Just How Precise
Is the Balancing Act
That Maintains Life?
December 1, 2006; Page B1
When you see the long list of everything that has to be just right for atoms, galaxies, planets and life to emerge in the universe, it's hard to avoid the conclusion that the fix was in. If the laws of physics and the fundamental constants of nature were the slightest bit different, the world would not exist, at least in the form we see it.
Such is the premise of the "anthropic principle." It asserts that the values of physical constants, such as the strength of gravity, are what they are because if they had other values there wouldn't be any scientists to marvel at it all.
If that seems like circular reasoning, well, so it seems to many astronomers and physicists. They recognize that nature has properties conducive to life, obviously, but still view the anthropic principle as a feeble answer to an age-old question, namely, whether a universe could exist if the laws of physics were different. (Or, as Einstein quipped, whether God had any choice in how He created the world.) Despite their discomfort with what felt like throwing in the towel, critics of anthropic reasoning have made little headway in coming up with a better explanation for why nature has properties so conducive to the emergence of life.
Some new studies may change that.
To get a sense of the challenge, consider how fine-tuned nature is. If gravity were stronger, then in the early universe hot spots of gas would have collapsed into black holes, rather than forming life-giving stars. If gravity were weaker, then our sun wouldn't have been able to hang on to its retinue of planets, which would spin off into space. Also bad for life. If the ghostly particles called neutrinos interacted differently, atoms heavier than helium wouldn't have blasted out of some exploding supernovas. A universe without carbon, oxygen and nitrogen isn't exactly lively.
Many of these quantities have to be precisely what they are for life to exist. Does that mean we're just really, really lucky?
Or maybe we're in this Goldilocks universe -- where nature's constants are not too big and not too small -- because "the" universe is actually only one neighborhood in a metropolis teeming with them. With so many universes, probability says that one will have life-giving values, so hey, why not ours? This idea has gotten a boost from string theory, which says there are oodles (10 raised to the 500th or so power) of universes. It could also be that our views about life are too parochial, and that weird life forms can exist in universes with no galaxies, shining stars or other things we assume life needs.
Maybe the anthropic principle is right: The universe is tuned for life because if it were not, no one would be here to notice.
For years, many scientists viewed anthropic reasoning as "the last refuge of scoundrels," says cosmologist Lawrence Krauss of Case Western Reserve University. "It was what you resorted to when you couldn't think of other explanations. But science has always tried to explain why the universe is the way it is. With the anthropic principle you're saying you can't explain why the fundamental constants have the values they do. It's giving up before you really get started."
That philosophical objection now has scientific company. Take the anthropic claim that atomic nuclei must have certain precise properties for helium to fuse into carbon and make our sun burn, and if they didn't the sun would fizzle and life wouldn't exist.
We gave up too soon, says Prof. Krauss, who makes this case in his book "Hiding in the Mirror," just out in paperback. It turns out that this property of atomic nuclei reflects something more basic, namely the strength and nature of the electromagnetic force. So the special traits of helium that let our sun shine do have a more fundamental explanation. There is no need to say "they have to be this way or we wouldn't be here to notice," as the anthropic camp does.
The anthropic principle was further undermined when scientists calculated what would happen if the universe lost one of its forces. There are four: gravity and electromagnetism, plus the strong force and weak force that act only at the subatomic level. The physicists erased the weak force and adjusted other physical parameters (all done mathematically), they reported in August in Physical Review D. Their calculations showed that the resulting pseudouniverse still made atoms, galaxies and stars that burned and cooked up elements like those in living beings, says Graham Kribs of the University of Oregon, Eugene.
This was surprising. It had been thought that in a "weakless universe" chemistry and nuclear physics would be so different from our real universe's that stars would not ignite and life (as we know it) would never emerge.
"But you get a universe that looks a lot like ours," says Prof. Kribs. The approach might work for other supposedly basic parameters of physics: although changing only one yields an uninhabitable cosmos, maybe you can change a few at once and, he says, "still get a universe with galaxies, stars and observers. I think it shows that we've been too parochial in our ideas about how to get a habitable universe."
If so, that lets out a lot of air from the anthropic balloon. Yes, our universe is fine-tuned for life, but other settings on the dial could also produce a cosmos of galaxies, stars and atoms -- and beings who wonder at it all.
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