4 ms·

Example of physics' 'unreasonable simplicity'?

by elevenoh 8y ago

Kurtose 8y ago
S = k. log W
evanb 8y ago
Everything but gravity seems exquisitely described, if you look close enough, by 22 parameters.
- thegabriele 8y ago
  Could you elaborate about the 22 parameters? Are you referring to universal constants or fundamental particles?
  - evanb 8y ago
    There are 3 generations of 4 fermions, each has a mass. One sets the scale of the theory, meaning we should express all the dimensionful quantities in terms of that mass. So, that gives 11 parameters. Then there are the mixing angles in the CKM matrix. For three generations, that matrix is a 3x3 unitary matrix = 9 parameters. But, we can absorb arbitrary phases into each quark field, but should add one back for the global U(1) phase for 9-6+1 = 4 parameters, 3 mixing angles and 1 CP-violating phase. We're up to 15. We have 3 forces in the Standard Model, each has a gauge coupling. 18. There's the Higgs vev and mass, 20. QCD admits a marginal topological quantity, θ_QCD. As far as anyone knows it's zero to many digits of precision. Still, it's in principle a free parameter of the Standard Model, so 21. Then there's the Planck mass (or equivalently, G), 22, which is the number I remember. I suppose now that we are certain neutrinos have mass I should include the parameters of the PMNS mixing matrix, if you're willing to count them in the Standard Model (they're not in the Glashow-Weinberg-Salaam work, for example). How many free parameters it contains depends on whether neutrinos are Majorana. If they're Dirac, it's 4 parameters (like the CKM matrix), if they're Majorana there are 2 additional CP-violating phases. So, 26 or 28 continuous parameters in the Cosmic Control Booth according to the Standard Model. There's of course discrete kinds of questions you can ask, like "Why is the gauge group SU(3) x SU(2) x U(1)"; I'm not sure how to count such a choice. I think it's fair to ask, "Here's the physical theory with the matter content set, what are the free parameters?".
matt4077 8y ago
Physics is the poster boy for reductionism, i. e. the ability to split any situation into its parts, understand those, and then reassemble a complete model that actually describes the world. Hence the jokes about spherical chickens (the approach works, but not for chickens). Physics has also taught us to expect absurdly simple laws as the inner workings of seemingly complex observations. e = mcc would feel like a cruel joke on anyone trying to grapple with how reality works pre-Newton. This mindset, and the so obvious wins of physics in its golden age (ca 1900-1970), from the atom bomb to the moon landing, also set unreasonable expectations for the other sciences. Hence, people expected no less than a cure for ageing from the unraveling of the genetic code and the decryption of the human genome. Yet, as it turns out, biology cannot be reduced in the way that physics can. Genetics is a madman’s den of complexity, nonlinearity, and unpredictability. It’s almost literally what you would expect from a few million years of Perl snippets evolving. The same is true of neuroscience, meteorology, sociology, and, to a lesser degree, chemistry.
- cinquemb 8y ago
  >Yet, as it turns out, biology cannot be reduced in the way that physics can. Genetics is a madman’s den of complexity, nonlinearity, and unpredictability. It’s almost literally what you would expect from a few million years of Perl snippets evolving. The same is true of neuroscience, meteorology, sociology, and, to a lesser degree, chemistry. I would say that we cannot to sufficient degree today (the 0 to 1) that people are expecting from the endless hype, but the mathematics used to describe/locate/correlate brain activity (LCMV beamforming + DSP + MCMC priors), and speeding of the design process of molten salts are getting a lot better/more accessible over time (relying on mathematics from local spin density approximations + gradient density correction theories + UNIFAC).
- denzil_correa 8y ago
  > Yet, as it turns out, biology cannot be reduced in the way that physics can Most "systems" we have (including physics) are complex, non-linear and dynamic [0]. Some of them are relatively less complex than the others but they are still complex nonetheless. [0] https://www.art-sciencefactory.com/complexity-map_feb09.html https://www.art-sciencefactory.com/complexity-map_feb09.html

Example of physics' 'unreasonable simplicity'?

