system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't energy be made/destroyed? Does that mean we will eventually run out of energy?
gpt
>Why can't energy be made/destroyed?

This is actually a *really* deep question that we're not entirely certain is correct, *but* from every system we have ever interacted with or otherwise studied, we have observed that energy must be conserved in the process. Energy doesn't just spontaneously come into existence (or leave it); if it did, it would cause all sorts of odd things to happen that we would have noticed by now.

Furthermore, if you buy that matter is stuff, and matter and energy are related through relativity (e = mc^2), then it seems relatively straightforward; a set amount of stuff existed in the Big Bang, and that set amount of stuff hasn't increased or decreased in size, number, amount, or whatever since the Big Bang.

>Does that mean we will eventually run out of energy?

Yes and no. Energy isn't destroyed; when you use energy, it doesn't suddenly go away, it's just transformed into a different kind of energy. That energy is dissipated into the Universe and is no longer usable for any process. Eventually, when all energy in the Universe is dissipated in such a way, no process will be possible anywhere. This is the idea of the Heat Death of the Universe.