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I used to believe that the history of physics gave unwavering evidence that there is always a deep reason for the patterns and phenomena we observe: maybe not f

by Steuard 12y ago

I used to believe that the history of physics gave unwavering evidence that there is always a deep reason for the patterns and phenomena we observe: maybe not for the specifics of everyday life, but certainly for fundamental facts. (Think of how atomic theory made sense of the elements, or how nuclear physics explained how the sun could shine for so long, or how the unification of electricity and magnetism miraculously turned out to explain optics as well.) So I was convinced that we would someday find a fundamental theory that would be able to predict things like the fine structure constant or the charge to mass ratio of the electron. But eventually someone pointed out that before we understood the history and nature of the solar system, natural philosophers looked for similarly deep explanations for the orbits of the planets. Kepler once proposed a deep connection between the (five) gaps between the six known planets and the five platonic solids (see, e.g. http://www.pbs.org/wgbh/nova/blogs/physics/2011/12/beautiful-losers-keplers-harmonic-spheres/ http://www.pbs.org/wgbh/nova/blogs/physics/2011/12/beautiful...), and Bode's law for planetary orbits was widely accepted until Neptune was discovered in the "wrong" place in 1846 (see http://en.wikipedia.org/wiki/Titius%E2%80%93Bode_law http://en.wikipedia.org/wiki/Titius%E2%80%93Bode_law). Today, we understand that there is no reason to expect any particular pattern of planetary orbits: solar systems are a dime a dozen in the galaxy, and their details are accidents of history. So while I don't like the idea, I've gradually come to accept that the "fundamental physical constants" of our universe could conceivably turn out to be just as arbitrary as the ratio of Jupiter's major orbital axis to Saturn's.

placebo 12y ago
Not sure this analogy holds. Although the ratio of Jupiter's and Saturn's major orbital axis might seem arbitrary, given all the prior conditions to the orbit formations, current physics theories perhaps could have theoretically predicted this ratio long before it came to be. In the same way, physicists would like an elegant model that would predict or explain the constants in a way that makes more sense in a larger picture rather than having them as some magic numbers.
- Steuard 12y ago
  Exactly. That's pretty much what multiverse models suggest might be true for "fundamental constants": if you somehow knew the precise conditions of our part of the universe in the moments leading up to our big bang (and the parameters of whatever process triggered it: quantum fluctuations or whatever), you could in principle predict things like the charge to mass ratio of the electron. (E.g. if you knew the precise shape and fluxes of our 6-dimensional Calabi-Yau compactification manifold in string theory, you could work out the low-energy field content and coupling constants of the resulting universe.) [String phenomenology isn't really my field, but I certainly haven't had a lot of luck deriving a unique background from pure theory. I did once think that I'd found a model that predicted the cosmological constant to within an order of magnitude or two, but that obviously didn't pan out.]
rndn 12y ago
That’s the idea of an infinite number of onion layers [1]. What I find intriguing is that if you assume that everything is based on cause and effect, then (I think) you necessarily run into an infinite regress problem (the cause of a cause of a cause …) unless you define some "uncaused cause", or the concept of causation breaks down at some point. [1] https://en.wikipedia.org/wiki/Theory_of_everything#Infinite_number_of_onion_layers https://en.wikipedia.org/wiki/Theory_of_everything#Infinite_...
- JadeNB 12y ago
  > What I find intriguing is that if you assume that everything is based on cause and effect, then (I think) you necessarily run into an infinite regress problem (the cause of a cause of a cause …) unless you define some "uncaused cause", or the concept of causation breaks down at some point. Another possible resolution is a cyclic picture (something like https://en.wikipedia.org/wiki/Cyclic_model https://en.wikipedia.org/wiki/Cyclic_model), in which the cause of the cause of the cause of … may be the original event.
  - rndn 12y ago
    Isn’t that an infinite regress problem?
    - JadeNB 12y ago
      > Isn’t that an infinite regress problem? I can certainly see the sense in which it might be said to be, but I think that's not the sense in which the term is originally meant. I tried to come up with an explanation of why I think they were meaningfully different by an appeal to mathematical analogy, but I'm not sure that it's convincing. Fermat argued as follows: a positive integer solution to `x^4 + y^4 = z^4` could always be converted into a smaller such solution, and you can't produce ever-smaller positive integers forever, so there weren't any such solutions in the first place. I'd say that this is clearly an infinite regress (though it was actually called infinite descent). On the other hand, consider the problem of subtracting 1. In the system of ordinary (not-necessarily-positive) integers, this leads to a (non-paradoxical) infinite regress; whereas, in the system of integers modulo some fixed positive integer, it leads to a (non-paradoxical) circularity (where repeatedly subtracting 1 from a number will eventually yield that number itself). I think that it is reasonable to call these different phenomena.

