Emilio Pisanty
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 4h comment Does the electrons in Stern-Gerlach aplliance change their energies and how? Not really - on exit, it will be an entangled state with equal amplitudes on spin up on the up track plus spin down on the down track. Only then do you perform the projective measurement on position, which thereby also collapses the spin state as well. There's additional subtleties at play (particularly the fact that the 'energy' of the system includes the interaction Hamiltonian used to perform the measurement) but that's enough to be getting on with. 5h comment Homogeneity and isotropy and derivation of the Lorentz transformations One relevant avenue for your question is Doubly special relativity (and links therein). 5h comment Homogeneity and isotropy and derivation of the Lorentz transformations It also bears mention that there are many ways to construct the Lorentz transformations from the Einstein postulates, but it is very hard to determine whether they implicitly call on the isotropy and homogeneity of spacetime. Most do, but it can be hard to pinpoint exactly where (or it can be easy to weasel that implicit dependence over to some other part of the proof, without even noticing). Ultimately, asking "does one have to assume X to prove Y" is equivalent to asking "is Y consistent with situations where ¬X?", and that is generally a hard question. 5h comment Homogeneity and isotropy and derivation of the Lorentz transformations Fair enough, but keep in mind that there are several (very different) common ways to derive the Lorentz transformations. Unless you reference appropriately, it is hard to know what you mean, and that hinders your question somewhat. 5h comment Homogeneity and isotropy and derivation of the Lorentz transformations @user35305 Just because A and B imply C, it doesn't mean that there can't be independent propositions D and E which also imply C. Your question really boils down to "are the Einstein postulates consistent with non-isotropic and/or inhomogeneous spacetime?", which is tricky to answer. 5h comment Homogeneity and isotropy and derivation of the Lorentz transformations When you say 'the derivation', do you have a specific one in mind? (e.g. this one?) If so, you should provide a reference. 5h comment Does the electrons in Stern-Gerlach aplliance change their energies and how? "When an electron goes thru a Stern-Gerlach appliance it changes its spin projection" - no, not at all, or at the very least only in an interpretation-dependent way. It is equally as accurate (i.e. not much) to say that the electron 'already had' that projection; other interpretations will insist that it is meaningless to talk about the electron's spin projection before the measurement, so the 'change' is also meaningless. 6h revised How is 6W equivalent to 40W, as claimed by adverts for LED light bulbs? Removed misleading terms from title; improved grammar. 6h revised Momentum equation of a beam hitting a stationary target to create antiprotons Minor formatting fixes. 1d comment Are units of angle really dimensionless? If you want to include degrees into a dimensions analyser, the only consistent way is to assign to the degree symbol $°$ the numeric value $\pi/180\approx0.01745$. It sounds weird at first, but it works! 2d comment Dipole moment of a single point charge @auxsvr Hence the careful qualifying of the entire post to apply only to charged systems where relevant. 2d comment Diagonalisation: Schmidt vs eigenvalue - when to use which? In short, the Schmidt decomposition applies to state vectors (in particular, to bipartite states, which admit a matrix structure), and the eigenvalue diagonalization applies to operators (which includes density matrices). 2d comment heat as a low quality energy Regarding your link, it's important to note that it does not contradict lucas's statement. For a process that's cyclic on the system, the net work performed by the system is equal to the net heat taken in by the system, but that is different from the total heat offered to the system from the hot reservoir (and which differs from the net heat taken in by the heat dumped into the cold reservoir). 2d comment heat as a low quality energy The answer to your comment is as dmckee said - not only does it require energy to produce a cold reservoir, it requires provably ≥ energy than you would be able to extract as work using that reservoir. And, again, this is explained in depth in any thermodynamics textbook. 2d comment heat as a low quality energy @ergon To be honest I do not recall having answered previous answers of yours (nor do I doubt having done so if you say I did, meaning that each answer has been independent of the others). If the answers seem pitched at a low level to you, then take that as constructive criticism that the question text as posed is also pitched at a low level; if you have a more sophisticated question then make sure it shines through in your text. As it is, on the text there is precious little evidence that you understand the material even at introductory level, I'm afraid. 2d comment Dipole moment of a single point charge Because the system is neutral, in which case (as opposed to a system with nonzero total charge) the dipole moment is indeed independent of the coordinate origin. That's a simple calculation which you should be able to perform. 2d revised Dipole moment of a single point charge Formatting edits. 2d answered Dipole moment of a single point charge 2d revised Rotation of Spacetime $\Rightarrow$ Change in orbit/path Title formatting. Apr 28 comment Lower limit for atomic number in case of imaginary ion with Z < 1 arXiv:1102.4493 appears to at least be relevant literature, with Fig. 7 putting the critical charge at maybe $Z_c\approx0.9$.