Summary

Stephen William Hawking, CBE CH (Oxford, January 8, 1942 - Cambridge, March 14, 2018), was a British cosmologist, physicist, mathematician, astrophysicist, academic and popularizer of science, among the world's most influential and well-known theoretical physicists, best known for his studies on black holes, quantum cosmology and the origin of the universe.

His most notable contributions include Hawking radiation, the cosmological theory of the boundless beginning of the universe (fruitful collaboration with other scientists has contributed to the development of numerous physical and astronomical theories: the multiverse, galactic formation and evolution, and cosmic inflation. These theories, always explained with clarity and simplicity, have reached the general public through numerous popular science texts.

Constrained to physical immobility and unable to speak independently since the 1980s due to a degenerative motor neuron disease (MND) diagnosed as early as 1963 (probably a rare and slowly progressing form of amyotrophic lateral sclerosis, or ALS), Hawking was confined to a wheelchair and forced to communicate with a speech synthesizer. In spite of this, his public image, mediated by numerous appearances in documentaries and television shows, has become one of the popular icons of modern science, as was the case with Albert Einstein in the past.

Holder of the Lucasian Chair of Mathematics at the University of Cambridge, he was until his death director of the Cambridge Department of Applied Mathematics and Theoretical Physics. A member of the Royal Society, Royal Society of Arts and Pontifical Academy of Sciences, in 2009 he received the Presidential Medal of Freedom, the highest honor of the United States of America, from U.S. President Barack Obama.

The son of scientist Frank Hawking (1905-1986) and Isobel Eileen Walker (1915-2013), Stephen William Hawking was born in Oxford on January 8, 1942, exactly 300 years after Galileo's death, as he himself liked to recall. His parents, although their own families were not financially stable, attended Oxford University, where his father studied tropical medicine and his mother studied Philosophy, Politics, and Economics. The two met shortly after the beginning of World War II, at a medical research institute where Frank worked as a researcher and Isobel as a secretary. After residing for some time in Highgate, the bombing of London caused Isobel to mature in her decision to give birth, for safety's sake, in Oxford. In 1950, when her father became head of the parasitology division at the National Institute for Medical Research, the Hawking family moved to St Albans, Hertfordshire.

Academic training

Stephen Hawking undertook his studies at Byron House School; he later blamed its "progressive methods" for his initial difficulty in learning to read. At the age of eight he attended, for a couple of months, St Albans High School for Girls. Then Radlett School for a year and, from September 1952, St Albans School.

The father wanted his son to attend Westminster School. However, because he was ill on the day of the scholarship test, and the family could not afford the tuition fees, Hawking remained at St Albans School. During these years, Hawking developed his early scientific interests, which, although opposed by his father who leaned toward a medical career, led him to decide to study mathematics.

Stephen began his college education in October 1959, at the age of 17, at University College of Oxford University. Because his flagship college at the time did not accept mathematics students, Hawking decided to study physics and chemistry. He was the youngest among his classmates and found academic work "ridiculously easy." Between his second and third years of study, Hawking struggled "to be just one of the boys." He developed a great interest in music, science and science fiction.

Hawking estimated that he studied about 1,000 hours during his three years at Oxford. An honors degree, first class, was a necessary condition for acceptance into the graduate program in cosmology, at the University of Cambridge. He was very upset the night before the exams, but finally managed to get his first-class grade.

After graduating with honors in natural sciences, he began his graduate work at Trinity Hall, Cambridge, in October 1962.

At that time, the most debated topics in the community of theoretical physicists concerned the origin of the universe and the Big Bang. During 1965, he made this issue his own, analyzing it in his own dissertation.

In March 1966, Hawking was awarded a research fellowship at Gonville and Caius College. That same year he received his doctorate in applied mathematics and theoretical physics and won, tied with Roger Penrose, the Adams Prize, with a paper entitled Singularities and the Geometry of Space-Time.

Illness and disability

Arriving in 1963 in Cambridge, the 21-year-old Hawking began to experience some difficulties in the use of his limbs (which resulted in a number of falls), such that he underwent medical investigations (a myelography and a muscle biopsy). The diagnosis was inauspicious, as he was found to be suffering from a degenerative motor neuron disease, which impaired the governing function of muscle contraction: specifically, amyotrophic lateral sclerosis (ALS) or a related disease was thought to be involved. Hawking began using a cane and later a wheelchair. Despite the depression that followed his diagnosis, according to which he theoretically had only two years to live, he continued his studies briskly, later marrying Jane Wilde, his first wife, who would serve as his nurse and by whom he would have three children-Robert (1967), Lucy (1970), and Tim (1979).

The course and progression of Hawking's disease was unusually long and slow, however, as the scientist lost his movements and use of speech only after more than 20 years and died after more than 50 years, whereas usually ALS patients lose these abilities within 5-10 years and have a much reduced life expectancy; in addition to eye movements, which usually persist even in full-blown ALS, he also retained some facial movements and, until the 1990s, even some minimal hand movements (which in ALS patients are lost in a much shorter time).

