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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 More information and historical references can be found in a beautiful article by Gander and Wanner.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