The End of the Universe
The universe was created through the Big Bang, when all matter existed in a tiny, compact, and dense point that eventually exploded. Interestingly enough, the death of the universe may end similarly to its beginning. Cosmologists have come up with three possibilities with how this end could occur: the Big Freeze, the Big Rip, and the Big Crunch.
Ever since the Big Bang, the universe has been expanding, pulling galaxies farther away from each other. The further away they are pulled from each other, the faster the speed in which the mysterious force separates them accelerates. This force is called dark energy. However, there is another force that pulls galaxies together: gravity. These two opposing forces are constantly working against each other, pulling galaxies in opposite directions. In the end, the stronger force will determine which of the possible endings may occur.
The Big Freeze
The Big Freeze is also referred to as Heat Death. In the Big Freeze, dark energy would prevail. The force would just be strong enough for galaxies to be separated to the point of the force of gravity gradually weakening the farther apart they are. The expansion would accelerate as the universe continues getting larger, pulling galaxies father and farther away from each other. Soon, the force would be strong enough for solar systems within galaxies to begin to separate, then celestial objects. This separation would continue until the distance between these objects, like planets, suns, and moons, was great enough for their solar systems to disperse. As they would be solitarily floating in the universe, the quantity of energy they emit would decrease. This has to do with entropy, the amount of energy that cannot be used for useful work. As the universe continues to expand, entropy increases, meaning that energy within an isolated system will slowly spread out until it is evenly spread and in equilibrium. In this case, the universe is an isolated system as there is nothing it is expanding into that can provide it with additional energy. This will happen due to matter decaying and spreading out, no longer concentrated in certain areas as it is now. Along with this, the gas clouds necessary for the formation of stars will be exhausted, eventually becoming so thin that no new stars could be created. Stars would eventually die and this, in addition to no new ones being created, will make the universe dark. As the stars collapse into themselves, black holes will be created, though they too will ultimately evaporate. Although the universe will continue expanding, the amount of matter does not increase, making it diluted. At this point, entropy is at its maximum and all activity in the universe ends, resulting in its death.
The Big Rip
Similar to the Big Freeze, the force of dark energy wins over gravity. This difference, however, is that in the Big Freeze, matter remains intact and simply decays over time. On the other hand, in the Bigs Rip, matter is torn apart in the big rip due to the expansion of the universe accelerating to the point of gravity no longer being able to compensate for it. The universe expands at a rate so fast, that parts of it are torn apart as they are separated. First, larger structures, like galaxies, would be ripped apart. This is because the space between them expands very quickly. Following this, celestial objects, like stars and planets, would die as the gravity holding them together is not strong enough, forcing them to dissolve. This process continues until the universe expands and accelerates fast enough for even atoms to be affected, forcing them to disperse. At this point, the speed of the expansion is faster than even the speed of light. After this, all the particles of matter in the universe will no longer be able to interact with other particles, resulting in the end of the universe.
The Big Crunch
Unlike with the Big Freeze and the Big Rip, the force of gravity is stronger than and prevails over the force of dark energy. The results of the Big Crunch are opposite of those of these previously mentioned possible endings as, instead of the rate of expansion of the universe increasing and becoming faster, it will slow down and eventually stop. Gravity will pull galaxies together and merge them, making the temperature of the universe increase as the amount of space decreases. Over time, the temperature will rise enough to be hotter than the surface of some stars. The universe will begin collapsing into itself and atoms will be ripped apart. Shortly after, black holes will form and encompass everything, then combine to form a single, enormous black hole. Right before the Big Crunch, this black hole containing all matter will envelop the universe and itself, before condensing into a single tiny point, much like that of before the Big Bang. The Big Crunch is connected to the Big Bounce, in which this compression is simply a contraction of the universe before it expands, creating a new universe. This would be the third possibility the universe could die.
The Cyclic Universe Theory
The Cyclic Universe Theory suggests that the universe could be an infinite pattern, constantly creating and destroying itself. If true, this means that our current universe is created from the end of the previous universe, and that universe was created from the end of the one before that, and so on and so forth. The Big Bounce Theory is a possible form of this one, which suggests that there are periods of expansion and contraction in the universe, and that our current expanding universe is simply a phase of it. If this is the case, then it would be impossible to tell how many times this has occurred and if this is one of them. The Big Bounce Theory is connected to the Big Crunch and similar to the Big Bang through its expansion. It is similar to the original dense point containing all matter, before the Big Bang, exploding to become our universe.
Cosmoknowledge. (2020, October 26). What Is The Big Bounce Theory [Video]. Youtube. https://youtu.be/oL0wBq9CQLA
Hlozek, R. (n.d.). The death of the universe. Retrieved January 29, 2021, from https://www.ted.com/talks/renee_hlozek_the_death_of_the_universe#t-176544
Keus, V. (n.d.). Three ways the universe could end. Retrieved January 29, 2021, from https://www.ted.com/talks/venus_keus_three_ways_the_universe_could_end?language=en
Kurzgesagt – In a Nutshell. (2014, February 3). Three Ways to Destroy the Universe [Video]. Youtube. https://youtu.be/4_aOIA-vyBo
Mack, K. (2020, December 26). How 'heat death' will destroy the universe. Retrieved January 30, 2021, from https://bigthink.com/videos/heat-death-universe
Magazine, A. A., & Stuart, C. (2020, September 11). Was there a bang at the end of the universe? Retrieved January 29, 2021, from https://www.space.com/gravitational-waves-big-bang.html