Hawking radiation: no more mysteries. Hawking radiation: concept, characteristics and problems of theory Hawking particles

Hawking radiation is the process of emission of various elementary particles, which was theoretically described by the British scientist Stephen Hawking in 1974.

Long before the publication of Stephen Hawking's works, the possibility of particle radiation from black holes was expressed by the Soviet theoretical physicist Vladimir Gribov in a discussion with another scientist, Yakov Zeldovich.

While studying the behavior of elementary particles near a black hole, thirty-year-old Stephen Hawking visited Moscow in 1973. In the capital, he was able to take part in a scientific discussion with two outstanding Soviet scientists, Alexei Starobinsky and Yakov Zeldovich. After working on Gribov's idea for some time, they came to the conclusion that black holes can radiate due to the tunneling effect. The latter means that there is a probability that a particle can overcome any barrier, from the point of view of quantum physics. Having become interested in this topic, Hawking studied the issue in detail and in 1974 published his work, which later named the mentioned radiation after him.

Stephen Hawking described the process of particle emission from a black hole somewhat differently. The root cause of such radiation is the so-called “virtual particles”.

In the process of describing the interactions between particles, scientists came to the idea that interactions between them occur through the exchange of certain quanta (“portions” of some physical quantity). For example, electromagnetic interaction in an atom between an electron and a proton occurs through the exchange of photons (carriers of electromagnetic interaction).

However, then the next problem arises. If we consider this electron as a free particle, then in no way can it simply emit or absorb a photon, according to the principle of conservation of energy. That is, he cannot simply lose or gain any amount of energy. Then scientists created so-called “virtual particles”. The latter differ from real ones in that they are born and disappear so quickly that it is impossible to register them. All that virtual particles manage to do in a short period of their lives is to transfer momentum to other particles, without transferring energy.

Thus, even empty space, due to some physical fluctuations (random deviations from the norm), is simply teeming with these virtual particles that are constantly being born and destroyed.

Hawking radiation

Unlike Soviet physicists, Stephen Hawking's description of radiation is based on abstract, virtual particles that are an integral part of quantum field theory. A British theoretical physicist is looking at the spontaneous emergence of these virtual particles from a black hole. In this case, the powerful gravitational field of a black hole is capable of “pulling apart” virtual particles even before they are destroyed, thereby turning them into real ones. Similar processes are experimentally observed at synchrophasotrons, where scientists manage to pull these particles apart, while expending a certain amount of energy.

From the point of view of physics, the emergence of real particles with mass, spin, energy and other characteristics in empty space “out of nothing” contradicts the law of conservation of energy, and therefore is simply impossible. Therefore, to “transform” virtual particles into real ones, energy will be required, no less than the total mass of these two particles, according to the well-known law. A black hole also expends this amount of energy to pull away virtual particles at the event horizon.

As a result of the pulling process, one of the particles, located closer to the event horizon or even below it, “turns” into a real one and is directed towards the black hole. The other, in the opposite direction, sets off on a free voyage through outer space. Having carried out mathematical calculations, one can be convinced that even despite the energy (mass) received from a particle falling on the surface of a black hole, the energy spent by the black hole on the process of being pulled apart is negative. That is, ultimately, as a result of the described process, the black hole only lost a certain amount of energy, which, moreover, is exactly equal to the energy (mass) possessed by the particle that flew “outside.”

Thus, according to the described theory, although the black hole does not emit any particles, it contributes to this process and loses equivalent energy. Following Einstein’s already mentioned law of the equivalence of mass and energy, it becomes clear that a black hole has nowhere to take energy from except from its own mass.

To summarize all of the above, we can say that a black hole emits a particle and at the same time loses some mass. The latter process was called "black hole evaporation." Based on the theory of Hawking radiation, one can guess that after some time, although very long (trillions of years), black holes simply .

