The Anthropic Cosmological Principle
It has been observed that cosmologists are often wrong but seldom uncertain, and the authors of this long, fascinating, exasperating book are no exceptions. They are John Barrow, astronomer at the University of Sussex, and Frank Tipler, Tulane University mathematical physicist. Physicist John Wheeler provides an enthusiastic foreword. No one can plow through this well-written, painstakingly researched tome without absorbing vast chunks of information about QM (quantum mechanics), the latest cosmic models, and the history of philosophical views that bear on the book’s main arguments.
Just what is this “anthropic principle” that has become so fashionable among a minority of cosmologists, and is arousing such passionate controversy? As the authors make clear in their introduction, there is not one principle but four. Each is more speculative than the previous one, with the fourth blasting the authors out of science altogether into clouds of metaphysics and fantasy.
The simplest of the four is called (the authors are fond of acronyms) WAP, or the Weak Anthropic Principle. Although it goes back to Protagoras’s famous declaration that “man is the measure of all things,” its modern cosmological form seems first to have been stated by the physicist Robert Dicke in the late 1950s. As Barrow and Tipler readily admit, it is a trivial tautology, totally noncontroversial. It merely proclaims that because we exist the universe must be so constructed as to allow us to have evolved. The laws of nature clearly must be such as to permit, if not actually force, the formation of CHON (carbon, hydrogen, oxygen, and nitrogen), the four elements essential to life as we know it.
Does this mean that all life must be carbon based? Although the authors believe this, it does not follow from WAP. Even if there is noncarbon life elsewhere in the universe, the fact that we are carbon imposes a variety of tight restraints on the universe and its past. For example, the cosmos has to be about 15 billion years old. Why? Because, the authors argue, elements necessary to organic molecules are cooked inside stars. If the universe were much younger, those elements would not be available and we wouldn’t be here. If the universe were much older, all the suns would have burned out, and we wouldn’t be here either.
WAP was invoked over and over again in earlier centuries by proponents of the design argument for God. It was WAPish to point out that if the earth were slightly closer to the sun, like Venus, water would boil away and carbon life would be impossible. If the earth were slightly farther from the sun, water would freeze and Earth would have the barren deserts of Mars. Theists liked to note that when water freezes it expands and floats on water, otherwise lakes and rivers would freeze to the bottom in winter and all their life be destroyed. If Earth did not have an ozone atmosphere, animals could not survive ultraviolet radiation. And so on. Hundreds of similar arguments, most of them analyzed by Barrow and Tipler, seem to show that our universe, and especially our planet, were carefully designed to permit us to exist.
The close ties between WAP and the creation hypothesis impel the authors to write almost one hundred pages on traditional proofs of God from design. It is an excellent history, followed by almost as long a section on more recent teleological arguments. There are informative discussions of such post-Darwinian “process” thinkers as Henri Bergson, Samuel Alexander, Alfred Whitehead, and Charles Hartshorne, who see the universe as rolling toward a predetermined goal, as well as “process theologians” who anchor the goal in God.
If WAP were all there is to the anthropic principle, the book would not have been worth writing. The authors continually stress the triviality of asserting no more than that the universe has a structure that makes carbon life possible. It is easy to caricature such retrograde reasoning. Instead of saying I am here because my parents met, I say that because I am here I know my parents met. How lucky for vacationers that sandy beaches are so near the sea! From the fact that I wear spectacles I can deduce the positions of my ears and nose. If a chess game ends with no queens on the board, I can infer with iron logic that both queens were captured. From the present state of the world one can obviously make all sorts of highly probable, sometimes certain, conjectures about its distant past.
But there is more to the anthropic principle than WAP. The next step is SAP, the Strong Anthropic Principle. Proposed in 1974 by the British cosmologist Brandon Carter, it maintains that life of any sort is impossible unless the basic laws of nature are exactly what they are. Consider gravity. If it were slightly stronger, the cosmos would long ago have stopped expanding, gone the other way, and collapsed into a black hole before galaxies could form. If gravity were slightly weaker, it would have expanded too rapidly to allow matter to clump into stars. In either case, you and I wouldn’t be here.
The strength of gravity is one of a dozen or more constants called dimensionless because they are independent of any measuring system. If one banana is twice as long as another, the number two is the same whether you measure the banana in inches or centimeters. It turns out that these fundamental constants are so finely tuned that if they varied ever so slightly, there couldn’t be any carbon atoms and we wouldn’t be here. Instead of saying we are here because the constants are precisely what they are, SAP turns it around. We are here, therefore the constants had to be what they are.
