Miscellaneous Quotations on Big Bang Cosmology

“The term ‘big bang’ was coined with derisive intent by Fred Hoyle, and its endurance testifies to Sir Fred's creativity and wit. Indeed, the term survived an international competition in which three judges — the television science reporter Hugh Downs, the astronomer Carl Sagan, and myself — sifted through 13,099 entries from 41 countries and concluded that none was apt enough to replace it. No winner was declared, and like it or not, we are stuck with ‘big bang.’”

— Timothy Ferris, The Whole Shebang, New York: Simon & Schuster, 1996, p. 323n.

“Ten or twenty billion years ago, something happened — the Big Bang, the event that began our universe. Why it happened is the greatest mystery we know. That it happened is reasonably clear. All the matter and energy now in the universe was concentrated at extremely high density — a kind of cosmic egg, reminiscent of the creation myths of many cultures — perhaps into a mathematical point with no dimensions at all. It was not that all the matter and energy were squeezed into a minor corner of the present universe; rather, the universe, matter and energy and the space they fill, occupied a very small volume. There was not much room for events to happen in.

“In that titanic cosmic explosion, the universe began an expansion which has never ceased. It is misleading to describe the expansion of the universe as a sort of descending bubble viewed from the outside. By definition, nothing we can ever know about was outside. It is better to think of it from the inside, perhaps with grid-lines — imagined to adhere to the moving fabric of space — expanding uniformly in all directions. As space stretched, the matter and energy in the universe expanded with it rapidly and cooled. The radiation of the cosmic fireball, which, then is now, filled the universe, moved through the spectrum — from gamma rays to X-rays to ultraviolet light; through the rainbow colors of the visible spectrum; into the infrared and radio regions. The remnants of that fireball, the cosmic background radiation, emanating from all parts of the sky can be detected by radio telescopes today. In the early universe, space was brilliantly illuminated. As time passed, the fabric of space continued to expand, the radiation cooled and, in ordinary visible light, for the first time space became dark, as it is today.”

— Carl Sagan, Cosmos, New York: Ballantine Books, 1993, pp. 200-201.

“A born cosmologist, [Alexander] Friedmann taught himself relativity—terra incognita to his colleagues at Petrograd—and discovered that if the general theory was correct the universe must either expand or contract. He was thus the first to purpose a mathematical model of an expanding universe, one of the genuinely innovative ideas of modern times. He sent word of his findings to Einstein, but Einstein was then at the peak of his celebrity and had to deal with stacks of such letters and was not infallible, and Friedmann was rebuffed. He tried to visit Einstein in Berlin, but Einstein was on vacation in the country, and Friedmann was turned away. There matters stood until Einstein, acceding to the request of another Russian physicist, looked again at Friedmann's paper, and began to change his mind. At first he retreated to the position that Friedmann's result ‘while mathematically correct is of no physical significance.’ Then he found an error in his own couterargument. Ultimately he admitted that the unheralded Friedmann was right: The universe of relativity was a dynamic universe.

“Further research along these lines was undertaken by the Belgian cosmologist Georges Lemaītre, who independently arrived derived Friedmann's results, and by Howard P. Robertson in the United States and Arthur G. Walker in England. Their work led to a fully realized geometric description of a homogeneous, expanding cosmos, known since as the Friedmann-Lemaītre-Robertson-Walker model. Friedmann, however, lived to see none of these developments. He died on September 16, 1925, at the age of thirty-seven—of typhoid fever according to some colleagues or, according to [George] Gamow [one of his pupils], of an illness brought on by exposure suffered during one of his meteorological balloon excursions.

“While relativistic models of the cosmos were blooming in the lofty towers of European theoretical physics, steps in deep-space observations were being taken by American astronomers, who, typically, were familiar with neither relativity nor its cosmological implications. [...] But few American astronomers read this work or saw any useful connection between their own research at the telescope and the theorists' musings about whether the universe expands. And yet, in one of the eeriest coincidences in the history of science, these astronomers soon began independently to find evidence of cosmic expansion.”

— Timothy Ferris, The Whole Shebang, New York: Simon & Schuster, 1996, pp. 42-43.

