Ask Ethan: Did life begin when the Universe was room temperature? | by Ethan Siegel | Starts With A Bang! | Aug, 2025
The Universe was born incredibly hot, and has expanded and cooled ever since. Could life have begun back when space was “room temperature?”
Our Universe, as we observe it today, is vast and isolated, with enormous amounts of space between the stars, and with stars clustered into trillions galaxies scattered across tens of billions of light-years. It’s also extraordinarily cold; aside from the starlight that heats up matter locally, there’s only a very low-energy background of radiation coming from the cosmos itself: a thermal bath of blackbody radiation at 2.725 K, or less than three degrees above absolute zero. But our current situation only came about because our Universe has been expanding, gravitating, and cooling for the past 13.8 billion years.
Early on, it was smaller, denser, more uniform, and also hotter, leading all the way back to the earliest moments of the hot Big Bang, and to temperatures that far exceeded even the stupendous energies achieved at the Large Hadron Collider. At some point in cosmic history — in between then and now — the Universe itself must have been a rather temperate place: right around what we consider “room temperature” today. Could that have provided the perfect conditions for…
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