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Diego Mazón


Jul
12
awarded  Yearling
Jun
18
awarded  Enlightened
Jun
18
awarded  Nice Answer
Jun
16
comment Is electric charge truly conserved for bosonic matter?
@Void As I don't see where you confusion comes from, let try to help by saying that in non-relativistic quantum with an EM field, the charge density is just $\psi^*\,\psi$ and current density is the imaginary part of $\psi^*\vec D \psi$. The depends explicitly on $A$ for both bosons and fermions. It is this current, rather than that with non-covariant derivatives, the one that is gauge invariant. This expression with covariant will give a dependence on the kinematical motion of the particle.
Jun
16
comment Is electric charge truly conserved for bosonic matter?
@Void The canonical formalism doesn't cover up anything. It's everything clear and there isn't anything incompatible at all, 2) You just cannot put all temporal derivatives equal to zero, This is not a sensible physical limit as far as I can see. How do you justify that limit? It is a different dynamics rather than a limit. 3) I don't understand how that relate to this issue.
Jun
16
comment Is electric charge truly conserved for bosonic matter?
@Void 1) When you switch on the external homog electrostatic field, the dynamics of the matter fields $\phi$ change in such a way that they compensate the change in $A_0$. This is the gauge covariant version in configuration space (no canonical momentum). Another way to see it is fixing the temporal gauge, where there is no explicit dependence on $A$. So the external homog field is just $A_0=0$, $\vec A=\vec E_0 \, t$. Neither particles disappear nor their charge vanish. They just change their motion.
Jun
16
comment Is electric charge truly conserved for bosonic matter?
I have answered all your questions in full detail. What do you not understand?
Jun
15
revised Is electric charge truly conserved for bosonic matter?
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revised Is electric charge truly conserved for bosonic matter?
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Jun
12
answered Is electric charge truly conserved for bosonic matter?
Mar
21
awarded  Good Question
Mar
13
comment What fundamental principles or theories are required by modern physics?
S-matrix is connected with change in time, not space!!
Mar
13
comment What fundamental principles or theories are required by modern physics?
"except to the extent that you place boundary conditions" That's not enough? 1)Asymptotic states are defined with respect to time, not space. 2)Amplitudes (computed from path integrals as you like) are causal. Causal is a space-time property, what's the space-space equivalent? 3) Time plays a role in quantum mechanics in connection with measurement even when there is no evolution (H=0). I agree that both are exact as far as we know, we aren't discussing that.
Mar
12
comment What fundamental principles or theories are required by modern physics?
@RonMaimon Note that I'm not claiming they aren't equivalent; only that it's not that clear.
Mar
12
comment What fundamental principles or theories are required by modern physics?
@RonMaimon I think you are at least oversimplifying the equivalence between boost and spatial rotations. The rotational group is compact, unlike the Lorentz group. Also, the different roles that time plays in a quantum theory might make boost different. The equivalence btw spatial rotations and boost is not as obvious as the 4d approach to Special Relativity apparently suggests. Causality could be another reason. In addition, rotational inv is more fundamental in that breaking rotational inv. implies Lorentz violation, whereas the reverse is false.
Feb
8
comment Why not using Lagrangian, instead of Hamiltonian, in non relativistic QM?
@StanShunpike In order for a theory to be Poincare invariant, the Lagrangian needs to be a Poincare scalar, what it is easy to see. The equivalent condition in the Hamiltonian formalism is that there is a Poincare algebra with the Hamiltonian as the zero component of the 4-momentum. This condition needs to be checked, as it is not elemental to see.
Jan
27
comment If a star were to suddenly dissapear, would it still have gravity?
@WetSavannaAnimalakaRodVance Yes. classical = non-quantum in my vocabulary.
Sep
29
reviewed Approve Lagrangian mechanics is different form Newtonian?