The Whole Shebang: A State-of-the Universe(s) Report
The Inflationary Universe: The Quest for a New Theory of Cosmic Origins
Before the Beginning: Our Universe and Others
On a summer weekend a few years ago my wife and I visited friends at their ranch in the Glass Mountains of West Texas. After dinner we sat outside on lawn chairs and looked up at the sky. Far from city lights, in clear, dry air, and with the moon down, we could see not only Altair and Vega and the other bright stars that you can see from anywhere on a cloudless summer night, but also an irregular swath of light running across the sky, the Milky Way, as I had not seen it in decades of living in cities.
The view is something of an illusion: the Milky Way is not something out there, far from us—rather, we are in it. It is our galaxy: a flat disk of about a hundred billion stars, almost a hundred thousand light years across, within which our own solar system is orbiting, two thirds of the way out from the center. What we see in the sky as the Milky Way is the combined light of the many stars that are in our line of sight when we look out along the plane of the disk, almost all of them too far away to be seen separately. Staring at the Milky Way and not being able to make out individual stars in it gave me a chilling sense of how big it is, and I found myself holding on tightly to the arms of my lawn chair.
Astronomers used to think that our galaxy was the whole universe, but now we know that it is one of many billions of galaxies, extending out billions of light years in all directions. The universe is expanding: any typical galaxy is rushing away from any other with a speed proportional to the distance between them. As the universe becomes less crowded it is also becoming colder. Observing what is happening now, and using what we know of the laws of physics, we can reconstruct what must have been happening in the past.
Here is the account that is now accepted by almost all working cosmologists. About 10 to 15 billion years ago, the contents of the universe were so crowded together that there could be no galaxies or stars or even atoms or atomic nuclei. There were only particles of matter and antimatter and light, uniformly filling all space. No definite starting temperature is known, but our calculations tell us that the contents of the universe must once have had a temperature of at least a thousand trillion degrees centigrade. At such temperatures, particles of matter and antimatter were continually converting into light, and being created again from light. Meanwhile, the particles were also rapidly rushing apart, just as the galaxies are now. This expansion caused a fast cooling of the particles, in the same way that a refrigerator is cooled by the expansion of the freon gas in its coils. After a few seconds, the temperature of the matter, antimatter, and light had dropped to about ten billion degrees. Light no longer had enough energy to turn into matter and antimatter. Almost all matter and antimatter particles annihilated each other, but (for reasons that are somewhat mysterious) there was a slight excess of matter particles—electrons, protons, and neutrons—which could find no antimatter particles to annihilate them, and they therefore survived this great extinction. After three more minutes of expansion the leftover matter became cold enough (about a billion degrees) for protons and neutrons to bind together into the nuclei of the lightest elements: hydrogen, helium, and lithium.
For three hundred thousand years the expanding matter and light remained too hot for nuclei and electrons to join together as atoms. Stars or galaxies could not begin to form because light exerts strong pressure on free electrons, so any clump of electrons and nuclei would have been blasted apart by light pressure before its gravity could begin to attract more matter. Then, when the temperature dropped to about three thousand degrees, almost all electrons and nuclei became bound into atoms, in what astronomers call the epoch of recombination. (The “re” in “recombination” is misleading. At the time of recombination electrons and nuclei had never before been combined into atoms.) After recombination, gravitation began to draw matter together into galaxies and then into stars. There it was cooked into all the heavier elements, including those like iron and oxygen from which, billions of years later, our earth was formed.
This account is what is commonly known as the big-bang cosmology. As the term is used by cosmologists, the big bang was not an explosion that occurred sometime in the past; it is an explosion involving all of the universe we can see, that has been going on for 10 to 15 billion years, since as far back in time as we can reliably trace the history of the universe, and it will doubtless continue for billions of years to come, and perhaps forever.
Though the big-bang cosmology is a great scientific achievement, it has not answered the most interesting question: What is the origin of the universe?—not what happened in the first three hundred thousand years of the big bang, or in its first three minutes, or in its first few seconds, but at the very start, if there was one, or even before. In 1992 I was among a group of physicists trying to sell Vice President Gore on the need for a large new elementary particle accelerator, the Superconducting Super Collider. Knowing that even people who couldn’t care less about the laws of physics are curious about cosmology, we described how this instrument might lead to the discovery of mysterious particles that are thought to inhabit the voids between the galaxies and to make up most of the matter of the universe. The Vice President listened politely and promised warm support from the Clinton administration.1 Then, just as he was leaving, he turned back into the room, and diffidently asked if we could tell him what happened before the big bang.
