Langevin equation describes the brown motion. But I don't understand the nose term η(t) in the equation. What's the relationship between η(t) and the force proportional to the velocity due to stoke's law? I mean they both belong to the force between the collisions with the molecules of the...
Yes，I have to say I made a simple mistake. E can be nonzero even its curl is 0. But I think the question is clear now. Your question's condition that both E and B both equal 0 can not be satisfied. So there should not be a question"how can one say that regions of A≠0 but B=E=0 produce no...