The Inflationary Universe by Alan Guth (PDF)

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This is the compelling, first-hand account of Alan Guth’s paradigm-breaking discovery of the origins of the universe—and of his dramatic rise from young researcher to physics superstar. Guth’s startling theory—widely regarded as one of the most important contributions to science during the twentieth century—states that the big bang was set into motion by a period of hyper-rapid “inflation,” lasting only a billion-trillion-billionth of a second. The Inflationary Universe is the passionate story of one leading scientist’s effort to look behind the cosmic veil and explain how the universe began.

User’s Reviews

Editorial Reviews: About the Author Alan Guth is V. F. Weisskopf Professor of Physics at the Massachusetts Institute of Technology. In addition to being elected to the National Academy of Sciences and receiving many other academic awards, Newsweek has called him one of “The Top 25 American Innovators,” and Science Digest has ranked him among the “100 Brightest Scientists Under 40.”

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⭐Alan Harvey Guth (born 1947) is an American theoretical physicist and cosmologist, who is Professor of Physics at the Massachusetts Institute of Technology.[NOTE: page numbers below refer to the 358-page paperback edition.]He wrote in the Preface to this 1997 book, “this book is aimed primarily at the nonscientist with an interest in science… I have attempted to explain how particle theorists use the mathematics of fields …to describe quantum particles, and how the properties of these fields lead ultimately to a mechanism—inflation—that can explain the origin of essentially all the matter and energy in the observed universe… In this book the development of inflation is recounted from a personal vantage point, since that is that I know best. It is definitely not intended as a thorough history of the research relevant to this work… I have attempted, nonetheless, to honestly describe the roles of the people with whom I interacted, since these were the players in the drama that I wanted to recreate.” (Pg. xiv)He outlines, “The inflationary universe is a theory of the `bang’ of the big bang. The theory of inflation modifies our understanding of just the first tiny fraction of a second of the history of the universe, and then the description merges with that of the standard big bang theory, preserving all the successes of the older theory. But, because inflation explains the bang itself, it is a richer description, providing answers to a number of questions that the traditional big bang theory cannot address. It even allows us to consider such fascinating questions as whether other big bangs are continuing to happen far away, and whether it is possible in principle for a super-advanced civilization to recreate the big bang.” (Pg. xiii)He explains, “The central feature of the theory is a brief period of extraordinarily rapid expansion, or inflation… After the stupendous growth spurt of inflation the description merges smoothly with the standard big bang theory… the inflationary theory shows how all the mass could evolve from an initial seed weighing only about an ounce, with a diameter more than a billion times smaller than a proton… While the final verdict on inflationary cosmology is not yet in, the basic outline of the theory seems very persuasive… If inflation is correct, then the inflationary mechanism is responsible for the creation of essentially all the matter and energy in the universe. The theory also implies that the observed universe is only a minute fraction of the entire universe, and it strongly suggests that there are perhaps an infinite number of other universes that are completely disconnected from our own… it now seems likely that Lucretius was wrong. Conceivably, EVERYTHING can be created from nothing. And `everything’ might include a lot more than what we can see.” (Pg. 14-15) Later, he adds, “The inflationary universe theory derives from the big bang theory and adds to it, but does not replace it.” (Pg. 34)He states about the big bang theory, “the matter is assumed to have uniformly filled all of space at all times, right back to the instant of the big bang. There is no edge and to center to the distribution of matter. The expansion of the universe happens homogeneously, with every galaxy (on average) moving away from every other galaxy, as the entire space expands… [a questioner might object] It is hard to imagine what could possibly cause an explosion to happen simultaneously throughout the universe… Here I freely admit that the questioner has a good point—the idea of a simultaneous explosion throughout the universe does seem hard to accept… One of the attractive features of the inflationary universe theory is a new understanding of the homogeneity of the big bang. The inflationary universe can explain why the big bang explosion occurred homogeneously throughout the observed universe, while at the same time the theory suggests that the observed universe is only a minute part of a vastly larger space that is far from homogeneous.” (Pg. 74-75)He acknowledges, “one comes to a point of infinite density, infinite pressure, and infinite temperature… [that] is also frequently called a singularity… It is often said… that this singularity marks the beginning of the universe, the beginning of time itself. Perhaps this is so, but any honest cosmologist would admit that our knowledge here is very shaky. The extrapolation to arbitrarily high temperatures takes us far beyond the physics that we understand, so there is no good reason to trust it. The true history of the universe … remains a mystery that we are probably still far from unraveling… If the extrapolation … is not trustworthy, then a description such as `one second after the big bang’ also becomes ambiguous.” (Pg. 