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visits member for 3 years, 11 months
seen 11 hours ago

I do not participate on this site any longer, except to respond to comments regarding my own text, if that text is unavailable in another form. I do not accept the political moderation atmosphere here, it is not compatible with open science. Unfortunately, this seems to be a recurring pattern on such sites--- they grow with promises of open participation, and then shut down in a phase transition of censorious moderatorship. Hopefully physicsoverflow.org will be the first exception to this rule, as the policies there were crafted specifically to avoid this phenomenon.


Mar
13
comment What fundamental principles or theories are required by modern physics?
@drake: Actually, there is a topological difference, in that there are two boundaries to time, past and future, but these are two boudaries to the light cone. I don't know whether this counts as a "difference between space and time", obviously there is a psychological difference, and there is an entropy difference, but I think you mean something else.
Mar
13
comment What fundamental principles or theories are required by modern physics?
@drake: S-matrix is both, because the asymptotic states go to infinity in space at infinity in time, they are simply asymptotic in both senses, and the asymptotic states are relativistically invariant, and the relativity transformations on plane waves don't have any strange singling out of time. exp(i(kx + w t)) is manifestly Lorentz invariant and treats time and space more or less equally (only the metric sign is different), with x,t vector and w,k covector, and these asymptotic states are the only "real" thing in an S-matrix point of view.
Mar
13
comment What fundamental principles or theories are required by modern physics?
... regarding measurement, that's a philosophical issue, I take many-worlds to avoid dealing with philosophy. The modern S-matrix ideas are holographic, so you imagine that all the dynamics is happening on a cosmological horizon, so that there is no real difference between space and time anymore, they can both be considered to be reconstructed from the boundary theory, but on the boundary, you can consider boundary time as distinguished, blah blah, it's mostly philosophy. It is possible to define boundary path integrals using space-boundary conditions at all time too, by the way.
Mar
13
comment What fundamental principles or theories are required by modern physics?
@drake: If you define the boundary conditions as Schwinger did, using space-like hypersurfaces and the precise values of fields, then you are right, and time is a little distinguished (although conceptually less than in other formalisms). But if you follow Wheeler and Feynman and define the boundary conditions through scattering states, they are plane waves, and these are asymptotic conceptions equally in both time and space. The S-matrix formulation treats both space and time equally, even in the boundary conditions. Causality in S-matrix is analyticity, which is not a space-time property.
Mar
12
comment What fundamental principles or theories are required by modern physics?
@drake: In the path integral, there is no difference between time and space in quantum mechanics, except to the extent that you place boundary conditions. The relation between rotations and boosts in the path integral formalism is the same as in the classical 4d view. This is Feynman's motivation for doing path integral in the first place, making a "space-time" quantum mechanics. I don't consider boosts and spatial rotations as different, nor the spatial part is somehow more fundamental than the boost part, but whatever floats your boat, it's all psychology, both symmetries are exact.
Mar
12
comment What fundamental principles or theories are required by modern physics?
@DWin: If by "abandon rotational symmetry" you mean "abandon Lorentz symmetry", then yes. Lorentz symmetry is just a generalization of rotational symmetry, so they are comparable, but toy model people generally keep rotational invariance. Ultimately it's just a statement about the psychology of builders of toy models. Hamiltonian mechanics and quantum mechanics can work in systems with no symmetries at all, they don't make any symmetry claims, just that the dynamics is symplectic or unitary. The symmetries in nature just narrow down the models to the ones which are empirically appropriate.
Mar
12
comment What fundamental principles or theories are required by modern physics?
@DWin: It's just a silly opinion, the homogeneity of space can be preserved by a translationally invariant theory with preferred axes, so that rotation invariance is broken. For example, if you imagine a crystal with teeny-tiny atoms, the long-distance theory is translation invariant and not rotationally invariant, and this is perhaps psychologically ok. The theories that postulate relativity violations all maintain exact translation invariance, so the preference of theory builders is to break relativity first, so rotational invariances (like relativity violations) is less compelling, I guess.
Mar
6
comment How can it be that the beginning universe had a high temperature and a low entropy at the same time?
