# Gauss Law for Magnetism,Non Instantaneous Field Propagation

Is the magnetic force instantaneous? And, are all field lines established simultaneously? Otherwise, for example, the field line marked 'L' will take longer time to propagate than the ones above it, so there will be a net outward flux in the time when L is out and not yet in into the surface.What happens to Gauss Law then?

Are all the field lines established simultaneously, like 'L',that stretches out so far, and the straight one? If not, then the force between the magnets must increase with time.

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Changes in magnetic field (and hence magnetic field itself) travel with speed of light. Bar magnet picture could be confusing. Think of a wire. When you switch on current through it then it is clear that magnetic field will expand out in circles (rather than directed lines), and so Gauss's law would be fine. – user10001 Jul 26 '12 at 17:19
The question is not clear. What's the imagined violation? The field lines are produced in many closed loops that grow and leave behind the static field at long times, so that Gauss's law is never violated. – Ron Maimon Jul 27 '12 at 6:40
@Ron Maimon : I've actually imagined field lines as "snakes", each with a head and a tail. – Swapnanil Saha Aug 7 '12 at 16:38
@SwapnanilSaha: well, stop doing that. Imagine them as rings. Only E fields are snakes. – Ron Maimon Aug 8 '12 at 16:40
@Ron Maimon : Also the G ones, right? – Swapnanil Saha Aug 9 '12 at 12:58