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Friday, October 24, 2008

Why a Fine-Tuned Universe?

FROM ROBIN COLLINS, PROFESSOR OF PHILOSOPHY AT MESSIAH COLLEGE: Science is commonly thought to have undercut belief in God. As Nobel Prize winning physicist Steven Weinberg famously remarked, “the more we find out about the universe, the more meaningless it all seems.” Yet, the discoveries of modern physics and cosmology in the last 50 years have shown that the structure of the universe is set in an extraordinarily precise way for the existence of life; if its structure were slightly different, even by an extraordinarily small degree, life would not be possible. In many people’s minds, the most straightforward explanation of this remarkable fine-tuning is some sort of divine purpose behind our universe.
This fine-tuning falls into three categories: the fine-tuning of the laws of nature, the fine-tuning of the constants of physics, and the fine-tuning of the initial conditions of the universe. “Fine-tuning of the laws of nature” refers to the fact that if the universe did not have precisely the right combination of laws, complex intelligent life would be impossible. If there were no universal attractive force (law of gravity), for example, matter would be dispersed throughout the universe and the energy sources (such as stars) needed for life would not exist. Without the strong nuclear force that binds protons and neutrons together in the nucleus, there would not be any atoms with an atomic number greater than hydrogen, and hence no complex molecules needed for life. And without the Pauli-exclusion principle, all electrons would fall to the lowest orbital of an atom, undercutting the kind of complex chemistry that life requires.
Some fundamental physical numbers governing the structure of the universe—called the constants of physics—also must fall into an exceedingly narrow range for life to exist. For example, many have estimated that the cosmological constant—a fundamental number that governs the expansion rate of empty space—must be precisely set to one part in 10120 in order for life to occur; if it were too large, the universe would have expanded too rapidly for galaxies and stars to form, and if it were too small, the universe would have collapsed back on itself. As Stephen Hawking wrote in his book A Brief History of Time, “The remarkable fact is that the values of these numbers [i.e. the constants of physics] seem to have been very finely adjusted to make possible the development of life.” Finally, the initial distribution of mass energy at the time of the big bang must have an enormously special configuration for life to occur, which Cambridge University mathematical physicist Roger Penrose has calculated to be on the order of one part in 1010123. This is an unimaginably small number.
Are there alternatives to explaining this fine-tuning by divine creation? Perhaps the most widely advocated alternative is the so-called multiverse hypothesis. According to this hypothesis, there is an enormous number of universes with different initial conditions, values for the constants of physics, and even different laws of nature. Simply by chance, at least one universe will have the “winning combination” for life, and the beings that evolve in that universe will look back and be astonished at how lucky they are. We are thus merely the product of a “cosmic lottery.”
How did these universes come into existence? Typically, the answer is to postulate some kind of physical process, which I will call a “universe generator.” A problem with this hypothesis is that it seems that the universe generator itself must have just the right set of laws (and initial conditions) to produce even one life-sustaining universe. After all, even a mundane item such as a bread-making machine, which only produces loaves of bread instead of universes, must have the right set of mechanisms and programming, along with precisely the right ingredients (flour, yeast, gluten, and so on) in precisely the right proportions, to produce decent loaves of bread.
Indeed, if one carefully examines the most popular and well-developed universe-generator hypothesis—that arising out of inflationary cosmology combined with superstring theory—one finds that it must have precisely the right fields and laws to generate life-permitting universes. Eliminate one of the fields or laws, and no life-sustaining universes would be produced. This means that the hypothesis merely pushes the issue of fine-tuning up one level to that of the universe generator itself.
Finally, one could claim that the universe exists as an inexplicable fact, without any need for further explanation. According to this idea, our existence is just an extraordinarily “lucky accident,” and there is nothing more to be said. It is important to note that we cannot absolutely rule out this possibility; extraordinarily improbable things happen all the time, and our universe could be one of them. But I believe we can say that the fine-tuning of the universe provides significant evidence in support of divine creation over this hypothesis. The reason for this can be articulated in terms of what is often called the "likelihood principle," but which I call the “surprise principle.” Roughly, this principle states that whenever a body of evidence is much more surprising under one hypothesis than another, it counts as evidence in favor of the hypothesis under which it is least surprising. Imagine a murder trial in which the defendant’s fingerprints match those on the murder weapon. Under typical circumstances, the jury would take this as strong evidence of guilt. Why? The match would be judged unsurprising under the guilt hypothesis, but very surprising under the innocence hypothesis. Therefore, the surprise principle says it counts as strong evidence in favor of the guilt hypothesis. Of course, it does not absolutely prove guilt; the match could have happened by chance, even if the chance of that happening is judged to be very small.
Similarly, it could be argued, given the fine-tuning, that the existence of a life-permitting universe is very surprising under the brute fact hypothesis, but not under theism. Therefore, by the surprise principle, fine-tuning provides significant evidence in favor of theism over the brute fact hypothesis. Nonetheless, it does not prove theism is true, or even show it is the best explanation of the universe. So faith—understood as a special mode of knowing similar to our ethical intuitions—still plays an essential role in belief in God, but the fine-tuning offers significant confirming evidence for this belief. In any case, the fine-tuning evidence offers a significant challenge to those who claim that the findings of science undercut belief in God.

