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Comment by FreeHugs | Hacker News Reader

    Meaning if there are 24 factors crucial for life to
    evolve, and each has a 10% chance of occurring - it's
    actually quite likely only one planet would win on
    this lottery.

Is it? What is the probability?

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I believe the post above was working out math that would make it so the probability would be 1 / #(of planets in the universe), which, following the law of large numbers, would mean that given an infinite number of universes, those universes would tend to have exactly one planet (Earth in our universe's case) that would have life.

In other words, the odds of there being life elsewhere in the universe is:

a very large number of planets * a very small chance of life forming = ???

We don't really know how small the chances of life are. It may be that the chances of life forming are so small it dwarfs the number of planets in magnitude. It may be an incredible miracle that we live.

It seems that whenever an article says "there are more planets than we expected", someone concludes "this makes it more likely that there is life somewhere out there", but it's also fair to conclude that "this means the odds of life forming are lower than we previously thought" since we haven't actually found any other life. As Fermi asked, where is everybody?

Phrased differently: the expected number of such planets is 1.

In most variations of such a calculation the expected number of planets would be 0. The fact that the actual answer is >= 1 might suggest that the calculation is not an accurate representation of reality.

I'm not sure I'm understanding. It is a well-defined probability question to ask about the "expected number" of planets with life if there are 10^24 of them each with probability 10^-24, and the answer is 1.

Yes it will be approaching 1, the same as for 10^24 coin tosses the number of heads would be approaching 50% (or 5*(10^23)).

Given the definition of "expected value," it is identically 1 (as opposed to merely "approaching it"). Sorry, I'm not trying to be pedantic.

https://en.wikipedia.org/wiki/Expected_value

You're absolutely correct - not being a native English speaker, I read "expected value" as a common phrase, not a probability theory term. Thanks

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