Interesting Facts

• Many people fear that black holes could form at the Large Hadron Collider (LHC), and possibly pose a threat to the lives of earthlings. The birth of black holes at the LHC is possible only in the case of the existence of additional dimensions of space-time and the presence of powerful gravitational interaction at short distances. However, a microscopic black hole formed in this way will instantly evaporate due to Hawking radiation.
• Based on Hawking radiation, a singular reactor or a collapsar reactor can operate - a hypothetical device that generates microscopic black holes. The radiation energy generated as a result of their evaporation will be the main source of energy for the reactor.

Although the Large Hadron Collider looks menacing, it is nothing to be afraid of due to Hawking radiation

• After publishing his work on black hole radiation, Stephen Hawking argued with another famous scientist, Kip Thorne. The subject of dispute was the nature of the object claiming to be a black hole, called . Although Hawking's work was based on the assumption of the existence of black holes, he argued that Cygnus X-1 is not a black hole. It is noteworthy that the bets were subscriptions to magazines. Thorne's bid was a 4-year subscription to the satirical magazine Private Eye, while Hawking's bid was a one-year subscription to the erotic magazine Penthouse. Stephen argued the logic of his statement in the dispute as follows: “even if I turn out to be wrong in asserting the existence of black holes, then at least I will win a subscription to the magazine”

Hawking and microgravity (VomitComet)

In such a scenario, all other information about the matter that formed the black hole or falls into it (for which "hair" is used as a metaphor) "disappears" beyond the black hole's event horizon and is therefore preserved but will not be accessible to outside observers.

In 1973, Hawking traveled to Moscow and met with Soviet scientists Yakov Zeldovich and Alexei Starobinsky. In discussions with them about their work, they showed him how the uncertainty principle meant that black holes should emit particles. This called into question Hawking's second law of black hole thermodynamics (that is, black holes cannot get smaller), since they must lose mass as they lose energy.

Moreover, it supported the theory put forward by Jacob Bekenstein, a graduate student at John Wheeler University, that black holes should have a finite, non-zero temperature and entropy. All this contradicted the “no hair theorem.” Hawking soon revised his theorem, showing that when quantum mechanical effects were taken into account, black holes were found to emit thermal radiation of a certain temperature.

In 1974, Hawking presented his findings and showed that black holes emit radiation. This effect became known as "Hawking radiation" and was initially controversial. But by the end of the 70s and after the publication of further research, the discovery was recognized as a significant breakthrough in the field of theoretical physics.

However, one of the consequences of such a theory was that black holes gradually lose mass and energy. Because of this, black holes that lose more mass than they gain should shrink and eventually disappear - a phenomenon now known as black hole "evaporation".

In 1981, Hawking proposed that information in a black hole is irreversibly lost when the black hole evaporates, which became known as the "black hole information paradox". He argued that physical information could disappear forever into a black hole, allowing many physical states to converge on a single one.

The theory turned out to be controversial because it violated two fundamental principles of quantum physics. Quantum physics states that the complete information of a physical system—the state of its matter (mass, position, spin, temperature, etc.)—is encoded in its wave function until the function collapses. This in turn leads to two other principles.

The first, quantum determinism, states that - given the present wave function - future changes are uniquely determined by the evolution operator. The second - reversibility - states that the evolution operator has an inverse side, which means that past wave functions are also unique. The combination of these principles leads to the fact that information about the quantum state of matter must always be preserved.

Hawking at the White House to receive the Medal of Freedom

By suggesting that information disappears after a black hole evaporates, Hawking essentially created a fundamental paradox. If a black hole can evaporate, thereby causing all information about the quantum wave function to disappear, then the information could in principle be lost forever. This question has become the subject of debate among scientists and remains virtually unresolved to this day.

Yet by 2003, there was some consensus among physicists that Hawking was wrong about the loss of information in a black hole. At a lecture in Dublin in 2004, he admitted that he had lost a bet on the topic to John Preskill of Caltech (which he made in 1997), but described his own and somewhat controversial solution to the paradox: perhaps black holes can have more than one topology.

