Stephen William Hawking (1942 – 2018), probably the best- known physicist since Albert Einstein, is Lucasian Professor of Mathematics at Cambridge University. Hawking’s work with the more exotic areas of theoretical physics and his best-selling book *A Brief History of Time* have earned him a place in the public eye as well as in his own chosen world of physics. He is best known for his contributions to black hole theory and scientific cosmology.

**Physics: The Background**

Hawking’s ideas of time were influenced by the work of scientists and philosophers over two millennia. Aristotle, for example, made many statements about the arrangement of the universe. The whole world was spherical and finite, he postulated in the 4th century BCE. The earth was at the center of the Aristotelian universe, surrounded by one concentric sphere each for the sun, the moon, Mercury, Mars, Venus, Jupiter, and Saturn, and one sphere for the stars. The outermost sphere, containing the stars, was considered superior to the sphere in which the earth resided, and was supposed to be composed of an element called the ether. This concept of interstellar ether would persist in various forms through the early 20th century. The space occupied by the earth, however, was made of the four classical elements of earth, air, fire, and water. Furthermore, on the surface of the earth, the heavier of two bodies that had the same shape would fall faster. Many of Aristotle’s postulates were eventually proved false, but his ideas nevertheless became firmly entrenched in science.

Nicolaus Copernicus, over a millennium later in the early 1500s, made the next great development in astronomy. His theory, based on observation, stated that the earth makes not only one complete rotation on its axis per day (as well as executing a slight wobble around this axis) but also one complete revolution around the sun each year, producing the seasons. The sun was placed uncompromisingly at the center of the universe. The earth took its place among the other planets in orbit around the star, with an orbital period of one year. Copernicus retained the celestial spheres of the Ptolemaic and Aristotelian theories, but he associated a greater orbital radius with a longer planetary year, which necessitated a rearrangement of the five known planets into their proper order.

Early in the tumultuous 17th century, an Italian scientist named Galileo Galilei was at the heart of a battle over the Copernican model of the universe. With his innovative new telescope, Galileo discovered Venus’s phases, Jupiter’s four largest moons, sunspots, and the moon’s topographical features. Venus was of particular interest, since its phases proved that the planets revolved around the sun. In addition, Galileo’s observations showed that not everything must orbit the sun directly. His discoveries were not limited to the heavens; Galileo conducted experiments that yielded the laws of both falling and projected bodies. His legendary experiment of dropping two objects from the Leaning Tower of Pisa is just one example of Galileo’s many attempts to explain the universe. Galileo’s work, together with that of Johannes Kepler, led directly to the epitome of classical physics that was Sir Isaac Newton’s lifework.

Newton, who was born in the same year that Galileo died, tied together many of the loose ends of classical physics with strings of mathematics. He is the generally accepted founder of modern calculus. Newton sought to explain natural philosophy, as physics and chemistry were collectively known at the time, with his mathematics. His early work was with optics, and led to the invention of the reflecting telescope, which caused fewer color anomalies than Galileo’s refracting model. He later turned his attention to gravity, recognizing that the same force kept the earth orbiting the sun and made apples fall to the ground. Newton derived a law that explained almost every behavior of gravity. The inverse square law calculates the strength of gravity dependent upon the distance between two objects. Newton used this equation to calculate the attraction in the solar system and to explain both the tides and the moon’s motions to a high degree of accuracy. Though many of his equations are still used today, Newton’s work was based upon a model of the universe that would soon be radically changed. The picture of a threedimensional space full of Aristotle’s ether, with an absolute measure of time that never warped, was shattered irretrievably by a Swiss patent clerk named Albert Einstein.

