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490211
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location New York City
age 41
visits member for 3 years, 11 months
seen 6 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.


Jan
31
awarded  Nice Answer
Jan
29
awarded  Revival
Jan
29
comment Is spacetime moving in general relativity?
@dcgeorge: "frame dragging" is where the inertial frame near a body is partly rotating with the body. Spacetime is not a material ether, it's a collection of vectors that define orthonormality. The popular pictures are misleading and your intuition is false.
Jan
20
comment Deterministic quantum mechanics
@annav: Thanks.
Jan
15
comment Do neutron stars reflect light?
@RobJeffries: The model is a neutron ball with a proton gradient, I don't know about the theoretical status of the nuclear pasta models, they are high-temperature models as far as I can see, relevant only during collapse, not low temperature models. The other answer explained the crust, I just explained the general phenomenon of reflectivity in a free conducting surface. A neutron ball has a proton gradient with a free conductive surface, regardless of what other people say. As I understand it, this is the right model for a cold neutron star, with a sharp phase transition at the crust.
Jan
15
comment Do neutron stars reflect light?
@RobJeffries: True, but the question was asking about what you would see if you could bounce light off the neutron star surface, not off the ordinary matter crust. The protons are the charged reflectors capable of motion, and these free charges is what is dominating the reflection properties of the surface. Sure, the crust would be different, but the question was about the nuclear material inside. It might be possible to ask this properly by imagining blasting off the normal matter and looking fast, before it has a chance to reform, or by using a gamma that can penetrate the outer layers.
Jan
14
comment Do neutron stars reflect light?
@RobJeffries: Their is an equilibrium density of protons among the neutrons, because neutron purification by gravitational instability is never perfect. The extra protons collect on the surface. The ordinary matter is a separate thing, forming what is called an "atmosphere" over the neutron star surface. The nuclear ball contains a proton fraction in thermodynamic equilibrium through beta decay.
Jan
8
comment What future technologies does particle physics and string theory promise?
@LarryHarson: I'm not 100% sure about the dates, but I was under the impression that tensor analysis was around in Riemann's time in 1860s or 1870s, since Riemann was discussing tensors. It easier than the stupid vector algebra, includes it as a (not interesting) special case, and the mystical significance of "dot" and "cross" product is definitely derived from their role in quanternions, which is a complete red-herring. Vector calculus for sure post-dates Maxwell, because Maxwell used quaternions. The quaternions are a poor fit for physics, as is vector calculus. Only tensor calculus works.
Jan
7
comment What future technologies does particle physics and string theory promise?
@EmilioPisanty: He's talking about undergrad style vector calculus, which is a sterile offshoot of the quaternion algebra (the dot product is the real part of the quaternion product of two three-vectors represented as wholly imaginary quaternions, while the cross product is the imaginary part). This formalism is sterile. But the associated tensor formalism developed earlier is not sterile, and is what people use to discuss general representations and so on. Kelvin wasn't so far off base here.
Dec
29
awarded  Nice Answer
Dec
28
comment How to choose a suitable topic for PhD in Physics?
@lionelbrits: What could possibly solve the Born rule issue? If you formulate it properly, with logical positivism, you see it is a question of pure philosophy, meaning it cannot be answered, and is likely meaningless. It's analogous to questions of a-priori probability in philosophy in 19th century discussions of Baysianism, and Everett understood this already in 1957. But thats within MWI, assuming QM is exact. If QM is approximate but wrong, and there's a deeper structure, there will be a different notion for probability, maybe classical probability.
Dec
27
comment How to choose a suitable topic for PhD in Physics?
So 'tHooft gave a real question: can you find a realistic system (like a CA) which is approximately QM for certain internal observers? If the CA is realistic, it can't be exponentially huge, so it can't do quantum computation. So you are asking whether you find a realistic system which approximates QM and doesn't require exponential resources (so doesn't allow for quantum computation). These questions are important, they might be "interpretation" questions perhaps, but they aren't trying to adjust a philosophy to match standard QM predictions. Bohm is like this, but Bohm is too big to be real.
Dec
27
comment How to choose a suitable topic for PhD in Physics?
@lionelbrits: It's not open, in the sense that Everett solves it, meaning that it gives a realistic picture which reduces to Copenhagen, modulo logical positivism. Once you understand positivism, Everett, and Copenhagen, there is nothing more to say regarding interpretation of standard QM, it's solved. It's all (pointless) philosophy from this point on. The open questions are not measurement or interpretation exactly, rather they are about QM itself--- whether QM is correct or not! The modern work regarding foundations that is most interesting is about modified QM, like 'tHooft said once.
Dec
21
comment Underground explosions due to plate tectonics and natural gas pockets
@Michael: It's difficult because the initial estimates are uncertain, and there is pressure below, so that the oil might be migrating from lower down from a larger reservoir, or continuously migrating from the mantle. It also depends on whether there is still a path for the hydrocarbons to migrate, it's a tough question. It would require a detailed way to estimate the length of time since the oil arrived from the mantle, and radioactive decay markers might be used for this, if you have some idea of what the radioactive signature of the mantle oil is. I don't know any more than anyone else.
Dec
21
comment Is space unending?
@LarryHarson: Fields by definition are at a spacetime point. They don't move. The excitations move. The excitations move outward, and at the horizon, move outward at the speed of light as considered relative to the observer at the origin. But the fields themselves are defined on the interior, and can't move. It's a terminology issue, there is no actual question here regarding anything meaningful.
Dec
18
comment Underground explosions due to plate tectonics and natural gas pockets
@Michael: There's no such thing as non-abiotic oil, so you should just call it "oil". Nobody knows the answer to your question, because it isn't studied anymore, since the breakup of the USSR.
Dec
18
comment Is space unending?
@Michael: fields don't move.
Dec
4
awarded  Enlightened
Dec
4
awarded  Nice Answer
Nov
22
awarded  Nice Question