The most important impact of dark energy is that the universe’s expansion will never slow down. Normal matter - people, planets, stars, and anything else you can see - comprises just about 5 percent of the cosmos. 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.
Some mysterious force was pushing the cosmos apart from within. They found that the distant explostions - which should all have the same intrinsic brightness - were dimmer, and therefore farther away, than expected. 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. In the years since then, the discovery of dark energy has robbed us of a shot at this eternal rebirth. We’d be gone, but the Big Bang/Big Crunch cycle could infinitely repeat. Perhaps this process could even spark another Big Bang, the thinking went. In this scenario, the cosmos would collapse back into an infinitely dense singularity like the one it emerged from. Astronomers’ measurements suggested there was enough matter in the universe to overcome expansion and reverse the process, triggering a so-called Big Crunch. Until a few decades ago, it looked like that expansion would eventually end. Some 13.8 billion years ago, our universe was born in the Big Bang, and it’s been expanding ever since.
At this point, the universe’s final temperature will hover just above absolute zero. It’s a fitting description for the day when all heat and energy is evenly spread over incomprehensibly vast distances. Our cosmos’ final fate is a long and frigid affair that astronomers call the Big Freeze, or Big Chill. But if you were immortal, you’d probably wish it would.
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