Here’s the belated TITMT from The Art of Getting By.

What are your thoughts on life outside of Earth? Do you believe in aliens? If so, what do you think when you think about them? I am purposely being vague here in the hopes you’ll expand upon your own.

Life almost certainly exists outside of Earth. I wouldn’t even be surprised if we found evidence of bacterium that once lived in our own solar system. Furthermore, given these facts:

• There are about 100 billion stars in the typical galaxy.
• There are about 125 billion galaxies in the universe.
• The age of the universe if about 14 billion with many more times that of potential life-supporting years to go.

I would guess that intelligent life has evolved somewhere else in the universe. And if it hasn’t, it will eventually.

For the fun of it, let’s do a little speculative math. Let’s say the number of stars in the universe to be 10^22 (100 billion stars per galaxy times 100 billion galaxies). It took less than 5 billion years to evolve intelligent life on this planet, but lets suppose we were lucky and it usually takes about 10 billion. Finally, this is the biggest speculation of all is how long can the universe continue to support life. The few numbers I could find on this topic but the number between 24 billion (in the event of an early Big Crunch) and 3.65 trillion (the universe expands without end). I’ll just pick a convenient number in that range: 100 billion. This means that there are about 10 billion (100 billion years of universe divided by 10 billion years required for evolution) intelligent life creating opportunities at a given location.

Thus 10^22 possible places for life (stars) times 10^10 temporal opportunities of intelligent life results in a total of 10^32 (100,000,000,000,000,000,000,000,000,000,000) chances for intelligent life. This has to be multiplied by the chances that any given star will evolve intelligent life, given the opportunity. Those odds would be calculated something like this:

(probability that the star is of the right ‘type’) * (probability that a star will have a potential life-supporting planet) * (probability that the planet(s) will be around long enough to create life) * (probability that life will spontaneously form) * (probability that intelligent life will form)

These are extraordinarily difficult parameters to estimate, but even if the odds are one in 10^20, that means the expected number of intelligent species the universe will produce in it’s life time is 1 trillion. The odds may be much worse than that, say 1 in 10^50, in which case, we’d expect to see no intelligent species. Yet we see at least one: humans. Unfortunately, one data point is not enough to draw a conclusion about the probability of forming an intelligent species. Worse yet, the odds of another intelligent species overlapping with the existence of our own, and being close enough to detect and both of us developing technologies that can A) reach each other and B) detect each other, makes the chance of us learning of another very unlikely.

This whole analysis, of course, glosses over many, many assumptions. For anyone who stumbled across this website looking for data of this nature, this number should be considered as a back-of-an-envelope calculation done by an armature. This is really just for the fun of it.