“In groundbreaking papers in 1922 and 1924, [Alexander] Friedmann demonstrated mathematically that the universe could very well be a dynamic system that, regulated by the gravity of general relativity, could expand indefinitely or collapse back on itself like a deflated balloon. A third possibility was that the universe was in a state of precise balance between infinite expansion and collapse. What would determine the true dynamic of the universe? According to Friedmann, the average density of mass within the universe would define how space curved as described by general relativity. Such a curvature would establish the way the universe changed over time.

“Einstein would have none of this. Philosophically insecure with anything but a static universe, he had inserted into the equations of general relativity his famous ‘cosmological constant.’ This was a mathematical contrivance aimed at preventing just the kinds of unstable universe predicated by Friedmann who, in making a number of simplifying assumptions, had removed the constant from his own mathematical calculations. [“It was later shown theoretically that Einstein's universe with its cosmological constant is also unstable and ought eventually to collapse or blow up unless other factors—still unknown—are at work.”]”

— John C. Mather and John Boslough, The Very First Light, New York: Basic Books, 1996, p. 36.

“If the universe were expanding, the question remained: What had it expanded from? Georges Lemaītre, one of the strangest characters to wander onto the stage of twentieth-century physics, was the first one to attempt an answer. Born in Belgium in 1894, Lemaītre was plump, irritating, and ahead of his time. In 1927, unaware of Alexander Friedmann's work, Lemaītre published a paper in an obscure Belgian journal in which he drew a mathematical theory that linked general relativity with the comparatively few redshifts that already had been seen. Lemaītre concluded in the paper that the universe must be expanding. His hypothesis was two years before Hubble's announcement that he had discovered galaxies in recession.

“Later the same year at the fifth Solvay conference on physics in Brussels, Lemaītre tried to get Einstein's attention. Normally tolerant and kind, Einstein pushed him aside abruptly, saying, ‘Vos calcus sont corrects, mais vorte physique est abominable.’ [Your calculations are correct, but your physical insight is abominable.] Undeterred by Einstein, already the most famous physicist in the world, and bolstered by the confirmation Hubbles's redshift observations had given his new theory, Lemaītre extrapolated his theory to what seemed to him its logical conclusion: The universe must have originated in a primordial explosion.

“A letter Lemaītre wrote to Nature magazine in 1931 was effectively the charter of what was to become the Big Bang theory. He theorized that this primordial explosion, occurring on ‘a day without yesterday,’ had burst forth from an extremely dense point of space and time. He began calling this the ‘primeval atom.’ By now Lemaītre had become a celebrity in his own right for his revolutionary ideas. At an immense gathering of the British Association for the Advancement of Science in London the same year, he speculated before an audience of several thousand scientists that the cosmic rays may have originated in the primordial explosion. Eventually, he thought, they might prove to be material evidence of the universe's ‘natural beginning.’”

— John C. Mather, John Boslough, The Very First Light, New York: Basic Books, 1996, pp. 41-42.

“But in 1929, Edwin Hubble made the landmark observation that wherever you look, distant galaxies are moving rapidly away from us. In other words, the universe is expanding. This means that at earlier times objects would have been closer together. In fact, it seemed that there was a time, about ten or twenty thousand million years ago, when they were all at exactly the same place and when, therefore, the density of the universe was infinite. This discovery finally brought the question of the begging of the universe into the realm of science.

“Hubble's observation suggested that there was a time, called the big bang, when the universe was infinitesimally small and infinitely dense. Under such conditions all the laws of science, and therefore all ability to predict the future, would break down. If there were events earlier than this time, then they could not affect what happens at the present time. Their existence can be ignored because it would have no observational consequences. One may say that time had a beginning at the big bang, in the sense that earlier times simply would not be defined. It should be emphasized that this beginning in time was very different from those that had been considered previously. In an unchanging universe a begging in time is something that has to be imposed by some being outside the universe; there is no physical necessity for a beginning. One can imagine that God created the universe at literally any time in the past. On the other hand, if the universe is expanding, there may be physical reasons why there had to be a beginning. One could imagine that God created the universe at the instant of the big bang, or even afterwards in just such a way as to make it look as though there had been a big bang, but it would be meaningless to suppose that it was created before the big bang. An expanding universe does not preclude a creator, but it does place limits on when he might have carried out his job!”

— Stephen Hawking, A Brief History of Time, New York: Bantam Books, 1998, p. 9.

