[hugh_]

It's actually shocking how little reason there is to believe in a single set of underlying natural laws when you consider these issues with an open mind.

What's the alternative to a single set of natural laws?

Perhaps one set of natural laws that applies around here, and a slightly different set that applies in Andromeda, but only on Tuesdays? But surely the two sets, plus the Andromeda/Tuesdays restriction, put together form one slightly more complicated set of physical laws?

Perhaps an infinite set of subtly different natural laws which apply at different points in space and time? But that's still just one very large set of laws, right?

[foldr]

>What's the alternative to a single set of natural laws?

I take the point that however many natural laws there are, there is a set containing all of them. However, you did delete the important adjective "underlying" when asking your question. Isn't it pretty clear what it would mean for there to be no single set of underlying natural laws? It would mean, for example, that laws of chemistry would not necessarily be reducible to laws of physics, laws of psychology would not necessarily be reducible to laws of biology, etc. etc. You may think that this is wrong, but it's a perfectly intelligible idea.

Cartwright argues that there is no "ultimate", universal set of laws to which all other true laws inevitably reduce. From her point of view, laws are relatively local and specific. She goes through a lot of physical phenomena, particularly involving lasers, and shows that although physicists are able to make very precise predictions, they virtually never make these predictions merely by special-casing general principles. Her argument (which I don't have the space or expertise to summarize here) is that there is consequently no reason to think that the general principles are really true, even though they are fantastically interesting and useful.

Also, you seem to be tacitly assuming that all natural laws are necessarily going to be laws of physics, but that is one of the questions at issue. E.g., are we right to assume that all the laws of chemistry are "in principle" reducible to physics, even though we can never hope to make such a reduction in practice? Perhaps that is just a kind of unjustified faith in the unity of reality.

Anyway, I am sort of on the fence on these issues, but I found her arguments unexpectedly persuasive. It really is surprising how non-stupid the idea of a pluralistic reality is when you look at these questions in detail.

[hugh_]

E.g., are we right to assume that all the laws of chemistry are "in principle" reducible to physics, even though we can never hope to make such a reduction in practice?

Actually, making that reduction in practice is pretty much what I do for a living.

[foldr]

Yes, I'm not suggesting that there's a complete disconnect between physics and chemistry, but we're a long way from having a complete understanding of how all chemical reactions work at the physical level. That is, an actual proof that all known laws of chemistry are mathematical consequences of the laws of physics (without making too many fudges, simplifying approximations, etc. etc.)

This is not in any way intended as a criticism of physicists or chemists, in case it comes across like that. They're both incredibly successful at what they do.

Just googling around, this paper gives quite a nice overview of what sensible scepticism about the possibility of reduction looks like: http://www.springerlink.com/content/v05g613468p6xk17/