Stephen Hawking, the scientist who changed our understanding of the Universe, has died

British theoretical physicist Stephen Hawking on Wednesday, March 14, passed away at the age of 76. The scientist, who has spent most of his life in a wheelchair, is widely known as a popularizer of science, in recent years he paid great attention to such problems of mankind as global warming, the state of the environment and social inequality.

On the life and the main scientific achievements of the cosmologist - in the material "Tapes.ru".

“He was a great scientist and an extraordinary man, whose work and heritage will live for many years. His courage and perseverance with brilliance and humor inspired people around the world. We will miss him ", - the British newspaper gives a statement of the children of the physicist Robert, Timothy and Lucy The Guardian.

Life and disease

Stephen Hawking was born on January 8 1942 in Oxford (United Kingdom), where his parents moved from London during World War II. The father of the future physicist was a physician, and his mother was an economist, they both graduated from Oxford University. Hawking followed in their footsteps, graduating from the physics department of the same university in 1962, after which he continued his education at Cambridge University, where he received his doctoral degree at 1966.

In 1963, Hawking was diagnosed with amyotrophic lateral sclerosis. This chronic disease of the central nervous system subsequently led to almost complete paralysis of the scientist. In the 1985 year, Hawking suffered a tracheostomy after pneumonia, and therefore lost the ability to speak. At the same time, the scientist began to use a speech synthesizer, and from 1997, a computer controlled by a sensor attached to the mimic muscle of the cheek.

Hawking was married twice. In 1965, a scientist married Jane Wilde, a student at the University of Cambridge linguistic department. The couple had two sons, Robert (in 1967) and Timothy (in 1979), and a daughter, Lucy (in 1970). After more than 20 years of life together, the couple broke up. The second time Hawking got married in the 1995 year. His wife was a nurse, Eline Mason, with whom the scientist broke up in 2006 year.

Singularity and entropy

Stephen Hawking's career began in the 1960s, when the third of the classic experiments was carried out, confirming the validity of Albert Einstein’s general theory of relativity (the experience of Robert Pound and Glen Rebka, demonstrated at Harvard University, showed the so-called gravitational red shift its passage near a massive object, for example, a star).

When it finally became clear that Einstein's theory was correct, it was time to study its most exotic consequences: the expansion of the Universe (after the Big Bang) and the possibility of the existence of black holes - objects that cannot be fallen from their bodies or radiation.

The big bang, in fact, the birth of the observable world, and black holes are associated with gravitational singularities, a feature of spacetime, where the equations of the general theory of relativity lead to physically incorrect solutions. It is precisely to singularities that Hawking's first scientific works are devoted. In his dissertation, Hawking applied the theorems formulated by his colleague, the British mathematician Roger Penrose, to the entire Universe.

Penrose was the first to explain the occurrence of a black hole by a gravitational singularity. According to Penrose, the star turns into a black hole due to a gravitational collapse, accompanied by the birth of a trap surface. Penrose's theorem is considered the first major mathematically rigorous result of Einstein's theory, and Hawking's contribution was that he showed that the Universe was in a state of infinite mass density at the time and before the Big Bang.

At the beginning of 1970, Hawking with Brandon Carter and David Robinson partially proved the hypothesis of American physicist John Wheeler, known today as the “hair” absence theorem for black holes. According to the theorem, isolated uncharged black holes, described in the Schwarzschild space-time, are characterized by only two parameters: mass and angular momentum. "Hair" in this case - all the other parameters.

"This theory (Einstein - approx. "Tapes.ru") leads to the following two predictions for the universe. First, the final stage of the evolution of a massive star is a collapse beyond the event horizon, and a black hole forms, inside of which there is a singularity. Secondly, in our past there is a singularity, which in some sense is the beginning of the observable universe, ”wrote Hawking and his co-author John Ellis in 1973 in the monograph“ Large-scale space-time structure ”.

In 1960, black holes were attempted to be described not only with the help of the general theory of relativity, but also with the methods of quantum mechanics. Hawking went the other way and applied thermodynamics to black holes. The entropy of a black hole, as established by the Israeli physicist Jacob Bekenstein, is proportional to its area. Hawking, systematically applying thermodynamics to black holes, obtained an exact expression for the entropy of a black hole.

Main result

In 1970, Hawking visited the USSR and met with physicist Jacob Zeldovich. In a conversation with Soviet scientists, he learned that the well-known Soviet physicist Vladimir Gribov considers it undeniable that black holes, due to vacuum fluctuations, can evaporate. On the horizon of events (the surface limiting a black hole, penetrating into which a particle in the classical description cannot leave it) pairs of virtual particles are formed: one of them flies away from the black hole, the other falls into it, thereby reducing its mass (this is a popular explanation Hawking radiation, which in reality is somewhat more complicated and is associated with the Unruh effect).

Unfortunately, Gribov did not publish a single article on this subject, while Hawking quantitatively calculated the thermal spectrum of a black hole. For example, the temperature of a black hole of solar mass is about one millionth of a Kelvin. It is impossible to distinguish such a low temperature from noise by modern astronomical methods. The study of the emission of black holes, many consider the main work of Hawking.

Wave function of the universe

Later, the scientist tried to investigate black holes with the help of a functional integral — an extremely powerful mathematical apparatus of quantum field theory. Unfortunately, the methods that are effective in quantum field theory have not been effective in the naive (that is, not in the framework of string theory) description of gravity.

Applying quantum mechanics to the entire universe at once, Hawking also tried to determine the properties of its wave function. For the first time, the wave function of the world and the equation describing it were considered by American physicists John Wheeler and Bruce Dewitt. Hawking, along with co-author James Hartley of the United States, proposed their function, obeying the Wheeler-DeWitt equation. In this way they tried to describe the world on a pre-Blanc scale. From the analysis of such a wave function, it followed that at the time of the Big Bang there was only space without time in the Universe.

The concept of Hawking and Hartley admits the existence of parallel worlds for which a single wave function is defined. In this variety of universes, the reality observed by man is only one of the possible. Apparently, the structure of the world is somewhat more complicated than the theories of Wheeler, DeWitt, Hawking and Hartley, suggesting the existence of the wave function of the Universe, although discussions about it continue to this day.

Fame

Hawking received wide popularity after his popular science book "A Brief History of Time" was published in April 1988. The work, translated into dozens of languages, has been published with a total circulation of more than 10 million copies. The image of a scientist in a wheelchair, engaged in the study of the most unusual properties of the universe, did not leave anyone indifferent.

In 1990, Hawking continued the study of black holes, proposing a weak version of the principle of space censorship. In a strong form, the statement that singularities, that is, not hidden from an external observer, singularities are impossible in space-time, was formulated by Penrose in 1973 year. In particular, for a black hole, singularities should be under its event horizon. Penrose, in contrast to Hawking, believes that the principle of space censorship is carried out immediately in the whole space-time.

In the past 20 years, Hawking has been interested in the information paradox of black holes. At first, he argued that the information carried by objects that fell into a black hole is not preserved, but then changed his mind. In his latest works, Hawking argued that information is not lost, but is transformed into an unsuitable form for human use. This, in particular, is the focus of his research, conducted jointly with Malcolm Perry and Andrew Strominger.

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