If that's metaphysics, then every famous physicist--Newton to Einstein to Feynmann--has been a strong believer in the power of metaphysics.

Fine, but that doesn't make the "power " any more or less valid, only that it seems to be useful thus far.

If I see a coin come up heads twenty times in a row, I'm going to use the power of induction to predict that the coin is biased towards heads. Induction tells me that, the more something has happened in the past, it's more likely to continue to do so in the future. I trust induction because induction has worked for me before.

Somewhere out there in mind-space is someone who believes in anti-induction: each coin flip of heads convinces him that the coin is biased toward tails. Anti-induction tells him that, the more something has happened in the past, the less likely it is to do so in the future. If asked why he trusts anti-induction, he exclaims: "Because it's never worked before!"

That said, just because these two minds are possible in mind-space, doesn't mean that they're equally likely to form naturally in any given physical universe. In fact, to our intuition, one of the two seems particularly unlikely...

Credit to http://lesswrong.com/lw/t9/no_license_to_be_human/

Well, then this just basically becomes a philosophical argument about the justification for empiricism/inductive-reasoning. Can we axiomatically prove that just because the sun has risen in the morning for the last 10,000 mornings that it will do so tomorrow? No. Neither can be sure that just because every single major advance in physics has come because of simplification/beauty that the next one will come the same way.

But you'd be a fool to bet otherwise.

Well, I certainly wouldn't want to be a fool. I might be of course, especially compared to the many people I know who are smarter than myself.

I think though that your argument is basically an 'appeal to ridicule' fallacy. You are making it sound like my statement is the philosophical equivalent of 'we can't be sure the sun will rise tomorrow'. It isn't, it is simple the statement that the current zoo of particles may well all be fundamental, with no 'simpler' theory underlying them.

Secondly, I think your statement that 'every single major advance in physics' has been a simplification is debatable.

Thirdly, extrapolating from that that every new advance will be found using the same heuristic is also debatable. If there really is to be a scientific breakthrough of the magnitude of a Newton, it seems likely (almost by definition) that it will be from an unexpected avenue of thought - seeing that the expected ones have been well researched and haven't been all that productive.

I guess it makes sense to bet on a unifying theory if you are a career particle physicist. There's a Nobel prize in it. It doesn't make sense to bet on the opposite notion, since there are probably no breakthroughs that way.

I do think your statement is the philosophical equivalent of 'we can't be sure the sun will rise tomorrow', except that it differs by degree. (The sun has risen thousands of times in my personal experience, and bazillions of times in the experience of humans, while only a handful of fundamental physics discoveries have been made.) In either case, it's a question of justifying the claim that "In situations of type A, X has always been true in the past. Therefore, in situations of type A in the future, X will be true".

Likewise your simple statement that "the current zoo of particles may well all be fundamental, with no 'simpler' theory underlying them." is analogous to "the sun will collapse into a black hole tomorrow". Again, just a difference of degree.

[I should stress here that the justification for empiricism is an age-old philosophical problem which isn't easy to understand, much less solve. However, I think that a proper understanding of the history of physics gives very convincing (though maybe not the-sun-will-rise convincing) evidence that simplicity and beauty will be found at the bottom of the particle zoo.]

I don't understand what the true statement

>If there really is to be a scientific breakthrough of the magnitude of a Newton, it seems likely (almost by definition) that it will be from an unexpected avenue of thought - seeing that the expected ones have been well researched and haven't been all that productive.

has to do with our current discussion.

Lastly, (basically) no career particle physicist think that any Nobel prizes will be awarded for a unifying theory in their lifetime. (See, for instance, http://www.math.columbia.edu/~woit/wordpress/?p=2998). Perhaps, if we're lucky, there will be a somewhat simplifying theory (which gets a Nobel prize) but that certainly couldn't come from the dominant research avenue, string theory.

It's not just metaphysics though, right? More complex models have more moving parts and require more energy and information to specify. I feel like, in a wholly qualitative but empirically guided fashion, there is a natural savings to simplicity.

Well, I agree with that, it's been a fruitful heuristic, but it doesn't need to hold in every case.

No you're totally right, there's nothing that says it has to be that way. But since it seems that all of the elementary particles coalesced out of a relatively homogenous energy field after the Big Bang, it doesn't seem unlikely that all of the particles could be explained by tiny permutations in an underlying universal field.