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Apr
16
comment Can nowadays spin be described using path integrals?
Google books allows to see the relevant pages online: books.google.de/…
Mar
9
comment Could Gamma ray bursts be caused by matter-antimatter annihilation?
I'm talking about these ones: en.wikipedia.org/wiki/Gamma-ray_burst
Mar
1
comment How can the product of two real linear operators be not real?
And self-adjoint/Hermitian means the operator has real eigenvalues?
Mar
1
comment How can the product of two real linear operators be not real?
I cannot find the word Hermitian on the page before. But maybe you are referring to this sentence: "A linear operator may equal its adjoint, and it is then called self-adjoint. It corresponds to a real dynamical variable, so it may be called alternatively a real linear operator." So for Dirac a real linear operator is a self-adjoint operator and an imaginary operator is then a non-self-adjoint operator?
Jan
12
comment Less than absolute zero possible?
A recent paper in Nature (nature.com/nphys/journal/v10/n1/full/nphys2815.html) claims, that negative temperature is a concept based on an inconsistent definition of entropy, see also my answer here: physics.stackexchange.com/a/93398/1648
Jan
11
comment Is it possible to split baryons and extract useable energy out of it?
So one cannot fire an electron onto a proton and by that converting it into a neutron (inverse beta decay/electron capture), waiting for the neutron to beta decay and hope that the electron that comes out has more energy than the electron that I used to begin with? But what if that happens in a radioactive nucleus or otherwise exited nucleus? Couldn't the electron that comes out have a bit more energy than the incoming one, by taking with it some energy from the nucleus?
Nov
3
comment Why are Only Real Things Measurable?
I made further edits to my answers and removed Dirac's quote from two of them.
Nov
3
comment QM without complex numbers
I do not disagree with your answer. One can for sure formulate QM in a way that uses pairs of real numbers instead of complex ones. However as Dirac points out, one has to be aware that in QM measurements might not commute. If one would formulate QM with pairs of real numbers, it would be more difficult to distinguish between pairs of real numbers, where measurements commute and between pairs of real numbers, where measurements don't commute.
Nov
3
comment QM without complex numbers
I'm not sure if that is a good example, but think about the wave function described by Schrödingers equation. One could split Schrödingers equation into two coupled equations, one for the real and one for the imaginary part of the wave function. However one cannot measure the phase and the amplitude of the wave function simultaneously, because both measurements interfere with each other. To make this manifest, one uses a single equation with a complex wave function, and generates the observable real quantity by squaring the complex wave function.
Nov
3
comment Why are Only Real Things Measurable?
Dear Qmechanic, I believe otherwise and I'm willing to take the risk and let the crowd decide if my answers are relevant or not for the questions. I don't care about the reputation points. If I get any, I promise I will donate them to Dirac.
Nov
3
comment Quantum version of the Galton Board
Thank you! Your last reference also led me to this article in Wikipedia with a picture of the distribution: en.wikipedia.org/wiki/Quantum_walk . However, is it true that neither for the fermion nor for the boson case the resulting distribution can be expressed in closed form?
Nov
3
comment About the complex nature of the wave function?
Dear Qmechanic, isn't is also frown upon to copy-paste identical comments? ;-) However I admit, that my answers were too similar. So I tried to follow your suggestion (iii) and personalized my answers to address the specific question in a better way. However I still believe the quote from Dirac is very relevant and important, so I will refer to it in every answer.
Nov
3
comment Can one do the maths of physics without using $\sqrt{-1}$?
Dear Qmechanic, isn't is also frown upon to copy-paste identical comments? ;-) However I admit, that my answers were too similar. So I tried to follow your suggestion (iii) and personalized my answers to address the specific question in a better way. However I still believe the quote from Dirac is very relevant and important, so I will refer to it in every answer.
Nov
3
comment Why are Only Real Things Measurable?
Dear Qmechanic, isn't is also frown upon to copy-paste identical comments? ;-) However I admit, that my answers were too similar. So I tried to follow your suggestion (iii) and personalized my answers to address the specific question in a better way. However I still believe the quote from Dirac is very relevant and important, so I will refer to it in every answer.
Nov
3
comment QM without complex numbers
Dear Qmechanic, isn't is also frown upon to copy-paste identical comments? ;-) However I admit, that my answers were too similar. So I tried to follow your suggestion (iii) and personalized my answers to address the specific question in a better way. However I still believe the quote from Dirac is very relevant and important, so I will refer to it in every answer.
Jun
27
comment How can “quantum particles have positive masses, even though the classical waves travel at the speed of light”?
When you are saying gluon have a classical wave, do you mean gluons can be described by a classical wave equation?
Jun
4
comment Can one define an acceleration operator in quantum mechanics?
Isn't $\dfrac{i}{\hbar}[\hat U, \frac{\hat P}{m}] = \frac{U (\vec x)}{m} \nabla - \frac{\nabla U(\vec x)}{m}$ ?
Feb
4
comment Can silicon droplets bouncing on a vibrating surface be a model for Quantum Mechanics?
see here: link.aps.org/doi/10.1103/PhysRevLett.97.154101 or here nature.com/nature/journal/v437/n7056/abs/437208a.html
Aug
20
comment Why do people categorically dismiss some simple quantum models?
See also physics.stackexchange.com/a/17035/1648
May
30
comment Can a charged black hole interact via electromagnetism?
@RonMaimon I always thought photons are travelling at the speed of light. I guess you are talking about virtual photons, aren't you?