In addition to this, although tracheotomized and subjected to assisted ventilation, he retained independent breathing during sleep and in times of need and never made use of ventilators during the day, except during periods when he had respiratory problems. For these reasons, it has never been clarified with certainty what disease he suffered from; some argued that it was progressive muscular atrophy (PMA), similar in symptomatology to ALS and belonging to the same group of neurological diseases (so much so that until a few decades ago it was considered only a clinical variant of ALS) but much less aggressive and lethal, as it affects only the second motor neuron. Some experts, as well as Hawking himself, argued instead that his disease might be a particular and atypical form of ALS, which would severely damage only the second motor neuron; in the more common form of ALS, however, both motor neurons are affected equally, sometimes even in conjunction with the brain bulb. Hawking's disease actually affected the first motor neuron as well from early on (though less seriously than the second), prompting the diagnosis to lean toward a non-extreme form of ALS, given the dysarthria and suffering in his facial and swallowing muscles that affected him from the 1970s onward.

Many physicians who treated Hawking contend that his ALS may have been of an uncommon type among the many variants of the disease, i.e., related to a defect in vitamin malabsorption, slow in progression, and juvenile in onset; these two features are related; in ALS, the juvenile form is the least virulent and at some point appears to stop. Hawking also received constant care and assistance-which prevented him from respiratory failure and malnutrition with dehydration, i.e., the two main causes of death in sufferers along with infections-and his sedentary and exclusively intellectual work allowed him not to overexert his body and, at the same time, to keep his mind active; this contributed to his surviving for an unusually long time for a person in his condition. Only 5 percent of patients with this strain of the disease reach 20 years, and there are very few cases of such long survival; the survival of the majority-75 percent-is between two and five years, with 20 percent surviving without reaching 20. A case similar to Hawking's is that of musician Jason Becker, who also suffered from juvenile ALS, which later stabilized. The few other patients with symptoms like Hawking's, however, require continuous artificial ventilation. Nigel Leigh, professor of clinical neurology at King's College, had analyzed Hawking's case, describing it as "exceptional." From the 1980s onward he required continuous care for 24 hours a day, but he hardly ever resorted to artificial nutrition or PEG, but only assisted feeding with non-solid foods with the help of personal nurses, since he underwent pharyngeal and tracheal separation surgery in the 1990s. There have been medical studies on the hypercaloric and hypervitaminic diet, free of gluten and vegetable oils, followed by Hawking, that it contributed to his longevity.

In 1985 Hawking was stricken with severe pneumonia and underwent a permanent tracheotomy, which resulted in the loss of his vocal function. He revealed that while he was in a medically induced coma, doctors wanted to take him off the machines, but it was his wife Jane who objected.

A Cambridge technician, computer engineer David Mason, then the husband of what would later become Hawking's second wife, Elaine, built for him a speech synthesizer that turned what Hawking typed into sound on a special computer, which was then connected to his wheelchair according to a system invented by Mason himself. In this way Hawking could communicate, albeit very slowly (no more than fifteen words per minute). In 2009 he again risked his life because of pneumonia, a condition that also affected him later. His condition remained more or less stable from the mid-1980s until his death, although by the second half of the 2000s, due to weakness from aging, he gradually lost the imperceptible movements in his fingers that enabled him to move his electric wheelchair independently and write on the keyboard.

As a result of these problems in his finger movements (which made him able to compose less than five words per minute, averaging only one or two), a facial recognition system was then developed for him, which turns the slightest movements of his mouth, right cheek and eyebrows into words, connected to the computer via infrared on his glasses; this software, perfected in 2011, can also read eye movements and translate them into words and sentences. With this system Hawking could express himself with about 10 words per minute.

In 2013 this support was enriched by a new program, a brain scanner that also allows for the reading of some particular brain impulses, which are turned into data and then into some symbols, sounds, and words. This system was developed in the event that the professor was struck by a locked-in syndrome, which would completely prevent him from any physical movement, even minimal; this condition did not manifest itself, so Hawking never took advantage of the new system.

University lecturer

The disease did not affect his intellectual faculties in the slightest, making him able to carry out the studies and achieve the great results for which he is known. In the period from 1965 to 1970 he developed some theories explaining the evolution of the universe. In 1970 he continued his studies on black holes and also became involved in popularization, with the writing of his "masterpiece" and best seller From the big bang to black holes. A Brief History of Time, published in 1988, selling more than 9 million copies worldwide.

In 1974 he joined the Royal Society and was invited to the California Institute of Technology (Caltech) by Kip Thorne, and then returned to Europe the following year.

In 1979 he was appointed to the Lucasian Chair of Mathematics at Cambridge, a post that had been held by Sir Isaac Newton and Paul Dirac.

In 1982 he was appointed a Commander of the Order of the British Empire by Queen Elizabeth II, but Hawking declined the knighthood (Knight Bachelor, with the title "Sir" placed before his proper name). He later stated that he detested the very concept of "knighthood."

In 1986 Hawking was appointed a member of the Pontifical Academy of Sciences.

On Sept. 30, 2009, he left the Lucasian chair, being replaced by Michael Green; he remained director of the Department of Applied Mathematics and Theoretical Physics until his death.

