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Based on all we currently know about fundamental physics and cosmology, the most logically consistent and parsimonious picture of the universe as we know it is a natural one, with no sign of design or purposeful creation provided by scientific observations. --Victor Stenger
If things were different, things would not be the way things are. --Bob Park
The odds against us were astronomical. -- George Will
The anthropic principle is the belief that it is virtually impossible that a number of factors in the early universe, which had to be coordinated in order to produce a universe capable of sustaining advanced life forms, could have happened by chance. This belief is taken by some as good evidence that this universe was probably created by a very powerful and intelligent being (like the god of Abraham). If the mass of the universe and the strengths of the four basic forces (electromagnetism, gravitation, and the strong and weak nuclear forces) were different or weren't "fine-tuned" to work together the way they do, the universe as we know it would not exist. A delicate balance of physical constants is "necessary for carbon and other chemical elements beyond lithium in the periodic table to be cooked in stars."* In short, a lot of things had to happen together for us to exist (the so-called "anthropic coincidences"). Some physicists find it odd, apparently, that we exist only at a time in the history of the universe when we could exist. These same physicists do not find it odd, apparently, that most of the universe that we know is inhospitable to life. Some might wonder: If everything is so fine-tuned for life, how come the rest of the universe isn't teeming with life?
Physicist Victor Stenger summarizes the anthropic principle this way:
... earthly life is so sensitive to the values of the fundamental physical constants and properties of its environment that even the tiniest changes to any of these would mean that life as we see it around us would not exist. This is said to reveal a universe in which the fundamental physical constants of nature are exquisitely fine-tuned and delicately balanced for the production of life. As the argument goes, the chance that any initially random set of constants would correspond to the set of values they happen to have in our universe is very small; thus this precise balancing act is exceedingly unlikely to be the result of mindless chance. Rather, an intelligent, purposeful, and indeed personal Creator probably made things the way they are. (For a good overview of the specifics of the alleged fine-tuning, see Stenger's article "The Anthropic Coincidences: A Natural Explanation.")
We wouldn't exist and be conscious of the world around us if the world around us wasn't compatible with our existence. Or, as physicist Bob Park put it: "If things were different, things would not be the way things are."
Another way of framing it is popular among those who hope science will quit sledge-hammering their faith:
Physicists have stumbled on signs that the cosmos is custom-made for life and consciousness. It turns out that if the constants of nature - unchanging numbers like the strength of gravity, the charge of an electron and the mass of a proton - were the tiniest bit different, then atoms would not hold together, stars would not burn and life would never have made an appearance. (Sharon Begley, Newsweek, July 1998.)
Yes, if things had been different, we wouldn't be here. But they weren't and we are. Anyway, for all I know, if a few neurotransmitters went north instead of south in my brain, I'd be proclaiming that physics proves Muhammad is the god of Abraham's prophet. But they didn't and I'm not. Still, if things were different, they'd be different. Anyway, the improbability of something that's already happened is a bit misleading and, ultimately, meaningless. As John Allen Paulos says:
... rarity by itself shouldn't necessarily be evidence of anything. When one is dealt a bridge hand of thirteen cards, the probability of being dealt that particular hand is less than one in 600 billion. Still, it would be absurd for someone to be dealt a hand, examine it carefully, calculate that the probability of getting it is less than one in 600 billion, and then conclude that he must not have been dealt that very hand because it is so very improbable. (Innumeracy: Mathematical Illiteracy and its Consequences)
It would be even more absurd to declare that a miracle must have happened and that an intelligent force of supernatural dimensions must be at work behind every bridge hand.
The expression 'anthropic principle' was coined by physicist Brandon Carter. There are several variations of the anthropic principle, including a version that seems identical to classical philosophical idealism: the universe only exists because we perceive it.* This is true, and extremely profound and trivial at the same time.
Since we don't have anything to compare our universe to, however, it seems presumptuous to assert that we know the statistical improbability of the factors occurring that were necessary for it to exist. What if there are many universes? Ours could be quite common and not require a Fine-Tuner of any sort. Or, ours could be one of a zillion billion universes of every make imaginable, many of which produce outcomes similar to ours from very different initial conditions. Who knows? Also, it doesn't seem to imply anything about a designer to point out that we exist at the only time in the history of the universe when we could perceive the universe and if a number of factors had been different we would not be here now. Nothing is implied about a designer by the fact that billions of years ago we could not have existed and the universe was as much a pipe dream as we were then. Nor does anything seem to be implied by the fact that in a few billion years this planet will start to die and in a few billion years after that there will be no possibility of life here. However, to note this is to guarantee that one will not be awarded the Templeton Prize. On the other hand, to argue for some variation of the anthropic principle almost guarantees a physicist the prize, "the largest prize for intellectual accomplishment in existence."*
Can you imagine the number of conditional probabilities that had to occur for a guy from rural Tennessee like John Templeton (1912-2008) to get into Yale and Oxford, make billions in developing mutual funds, and find scientists willing to take a ton of money from him for trying to prove that science supports a world of spirits despite the overwhelming evidence to the contrary? Yet, despite the unbelievable odds against such a thing happening, it happened. And it doesn't seem odd at all that there should be some connection between the anthropic principle and the philanthropic principle: if you have enough money, you can buy just about anything.
anthropic-principle.com (Nick Bostrom, Faculty of Philosophy, Oxford University)