I see this come up a LOT and I've even gone over the subject previously! But I needed to put my words here to explain how I see that life is not only probable - insofar as we have direct evidence of life existing here on Earth. But is, I think, more likely than a good selection of folk would care to accept.
Understanding 'Chance'
Let's start by understanding 'chance'. Think of probability as the likelihood of a particular event happening out of all the possible events.
- Think of probability as how likely something is to happen.
- Imagine rolling a dice and trying to guess the number.
Expressing Probability
- For rolling a 6 on a dice, the chance is 1 out of 6 possible outcomes.
- We can express this as 1/6 or 1:6.
- I prefer the ratio notation, so I'd say the probability is 1:6 for a single dice roll.
In the topic of this post, there are the possible outcomes:
- life exists
- life does not exist
Hypothetical
Proteins and RNA
Forgive the following, but I'm going to vastly oversimplify some details about cumulative probability over time. Let us, for the sake of the following hypothetical, contemplate that the chance of life occurring on any given planet is one in four centillion. This is a phenomenally minuscule contemplation. The number representing it is gargantuan (too large to write here) - I use this as a base number as it is derived from the idea of RNA combining in just the right way such that it can cartelize for the purpose of Abiogenesis.
1:{four centillion}
Passage of Time (highly simplified)
Now, let us expand this hypothetical in that: for every year that has passed (in which there are viable places for life to exist), thirty-one million occurrences of the probability event are resolved. That means some 4.1 approximate quadrillion points of information for testing (I'm rounding to simplify).
13,000,000,000
For this hypothetical, this now reduces the probability to a still ridiculous but now more comprehensible one in one quinquagintillion (yes, that's a real number) but importantly the 'size' of the number has dropped from 602 digits to merely 164 digits. Let's continue.
1: {one quinquagintillion}
Potential locations (again, highly simplified)
This insane number must now be modified by the number of locations at which there can be a successful outcome. Our universe is so vast that even the most powerful measurements we have only account for a fraction of what is out there, and that fraction already accounts for billions, of billions of planets.
To simplify this (just to keep the thought experiment going...) let's say there are one hundred billion possible planets - and to say this is a simplification is an understatement, realistically this is closer to the number just in our local area of space, let alone the incredible space beyond it.
100,000,000,000
Well, all those events events over 100b locations (which is easy multiplication, honest!) Leaving one duoquinquagintillion. An even sillier-sounding number, but smaller - now only 153 digits. Which is, sufficed to say, still rather bloody huge odds.
1: {one duoquinquagintillion}
Impossible Odds?
Every Possible Chemical Interaction:
A Review
In Conclusion - Is this useful, or even interesting?
Well, to me yes, by extrapolating the numbers I found that even where there are only 13 million years of potential occurrences the probability of success is significantly higher than 0:1 likely to occur. To me, this suggests that if we were ever to come close to understanding key details we could extrapolate a probability of life.
We'd need to know how many possible 'places' life can occur, and we'd also have to determine the number of events at which life can occur, both of which are likely utterly impossible for any human to ever truly come to know.
A similar train of thought is explored here: www.science20.com - odds life could begin by chance
