I’m reading “Manifold: Time”, a good science fiction yarn, and I’ve plowed about halfway through it. In the latest happenings, the protagonist(s) get a glimpse of the future– the far future. It raises some fascinating issues.
According to recent scientific measurements, our universe is about 13.4 billion years old. That’s obviously a very long time; in comparison humanity has been around for the merest blink of an eye. But consider that the sun will probably continue burning for another few billion years– eventually bloating to become a red giant, then shrinking to die quietly as a dwarf star.
Beyond that, as the eons pass, the stellar population of the galaxy will continue to age. Stars will die, some as spectacular supernovas, and in their death throes will give birth to new stars. But as time marches inexorably onward, fewer and fewer new stars will be born. The raw material to build them will become more rare. The black hole at the center of the galaxy– currently massing several million stars– will grow as it engulfs stars near the galactic core.
Continue farther into the future, when stellar fusion begins to run down. The universe has expanded to the point where the energy density is frightfully low, and only small local energy sources provide any warmth in a rapidly-cooling cosmos. As the clock marches into the hundreds of billions of years, the stars burn out and space goes dark.
Trillions of years pass. Black holes are the only viable energy sources, because as they swallow entire galaxies, and even clusters of galaxies, they give off gravitational radiation. Hopefully future civilizations will know how to harness that energy, because it will be one of the few ways to sustain life.
The exponents climb: hundreds of trillions of years, and still farther. Matter itself begins to come apart as proton decay steps in. Atoms can no longer remain stable; they simply dissolve into quarks. There is virtually no energy left anywhere– the universe has expanded to the point where it is near absolute zero.
And in the end– the very very end– there is nothing. Matter and energy have completely evaporated: consumed by black holes, dissolved into constituent particles. Space is cold, dark, and empty.
Kind of puts things in perspective. Enjoy what you have, because eventually it’ll be gone.