system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If microwaves work by heating water molecules, how do they heat things without water molecules, like plates?
gpt
It doesn't just heat water, it's just that water is good at absorbing the microwave radiation. 

The microwave is designed so the inside wall reflects as much of the radiation as possible. So if there is a photon which completely penetrates whatever you put into the microwave, it's probably just going to bounce off the wall and make another pass - until it's absorbed by something. So regardless of what you put into the microwave, it's going to receive a similar of power, be it an empty plate or a huge bowl of soup.