Plutonium

Source - https://xkcd.com/2115/

Rollover Text - It's like someone briefly joined the team running the universe, introduced their idea for a cool mechanic, then left, and now everyone is stuck pretending that this wildly unstable dynamic makes sense.

See, it's funny because the concept of a solid chunk of metal just generating energy for billions of years is just ridiculous.

Except that it isn't.