In a 2005 paper he published on the topic, Information Loss in Black Holes, he argued that the information paradox is explained by studying all the alternate histories of universes, where the information loss in one with black holes is compensated for in another without them. As a result, in January 2014, Hawking called the black hole information paradox his “biggest mistake.”

Hawking and Peter Higgs at the Large Hadron Collider

In addition to expanding our understanding of black holes and cosmology using general relativity and quantum mechanics, Stephen Hawking was also instrumental in bringing science to a wider audience. During his long scientific career, he also published many popular books, traveled and lectured widely, and appeared on television shows and films.

During his career, Hawking also became a distinguished educator, personally graduating 39 successful students with doctorates. His name will remain in the history of the search for extraterrestrial intelligence, and the development of robotics and artificial intelligence. On July 20, 2015, Stephen Hawking helped launch Breakthrough Initiatives, an initiative to search for extraterrestrial life in the universe.

Without a doubt, Stephen Hawking is one of the most famous scientists alive today. His work in astrophysics and quantum mechanics led to breakthroughs in our understanding of space and time, and also generated much controversy among scientists. Hardly any living scientist has done so much to attract the attention of the general public to science.

There is something in Hawking from his predecessor Albert Einstein, another influential and famous scientist who did everything to fight ignorance and develop science. But what's particularly impressive is that everything Hawking did in his life (from a certain point on) was in the pursuit of a stubborn battle against a degenerative disease. (Read, for example, while remaining completely motionless.)

Hawking lived for more than 52 years with a disease that, according to doctors, should have claimed his life within 2 years. And when the day comes when Hawking is no longer with us, time will undoubtedly place him alongside the likes of Einstein, Newton, Galileo and Curie as one of the greatest scientists in human history.

The greatest cosmologist and theoretical physicist of our time. Born in 1942, the future scientist began to experience health problems at the age of 20. Amyotrophic lateral sclerosis made it very difficult to study at the Department of Theoretical Physics at Oxford, but did not prevent Stephen from leading a very active, eventful lifestyle. He married in 1965 and became a Fellow of the Royal Society of London in 1974. By this time he had already had a daughter and two sons. In 1985, the scientist stopped speaking. Today, only one cheek has retained mobility in his body. It seemed completely motionless and condemned. However, in 1995 he marries again, and in 2007... he flies in zero gravity.

There is no person on Earth who is deprived of mobility and lives such a full, useful and interesting life.

But that's not all. Hawking's greatest development was the theory of black holes. “Hawking’s theory,” as it is now called, radically changed scientists’ long-standing understanding of the Black Holes of the Universe.

At the beginning of work on the theory, the scientist, like many of his colleagues, argued that everything that gets into them is forever destroyed. This information paradox haunted military personnel and scientists around the world. It was believed that it was impossible to establish any properties of these space objects, with the exception of mass.

Having studied black holes in 1975, Hawking found that they constantly emit a stream of photons and some other elementary particles into space. However, even the scientist himself was sure that “Hawking radiation” was random, unpredictable. The British scientist initially thought that this radiation did not carry any information.

However, the property of a brilliant mind is the ability to constantly doubt. Hawking continued his research and discovered that the evaporation of a Black Hole (i.e., Hawking radiation) is quantum in nature. This allowed him to conclude that information falling into the Black Hole is not destroyed, but changed. The theory that the state of the hole is constant is correct when viewed from the point of view of non-quantum physics.

Taking into account quantum theory, the vacuum is filled with “virtual” particles that emit different physical fields. The strength of the radiation changes constantly. When it becomes very strong, particle-antiparticle pairs can be born directly from the vacuum at the event horizon (boundary) of the Black Hole. If the total energy of one particle turns out to be positive, and the second - negative, if at the same time the particles fell into a Black Hole, then they begin to behave differently. The negative antiparticle begins to reduce the rest energy of the Black hole, and the positive particle tends to infinity.