Einstein made the biggest step forward in cosmology since Copernicus rearranged the solar system. He united Newton’s and Huygens’s theories of light and wrote the special theory of relativity. This second development, which at the time was understood by only a few physicists, secured Einstein a permanent place in the history of physics. The cornerstone of the theory of relativity is what Einstein called the principle of equivalence: there is no difference between constant acceleration and gravity. In the classic example, a person in an elevator that is moving through space with a constant acceleration equal to the gravitational force on Earth feels no different than if stationary in the elevator on Earth. From this postulate, Einstein realized that there is no absolute reference frame; every frame of reference is equally valid. Any of these frames can be considered stationary if it moves at a constant velocity, and anything within one of these frames will obey Newton’s laws of physics. The same holds for any person moving at a constant velocity relative to another frame of reference. Not only did Einstein change the definitions of movement and rest, he also rewrote gravity. Out of the relativity theories came the image of spacetime, a four-dimensional medium through which everything moves and that can be pulled or folded like fabric. Ether was expelled from scientific thought. Gravity was no longer a force, but a warpage of spacetime. Any object trying to travel along a straight line would get caught in a massive object’s gravity-caused spacetime warp and follow the circular or elliptical path made by the warp—in other words, it would orbit the massive object. In his later work, Einstein tried to unite the weak and strong nuclear forces with the electromagnetic force and gravity. He failed, and many scientists, including Hawking, are still trying to accomplish the same feat 50 years later.

**Life**

Hawking’s interest in cosmology had its roots in his early childhood, long before his mathematical and scientific aptitudes emerged around age 14. He always liked controlling things, and he built a great number of models during his childhood. Hawking enjoyed the theoretical work inherent in designing the models. When he was a young man, his mother watched him walk home one night after the streetlights were turned out. He watched the stars, and she sensed that he always would, despite his dislike of observational astronomy.

Much of Hawking’s best work has been done in conjunction with Roger Penrose, the eminent mathematician. When Hawking was one of Dennis Sciama’s Ph.D. students, the postgraduate group benefited greatly from attending a series of lectures that Penrose had given on singularities, the unpredictable points of infinite density found at the center of black holes. Hawking immediately began applying Penrose’s ideas to the entire universe. Later in Hawking’s career, he worked directly with Penrose to investigate the big bang singularity.

*Childhood and Adolescence*

Hawking was born on January 8, 1942, in Oxford to Isobel and Frank Hawking. His father was a medical doctor who specialized in tropical diseases. When he was 8, the Hawkings moved to the small town of St. Albans. Hawking has since described the place as conformist. His family felt out of place and was considered outlandish by their neighbors.

Isobel was an ex-Communist who still had strong left-wing sympathies that she passed on to her oldest son. She liked to travel while her husband was in Africa, and the family visited many exotic places. Hawking modeled himself after his often-absent father.

He entered St. Alban’s, an excellent secondary school, at age 10. He was awkward, lisped, and was poor at anything physical. He developed passions for mathematics and classical music. Hawking gained a group of friends similar to himself, considered rather geeky by their peers. They built a basic computer called LUCE, which they programmed to solve addition problems. In their teens, the group experimented with the metaphysical. After attending a lecture that outlined problems with reports of ESP success, Hawking decided that everything metaphysical was either false or had a scientific, rather than supernatural, explanation. He has retained the same view throughout his life.

When picking classes one year, Hawking had a dispute with his father over a mathematics class. Hawking’s father considered mathematics to have few career options. However, Frank lost the argument and Hawking continued his study of math. Hawking applied to University College at Oxford, his father’s alma mater. At 17, he made it through the grueling admissions exams and interrogation-style interviews, was accepted, and received a scholarship.

*College and Postgraduate Study*

The first year of college did not go very well for Hawking. He suffered from depression, had few friends, and was bored with the work. At the time, he has said, no one worked especially hard in Oxford. The academic load was light; for an intelligent person, college was easy. Hawking has said he worked, on average, about an hour per day through his 4 years at Oxford. The second year, he joined the rowing team and became popular almost immediately. Social events suddenly opened to him, and Hawking threw himself into the center of college life with gusto. He admits to drinking his fair share and playing many practical jokes. In this spirit, Hawking finished his studies and realized that he had not prepared properly for his final exams. In England, not all college degrees are created equal. A graduate could finish with a first, second, or lower-class degree. The class depended upon the student’s grade on the final exams. Hawking’s score was on the borderline between a first- and second-class degree, which necessitated that Hawking explain his plans to the college authorities. He did so, received a first-class degree, and entered Cambridge in October 1962.

