I asked a couple of questions about magnetism before and I have to say I was not fully convinced by the answers – so here is another way of stating what puzzles me.
Imagine a static magnet. Now magnetism cannot propagate instantaneous as if it did the magnet would surely immediately cease to be magnetic – even though we know, via Oblers’s Paradox if nothing else, that the universe is finite, we must surely also assume it is very large and contains a very large number of magnetic objects.
So magnetism is propagated at some finite speed. Naturally we will assume that speed is , the speed of light and the propagation is via photons. But what are these photons?
If they are real, physical particles, then they must carry energy and so the magnet should ‘run down’ – otherwise it would be a perpetual motion machine. But static magnets apparently run down very slowly – so slow I have never been aware of it really happening, though I have no doubt it does.
So what else might they be? Presumably a function of quantum electrodynamics (QED) as formulated by Feynman? In this case then the energy of these “virtual” photons is a function of the uncertainty principle.
This would essentially mean that the strength of these magnetic photons would be limited by where is the energy of the QED photon, time and the familiar Planck constant – a very small number indeed.
Here the particles can come and go in an instance or presumably, live mysteriously for a very long time at very low energies. But no actual energy is expended unless this virtual photon is “observed”.
So, is this right? And if it is, how did anyone explain magnetism before QED? And if it is wrong how do magnetic fields propagate.
- Why the symbol for magnetic field is ‘B’ (johndcook.com)
- The Meaning of the Speed of Light (unapologetic.wordpress.com)
- Energy and the Magnetic Field (unapologetic.wordpress.com)
- How Do Magnets Work (eoghann.com)
- Lasers plus a crushing magnetic field may make fusion more efficient (arstechnica.com)
- The Propagation Velocity of Electromagnetic Waves (unapologetic.wordpress.com)
- #1: Magnets (seanmaguire16.wordpress.com)