Mitchell Porter

2,223 reputation

1319

bio	website	taufunctionsquared.blogspot.c…
	location
	age
visits	member for	2 years, 4 months
	seen	26 mins ago
stats	profile views	1,253

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
1319 badges		location			seen	26 mins ago

summary answers questions tags badges favorites bounties reputation activity

253 Comments

suggestions reviews revisions comments badges posts accepts all

1h	comment	Was TP Singh right to say that a theory of quantum gravity necessitates the Copenhagen Interpretation? String theory, at least in its S-matrix form, doesn't have this problem, because the histories only have to come together asymptotically, in the infinite past and infinite future. Anyway, to post a proper answer, I would want to review these arguments first.
1h	comment	Was TP Singh right to say that a theory of quantum gravity necessitates the Copenhagen Interpretation? michielm, Singh's motivation is an argument, also made by Penrose (and possibly by 't Hooft?), that there is some problem of principle regarding superpositions of space-time geometries. When Penrose made such an argument, I understood it as having to do with the problem of aligning the intrinsic time of the different histories in the superposition...
2h	comment	Was TP Singh right to say that a theory of quantum gravity necessitates the Copenhagen Interpretation? Nothing like Bohm; a bit like Orch-OR - Singh cites Penrose at the end arxiv.org/abs/0711.3773 - but Orch-OR is just an idea about how an unknown theory behaves. Singh has his own proposal regarding the nature of the underlying theory - I haven't read it yet, but see his paper.
14h	comment	Was TP Singh right to say that a theory of quantum gravity necessitates the Copenhagen Interpretation? So to get to the real question here, we have to put Copenhagen out of the picture and say whether Singh has a a valid argument for one type of realist theory over a different type of realist theory.
14h	comment	Was TP Singh right to say that a theory of quantum gravity necessitates the Copenhagen Interpretation? A lot of people consider themselves Copenhagenists but then reify wavefunctions, and this is where the idea arises that Copenhagen is a theory of objectively existing wavefunctions that objectively collapse when a "measurement" is performed. But Copenhagenism is actually a positivistic, instrumentalist philosophy which only cares about predictions and observations, and not about an observer-independent objective reality.
14h	comment	Was TP Singh right to say that a theory of quantum gravity necessitates the Copenhagen Interpretation? The Copenhagen interpetation is a "subjective collapse" theory, in which the wavefunction isn't a real thing, it's more like a probability distribution, a device that makes predictions, and the "collapse" is just the modification to the wavefunction that you make when an observation gives you new information.
14h	comment	Was TP Singh right to say that a theory of quantum gravity necessitates the Copenhagen Interpretation? I just made a bunch of comments, I will try to say it again more compactly: The question, as stated, misrepresents Singh's position. Singh doesn't mention the Copenhagen interpretation at all. He offers a choice between two types of "realist" theory, many worlds, and an "objective collapse" theory in which the wavefunction spontaneously evolves into special eigenstates because of nonlinear dynamics.
2d	comment	What is the meaning of the concepts of “operator mixing” (and anomalous dimensions) But it seems clear that the original question was one capable of drawing a completely satisfactory answer, from someone who really knows the subject and was willing to review the basics a little.
2d	comment	What is the meaning of the concepts of “operator mixing” (and anomalous dimensions) I'm not competent to answer the question properly. It seems like operator mixing is about extra operators introduced by renormalization counterterms, and you have a square matrix of RGE parameters because it's really about a set of operators, where all the others arise as counterterms when you start with any one of them (so the entry Mij in the matrix would be, parameter pertaining to counterterm j when you start with operator i) ... but I got all that from Scholarpedia.
May 21	comment	What is the meaning of the concepts of “operator mixing” (and anomalous dimensions) I disagree with the closing of this question. It asks for definitions of terms, it mentions an equation in an article as an example of something to understand better, and it asks if they are known under other names. The upside of leaving it open is that someone might write an informative answer. What is the downside?
May 16	comment	How can string theory work without supersymmetry? Actually, the SO(16) x SO(16) string in that paper might already be an example of the type 0 string? Anyway, one thing to note is that some of these "nonsusy strings" still have a type of susy somewhere, e.g. on the worldsheet but not in spacetime.
May 16	comment	How can string theory work without supersymmetry? Along with the type 0 string, arxiv.org/abs/hep-th/9707148 is another example.
May 15	comment	What are the implications of the Nesvizhevsky experiment and followup experiments with ultracold neutrons? Technically they weren't quantum gravity experiments, they involved quantum mechanics in a gravitational field, which is different because the gravitational part can be treated classically.
May 3	comment	References for ADM formalism and cosmological perturbation theory @Qmechanic Maybe it's closure plus negative total votes that implies deletion, then...?
May 3	comment	References for ADM formalism and cosmological perturbation theory If this question has been closed, doesn't that mean it's going to be deleted? Which will also remove the useful lists of references here.
Apr 23	comment	Production vs. Collection, and Contaminants vs. Depositions, what might be missing in cold fusion research The "hello-type introduction" could go on your profile page.
Apr 22	comment	Motivation for the Deformed Nekrasov Partition Function mitchell.physics.tamu.edu/Conference/string2010/documents/… ... I think its chief utility lies somewhere in the space between M-theory and SQCD.
Apr 17	comment	Some Korean researchers saying that they solved Yang-mill existence and mass gap problem Yongmin Cho has been pushing this idea for more than ten years e.g. arxiv.org/abs/hep-th/0301013
Apr 14	comment	Vector and Spinor Representation in Ramond-Neveu-Schwarz Superstring Theory I suggest that you put an email address in your profile so that people can contact you. If someone who actually knows string theory could talk with you, they should be able to quickly identify what would be useful for you to learn next.
Apr 3	comment	Does the wave function/density state actually exist? @wnoise It's ultimately a question of quantum computational complexity and not proven. But all the known speedups obtained by quantum computers (e.g. in Shor's algorithm) are at best sub-exponential, suggesting that this is the true increment of complexity involved in passing from classical to quantum.