I don’t recall what we answered, but I am sure that it was not very enlightening. No one is certain what happened before the big bang, or even if the question has any meaning. When they thought about it at all, most physicists and astronomers supposed until recently that the universe started in an instant of infinite temperature and density at which time itself began, so that questions about what happened before the big bang are meaningless, like questions about what happens at temperatures below absolute zero. Some theologians welcome this view, presumably because it bears a resemblance to scriptural accounts of creation. Moses Maimonides taught that “the foundation of our faith is the belief that God created the Universe from nothing; that time did not exist previously, but was created….”2 Saint Augustine thought the same.
But opinions among cosmologists have been shifting lately, toward a more complicated and far-reaching picture of the origin of the universe. This new view is given prominence in the books under review by Timothy Ferris, Alan Guth, and Sir Martin Rees. All three books also give clear introductions to the standard big-bang theory and to the physical theories used by cosmologists.
Ferris is emeritus professor of journalism at the University of California at Berkeley, and an experienced writer on science for the general reader. He has an attractive, cool style, and his book is broad in scope, extending even into philosophical matters, but without the gushing or silliness that sometimes characterizes discussions of cosmology. Although he is not a working scientist, Ferris has a sure grasp of the science he describes. I do not think there is a better popular treatment of some of the topics that Ferris covers. (He tells some good stories too. Since the late 1960s, he writes, the physicist Ray Davis has been measuring the rate at which the sun emits the elusive particles known as neutrinos, by catching one now and then in a large tank of perchlorethylene, a common dry-cleaning fluid. After ordering 100,000 gallons of perchlorethylene from a chemical supply house, Davis began to receive advertisements from a supplier of coat hangers.)
Rees is an eminent astrophysicist, currently the fifteenth Astronomer Royal of England and professor at the University of Cambridge, and one of the best expositors of his subject. Because he has made important contributions to many problems of astrophysics, Rees is able to give the reader a better sense of how science is done than most philosophers of science, in the way that a good military memoir—by Grant, say, or Bradley—gives a better sense of the nature of war than the generalities of Sun Tzu or Clausewitz. He makes some telling points about science policy: he is, for example, dead right about the harm done to astronomical research by our commitment to the manned space program. He quotes Riccardo Giacconi, the first director of the Space Telescope Science Institute, as saying that if from the beginning it had been planned that an unmanned rocket instead of the space shuttle would put the Hubble Space Telescope into orbit, then seven similar telescopes could have been built and launched for what so far has been spent on just one. Rees’s book also evocatively describes scientists he has known—not only those, like Stephen Hawking and Roger Penrose, whose names are familiar to the public, but others who have also made major contributions to astrophysics, including Subrahmayan Chandrasekhar, Robert Dicke, John Wheeler, Yakov Zeldovich, and Fritz Zwicky.
Guth is a young professor of physics at MIT. Though this is his first book for the general reader, Guth writes engagingly and understandably. His book concentrates on research on the beginning of the universe to which he has made a major contribution, and so it is an important historical document as well as enjoyable to read.
In December 1979 Guth was a postdoctoral research associate visiting the Stanford Linear Accelerator Center, worrying about where he would get his next job. Together with a Cornell colleague, Henry Tye, he was studying the cosmological effects of certain physical fields. Fields are conditions of space itself, considered apart from any matter that may be in it. Fields can change from moment to moment and from point to point in space, something like the way that temperature and wind velocity are conditions of the air that can vary with time and position in the atmosphere. The most familiar example of a field is the gravitational field, which we all feel tugging us toward the center of the earth. Most people have also felt the magnetic field pulling a piece of iron in their hand toward the north or south pole of a bar magnet. In the modern theory of elementary particles known as the Standard Model, a theory that has been well verified experimentally, the fundamental components of nature are a few dozen different kinds of field.
Their support turned out to be tepid, and the project was cancelled by Congress.↩
This is taken from the second revised edition of the M. Friedlander translation of The Guide for the Perplexed (Routledge and Kegan Paul, 1904; reprinted by Dover Publications, 1956), p. 212.↩