Dedication
I wish to thank Peter Hubbard of HarperCollins for his encouragement. I am also indebted to my agent, Max Brockman, for his continued support of this project.
Contents
Dedication
Introduction by John Brockman
1. A Golden Age of Cosmology
Alan Guth
2. The Cyclic Universe
Paul Steinhardt
3. The Inflationary Universe
Alan Guth
4. A Balloon Producing Balloons Producing Balloons
Andrei Linde
5. Theories of the Brane
Lisa Randall
6. The Cyclic Universe
Neil Turok
7. Why Does the Universe Look the Way It Does?
Sean Carroll
8. In the Matrix
Martin Rees
9. Think About Nature
Lee Smolin
10. The Landscape
Leonard Susskind (with an introduction by John Brockman)
11. Smolin vs. Susskind: The Anthropic Principle
Lee Smolin, Leonard Susskind (with an introduction by John Brockman)
12. Science Is Not About Certainty
Carlo Rovelli (with an introduction by Lee Smolin)
13. The Energy of Empty Space That Isn’t Zero
Lawrence Krauss
14. Einstein: An Edge Symposium
Brian Greene, Walter Isaacson, Paul Steinhardt (with an introduction by John Brockman)
15. Einstein and Poincaré
Peter Galison
16. Thinking About the Universe on the Larger Scales
Raphael Bousso (with an introduction by Leonard Suskind)
17. Quantum Monkeys
Seth Lloyd
18. The Nobel Prize and After
Frank Wilczek
19. Who Cares About Fireflies?
Steven Strogatz (with an introduction by Alan Alda)
20. Constructor Theory
David Deutsch
21. A Theory of Roughness
Benoit Mandelbrot (with an introduction by John Brockman)
About the Author
Back Ads
Also by John Brockman
Credits
Copyright
About the Publisher
Introduction
In this, the fourth volume of The Best of Edge series, following Mind, Culture, and Thinking, we focus on ideas about the universe. We are pleased to present twenty-one pieces, original works from the online pages of Edge.org, which consist of interviews, commissioned essays, and transcribed talks, many of them accompanied online with streaming video.
Edge, at its core, consists of the scientists, artists, philosophers, technologists, and entrepreneurs at the center of today’s intellectual, technological, and scientific landscape. Through its lectures, master classes, and annual dinners in California, London, Paris, and New York, Edge gathers together the “third-culture” scientific intellectuals and technology pioneers exploring the themes of the post-industrial age. These are the people who are rewriting our global culture.
And its website, Edge.org, is a conversation. The online Edge.org salon is a living document of millions of words that charts the conversation over the past eighteen years. It is available, gratis, to the general public.
Edge.org was launched in 1996 as the online version of the Reality Club, an informal gathering of intellectuals that met from 1981 to 1996 in Chinese restaurants, artists’ lofts, the boardrooms of Rockefeller University and the New York Academy of Sciences, investment banking firms, ballrooms, museums, living rooms, and elsewhere. Though the venue is now in cyberspace, the spirit of the Reality Club lives on, in the lively back-and-forth conversations on hot-button ideas driving the discussion today. In the words of novelist Ian McEwan, a sometime contributor, Edge.org is “open-minded, free ranging, intellectually playful . . . an unadorned pleasure in curiosity, a collective expression of wonder at the living and inanimate world . . . an ongoing and thrilling colloquium.”
This is science set out in the largely informal style of a conversation among peers—nontechnical, equationless, and colloquial, in the true spirit of the third culture, which I have described as consisting of “those scientists and other thinkers in the empirical world who, through their work and expository writing, are taking the place of the traditional intellectual in rendering visible the deeper meanings of our lives, redefining who and what we are.”
For this volume—coming as it does in the wake of the recent stunning discovery of gravitational waves by the BICEP2 radio telescope at the South Pole, an apparent confirmation of the prime cosmological theory of inflation—we’ve assembled online contributions from some of Edge’s best minds, most of them pioneering theoretical physicists and cosmologists. They provide a picture of cosmology as it has developed over the past three decades—a “golden age,” in the words of MIT’s Alan Guth, one of its leading practitioners.
This Golden Age of Cosmology has reached a high point—not just with the recent revelations at the South Pole but with the 2012 discovery, by the Large Hadron Collider at CERN, of the long-sought Higgs boson, whose field is thought to give mass to the elementary particles making up the universe.
We lead off, appropriately enough, with a 2001 talk by Guth, the father of inflationary theory. Then, at an Edge gathering at Eastover Farm in Connecticut a year later, Guth goes head to head with Paul Steinhardt, who presents his rival theory of a cyclic universe—a theory that the new data on gravitational waves may put paid to. Stay tuned.
Andrei Linde, the father of “eternal chaotic inflation,” emphasizes the concepts of the multiverse and the anthropic principle that arose from it (“. . . different exponentially large parts of the universe may be very different from each other, and we live only in those parts where life as we know it is possible”).
Lisa Randall and Neil Turok elaborate on the theory of branes, two-dimensional structures arising from string theory—and whose existence is central to the cyclic universe.
