1. Big Bang

ALAN GUTH (1947 - )Alan GuthAlan Guth is a theoretical physicist and cosmologist, known mainly for his work on theory and how particle theory is applicable to the early, and particularly for the idea, which he developed around 1980, of and the inflationary, the idea that the nascent passed through a phase of exponential expansion soon after the, driven by a positive vacuum.Alan Harvey Guth was born on 27 February 1947 in the small town of New Brunswick, New Jersey, USA, to a middle-class Jewish couple, Hyman and Elaine Guth, owners of a small grocery store and a dry-cleaning establishment. His early childhood was unremarkable, although he showed a strong aptitude for mathematics. After attending several public schools, he skipped his senior year to enrol in a five-year program at the Massachusetts Institute of Technology (MIT), partly because he was concerned about being drafted for the Vietnam War, of which he strongly disapproved. He obtained both his bachelor’s and master’s degree in 1969, and a doctorate in 1972.In 1971, he married his high school sweetheart, Susan Tisch, and they were to have two children: Lawrence (1977) and Jennifer (1983). However, after graduating, Guth had a hard time finding a permanent job, partly because of the intense competition for university professor positions due to the baby boom, and he spent nine years traveling across the country pursuing temporary post-doctorate jobs related to physics, including time spent at Princeton (1971 to 1974), Columbia (1974 to 1977), Cornell (1977 to 1979) and at the Linear Accelerator Center at Stanford (1979 to 1980).His early focus at Princeton was on particle physics, particularly the study of, the that make up. However, his research became obsolete with the development of the theory of quantum chromodynamics, ironically developed right there at Princeton, unknown to Guth, which gave a new special property called “color”.In 1974, at Columbia, Guth turned more to cosmology and cosmogenesis, and particularly to work on (magnets with only one pole, which had been initially predicted in theory by James Clerk Maxwell’s equations, but were yet to be discovered in the real ).

Guth proposed that the process of spontaneous symmetry-breaking in the early described by Steven Weinberg’s “electroweak theory”, could produce very tiny discontinuities with the properties of.He first started to develop his theory of while at Cornell in 1978, when he was looking for solutions to the “flatness problem” of the model of the, and to the problem he himself had identified, the apparent lack of. Once again he made use of earlier work by Steve Weinberg, namely his (an attempt to unify the, and ).Guth’s proposed solution to these problems involved a very short but very rapid period of supercooling during a delayed phase transition, producing a “false vacuum” (an unstable, temporary state of the lowest possible of ).

As a result of, the false vacuum would eventually decay into a low- true vacuum, and Guth found that the decay of the false vacuum at the beginning of the could produce some amazing results, including a rapid expansion at ever-increasing rates, which he called.The incredibly vast expansion of the caused by “solved” both Robert Dickes flatness problem and Guth’s own problem. However, it also solved the “horizon problem” of the theory (the recent observation that the appeared to be extremely uniform thoughout the, with almost no variance, which was paradoxical because there should not have been enough time at the time of the creation of the for one end of the cosmos to have been in communication with the other end). According to Guth’s theory, however, the blew up so quickly that there was no time for the essential homogeneity to be broken, and the after would therefore have been very uniform, even though the parts were not still in touch with each other.Guth first released his ideas on in a seminar at the Stanford Linear Accelerator Center in early 1980, and he went overnight from being worried about his job prospects to being besieged with offers. He returned to MIT in 1980, becoming professor of physics in 1986.For some time, however, he could find no way to end (so that and could form), often referred to as the 'graceful exit' problem, and he considered his own theory something of a failure because of this.