Fred Hoyle was the most famous cosmologist in Britain in the early 1960s. Hawking applied for his Ph.D. study with Hoyle as his advisor, but Hoyle turned him down, and Hawking received Dennis Sciama instead. Once over his original disappointment, Hawking realized that Sciama was a better and more available advisor than Hoyle was. However, he was depressed again during his first semester. The work was difficult. Hawking had an insufficient grasp of mathematics, and although he could still stumble along with everyone else, he wasn’t doing as well as he was used to doing. During this period, he also began having motor problems. In the morning, Hawking had trouble getting his hands to work to tie his shoes. At one point, he fell down a flight of stairs at school and had temporary amnesia. He took an IQ exam to make sure no permanent damage had been done, but the trouble continued.

As soon as Hawking returned home for the holiday break, Isobel noticed his clumsiness. His father thought, naturally, that Hawking had picked up a foreign disease on a trip. Hawking missed the beginning of the next school term because he was in the hospital for tests. He was told that he had an unusual case, but his diagnosis didn’t arrive until after he returned to school: amyotrophic lateral sclerosis (ALS), better known as Lou Gehrig’s disease. Hawking’s prognosis was 2 years. The disease began developing quickly, forcing Hawking to walk with a cane. He spent a good deal of the next few months in his dorm room, deeply depressed.

Paradoxically, however, Hawking’s life was about to turn around. At his parents’ New Year’s Eve party in 1962, he met a young woman named Jane Wilde. The two fell in love quickly, and were soon engaged. Hawking realized that he needed his Ph.D. to support a family. Frank, Hawking’s father, went to see Sciama about shortening the time requirements for Hawking’s Ph.D., but Sciama refused. He treated Hawking no differently from any of his other students, which greatly endeared him to Hawking. Hawking’s fellow stu- dents—George Ellis, Brandon Carter, and Martin Rees—became his best friends and later his colleagues. Soon Hawking looked for a suitable thesis project. He became involved in solving some equations for a student of Hoyle’s that related to the expansion of the universe. The subject interested him greatly. When, shortly thereafter, he attended Penrose’s lectures on singularity theory and applied it to the big bang model of the universe, the two ideas coalesced into what would become Hawking’s thesis project. He graduated in 1965, after producing a manifesto on expanding universes, and married Wilde in July.

*Work and Marriage*

Hawking received a fellowship in Gonville and Caius College at Cambridge, in the Department of Applied Mathematics and Theoretical Physics (DAMTP). The young couple moved to a two- story cottage on Little St. Mary’s Lane.

The Hawkings entertained frequently. Hawking is known to all of his friends to be a very gregarious person and a trickster. During the mid-1960s, he cultivated an incredibly intelligent, cranky savant image. Though Hawking was still relatively unknown in the physics community, this image grew, along with his reputation for asking penetrating and sometimes uncomfortable questions at lectures, academic evidence of his love for mischief.

The mid 1960s were a very important time for Hawking. In 1967, his first child, Robert, was born. The next year, Hawking became a staff member of the Institute of Theoretical Astronomy. By that time, the ALS had restricted him to a wheelchair. His second child, Lucy, was born in November of 1970. Four years later he moved the entire family to California to do some work at Caltech. It was a happy time for the Hawkings, especially when, on their return to England, the Royal Society invited Hawking to be inducted as a Fellow. This accolade meant a great deal to him.

When the Hawkings returned from their trip to California, they moved to a larger, one-story house on West Road. Though it was a little farther away from Hawking’s office at the DAMTP, the single level made it easier for him to move around. The ALS had worsened again. From 1975-1976, Hawking’s work drew steadily more attention, earning him many awards: the Eddington MeDalí from the Royal Astronomy Society, the Pius XI MeDalí from the Pontifical Academy of Science, and the Royal Society’s Hughes MeDalí, among others. During the second half of the decade, the popular publicity Hawking received also rose dramatically. More honorary titles and awards piled up, including the Albert Einstein Award in 1978, esteemed more highly among physicists than the Nobel Prize.

