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Nov
14
revised Why is electric field zero inside a hollow metal sphere ?
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Nov
14
suggested suggested edit on Why is electric field zero inside a hollow metal sphere ?
Nov
13
revised How to compute the expectation value $\langle x^2 \rangle$ in quantum mechanics?
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Nov
13
revised How to compute the expectation value $\langle x^2 \rangle$ in quantum mechanics?
added 396 characters in body
Nov
13
answered How to compute the expectation value $\langle x^2 \rangle$ in quantum mechanics?
Nov
13
comment The role of representation theory in QM/QFT?
Hi @Nick i was not trying to be very rigorous in this answer. All i meant was that elements of group/algebra G of observables should be expressible in terms of elements of algebra A of fields. This of course follows from requirement of cyclicity of vacuum wrt A and as i think cyclicity of the vacuum wrt A is not a physical requirement but just one (though possibly only ?) way of implementing the requirement that observables be local expressions in terms of quantum fields. In algebraic approach too observables are required to be constructed out of elements of A in more abstract terms (right ?).
Nov
13
revised The role of representation theory in QM/QFT?
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Nov
13
revised The role of representation theory in QM/QFT?
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Nov
13
answered The role of representation theory in QM/QFT?
Nov
12
comment Have I discovered how to calculate the proton's mass using only integers?
Nice! but the problem here is that mass is a dimensionful quantity so the same integer representation may not hold in other units. It could perhaps be more useful if one can try to represent (say) the ratio of proton and electron mass as some such expression in terms of integers.
Nov
10
comment Does the axiom of choice appear to be “true” in the context of physics?
I think that Banach - Tarski theorem which depends crucially upon choice axiom may have some physical meaning - e.g. in terms of creation of more than one particles out of one when given with enough energy. However, the question of whether this is so or not belongs more to the domain of philosophy than physics.
Nov
4
answered Translations of field operators in QFT
Oct
24
comment Can someone identify this Landau reference?
This could be helpful.
Oct
22
comment What do I see if I move quickly past a charge surrounded by iron filings?
If 4-force in one inertial frame is zero then it will be zero in any other inertial frame too (simply because a zero vector is preserved under a linear transformation). For simplification replace iron fillings with a tiny magnet. Then in the rest frame this magnet doesn't feel any force because i) it can not respond to its own magnetic field ii) it is not moving relative to the charge. So the total 4-force on it is zero as observed in rest frame. Hence in any other frame too it will remain zero.
Oct
22
comment Do Christoffel symbols commute?
Do Christoffel symbols commute? As matrices they do not. See @Ron's answer. does $\Gamma^{e}_{db}\Gamma^{c}_{ea} = \Gamma^{c}_{ea}\Gamma^{e}_{db}$? Yes, because they are just numbers.
Oct
22
comment Do Christoffel symbols commute?
Ron's answer has quite useful information, and moreover its not irrelevant to OP's question. +1
Oct
22
comment Do Christoffel symbols commute?
They are just numbers; so yes, they commute.
Oct
22
comment What really is Spacetime?
Most physicists believe that i) Spacetime was created at big bang. ii) Energy controls its "shape" and "size" iii) If in some region of space you can create a high energy density then you can even create a hole in space time. iv) however nobody knows what spacetime would look like at such high energies, or even if it would exist or not. In particular, there is no agreement among physicists as to what should be a quantum theory of spacetime.
Oct
22
comment What really is Spacetime?
+1 good question :)
Oct
21
comment How to determine the probabilities for a cuboid die?
I think general solution to your conditions would be $P_{ab}=f(ab,bc,ca),P_{bc}=f(bc,ca,ab),P_{ca}=f(ca,ab,bc)$, where $f$ is a function which is symmetric in its second and third arguments, and goes to zero when its first argument goes to zero. For example $f(x,y,z)=x^n/(x^n+y^n+z^n)$ for any $n$ is also a solution.