Was the early universe a better environment for life to evolve?

Illustration for article titled Was the early universe a better environment for life to evolve?

Harvard astronomer Avi Loeb has just published a paper about how life might have flourished when our 13.8-billion-year-old universe was a mere 15 million years old. Back then, the whole universe was warmer — which means liquid water could exist even on planets that were distant from their stars.

Writes Loeb in the abstract for the paper:

In the redshift range 100<(1+z)<110, the cosmic microwave background (CMB) had a temperature of 273-300K (0-30 degrees Celsius), allowing early rocky planets (if any existed) to have liquid water chemistry on their surface and be habitable, irrespective of their distance from a star. In the standard LCDM cosmology, the first star-forming halos within our Hubble volume started collapsing at these redshifts, allowing the chemistry of life to possibly begin when the Universe was merely 15 million years old. The possibility of life starting when the average matter density was a million times bigger than it is today argues against the anthropic explanation for the low value of the cosmological constant.


Though we often think of the early universe as inhospitable, Loeb notes that if rocky planets existed, it would have been a great time to live on them. No matter where they were in the universe, they would have been bathed in constant warmth, with no need to depend on a star for energy. And the warmth would have made surface water a liquid, too, which would help life as we know it to develop.

Of course there is that little matter of matter density being "a million times bigger than it is today." Hard to say whether that would be a problem or not for the development of life. It certainly would have made our view of the heavens a lot different, and brighter.

The sad part about contemplating Loeb's idea is that it makes you wonder whether the universe was teeming with life back then, and we're merely the sad outliers who happened to evolve in the post-life era. All our potential friends in the universe might have lived (and eventually died out) billions of years ago.

Read the whole paper at Arxiv.

Thanks for the tip, Warren Siegal!


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Stephan Zielinski

For the folks arguing that there wouldn't have been time for the non-hydrogen elements to form: Loeb runs the numbers in section 2 of The Habitable Epoch of the Early Universe. Short version: yes, there's time, because extremely massive stars form and supernova themselves to smithereens almost immediately.

For the folks arguing that the early universe must have been too radioactive for life to make it: (A) levels of radiation that are bad news for us, single-celled life laughs at, (B) organisms can evolve radiation resistance, since it's just a question of redundancy and repair mechanisms, and (C) under a thick enough atmosphere, it doesn't much matter how much radiation there is flying around in interstellar space. The effectiveness of radiation shielding increases exponentially with its thickness. For instance, every additional 150 meters of air cuts the amount of ionizing radiation that penetrates it in half. (The corresponding number for water is 18 centimeters.)