Death

Hawking died in the early morning hours of March 14, 2018, at the age of 76, at his home in Cambridge. His three children Lucy, Robert and Tim were the first to make the announcement, without revealing the cause of death, stating that the death had been "serene," not specifying whether it occurred in sleep. The death certificate was made public the following June 3 and shows "motor neuron disease" as the cause of death, without mentioning whether Hawking had died of respiratory failure or infection or other common complications of ALS

His last television appearance had taken place during an interview in which he discussed with friend and colleague Neil deGrasse Tyson his views on the concepts of time and space before the Big Bang. On the day of his death, the flag of Gonville and Caius College in Cambridge was erected at half-mast and a condolence book was signed by students and visitors. At the end of the 2018 Paralympic Winter Games held in Pyeongchang, IPC President Andrew Parsons remembered Hawking through a closing speech. His solemnly private funeral was held on March 31 at St. Mary Major Church in Cambridge, a church at the prestigious university where he had taught for 50 years; although the scientist was an atheist, the funeral took place in an Anglican rite. Also present at the funeral were actors Eddie Redmayne and Felicity Jones, who had played the roles of Hawking himself and his wife Jane Wilde, respectively, in the film The Theory of Everything. His body was cremated and the ashes were interred in Westminster Abbey, near the gravesites of Isaac Newton and Charles Darwin.

His last words to the world appeared posthumously, in April 2018, in the form of a documentary entitled Leaving Earth: Or How to Colonize a Planet broadcast on Smithsonian TV Channel. His last research study, titled A smooth exit from eternal inflation?, about the origin of the universe, On the origin of the universe, was published by the Journal of High Energy Physics in May 2018.

Personal life

Hawking had two sisters, Philippa (1943) and Mary (1947), and an adopted brother, Edward (1956). In his spare time he was a big fan of the television series Doctor Who.

After graduating from Oxford, Hawking began dating Jane Wilde, a friend of his sister's whom he met shortly before his diagnosis. The two became engaged in October 1964 and were married on July 14, 1965.

During the early years, Jane lived in London. The couple traveled several times to the United States of America for physics conferences. Jane began a PhD program. From this first marriage the professor had his three children: in 1967 Robert and in 1979 Timothy. Hawking discussed his illness with Jane few times, although the responsibilities of home and family fell to her. Upon her appointment in 1974 at the California Institute of Technology in Pasadena, California, Jane suggested that one of her students live with them to help care for Hawking. The family spent a happy and stimulating year in Pasadena. Hawking returned there from Cambridge in 1975, settling in a new home and with a new job; as a reader he had Don Page, with whom he forged a close friendship at Caltech, corroborated by help in the family; he also had a secretary so that Jane could complete her dissertation. Hawking was Page's doctoral reviewer, along with Kip Thorne.

In December 1977 Jane met organist Jonathan Hellyer Jones while participating in activities in the local church choir. Hellyer Jones came into close contact with Hawking's family, and by the mid-1980s, he and Jane developed a close personal relationship. According to Jane, Hawking accepted the situation; Jane and Hellyer Jones decided not to break up the family and their relationship remained platonic for a long time. From 1980, Hawking's marriage remained strained for many years as Jane felt overwhelmed by the nurse's intrusion into their family life, as well as differences in views on issues such as religion.

In late 1990, Hawking began a romantic relationship with Elaine Mason, his personal nurse for years and wife of David Mason (the inventor of the communication system used by the scientist). Hawking told Jane shortly thereafter that he was leaving with Mason, so he left home in February 1991. Both Elaine and Stephen left their respective spouses; Jane was able to live with Jones.

After his divorce from Jane in 1995, Hawking married Elaine Mason in September, declaring "It's wonderful-I married the woman I love"; Jane instead married Jonathan Hellyer Jones the following year. After his second marriage, Hawking's family felt excluded from his life. For about five years in the early twenty-first century, there was a strong suspicion that Hawking was being mistreated by someone who was close to him and had to take care of him (he fell out of his wheelchair, fracturing his arm and bruising his face, and suffered some sunburns from sitting too long in the garden, as well as a cut from a shaving razor). Upon reports from the family and the press, police investigations were opened in 2004, mainly on Elaine but also on other nurses, also suspecting that some of them were manifesting Münchausen syndrome by proxy (a mental disorder that prompts one to cause physical harm to an incapacitated person, such as a young child or a disabled person, and then treat such harm without making the real cause understood and thus drawing positive attention to oneself); however, the investigation was soon closed because Hawking refused to press charges, always claiming that the injuries were the result of accidental falls and isolated distractions of the nurses.

In 2006, Hawking and Elaine Mason divorced. Press rumors, denied by Hawking's secretary, said the physicist had started a new relationship with another nurse. In his 2013 autobiography and in interviews, Hawking again denied that he had been physically abused or cheated on Elaine, attributing the divorce to a simple consensual decision by both of them: "Our marriage was passionate and stormy, but it was the press that painted me as a victim of domestic violence. Elaine did none of that." After 2006, Hawking resumed stable relations with his first wife Jane, his own children and grandchildren.

Hawking's main fields of research were cosmological theory and quantum gravity. Regarding quantum mechanics, he advocated the many-worlds interpretation. His work on quantum cosmology and the wave function of the universe, according to some, is the reason for the newfound interest in this theory.

Mathematical models and gravitational singularities

In the late 1960s, with his friend and Oxford colleague Roger Penrose, he worked on singularities in the solutions of the field equations from the theory of general relativity, focusing in particular on black holes. Singularities such as black holes had been discovered since Karl Schwarzschild's early studies, but they were limited to particular symmetric conditions of mass-energy distribution, so the question remained open as to whether singularities remained present even under less symmetric and more realistic conditions. In this regard, Hawking proved in 1971 the first of many theorems that provide a sufficient set of circumstances for the existence of gravitational singularities in spacetime. This work indicated that singularities are a general and not an occasional feature of general relativity, proving that the universe must have originated in the Big Bang, a singularity in which the very laws of general relativity cease to hold because of quantum effects.

