system
Given the following post, respond as if you're commenting on Reddit:
human
If atoms are made of almost entire empty space, why isn't everything we see translucent to a certain extent?
gpt
It is. Ever had a dental X-ray?

Most of the matter in the universe is transparent to *some* electromagnetic radiation, to a greater or lesser extent. As to why most of the stuff we interact with day-to-day is opaque, it's because photons in the visible-light part of the spectrum are about the same "size" as most molecules. So visible light can be absorbed and reflected by matter, which makes most everyday matter partially or completely opaque.

One might naturally ask why it is that this is true of *visible* light and not gamma rays or radio. That question actually kind of answers itself, if you turn it on its head. In order for light to be *visible* we have to be able to *see* it, which means it needs to interact promiscuously with the molecules in our retinas. We see "visible light" because "visible light" is the part of the spectrum that can interact with matter.