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Friday, May 8, 2009

Is the Universe Fine-Tuned for Life?

FROM RUSSELL STANNARD, EMERITUS PROFESSOR OF PHYSICS AT OPEN UNIVERSITY: "The more the universe seems comprehensible, the more it also seems pointless." Those are the words of Nobel laureate Steven Weinberg in his book The First Three Minutes. He goes on to dismiss human life as "a more-or-less farcical outcome of a chain of accidents."
It is not difficult to appreciate how one might arrive at such a gloomy assessment. Take, for example, the size of the universe. It takes 13.7 billion years for light to reach us from the farthest depths of space, even though it travels at 300,000 kilometers per second. Are we really expected to believe that God designed it as a home for humans? A case of over-design perhaps?
Most places in the universe are hostile to life. The depths of space are incredibly cold. The most prominent objects in the sky, the sun and the other stars, are balls of fire and thus not suitable places to find life. For the great majority of the history of the universe, there was no intelligent life. After the stars have exhausted their fuel, there comes the Heat Death of the universe—an infinity of time when there will again be no life. Hence the view that life is but a fleeting, accidental byproduct of no significance. Or is it?
Suppose you were put in charge of making a universe. You have freedom to choose the laws of nature and the conditions under which your imaginary universe operates. The aim is to produce a universe that is tailor-made for the development of life—the kind of universe a sensible God would have created if it were really intended primarily as a home for life.
Let us assume you start off your universe with a big bang. All the galaxies of stars are to be receding from each other in the aftermath of that great explosion. The first decision is how violent to make your big bang. You might feel, for example, that the actual big bang was somewhat excessive if the aim was simply to produce some life forms. How about something more discreet? It turns out that if you make the violence of your big bang somewhat less—only a little less—then the mutual gravity operating between the galaxies will get such a secure grip that the galaxies will slow down to a halt, and will thereafter be brought together in a big crunch. Moreover, this will happen in less time than the 13.7 billion years it took for us humans to appear on the scene in the actual universe. So, turn the wick down, and you will get no intelligent life.
All right, you might say, I'll turn the wick up a little. I'll make my big bang more violent than the actual one. What happens now is that the gases come out of the big bang so fast that they do not have time to collect together to form embryo stars before they are dispersed into the depths of space. Since there are no stars, you get no life. In fact, it turns out that as far as the big bang's violence is concerned, the window of opportunity is exceedingly narrow. If you are to get life in your universe, the thrust must be just right—and that is what our actual universe has managed to do.
The next point to consider is the force of gravity. How strong will it be in your imaginary universe? If you make it a little weaker than it actually is, you will collect gas together after the big bang. It will squash down, but there will not be enough of it to produce a temperature rise sufficient to light the nuclear fires. No stars, no life.
On the other hand, you must be careful not to have your gravity too strong. If it is, you will get only very massive types of stars. These burn exceedingly fast and last for only 1 million years. For evolution to produce intelligent life on a nearby planet, you must have a steady source of energy for 5,000 million years; you need a medium-sized star like the sun. Indeed, when you come to think of it, the sun is a remarkable phenomenon. After all, what is a star? It is a nuclear bomb going off slowly. Have you any idea how difficult that is to achieve? The amazing thing is that the sun manages this. The secret is the way the force of gravity in the sun conspires to feed the new fuel into the nuclear furnace at the center of the star. It does so at just the right rate for the nuclear fires (governed by the nuclear force, an entirely different force from that of gravity) to consume it at a steady rate extending over a period of 10 billion years.
So, in order for there to be life, the force of gravity—like the thrust of the big bang—must lie within a very narrow range of possible values. And the gravity of the actual universe does just that.
Next, you must turn your attention to the materials from which you wish to build the bodies of living creatures. This is no small matter. After all, what have you got coming from your big bang? The two lightest gases—hydrogen and helium—and precious little besides. And it has to be that way. Remember, we need a violent big bang to stop the universe from collapsing back in on itself prematurely. And because of that violence, only the lightest nuclei could survive the collisions occurring at that time, anything bigger getting smashed up again soon after its formation.
But you cannot make interesting objects like human bodies out of just hydrogen and helium. So the extra nuclei—those that go to making up the 92 different elements found on Earth—must be manufactured somehow after the big bang. That's where the stars have another important role to play. Not only do they provide a steady source of warmth to energize the processes of evolution, but they also first serve as furnaces for fusing light nuclei into the heavy ones that will later be needed for producing the bodies of the evolving creatures.
But this process is far from straightforward. Perhaps the most important atom in the making of life is carbon. In a sense, it is an especially "sticky" kind of atom, very good at cementing together the large molecules of biological interest. But forming a nucleus of carbon is by no means easy. Essentially, it consists of fusing three helium nuclei together—which is as unlikely as having three moving snooker balls collide simultaneously. It involves something called a "nuclear resonance," and the occurrence of this resonance is so highly fortuitous that its discoverer, one-time atheist Fred Hoyle, was moved to declare that "a commonsense interpretation of the facts suggests that a superintellect has monkeyed with the physics."
So, we have our precious carbon. A collision between some of these carbon nuclei and further helium nuclei yields oxygen—another vital ingredient for life—and so on. Thus, you must be sure to incorporate a fortuitous nuclear resonance in your imaginary universe.
Does this mean that the stage is now set for evolution to take over and convert these raw materials into human beings?
Not so. You have your materials, but where are they? They are in the center of a star at a temperature of about 10 million degrees. Hardly an environment conducive to life. The materials have to be got out. But how?
What happens in the actual universe is that a proportion of the newly synthesized material is ejected by supernova explosions. These occur when massive stars—several times the mass of our sun—run out of fuel. They suddenly collapse in on themselves. But that raises a problem. How can an implosion produce and explosion? This was a conundrum that exercised the minds of astrophysicists for many years.
The mechanism turned out to be the strangest imaginable. The material is blasted out by neutrinos. Neutrinos are famous for hardly ever interacting with anything. One could pass a neutrino through the center of the Earth to Australia 100 billion times before it had a 50:50 chance of hitting anything. Neutrinos are incredibly slippery. How fortunate they were not any more slippery than they are.
There are many other conditions that had to be satisfied in order for there to be intelligent life anywhere within the universe. The sum total of these "coincidences" goes under the name "the anthropic principle."
We are faced with the simple fact that the universe, far from being hostile to life as Weinberg would have us believe, has seemingly bent over backward to accommodate life. As the physicist Freeman Dyson has put it, "The universe knew we were coming."
The mysterious appropriateness of the universe for the evolution of life is something that calls for explanation. There are two main possibilities.
The first is to assert that our universe is not alone. There are a great many universes—perhaps an infinite number of them—and they are all run on different lines with their own laws of nature. The vast majority of them have no life in them because one or other of the conditions were not met. In a few, perhaps in only the one, all the conditions happen by chance to be satisfied and life was able to get a hold. The probability of a universe being of this type is small, but because there are so many attempts, it is no longer surprising that it should have happened. We, being a form of life ourselves, must of course find ourselves in one of these freak universes.
This is a suggestion that has been put forward by some scientists, but that does not make it a scientific explanation. For one thing, the other universes are not part of our universe and so, by definition, cannot be contacted. There is no way to prove or disprove their existence.
The second alternative is simply to accept that the universe is a put-up job; it was designed for life, and the designer is God. Now, one always gets a little bit worried over arguments in favor of the existence of God based on "design." The original argument from design held that everything about our bodies, and those of other animals, is so beautifully fitted to fulfill its function that it must have been designed that way—the designer being God—and therefore you must believe in God. The rug was pulled from under that argument by Darwin's theory of evolution by natural selection— at least in terms of it being a knockdown proof of God's existence, one aimed at convincing the skeptic.
So it is that I would urge caution on those religious believers tempted to make too much of this new argument from design, this time based on physics and cosmology. One can neither prove nor disprove God on the basis of such reasoning. All one can say is that if one already believes in God on other grounds—say, on the basis of religious experience—then the simplest explanation might be in terms of a Designer God. For religious believers, such an explanation introduces no fresh assumptions over and above what one already accepts as the explanation of other features of one's life.
Not that the alternative suggestion, the many-universes argument, is necessarily to be regarded as an atheistic theory. Certainly, it will be the theory favored by atheists. But it could well be that the God who used evolution by natural selection as the means for making intelligent creatures like ourselves (and a whole host of other interesting animals along the way) might well have used the same scatter-gun approach to make not only our life-friendly universe, but a whole host of other interesting universes—universes that carry no life, but could nevertheless be appreciated by God.

