Rare events can be common when dealing with large data sets. For example, the odds of being struck by lightning are more than one in a million, but as the US has a population of 350 million, two to three hundred people are struck by lightning every year!
When it comes to life in outer space, we know there is at least one occurrence among the 10^24 stars in the universe. We don’t know how common or rare Earth is, so we can’t calculate how often life will arise, but we can calculate the reverse odds, ie, how likely is it that Earth is the ONLY planet with life?
Please forgive a little math.
If we assume life arose due to some unknown number of rare independent events and we use a binomial model, our baseline is…
This means that all we know for sure is that life occurred at least once around 1,000,000,000,000,000,000,000,000 stars. Although we can’t calculate if life would occur elsewhere, we can use this information to calculate the reverse odds that no other star will have life.
Which would be…
We can then use the Poisson approximation, which is defined as a “distribution [that] can be applied to systems with a large number of possible events, each of which is rare. The number of such events that occur during a fixed time interval is, under the right circumstances, a random number with a Poisson distribution.”
In essence, the Poisson approximation will give us the worst-case scenario where utter chaos and completely random events resulted in life arising on Earth. In reality, evolution and natural selection (although being biological concepts) are notably NOT random. They’re naturally improving systems.
It’s important to realize we have no reason not to consider life arising naturally on other planets. We’ve found amino acids on comets. These are the building blocks of life on Earth. That these are naturally occurring and easy to find within our solar system suggests they’re everywhere.
And the scaffolding of life can be formed by something as simple as volcanic glass. Experiments have shown that amino acids on obsidian glass can naturally form into chains of nucleoside triphosphates in strands similar to RNA that are up to 200 letters long! That’s not enough for a cell to function, but it’s well on the way to a level of complexity where life could arise. The point being, we have every reason to think life can arise spontaneously in the right circumstances.
As we learn more about how life arose on Earth, we may find that the first lifeforms were driven by some proto-evolutionary process that wasn’t entirely random. And we have good reason to believe such systems exist in non-living objects, as the production of elements like carbon and oxygen in the heart of a star isn’t random. We can define these with accurate models. The same may be true of abiogenesis at some point as we learn more about the process, but for now, we’ll consider it to be entirely random and assume a worst-case scenario.
If life were completely and utterly random, the odds of there being no other life in the universe are…
Basically, there is a one in three chance we are entirely alone in the universe.
Or, if you’re an optimist, a 2/3rds chance we have neighbors 🙂
Full disclosure, I used ChatGPT to help with the calculations. You can find the output here.
