The universe’s expansion wasn’t slowing down at all - it was speeding up. They found distant blasts appeared dimmer, and were therefore farther away, than expected. In the late 1990s, two separate groups of scientists were surveying the distant universe, studying dying stars called type Ia supernovae, which serve as standard candles that help establish cosmic distances. “Just because we might find a cold, empty universe an unappealing future doesn’t mean that that’s not where things are headed,” Columbia University physicist Peter Woit writes on his blog, Not Even Wrong. Unfortunately, reality is not always so relatable. A revolution in understanding black holes was underway, and Wheeler saw each one as an “experimental model” of the universe’s final state.īut Wheeler’s Big Crunch fondness was partially born from aesthetics, he admitted. In the 1970s and 1980s, physicist John Wheeler, who helped coin the term black hole, became a leading proponent of the Big Crunch. 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 1960s and 1970s, when astronomers added up all the matter 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 hole. With enough matter, gravity would eventually halt the cosmos’ expansion, causing it to come crashing back inward. These calculations showed that our universe’s destiny is determined by its density, and it could either expand or contract, rather than remain in a steady state. In 1922, Russian physicist and mathematician Alexander Friedmann derived a famous set of equations aptly named the Friedmann equations. To find out which is right, astronomers had to fast-forward the evolution of the universe. There are two main ways for an expanding universe to die: The cosmos could eventually collapse back in on itself, or it could continue inflating forever. With its foundations firmly fixed, cosmology turned to the next great question: How will the universe end? Pressing rewind on that expansion ultimately revealed that the entire universe was born in a violent Big Bang some 13.8 billion years ago. Humanity had discovered that the universe is expanding. And when Edwin Hubble meticulously measured their motions, he showed these galaxies were indeed moving away from our own. However, around the same 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. “Einstein was not 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. So Einstein added a fudge factor - a cosmological constant - that held the universe in a more appealing steady state. His equations implied a universe in motion, either expanding or contracting. However, as Albert Einstein formulated his theories of relativity, he noticed signs of something strange. Our cosmos appeared static - it had always been, and would always remain, roughly the same. Roughly a century ago, astronomers thought that our Milky Way Galaxy was the entire universe. The universe didn’t always seem destined to end this way. Rather than meeting its end through fire and brimstone, the cosmos will likely succumb to “heat death.” Astronomers call it the Big Freeze. Finally, the last traces of heat will disappear. All lingering matter will be gobbled up by black holes until there’s nothing left. Slowly, stars will fizzle out, turning night skies black. Trillions of years in the future, long after Earth is destroyed, the universe will drift apart until galaxy and star formation ceases. But the best evidence points to a distant Armageddon filled with more existential dread than the Book of Revelation. Until rather recently, astronomers thought the cosmos would repeatedly expand and collapse in an infinite cycle of cosmic death and rebirth. And now science actually has the knowledge and tools to attempt an answer. How will the universe end? Humanity has pondered this question for thousands of years.
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