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Comment by foldr | Hacker News Reader

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Some of that sounds a little dogmatic in itself. It's an interesting historical fact that the idea of there being a deep underlying unity in nature was originally a religious one. In a time before there were any examples of really successful science, the idea that the universe might actually be comprehensible to us on a deep level seemed pretty loopy unless you believed that it was deliberately constructed to be intelligible. After all, the universe isn't all that comprehensible to any other form of life on earth -- why should we be so special if we are not in fact special? So in a sense, the idea that science is possible has its roots in a particular sort of religious belief.

Anyway, that is not intended as an argument in favor of religious belief today. But it's worth asking whether any rational justification could have been given in the 13th century for a belief in the deep underlying unity of the universe, before we had available the fruits of the research based on that assumption. I think it would have been far more sensible in those days to believe that the universe is just a complicated place with a lot of different kinds of stuff in it, and a lot of different kinds of principle governing what happens to that stuff.

Interestingly, this sort of pluralistic conception of reality is coming back into fashion in some circles, under the heading of the "dappled universe". Nancy Cartwright's work on these topics is really interesting. (FTR: She is trained as a physicist and has no religious agenda.) 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.

edit: There's a good (somewhat critical) review of one of Cartwright's book's here [doc]: http://personal.lse.ac.uk/CARTWRIG/PDF%20various/Book%20revi...

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?

>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.

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.

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/

However, as you illustrate yourself, it is no longer the 13th century and we have a large amount of evidence to suggest the relationships between things extend further than a simple jumble of complicated and unrelated data. I don't think it's dogmatic to point this out at all, I think it's dogmatic to deny it, needing to roll the clock back over six hundred years to posit a situation where the evidence may indicate otherwise.

Even if that were granted, I'm still not so certain that it makes sense. Humans have been finding laws to apply for much of recorded history. I realise it's quite a long way from the elegance of something like general relativity to the simplicity of something like pythagoras' theorem, but the emergence of the former depended upon the epistemological grounding of the latter.

It was not my intent to make allusions to a unifying great spirit or any such nonsense, merely that for the vast majority of recorded history searching for the patterns and relations in material reality has given humanity most of it's most spectacular successes. To cast this all away and try to parcel everything into microscopic localities which are not thematically related at all and thus discard what can be learned by taking a wider view.

That said, I'll check out the dappled universe idea, I've not come across it before. It amuses me more than a little that this particular concept is being pushed by someone neatly straddling the disciplines of philosophy and physics though, isn't that in itself something of a defense of a broader view?

>we have a large amount of evidence to suggest the relationships between things extend further than a simple jumble of complicated and unrelated data.

Oh yes, of course. But there's a lot of middle ground between a complete jumble and complete unity. I don't think anyone is suggesting that there are no regularities at all, just that the ones that there are may be relatively local and particular. (They're still pretty damn impressive for all that, though.)

I think this is an aesthetic problem in a way. Everyone seems to have a kind of Platonic aesthetic these days -- everything has to be ultimately simple and unified and abstractly beautiful. If you'll excuse a stupid metaphor, it's sort of a question of how you visualize God's office. Does it just have a plain desk with a couple of pens and two equations written neatly on a notepad, or is it a huge jumble of dusty books and papers covering every conceivable topic at every conceivable level of analysis? I think part of the reason for my "conversion" to the dappled view of things was that I started to find the Platonic aesthetic less and less appealing. (Of course, it might be a really bad idea to let aesthetic considerations have this much influence, but maybe that's another topic.)

>It amuses me more than a little that this particular concept is being pushed by someone neatly straddling the disciplines of philosophy and physics though, isn't that in itself something of a defense of a broader view?

I think it's a bad kind of slippery slope argument to go from "there are some interesting connections between some things" (certainly true) to "everything is deeply connected and unified" (plausible, appealing in some ways, but not something a rational person has to believe).

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