Greg Graviton
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 Apr 13 awarded Popular Question Mar 31 comment Quantum entanglement vs classical analogy @LousyCoder You have to be careful about when to measure what. In this case, the protocols are: A) First, Alice measures $S_y$. Then, Bob measures $S_y$. B) First, Alice measures $S_x$. Then, Bob measures $S_y$. Then, Alice measures $S_y$. The paradox is that in the situation A), both measurements of $S_y$ will be perfectly anticorrelated, but in situation B), the measurements of $S_y$ will not be correlated anymore. Jan 17 comment Quantum entanglement vs classical analogy @Relative0 The balls have two properties (spin $S_x$ and spin $S_y$), not just one (color). Be careful about $x$ and $y$. The paradox is that each property is perfectly correlated between the balls, but measuring property $y$ of the 2nd ball after measuring property $x$ of the 1st ball does not give you information about property $y$ of the first ball! Nov 9 awarded Yearling Sep 2 awarded Notable Question Aug 8 awarded Good Answer Jun 4 awarded Populist Mar 1 awarded Benefactor Feb 28 accepted Dirac operator in curved spacetime in 2 dimensions – hermitian? Feb 28 comment Dirac operator in curved spacetime in 2 dimensions – hermitian? @HydroGuy: Ooh, I like that way of putting it. It's not entirely obvious that being real on all fields $ψ$ is equivalent to the operator being hermitian, but if I remember correctly, that is true in complex Hilbert spaces. Feb 27 comment Dirac operator in curved spacetime in 2 dimensions – hermitian? Thanks, but could you expand on why the Lagrangian has to be hermitian? For instance, I get that the Hamiltonian has to be hermitian, so the potential energy of the Lagrangian should be of the form $-\psi^{\dagger}H\psi$ with $H$ a hermitian operator. What about the time derivatives, though? Also, you say "pseudo-hermitian" due to the fact that $\overline{\psi}$ differs from the adjoint $\psi^\dagger$ by the matrix $\gamma^0$? Feb 19 asked Dirac operator in curved spacetime in 2 dimensions – hermitian? Nov 9 awarded Yearling Nov 3 comment Theory behind patterns formed on Chladni plates? Actually, Chladni plates are not described by the wave equation, i.e. by the eigenfunctions of the Laplacian, but by the eigenfunctions of the biharmonic operator, i.e. the Laplacian squared. More information and historical references can be found in a beautiful article by Gander and Wanner. Even if you try to derive the wave equation for a string, using the "masses connected by strings" model, you have to assume that it is under tension, i.e. the springs are pre-stretched, or you will get the biharmonic operator and not the wave equation. Oct 26 awarded Nice Question Oct 16 awarded Enlightened Oct 15 awarded Nice Answer Jul 2 awarded Curious May 22 awarded Nice Question Feb 16 accepted Propagator for Dirac equation in real space