Does not a photon (particle, wave, whatever) always go to infinity? What stops it?
>> What stops it?<<
It goes to infinity until it hits something that stops it, although physicists usually to say "scatters" instead of "hits."
A photon is a little bitty snip of electric field and a little bitty snip of magnetic field kind of wrapped around each other so that each traps the other, and each keeps regenerating the other.
This amazing balanced dance only works if the whole shebang is moving at the speed of light through some non-conducting medium. Anything happens to disturb that, and the phonton pops like a bubble.