Science & Technology

Billions of Years Ago, the Universe May Have Been Teeming With Life

The universe is a cold, dark place. For a planet to support life, it has to be extremely lucky: close enough to its home star to keep water from freezing, far enough away to keep it from boiling off. We've only found a handful of planets that sit in this "habitable zone," and we don't know if any contain life. But what if it's not the place that's important, but the time?

Not Too Hot, Not Too Cold

13.8 billion years ago (sing along if you know the words), the universe started as a singularity that exploded in a trillionth of a trillionth of a second, doubling and re-doubling and re-re-doubling in size at a rate faster than the speed of light. Suddenly, instead of an impossibly dense fleck of matter, the universe was a hot, garden-variety-dense soup of particles, all quarks and gluons and photons and electrons. How hot was it? It was so hot that particles couldn't even coalesce into the building blocks of atoms yet. We're talking hundreds of times hotter than the sun. It was so hot that we can still see its evidence in what's known as the cosmic microwave background.

But just like a pie fresh from the oven, the universe gradually cooled. Particles turned into atoms and atoms turned into stars, and little by little, everything spread out and cooled off as the universe expanded. But somewhere between being too hot for atoms to form and becoming a cold, dark void, space was, well, kind of warm. It was warm enough for liquid water to exist — not just on planets, but everywhere. Seeing as how liquid water is our telltale sign for life, this is a very big deal.

Things stayed that way for several million years. That might not be enough for intelligent life to arise (it took humans at least 160 million years to evolve from the first mammals, after all) but it's certainly enough for some kind of life. Single-celled life, perhaps, but life all the same.

All the Parts in Place

It wasn't just the balmy temperature that could have made life possible during this "habitable epoch," as Avi Loeb, the astronomer behind this theory, calls it. There would be enough energy left from the Big Bang to give the formation of life a leg up. And because stars and rocky planets would be new on the scene, there wouldn't be as much cosmic radiation and destructive debris whipping around, ready to smash into a new planet.

But that also poses a problem. A lot of the elements that you require to live were formed in supernovae: the explosive deaths of old stars. Since stars weren't old enough to die yet, the early universe wouldn't have even formed carbon, much less heavier elements like iron. If life did exist, it would have looked different than the life we know.

Loeb's habitable epoch, if real, does blow one other theory out of the water: the anthropic principle. This principle says that the universe has all the elements to support life simply because if it didn't, we wouldn't be here to wonder about it. But if Loeb is right, then during the habitable epoch, a lot of those elements were wildly different, and yet life would have existed. Maybe life doesn't depend on the rules of the universe as we see them. Maybe instead, life thrived on different rules, and us being here today is a rare exception.

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Learn more about our universe's beginning with "Big Bang: The Origin of the Universe" by science writer Simon Singh. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Ashley Hamer January 26, 2018

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