Black hole studies

Together with Brandon Carter, W. Israel and D. Robinson, he provided the mathematical proof of John Archibald Wheeler's No-Hair Theorem, namely, that black holes are characterized by only three properties: mass, angular momentum and electric charge. Regarding this, one recalls the dispute that pitted him against Jacob Bekenstein, but they eventually agreed on a similar description of black hole entropy. With Bardeen and Carter, he also proposed the four laws of black hole thermodynamics, in analogy with classical thermodynamics, so as not to violate especially the second principle of thermodynamics. In the area of singularity theorems, Penrose and Hawking proposed that there is no such thing as a naked singularity, that is, an isolated singularity not surrounded by the event horizon, because according to them a singularity should not be visible from the outside because of a principle they called "cosmic censorship." The question about the existence of naked singularities remains open to this day. In 1972 Hawking enunciated the Hawking area theorem, according to which the total area of a black hole never decreases.

In 1974 he showed that thermodynamically, black holes are black bodies and are described by the laws of thermodynamics: that is, they possess a temperature and entropy defined by their gravitational field and surface area. Consequently, despite the area theorem, they should radiate, thanks to a quantum phenomenon, subatomic particles (as well as producing flashes of gamma rays, x-rays and giving rise to the brightness of quasars).

This radiation, known as Hawking radiation, has thermal characteristics and should lead to the progressive decrease in mass of the black hole. The quantum mechanism that produces this radiation is needed because, on the event horizon, pairs of virtual particles and antiparticles that are normally emitted in the vacuum by quantum fluctuations could separate, one of which could fall into the black hole and the other could escape it, instead of both annihilating immediately after their creation. The black hole would then absorb an antiparticle before it annihilates with the corresponding particle outside the black hole; the particle is instead allowed to escape, and is detectable in the form of radiation. The corresponding antiparticle, on the other hand, will annihilate with a particle of the matter inside the black hole, thereby decreasing its mass until the so-called "evaporation" is complete after about 1066 years (10100 or more for large-mass black holes).

However, the possible end result of a black hole evaporating is still unclear, although Hawking speculated that black holes can become very small and then explode with extreme force. in 1975 with colleague Kip Thorne that Cygnus X-1 (a probable stellar black hole) was not a black hole, on the grounds that he had devoted his life to studies of black holes and, if they did not exist, at least he would console himself by winning a bet. The British physicist decided to give up and admitted that he had lost the bet to Thorne when, starting in 1990, observational data reinforced the hypothesis of the black hole's existence, now largely confirmed.

The black hole information paradox implies that information could "disappear" once it ends up in a black hole, allowing many initial physical states to evolve into the exact same state. Particles and bodies that end up in a black hole contain a lot of information about their state and shape, but the black hole can be described with only a few variables (mass, angular momentum, and electric charge), so it is unclear whether all the information of the particles that ended up in the black hole is preserved inside it. In particular, the crucial question is whether the information can escape, or on the contrary is destroyed, as the black hole slowly evaporates. Violation of the conservation of information would result in violation of the unity of the theory that is supposed to describe quantum gravity, a fact considered unnatural.

For this problem, Hawking has proposed several solutions; for example, he has endorsed the idea that particles can cross the event horizon by the tunneling effect, thus being able to carry information out of the black hole. Alternatively, he argues it is possible that information could instead come out of a white hole, or as information degraded by the black hole itself with radiation. Another solution he supports is that black holes may be black stars, that is, bodies entirely analogous to the stellar black hole but without an event horizon.

In 2015, he came up with a new mathematical solution to the paradox, which he considered to be the final one and published in January 2016, according to which the black hole always preserves information while erasing it, in partial derogation of the no-hair theorem: some particles would leave a two-dimensional holographic imprint on the event horizon, so the information, though partial and chaotic, survives and comes back with the radiation, and neither general relativity nor quantum mechanics or the law of conservation of energy are violated.

In the paper published on the Web, Hawking and colleagues Malcolm J. Perry of Cambridge University and Andrew Strominger of Harvard explain, in Strominger's summary words, that "we have shown that when a charged particle enters, it adds a photon to the black hole. So 'hairs' are added to the black hole"; the photon produced by the negative particle entering the black hole, and causing it to lose mass through annihilation, does not enter the interior of the object. According to Hawking, these "hairs" or "hairs" - Wheeler by "hairs" meant something that might protrude from the black hole to reveal details of the object that created it, particularly the magnetic field lines of a star - are experimentally demonstrable and remain on the event horizon being very small and massless. If the photon (or alternatively a graviton) is "soft" ("soft photon," with a zero-point energy, too low to be detected), the black hole retains the same energy but a different angular momentum, which would lead to the escape of a kind of "snowflake" with properties related to its origin and history. It might be possible, then, by analyzing the magnetism and related effects of black holes, to recover information about the objects that created them, and the determinism of physical laws would not be circumvented by the paradox.

