefore, the researchers wondered whether it would be possible to throw an object into the interior so hard that the black hole rotates enough to reduce its area.

“You’re going to make it spin more, but not enough to make up for the bulk you just added,” Isi said. “Whatever you do, the mass and spin will make sure you have more area in the end.”

To test this theory, the researchers analyzed gravitational waves or ripples in the space-time structure that were created 1.3 billion years ago by two huge black holes spiraling towards each other at high speed. These were the first waves discovered in 2015 by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), a 3,000-kilometer laser beam that is able to detect the slightest distortions in space-time based on their change in length.

By splitting the signal in half – before and after the black holes merged – the researchers calculated the mass and spin of both the original and the new combined black holes. These numbers, in turn, allowed them to calculate the surface area of each black hole before and after the collision.

“If they spin around each other faster and faster, the amplitudes of the gravitational waves increase more and more until they finally crash into one another – and create this big wave surge,” said Isi. “What remains is a new black hole that is in this excited state, which you can then examine by analyzing its vibration. It’s like pinging a bell, the specific pitches and durations with which it rings will tell you the structure of that bell and what it is made of. “

The surface area of the newly created black hole was larger than that of the first two combined, which confirmed Hawking’s law of area with a confidence level of greater than 95%. According to the researchers, their results are pretty much what they expected. General relativity – where the law of area comes from – does a very effective job of describing black holes and other large-scale objects.

The real puzzle, however, begins when we try to integrate general relativity – the rules of large objects – with quantum mechanics – those of the very small ones. Strange events begin that devastate all of our hard and fast rules and completely break the territorial law.

This is because black holes cannot shrink according to general relativity, but according to quantum mechanics. The iconic British physicist behind the area law also came up with a concept known as Hawking radiation – where a tooth made of particles is emitted at the edges of black holes by strange quantum effects. This phenomenon causes the black holes to shrink and eventually evaporate over a period of time that is many times longer than the age of the universe. This evaporation can occur over periods of time long enough not to violate the law of area in the short term, but that is a small consolation for physicists.

“Statistically speaking, the law is broken over a long period of time,” said Isi. “It’s like boiling water, you get steam evaporating from your pan, but if you limit yourself to just looking at the disappearing water in it, you might be tempted to say that the pan’s entropy is decreasing. But if you do. .. If you take the steam into account, your overall entropy has increased. It’s the same with black holes and hawk radiation. “

After the area law has been established for short to medium periods of time, the researchers’ next steps will be to analyze data from more gravitational waves to get deeper insights that could be gleaned from black holes.

“I am obsessed with these objects because they are so paradoxical. They are extremely mysterious and confusing, but at the same time we know that they are the simplest objects there are,” said Isi. “This, along with the fact that they hit gravity and quantum mechanics, makes them perfect playgrounds for our understanding of reality.”

The researchers published their results on May 26 in the Journal of Physical Review Letters.

Originally published on Live Science.

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