But, after he read a paper in late 1981 by the Russian physicist Andrei Linde (who had been working on the problem independently) and other work by Paul Steinhardt (who had also been working on the graceful exit problem), he began to exchange papers with these other theorists, thus helping each other work out theory, and there have been many other refinements and revisions since Guth's original model.More recently, Guth has expressed his belief that our is just one of many that came into existence among countless others as part of a. According to this theory, never ends, but continues expanding at an exponential rate, with additional being created all the time as 'bubbles' within the process (in some ways similar to ’s discredited ). He believes that the entire cosmos was created by quantum fluctuations from nothingness (which he argues is perfectly consistent with the because its total value remains zero), and is quoted as saying that “the is the ultimate free lunch”.Guth continues to lecture at the Massachusetts Institute of Technology (MIT), and has written over 60 technical papers related to the effects of and its interactions with particle physics. He has won many awards and medals, including the Medal of the International Center for Theoretical Physics and the Eddington Medal. His 1998 book, “The Inflationary Universe: The Quest for a New Theory of Cosmic Origins”, became a popular best-seller. Alan Guth BooksSee the additional sources and recommended reading list below, or check the page for a full list. Whenever possible, I linked to books with my amazon affiliate code, and as an Amazon Associate I earn from qualifying purchases.

Purchasing from these links helps to keep the website running, and I am grateful for your support!.by Alan Guth (Author).

For, the Big Bang ended on a summer day in 1999 in Cambridge, England. Sitting together at a conference they had organized, called “,” the two physicists suddenly hit on the same idea. Maybe science was finally ready to tackle the mystery of what made the Big Bang go bang. And if so, then maybe science could also address one of the deepest questions of all: What came?Steinhardt and Turok—working closely with a few like-minded colleagues—have now developed these insights into a thorough alternative to the prevailing, Genesis-like view of cosmology.

According to the, the whole universe emerged during a single moment some 13.7 billion years ago. In the competing theory, our universe itself in an endless cycle of creation. The latest version of the cyclic model even matches key pieces of observational evidence supporting the older view.This is the most detailed challenge yet to the 40-year-old orthodoxy of the Big Bang. Some researchers go further and envision a type of infinite time that plays out not just in this universe but in a —a multitude of universes, each with its own laws of physics and its own life story. Still others seek to revise the, rendering the concept of a “beginning” meaningless.All of these cosmology heretics agree on one thing: The Big Bang no longer defines the limit of how far the human mind can explore. Big Idea 1: The Incredible BulkThe latest elaboration of Steinhardt and Turok’s cyclic cosmology, spearheaded by Evgeny Buchbinder of Perimeter Institute for Theoretical Physics in Waterloo, Ontario, was.

Yet the impulse behind this work far predates modern theories of the universe. In the fourth century A.D., St. Augustine pondered what the Lord was doing before the first day of Genesis (wryly repeating the exasperated retort that “He was preparing Hell for those who pry too deep”).

The question became a scientific one in 1929, when Edwin Hubble determined that the universe was expanding. Extrapolated backward, Hubble’s observation suggested the cosmos was flying apart from an explosive origin, the fabled Big Bang.In the standard interpretation of the Big Bang, which took shape in the 1960s, the formative event was not an explosion that occurred at some point in space and time—it was an explosion of space and time. In this view, time did not exist beforehand.

Even for many researchers in the field, this was a bitter pill to swallow. It is hard to imagine time just starting: How does a universe decide when it is time to pop into existence?For years, every attempt to understand what happened in that formative moment quickly hit a dead end. In the standard Big Bang model, the universe began in a state of near-infinite density and temperature. At such extremes the known laws of physics break down. To push all the way back to the beginning of time, physicists needed a new theory, one that blended general relativity with quantum mechanics.The prospects for making sense of the Big Bang began to improve in the 1990s as physicists refined their ideas in, a promising approach for reconciling the relativity and quantum views. Nobody knows yet whether string theory with the real world—the, a particle smasher coming on line later this year, may provide some clues—but it has already inspired stunning ideas about how the universe is constructed. Most notably, current versions of string theory posit seven of space in addition to the three we experience.Strange and wonderful things can happen in those extra dimensions: That is what inspired Steinhardt (of Princeton University) and Turok (of Cambridge University) to set up their fateful conference in 1999.

“We organized the conference because we both felt that the standard Big Bang model was failing to explain things,” Turok says. “We wanted to bring people together to talk about what string theory could do for cosmology.”The key concept turned out to be a “brane,” a three-dimensional world embedded in a higher-dimensional space (the term, in the language of string theory, is just short for membrane). “People had just started talking about branes when we set up the conference,” Steinhardt recalls. “Together Neil and I went to a talk where the speaker was describing them as static objects.

