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The universe will last for more than a googolplex years, with its lifespan related to that of humanity. Its geometry is a function of its overall density, with a critical value, omega, determining whether it is closed, flat, or open. Currently, the universe appears flat and is expanding at an accelerating pace due to dark energy. If it continues to expand, galactic superclusters, local clusters, galaxies, and stars will eventually fall apart. However, humanity can prolong its existence by using arrangements of matter and energy, such as black holes.
According to the best guesses of contemporary cosmologists, the universe will continue to last for an extremely long time, something more than a googolplex year. A googolplex is a very large number: 1010100. Some estimates are even larger. The question of how long it will last is related to the question of how long the human species, or our descendants, will last, barring some disaster that will wipe out all people prematurely.
The universe is known to be expanding, but a frequently asked question is whether or not this expansion will continue indefinitely. Current signs indicate that not only is an expansion taking place, it is happening at an accelerating pace. This can be attributed to a negative pressure throughout the universe, referred to as dark energy, a cosmological constant, or a quintessence. The notion of a cosmological constant was first formulated by Einstein.
Predictions about the lifespan of the universe are traditionally associated with its overall geometry. Its geometry is a function of its overall density. Here a critical value, omega (ω), comes into play.
If the density of the universe is greater than , it is closed, meaning it has a spherical spatial geometry. In a closed universe, if a person travels far enough, they return to their starting point, just like on planet Earth. If its density is approximately equal to , it is flat, meaning that without dark energy, the rate of expansion will slow down and asymptotically approach zero. If the density is less than ω, it is open, meaning it has negative overall curvature and will expand indefinitely with or without dark energy.
Currently, it appears that the universe is flat. The problem with the above analysis is that, with enough dark energy, it will expand indefinitely, no matter what its geometry. Recent studies show that the universe probably contains so much dark energy.
If the universe continues to expand for a very long time, eventually galactic superclusters will fall apart, followed by local clusters, galaxies themselves, and finally individual stars and atoms. If the descendants of humanity are clever about what arrangements of matter they use to instantiate and empower themselves, however, they can prolong their existence almost indefinitely. For example, even black holes produce some energy through Hawking radiation, which life could cluster around and use to its advantage even if the stars burned out. Living indefinitely in an ever-expanding universe wouldn’t be a picnic, but it’s probably preferable to living in a closed universe that collapses in on itself in a fiery Big Crunch.
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