Sean Carroll ponders the mystery of “why our observable universe started out in a state of such pristine regularity and order.”
Martin Rees, the U.K.’s Astronomer Royal, speculates on whether we are living in a simulation produced by a superintelligent hypercomputer.
Lee Smolin discusses the nature of time. Then he and Leonard Susskind (string theory’s father) engage in a gentlemanly donnybrook over Smolin’s theory of cosmological natural selection and the efficacy of the anthropic principle.
Brian Greene, Paul Steinhardt, and Einstein biographer Walter Isaacson speculate on how Einstein might view the theoretical physics of the 21st century, and Steinhardt and Greene come to gentlemanly blows over string theory.
In a calmer vein:
Science historian Peter Galison muses on the similarity, and fundamental dissimiliarity, between two contemporaries and giants of early 20th-century physics, Einstein and Poincaré; Arizona State University cosmologist Lawrence Krauss throws up his hands at the conundrum of dark energy; Carlo Rovelli (Professeur de classe exceptionelle, Université de la Méditerranée) recommends a willingness to return to basics; and Nobelist Frank Wilczek relishes a future devoted to “following up ideas in physics that I’ve had in the past that are reaching fruition.”
Berkeley’s Raphael Bousso, too, is an optimist. (“I think we’re ready for Oprah, almost . . . [W]e’re going to learn something about the really deep questions, about what the universe is lik
e on the largest scales, how quantum gravity works in cosmology.”)
Seth Lloyd, a quantum mechanical engineer, explains how the universe can, in a sense, program itself; Steven Strogatz sees cosmic implications in the synchronous flashing of crowds of fireflies; and Oxford physicist David Deutsch predicts that his “constructor theory” will eventually “provide a new mode of description of physical systems and laws of physics. It will also have new laws of its own, which will be deeper than the deepest existing theories such as quantum theory and relativity.”
And finally, as a kind of envoi, the late Benoit Mandelbrot, nearing eighty, looks back on a long career devoted to fractal geometry and newly invigorated: “A recent, important turn in my life occurred when I realized that something I have long been stating in footnotes should be put on the marquee. . . . I’m particularly long-lived and continue to evolve even today. Above a multitude of specialized considerations, I see the bulk of my work as having been directed toward a single overarching goal: to develop a rigorous analysis for roughness. At long last, this theme has given powerful cohesion to my life.”
A Golden Age of Cosmology it may be, but you will find plenty of roughness—of doubt and disagreement—here. In spite of its transcendent title, this collection is hardly the last word. In the months (and the years) ahead, as the Large Hadron Collider pours out more data about the microworld and powerful telescopes and satellites continue to confirm—or, who knows, cast fresh doubt on—our leading theories of the macroworld, the arguments will surely continue.
May the conversation flourish!
John Brockman
Editor and Publisher
Edge.org
1
A Golden Age of Cosmology
Alan Guth
Father of the inflationary theory of the Universe and Victor F. Weisskopf Professor of Physics at MIT; inaugural winner, Milner Foundation Fundamental Physics Prize; author, The Inflationary Universe: The Quest for a New Theory of Cosmic Origins
It’s often said—and I believe this saying was started by the late David Schramm—that today we are in a golden age of cosmology. That’s really true. Cosmology at this present time is undergoing a transition from being a bunch of speculations to being a genuine branch of hard science, where theories can be developed and tested against precise observations. One of the most interesting areas of this is the prediction of the fluctuations, the nonuniformities, in the cosmic background radiation, an area I’ve been heavily involved in. We think of this radiation as being the afterglow of the heat of the Big Bang. One of the remarkable features of the radiation is that it’s uniform in all directions, to an accuracy of about 1 part in 100,000, after you subtract the term that’s related to the motion of the Earth through the background radiation.
I’ve been heavily involved in a theory called the inflationary universe, which seems to be our best explanation for this uniformity. The uniformity is hard to understand. You might think initially that maybe the uniformity could be explained by the same principles of physics that cause a hot slice of pizza to get cold when you take it out of the oven; things tend to come to a uniform temperature. But once the equations of cosmology were worked out so that one could calculate how fast the universe was expanding at any given time, physicists were able to calculate how much time there was for this uniformity to set in.
They found that in order for the universe to have become uniform fast enough to account for the uniformity we see in the cosmic background radiation, information would have to have been transferred at approximately a hundred times the speed of light. But according to all our theories of physics, nothing can travel faster than light, so there’s no way this could have happened. So the classical version of the Big Bang theory had to simply start out by assuming that the universe was homogeneous—completely uniform—from the very beginning.
The inflationary universe theory is an add-on to the standard Big Bang theory, and basically what it adds on is a description of what drove the universe into expansion in the first place. In the classic version of the Big Bang theory, that expansion was put in as part of the initial assumptions, so there’s no explanation for it whatsoever. The classical Big Bang theory was never really a theory of a bang; it was really a theory about the aftermath of a bang. Inflation provides a possible answer to the question of what made the universe bang, and now it looks like it’s almost certainly the right answer.
