Does the Past Hypothesis Need an Explanation?
There is a very nice interview with Craig Callender about philosophy of physics and metaphysics at 3ammagazine.
An excerpt from the interview is below. Craig brings up the question of whether the low entropy condition of the universe- the “past hypothesis” PH- requires explanation in that without an explanation of the PH a fundamental theory is deeply incomplete. He is skeptical that the PH “cries out” for an explanation any more than any apparently fundamental law does and suggests that it may be a fundamental law. I am with Craig because the claim (made for example by Penrose) that the low entropy condition is very unlikely and so demands an explanation already assumes that it is not a law and also since I think that on David Lewis’ BS account of laws (properly understood) it is plausible that the PH is lawful; that it is a component of the ideal best theory (true theory that best maximizes simplicity, informativeness etc.) I would be interested in what others think about this or the other issues that come up in the interview. Let’s see where the conversation goes.
“Philosophers are raised reading Socrates, who tried to be a gadfly to conventional wisdom. Here I’m just trying to be a similar kind of pest to a prevailing opinion in physics. Scores and scores of our best physicists say that one of the great unresolved problems of physics is that it doesn’t explain the initial low entropy state of the universe. I want to express some healthy skepticism about this claim.
At least two thoughts motivate this skepticism. First, suppose we judge the constraint on initial conditions to be lawlike. (I think that there are some powerful arguments for this.) Then all the universes that don’t begin in a low entropy state are, strictly speaking, unphysical and have zero probability. The initial state is then hardly monstrously unlikely (hence demanding explanation), but rather has probability one!
Second, won’t the problem just creep up on you again? The new theory that explains the initial state of the universe will have unexplained explainers in it too. Every theory does. Then presumably one of the great unsolved problems of the new physics will be to explain those unexplained explainers. How deep in unobserved physics do we go before we say enough?”