system
Given the following post, respond as if you're commenting on Reddit:
human
How does transparency work?

As far as I can tell, there aren't little holes for the photons to jump through in my window.

I'm curious to know the mechanism behind transmitting light through a transparent material in addition to the obvious case of how it gets through the air we breathe.
gpt
So there are two different primary mechanisms for transparency.

1) Materials have what is called a "bandgap". In this bandgap, electrons in the material cannot have certain values of energy. That is, imagine a ball - you can give the ball any energy you want. But in a material, if you pretend the electrons are balls, they can actually only have certain energy values.

Now in order for a material to interact with light, the light must be absorbed. So lets say you have an electron at some energy which tries to absorb the photon. If the total energy of the electron after the absorption was not allowed in the material, then the photon can't be absorbed at all, and the photon just passes through. This is the mechanism of transparency for many everyday materials.

Also aside from just the energy, the momentum of the light must be conserved. This leads to a more complicated process, but sufficed to say that absorbing X energy and Y momentum from a photon can be prohibited in a material, meaning that the light won't be absorbed at all.

2) The second mechanism of transparency is where the photons have too much energy to interact with the electrons. In order for the electrons to interact with the photons, they have to pick up the photon energy.

Imagine you are sitting on a swing. If someone pushes you nice and slow, you will start swinging and absorb their energy, and your swinging frequency will match up with their pushing frequency. But if some asshole comes up to you and starts quickly hammering on your back then you're not going to go swinging really quickly, you're going to sit there and vibrate while all that energy in your back dissipates and rattles up the chain.

The same process happens in electrons - if the incident photon has an energy too high then the electron can't respond fast enough to capture that energy. Therefore, the photon will pass right through the material. This is the mechanism of transparency for things such as x-ray beams going through your bones.

As you can see, transparency is actually a very difficult topic and is quite complicated.