Afterward we both asked the same question: What happens if the branes can move? What happens if they collide?”A remarkable picture began to take shape in the two physicists’ minds. A sheet of paper blowing in the wind is a kind of two-dimensional membrane tumbling through our three-dimensional world.

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For Steinhardt and Turok, our entire universe is just one sheet, or 3-D brane, moving through a four-dimensional background called “the bulk.” Our brane is not the only one; there are others moving through the bulk as well. Just as two sheets of paper could be blown together in a storm, different 3-D branes could collide within the bulk.The equations of string theory indicated that each 3-D brane would exert powerful forces on others nearby in the bulk. Vast quantities of energy lie bound up in those forces.

A collision between two branes could unleash those energies. From the inside, the result would look like a tremendous explosion. Even more intriguing, the theoretical characteristics of that explosion closely matched the observed properties of the Big Bang—including the cosmic microwave background, the afterglow of the universe’s fiercely hot early days. “That was amazing for us because it meant colliding branes could explain one of the key pieces of evidence people use to support the Big Bang,” Steinhardt says. (Credit: NASA)Three years later came a second epiphany: Steinhardt and Turok found their story did not end after the collision. “We weren’t looking for cycles,” Steinhardt says, “but the model naturally produces them.” After a collision, energy gives rise to matter in the brane worlds.

The matter then evolves into the kind of universe we know: galaxies, stars, planets, the works. Space within the branes expands, and at first the distance between the branes (in the bulk) grows too. When the brane worlds expand so much that their space is nearly empty, however, attractive forces between the branes draw the world-sheets together again. A new collision occurs, and a new cycle of creation begins. In this model, each round of existence—each cycle from one collision to the next—stretches about a trillion years. By that reckoning, our universe is still in its infancy, being only 0.1 percent of the way through the current cycle.The cyclic universe directly solves the problem of before. With an infinity of Big Bangs, time stretches into forever in both directions.

“The Big Bang was not the beginning of space and time,” Steinhardt says. “There was a before, and before matters because it leaves an imprint on what happens in the next cycle.”Not everyone is pleased by this departure from the usual cosmological thinking. Some researchers consider Steinhardt and Turok’s ideas misguided or even dangerous.

“I had one well-respected scientist tell me we should stop because we were undermining public confidence in the Big Bang,” Turok says. But part of the appeal of the cyclic universe is that it is not just a beautiful idea—it is a testable one.The standard model of the early universe predicts that space is full of gravitational waves, ripples in space-time left over from the first instants after the Big Bang.

These waves look very different in the cyclic model, and those differences could be measured—as soon as physicists develop an effective gravity-wave detector. “It may take 20 years before we have the technology,” Turok says, “but in principle it can be done. Given the importance of the question, I’d say it’s worth the wait.” BIG IDEA 2: Time’s ArrowWhile the concept of a cyclic universe provides a way to explore the Big Bang’s past, some scientists believe that Steinhardt and Turok have skirted the deeper issue of origins. “The real problem is not the beginning of time but the arrow of time,” says Sean Carroll, a theoretical physicist at Caltech.

“Looking for a universe that repeats itself is exactly what you do not want. Cycles still give us a time that flows with a definite direction, and the direction of time is the very thing we need to explain.”In 2004 Carroll and a graduate student of his, Jennifer Chen, came up with (pdf) to the problem of before. In his view, time’s arrow and time’s beginning cannot be treated separately: There is no way to address what came before the Big Bang until we understand why the before precedes the after. Like Steinhardt and Turok, Carroll thinks that finding the answer requires rethinking the full extent of the universe, but Carroll is not satisfied with adding more dimensions. He also wants to add more universes—a whole lot more of them—to show that, in the big picture, time does not flow so much as advance symmetrically backward and forward.Barbour argues that time is an illusion, with each moment—each “Now”—existing in its own right, complete and whole.The one-way progression of time, always into the future, is one of the greatest enigmas in physics.

The equations governing individual objects do not care about time’s direction. Imagine a movie of two billiard balls colliding; there is no way to say if the movie is being run forward or backward. But if you gather a zillion atoms together in something like a balloon, past and future look very different. Pop the balloon and the air molecules inside quickly fill the entire space; they never race backward to reinflate the balloon.In any such large group of objects, the system trends toward equilibrium. Physicists use the term entropy to describe how far a system is from equilibrium. The closer it is, the higher its entropy; full equilibrium is, by definition, the maximum value.