Inflationary theory takes advantage of results from modern particle physics, which predicts that at very high energies there should exist peculiar kinds of substances which actually turn gravity on its head and produce repulsive gravitational forces. The inflationary explanation is the idea that the early universe contains at least a patch of this peculiar substance. It turns out that all you need is a patch; it can actually be more than a billion times smaller than a proton. But once such a patch exists, its own gravitational repulsion causes it to grow rapidly, becoming large enough to encompass the entire observed universe.
The inflationary theory gives a simple explanation for the uniformity of the observed universe, because in the inflationary model the universe starts out incredibly tiny. There was plenty of time for such a tiny region to reach a uniform temperature and uniform density, by the same mechanisms through which the air in a room reaches a uniform density throughout the room. And if you isolate a room and let it sit long enough, it will reach a uniform temperature as well. For the tiny universe with which the inflationary model begins, there’s enough time in the early history of the universe for these mechanisms to work, causing the universe to become almost perfectly uniform. Then inflation takes over and magnifies this tiny region to become large enough to encompass the entire universe, maintaining this uniformity as the expansion takes place.
For a while, when the theory was first developed, we were worried that we would get too much uniformity. One of the amazing features of the universe is how uniform it is, but it’s still by no means completely uniform. We have galaxies and stars and clusters and all kinds of complicated structure in the universe that needs to be explained. If the universe started out completely uniform, it would just remain completely uniform, as there would be nothing to cause matter to collect here or there or any particular place.
I believe Stephen Hawking was the first person to suggest what we now think is the answer to this riddle. He pointed out—although his first calculations were inaccurate—that quantum effects could come to our rescue. The real world is not described by classical physics, and even though this was very high-brow physics, we were in fact describing things completely classically, with deterministic equations. The real world, according to what we understand about physics, is described quantum mechanically, which means, deep down, that everything has to be described in terms of probabilities.
The “classical” world we perceive, in which every object has a definite position and moves in a deterministic way, is really just the average of the different possibilities the full quantum theory would predict. If you apply that notion here, it’s at least qualitatively clear from the beginning that it gets us in the direction we want to go. It means that the uniform density, which our classical equations were predicting, would really be just the average of the quantum mechanical densities, which would have a range of values that could differ from one place to another. The quantum mechanical uncertainty would make the density of the early universe a little bit higher in some places, and in other places it would be a little bit lower.
So, at the end of inflation, we expect to have ripples on top of an almost uniform density of matter. It’s possible to actually calculate these ripples. I should confess that we don’t yet know enough about the particle physics to actually predict the amplitude of these ripples, the intensity of the ripples, but what we can calculate is the way in which the intensity depends on the wavelength of the ripples. That is, there are ripples of all sizes, and you can measure the intensity of ripples of different sizes. And you can discuss what we call the spectrum—we
use that word exactly the way it’s used to describe sound waves. When we talk about the spectrum of a sound wave, we’re talking about how the intensity varies with the different wavelengths that make up that sound wave. We do exactly the same thing in the early universe, and talk about how the intensity of these ripples in the mass density of the early universe varied with the wavelengths of the different ripples we’re looking at. Today we can see those ripples in the cosmic background radiation.
The fact that we can see them at all is an absolutely fantastic success of modern technology. When we were first making these predictions, back in 1982, at that time astronomers had just barely been able to see the effect of the Earth’s motion through the cosmic background radiation, which is an effect of about one part in a thousand. The ripples I’m talking about are only one part in 100,000—just 1 percent of the intensity of the most subtle effect it had been possible to observe at the time we were first doing these calculations.
I never believed we would ever actually see these ripples. It just seemed too far-fetched that astronomers would get to be a hundred times better at measuring these things than they were at the time. But to my astonishment and delight, in 1992 these ripples were first detected by a satellite called COBE, the Cosmic Background Explorer, and now we have far better measurements than COBE, which had an angular resolution of about 7 degrees. This meant that you could see only the longest wavelength ripples. Now we have measurements that go down to a fraction of a degree, and we’re getting very precise measurements now of how the intensity varies with wavelength, with marvelous success.
About a year and a half ago, there was a spectacular set of announcements from experiments called BOOMERANG and MAXIMA, both balloon-based experiments, which gave very strong evidence that the universe is geometrically flat, which is just what inflation predicts. By flat I don’t mean two-dimensional; I just mean that the three-dimensional space of the universe is not curved, as it could have been according to general relativity. You can actually see the curvature of space in the way that the pattern of ripples has been affected by the evolution of the universe. A year and a half ago, however, there was an important discrepancy that people worried about, and no one was sure how big a deal to make out of it. The spectrum they were measuring was a graph that had, in principle, several peaks. These peaks had to do with successive oscillations of the density waves in the early universe and a phenomenon called resonance that makes some wavelengths more intense than others. The measurements showed the first peak beautifully, exactly where we expected it to be, with just the shape that was expected. But we couldn’t actually see the second peak.
The Universe_Leading Scientists Explore the Origin, Mysteries, and Future of the Cosmos Page 1