86-87) He adds, “So how far back should we trust the equations of the big bang theory? There is of course no definitive answer. If you asked a dozen physicists, you would probably get fourteen different answers along with five of six abstentions… I will nonetheless argue that such extrapolations are not crazy, as long as one is interested in qualitative features that do not depend on having all the details right.” (Pg. 88-89)He points out, “one must realize that grand unified theories [GUT] are not seen as the ultimate fundamental theory of nature. First, the ultimate theory must include gravity, which grand unified theories do not. Second, the grand unified theories are too ugly to be serious candidates for the ultimate theory. In particular, even the simplest GUT contains over twenty parameters… numbers… that must be measured experimentally before the theory can be used to make predictions.) Most particle physicists believe that the ultimate theory will be much simpler, with few if any free parameters… When we say that the unification scale is `put in by hand,’ we mean that we presently have no understanding of why this hypothetical calculation of the future will give such a large number. So the advocates of grand unified theories are hoping that someday the reason will be found.” (Pg. 135)He recalls, “The energy that had been stored in the Higgs fields would produce high energy particles which would collide and create other particles… The excess of matter over antimatter could be established immediately after the decay of the false vacuum… I do not remember every trying to invent a name for this extraordinary phenomenon of exponential expansion, but my diary shows that by the end of December I had begun to call it `inflation.'” (Pg. 176) Later, he enthuses, “To a theoretical physicist, there is no greater joy than to see that this curious activity that we call calculation—the depositing of ink on paper, followed by throwing away the paper and depositing new ink on more paper—can actually tell us something about reality!” (Pg. 243)He asserts, “such a localized big bang does not yet have an accepted name… I will call such a region a `pocket universe’… our entire observed universe is believed to be only a minute fraction of one of these pocket universes. The pocket universe… is only a minute fraction of all that exists… The process… goes on forever, producing an infinite number of pocket universes at an ever-increasing rate… Thus, a region of false vacuum does not produce merely one universe, but instead produces an infinite number of universes! In the cosmic shopping mall, an infinity of pocket universes can be purchased for the price of one… As the pocket universes live out their lives and recollapse or dwindle away, new universes are generated to take their place… While life in our pocket universe will presumably die out, life in the universe as a whole will thrive for eternity… eternal inflation … implies a panoramic view of the whole universe that captures the same emotional appeal as the steady-state theory.” (Pg. 246-248)He admits, “Since the other pocket universes would be far too remote to ever observe, the concept of eternal inflation does not lead to directly testable predictions.” (Pg. 249) He adds, “Because the properties of the observed universe are determined by the physics of inflation, they tell us nothing about what existed before inflation. The question of how it all began remains philosophically important, and it might still be possible to make persuasive arguments to justify some particular theory. However, if eternal inflation is correct, it will unfortunately be impossible to ever test these arguments by observation.” (Pg. 250) Nevertheless, he contends, “Given the plausibility of eternal inflation, I believe that soon any cosmological theory that does not lead to eternal reproduction of universes will be considered as unimaginable as a species of bacteria that cannot reproduce.” (Pg. 252)He notes, “Alexander Vilenkin… suggested that the universe was created by quantum processes starting from `literally NOTHING,’ meaning not only the absence of matter, but the absence of space and time as well… whether one can visualize it or not, Vilenkin showed that the concept of absolute nothingness is at least mathematically well-defined, and can be used as a starting point for theories of creation.” (Pg. 273) He adds, “While the attempts to describe the materialization of the universe from nothing remain highly speculative, they represent an exciting enlargement of the boundaries of science… it would mean that the existence and history of the universe could be explained by the underlying laws of nature. That is, the laws of physics would imply the existence of the universe. We would have accomplished the spectacular goal of understanding why there is something rather than nothing… If the creation of the universe can be described as a quantum process, we would be left with one deep mystery of existence: What is it that determined the laws of physics?” (Pg. 276)He concludes, “It is fair to say that inflation is not proven, but I believe that it is rapidly making its way from working hypothesis to accepted fact… inflation is at present the unique theory which allows us to calculate, to 15 decimal places, the mass density of the universe at one second after the big bang… Whether the prediction of a critical mass density for the early universe is said to be `bland’ or not, this kind of precision is extraordinarily impressive. There is a strong suggestion that some form of inflation is responsible for the universe that we inhabit.” (Pg. 286-287)Guth is one of the most important figures in modern cosmological theory; and this book is (for a theoretical scientist!) unusually well-written and interesting. It will be virtually “must reading” for anyone seriously studying modern cosmological theories.