Another theory supported by Hawking hypothesizes the presence of primordial black holes, generated by fluctuations in mass-energy density in the very first moments of the universe's life rather than by the collapse of a massive star. These micro black holes, being able to have a lower mass than those generated by stellar collapses, would emit more intense radiation and thus be detectable by probes and astronomical observatories. If these radiations were indeed detected, they would allow experimental verification of the existence of Hawking radiation.

Experimental evidence

Primordial black holes and Hawking radiation (unlike other rays or effects from outside black holes) have never been observed until now; the main attempts to observe these phenomena are concentrated in the gravitational waves of the cosmic background radiation. The absence of experimental evidence for his theories is perhaps at the root of Hawking's failure to win the Nobel Prize in Physics, Some experiments have reproduced systems in the laboratory that behave similarly to black holes, where the radiation emission, however, is represented by acoustic waves. Indeed, in May 2016, based on the data collected and Hawking's theory, Jeff Steinhauer, of the Israeli Technion Institute in Haifa, claimed to have simulated a black hole in the laboratory, verifying the theory of evaporation of objects as described by the British physicist 42 years earlier. According to the Times, this theory and related demonstration could have actually earned him the Nobel Prize.

Cosmological models

Hawking's contributions were very important in the development of the standard model of cosmology, which implies the hot Big Bang. In collaboration with James Hartle, he then developed from the 1980s a model of quantum cosmology in which the universe has no boundary in spacetime, replacing the Big Bang, understood as the initial gravitational singularity, with a mathematical model that he describes by analogy as the region of an Earth pole: no one can travel further north or south than the respective poles since there is no boundary at such a place (arriving at the bare singularity becomes impossible as in the Zeno stage paradox).

Originally, the new proposal envisioned a closed sphere-like shape of the universe, but discussions with Neil Turok led to the conclusion that the proposal of no boundary conditions, characterized by the instanton and imaginary time (unlike real time which is bounded by spacetime, it can be unbounded), is valid even in the case of an open universe, such as a dome with flat Euclidean geometry. However, this model is different from other similar ones, such as the steady-state theory.

According to Hawking, it is also possible that matter and energy were condensed, in this unbounded state, in a primordial black hole, from which they emerged because of the quantum and relativity laws. Hawking also argued that the Big Bang is an inverse black hole, thus similar to a white hole, both being singularities. So matter could come out later, passing through a wormhole, a spacetime gap hypothesized by general relativity, to another point in the universe (this would be easy especially in "doughnut" or toroid shaped universe), or from a white hole in another universe, if the black hole is rotating and very large (but it will not be able to go back). This idea was taken up by Lee Smolin for his theory of cosmological natural selection, an alternative multiverse model to string theory, in which black holes create parallel universes.

Together with CERN's Thomas Hertog, in 2006 Hawking devised a further development of his boundaryless proposal, a "top-down cosmology" model (from large structures to small ones, a Fine-tuned Universe model that opposes the "bottom-up" model, i.e., from yesterday to today), whereby the universe had no unique initial state, and therefore it is inappropriate for physicists to attempt to formulate a theory that tries to predict the current configuration of the universe from a precise initial state. Hawking's top-down cosmology postulates that the present can select the past from a superposition of many possible histories (Richard Feynman's so-called sum over histories or integral over paths, already used for the boundaryless model; in it every particle follows every possible history). According to this mathematical theory, it is inevitable to discover the present physical constants of our universe, since the present universe "selects" only those past histories that led to the present conditions.

As in the many-worlds interpretation, and just as in natural selection, stories in which physical constants and conditions are not suitable for the development of life either collapse or simply do not allow the emergence of intelligent beings capable of asking questions about the origin and nature of the universe. There are those who attribute to this, and to Hawking's earlier work on the wave function of the universe, the reason for the theoretical physics community's newfound interest in the many-worlds theory, as an alternative to the most popular of the interpretations of quantum mechanics, the Copenhagen interpretation (according to which only one story continues, parallel stories collapse immediately). This provides an anthropic explanation for why we are in a universe that allows for the existence of stable matter and life, without for that matter having to invoke the existence of multiple universes, which Hawking in any case does not rule out at all, since the top-down model he describes is part of M-theory and fits even with extra dimensions. In fact, he has never ruled out the multiverse theory, that is, the possibility of multiple universes (predicted by many cosmological models), each with its own relative birth and peculiar physical laws, and various theories of eternal or self-reproducing universes. Hawking therefore states that even if the Big Bang 13.7 billion years ago might not even be the absolute beginning; the universe or universes would be eternal, self-created and self-reproducing. If there are many universes, then the law of probability explains the apparent perfection of the one where we live, in an "evolutionary" sense, particularly the possibility that the Earth developed life, especially if it is rare (the so-called Earth rarity hypothesis). These theories were very important in the development of Hawking's religious conception. Order in the past was attributed to the creator; today it may also appear to be merely the result of the law of large numbers, implied, as a natural sequel, in these theories.

His other works in theoretical cosmological physics concern helium nucleosynthesis in post-Big Bang anisotropy, a mathematical model of Large N cosmology or N-Body Cosmology, the matrix density of the universe, the large-scale topology and structure of the universe, "newborn" universes, the Yang-Mills instanton, the nature of spacetime, gravitational radiation, as well as various philosophical and theological issues, up to studies in astrobiology and futurology.