From the outside, this process looks like evaporation coming from a Black Hole. This is what is called “Hawking radiation”. The scientist found that this “evaporation” of distorted information has its own thermal spectrum, visible to instruments, and a certain temperature.

Hawking radiation, according to the scientist himself, indicates that not all information is lost and disappears forever in the Black Hole. He is confident that quantum physics proves the impossibility of complete destruction or loss of information. This means that Hawking radiation contains such information, albeit in a modified form.

If the scientist is right, then the past and future of Black holes can be studied in the same way as the history of other planets.

Unfortunately, the opinion about the possibility of traveling through time or to other universes using Black Holes. The presence of Hawking radiation proves that any object that falls into a hole will return to our Universe in the form of altered information.

Not all scientists share the British physicist's beliefs. However, they also do not dare to challenge them. Today, the whole world is waiting for Hawking’s new publications, in which he promised to confirm in detail and conclusively the objectivity of his theory, which turned the scientific world upside down.

Moreover, scientists managed to obtain Hawking radiation in laboratory conditions. This happened in 2010.

There is a phenomenon that reflects such different phenomena as black holes and elementary particles in their interaction. Is this Hawking radiation or quantum...

From Masterweb

26.06.2018 18:00

Black holes and elementary particles. Modern physics ties together the concepts of these objects, the first of which are described within the framework of Einstein's theory of gravity, and the second - in the mathematical constructions of quantum field theory. It is known that these two beautiful and many times confirmed experimentally theories are not very “friendly” with each other. However, there is a phenomenon that reflects such different phenomena in their interaction. This is Hawking radiation or quantum evaporation of black holes. What it is? How does it work? Can it be detected? We will talk about this in our article.

Black holes and their horizons

Let us imagine some region of the space-time continuum occupied by a physical body, for example, a star. If this region is characterized by such a ratio of radius and mass in which the gravitational curvature of the continuum does not allow anything (even a light ray) to leave it, such a region is called a black hole. In a sense, it really is a hole, a gap in the continuum, as it is often depicted in illustrations using a two-dimensional representation of space.

However, in this case we will be interested not in the yawning depth of this hole, but in the boundary of the black hole, called the event horizon. When considering Hawking radiation, an important feature of the horizon is that crossing this surface permanently and completely separates any physical object from outer space.

About vacuum and virtual particles

In the understanding of quantum field theory, vacuum is not emptiness at all, but a special medium (more precisely, a state of matter), that is, a field in which all quantum parameters are equal to zero. The energy of such a field is minimal, but we should not forget about the uncertainty principle. In full accordance with it, the vacuum exhibits spontaneous fluctuation activity. It is expressed in energy vibrations, which does not violate the law of conservation.

The higher the peak of the vacuum energy fluctuation, the shorter its duration. If such a vibration has an energy of 2mc2, sufficient to produce a pair of particles, they will appear, but will immediately annihilate without having time to fly apart. In this way they will dampen the fluctuation. Such virtual particles are born due to the energy of the vacuum and return this energy to it upon their death. Their existence has been confirmed experimentally, for example, by recording the famous Casimir effect, which demonstrates the pressure of a gas of virtual particles on a macroobject.

To understand Hawking radiation, it is important that particles in such a process (be it electrons with positrons or photons) are necessarily born in pairs, and their total momentum is zero.

Armed with vacuum fluctuations in the form of virtual pairs, we will approach the edge of the black hole and see what happens there.

At the edge of the abyss

Thanks to the presence of an event horizon, a black hole is able to interfere with the process of spontaneous vacuum oscillations. The tidal forces at the surface of the hole are enormous, and the gravitational field here is extremely inhomogeneous. It enhances the dynamics of this phenomenon. Pairs of particles should be created much more actively than in the absence of external forces. The black hole expends its gravitational energy on this process.