“Edwin Hubble's discovery of the expansion of the universe promoted theorists to consider that if the cosmic matter density is decreasing, than there must have been a time long ago when everything in the universe was as hot and dense as the center of a star — and perhaps even hotter and denser than that. The Belgian cosmologist Georges Lemaītre dubbed this original state the ‘primordial atom,’ and wondered whether the universe might have begun expanding through a process roughly analogous to the radioactive decay of an unstable atomic nucleus. Lecturing in the early 1930s, in the library of Mt. Wilson observatory offices in Pasadena to an audience that included Albert Einstein, Lemaītre declared: ‘In the beginning of everything we had fireworks of unimaginable beauty. Then there was the explosion followed by the filling of the heavens with smoke. We come to late to do more than visualize the splendor of creation's birthday.’ Lemaītre account of genesis was long on oratory and short on specifics — and where it did get specific it was wrong — But Einstein, who understood that style can count for as much as substance, arose at the end of the talk and called it: ‘the most beautiful and satisfying interpretation I have listened to.’ Neither Lemaītre as a physicist nor physics as a discipline was yet up to the task of analyzing the big bang. But by viewing the early universe through the lens of nuclear physics, Lemaītre inaugurated what was to become a potent collaboration between cosmologist interested in cosmic evolution and high energy physicists capable of calculating thermonuclear events in the early universe.”

— Timothy Ferris, The Whole Shebang, New York: Simon & Schuster, 1996, pp. 108-109.

“In the late 1940s George Gamow, a Russian-born physicist then teaching at George Washington University, and two young colleagues, Ralph Alpher and Robert Herman, had begun investigating what would come to be called the Big Bang model for the creation of the universe. Although not adept at everyday maters such as spelling or even mathematics, Gamow possessed an unusual genius for asking penetrating questions and broaching new ideas for his colleagues to pursue.

“Born in Odessa in 1904, Gamow had studied at the University of Petrograd in St. Petersburg during the 1920s with the theorist Alexander Friedmann, who had speculated mathematically on the ways the universe might evolve in brilliant new solutions to Einstein's field equations of general relativity. Later Gamow moved on to the university in Göttingen, Germany, where he performed so well in particle physics that he drew the attention of Niels Bohr. Bohr was a Danish theorist who by then was legendary for his role in the creation of quantum mechanics, the branch of physics devoted to the fundamental particles of matter and the forces controlling them. In 1928 Gamow formulated an early theory about radioactive decay and was one of the first physicists to address the problem of how stars evolved.”

— John C. Mather, John Boslough, The Very First Light, New York: Basic Books, 1996, pp. 30-31.

“[Fred Hoyle devoted] his life to fighting the notion that the cosmos began at a certain point in time, with a big bang. He preferred the view Aristotle held millennia earlier: The universe has always existed, and always will. A turning point in Hoyle's young life came at age thirteen, when his parents gave him the gift that has changed so many other young lives: a small telescope. They allowed him to stay up all night looking at the stars and planets. As fate would show, Hoyle and Gamow had more in common than the fact that each had received a telescope in his thirteenth year. Each was a father, intellectually speaking, and each exploded with far more ideas than could ever be true. After working on radar in England during the Second World War, Hoyle became an astronomy Professor at Cambridge University. He also began developing talks about astronomy on BBC radio and writing popular articles and books. Like Gamow, Hoyle was becoming a highly visible interpreter of science to laypeople. During one of his popular radio broadcasts in 1950 Hoyle coined the phrase big bang as a description of Gamow's repugnant (to Hoyle) theory. Hoyle had meant the term to be derogatory, but it was so compelling, so stirring of the imagination, that it stuck, but without the negative overtones. Hoyle became the most visible proponent of an alternative theory to big bang, known as the steady state theory. The struggle for intellectual supremacy between these two theories dominated cosmology for almost two decades.”

— George Smoot and Keay Davidson, Wrinkles in Time, New York: William Morrow & Company, 1993, pp. 67-68.

“It did not help adherents of the Big Bang that Gamow was its most vocal supporter. Or that Einstein, now living out his remaining years in Princeton as the world's most famous scientist, was still philosophically more comfortable with a static universe. Or, most important, that [Ralph] Alpher and [Robert] Herman's prediction of the cosmic background radiation, which could not plausibly be accounted for in steady-state cosmology, had been all but forgotten during the 1950s. With problems on both sides, neither was a clear winner. This was how matters stood until the early spring of 1965, cosmology stalemated.