In the 1980s Hawking also became involved in the theoretical idea of the arrow of time, the laws of thermodynamics, and the discussion of inflation theory, together with early proponents Alan Guth and Andrej Linde, hypothesizing with them the possible theoretical existence of a cosmological constant of quantum origin (vacuum energy or zero-point energy), for whose apparent disappearance various hypotheses were made; with the discovery of the accelerating universe such a constant, already introduced by Einstein as a mathematical artifice, was reconsidered and identified with dark energy.

Hawking's last theoretical work, completed shortly before his death together with Thomas Hertog and published after his passing, focuses on the existence of the multiverse, in the version based on the theory of eternal inflation that presumably originated at the time of the Big Bang that also created our universe, which was ultimately destined for thermal death. It is a paper that builds on the studies of Andrej Linde (bubble theory) and an advanced version of Hartle-Hawking's boundaryless state theory. Hertog described the paper as "Stephen's original boundaryless model on a more solid mathematical basis. This would succeed in limiting the multiverse to a finite and manageable set (of universes), thus allowing the model to be tested." Traces of hypothetical other universes could be identified by studying the cosmic background radiation.

As part of another long-standing scientific controversy, Hawking had emphatically claimed, and bet, that the Higgs boson would never be found. The particle had been proposed by Peter Higgs as part of the Higgs field theory in 1964. Hawking and Higgs were engaged in a heated public debate on the issue in 2002 and again in 2008, with Higgs criticizing Hawking's work, complaining that Hawking's "celebrity allows him instant credibility that others do not have." When the particle was discovered in July 2012 at CERN, following the construction of the Large Hadron Collider, Hawking quickly admitted that he had lost the bet and declared that Higgs should win the Nobel Prize in Physics,

Since the 2000s, Hawking has also been interested in string theory and has focused with others, such as the aforementioned Turok and Michio Kaku, on M-theory, a possible theory of everything that intends to unify the five variants of string theory and that is also developed around the concept of the multiverse, explaining the conditions so suitable of our universe for human life.

In 1988 he asserted that the existence of other galaxies and the large-scale homogeneity and isotropy of the universe seems at odds with the strong anthropic principle: "The universe must have those properties that allow life to develop within it at some point in its history." On similar positions are the theories of Frank Tipler, John D. Barrow and Brandon Carter. Following his adherence to the M-theory model, however, he changed his opinion and became a firm believer in the principle. At first he was puzzled about the validity of M-theory, but later became convinced that it is a convincing theory, not only because of its explanation of the strong anthropic principle, but especially because it unifies superstring theory and supergravity theory, providing an adequate solution to the apparent irreconcilability of quantum and relativity. At present, there is no direct experimental evidence to support string theory and M-theory.

Policy

Hawking has repeatedly expressed progressive positions politically and socially. He has openly defended the U.K.'s public health system, which has been progressively reduced since the 1980s, saying that he has received excellent medical care there, and thought it was important to set the record straight by testifying to the benefits of universalist health care. He also supported the Labor Party. Some controversy arose when he cancelled his presence at some scientific conferences and public meetings held in Israel as a protest against Israeli policy toward Palestinians in the Gaza Strip. In 2014, he called for an end to the Syrian civil war. He has also spoken out against Brexit.

Future of humanity

Repeatedly, the scientist affirmed the need for humanity to be able to create space colonies and expressed his anxieties about the possibility that humans could self-destruct, through the destruction of the environment, the spread of genetically modified viruses as biological weapons, the construction of artificial intelligence that could "rebel" against human beings or the outbreak of nuclear war. However, he also stated that "we should be afraid of capitalism, not robots: the greed of humans will lead to economic apocalypse." Regarding the unequal distribution of wealth, he said:

On September 25, 2015, The Global Goals initiative was launched worldwide, featuring Hawking along with many other activists and artists, including Malala Yousafzai, Anastacia, Stevie Wonder, Kate Winslet, Bill and Melinda Gates, Jennifer Lawrence, Queen Rania of Jordan, Jennifer Lopez, Meryl Streep, and many others. World leaders pledged to meet 17 global goals to be achieved over the next 15 years, the most important of which are eliminating extreme poverty, fighting inequality and injustice, and committing to climate change.

Disability rights

Hawking was also committed to the rights of the disabled, especially those in his own condition, and supported the right to euthanasia and assisted suicide.

In 2012 he took part in the opening ceremony of the London Paralympics, while in 2014 he joined the Ice Bucket Challenge campaign, a gesture to raise awareness of ALS sufferers, although it was his children and grandchildren who had the bucket of ice water dumped on his head instead, as making such a gesture would have put him at no small risk of a relapse of the pneumonia that had struck him in 2013.

Extraterrestrial life

Hawking has been a firm believer in the existence of intelligent extraterrestrial life forms in the universe, given its vastness; however, he has made it clear that he believes humans would do better not to seek direct contact, because if any alien beings were able to reach us, it would mean that they are in possession of much more advanced technologies than humans, and if they were hostile, such technologies would make them capable of causing enormous damage to Earth and humanity in a short time. However, he has shown interest in research studies of such alien life, such as that of SETI. Given the distance that would separate us from worlds inhabited by extraterrestrial civilizations and the little concrete evidence for their existence, Hawking has been skeptical of the extraterrestrial hypothesis about UFOs, leaning toward natural phenomena, misinterpretations, hoaxes, or secret military aircraft (in this regard, he said, "since many sightings have a more conventional explanation, it is reasonable to say that unidentifiable UFOs have an equally conventional origin."