Nothing prevents one of the particles from “diving” under the event horizon if its momentum is directed accordingly and the birth of the pair occurs almost at the very horizon (in this case, the hole spends energy on breaking the pair). Then there will be no annihilation, and the partner of the nimble particle will fly away from the black hole. As a result, the energy and, therefore, the mass of the hole decreases by an amount equal to the mass of the fugitive. This “weight loss” is called black hole evaporation.

When describing the radiation of black holes, Hawking operated with virtual particles. This is the difference between his theory and the point of view of Gribov, Zeldovich and Starobinsky, expressed in 1973. Soviet physicists then pointed to the possibility of quantum tunneling of real particles through the event horizon, as a result of which the black hole should have radiation.

What is Hawking radiation

Black holes, according to the scientist’s theory, do not emit anything themselves. However, photons leaving a black hole have a thermal spectrum. To an observer, this “outflow” of particles should look as if the hole, like any heated body, is emitting some kind of radiation, naturally losing energy in the process. You can even calculate the temperature comparable to Hawking radiation using the formula PM=(h∙c3)/(16п2∙k∙G∙M), where h is Planck’s constant (not given!), c is the speed of light, k is Boltzmann’s constant, G is the gravitational constant, M is the mass of the black hole. Approximately this temperature will be equal to 6.169∙10-8 K∙(M0/M), where M0 is the mass of the Sun. It turns out that the more massive the black hole, the lower the temperature corresponding to the radiation.

But a black hole is not a star. Losing energy, it does not cool down. Vice versa! As the mass decreases, the hole becomes “hotter.” The loss of mass also means a decrease in radius. As a result, evaporation occurs with increasing intensity. It follows that small holes must complete their evaporation with an explosion. True, for now the very existence of such microholes remains hypothetical.

There is an alternative description of the Hawking process, based on the Unruh effect (also hypothetical), which predicts the registration of thermal radiation by an accelerating observer. If it is connected to an inertial reference frame, it will not detect any radiation. For an observer, the vacuum around an accelerated collapsing object will also be filled with radiation with thermal characteristics.

Information problem

The trouble that Hawking's radiation theory has created is due to the so-called "no hair theorem" of a black hole. Its essence, briefly, is as follows: the hole is completely indifferent to what characteristics the object that fell beyond the event horizon had. The only thing that matters is the mass by which the hole has increased. Information about the parameters of the body that fell into it is stored inside, although it is inaccessible to the observer. And Hawking's theory tells us that black holes, it turns out, are not eternal. It turns out that the information that would have been stored in them disappears along with the holes. For physicists, this situation is not good, since it leads to completely meaningless probabilities for individual processes.

Recently, there have been positive developments in resolving this paradox, including the participation of Hawking himself. In 2015, it was stated that, thanks to the special properties of vacuum, it is possible to identify an infinite number of parameters of a hole’s radiation, that is, to “pull” information out of it.

Registration problem

The difficulty of resolving such paradoxes is compounded by the fact that Hawking radiation cannot be detected. Let's take another look at the formula above. It shows how cold black holes are - hundred-millionths of a Kelvin for holes of solar mass and a three-kilometer radius! Their existence is highly doubtful.

There is, however, hope for microscopic (hot, relict) black holes. But until now no one has observed these theoretically predicted witnesses to the earliest eras of the Universe.

Finally, we need to add a little optimism. In 2016, a message appeared about the discovery of an analogue of quantum Hawking radiation in an acoustic model of the event horizon. The analogy is also based on the Unruh effect. Although it has a limited scope of applicability, for example, it does not allow studying the disappearance of information, there is hope that such research will help in creating a new theory of black holes that takes into account quantum phenomena.

