If the Universe Collapses and Explodes Into the Universe Again

The Beginning to the End of the Universe: The Big Crunch vs. The Big Freeze

Astronomers once thought the universe could collapse in a Large Crunch. Now most agree it will end with a Big Freeze.

This story comes from our special January 2021 issue, "The Beginning and the End of the Universe." Click here to purchase the full event.


How will the universe end? Humanity has pondered this question for thousands of years. And now science really has the cognition and tools to attempt an reply.

Until rather recently, astronomers thought the cosmos would repeatedly expand and collapse in an infinite cycle of cosmic death and rebirth. Only the all-time show points to a distant Armageddon filled with more than existential dread than the Book of Revelation. Trillions of years in the future, long after World is destroyed, the universe will drift apart until galaxy and star formation ceases. Slowly, stars volition fizzle out, turning night skies blackness. All lingering matter will be gobbled upwards by blackness holes until at that place'due south nix left. Finally, the last traces of heat will disappear.

Rather than meeting its stop through fire and brimstone, the creation will probable succumb to "heat death." Astronomers call it the Big Freeze.

Blastoff and Omega

The universe didn't ever seem destined to end this way. Roughly a century ago, astronomers thought that our Milky way Galaxy was the entire universe. Our cosmos appeared static — it had always been, and would always remain, roughly the aforementioned. Nevertheless, as Albert Einstein formulated his theories of relativity, he noticed signs of something foreign. His equations implied a universe in motion, either expanding or contracting. So Einstein added a fudge cistron — a cosmological constant — that held the universe in a more than appealing steady country.

"Einstein was non being stupid; he was feeling the feeling of astronomers," says Nobel Prize-winning cosmologist John Mather, the head scientist for NASA's James Webb Space Telescope.

Nevertheless, around the aforementioned time, astronomers began to accept that some of the fuzzy spiral-shaped nebulae they observed through their telescopes were not collections of stars in our galaxy. They were other galaxies entirely. And when Edwin Hubble meticulously measured their motions, he showed these galaxies were indeed moving away from our own. Humanity had discovered that the universe is expanding.

Pressing rewind on that expansion ultimately revealed that the entire universe was built-in in a violent Big Blindside some thirteen.8 billion years agone. With its foundations firmly stock-still, cosmology turned to the side by side slap-up question: How will the universe stop?

At that place are two main means for an expanding universe to die: The cosmos could somewhen collapse dorsum in on itself, or it could continue inflating forever. To find out which is right, astronomers had to fast-forward the evolution of the universe.

The Big Crunch

In 1922, Russian physicist and mathematician Alexander Friedmann derived a famous ready of equations aptly named the Friedmann equations. These calculations showed that our universe's destiny is determined by its density, and it could either aggrandize or contract, rather than remain in a steady state. With enough affair, gravity would eventually halt the creation' expansion, causing it to come up crashing back inward.

In the 1960s and 1970s, when astronomers added upwards all the affair in the known universe, they calculated there was enough mass that the cosmos should ultimately collapse to an infinitely dense state, or perhaps even a gargantuan black pigsty.

Some speculated that once compressed into an infinitely small point — the Big Crunch — the universe would kickstart yet another expansion, or Big Bounce.

In the 1970s and 1980s, physicist John Wheeler, who helped coin the term blackness hole, became a leading proponent of the Big Crisis. To him, information technology was an obvious fate. A revolution in understanding blackness holes was underway, and Wheeler saw each one as an "experimental model" of the universe's last land.

Merely Wheeler'due south Large Crunch fondness was partially born from aesthetics, he admitted. It was easy to film.

The Big Freeze

Unfortunately, reality is non always so relatable.

"Just because we might find a cold, empty universe an unappealing hereafter doesn't mean that that'due south not where things are headed," Columbia University physicist Peter Woit writes on his blog, Not Even Incorrect.

In the belatedly 1990s, 2 split up groups of scientists were surveying the distant universe, studying dying stars called type Ia supernovae, which serve as standard candles that help establish catholic distances. They found distant blasts appeared dimmer, and were therefore further away, than expected. The universe'south expansion wasn't slowing downwardly at all — it was speeding up. The teams had independently stumbled onto night free energy, shattering existing models of the universe. (See "The mystery of dark energy," page 53.)

The expectation-defying discovery of dark energy showed the universe was very unlikely to plummet in a Big Crunch. Even with all the matter in the universe tugging inwards, gravity will never be strong enough to overcome the inflating effect of night free energy. In other words, the ballooning universe is destined for a Big Freeze.

These days, astronomers recall normal matter comprises only 5 percent of the universe'south contents. Meanwhile, dark matter makes upward some 26 percent, and dark free energy accounts for the terminal 69 percentage. Dark free energy, it turns out, seems to be the existent-earth forcefulness behind Einstein's cosmological constant, which plays a major office in preventing a Large Crunch-style plummet.

Cheers to the expansion caused by dark energy, inside a couple of trillion years, all but the closest galaxies will be too far away to encounter. Then, mayhap 100 trillion years subsequently, star formation will cease, as dense stellar remnants similar white dwarfs and black holes lock upwardly whatsoever remaining textile.

About a googol years from now — that'southward a 1 followed past 100 zeroes — the last objects in the universe, supermassive black holes, will finish evaporating via Hawking radiations. After this, the universe enters a and so-called Night Era, where matter is just a distant retention.

The 2nd law of thermodynamics suggests that entropy will keep increasing in a system (such as the cosmos) until information technology hits a maximum level. In real terms, that means that at some point, the universe will ultimately achieve a state where all energy — and, hence, heat — is uniformly distributed. The final temperature of the entire universe will hover a smidge above absolute zero.

So, rather than mirroring Revelation, the death of our cosmos will likely resemble the beginning of Genesis: All will be empty and dark.

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Source: https://astronomy.com/news/magazine/2021/01/the-beginning-to-the-end-of-the-universe-the-big-crunch-vs-the-big-freeze

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