system
Given the following post, respond as if you're commenting on Reddit:
human
What's the difference between a free photon and photon as a force carrier?

I want to understand how photons work. Apparently the light that flies through the void of space is made from photons. But the electromagnetic fields that surround us at all times, including our TV and WiFi and what have you, are also made of photons that carry interactions between charged particles. And somehow, in both cases photons are bosons, have no mass and no charge. I understand that by "light" we usually understand just its IR, visible and UV spectra, and that light and radio and gamma rays are actually all EM, just of different frequencies, but still, how does all that work? If light is made of photons, why doesn't light have charge? If electromagnetism is carried by photons, why don't they have charge? What's the difference between a photon of light that flew into my eye after being emitted by the Sun, and photon that carries my WiFi signal?
gpt
Photons as “force carriers” are **virtual** photons. We have some FAQ entries on virtual particles that you may want to read.

But to summarize them, virtual particles don’t literally exist. If you try to interpret them as particles that literally exist, you reach nonsensical conclusions, like photons having nonzero (or even imaginary) mass, and having more than two linearly independent polarization states.

Why don’t photons have charge? That’s just what we observe to be true. The gauge group of the electromagnetic force is Abelian, so photons don’t directly self-interact.

If you look at a non-Abelian gauge theory, like the theory of the strong force, that’s not the case.