“Had Arno Penzias and Robert Wilson known in 1964 of the prediction of Alpher and Herman sixteen years earlier, the two Bell scientists would have been spared a year's work trying to uncover the source of the noise in their horn antenna. Had [Robert] Dicke been aware of the prediction, he could have begun work on his own antenna years earlier without having to wait for Jim Peebles to do the theoretical calculations from scratch.”

— John C. Mather, John Boslough, The Very First Light, New York: Basic Books, 1996, pp. 49-50.

“Arno Penzias comes from a Jewish family in Munich. He was born in 1933, on the same day (26, April) that the Gestapo was formed. The family was one of the last to get out of Nazi Germany to England in 1939—Arno and his brother were sent on in the spring, and were later followed by his father and, finally, mother. Reunited, the family left England in December 1939, sailing for New York, where they landed in January 1940 and stayed. Education provided the opportunity for this son of an impoverished immigrant family to make his way in the world, and in 1954 Penzias graduated from the City College of New York with a degree in physics. After two years in the Army Signal Corps, he joined Columbia University as a graduate student, working for his PhD, which was awarded in 1962. […]

“[Robert] Wilson comes from a very different background to Penzias. Born in Houston, Texas, in 1936, he is the son of a chemical engineer, and both his parents went to college. With straight A's in all his science courses at Rice University, in Houston, when Wilson graduated in 1957 he was offered places in the graduate schools at both MIT and Caltech, the two premier scientific research institutes in the US; he chose Caltech, but with no clear idea of just what line of research he would like to take up. There, he was influenced by two British astronomers—Fred Hoyle, who taught the cosmology course during a spell as visiting professor at Caltech, and whose presentation left Wilson with a fondness for the Steady State theory; and David Dewhirst, who suggested that Wilson might like to work with John Bolton, an Australian radio astronomer then at Caltech. [...] Where as Penzias left Columbia just before completing his PhD, Wilson stayed on at Caltech for a year after completing his, in 1962. So it was in 1963 that, hearing about Bell Labs' interest in radio astronomy and the availability of the still relatively new horn antenna at Crawford Hill, he decided to take the plunge, and joined Penzias in New Jersey.”

— John Gribbin, In Search of the Big Bang, New York: Penguin Books, 1998, p. 161.

“Walter Sullivan, a Times science writer, had heard about the detection of the cosmic microwave background from an editor at the Astrophysical Journal. He called [Arno] Penzias for the details. Neither Penzias nor Wilson had thought much would come of Sullivan's call. In his article, Sullivan correctly explained the importance of Penzias and Wilson's discovery of isotropic radiation at approximately 3º Kelvin with a wavelength of just over 7 centimeters: the fact that the radiation was isotropic meant it was the same across the sky. This was precisely what those astronomers who supported the Big Bang hypothesis had expected.

“Radiation that was a remnant of the Big Bang, which had occurred everywhere in the universe at once, should have been of equal intensity everywhere. Of course, a measurement at only one frequency could not prove conclusively that the radiation was blackbody radiation from the Big Bang (a finding that would not occur for twenty-five years). The discovery by the Bell Labs scientists soon was confirmed by the Princeton team had to a shorter wavelength. The blackbody nature of the background radiation was something Big Bang astronomers also expected. As we've already seen, this kind of radiation occurs whenever particles collide in a thermal equilibrium of the kind that might occur inside a black box. The Big Bang should have produced extremely intense particle collisions. Most cosmologist—not including Fred Hoyle, of course, and the other who still believe in a steady-state universe—were now believers: a huge amount of blackbody radiation had been produced during the earliest moments of the universe and was still present in a sufficient quantity to detect (the test of its blackbody spectrum being, of course, one of the most important reasons for flying the COBE).

“Robert Wilson met George Gamow for the first and only time in December 1965 at a hotel in New York City during the annual Texas symposium on Relativistic Astrophysics. By then the discovery of the background radiation was already well established not only in astrophysical circles but in the public mind as well. Even the reluctant Wilson had started becoming a believer. Gamow seemed somewhat upset over the fact that no credit had been given him for the early theoretical prediction of the cosmic background temperature, Wilson recalled. ‘If I lose a penny and someone finds it in the same place where lost it, then I still know it's my penny even if I can't prove it.’ Gamow told Wilson. Wilson was dumbfounded. This was a first time he learned that anybody other than Dicke and Peebles had worked out a theoretical scheme that would account for their famous accidental discovery with the horned antenna. Whether Gamow at the time sought scientific credit for himself or his colleagues Alpher and Herman is not clear. Gamow himself had not published a word about the background radiation before Alpher and Herman's 1848 paper, contrary to what has been written in many popular accounts, including one by Peeples and Wilkinson published by 1983.