@IvanLerner: Not all theoretical questions are a "matter of faith", I don't even know what that means. I know what YOU mean, however--- you mean "if people disagree with you, then it's not settled." Sorry, people can disagree long after a matter is settled, even settled experimentally. You can't use social mechanisms to decide whether something is settled or not.
Mar
6
comment How can it be that the beginning universe had a high temperature and a low entropy at the same time?
@IvanLerner: It's not exactly an experimental question, that's the problem--- it's a pure theoretical question: "why does the early universe have low entropy?" All experiment can answer is "The early universe had low entropy" and "the thermal fluctuations are such and so". When you are answering a theoretical question, you need a larger framework of theory to understand inside, and this is built up by a process of steps of theory. Scientific theories are definitely absolute, they rule out nonsense. The sun does not in any way go around the Earth (the center of rotation is inside the sun).
Mar
5
comment How can it be that the beginning universe had a high temperature and a low entropy at the same time?
@IvanLerner: What you are saying is the awful popular misunderstanding of science: confusing social consensus (which is worthless) with evaluating ideas by critical review (which is valuable). The ideas stay correct even when the majority of idiots say otherwise. The Earth still went around the sun even when a majority of people said it didn't. The social process only converges to the truth in the long term, after all the mocking and heckling is said and done. In this case, I don't need to wait, because there is no cogent counterargument, just as in the case of the Earth going around the sun.
Mar
5
comment How can it be that the beginning universe had a high temperature and a low entropy at the same time?
@IvanLerner: No, no, no! What I have is understanding. What the other idiots have is social consensus, they are going by authority. They are objectively wrong, and Davies is objectively right, and when you start mocking them, that's when consensus changes. The reason it wasn't appreciated earlier is that the holographic viewpoint implicit in Davies argument (the entropy is of a single causal patch) is incompatible with common earlier pictures of global cosmology and global solutions to GR, but the holographic picture won in the 1990s, and is now folklore, allowing Davies to get recognition.
Mar
4
comment Why do rockets accelerate fastest horizontally?
@Taemyr: No, no, no! This is both completely intuitively obvious, and not what they were talking about. They were asking about acceleration relative to the gravity pull, which way is best to accelerate, and the idiotic intuition they were exploiting is that the Earth's rotation is helping you in some way. Pay attention to the actual question, don't make up nonsense to make authority look less stupid than it always is.
Mar
3
comment Why do rockets accelerate fastest horizontally?
@Taemyr: That was not the question, it's your personal nonsense stretched interpretation to make sense of the answer. One must never be charitable toward idiots. The assumption that the orbit is circular was never made here, and I am sure it was never made in the program. It is possible that your correct statement is what the idiots at the TV station misinterpreted to make their stupid question, but there is next to no chance that QI got it right, because, from experience, TV never gets anything scientific right, because they don't have this kind of open review, and TV is written by stoners.
Mar
3
comment How can it be that the beginning universe had a high temperature and a low entropy at the same time?
@asmaier: Yes, thanks for the proper reference. I guess Journal of Theoretical Physics cares more about its profit margin than science.
Mar
2
awarded  Necromancer
Mar
1
awarded  Necromancer
Feb
20
comment Why you need a graviton when you have the higgs boson?
@StanShunpike: Classical gravitational waves are, in quantum mechanics, just a bazillion gravitons all propagating together. I don't know what you are asking.
Feb
18
comment Why you need a graviton when you have the higgs boson?
@StanShunpike: The "classical graviton" is just gravitational wave emission, it isn't quantized into particles classically, it can't be in a superposition of configurations, and it doesn't make full sense when you try to make it interact with quantum mechanical atoms.
Feb
1
comment Is spacetime moving in general relativity?
@dcgeorge: That statement means something different to a person who studied General Relativity than it does to you. To a relativist, it means that the frames are tilted around the rotating object. To you, it means that space is a fluid ether which is pulled around the object. It's just because the implicit ether model is wrong, and no relativist has it in mind when they talk about 'dragging spacetime'.
Jan
31
awarded  Nice Answer