Mitchell Porter

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Physics Stack Exchange users whose comments are worth studying include Lubos Motl and Ron Maimon (now at http://www.quora.com/Ron-Maimon). Also see http://arxiv.org/abs/hep-ph/0207124 for a review of physics since the standard model.

	2,223 reputation	bio	website	taufunctionsquared.blogspot.c…	visits	member for	2 years, 4 months
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Dec 10	awarded	Announcer
Dec 5	awarded	Caucus
Dec 4	comment	How quarks converted into leptons It's the detailed interaction of the particles with the electromagnetic field which suggest fractionally charged constituents, e.g. physics.ohio-state.edu/~kass/P780_L8_sp03.ppt slides 13-14 (decay of vector mesons) or arxiv.org/abs/hep-ph/0210054 (various other processes).
Dec 4	comment	Do unoriented strings possess asymptotic states? ... a baryon, a collection of N strings terminating on a compact brane. A non-gauge-invariant object like a diquark might be part of a baryon, e.g. you would think of a brane with 3 strings attached, and two of the strings very short, so that the third, long string can then be conceived as connecting a quark and a "diquark object". But all this would be just one way that gauge theory embeds in string theory. A truly comprehensive account might list half a dozen ways to get one from the other.
Dec 4	comment	Do unoriented strings possess asymptotic states? The right way to visualize perturbative string theory is as defined by Riemann surfaces (possibly with boundaries) with marked points corresponding to the asymptotic states. (A conformal rescaling of the worldsheet is used to map the infinite string history onto the finite Riemann surface.) An unoriented string could be conceived as an equal superposition of oppositely directed oriented strings... Concerning the relation with gauge theory: an individual "quark" would be a string between a color brane and a flavor brane; a meson, a string between two flavor branes...
Dec 2	comment	How quarks converted into leptons Since this is the direction of your thinking I will point out arxiv.org/abs/hep-ph/0408305 which is a paper trying to unify "iquarks" (author's name for quarks with integer charge) with leptons. That is a paper with no citations and it's probably making a mathematically wrong argument somewhere. If you want to understand what physicists already think, you need to understand fractionally charged quarks, and the SU(5) theory might help too. But people follow their own ideas right or wrong, and maybe you can learn something else from this professional paper even if it is wrong.
Dec 2	comment	How quarks converted into leptons Normally by "lepton" we mean particles that don't interact via QCD. You seem to be thinking of "integer charged quarks"? That is an old idea, but there are some (difficult) experiments which do seem to falsify it directly. Also, the fractional charges start to make sense in a unified theory like SU(5) grand unified theory.
Dec 2	comment	How quarks converted into leptons Quarks aren't observed because of en.wikipedia.org/wiki/Color_confinement ... someone will post about this. Like anna said, in your diagram, the quark and antiquark confined in the pion are annihilated, but that is a different thing, it is not the reason why you don't get single free quarks (except at very high temperatures).
Nov 24	answered	Help an aspiring physicists what to self-study
Nov 24	comment	Who are some prominent groups or individuals pursuing realist physics? "Who are some prominent groups or individuals pursuing realist physics?" Anyone pursuing a realist interpretation of QM or a realist subquantum theory. Also, any sort of ontological inquiry into physics - any inquiry into what's actually there, and not just into what algorithms make the right predictions - tends to be realist. But what to make of QM is the central problem.
Nov 20	comment	Are there any list of String Theory Equations? Neo, the exact equations to use depend on the sign of the "cosmological constant" (+, 0, -) and on the shape of the extra dimensions. Mail me at the address in my profile and we can discuss the details.
Nov 19	comment	Are there any list of String Theory Equations? And in the case of string theory it's all the more justified, precisely because the definition of the theory is a highly nontrivial thing, and so this question is an opportunity for someone to give a highly informative answer.
Nov 18	comment	Are there any list of String Theory Equations? Why is this closed?! Asking for the basic equations behind a theory isn't off-topic or open-ended.
Nov 18	awarded	Revival
Nov 16	comment	Have I discovered how to calculate the proton's mass using only integers? Fred, the bottom line here is that a kilogram is an arbitrary unit of mass, and if you used a different unit, you would have a different number to explain. The actual numbers in physics that people seek to explain are quantities like "ratio of proton mass to electron mass", which don't depend on units.
Nov 14	comment	Is physics rigorous in the mathematical sense? The ideal of rigor for science is the hypothetico-deductive method. You make a hypothesis, deduce its consequences, and then test them against reality. The mathematical formalization of this process would be something like the AIXI algorithm in computer science, which uses data to make causal models. Also see the whole field of statistics, and its methods for establishing the likelihood of a hypothesis. The difference between mathematics and physics is that in physics you use empirical data as an input. But you can still be rigorous in your methods.
Nov 11	comment	Does the Higgs Mechanism contradict Entropic Gravity? Entropic gravity has other problems arxiv.org/abs/1108.4161 arxiv.org/abs/1108.5240.
Nov 8	awarded	Announcer
Oct 30	comment	Reference-request: Computational science and physics ... or exactly how mathematics relates to reality. Galileo's remark is a poetic statement that there is some form of connection but states no details. Unless you adopt the pythagorean position that "reality is mathematics", you need some broader ontological idea in which "number" is just one "aspect" of reality, but that is a nature-of-reality question. It's metaphysics, it's about whether reality consists of "things with properties" or something else entirely.
Oct 30	comment	Reference-request: Computational science and physics UGPhysics, I don't think you know what you're asking. Computability has a specific technical meaning, see "Turing computability". You could hypothetically have a theory of physics that was technically noncomputable, but the only part that could be tested would be a computable truncation of the theory. Insisting that a theory includes an algorithm for making quantitative predictions is just the bare minimum requirement for it to be testable, and doesn't say anything about whether reality contains anything noncomputable in the technical sense, whether reality is "mathematical" ...