So the path from low entropy (all the molecules in one corner of the room, unstable) to maximum entropy (the molecules evenly distributed in the room, stable) defines the arrow of time. The route to equilibrium separates before from after. Once you hit equilibrium the arrow of time no longer matters, because.“Our universe has been evolving for 13 billion years,” Carroll says, “so it clearly did not start in equilibrium.” Rather, all the matter, energy, space, and even time in the universe must have started in a state of extraordinarily low entropy. That is the only way we could begin with a Big Bang and end up with the wonderfully diverse cosmos of today. Understand how that happened, Carroll argues, and you will understand the bigger process that brought our universe into being.To demonstrate just how strange our universe is, Carroll considers all the other ways it might have been constructed.

Thinking about the range of possibilities, he wonders: “Why did the initial setup of the universe allow cosmic time to have a direction? There are an infinite number of ways the initial universe could have been set up. An overwhelming majority of them have high entropy.” These high-entropy universes would be boring and inert; evolution and change would not be possible.

Such a universe could not produce galaxies and stars, and it certainly could not support life.It is almost as if our universe were fine-tuned to start out far from equilibrium so it could possess an arrow of time. But to a physicist, invoking fine-tuning is akin to saying “a miracle occurred.” For Carroll, the challenge was finding a process that would explain the universe’s low entropy naturally, without any appeal to incredible coincidence or (worse) to a miracle. Norman)Carroll found that process hidden inside one of the strangest and most exciting recent elaborations of the Big Bang theory. In 1984, MIT physicist that the very young universe had gone through a brief period of runaway expansion, which he called “inflation,” and that this expansion had blown up one small corner of an earlier universe into everything we see. In the late 1980s Guth and other physicists, most notably, now at Stanford, saw that inflation might happen over and over in a process of “eternal inflation.” As a result, pocket universes much like our own might be popping out of the uninflated background all the time.

Big Bang

This multitude of universes was called, inevitably, the multiverse.Carroll found in the multiverse concept a solution to both the direction and the origin of cosmic time. He had been musing over the arrow of time as far back as graduate school in the late 1980s, when he published papers on the feasibility of time travel using known physics.

Eternal inflation suggested that it was not enough to think about time in our universe only; he realized he needed to consider it in a much bigger, multiverse context.“We wondered if eternal inflation could work in both directions,” Carroll says. “That means there would be no need for a single Big Bang. Pocket universes would always sprout from the uninflated background.

The trick needed to make eternal inflation work was to find a generic starting point: an easy-to-achieve condition that would occur infinitely many times and allow eternal inflation to flow in both directions.”A full theory of eternal inflation came together in Carroll’s mind in 2004, while he was attending a five-month workshop on cosmology at the University of California at Santa Barbara’s famous Kavli Institute of Theoretical Physics with his student Jennifer Chen. “You go to a place like Kavli and you are away from the normal responsibilities of teaching,” Carroll says. “That gives you time to pull things together.” In those few months, Carroll and Chen worked out a vision of a profligate multiverse without beginnings, endings, or an arrow of time.“All you need,” Carroll says, with a physicist’s penchant for understatement, “is to start with some empty space, a shard of, and some patience.” Dark energy—a embedded in empty space, whose existence is strongly confirmed by recent observations—is crucial because quantum physics says that any energy field will always yield random fluctuations. In Carroll and Chen’s theory, fluctuations in the dark-energy background function as seeds that trigger new rounds of inflation, creating a crop of pocket universes from empty space.“Some of these pocket universes will collapse into black holes and evaporate, taking themselves out of the picture,” Carroll says. “But others will expand forever. The ones that expand eventually thin out. They become the new empty space from which more inflation can start.” The whole process can happen again and again.

Amazingly, the direction of time does not matter in the process. “That is the funny part. You can evolve the little inflating universes in either direction away from your generic starting point,” Carroll says. In the super-far past of our universe, long before the Big Bang, there could have been other Big Bangs for which the arrow of time ran in the opposite direction.On the grandest scale, the multi­verse is like a foam of intercon.