Kurtose 8y ago

S = k. log W

evanb 8y ago

Everything but gravity seems exquisitely described, if you look close enough, by 22 parameters.

thegabriele 8y ago
Could you elaborate about the 22 parameters? Are you referring to universal constants or fundamental particles?
- evanb 8y ago
  There are 3 generations of 4 fermions, each has a mass. One sets the scale of the theory, meaning we should express all the dimensionful quantities in terms of that mass. So, that gives 11 parameters. Then there are the mixing angles in the CKM matrix. For three generations, that matrix is a 3x3 unitary matrix = 9 parameters. But, we can absorb arbitrary phases into each quark field, but should add one back for the global U(1) phase for 9-6+1 = 4 parameters, 3 mixing angles and 1 CP-violating phase. We're up to 15. We have 3 forces in the Standard Model, each has a gauge coupling. 18. There's the Higgs vev and mass, 20. QCD admits a marginal topological quantity, θ_QCD. As far as anyone knows it's zero to many digits of precision. Still, it's in principle a free parameter of the Standard Model, so 21. Then there's the Planck mass (or equivalently, G), 22, which is the number I remember. I suppose now that we are certain neutrinos have mass I should include the parameters of the PMNS mixing matrix, if you're willing to count them in the Standard Model (they're not in the Glashow-Weinberg-Salaam work, for example). How many free parameters it contains depends on whether neutrinos are Majorana. If they're Dirac, it's 4 parameters (like the CKM matrix), if they're Majorana there are 2 additional CP-violating phases. So, 26 or 28 continuous parameters in the Cosmic Control Booth according to the Standard Model. There's of course discrete kinds of questions you can ask, like "Why is the gauge group SU(3) x SU(2) x U(1)"; I'm not sure how to count such a choice. I think it's fair to ask, "Here's the physical theory with the matter content set, what are the free parameters?".

matt4077 8y ago

Physics is the poster boy for reductionism, i. e. the ability to split any situation into its parts, understand those, and then reassemble a complete model that actually describes the world. Hence the jokes about spherical chickens (the approach works, but not for chickens). Physics has also taught us to expect absurdly simple laws as the inner workings of seemingly complex observations. e = mcc would feel like a cruel joke on anyone trying to grapple with how reality works pre-Newton. This mindset, and the so obvious wins of physics in its golden age (ca 1900-1970), from the atom bomb to the moon landing, also set unreasonable expectations for the other sciences. Hence, people expected no less than a cure for ageing from the unraveling of the genetic code and the decryption of the human genome. Yet, as it turns out, biology cannot be reduced in the way that physics can. Genetics is a madman’s den of complexity, nonlinearity, and unpredictability. It’s almost literally what you would expect from a few million years of Perl snippets evolving. The same is true of neuroscience, meteorology, sociology, and, to a lesser degree, chemistry.

cinquemb 8y ago
>Yet, as it turns out, biology cannot be reduced in the way that physics can. Genetics is a madman’s den of complexity, nonlinearity, and unpredictability. It’s almost literally what you would expect from a few million years of Perl snippets evolving. The same is true of neuroscience, meteorology, sociology, and, to a lesser degree, chemistry. I would say that we cannot to sufficient degree today (the 0 to 1) that people are expecting from the endless hype, but the mathematics used to describe/locate/correlate brain activity (LCMV beamforming + DSP + MCMC priors), and speeding of the design process of molten salts are getting a lot better/more accessible over time (relying on mathematics from local spin density approximations + gradient density correction theories + UNIFAC).
denzil_correa 8y ago
> Yet, as it turns out, biology cannot be reduced in the way that physics can Most "systems" we have (including physics) are complex, non-linear and dynamic [0]. Some of them are relatively less complex than the others but they are still complex nonetheless. [0] https://www.art-sciencefactory.com/complexity-map_feb09.html https://www.art-sciencefactory.com/complexity-map_feb09.html