“A 1948 paper in Nature by Gamow, widely cited as the first theoretical prediction of a 10º – Kelvin background temperature, was concerned with primordial nucleosynthesis and early galaxy formation. It made no mention of background radiation. In any event, by early 1967 Gamow and his colleagues, Alpher and Herman, had become ‘very perturbed by how our early work continued to be ignored.’ Gamow suggested to Alpher and Herman that they try to set the historical record straight. They made the attempt in a lengthy article the three wrote the same year. Their choice of journals, Proceedings of the National Academy of Sciences, was unfortunate because it is a publication for all scientists and not for one specific discipline, which is what really interests any scientist with his salt. The piece documented Alpher and Herman's theoretical work on the cosmic background radiation in the 1940's as well as their joint efforts with Gamow on galaxy and star formation. But almost no astronomers were physicists read it with. Gamow lived out his life in relative obscurity at the University of Colorado in Boulder. He died in 1968, still believing he had not received due credit for his early work on the origin of the universe. By the mid-1970s Big Bang cosmology was almost universally established in the minds of astrophysicist and theorists. In the summer of 1978, Penzias read an article in Omni magazine stating that he would be awarded the Nobel Prize.”

— John C. Mather, John Boslough, The Very First Light, New York: Basic Books, 1996, pp. 62-64.

“The big bang theory implied that as the universe expanded there should have come a time, nowadays reckoned at about five hundred thousand years after the beginning, with the primordial plasma thinned out sufficiently to become transparent to light. Physicists call this event photon decoupling, meaning that photons, the particles that constitute light and other forms of electromagnetic energy, were at this point set free. Thereafter they did not often interact with one other, or with matter, but went souring unhampered throughout the constant expanding reaches of cosmic space. Hence most of them should still be around today. Cosmic expansion would have stretched out, increasing their wavelengths from those of light to the wavelengths we call microwave radio. In microwave frequencies it is convenient to express energy in terms of temperature — as does, say, the instruction manual that accompanies a microwave oven — so another way to reason through this argument is to say that the universe, having once been hot, should remain a bit warm even today. Physicists theorizing about the existence of this cosmic microwave background, or CMB, calculated that this should have a temperature of about three degrees above absolute zero. They also noted that it would display a ‘black body’ spectrum, as is dictated by the relevant quantum physics equations, and that it should be isotropic, meaning that any observer, anywhere in the universe, should measure the background as having the same temperature everywhere in the sky […] In 1989, the American space agency launched a satellite designed to study the CMB from orbit, where its detectors were free from the interference of Earth's atmosphere. Preliminary findings obtained by the COBE (Cosmic Background Explorer) satellite were announced the following year, and turned out to constitute a stunning confirmation of the big bang model. The CMB is indeed isotropic — that is, it has equal intensity all over the sky, as anything genuinely universal must. And, as expected, its temperature is about three degrees above absolute zero — 2.72 degrees, to be exact.”

— Timothy Ferris, The Whole Shebang, New York: Simon & Schuster, 1996, pp. 32-33.

“The announcement—that the [COBE] satellite's orbiting instruments had detected tiny variations in the cosmic background radiation—electrified the cosmological community, and drew headlines around the world. Many astrophysicists believed that the discovery confirmed the reigning cosmological model, the Big Bang theory, beyond the shadow of a doubt, perhaps solving the mystery of the universe's origin once and for all. Stephen Hawking, the Cambridge University theorist and best-selling author of A Brief History of Time, was the most effusive of all: ‘It is the discovery of the century, if not of all time.’

“High praise, indeed. The reason for Hawking's exuberance was that the COBE discovery had gone right to the heart of cosmology, the science that seeks to explain the very origin and structure of the universe. Did the universe begin at a specific point in time, or has it always existed? For thousands of years most scientists regarded this question as one beyond their concern, lying within the metaphysical realms of philosophers or theologians. Not until the middle of this century did physicists and astronomers begin acquiring theories powerful enough and experimental equipment sensitive enough to begin addressing the problem. COBE had shown emphatically that the universe is not static, but has changed remarkably over time.”

