While biological ID isn't worth much, there's a curious idea from physics that has even the reputable scientists wondering. It has to do with the number of parameters (by some estimates, around thirty of them) in the Standard Model of Particle Physics and the Theories of Relativity that don't appear to be derivable from first principles; in other words, we know of no compelling reason why they are the values they are, and those values are only known empirically.
More eye-opening is the fact that for most of them, if they held any other values -- in some cases, off by only a couple of percent either way -- the universe would be uninhabitable.
Here are a few examples:
- The degree of anisotropy (unevenness in density) of the cosmic microwave background radiation. This is thought to reflect the "clumpiness" of matter in the early universe, which amounts to about one part in ten thousand. If it was only a little bigger -- one part in a thousand -- the mutual attraction of those larger clumps of matter would have triggered early gravitational collapse, and the universe would now be composed almost entirely of supermassive black holes. Only a little smaller -- one part in a hundred thousand -- and there would have been insufficient gravitational attraction to form stars, and the universe would be a thin, cold fog of primordial hydrogen and helium.
- The fact that electrons have a spin of one-half, making them fermions. Fermions have an odd property; two can't occupy the same quantum mechanical state, something called the Pauli Exclusion Principle. (Bosons, such as photons, don't have that restriction, and can pass right through one another.) This feature is why electrons exist in orbitals in atoms. If they had integer spin, there would be no such thing as chemistry.
- The masses of the various subatomic particles. To take only one example, if the quarks that make up protons and neutrons were much heavier, the strong nuclear force would all but evaporate -- meaning that the nuclei of atoms would fly apart. (Well, more accurately, they never would have formed in the first place.)
- The value of the fine-structure constant, which is about 1/137 (it's a dimensionless number, so it doesn't matter what units you use). This constant determines, among other things, the relative strength of the electromagnetic and strong nuclear forces. Any larger, and atoms would collapse; any smaller, and they would break apart into their fundamental particles.
- The value of the gravitational constant G. It's about 6.67 x 10^-11 meters cubed per kilogram per second -- i.e., a really tiny number, meaning gravity is an extremely weak force. If G was larger, stars would burn through their hydrogen fuel much faster, and it's doubtful they'd live long enough for planets to have time to evolve intelligent life. If G was smaller, there wouldn't be enough gravitational pull to initiate fusion in the first place. No fusion = no stars.
- The flatness of the universe. While space near massive objects is curved as per the General Theory of Relativity, its overall shape is apparently Euclidean. Its makeup -- around 5% conventional matter and energy, 25% dark matter, and 70% dark energy -- is exactly what you'd need to generate a flat universe.
- The imbalance between matter and antimatter. There appears to be no reason why, at the Big Bang, there weren't exactly equal numbers of matter and antimatter particles created. But in fact -- and fortunately for us -- there was a very slight imbalance favoring matter. The estimate is that there was about one extra unpaired matter particle out of every one hundred million pairs, so when the pairs underwent mutual annihilation, those few extra particles were left over. The survivors became the matter we have today; without that tiny imbalance, the entire universe today would be filled with nothing but photons.
- The cosmological constant -- a repulsive force exerted by space itself (which is the origin of dark energy). This is the most amazing one, because for a long time, physicists thought the cosmological constant was exactly zero; Einstein looked upon his introduction of a nonzero cosmological constant as an inexcusable fudge factor in his equations, and called his attempt to shoehorn it in as his "greatest blunder." In fact, recent studies show that the cosmological constant does exist, but it's so close to zero that it's hard to imagine -- it's about a decimal point, followed by 121 zeroes, followed by a 3 (as expressed in Planck units). But if it was exactly zero, the universe would have collapsed by now -- and any bigger than it is, and the expansion of space would have overwhelmed gravity and torn apart matter completely!
And so on and so forth. The degree of fine-tuning that seems to be required to set all these independent parameters so that the conditions are juuuuuust right for our existence (to borrow a phrase from Baby Bear) strikes a lot of people, even some diehard rationalist physicists, as mighty peculiar. As cosmologist Fred Hoyle put it, "It looks very much as if a super-intellect has monkeyed with physics as well as with chemistry and biology."
The idea that some Master Architect twiddled the knobs on the various constants in physics, setting them exactly as needed for the production of matter and ultimately ourselves, is called the Strong Anthropic Principle. It sets a lot of people's teeth on edge -- it's a little too much like the medieval idea of humanity's centrality in the universe, something that was at the heart of the resistance to Copernicus's heliocentric model. It seems like all science has done since then is to move us farther from the center -- first, the Earth orbits the Sun; then, the stars themselves are suns, and our own Sun is only a smallish and rather ordinary one; then, the Sun and planets aren't central to the galaxy; and finally, our own galaxy is only one of billions.
Now, suddenly, the fine-tuning argument has seemingly thrust us back into a central position. However small a piece of the cosmos we actually represent, was it all set this way for our benefit?
In his book The Cosmic Landscape: String Theory and the Illusion of Intelligent Design, theoretical physicist Leonard Susskind answers this with a resounding "no." His argument, which is sometimes called the Weak Anthropic Principle, looks at the recent advances in string theory, inflation, and cosmology, and suggests that the apparent fine-tuning is because the cosmos we're familiar with is only one pocket universe in a (much) larger "landscape," where the process of dropping into a lower energy state triggers not only expansion, but sets the values of the various physical parameters. Afterward, each of those bubbles is then governed by its own physics. Most would be inhospitable to life; a great many probably don't have atoms heavier than helium. Some probably have very short life spans, collapsing almost immediately after formation. And the models suggest that the number of different possible configurations -- different settings on the knobs, if you will -- might be as many as ten to the five-hundredth power.
That's a one followed by five hundred zeroes.
Susskind suggests that we live in this more-or-less friendly one not because the constants were selected by a deity with us in mind, but because if our universe's constants had any other value, we wouldn't be here to ask the question. It might be extremely unlikely that a universe would have exactly these settings, but if you have that many universes to choose from, they're going to show up that way somewhere.
We only exist because this particular universe is the one that got the values right on the nose.
While I think this makes better sense than the Master Architect idea of the Strong Anthropic Principle -- and I certainly don't want to pretend I could argue the point with a physicist of Susskind's caliber -- I have to admit feeling a twinge of discomfort still. Having all of those parameters line up so perfectly just seems like too much of coincidence to swallow. It does occur to me that in my earlier statement, that the constants aren't derivable from first principles, I should amend that by adding "as far as we understand at the moment." After all, the geocentric model, and a lot of other discredited ideas, were discarded not because they overestimated our importance, but because we got better data and used it to assemble a more accurate theory. It may be that some of these parameters are actually constrained -- they couldn't have any other value than the one they do -- we just haven't figured out why yet.
After all, that's my main criticism of Intelligent Design in biology; it boils down to the argument from incredulity -- I can't imagine how this could have happened, so it must be that God did it.
That said, the best models of physics we now have don't give us any clue of why the thirty-odd free parameters in the Standard Model are what they are, so for now, the Weak Anthropic Principle is the best we can do, at least as far as scientific approaches go. That we live in a Baby Bear universe is no more mysterious than why you find fish in a lake and not in a sand dune. Our hospitable surroundings are merely good fortune -- a lucky break that was not shared in the other ten-to-the-five-hundredth-power universes (minus one) out there in the cosmic landscape.
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