Religious conception

In the last years of his life Hawking declared himself an atheist, although he had in the past expressed an interest in a pantheistic, nontranscendent view, such as that of Albert Einstein, or a kind of deism, as noted in the final chapter of his book From the Big Bang to Black Holes, in which he uses the phrase "mind of God." Hawking stated that he was "not religious in the normal sense" and believed, based also on his own strictly cosmological beliefs, that "the universe is governed by the laws of science. The laws may have been decreed by God, but God does not intervene to break the laws."

He argued in a 2011 article that God cannot be reconciled with science and is not related to our world. In this regard, he also argued, based on his own cosmological model, and in opposition to Thomism and in adherence to materialism, that existence has no "cause" and that there is therefore no cause (i.e., God) prior to it. The same article states that Hawking was actually agnostic, although his position was specifically ignostic, i.e., that of one who considers neither useful nor possible a statement about the existence of God, which remains only a truth of faith (a position similar to that of Pierre Simon Laplace). He never specified, until 2011, whether or not he believed in God or another higher entity: in the book, The Grand Design, co-written with physicist Leonard Mlodinow, he elaborated a cosmological theory that intends to explain the origin of the universe, which, as the scientist states in an interview in The Times "was not created by God." Also regarding the relationship between religion and science, Hawking here argues that they are not reconcilable, for as he stated again in the Times, "there is a fundamental difference between religion, which is based on authority, and science, which is based on observation and reasoning. And science will win because it works."

In 2011, he specifically stated that he does not believe in the existence of a Creator God (without commenting on religions that do not speak of "creation" instead) because it is not necessary to explain the universe, as he considers non-existent what would be "out of time," and there was no time before the Big Bang, unless the multiverse exists, based on his own boundary-less cosmological model. He asserted that this is the simplest explanation, for the very same reason, that a disease is derived from a physical cause, he does not need metaphysics to explain it, bringing his own personal situation as an example.

The universe and the peculiar conditions that seem to have been providentially created to allow us to exist (finely tuned universe) are answered by the strong anthropic principle, whereby this universe simply turns out to be, among the many originated in a quantum event (multiverse), the one suitable for our existence by selection and law of large numbers, and even the creation of an entire universe out of "nothing" or without boundaries can find a satisfactory explanation in what we observe and interpret through our physical models, eliminating the need for external intervention.

In contrast, according to critics, Hawking would not explain how, for example, a law of gravity could exist without gravities, just as he does not explain how a law of quantum mechanics that precedes the universe is conceivable since it actually presupposes it; moreover, he would be taking for granted the theoretically elaborated ideas of M-theory. Hawking responds to these objections that there is no need for a Creator to create physical laws since they simply exist intrinsically in matter

Hawking also claimed that he was primarily interested in the workings of the universe, without fully investigating why they exist, as these are non-scientific fields that science should not therefore consider. He also claimed that physics is the new philosophical metaphysics, as he makes explicit in the incipit of The Grand Design. In this regard he stated that he felt himself "a positivist."

Hawking, despite not being a believer, was a member of the Pontifical Academy of Sciences for many years.

Stephen Hawking has appeared many times in mass culture or documentaries. The professor said he believed that his notoriety in the popular imagination was mainly due to his image as a "disabled genius," as a person who achieves study results of great difficulty and relevance despite being seriously ill, rather than to his research, which is very technical and known in depth only by other experts in his fields of study. In 1994 he collaborated, lending his synthesized voice, on the track Keep Talking, contained on Pink Floyd's album The Division Bell. Stephen Hawking's early career at Cambridge University inspired the 2004 BBC-produced television film Hawking, in which the scientist is played by Benedict Cumberbatch.

In 2008 the film Superhero - The Most Gifted Among Superheroes (Superhero Movie) was released, directed and scripted by Craig Mazin, where Stephen Hawking is played by Robert Joy and is the subject of caricatures.

Stephen Hawking also participated in the production of a Discovery Channel program entitled Stephen Hawking's Universe, in which the astrophysicist, in each episode, addresses a topic on the birth of the universe. The program consists of three episodes: The big bang, Black holes, and The birth of stars and planets. The various films illustrating cosmic phenomena are made by NASA.

In 2011, Hawking made a documentary in which he appears in first person for the Discovery Channel's Curiosity series, Stephen Hawking's Grand Design, based on the essay The Grand Design, extended in 2010 with physicist Leonard Mlodinow. The film alternates between parts explained by Hawking himself via his voice synthesizer and others in which his text is read by the voiceover of actor Benedict Cumberbatch.

Hawking appeared in person in episode 26 of season 6 of Star Trek: The Next Generation, performing in a poker game with Einstein, Newton, and Commander Data. Hawking has also appeared numerous times in Matt Groening's animated series: most notably, in some episodes of The Simpsons (with a computer equipped with special gadgets) and Futurama (both as a normal version and as a talking head), in an episode of Dexter's Lab he appears as Professor Hawk: a human with half a robot body who speaks with a voice synthesizer, a clear reference to the professor; in seven episodes of The Big Bang Theory series (which stars four young, genius scientists) also in person and in Two Fantasy Parents, where he "proves" to Timmy's teacher that under special circumstances 2+2 makes 5; he also appears as Brian Griffin's professor in The Griffins, in the episode Brian Goes Back to College.

