system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 How does a fridge make things cold?

I have had this question in my head for the longest time, and I just can’t wrap my mind around it. How does a fridge make what is inside it cold? I am familiar already with the concept of adding heat by adding energy, but the other way around just doesn’t seem to work... Do refrigerators just subtract (?) energy from within themselves? Do they just rely on wind and cold air?
gpt
It was already known that compressing a gas makes it hot. Someone got the neat idea that, well, what if we let it cool down, then uncompress it again? It'll be really cold! That's basically how refrigerator and air conditioning compressors work.