Originally posted by Decker
I have a question about photons. They compose light, right? They are particles with zero mass, no electric charge, and an indefinitely long lifetime, right?
Well, I'm no expert on this, but I think those are essentially correct. The thing about zero mass should be zero
rest mass. Photons do have momentum. A subtle distinction, perhaps, but it's an important one. Also, I don't know what you mean by an indefinitely long lifetime. It's not infinitely long; a photon ends when it absorbed. Even if you meant it has an infinitely long half life, that's a bulk property. A free neutron has a half life of about ten minutes on average, but an individual neutron can decay in ten mincroseconds or less or ten millenium or longer. You don't know beforehand. In all cases, the lifespan on any individual particle is indefinate.
The thing that seems weird to me is - if they have zero mass, what keeps them from going faster, in fact - how can they even physically exist with 0 mass? It would seem to me that something with 0 mass could be capable of instant speed. Obviously, this is wrong. But why? What keeps light/photons "existing" the way they do?
They're going as fast as they can. The structure of space time doesn't allow them to go faster. And why shouldn't they exist without mass? Things exist without charge. As far as I know, the only thing that's absolutely necessary for something to exist is energy, and they have that.
I'm not sure what you mean by "instant speed." When a photon is emitted from an atom, say, it begins it's existence moving at the speed of light. It has that speed instantly. Particles without mass cannot go slower than that, not even for an instant. I suspect you meant to say "infinite speed," but that concept doesn't make sense in our universe.
What allows a photon to continue to exist is that it's an oscillating electromagnetic field. You can't have a static electric field without a charge, but the photon is an uncharged particle. So it's electric field decays. But change in an electric field induces a magnetic field. But, you can't have a static magnetic field without a current to anchor it, and you can't have a current without a charged particle, so the magnetic field decays too. And that induces an electric field, which gets us back to where we started. And so on, and so on. The photon is the continual inducement of these fields because the fields cannot be maintained statically. As I understand it, that's why the photon has to be moving, and move it sure does!
Also, doesn't having a set "smallest amount of a physical quantity that can exist independently" seem illogical? (to me, it seems like logic should say you can break something down [that exists] indefinitely.) Obviously I am wrong, but how?
Well, I don't have a problem with that. There's at least as much philosophical problem with breaking things down infinitely, isn't there? Logically, don't you have to get to a point where breaking something down has to chage the essential nature of the substance? For example, you can only divide a glass of water a few dozen times before you have to break down a water molecule into hydrogen and oxygen, and then it's not water any more. At some point, shouldn't the nature of reality itself have to break down, and so, since this can't happen, provide a floor below which you can't go?
It's an interesting differnce of perspective, though.
