Starting at 10-25 seconds after the start of the universe (inflation) and ending 1015 years later (with the ultimate fate of the universe), the timeline of the universe is an incomprehensibly long and fascinating one. To help understand the forces that led to life as we know it and to get an idea of what’s going to happen in the (distant) future, theoretical astrophysicist Ethan Siegel has broken down the details in a wonderfully accessible and enlightening complete history of the universe (with pictures!).
Those last couple of steps on the timeline are particularly humbling:
100 billion years: the Universe has expanded so much that our local group, having merged into a giant elliptical galaxy, is the only one left in the visible Universe!
We’ve got a long time left of stars going through the great cosmic life-cycle, burning their fuel, exploding, triggering star formation, and burning their new fuel. But this is limited; there’s only a finite amount of hydrogen and other elements to burn via nuclear fusion. The skies will eventually go completely dark, as the last of the dim, red dwarf stars (the longest-lived ones) exhaust their fuel.
1015 years: the last bit of hydrogen is burned up, and our entire Universe goes dark, being populated only by black holes, neutron stars, and degenerate dwarf stars, which eventually themselves cool, fade, and turn black.
And that’s the entire Universe, from the very beginning of what we can sensibly say about it to the far distant future!