— John C. Mather, John Boslough, The Very First Light, New York: Basic Books, 1996, pp. xvii-xviii.

“Not often in science do competing hypotheses rise or fall as the result of only one experimental finding or discovery. This is something that should occur more frequently, according to the ideas of Sir Karl Popper, an Austrian born philosopher of science who died in 1994. Popper argued that science should be a process in which various hypotheses are created to predict natural phenomena that then can be tested or observed. If the prediction fails, then the hypothesis should be abandoned. Thomas S. Kuhn, a historian of science at Princeton at the time Dicke and his colleagues met with Penzias and Wilson, argued effectively that Popper's scenario rarely happened in the real world of scientific enterprise. In fact, Kuhn maintained, it was an idealized way of looking at scientific progress. According to Kuhn, who coined the term ‘scientific paradigm’ in his 1962 book The Structure of Scientific Revolutions, acceptance of a new hypothesis among scientists usually occurs only as adherents of an older, no longer valid hypothesis either die or lose influence within the scientific community.

“Neither Kuhn's nor Popper's concept of how science progresses—or, in their opinion, should progress—applies fully to the case of the competing steady-state and Big Bang theories. This is because neither of these hypotheses was entrenched within the astronomy community. Astronomers were about equally divided in their support of each one. Yet, as events unfolded, Popper's idealized principle seemed to predict the outcome more than Kuhn's more cynical concept.

“With neither theory fully acceptable to astronomers before the discovery of the cosmic background radiation, the scientific credibility of the competing hypotheses was the determining factor—not the prevailing cultural climate among astronomers. In the light of the new discovery, the Big Bang theory was the clear winner for the simple reason that the steady-state model did not predict and could not reasonably account for the presence of the cosmic background radiation. On the other side, the Big Bang theory not only predicted the background radiation but required it.”

— John C. Mather, John Boslough, The Very First Light, New York: Basic Books, 1996, pp. 51-52.

“The picture of an expanding universe implies that something cataclysmic must have occurred in the past. If we reverse the expansion of the universe and trace it backward in time, we appear to encounter a ‘beginning,’ at which everything hits everything else: all the mass in the universe is compressed into a state of infinite density. This state is known as the ‘initial singularity.’ The specter of its presence in our past has sparked all manner of metaphysical and theological extrapolations of the ideas of modern cosmology. […]

“In the early 1930s, many cosmologists were loath to believe that the expansion really pointed to a singular beginning of infinite density. Two objections were raised. If we try to squeeze a balloon down to smaller and smaller size, we find our efforts opposed and ultimately defeated by the pressure exerted by the molecules of air within the balloon. As the volume in which they are free to move is decreased, they beat harder upon its boundaries. Likewise with the universe; we would expect the pressure exerted by the matter and radiation within the universe to prevent its ever being squeezed to zero volume. It might rebound, like a collection of colliding pool balls. Others claimed that the idea of an initial singular point of infinite density arose only because we had adopted a picture in which the universe was expanding at the same rate in every direction. Thus when the expansion was traced backward everything arrived at one point simultaneously. If, however, the expansion were slightly asymmetrical (and in reality it is), then when we traced it backward the imploding material would be out of step, so it might well avoid producing a singularity.

“When these objections were explored, they failed to remove the expected singularity. In fact, the addition of pressure actually assisted its creation, because of Einstein's famous discovery that energy and mass are equivalent (E=mc²). Pressure is just another form of energy and thus is equivalent to mass; when it grows very large, it creates a gravitational force that opposes the repelling effect we usually associate with a pressure. Trying to avoid the singularity by increasing pressure was self-defeating; it actually made the singularity worse! Moreover, when Einstein's theory of gravitation was used to find other possible types of universes—universes that expand at different rates in different directions, or possess variations from place to place—the singularity remained. It was not just an artifact of symmetrical universe models. It seemed to be ubiquitous.”

— John D. Barrow, The Origin of The Universe, New York: Basic Books, 1994, p. 37-39.