However, things were not so rosy on the home front. Hawking’s marriage was undergoing continuous stresses. Jane, a devout Roman Catholic, was aggravated by her husband’s efforts to explain everything with science. Hawking argued with Jane more than once about the role and designated abilities of a divine Creator. In addition, Jane wanted to pursue her own career, and felt that she was a mere appurtenance to Hawking. These problems eventually led to their divorce in 1990. In the 1970s, however, that was still far in the future, and in 1979 Hawking’s last child, Timothy, was born. The same year, Hawking was made the Lucasian Professor of Mathematics, Newton’s chair at the University of Cambridge.

At this point, with a new baby and two private school tuitions to pay for, there was a dearth of money. Without telling anyone, Hawking began working on a popular cosmology book, but the dream wouldn’t bear fruit for years. In the meantime, more accolades poured in. In 1981, Hawking was knighted a Commander of the British Empire, and four colleges, including Notre Dame and Princeton University, made him an honorary doctor of science the next year. In 1985, he embarked on a world lecture tour and had his portrait hung in England’s National Gallery. However, the same summer his voice was silenced forever. One night in July, he choked in his hotel room. He was diagnosed with pneumonia and Jane was told that she would have to allow the doctors to cut a hole in his trachea to insert a breathing device. Hawking would no longer be able to speak, but he would live. She approved the operation. A short time later, Walt Waltosz sent a computer voice synthesizer called the Equalizer to Hawking. With this program installed on a wheelchair-mounted computer, Hawking can deliver lectures and speak more intelligibly than before the tracheotomy, although at the reduced rate of about 10 words per minute.

In 1990, Hawking and Jane divorced, and he moved in with one of his nurses, Elaine Mason. The reports of abuse that circulated shortly after their marriage have been strongly denied by Hawking, who refused to press charges.

**Major Ideas**

Hawking has had many ideas that, cumulatively, have changed the faces and directions of cosmology and black hole research. The earliest idea, the one that eventually blossomed into his Ph.D. dissertation, was to apply Penrose’s singularity theory to the universe. An offshoot of this concept was the proof, accomplished with Penrose’s help, that the big bang was a naked singularity at the beginning of time. At the time, big bang cosmology contended with Hoyle’s pet theory of a “steady-state” universe, which did not recognize an expanding and evolving universe from a cosmic point of origin billions of years ago. Hawking no longer agrees with this steady-state hypothesis or his earlier big bang theory. Instead, he now proposes his own “no-boundaries” theorem, which implies a finite universe without a beginning in time before the big bang. This theorem has had an important impact on cosmology, helping to eliminate the steady-state concept altogether.

Hawking also realized, getting into bed one night in 1970, that the event horizon of a black hole does not shrink, but grows with all matter that enters it. His most famous discovery, Hawking radiation, led from this idea. The result of a 1973 argument with a graduate student about entropy also helped Hawking formulate this discovery. The corollary of Hawking’s nocturnal epiphany was the surprising fact that black holes, known for dragging everything in their vicinity past the “point of no return,” actually emit particles. Hawking also developed the concept of “miniholes,” tiny black holes that can form only in certain conditions and that radiate massive amounts of energy.

More recently, Hawking has taken Richard Feynman’s method of finding the most likely path of a particle in quantum physics, known as the “sum-over-histories” or “path integral” approach, and applied it to the entire universe. This groundbreaking concept led to his no-boundaries theorem, developed in the early 1980s, which states that the big bang did not have a spacetime singularity, and neither will a potential big crunch scenario. Hawking is still working at Cambridge, further developing this concept and that of imaginary time.

**Publications**

Over the almost 5 decades that Hawking has been researching cosmology and black holes, he has published half a dozen important works. Only one of these, *A Brief History of Time,* has found an audience outside theoretical physicists. The first major paper he wrote, “Singularities and the Geometry of Spacetime,” was in conjunction with Penrose. It won the duo the Adams Prize in 1966, when Penrose was working for Birkbeck College. This paper detailed their work on the singularity theorems.