⭐I read this book a few years ago and bought a new copy to read again. Alan Guth wrote perhaps the best book on Cosmology and the Big Bang. It is written in a non-technical style with advanced concepts clearly explained. I can think of no better imtroduction to Cosmology. Guth rescued the Big Bang with his theory of Inflation, and should have received a Nobel (perhaps shared with Alexei Linde). This book is essential reading for anyone interested in the origins and structure of the Universe.

⭐Alan Guth is one of the outstanding physicists of our times, and it feels great to read this book written about his own discovery. The author reveals one of the deepest secrets about our universe called cosmic inflation. The book documents the drama in his life as a physicist, and his struggle to make a decision about working in the area of monopoles, when he has doubts about his own strength in the field. Being cautious about his calculations and conclusions, feeling low when discouraged, and sometimes ridiculed by his superiors, yet at the same time feeling triumphant when his peers find his work outstanding. The author describes his experience beautifully.A brief summary of this book is as follows: A natural consequence of the properties of Grand Unified Theories (GUT) is that the universe at a very young age may have gone through a very rapid expansion in a very short time and then returned to a more leisurely rate of growth dictated by the standard big bang theory. Hubble’s constant illustrate that the universe is undergoing homogeneous expansion. The first turning event for the author is when physicist Bob Dicke proposed that the value of omega (the ratio of actual mass density to critical mass density) at one second after the big bang was between 0.999999999999999 and 1.000000000000001. If the value was less than this then the universe would have expanded forever and galaxies would never had time to form; on the other hand if the value was slightly more than this, then the universe would have collapsed sooner before it had any chance to grow to this big. This ratio was expected to be very close to one, this is called flatness problem: The big bang theory has no explanation for this ratio. According to general relativity, the mass density of the universe not only slows the cosmic expansion, but it also causes the universe to curve. If the mass density is higher than the critical density; then space curves back on itself forming a spatially closed universe. In such a universe, the sum of the angles a triangle is more than 180°. If the mass density is less than the critical density, then the space is curved in the opposite sense, and the sum of the angles of a triangle would be less than 180°. If the mass density is equal to the critical density, the space is known to be flat, which means that an ordinary Euclidean geometry is valid (the sum of the angles in a triangle is 180°.) The observed universe is remarkably balanced to stay flat!The second turning point for the author is when physicist Steven Weinberg accounted for the large asymmetry between the baryons (matter) and anti-baryons (antimatter). Since in the early universe protons and neutrons did not exist, but only quarks existed. His calculations showed that for every 300 million quarks there was equal number of anti-quarks less one. At 10exp(-6) seconds after big bang, all matter was annihilated by anti-matter, and the residual matter resulted in the present abundance of matter, but he did not offer an explanation what caused this matter-antimatter inequality. The third problem that needed an explanation is that the big bang theory of Friedman, Lemaitre, Hubble, and others describes the universe as a giant refrigerator cooling and expanding forever, and the remnants of this bang still exists today as an afterglow of 2.7K background microwave radiation. The large scale uniformity of the observed universe is clearly reflected in this, which is known to have been released after 300,000 years of the big bang (before this time the universe was too foggy (dense) for the glow to appear). It has the same temperature in all directions with a remarkable accuracy. Simple calculations show that at this time of the universe, the opposite side of the universe would be separated by a distance 100 horizon distances (90 billion light years), and since light can not travel more than one horizon distance due to specail relativity, it needed an explanation. This is referred to as the horizon problem.Prior to 10exp(-37) seconds after the big bang, the radius of the universe was only 10exp(-52) meters. At this time GUT predicts that the super-hot matter would have undergone phase transition (sudden change in the behavior of the matter) and the universe went through a tremendous exponential expansion called inflation to spectacular size of 10exp(23) times the size of visible universe. The inflation is driven by the physics of GUT, a patch of false vacuum, volume 10exp(-26) cubic centimeters and a mass of 10exp(-32) solar masses (about 25 grams); this corresponds to a density of (10exp(80) per cubic centimeter; lead to inflation and thus the universe evolves out of nothing at all. The author calls this an ultimate free lunch.The mechanism of inflation involves false vacuum, which is a peculiar form of matter that existed in the form of fields. This is meta-stable and has negative pressure which creates repulsive gravitational fields that can drive the universe into a period of exponential expansion. After more than 100 doubling time, the inflation stops by forming bubbles. The later theories propose that inflation continues as the fields roll gently towards a minimum energy value, and a single bubble becomes large enough to encompass the entire observed universe. This is called graceful exit problem because end inflation preserves the uniformity. This also solves the horizon problem, the flatness problem and also generates density perturbations that would later become the seeds for galaxy formation. As long as the exponential expansion continues long enough; the value of omega reaches one with great accuracy. As inflation proceeds, the matter that was present at the beginning would be diluted to irrelevance, while space becomes filled with the exquisitely uniform mass density of the false vacuum.1.

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⭐Really well told story about how the Inflation theory came about, what it means and why it’s the most favored pre-big bang model out there. Have seen the author speak on media programs before and his voice comes through very well in this book. It’s logical, concise and easy to follow. My highest level of Physics is officially GCSE but I have educated myself to some extent beyond that since then and so found the concepts to be understandable. No real math to speak of (just as well) but you do need to have an idea about cosmology and maybe a little quantum theory if you want to really get to grips with the content. At least as well written as “A Brief History of time” – maybe better. Well worth a read.

⭐This book doesn’t talk only about the physics of the inflationary theory but also about the experience that Alan Guth (the book’s author) lived before getting to the famous theory.Each chapter is a mix of personal life and science in a perfect equilibrium (not too much of the first nor too much of the last) starting from the classical big bang theory problem till how he invented Inflation (thanks also to some of his colleagues) and how inflation is capable of solving these problem.In the lasts chapters the author explains some expansions of the original theory arriving to the possible existence of a multiverse.

⭐really excellent addition to any library on cosmology – fills in gaps and looks at things from slightly different directions to give really good insights for people like me who are taking a while to get their heads round the whole incredible universe thing..

⭐Reading this book has allowed me to understand the origin of the Universe, I believe Alan Guth has made a breakthrough which deserves a Nobel Prize.

⭐Probably the best (popular science) book on Inflationary Cosmology every written.

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