In his 1925 poem “The Hollow Men,” English poet T. S. Eliot wrote “this is the way the world ends / not with a bang but a whimper,” referring to the irony of modernity. But Eliot could have easily been speaking about the cosmic condition-- how everything may end. Cosmologists generally agree on the Universe’s beginning, as an instantaneous, seething quantum inflation of space, time, and energy— the Big Bang. But its swan song is open to debate, with several theoretical scenarios in play.
Since the Big Bang, the Universe has continually expanded. In fact, the expansion seems to be accelerating, under the influence of enigmatic dark energy. On the losing side of a cosmic tug-o-war is gravity. A critical question is whether dark energy will always prevail, or might gravity gain the upper hand.
If gravity triumphs, expansion will slow, then reverse. The Universe will rewind toward its initial state, gradually condensing and warming. Eventually, the temperature everywhere will reach the point where all matter deconstructs into fundamental particles— and beyond, where known physical laws unravel. This scenario is called the Big Crunch. A variation on this is the Big Bounce, where quantum fluctuation in the final moments may spontaneously reverse the Crunch, generating a new Big Bang.
If dark energy reigns, expansion will continue unabated, leading to one of two scenarios-- the Big Freeze, or the Big Rip. In the Big Freeze, space grows ever sparser and colder until it reaches full thermodynamic equilibrium, at which point all motion in the cosmos will cease. With this will come the end of time— after all, how do you measure time where absolutely nothing can happen? In the Big Rip, the expansion rate quickens to infinity, completely rending all space, matter, and energy into non-existence. And once again, time will die.
An esoteric possibility is the Big Slurp, where the Universe collapses under the hypothetical phenomenon of false vacuum decay. Simply put, empty space has a minimum level of quantum energy, but whether it is the absolute minimum is unclear. If it is not, space could spontaneously drop to a new minimum, completely destroying all quantum fields (and all else) with it.
To paraphrase English poet Robert Herrick, if you are panicking over the time left to “gather ye rosebuds while ye may”, there’s good news. The timeframe for these scenarios ranges from 10e11 to 10e100 years— at least ten times the Universe’s current age of 14 billion years. None of us will live to witness this extreme future. These scenarios are also speculative, extrapolations based on current cosmological understanding. Perhaps none will transpire. Come what may, bang or whimper, give thanks that there is a cosmos-- rather than none at all.
Western Slopes Skies is produced by the Black Canyon Astronomical Society. This episode was written and voiced by Michael T. Williams.
Links of interest:
Fate of the Universe
Chronology of the Universe
https://www.youtube.com/watch?v=uD4izuDMUQA">Timeline of the Future -- a sobering 30 minutes into the extreme future