The end of the universe

Ever heard of the Big Bang? It’s the most widely accepted theory that explains the origins of the universe. Essentially, the Big Bang theory asserts that the universe formed in a massive explosion about 13.8 billion years ago. Prior to that, it is believed that all matter was condensed into a singularity, or an extremely compact and infinitely dense ball of matter. When that singularity suddenly began to inflate, it spread out into the exponentially expanding universe that we see today.

Theories for how the universe will end are closely related to this same expanding nature. Will the universe ever stop growing? Could it contract? And, what happens if it does?

A few notable theories attempt to answer these questions: the Big Rip, the Big Freeze, and the Big Crunch.

The Big Rip

The Big Rip operates on the assumption that the universe will continue to expand at an increasing acceleration. As the universe grows at a faster and faster rate, the Big Rip claims that the perpetual acceleration will ultimately tear the universe apart.

As astronomer Yvette Cendes explains:

Imagine a driver who keeps a foot on the gas pedal of a car with no top acceleration. As the car goes faster and faster — the speed of the velocity change itself increasing over time — the car would eventually fly apart in pieces as friction took its toll.

The same idea takes place with the Big Rip. As distant objects accelerate away from us at faster rates, gravitationally bound galaxies and solar systems would unravel. Any remaining stars or planets would explode. In this way, from the largest galaxies to the universe’s individual atoms, it is believed that the expansion of space could eventually rip it all apart.

If the Big Rip were to take place, scientists predict that it would take 22 billion years to arrive. Then, the universe itself would explode into a new singularity of infinite energy.

The Big Freeze

The Big Freeze declares an even more bleak end to the universe.

Astrophysicist Katie Mack describes it as a future that is “marked by increasing isolation, inexorable decay, and an eons-long fade into darkness.”

Like the Big Rip, the Big Freeze theory operates under the belief that the universe will continue to expand. However, the Big Freeze claims that the universe will end because of a halt in astrophysical activity rather than a whirlwind that tears the universe apart.

As the universe expands and objects get farther apart, the matter that is used to fuel the birth of new stars and the growth of galaxies will be dispersed too far apart. Star formation would completely cease in 100 trillion years once all available matter is exhausted. The galaxies that the stars reside in would also stop growing. Black holes too would eventually evaporate.

As a result, this suffocating process would be accompanied by a rise in entropy, or the degree of randomness and chaos in the universe. As the universe approaches its maximum entropy, all heat and energy is distributed evenly across the universe, plateauing at a minimum temperature. Oddly enough, this trait has led to the nickname “heat death” that is also used to describe the Big Freeze.

The end of mechanical motion and astrophysical activity collectively transforms the universe into a lifeless void with its energy spread too thin across the universe.

The Big Crunch

The third theory for the end of the universe takes on a new approach altogether, exploring what would happen if the expansion of the universe reversed. Because of the gravitational pull of all the matter within the universe, it could seem reasonable for the universe to someday re-collapse into itself.

In this scenario, the Big Crunch would entail a series of galaxies and stars crashing into each other, destroying any life on neighboring planets. As the universe contracts, temperature and density would increase until the Big Crunch mirrors the beginning of the Big Bang itself, reaching a miniature singularity.

Some scientists speculate that the Big Crunch could lead the way for a new universe, creating a Big Bounce and starting a new cycle of expansion and contraction. This invites the idea that our universe itself is just part of an endless cycle of Big Bangs, Crunches, and Bounces.

Which theory is right?

Today, most scientists agree that the universe will continue to expand, making the Big Crunch extremely unlikely. Instead, the Big Freeze seems to be the most common belief as it is a direct result of an expanding universe.

Still, even if the end of the universe is uncertain, we do know that it won’t be coming any time soon.

Cendes, Yvette. “How Will The Universe End?” Discover Magazine, Discover Magazine, 19 May 2019, www.discovermagazine.com/the-sciences/how-will-the-universe-end.

Siegel, Ethan. “The Five Ways The Universe Might End.” Forbes, Forbes Magazine, 4 Jan. 2019, www.forbes.com/sites/startswithabang/2019/01/04/the-five-ways-the-universe-might-end/?sh=65e713dd3496.

Skibba, Ramin. “Crunch, Rip, Freeze or Decay — How Will the Universe End?” Nature, Nature Publishing Group, 10 Aug. 2020, www.nature.com/articles/d41586-020-02338-w.

Williams, Matt. “What Is the Big Bang Theory?” Phys.org, Universe Today, 18 Dec. 2015, phys.org/news/2015–12-big-theory.html.

Woollaston, Victoria. “A Big Freeze, Rip or Crunch: How Will the Universe End?” WIRED UK, WIRED UK, 10 Oct. 2016, www.wired.co.uk/article/how-will-universe-end.

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