Originally posted by ImaFungi
Originally posted by mbkennel
Electric and magnetic fields exist everywhere without requiring a charge in the specific location, but they interact with charges. Light does travel
far and long and hit and interact with particles if the particles are charged. If it is a 'vacuum' there are no (real) particles to hit.
How do electric and magnetic fields exist everywhere without requiring a charge in the specific location? Literally every point in space is
electromagnetic field lines from one side of the universe to the other?
Yes. That's what a classical field theory means. Everywhere in space there is a vector which has a magnitude in the x, y,z directions for the electric
field and another one for the magnetic field.
It gets conceptually pretty complicated with quantum mechanics (you have a wave function of functions).
this question might be relevant here;how long on average does an electron stay excited after recieving photon? (depend on photon energy?)
Well, usually this is in the context of an electron & proton system (an atom). Under normal circumstances the electrons squish in as close as they can
to the nucleus (because the nucleus is positive and the electrons are negative) limited only by laws of quantum mechanics (which explains why they
don't crash into the nucleus: there is no allowed quantum state where that happens.
There is no truly 'average' time, it depends on the specific atom and the particular energy levels you are coming from and going to. But in most
cases it's microseconds say. There are some cases when the decay rate is much longer, that's known as 'flourescence'.
if there were 100 atoms in a row and the first one got hit with a photon, can it theoretically pass on that original photon without losing any
of the original energy to each subsequent atom, if they were in a vacuum would it be like a perfect newton's cradle?
If you had 100 atoms in a row, and their electrons were in the same excited state (higher energy) and you hit the first one the right way, then
subsequent atoms can emit photons which 'add up' in the same energy & momentum state perfectly evenly. If you add some feedback to make it
self-sustaining, this is called a 'laser'.
Does this mean the vacuum is a superconductor since it can carry em radiation without resistance?
Conductivity refers to motion of physical charges (almost always electrons), not electromagnetic waves. Electromagnetic waves propagate on their own,
and electric & magnetic fields also push around charged particles, and moving particles also make electromagnetic waves. (this is known as an
Yes, I guess you could say the vacuum is a 'superconductor' for electromagnetic waves, but people don't really talk that way since it was always
pretty obvious this was the normal state of things. Whereas for a superconductor, it is something exotic and rare, because in most cases electric
current in a physical medium will have some losses as the electrons bounce off of other matter. Superconductivity is a phenomenon whereby quantum
mechanics magically makes electrons which should
be bouncing off stuff not bounce.
Think of it this way. If you're in an open field, then it's not abnormal to be able to run from one side to another unmolested. But imagine you are
in a very crowded arena with people everywhere. You are always bouncing off of them or trying to evade them. A superconductor would be magic powers
which let you simply run straight through and magically avoid colliding with all the obstacles.
edit on 26-2-2013 by ImaFungi because: (no reason given)
edit on 28-2-2013 by mbkennel because: (no reason
edit on 28-2-2013 by mbkennel because: (no reason given)