Our universe is about 13 billion years old, and for roughly 3.5 billion of those years, life has been wriggling all over our planet. But what was going on in the universe before that time? It’s possible that there was a period shortly after the Big Bang when the entire universe was teeming with life. Harvard astronomer Avi Loeb calls this period the “habitable epoch,” and he believes that its existence changes how humans should understand our place in the cosmos.
We have one snapshot of life in the early universe, taken about 400,000 years after the Big Bang. This image is known as the Cosmic Microwave Background (CMB), and it’s what astronomers see when they aim their telescopes at the farthest edges of space, capturing light that has been traveling through the universe for billions of years—and from billions of years ago. Remember, light takes a while to reach Earth (it travels at only 186,000 miles per second), so the starlight you see in the sky at night is often thousands of years old. The CMB is a lot older than that. It’s from the time when the universe hadn’t yet developed stars.