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“In other words, what were the chances that ours is the only civilization ever? Putting in the exoplanet data, we found the answer to be 10 â€�22 , or one in ten billion trillion.

We called this number the “pessimism line"

To understand how to think about the pessimism line, imagine you were handed a very big bag of Goldilocks-zone planets.

Our results say the only way human beings are unique as a civilization-building species would be if you pulled out ten billion trillion planets and not one of them had a civilization.

That’s because Kepler has shown us that there must be ten billion trillion Goldilocks-zone planets in the universe.”
― Adam Frank, Light of the Stars: Alien Worlds and the Fate of the Earth