system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What makes mirrors reflective?
gpt
For this, it’s important to understand what light is, an electric and magnetic field that changes in strength as it travels as a wave.

When it hits a conductor, like a metal, the electrons in the metal move freely, riding the wave up and down like a beach ball on the ocean.  But when those electrons move, that motion causes another electromagnetic field to form.  The one from the electron ends up canceling the one that is the light going forward, and you’re left with only the one from the electron going backward.  Hence, reflection.

What’s weirder is that the electrons have a limit on how fast they can move, and if the light is too high a frequency, the electrons are getting pushed from both directions rather than riding the wave, so stay still.  So they stop reflecting.  The properties of the metal in question change their upper limit on how fast they can move, which causes certain metals to stop reflecting certain colors at different parts of the spectrum.  Copper stops reflecting in the red, gold in the greenish-yellow, and silver or aluminum in the UV.  This is why metals have different colors.