Five years later, Hawking was in print again, this time with fellow Sciama student, George Ellis. *The Large Scale Structure of Spacetime* built on this work, giving a description of the general theory of relativity and then explaining the importance of spacetime curvature. Singularities were explained through the structure of spacetime, and proven to be unavoidable in black holes and at the big bang.

*General Relativity: An Einstein Centenary Survey,* published in 1979 with Werner Israel, was written as a tribute to one of the greatest scientists of the 20th century. It gave an overview of what had been accomplished with Einstein’s mathematical brainchild, the general theory of relativity.

Hawking coauthored and coedited *Superspace and Supergravity* with M. Rocek. This compilation of essays, published in the United States in 1981, covered the then-current attempts to create the unified field theory, the set of mathematical formulae that would explain every physical phenomenon. This effort has been foiled every time by nonsensical answers produced when the equations for quantum theory and relativity are combined.

The next year Hawking published *The Very Early Universe,* which covered what was then known about the big bang and the moments shortly thereafter.

His most famous publication, *A Brief History of Time,* was published in spring 1988. Hawking’s usual publisher, Cambridge University Press, offered him the largest book deal in their history, 10,000 British pounds. Hawking, however, insisted upon more money and instead accepted Bantam’s bid of 250,000 American dollars. Manuscript editing began, and problems arose. After learning to be concise so he could communicate more rapidly using the Equalizer, Hawking needed to use many more words to explain his work to laypeo- ple. Eventually, the book was deemed readable. In the meantime, other countries’ offers were pouring in: Germany, Japan, China, Russia, and half a dozen others. Bookstores immediately sold out upon *A Brief History of Time*‘s release. Five hundred thousand copies had been sold by summer. It remained on the *New York Times’* best-seller list for 53 weeks, and on the *Sunday Times of London’*s for more than 200 weeks. Soon producers were clamoring for film rights, and a documentary, also called *A Brief History of Time,* was released in 1991.

The following sections review Hawking’s work and ideas in greater detail.

**The Work**

*Black Holes*

Around the time when Hawking began working in the field of theoretical physics, many things that are now well known had yet to be discovered. White dwarf stars—small, brightly burning remnants of stars like the sun—had been observed, but anything denser than these objects was considered impossible. Quantum theory predicted neutron stars, but since most of these are dim, their existence had not been verified. Theoretically, black holes were known to form at around three solar masses, and physicists believed that one of these exotic phenomena would bend spacetime completely around itself.

Hawking’s first research project was on black holes, and as soon as he received his Ph.D., he and Penrose began work on finding out more about singularities. They proved mathematically that in our spacetime, certain situations necessitate singularities. At the time, these were considered to be a glitch in Einstein’s theory of relativity and even more absurd than black holes. Hawking and Penrose’s breakthrough work gave the proof. Penrose’s mathematical method was a perfect match for Hawking’s understanding and physical applications.

In the 1960s, Hawking helped establish the theory of black holes and brought them out of the realm of science fiction. Penrose had already proved that a black hole could not form without a singularity at its heart, but the entire concept still garnered skepticism until 1973. That year, the new field of X-ray astronomy turned up Cygnus X-1, an X-ray source that has a 95% probability of being a black hole, according to Hawking.

In 1970, Hawking turned his attention to the event horizon of a black hole. The event horizon is defined as the point where all of the trapped light rays that almost escaped hover, also known as the point of no return for incoming matter. Hawking realized that singularity theory could be applied to black holes. An American graduate student, Jacob Bekenstein, published an article claiming that a black hole’s entropy, its measure of disorder, was the same as its event horizon. Hawking was horrified; a black hole couldn’t have entropy. According to the second law of thermodynamics, the entropy of the universe should increase with time. Hawking, however, thought entropy around a black hole decreases because the black hole swallows disordered matter, leaving nearby space more orderly. When he tried to prove that Bekenstein was wrong, Hawking instead proved the student partially right. This discovery became known as Hawking radiation. The entropy of a black hole is proportional to its surface area, defined by the event horizon. Furthermore, this area can never decrease, but only increase as matter and energy fall inward. These two ideas, Hawking radiation and the increasing event horizon, were major advances in black hole theory.

