Rare Earth Hypothesis vs. Reason

As you probably have gleaned from the title of this post, I disagree with the Rare Earth hypothesis-- that is, the theory that the spectacular coincidences and conditions that led to complex (not even necessarily intelligent) life on this planet is so statistically remote that it is extremely unlikely that any other planet in the universe has evolved complex life. The term (and hypothesis) comes from a book by Peter Ward and Donald Brownlee.

Now, I have not read this book, and therefore I am not fully versed in their arguments. I plan to read the book and make a more detailed argument, but I wanted to lay down my base hypothesis first. Also, Wikipedia does an ok job at summarizing their argument.

So, before we get to their equation, let's look over some data:

• It is estimated that there are 200-400 billion stars in the Milky Way Galaxy.
• It is estimated that there are about 100 billion (10¹¹) galaxies in the universe.
• Galaxies tend to contain between ten million (10⁷) and one trillion (10¹²) stars.

Now let's crunch those numbers. With simple math, we can conclude that the average galaxy has 10^9.5 stars. So, to calculate the total number of stars in the universe we need 10¹¹ * 10^9.5, which gives us, with rounding, 10²⁰ stars. (That's 100,000,000,000,000,000,000 stars.) That's a lot. If each star was the size of a tennis ball, stacked up they could reach the moon from the earth (avg. distance) almost 17.5 million times.

Now let's make some guesses. In the famous Drake Equation, it is estimated that half of all stars will have planets. So that gives us a more manageable number of 10¹⁰ stars with planets. For the sake of argument, let's say that our solar system is fairly typical, and maybe the average number of planets in a solar system is around 6. I think I am being generous to the Rare Earth-ists here, as a solar system could easily have tens of planets, not to mention life-supporting moons. That gives us 6 * 10¹⁰ planets in the universe. Disregarding the Drake estimate of 2 planets per star supporting life, let's say that, I don't know, 1/8 of planets support complex life.

So, we have finally arrived: 60,000,000,000 planets could support life. Sixty billion seems to be far from the estimate of 1. If my estimates have an error of 99.9%, there would still be 7,492,500,000 planets supporting complex life. Of course, some of that may have died off already, and most (statistically) we would never be able to find. (If you read the numbers above, and you're good with visualization, you should already have realized the size of the haystack in which we are searching for a proverbial, uh, 60 billion needles.)

As I have said, I will in fact be making a more detailed argument later. However, I assert that the vast immensity of the universe makes the Rare Earth theory extremely unlikely, statistically. And I haven't even broached the subject of carbon-based vs. non-carbon-based life or the general assumptions of what a 'life-supporting planet' requires.

QED.