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awarded  Popular Question
Jul
2
awarded  Inquisitive
Jul
2
awarded  Curious
Jun
13
comment If QFT is a sum over 1-D topologies and String Theory over 2-D topologies, what is the corresponding theory for N-D topologies?
Ah, thanks, I hadn't found those before. They do basically ask the same question, although I would complain that their answers are too technical (if I was a string theorist I would know the answer already!)
Jun
13
comment If QFT is a sum over 1-D topologies and String Theory over 2-D topologies, what is the corresponding theory for N-D topologies?
But I thought that p-branes emerged within string theory (which I'm defining is a theory of 1-dimensional strings and no larger), ie that there are dualities between stacks of strings and higher dimensional branes, and that therefore it isn't clear that these things represent the next logical step in the progression described in my post. Does the 1-D theory perturbatively "contain" through dualities the physics of all higher dimensional objects? Or are these branes really a separate theory altogether of higher dimensional objects? What connects the different dimensional theories?
Jun
13
asked If QFT is a sum over 1-D topologies and String Theory over 2-D topologies, what is the corresponding theory for N-D topologies?
May
11
comment How do we know that nonperturbative canonical quantum gravity is wrong?
"If this is so, and if the sum is over arbitrarily small space-time structure, then there is a serious problem, because high dimensional topologies are known to be non-classifiable, so that it is impossible to give an algorithm which will sum over each topology once and only once." -- Why isn't this also a problem in the path integral over string worldsheets?
May
1
comment Does quantum mechanics violate the equivalence principle?
How are these violations of the equivalence principle consistent with Weinberg's 1960's general proofs of the equivalence for spin-2 fields? (see: journals.aps.org/pr/abstract/10.1103/PhysRev.135.B1049). Doesn't his argument apply specifically to momentum eigenstates?
May
1
comment Does quantum mechanics violate the equivalence principle?
How are these violations of the equivalence principle consistent with Weinberg's 1960's general proofs of the equivalence for spin-2 fields? (see: journals.aps.org/pr/abstract/10.1103/PhysRev.135.B1049).
Apr
27
asked Has the idea of holeum been debunked?
Mar
20
comment Can or does the Casimir effect play a role in solving the electron self-energy problem?
@JánLalinský, I think the issue is not the introduction of substructure, but just the consistency of a point-like electron that has no well-defined mathematical limit.
Mar
18
comment Can or does the Casimir effect play a role in solving the electron self-energy problem?
@JánLalinský, I tend to think it is a problem given that Feynman dedicates a few pages to it in his Feynman Lectures and seems genuinely perplexed by it.
Mar
17
revised Can or does the Casimir effect play a role in solving the electron self-energy problem?
added link to a related question
Mar
17
comment Can or does the Casimir effect play a role in solving the electron self-energy problem?
@JánLalinský, maybe you aren't familiar with the classical problem of electron self-energy? I agree with your statements, but I think that normally you would consider how much energy it takes to "assemble" the electron. Even though the electron is considered elementary, there is no explanation for what "holds it together."
Mar
17
asked Can or does the Casimir effect play a role in solving the electron self-energy problem?
Mar
13
comment Are quantum decoherence and Everettian approaches to the measurement problem necessarily distinct?
My problem is that your last sentence seems directly at odds with assuming reality of the universal wave function. I don't see how you can maintain both pictures simultaneously.
Mar
7
awarded  Favorite Question
Feb
7
comment Twin Paradox - different approaches
@John Rennie, the point is that without the equivalence principle the traveling twin has no way of knowing whether she is following a geodesic or not, despite feeling herself accelerate. The acceleration could be because the pilot fired engines and caused a kink in her worldline, or it could be that the engines were fired in coincidence with a passing gravitation body, such that there is no kink in her worldine. Through her telescope she observes the other twin accelerate, and so depending on her interpretation of her own acceleration she can come to different conclusions about her twin.
Feb
7
comment Twin Paradox - different approaches
@John Rennie, again, just because there is one way of calculating it within SR that gives the correct answer, doesn't itself represent any evidence against an internal inconsistency. I don't have access to MTW so I don't know exactly what argument you are referring to, although I'm well aware of the "canon" that you don't need GR to solve the twin paradox. I think this canon is wrong, for reasons that I don't think are particularly difficult to understand. I would appreciate it if you could point out specifically what mistake is made by the twin in my above example.
Feb
6
comment Twin Paradox - different approaches
@joshphysics, your example is precisely what I warned against. That is, giving one solution and then calling it a day. The problem is that from the traveling twin's perspective, SR provides multiple equally valid ways of answering the question. The way of answering that I provided is not a misapplication of SR. The twin looks out his telescope and traces the arc length of the earth twin, and determines it is longer than her own. From her perspective, she has been stationary, with acceleration due to rockets used during a passing gravitating object.