Well, eventually the sun will explode into a red giant; and if we make it past that somehow, the universe will cool down and spread out so much that we won't be

Well, eventually the sun will explode into a red giant; and if we make it past that somehow, the universe will cool down and spread out so much that we won't be able to have enough energy to do stuff. So, even if we don't "go extinct", either our solar system or our universe will. Still, I think the question on people's minds is whether it's 2 Billion years, 200 years, or - if the US and Russia play their nuke cards - maybe less :-(