“According to the standard big-bang theory the universe came into existence in a moment of infinite temperature and density some ten to fifteen billion years ago. Again and again when I have given a talk about the big-bang theory someone in the audience during the question period has argued that the idea of a beginning is absurd; whatever moment we say saw the beginning of the big bang, there must have been a moment before that one. I have tried to explain that this is not necessarily so. It is true for instance that in our ordinary experience however cold it gets it is always possible for it to get colder, but there is such a thing as absolute zero; we cannot reach temperatures below absolute zero not because we are not sufficiently clever but because temperatures below absolute zero simply have no meaning. Stephen Hawking has offered what may be a better analogy; it makes sense to ask what is north of Austin or Cambridge or any other city, but it makes no sense to ask what is north of the North Pole.”

— Steven Weinberg, Dreams of a Final Theory, New York: Pantheon Books, 1992, pp. 173-174.

“Inflationary cosmology is a new twist on the big-bang theory. It doesn't in any way do away with the big-bang theory. It's completely consistent with everything that's been talked about in terms of the big-bang model. What it does is change our conception of the history of the first small fraction of a second of the big bang. According to the new theory, the universe during this sliver of time underwent a period of inflation, a brief era of colossal expansion.

“There are two key features that are different in inflationary cosmology from the standard big bang. One is that the inflationary model contains a mechanism by which essentially all the matter in the universe can be created during the brief period of inflation. In the standard big-bang model, by contrast, it was always necessary to assume that all the matter was there from the beginning, and there was no way to describe how it might be created. By the way, the inflationary production of matter is consistent with the principle of energy conservation, even though it can literally produce a universe from almost nothing. Energy is still conserved—this is all calculated in the context of standard classical general relativity. The unusual feature is that gravity plays a major role in the energy balance. It turns out that the energy of a gravitational field—any gravitational field—is negative. During inflation, as the universe gets bigger and bigger and more and more matter is created, the total energy of matter goes upward by an enormous amount. Meanwhile, however, the energy in gravity becomes more and more negative. The negative gravitational energy cancels the energy in matter, so the total energy of the system remains whatever it was when inflation started—presumably something very small. The universe could, in fact, even have zero total energy, with the negative energy of gravity precisely canceling the positive energy of matter. This capability for producing matter in the universe is one crucial difference between the inflationary model and the previous model.”

— Alan Guth, "A Universe in Your Backyard," The Third Culture: Beyond the Scientific Revolution, New York: Simon & Shuster, 1995, pp. 278-279.

“We have at present only two kinds of physics to choose from, classical and quantum; and classical physics, as Alex Vilenkin notes, ‘fails to describe the beginning of the universe’ Its breakdown is clearly signaled by the fact that general relativity invokes a singularity a time zero, which is to say that its equations yield infinities and can produce no meaningful result. Roger Penrose and a youthful Stephen Hawking proved this in 1970, in theorems demonstrating that if gravitation is always attractive and if the universe has anything like the matter density we observe to have, then there must have been a singularity at the outset of time. so we are left with quantum cosmology — the attempt to apply quantum precepts, previously employed in studying subatomic particles and fields, to the universe as a whole.”

— Timothy Ferris, The Whole Shebang, New York: Simon & Schuster, 1996, pp. 249-250.

“Where did all the matter and radiation in the universe come from in the first place? Recent intriguing theoretical research by physicists such as Steven Weinberg of Harvard and Ya. B. Zel'dovich in Moscow suggest that the universe began as a perfect vacuum and that all the particles of the material world were created from the expansion of space…

“Think about the universe immediately after the Big Bang. Space is violently expanding with explosive vigor. Yet, as we have seen, all space is seething with virtual pairs of particles and antiparticles. Normally, a particle and anti-particle have no trouble getting back together in a time interval…short enough so that the conservation of mass is satisfied under the uncertainty principle. During the Big Bang, however, space was expanding so fast that particles were rapidly pulled away from their corresponding antiparticles. Deprived of the opportunity to recombine, these virtual particles had to become real particles in the real world. Where did the energy come from to achieve this materialization?

“Recall that the Big Bang was like the center of a black hole. A vast supply of gravitational energy was therefore associated with the intense gravity of this cosmic singularity. This resource provided ample energy to completely fill the universe with all conceivable kinds of particles and antiparticles. Thus, immediately after the Planck time, the universe was flooded with particles and antiparticles created by the violent expansion of space.”

— William J. Kaufmann, Universe, New York: W. H. Freeman & Company, 1985, pp. 529-532.