Hawking radiation is, simply, the radiation that a black hole emits. This radiation adds disorder to the universe at a rate that perfectly maintains the second law of thermodynamics. It can be described by visualizing a particle and its antiparticle, for instance, an electron and a positron. The particle pair comes into existence by borrowing some of the immense stored energy in the black hole and converting it to matter. Such particles are known as virtual pairs, because they are born and annihilate each other so fast that one cannot detect their existence directly. These pairs turn up very close to the horizon, and one particle is pulled away from the other by the hole’s gravity.

This pulling channels more of the black hole’s energy into the particle that escapes while the other falls into the hole. The escaping particle therefore appears to have been emitted by the hole, and carries part of the hole’s mass away with it. Hawking found that in this manner a black hole would, over eons, lose its mass at an accelerated rate, until it became so small that it exploded, spraying radiation in every direction. Hawking was sure his calculations were wrong, but was convinced otherwise by Penrose and Sciama. Upon further investigation, Hawking found that the temperature of a black hole depends inversely upon its mass, and the higher the temperature, the sooner the hole would explode.

*History of the Universe*

The origin of the universe was not generally considered in the realm of science until the 1950s. The big bang had been predicted through Einstein’s equations, and physicist Alexander Friedmann had even calculated the three universes allowed by Einstein’s equations. Einstein tried his best to discredit these ideas, preferring the idea of the “cosmic egg,” an immense atom-like mass that exploded, releasing the universe’s matter. On the whole, however, the subject was merely ignored.

The big bang was, in fact, given its name by its most famous opponent, Fred Hoyle. He proposed the so-called steady-state hypothesis in which the universe expanded very slightly and had no temporal origin or end. The big bang was a label born of sarcasm. However, the name stuck, and Hawking’s doctoral thesis proved several problems with the steady-state concept, soon to be discarded entirely. During his work with Penrose from 1965 to 1970, Hawking helped to prove that the big bang had a singularity from which the entire universe expanded, and that the potential big crunch would also have a similar structure.

In 1975, Hawking focused solely on the big bang. During the previous year, he had met his next set of colleagues at Caltech: Kip Thorne and Don Page. Years before, George Gamow, Ralph Alpher, and Robert Herman made predictions for a ubiquitous radiation background left over from the big bang. In 1965, Arno Penzias and Robert Wilson discovered it. The anticipated temperature, about 2.73° Kelvin, and wavelength, microwave range, were confirmed. The background radiation prediction was a success that helped secure the position of the big bang theory. Hawking probed ever farther back, trying to understand the moment of the big bang itself, the point at which time started. Due to the geometry of the big bang, there is no time before the event, and no one can discover what happened before the Planck time, about 10^{-43} seconds. Hawking kept trying, though, and created a more densely populated view of the early universe than previous scientists did. Cosmologists before Hawking, including Hoyle, had described the conditions and time frame that produced the most abundant elements in the universe: hydrogen, helium, and deuterium. These are the elements that stars burn for fuel, creating the heavier elements, like carbon, by nuclear fusion. However, the image of the first few hours and years after the big bang was a picture of radiation and atomic nuclei floating in an evenly distributed, hot morass of expanding space.

Hawking did not like this picture; if everything was evenly distributed, how did galaxies and stars form in the first place? There was some amount of irregularity, he decided, and was vindicated with the discovery of discrepancies in some areas of the background radiation. Hawking drove farther: If there were irregularities, there would be greater gravity in certain areas. These extremely pressurized areas might create unusually tiny black holes that evaporate quickly when compared to their contemporary stellar counterparts. These should still exist, and some might be exploding close enough for us to detect their gamma ray death throes. Unfortunately, most gamma ray bursts detected have been explained using more standard descriptions than Hawking’s mini-holes.

