system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can the universe constantly expand with no end?

I'm not sure if text is allowed here but I would love this explained like im five, basically throw it at me in a really simple way.

Surely an explosion cannot continue forever and would have to end at some time, right? So why does it not?
gpt
Firstly, the big bang is **not** an explosion. Nor is the universe expanding like some kind of ball or balloon, getting bigger and bigger, displacing more and more of the atmosphere. Instead, think of the expansion of the universe like the surface of the balloon as it expands. Or hell, skip the balloon part, imagine an infinite plane expanding.

Each point on the universe is expanding away from every other point on the universe, with the rate of expansion proportional to the distance between said points.

>Surely an explosion cannot continue forever and would have to end at some time, right? So why does it not?

This idea is based around a "explosion" model which doesn't reflect reality. The expansion of the universe despite the pull of gravity is caused by dark energy, which causes negative pressure and "pushes" things apart.

Now, you may say, what about conservation of energy? Doesn't this violate that? 

Yes, and there's no problem in that. The universe does not conserve energy. The conservation laws come from Noether's theorem. The tl;dr is that if a system is time-translationally invariant (in simpler words, things work the same no matter what time it is), then there is conservation of energy. An expanding universe does not fit this criteria. 

The ultimate fate of the universe depends on its curvature. For now, we think it's flat from empirical observations, which means a heat death is in store for us.