Extraterrestrial Life as a Statistical Certainty

Throughout history, men of religion have striven to place humanity and, by extension, Earth at the center of everything. From wrongheaded notions of a geocentric universe to fanciful delusions of humankind having been specially created in the image of a god, the breathtaking ego our species exhibits—a self-importance enabled through, and justified by, religion—desperately has to be exorcised, like a malevolent demon from a pious innocent. In this brief post, I shall tackle the contention that Earth is special and worthy of its enviable standing because it is a planet on which life emerged.

In Lawrence Krauss' fascinating book A Universe From Nothing, he makes multiple mentions of the 400 billion galaxies in the observable universe, of which our Milky Way galaxy is merely one. The Milky Way galaxy contains 200 to 400 billion stars, which, it should be noted, is not a uniquely high number; for instance, the Andromeda galaxy hosts one trillion stars, which rather makes the Milky Way seem puny by comparison. And, as Popular Science has reported, on average, each star in the Milky Way has at least one planet (and probably more than one).

So, how can we extrapolate the probability of life on other planets from these facts and figures? We cannot demonstrate its existence for sure, of course, but we can statistically prove the tremendous, overwhelming likelihood of its being there.

If the Milky Way contains something like 300 billion stars, then, for purposes of our statistical analysis, let's be conservative and halve that number to 150 billion stars as the average number across all 400 billion galaxies in the observable universe. (Remember, this is hardly an outlandish estimate, considering that the Andromeda galaxy hosts a trillion stars.) And let's say that every star has a single planet on average. (Again, this is an extremely conservative estimate, given that, as Popular Science quoted astronomer Seth Shostak as having said, “[T]he number of planets in the Milky Way is probably like five or 10 times the number of stars.”) So, that's 400 billion (times) 150 billion (times) one to arrive at 60,000,000,000,000,000,000,000 planets in the observable universe.

Let's set the odds of life ever emerging on any given planet at a million to one. In that case, life would emerge on 60,000,000,000,000,000 planets.

Let's set the odds of life ever emerging on any given planet at a billion to one. In that case, life would emerge on 60,000,000,000,000 planets.

Finally, let's set the odds of life ever emerging on any given planet at 10 billion to one. In that case, life would emerge on 6,000,000,000,000 planets. That means if the odds of life emerging are 10 billion to one, then life would emerge on about six trillion planets. As Lawrence Krauss astutely observes, "[T]he universe is big and old and, as a result, rare events happen all the time." Extraterrestrial life is a statistical certainty.

If Darwin illuminated biology by removing the need for a creator, and the Copernican Revolution demythologized astronomy by removing Earth from the center of anything, then perhaps this statistical argument will give the lie to religion-fueled delusions about life on Earth, including humans like us, being special...let alone lovingly and uniquely created.