system
Given the following post, respond as if you're commenting on Reddit:
human
Do objects physically change the wavelength of light or just absorb certain wavelengths and reflect others?

Also, how is light physically absorbed? What happens to it? Does it just hit the electrons and cause them to vibrate more?
gpt
When light hits an object, certain wavelengths are absorbed. In the process, the material's molecules move into a higher energy state (electrons go to higher energy orbitals).

The molecules stay in those higher energy states for a variable amount of time (which depends on the material) and then "relax" down to their original state. In doing so, the energy initially added by the light either gets converted to heat, in the former of increased molecular motion, or, more rarely, is given off by emission of a new photon, which we call fluorescence or phosphorescence.

Substances are coloured because their molecular structures lead them to absorb (and convert to heat) certain wavelengths of light and not others. 

There are cases where substances "scatter off" light at a different wavelength, but this effect (called the Raman effect) is incredibly weak and not detectable without specialized equipment.