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Mainly photons, black hole. Due to energy and "href="http://ru.wikipedia.org/wiki/%D0%97%D0%B0%D0%BA%D0%BE%D0%BD_%D1%81%D0%BE%D1 %85%D1%80%D0%B0%D0%BD%D0%B5%D0%BD%D0%B8%D1%8F_%D1%8D%D0%BD%D0%B5%D1%80%D0%B3 %D0%B8%D0%B8">the law of conservation of energy and , this process is accompanied by a decrease in the mass of the black hole, i.e., its “evaporation.” Theoretically predicted by Stephen Hawking in 1973. Hawking’s work was preceded by his visit to Moscow in 1973 , where he met with Soviet scientists Yakov Zeldovich and Alexander Starobinsky, they demonstrated to Hawking that, according to the uncertainty principle of quantum mechanics, spinning black holes should generate and emit particles.

The evaporation of a black hole is a purely quantum process. The fact is that the concept of a black hole as an object that does not emit anything, but can only absorb matter, is valid as long as quantum effects are not taken into account. In quantum mechanics, thanks to tunneling, it becomes possible to overcome potential barriers that are insurmountable for a non-quantum system.

In the case of a black hole, the situation looks like this. In quantum field theory, the physical vacuum is filled with constantly appearing and disappearing fluctuations of various fields (one might say “virtual particles”). In the field of external forces, the dynamics of these fluctuations changes, and if the forces are strong enough, particle-antiparticle pairs can be born directly from the vacuum. Such processes also occur near (but still outside) the event horizon of a black hole. In this case, a case is possible when the total energy i of the antiparticle turns out to be negative, and the total energy i of the particle turns out to be positive. Falling into a black hole, an antiparticle reduces its total rest energy, and hence its mass, while the particle is able to fly away to infinity. To a distant observer, this looks like radiation from a black hole.

What is important is not only the fact of radiation, but also the fact that this radiation has a thermal spectrum. This means that radiation near the event horizon of a black hole can be associated with a certain temperature

where is Planck's constant, c- speed of light in vacuum, k- Boltzmann constant, G- gravitational constant, and, finally, M- the mass of the black hole. By developing the theory, it is possible to construct the complete thermodynamics of black holes.

However, this approach to a black hole is in conflict with quantum mechanics and leads to the problem of information disappearance in a black hole.

The effect has not yet been confirmed by observations. According to general relativity, during the formation of the Universe, primordial black holes should have been born, some of which (with an initial mass of 10 12 kg) should finish evaporating in our time. Since the rate of evaporation increases as the size of the black hole decreases, the final stages should essentially be an explosion of the black hole. So far, no such explosions have been recorded.

Experimental confirmation

Researchers from the University of Milan claim that they were able to observe the effect of Hawking radiation, creating the antipode of a black hole - the so-called white hole. Unlike a white hole, which “sucks in” all matter and radiation from the outside, a white hole completely stops the light entering it, thus creating a boundary, an event horizon. In the experiment, the role of a white hole was played by a quartz crystal, which had a certain structure and was placed in special conditions, inside which the photons of light completely stopped. By illuminating the above-mentioned crystal with infrared laser light, scientists discovered and confirmed the existence of the re-emission effect, Hawking radiation.

Physicist Jeff Steinhauer from the Israel Institute of Technology in Haifa detected the radiation predicted by Stephen Hawking back in 1974. The scientist created an acoustic analogue of a black hole and showed in experiments that radiation of a quantum nature emanates from it. The article was published in the journal Nature Physics, and BBC News briefly reported on the study.
...It is not yet possible to detect this radiation from a real black hole, since it is too weak. Therefore, Steinhauer used its analogue - the so-called “blind hole”. To model the event horizon of a black hole, he took a Bose-Einstein condensate of rubidium atoms cooled to temperatures close to absolute zero.
The speed of sound propagation in it is very low - about 0.5 mm/sec. And if you create a boundary, on one side of which atoms move at subsonic speeds, and on the other, they accelerate to supersonic speeds, then this boundary will be similar to the event horizon of a black hole. In the experiment, atomic quanta - in this case phonons - were captured in a region with supersonic speed. The phonon pairs were separated, one was in one region, and the second was in another. The correlations recorded by the scientist indicate that the particles are quantum entangled.