Recent content by Demystifier

If the fields of the Standard Model are not fundamental, then what is? We don't know. It could be some other fields, or it could be strings, or it could be string fields, or it could be something more abstract as suggested by M-theory, or, if Lorentz invariance is not fundamental, it could even...

I disagree https://www.physicsforums.com/threads/simulating-physics-the-current-status-of-lattice-field-theories.1014629/#post-6626056

There are two kinds on infinities in QFT, UV infinities and IR infinities. UV infinities are due to using a continuum (in both space and time), while IR infinities are due to using infinite extension (in both space and time). And yes, it is known for sure that this is the case.

That's an illegitimate assumption unless ##q(t)## is ##t##-independent. If ##q(t)## depends on ##t## then the charge is not conserved, which is not compatible with Maxwell equations which imply charge conservation.

What do you mean by electron path? It's not even defined, except in the Bohmian interpretation. Since the thought experiment is defined in terms which do not depend on the choice of interpretation, the reversing can only refer to the wave function, not to the electron path. The Bohmian...

Schrodinger didn't know what is the physical meaning of the wave. He only used the nonrelativistic energy formula $$E=\frac{p^2}{2m}+ V(x)$$ Planck's formula $$E=\hbar\omega$$ and de Broglie's formula $$p=\hbar k$$ From this and the ansatz ##\psi=e^{-i\omega t} e^{i kx}## for ##V=0##, the...

If you draw the Feynman diagrams for absorption of one and two photons, you see that they have one and two vertices, respectively, so the latter is suppressed because it is a higher order in the perturbative expansion in ##\alpha##.

Pop science QM is written by actual physicists. They give the best explanation they can under the constraint of not using equations. So when a physicist gives such an explanation of QM in a pop science text, that's because he/she thinks it's essentially correct.

I don't think there is any difference between QM and QFT in that sense. You can certainly think of QFT in terms of ensemble, after all Ballentine in his book has a chapter on quantum optics, which is a QFT. More generally, for any interpretation of QM there is a corresponding generalization to QFT.

There is a simple but general principle how to determine whether a statistical ensemble describes well a real single system. The statistical ensemble is just a conceptual model for the notion of probability distribution. From the probability distribution ##p(x)## (where ##x## is a microscopic...

A canonical or grand-canonical ensemble is best understood as a small (but macroscopic) subsystem of a larger system. The larger system is usually assumed to be in a micro-canonical ensemble, meaning that its energy is well defined with almost perfect precision. Under these conditions the...

Fair enough. But in that case people like @PeroK should specify which interpretation they have in mind when they argue that environment is not needed for randomness. Because it looks as if he has some Copenhagen-like interpretation in mind, and yet environment-independent randomness does not...

Which is the standard interpretation. Of course, I am not advocating the standard (Copenhagen) interpretation, but I am pointing out that someone who does should find very plausible the idea that randomness is somehow related to the influence of the environment.

But according to standard QM the state represents a complete description of the system, there is nothing else except the state. Hence the deterministic description of an isolated system by the state is a complete description of an isolated system, at least according to standard QM.

I think I see now where is the problem. Many people don't understand very well how randomness arises in classical deterministic mechanics, they find it confusing. So when someone tells them that quantum randomness is a true randomness that does not arise from a classical-like determinism, they...