Hawking decided to find out how likely the universe is; literally, what the probability was of the universe developing this way. The only way to deduce this was to consider the entire universe to be one body, the same way that an atom or a proton is considered one unit. To accomplish this calculation, Hawking utilized Richard Feynman’s quantum sum-over-histories or path integral approach. This involves calculating all of the paths that a particle can take to get from point A to point Z, and each path’s probability. Very different paths usually cancel each other out, leaving a few similar, highly probable choices. That is exactly what happened when Hawking used the path integral for the universe. Working together with Jim Hartle, the duo discovered that a finite universe with no boundaries is one of the most likely types. The easiest way to understand the no-boundaries theory is to think of the earth, which is finite yet has no edges. Hawking was also able to eliminate the big bang singularity by introducing the idea of imaginary time, where the singularity can be thought of as the earth’s North pole. The earth grows in circumference from this ordinary point, like the universe did from the big bang. The earth also comes back to one point at the South pole, which represents the potential situation of the universe collapsing into a big crunch state. Hawking discovered, furthermore, that time would not reverse in the big crunch. This universe is completely self-contained, and time always moves forward.

Hawking presented his idea at a Vatican scientific conference. He still could not see back to the very beginning, but there was other progress. Quantum theory stated that the density of the original state was not infinite, which would help to explain the irregularities in the early universe; if the density had been infinite, there would have been no room for density variations.

The “chaotic inflation” concept also developed around this time. It states that there is an infinite universe beyond the boundaries of this one, with areas that are expanding and contracting. Some of these areas grow into their own universes. Alan Guth created the original inflation hypothesis, proposing that the universe is very uniform and its curvature nearly flat because it expanded from an extremely small, unstable state to a softball-sized stable state at a high velocity. Hawking vigorously defends both theories.

Hawking’s impact on modern cosmology cannot be overstated. He was instrumental in bringing black holes into the light of physical investigation to be considered seriously and, eventually, discovered. He has also given the physics community new tools and insights into the origin and history of the universe. In addition, Hawking has provided a union of important facets of relativity and quantum theory. Outside of his own direct research, he has also brought many of the obscure concepts and near-incomprehensible methods down to the level of the layperson, making the universe a little more accessible to the public.

In fact, social work is one of the areas where Hawking has used his celebrity most. Hawking has lent support and help multiple times to disabled people in battles against various agencies for heightened accessibility. The social and political awareness that Isobel instilled in her son has flowered in his crusades, where he is using his popularity to bring about change.

**Ideas and Beliefs**

*Cosmological*

Hawking has never been a person to leave others in doubt about his opinions, especially concerning cosmology. He believes that his noboundaries theory is the beginning of the complete union of the titans of physics: relativity and quantum theory. Hawking is confident that the answers to all of the questions humans have ever asked about the universe will be found mathematically, and most likely in the near future. He dislikes the anthropic principle’s explanation of all phenomena: Simply put, that everything is how humans observe it because if it was different, there would be no humans to observe it. Hawking wants solid, scientific answers to questions. Therefore, he has put his support behind the superstring theory, hoping that the final results of its calculations are as promising as those already known. However, he is reticent to believe in the extra, submicroscopic dimensions that string theories necessitate.

Hawking has also revised some of his earlier conjectures and discussed some exotic topics more closely associated with science fiction than with physics. He now thinks that mini-holes may be less common than he previously believed. He is also considering the possibility that when a black hole gets very small near the end of its life, it may just disappear from its region of the universe, removing its singularity as well. On the subject of determinism, Hawking thinks everything is probably determined, but no one can ever find out if it is. His opinion of time travel is thoroughly scientific. Since the uncertainty of the position and velocity of particles inherent in quantum physics can never be eliminated, quantum fluctuations would most likely destroy the tiny, opening wormhole necessary for time travel. Furthermore, if surrounding particles could travel through the wormhole, they would begin an ever-accelerating loop that would result in radiation too strong for any human to survive passing through. Hawking has called these ideas his “chronology protection conjecture,” an answer to the potential time causality problems produced by time travel.

*Social*

Hawking’s social conscientiousness is often found in his work as well as in his outside activism. An explanation of every question should be attempted, he asserts, no matter how daunting or controversial the subject is. No topic should be consigned to metaphysics or religion, in his opinion. The universe should always be under inspection until humanity as a whole understands everything, and this search for information should be conducted freely, without derision on the part of anyone else. Without passing judgment on the subject, Hawking also asserts that human engineering, with great advances in the capacity for knowledge, will occur very soon despite all efforts to stop it. Directed engineering, he states, will overtake evolution. Eventually, in Hawking’s opinion, humans will acquire enough wisdom to stop blowing themselves up, avoiding the complete destruction of the human species.