Robin Collins appears with John Leslie, Steven Weinberg, David Gross, the Rev. Dr. John Polkinghorne, Michael Shermer, and Paul Davies in "Why a Fine-Tuned Universe?" the seventh episode in the Closer to Truth: Cosmos, Consciousness, God TV series, hosted and created by Robert Lawrence Kuhn. The series airs Thursdays on the PBS HD network and many other PBS stations. Every Friday, participants will share their views on the previous day's episode.


Steven Carr said...

If things were different, it would be a miracle if life were to exist.

And we all know that there is no god who can work miracles.

V.V. Raman said...

No serious physicist can afford to be indifferent to the remarkable coincidence of numbers that could be interpreted in terms of some hidden intention at the very birth of the universe to make the eventual emergence of humans possible, whether or not one agrees with an anthropocentric interpretation of the fact. Not surprisingly, the physicist-celebrity Stephen Hawking wrote that "it would be very difficult to explain why the universe should have begun in just this way, except as the act of a God who intended to create beings like us. On the other hand, Freeman Dyson declared more cautiously: "As we look out into the universe and identify the many accidents of physics and astronomy that have worked together to our benefit, it almost seems as if the universe must in some sense have known that we were coming.”

Die-hard skeptics may wonder why so many silent eons were frittered away in the lighting and snuffing of stupendously vast stars before Homo sapiens could come to the fore. An all-powerful Designer could surely have come up with the appropriate combination of constants to manufacture a Darwin or an Einstein in short order and in a smaller span of space, without the tortuous and time-consuming route of supernova furnaces for synthesizing heavier elements.

While correctly recognizing that the universe is not anthropocentric, many scientists fail to see that science is, in its very mode, anthropic. Take away the human mind, and there can be no description of the world in terms of concepts like momentum and energy, let alone visible light, short-lived particles, and audible sound.

In any event, there are thinkers who seem to be conditioned to be averse to any mention of God. They are convinced there is nothing beyond matter and energy in space and time. In their opinion, those who speak of God and salvation are soft-hearted, misguided souls, unable to cope with the tribulations of life, people who naively continue to believe in a loftier version of the fairy tales of their infancy. The unswerving commitment of unbending materialists to the causal and the spatio-temporal, and their uncompromising rejection of anything spiritual can only be described (in terms of its deeply-felt attachment) as religious, much as they would abhor the epithet. Their understandable conviction about the physical world is perhaps indispensable for advances in science, but in its absolute certainty it is no less religious than the one which affirms that sooner or later we will all be saved.

Tim said...

i agree, eloquently spoken