The Big Freeze: How the universe will die
The universe may never end. But if you were immortal, you’d probably wish it would. Our cosmos’ final fate is a long and frigid affair that astronomers call the Big Freeze, or Big Chill.
It’s a fitting description for the day when all heat and energy are evenly spread over incomprehensibly vast distances. The final temperature of the cosmos will be just over absolute zero at this point.
The Big Bang’s accelerating expansion
Some 13.8 billion years ago, our universe was born in the Big Bang, and it’s been expanding ever since.
Until a few decades ago, it looked like the expansion would finally come to an end. The measurements of astronomers suggested that there was enough matter in the cosmos to overcome expansion and reverse the process, resulting in the so-called Big Crunch. In this scenario, the universe would collapse back into the infinitely dense singularity from which it emerged. Perhaps this process could even spark another Big Bang, the thinking went.
We’d be gone, but the Big Bang/Big Crunch cycle could infinitely repeat. In the years afterward, the discovery of dark energy has taken away our chance of eternal rebirth. Two distinct teams of astronomers announced in 1998 that they had measured rare exploding stars in the distant universe known as type Ia supernovas, which serve as “standard candles” for estimating distances.
They discovered that the distant explosions, which should all have the same intrinsic brightness, were dimmer and thus further away than expected. Some inexplicable force was tearing the universe apart from within.
This dark energy is now considered to account for around 69 percent of the universe’s mass, with dark matter accounting for the remaining roughly 26 percent. Normal matter – people, planets, stars, and everything else visible — accounts for only around 5% of the universe.
The most significant impact of dark energy is that the universe’s expansion will never slow down. It will only get worse.
Heat death of the universe
Decades of observations have only confirmed the findings of the researchers. All signs lead to a slow and lonely death that will last indefinitely. The scientific term for this fate is “heat death.” But things will be rather desolate for a long time before that happens.
In “just” a few trillion years, the universe will have expanded to the point that no distant galaxies will be visible from our own Milky Way, which will have long since merged with its neighbors. Eventually, 100 trillion years from now, all star formation will cease, bringing an end to the Stelliferous Era, which has been in effect since shortly after the beginning of our universe.
Galaxies will disappear much later, during the so-called Degenerate Era. Stellar remnants will fall apart. And any remaining substance will be locked within black holes.
In fact, black holes will be the last surviving sentinels of the universe as we know it. They will be the only “normal” matter left in the Black Hole Era. But eventually, even these titans will disappear,
Stephen Hawking predicted that black holes would slowly evaporate by releasing their particles into space. The smaller, solar-mass black holes will be the first to disappear. Hawking radiation will have killed off even supermassive black holes a googol years in the future (a 1 followed by 100 zeroes).
There will be no normal matter in the universe’s last “Dark Era,” which will last considerably longer than everything that came before it. And the law of thermodynamics states that all energy will eventually be distributed evenly in this time frame. The universe will eventually cool to just above absolute zero, the coldest temperature possible.
If this future seems dark and depressing, take comfort in knowing that every earthling will have died long before we have to worry about it. In fact, on this timeline of trillions of years, our own existence registers as a brief flash of sunlight before an infinite winter of darkness.