There are many things that Hawking does not believe in, as well. For instance, he avers that no civilization, regardless of where it is or how advanced it is, will ever be able to control the entire universe. In addition, he doesn’t believe that any alien civilization has visited Earth.

When discussing religion, Hawking can be extremely ambiguous. He has stated his belief to be that if a Creator does exist, there was a limited number of ways that the universe, initiated by this figure, could have evolved, regardless of that Being’s wishes. Hawking strongly advocates the viewpoint that no question should be left to religion. Yet in Hawking’s books there are multiple mentions of God, discussing his powers, knowledge, and role in the universe.

**Conclusion**

Stephen Hawking still works in his little office in the DAMTP at Cambridge. He oversees a few Ph.D. students and runs the relativity group. However, Hawking is largely free to work on his research. He is still pursuing his concepts of imaginary time and the no-boundary universe as the tools to find final cosmological answers.

Hawking’s contributions to physics are frequently ranked with the findings of Newton and Einstein. He has discovered many of the main features of black holes, partially united the theories of quantum mechanics and relativity, and proved enough of his work to win widespread recognition of black holes and singularities as real phenomena. Added to these accomplishments, he has managed to popularize a difficult area of science and developed new methods with which to analyze the beginning of the universe. The most productive era of Hawking’s work was several decades ago, but he has not retired yet.

Several areas that Hawking has been involved in are among the most widely investigated new sectors of research. Superstring theory has been gaining popularity since the 1980s, and may hold answers to the remaining unanswered cosmological questions. In string theory, the universe contains 11 dimensions—more or fewer depending upon which of the six interconnected theories one considers. What were particles and waves have been reconfigured into one-dimensional loops or strings of pure energy, so tiny that no equipment available can detect their shape. This theory has shown promise, but it is still being constructed and so cannot be used for all situations.

The short gamma ray bursts that Hawking had hoped would prove the existence of mini-holes are still something of a mystery. Most of these radiation events have been identified as colliding neutron stars, but recent reports of slightly longer bursts, in the range of a few seconds to almost 2 minutes long, cannot be explained so easily.

Gravitational waves, which are formed from the fabric of spacetime and, theoretically, ripple outward from colliding black holes, have been studied theoretically for some time. However, there is no concrete evidence to validate their existence. The subject has experienced a recent revival of interest, and the range of error in the calculations is down to about 20%.

*Emily Sobel*

** See also** Aristotle; Big Bang Theory; Big Crunch Theory; Black Holes; Copernicus, Nicolaus; Cosmogony; Cosmology, Inflationary; Einstein, Albert;

Experiments, Thought; Galilei, Galileo; Newton, Isaac; Quantum Mechanics; Relativity, General Theory of; Singularities; Time Dilation and Length Contraction; Time Warps; Universe, Origin of; Universes, Baby

**Further Readings**

Cropper, W. H. (2001). Affliction, fame, and fortune. In *Great physicists: The life and times of leading physicists from Galileo to Hawking* (pp. 452-463). New York: Oxford University Press.

Greene, B. (2004). *The fabric of the cosmos.* New York:

Random House.

Hawking, S. (1993). *Black holes and baby universes.*

New York: Bantam.

Hawking, S. (1996). *A brief history of time.* New York: Bantam.

Hawking, S. (2001). *The universe in a nutshell.* New

York: Bantam.

Hawking, S. (2003). *The illustrated history of*

*everything.* Beverly Hills, CA: New Millennium Press. McEvoy, J. P., & Zarate, O. (1997). *Introducing*

*Stephen Hawking.* New York: Totem.

Overbye, D. (1991). *Lonely hearts of the cosmos: The story of the scientific quest for the secret of the universe.* New York: HarperCollins.

White, M., & Gribbin, J. (1992). *Stephen Hawking: A life in science.* New York: Dutton.