Tuesday, June 28, 2005

Fine tuning: a new result

Cosmological ID is based on two facts:
  1. The fine-tuning of the universe
  2. The uniqueness of the universe
I have argued many times that cosmological ID is falsifiable, by disproving either of these points.

How does one disprove fine tuning? It is not in the way that is commonly believed. Take a simple example of fine-tuning: the strength of the strong nuclear force. If it were about two percent weaker, life-essential heavy elements would be unstable. If it were about two percent stronger, then quarks would not form into protons, so there'd be no ordinary matter at all. Two percent either way, and there would be no life.

Does this fine tuning rely on the fact that we do not have a fundamental theory regarding the strength of the nuclear force? No, not at all. If it did, then it would be legitimately subject to a God-of-the-gaps criticism. A more fundamental theory that calculated from first principles the strength of the force would not save the day for those who seek to discredit fine tuning. 1 A theory that predicts the strength of the nuclear force says nothing about the sensitivity of a habitable universe to the calculated value. We would still have the same fine tuning "problem." If anything, the appearance of design would be strengthened, for no longer would the "just right" value seem to be the result of a lucky accident, but rather the inevitable result of a highly designed first-principle law.

No, to disprove fine-tuning you have to show that the sensitivity to small changes in physical constants is an illusion. This will be exceedingly difficult. The disastrous effects of varying the strengths of the fundamental forces, the expansion rate of the universe, Planck's constant, etc. are straightforward and non-controversial.

And today, via Hugh Ross's daily reason, we have another example of fine-tuning, and example of a type which would still survive an unlikely dismantling of the sensitivity of life to the values of the physical constants.

A little background:

The moon is essential for life for a variety of reasons including the cleansing effects of the tides and the stability of the earths tilt and rotation.

The moon is big enough to provide these benefits, but if it were slightly bigger it would be unstable. 2

The moon probably formed as a result of a collision of a Mars-sized object with the earth, when our planet was about 250 million years old. This collision blasted away a poisonous atmosphere and left the earth with a "just right" mass such that its gravity can retain water vapor but not the slightly lighter (and toxic) ammonia and methane.

But where did this planetoid come from, and why didn't it obliterate the earth? Here is the abstract of a recent paper that tackles this question:
The current standard theory of the origin of the Moon is that Earth was hit by a giant impactor the size of Mars, causing ejection of iron-poor impactor mantle debris that coalesced to form the Moon. But where did this Mars-sized impactor come from? Isotopic evidence suggests that it came from 1 AU radius in the solar nebula, and computer simulations are consistent with its approaching Earth on a zero-energy parabolic trajectory. But how could such a large object form in the disk of planetesimals at 1 AU without colliding with Earth early on, before having a chance to grow large or before its or Earth's iron core had formed? We propose that the giant impactor could have formed in a stable orbit among debris at Earth's L4 (or L5) Lagrange point. We show that such a configuration is stable, even for a Mars-sized impactor. It could grow gradually by accretion at L4 (or L5), but eventually gravitational interactions with other growing planetesimals could kick it out into a chaotic creeping orbit, which we show would likely cause it to hit Earth on a zero-energy parabolic trajectory. We argue that this scenario is possible and should be further studied. (Belbruno and Gott, The Astronomical Journal, 129, 1724-1745, 2005)

Now, I have no clue whether this hypothesis will stand the test of time. But what is impressive about it is how "finely tuned" their hypothesis is—that a planetoid of just the right size could have struck the earth (at just the right time) with just the right type of glancing blow—it requires that the planetoid formed at one of the earth's Lagrange points. (Lagrange discovered five special points where a third, smaller mass can orbit at a fixed distance from the sun and earth. These are the only positions where the gravitational pull of the earth and sun precisely equals the centripetal force required for the smaller mass to rotate with them.)

If this result stands, it is a big "W" for team Cosmological ID.

1 More fundamental theories would effect the (in my opinion ill-advised) calculations of the probability of the universe, such as those made by Hugh Ross. That is why I do not include those calculations as a "plank" of cosmological ID. A hypothetical theory of everything would, in some sense, leave us with a probability of unity for a habitable universe. It would however, have no effect on the validity of the fine-tuning argument.
2 Dave Waltham, Astrobiology 4, No. 4: 460-468 (2004)

No comments:

Post a Comment