system
Given the following post, respond as if you're commenting on Reddit:
human
Is light made of particles, or waves?

This comment by RobotRollCall got me thinking: 

>"In a sensible, physically permitted inertial reference frame, the time component of four-velocity of a ray of light is exactly zero. Photons, in other words, do not age. (Fun fact: This is why the range of the electromagnetic interaction is infinite. Over great distances, electrostatic forces become quite weak, due to the inverse square law, but they never go to zero, because photons are eternal.)

>"In the notional reference frame of a photon, all distances parallel to the direction of propagation are contracted to exactly zero. So to a photon, emission and absorption occur at the same instant of time, and the total distance traveled is zero."

This sparks so many questions. Light is emitted radially from the sun, so does that mean that, if the range of electromagnetic radiation is infinite, an infinite number of photons are sent into space in all directions, just waiting to interact with something a billion light-years away? Wouldn't a wave-like definition make much more much more sense in that situation?

Honestly, I've never been convinced that light is made up of particles...

tl;dr What the F are photons?
gpt
Photons are particles. Period. End of paragraph.

To be more specific, photons are massless, uncharged vector bosons. They have no mass, no electric charge and a spin quantum number of 1, and they obey Bose-Einstein statistics. The behavior of photons is *extremely* well understood, and is essentially the same as the behavior of any other type of subatomic particle.

But *light,* however, is something else. Light — and by extension, things like radio waves and X rays and so on — is what you get when you put a bunch of photons together.

A photon left on its own behaves in a fairly simple manner. It moves in a straight line at the speed of light forever, until it's absorbed by a charged particle. Mostly.

But when you get a lot of photons together, new and curious behaviors emerge. When you consider a bunch of photons as a single thing — a ray of light, in other words — you see behavior that looks more like a wave phenomenon than a bunch of particles. Light can be very accurately modeled, in fact, as a wave phenomenon. The mathematical models that describe light as a wave phenomenon work extremely well … except when you try to apply them to things like the photoelectric effect. For that, you have no choice but to zoom in and examine light for what it really is: a bunch of particles. That's how Einstein got his Nobel prize, incidentally.

So to sum up, light is made of particles. Period. But those particles are not like little bowling balls. They cannot be modeled with classical mechanics. They have properties that can only be described with quantum mechanics, and it's those properties that cause light, when viewed at a larger scale, to look like a wave phenomenon.