Sunday, June 03, 2007

Why do birds sing?

Darling, you and I know the reason why The summer sky is blue, And we know why birds in the trees Sing melodies too.

Songwriter Meredith Willson, who wrote these lyrics, thought he knew why the sky is blue and birds sing. Nobel-prizewinning physicist Steven Weinberg thinks he knows too, and tells us in his book Dreams of a Final Theory.

The sky is blue because air molecules scatter short-wavelength blue light more effectively than other colors of the spectrum. The singing of birds is explained by molecular DNA. At an even deeper level, all of this molecular stuff can be reduced to quantum physics. Behind quantum physics are a few primal laws we have just begun to glimpse. Ultimately, says Weinberg, everything will be explained by a "final theory" of stunning simplicity, the glittering point where all lines of explanation converge.

The philosophy Weinberg is advocating is called reductionism: We understand nature best by breaking it down into its fundamental parts and actions. Biology is chemistry, chemistry is physics, physics is elementary particle physics, and elementary particle physics is (for the time being) the bottom of the ladder.

He writes: "Reductionism is not a guideline for research programs, but an attitude toward nature itself. It is nothing more or less than the perception that scientific principles are the way they are because of deeper scientific principles (and, in some cases, historical accidents), and that all these principles can be traced to one simple set of connected laws."

Weinberg's brand of reductionism has a nasty, inhuman odor about it. The idea that we are just a bunch of elementary particles bouncing about in the void is chilling and impersonal. If there is a meaning to the world, we would like it to be something more than whatever it is that elementary particle physicists will discover with their giant particle accelerators.

What we are looking for, in other words, is something more akin to blue summer skies and bird songs and you and I.

And to be fair, even Weinberg waffles. He calls his chapter on all of this "Two Cheers for Reductionism." He admits "historical accidents" into his definition. He allows that the present preeminence of elementary particle physics may be temporary. But at heart he's a true believing reductionist. His world view may be chilling and impersonal, but he insists it must be accepted, not because we like it, but because that's the way the world works. He believes elementary particle physicists have every right to claim their discipline is more fundamental than other branches of science, because it is. Period.

I first wrote about this when Weinberg's book was published back in 1992. And I took Weinberg to task. Reductionism is not science, I wrote. It's not even philosophy. It's a matter of faith, pure and simple, and the person who believes that love, music, blue skies, and the melodies of birds cannot, even in principle, be reduced to elementary particle physics has as much or as little basis for belief as the reductionist. Reductionism has been a successful guideline for research, I said, but as an attitude toward nature it's a flop.

At the time, I was impressed by developments that promised more holistic ways to understand the world. The advent of cheap and capacious computer power. The holistic mathematics of cellular automata and chaos theory. The work of people like Stuart Kauffman at the Santa Fe Institute. And so on. A new non-reductionist sort of science seemed to loom on the horizon.

Fifteen years later, that promise has little to show for it. I just looked through a few recent issue of Science and Nature: Every report is essentially reductionistic. Reduction remains far and away the most successful way of doing science. Whether this indicates something about the way the world works, or simply the present limitations of human knowing remains to be seen.

In 1993, I wrote: "By the end of the next century we might look back on reductionist theories of physics as hopelessly naive. And if we do, we shall certainly remark upon the hubris of 20th century physicists who thought a final theory was within our grasp."

Well, a little hubris may not be a bad thing for a scientist. Anyone who would attempt to explain the universe must possess some measure of arrogance. The important thing is to not let hubris get out of control. Here's my scientific "religion," which like Weinberg's is a matter of faith: No theory conceived by the human mind will ever be final. The universe is vast, marvelous, and deep beyond our wildest imagining -- its horizons will forever recede before our advance. All dreams of finality are futile. Period.

For the time being, reductionism reigns triumphant. You and I and Meredith Willson know there is more to a blue summer sky than is contained in Rayleigh's equation for the scattering of light, and more to singing birds than a four-letter code in the DNA. Which is why we need poets and songwriters. But concede this to Weinberg: Thanks to reductionist science, we know a hellava lot more about birds and blue skies than we used to.

Further Reading

Steven Weinberg, Dreams of a Final Theory (1992), is available from Amazon.

Nature's Imagination (1995), edited by John Cornwell, and with articles by Roger Penrose, Gerald Edelman, Freeman Dyson, and others, was one of those books that promised a more holistic science. It is out of print.

Discuss this essay and more over on the Science Musings Blog.