by Steuard 12y ago

placebo 12y ago

Not sure this analogy holds. Although the ratio of Jupiter's and Saturn's major orbital axis might seem arbitrary, given all the prior conditions to the orbit formations, current physics theories perhaps could have theoretically predicted this ratio long before it came to be. In the same way, physicists would like an elegant model that would predict or explain the constants in a way that makes more sense in a larger picture rather than having them as some magic numbers.

Steuard 12y ago
Exactly. That's pretty much what multiverse models suggest might be true for "fundamental constants": if you somehow knew the precise conditions of our part of the universe in the moments leading up to our big bang (and the parameters of whatever process triggered it: quantum fluctuations or whatever), you could in principle predict things like the charge to mass ratio of the electron. (E.g. if you knew the precise shape and fluxes of our 6-dimensional Calabi-Yau compactification manifold in string theory, you could work out the low-energy field content and coupling constants of the resulting universe.) [String phenomenology isn't really my field, but I certainly haven't had a lot of luck deriving a unique background from pure theory. I did once think that I'd found a model that predicted the cosmological constant to within an order of magnitude or two, but that obviously didn't pan out.]

rndn 12y ago

That’s the idea of an infinite number of onion layers [1]. What I find intriguing is that if you assume that everything is based on cause and effect, then (I think) you necessarily run into an infinite regress problem (the cause of a cause of a cause …) unless you define some "uncaused cause", or the concept of causation breaks down at some point. [1] https://en.wikipedia.org/wiki/Theory_of_everything#Infinite_number_of_onion_layers https://en.wikipedia.org/wiki/Theory_of_everything#Infinite_...

JadeNB 12y ago
> What I find intriguing is that if you assume that everything is based on cause and effect, then (I think) you necessarily run into an infinite regress problem (the cause of a cause of a cause …) unless you define some "uncaused cause", or the concept of causation breaks down at some point. Another possible resolution is a cyclic picture (something like https://en.wikipedia.org/wiki/Cyclic_model https://en.wikipedia.org/wiki/Cyclic_model), in which the cause of the cause of the cause of … may be the original event.
- rndn 12y ago
  Isn’t that an infinite regress problem?
  - JadeNB 12y ago
    > Isn’t that an infinite regress problem? I can certainly see the sense in which it might be said to be, but I think that's not the sense in which the term is originally meant. I tried to come up with an explanation of why I think they were meaningfully different by an appeal to mathematical analogy, but I'm not sure that it's convincing. Fermat argued as follows: a positive integer solution to `x^4 + y^4 = z^4` could always be converted into a smaller such solution, and you can't produce ever-smaller positive integers forever, so there weren't any such solutions in the first place. I'd say that this is clearly an infinite regress (though it was actually called infinite descent). On the other hand, consider the problem of subtracting 1. In the system of ordinary (not-necessarily-positive) integers, this leads to a (non-paradoxical) infinite regress; whereas, in the system of integers modulo some fixed positive integer, it leads to a (non-paradoxical) circularity (where repeatedly subtracting 1 from a number will eventually yield that number itself). I think that it is reasonable to call these different phenomena.