He is mentioned in Marvel's film The Avengers, in which he is compared to Bruce Banner (i.e., the Hulk). In 2013, another film was made about his life, also titled Hawking, in which he is played by different actors for each age of life: Arthur Pelling (child), Nathan Chapple (young), Finlay Macrae (boy), Martin King (adult), Joe Lovell (adult), and by himself (mature). The film was written by Ben Bowie, Stephen Finnigan, and Hawking himself.

In 2014 the film The Theory of Everything (The Theory of Everything) was released, directed by James Marsh, in which Hawking is played by Eddie Redmayne, who won the Academy Award for Best Actor in a Leading Role for this performance. In the same year, just a few months after the announcement of the release of The Endless River, Pink Floyd's latest album, it is confirmed that the track Talkin' Hawkin' will be featured on that album, in which, as in Keep Talking exactly twenty years earlier, Hawking's synthetic voice is featured.

The 2016 film Sausage Party - Secret Life of a Sausage features the character Eraser, a highly intelligent chewing gum who is confined to a motorized wheelchair and equipped with a voice synthesizer like Hawking, from whom he is also inspired in physical appearance.

In 2018 he is quoted, along with other great scientists in human history, in Genius, a song by Sia's supergroup LSD: "you'll be my Einstein, my Newton, my Galileo and my Hawking."

Hawking used his fame to advertise some products and brands, including a wheelchair, British Telecommunications, Specsavers, Egg Banking, On this occasion he used his name as a registered trademark.

Scientific treatises

The first three volumes are combined in the collection The Great Adventure of the Universe, Mondadori, 2012.

With the book "The Secret Key to the Universe," the first volume of The Great Adventure of the Universe series, the scientist won an Oscar Bestsellers, in 2009.

Sources

1. Stephen Hawking
2. Stephen Hawking
3. ^ By considering the effect of a black hole's event horizon on virtual particle production, Hawking found in 1974, much to his surprise, that black holes emit black-body radiation associated with a temperature that can be expressed (in the nonspinning case) as: T = ℏ c 3 8 π G M k , {\displaystyle T={\frac {\hbar c^{3}}{8\pi GMk}},} where T {\displaystyle T} is black hole temperature, ℏ {\displaystyle \hbar } is the reduced Planck constant, c {\displaystyle c} is the speed of light, G {\displaystyle G} is the Newtonian constant of gravitation, M {\displaystyle M} is the mass of the black hole, and k {\displaystyle k} is the Boltzmann constant. This relationship between concepts from the disparate fields of general relativity, quantum mechanics and thermodynamics implies the existence of deep connections between them and may presage their unification. It is inscribed on Hawking's memorial stone.[331] The equation's most fundamental implication can be obtained as follows. According to thermodynamics, this temperature is associated with an entropy, S {\displaystyle S} , such that T = M c 2 / 2 S , {\displaystyle T=Mc^{2}/2S,} where M c 2 {\displaystyle Mc^{2}} is the energy of a (nonspinning) black hole as expressed with Einstein's formula.[332] Combining equations then gives: S = 4 π G M 2 k ℏ c . {\displaystyle S={\frac {4\pi GM^{2}k}{\hbar c}}.} Now, the radius of a nonspinning black hole is given by r = 2 G M c 2 , {\displaystyle r={\frac {2GM}{c^{2}}},} and since its surface area is just A = 4 π r 2 , {\displaystyle A=4\pi r^{2},} S {\displaystyle S} can be expressed in terms of surface area as:[329][333] S BH = k c 3 4 ℏ G A , {\displaystyle S_{\text{BH}}={\frac {kc^{3}}{4\hbar G}}A,} where the subscript BH stands for either "black hole" or "Bekenstein–Hawking". This can be expressed more simply as a proportionality between two dimensionless ratios: S BH k = 1 4 A l P 2 , {\displaystyle {\frac {S_{\text{BH}}}{k}}={\frac {1}{4}}{\frac {A}{l_{\text{P}}^{2}}},} where l P = ℏ G / c 3 {\displaystyle l_{\text{P}}={\sqrt {\hbar G/c^{3}}}} is the Planck length. Jacob Bekenstein had conjectured the proportionality; Hawking confirmed it and established the constant of proportionality at 1 / 4 {\displaystyle 1/4} .[308][103] Calculations based on string theory, first carried out in 1995, have been found to yield the same result.[334] This relationship is conjectured to be valid not just for black holes, but also (since entropy is proportional to information) as an upper bound on the amount of information that can be contained in any volume of space, which has in turn spawned deeper reflections on the possible nature of reality.
4. ^ Queste particelle e antiparticelle compaiono continuamente per fluttuazione quantistica e seguendo il principio di indeterminazione di Heisenberg
5. ^ Per rispettare la legge di conservazione dell'energia complessiva, la particella che è precipitata nel buco nero deve avere energia negativa (rispetto a un osservatore che si trovi lontano dal buco nero).
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7. 2,0 2,1 MacTutor History of Mathematics archive. Ανακτήθηκε στις 22  Αυγούστου 2017.
8. 3,0 3,1 (Αγγλικά) SNAC. w6nk63ht. Ανακτήθηκε στις 9  Οκτωβρίου 2017.
9. Stephen William Hawking University of St Andrews (englanniksi)