system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is a vacuum the fastest substance for light to travel through?

Just like some mediums can increase speed of transfer (e.g conducting metals > vacuum for heat)
gpt
Heat and sound travel better through some materials because their travel is dependent on atoms of matter bumping into each other to transfer their energy (heat through conduction at least). Basically, they need a medium to hitch themselves to in order to travel, and generally the more medium available to them, the better (faster) they can travel, because having more atoms in close proximity means that more atom collisions will occur and transmit the energy.

Light doesn't require a physical medium to travel through. In fact, atoms just potentially get in light's way, making things worse.