In long chapters on physics, astrophysics, and biochemistry, often dense with technical details and mathematical formulas, Barrow and Tipler defend this reverse way of reasoning. A recurring theme is that SAP puts such narrow constraints on the constants and natural laws that it can lead to falsifiable predictions. Opponents of SAP take a dim view of this claim. The physicist Heinz Pagels, in a slashing attack on anthropic arguments in his article “A Cozy Cosmology,”1 dismisses WAP and SAP as pure flimflam. Although they may occasionally suggest testable conjectures, they do so in such obvious ways that nothing is gained by elevating them into new principles.
According to Barrow and Tipler, the first successful anthropic prediction was made by the University of Chicago geologist Thomas Chamberlain. Geological evidence indicates a great age for the solar system. If the sun did not feed on atomic energy, Chamberlain guessed, it would have long ago burned out and we wouldn’t be here. Chamberlain guessed right, but did he do anything except apply ordinary reasoning?
Writing just before the Barrow and Tipler book was published, Pagels cites a more recent example. England’s Stephen Hawking and Barry Collins once invoked the anthropic principle to explain why the universe is so isotropicâ€”the same in all directions. If it were less so, matter would not condense into galaxies and we wouldn’t be here. This, says Pagels, explains nothing. By contrast, the new inflationary models of the big-bang hypothesis of the origins of the universe actually do provide a plausible mechanism for isotropy. In old big-bang models the initial explosion would have produced permanent irregularities. In the inflationary models, immediately, after the bang the universe jumps from a trillionth the size of a proton to about the size of a softball. This sudden inflation smoothes out all irregularities, leaving an isotropic cosmos expanding at its present slow rate. In light of such speculations, the anthropic principle seems irrelevant. Surprisingly, Barrow and Tipler agree. They are strongly critical of Hawking and Collins for what they see as a misuse of the principle.
Similar efforts to use SAP as a tool for investigating the constants have been equally feeble, Pagels continues. Meanwhile, the new unified-field theories really are providing significant explanations of why the constants are what they are. WAP and SAP are so needless that they raise a new mystery. “How can such a sterile idea,” Pagels asks, “reproduce itself so prolifically?” He suspects it may be because scientists are reluctant to make a leap of faith and say: “The reason the universe seems tailor-made for our existence is that it was tailor-madeâ€Ś. Faced with questions that do not neatly fit into the framework of science, they are loath to resort to religious explanations; yet their curiosity will not let them leave matters unaddressed. Hence, the anthropic principle. It is the closest that some atheists can get to God.”
Leaving aside the hypothesis of a transcendent Creator, or a Mind that either is the universe or permeates the universe, what alternatives are left? Barrow and Tipler consider several possibilities.
One is the startling view that only one kind of universe is possibleâ€”the one we know. This was skillfully defended by the Harvard chemist Lawrence Henderson in two books that were largely ignored until recently: Fitness of the Environment (1913, reprinted in 1970 by Harvard University Press) and The Order of Nature (1917). Leibniz argued exactly the opposite. He believed an infinity of universes are logically possible, and God selected the one he liked best.
The authors discuss several variations of the many-possible-worlds view. Other universes could have the same laws as ours, but entirely different histories depending on different initial conditions before the big bang. Parallel worlds could flourish side by side in our familiar three-dimensional space, or in higher spaces, but because of limitations on the speed of light, no contacts between them are possible even if they are all in our space. We need not, however, assume infinite space. Alternate worlds could follow one another in some sort of supertime. Each explodes into existence, expands, contracts, and vanishes in the Big Crunch to be followed (whatever that means) by another fireball.
John Wheeler has a stupendous vision in which an infinity of universes pop in and out of existence, each with a randomly determined set of laws. Every logically possible universe appears an infinite number of times. (If an infinity of bridge hands are dealt, every possible distribution of the cards will be dealt an infinite number of times.) Of course only a tiny subset of these possible worlds will have forces and particles that permit life. This naturally emasculates any argument from design to God. It is not surprising we are in a universe that allowed us to evolve. How could it be otherwise?
The Wildest of all variants of the infinite-universe theme, designed to counter the standard Copenhagen interpretation of QM (named for the city where Niels Bohr worked), is the many-worlds interpretation. In the Copenhagen view, the central mystery is what happens when a quantum system is measured. Take the case of a single particle. Every particle has associated with it a set of probability waves in an artificially constructed multidimensional space. A single expression, called the wave function, gives the probabilities of a particle assuming each of its possible states when it is measured. Before measurement, all possible states of the particle are said to be mixed in some sort of weird potential sense. Not until the particle is measured does nature “decide,” by pure chance, what value to give a variable. At that instant the wave function is said to “collapse” from an indefinite to a definite state.
The Sciences (March/April 1985).↩
The Sciences (March/April 1985).↩