Wednesday, September 30, 2009

Summary of meeting last Saturday part 3 (of 3)

In my two previous posts, I introduced the anthropic principle, pointing out that, while it is non-controversial that the universe appears designed, the philosophical implications are. I mentioned that one of the biggest philosophical "loopholes" to the apparent design in the universe is something called the "selection effect", and I described the fallacies associated with it.

Before I go on, I must apologize, because I didn't give the selection effect point of view enough credit. There have been many attempts to formalize the selection effect argument in terms of conditional probabilities and Bayesian inference (for those math-oriented people out there), and this is a good thing. Critics of theistic inferences from the anthropic principle correctly point out that it isn't enough to simply say "it looks improbable, therefore God must have done it." However, even if you do carry out the calculations in a probabilistically careful manner, you do arrive at theistic interpretations. In addition, even in the mathematical arguments from the critics of theistic inferences, the selection effect is nothing more than an irrelevant red herring.

OK, sorry. I had to get that off my chest. You are welcome to ignore that paragraph if you want. On the other hand, if you wish to know more about it, I am happy to correspond with you, but I don't think I'll take up any more room about it here.

Moving on, I wrapped up the meeting discussing actual examples of fine tuning. The first, and perhaps simplest case of fine tuning to describe is the mass density of the universe. The universe is expanding, but gravity acts as a brake on the expansion. Early on in the universe's life, the rate of expansion had to be just right in order for life to exist today. If it was expanding too fast, the matter in the universe would have been to disperse in order to form galaxies, stars, and planets. On the other hand, if the expansion had been to slow, matter would have clumped up so much as to only produce things like black holes. In other words, there had to be just the right amount of matter in the universe to control the expansion rate so exquisitely that if even a "dime's worth" of mass had been added or subtracted from the universe, no life would have been possible. That's fine-tuning to one part in 10^60. (ie, more remote that winning the lottery eight times in a row).

However, the most extreme case of fine tuning known today -- one part in 10^120 -- has to do with something very mysterious called "dark energy". This phenomenon acts as sort-of an anti-gravity, causing the universe to expand faster! (You can imagine the surprise of astrophysicists when, in the late 1990's, more and more evidence accumulated that the universe's expansion is indeed accelerating.) I must admit I have no way to explain to you why dark energy -- sometimes known as the space energy density, and represented by a number called the "cosmological constant" -- is finely tuned, or what that means, but here are some quotes from scientific papers that lament this fine-tuning (and are unsettled about the possible theistic implications therein):
  • The "cosmological constant...would involve the most extreme fine-tuning problem known in physics, and for this reason many particle physicists would prefer any mechanism that would drive the cosmological constant to be exactly zero today." -- Lawrence Krauss, 1998
  • "This type of universe [one with such a cosmological constant], however, seems to require a degree of fine tuning of the initial conditions that is in apparent conflict with 'common wisdom'." -- Zehavi and Dekel, 1999
  • "If [the existence of such a cosmological constant] should become an established fact, we are also confronted with a disturbing cosmic coincidence problem. " -- Straumann, 1999
Keep in mind that these are not commentaries or popular articles, but quotes from papers by experts published in quite prestigious scientific journals.

Wow, this post got too long. Before I go, let me say one more thing. It was a really good discussion, and outside of the material I summarized here, we talked about cool topics like life on other planets (which I am skeptical of, but not in a big way), and the multiverse (which I believe is worse than speculation-squared).

Until next time...