SPEAKER 1: To close, we will briefly consider what the universe might hold for the future. This is, of course, completely speculative, as extrapolation is apt to be. One possibility, known as the Big Crunch, is that the universe's expansion will start slow. It will stop expanding, and then start to instead recollapse. As it collapses, galaxies will collide and coalesce. The density and temperature of the universe will increase. And ultimately, the universe ends in a fiery cauldron, just as it started.
This has led some to postulate a cyclical universe, in which a new Big Bang follows the Big Crunch, and new universes evolve out of old ones in eternal succession.
An alternative is that the universe eternally expands at an accelerated rate. Galaxies become more and more distant, and the night sky becomes increasingly empty. Ultimately, our galaxy is destined to be alone, as the island universe Kant postulated.
Finally, in a universe dominated by dark energy, the acceleration could be so extreme that even gravitationally-bound objects like galaxies are ripped apart by the rapid expansion.
In this Big Rip picture, 60 million years before the end of the universe, galaxies would be torn apart. Three months before the end, the solar system would be gravitationally unbound. A few seconds before the end, planets would be torn apart. And finally, atoms destroyed. 20 billion years from now, the universe would be comprised solely of isolated fundamental particles.
Finally, we come back to the simple graph we had at the start in understanding how the universe has evolved. The last century has enabled great insight since the universe's history, from the Big Bang theory to the accelerative expansion today. It's not clear however what the future holds, and we have a significant way to go to explain all the properties of the universe, including dark matter, dark energy, and the physics of the universe's inception.
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Cosmology uses observations of cosmic structures, like stars and galaxies, to understand the origin, evolution, and ultimate fate of the universe. Join Rachel Bean as she examines our current perception and evolving ideas of the universe.
This video is part 1 of 6 in The Puzzling Life of the Universe series.