The Big Freeze: How the universe will die

The cosmos will come to a close through a cold and lonely death called the Big Freeze.

The cosmos 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 is evenly spread over incomprehensibly vast distances. At this point, the universe’s final temperature will hover just above absolute zero. 

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 that expansion would eventually end. Astronomers’ measurements suggested there was enough matter in the universe to overcome expansion and reverse the process, triggering a so-called Big Crunch. In this scenario, the cosmos would collapse back into an infinitely dense singularity like the one it emerged from. 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 since then, the discovery of dark energy has robbed us of a shot at this eternal rebirth. In 1998, two separate teams of astronomers announced that they’d measured special exploding stars in the distant universe, called a type Ia supernova, which serves as “standard candles” for calculating distances. They found that the distant explostions — which should all have the same intrinsic brightness — were dimmer, and therefore farther away, than expected. Some mysterious force was pushing the cosmos apart from within.

This dark energy is now thought to make up some 69 percent of the universe’s mass, while dark matter accounts for another roughly 26 percent. Normal matter — people, planets, stars, and anything else you can see — comprises just about 5 percent of the cosmos. 

The most important impact of dark energy is that the universe’s expansion will never slow down. It will only accelerate. 

Heat death of the universe

Decades of observations have only confirmed researchers' findings. All signs now point to a long and lonely death that peters out toward infinity. The scientific term for this fate is “heat death.”

But things will be rather desolate long before that happens. 

"Just" a couple trillion years from now, the universe will have expanded so much 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, ending the Stelliferous Era that’s be running since not long after our universe first formed.

CAM