Recent content by Demystifier

Is analogue Hawking radiation, namely radiation of phonons in systems with sonic horizon, "known" physics?

Then something less mundane https://arxiv.org/abs/1311.4363

How about putting spherical mirror around the black hole?

The norm that you consider, as a function of ##a##, has a jump at ##a=0##. Therefore you cannot find the value at ##a=0## by considering the limit ##a\to 0##.

Yes.

Yes, but in that case you are no longer considering two photons. And by the way, the expression "Feynman rules" means something entirely different, it's related to perturbative Feynman diagrams, not to Feynman path integrals.

When you have two entangled photons, there is no such thing as amplitude of photon 1. There is only an amplitude for both photons together.

Electrodynamics (interaction of EM field with charged fields) is also nonlinear, but quantum electrodynamics is linear and the superposition principle is valid. The point is that electrodynamics, gravity, etc. are non-linear in the sense that Hamiltonian is a non-quadratic function of fields...

For a visualization, consider the surface of a cylinder. It is curled in one direction, but flat in another.

That's wrong. Have you ever seen any equation in quantum mechanics for a system with two or more particles?

No, both photons together are "one particle" in 6 dimensions.

I guess we are talking about nonrelativistic QM, not about QFT. If you have two particles, each moving in 3 dimensions, you can think of it as one particle in 6 dimensions. Write the path integral by pretending it's one particle in 6 dimensions, and you will get the right result.

The observables such as energy, momentum, angular momentum and charge are conserved in the sense that the corresponding operator does not have an explicit time dependence. Let ##A## be any observable conserved in that sense. If you measure A (and hence collapse the state) and then measure A...

That's right.

Right, but decoherence cannot be properly understood without its derivation. You can describe decoherence by phenomenological models without explicitly taking into account the environment, but such models lack deep understanding.