Russell Stannard appears with Sir Martin Rees, Leonard Susskind, Alexander Vilenkin, Lee Smolin, and Roger Penrose in "Is the Universe Fine-Tuned for Life and Mind?" the 35th episode in the Closer to Truth: Cosmos, Consciousness, God TV series. The series airs on PBS World (often Thursdays, twice) and many other PBS and noncommercial stations. Every Friday, participants discuss a recent episode.


V. V. Raman said...

Is the Universe fine-tuned for life?
The answer to this question will depend on what one means by the significant terms used in the question.
First the universe. We live in the only universe we know. It is entirely possible – and some theories in physics make this a not implausible possibility – that there are several other universes, There may or may not be any life in many of them. So there is nothing unique in the phenomenon of life to warrant a universe that is specially intended to make life a possibility in a remote niche of its stupendously vast stretch.
Next is fine-tuned. The implication is that conditions and parameters that could be arbitrarily arranged have been given optimal values for the attainment of a specific goal. Indeed, if the initial assignment of values had been different ever so slightly, the intended goal or current situation would and could not have been achieved. Note that the verb is used in the passive voice, but the customary by X has been omitted. That is to say, one leaves open the question: fine-tuned by whom? Perhaps the implication is that it was by an intelligent designer, but this is not a phrase one dares to use in scientific discussion these days. This is also a reason why most hard-core atheist physicists and biologists shudder to contemplate this sort of anthropic or biopic principle.
The third important word is life. That life is a remarkable property of agglomerations of inert matter on our planet is undoubtedly a perplexing situation. We know that life emerged on our planet because of the external conditions of temperature and atmospheric pressure for a sufficiently long time period of time, and the abundant availability of certain elements and compounds. Unique as life seems to be on our solar system, one can also imagine other entities in the universe that are unique to some planets and satellites: volcanoes, atmosphere, water/ice, common salt, and clay. Or again, orbiting planets and comets may be unique to some stars. On the basis of these could one argue, for example, that the universe was fine-tuned for rings around Saturn or planets with satellites?
In sum, then, the question cannot be answered with a simple yes or a no, although in probabilistic and cosmic history terms it seems highly unlikely that parameters were fine-tuned for such a late and fleeting event that was to occur several billions of years after the big bang genesis.
But the simplistic answer to the question could be, of course yes. Otherwise how could life have arisen at all?

V. V. Raman
May 9, 2009