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Comment by Flankk | Hacker News Reader

Nice work of science fiction. It is impossible to estimate the probability of these events with a sample size of one. It likely took billions of years for our planet to reach the right temperature and composition for life to form. It's probable that life readily forms given the right conditions. In my opinion, it makes more sense that it is rare for a planet to develop the right conditions for life. That doesn't really matter much given there are 700 quintillion planets in our universe.

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With bayesian probability a single observation can be informative (in the sense that a single observation leads to a change in distribution over hypotheses or parameters). It's a matter of narrowing down beliefs on weighted possibilities though, not a definitive answer on the state of reality.

The author doesn't rely on observation. They propose combinatorial models, obtain large time estimates and notice that observation is consistent with these estimates because sample size one, it's a coincidence.

You raise good points but the following:

> It likely took billions of years for our planet to reach the right temperature and composition for life to form

.. is not true. As mentioned by Wikipedia below, life formed surprisingly "fast" and its earliest appearance is pushed back every year.

> The age of the Earth is about 4.54 billion years;[49][50][51] the earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago.[52][53][54] Some computer models suggest life began as early as 4.5 billion years ago.[4][5]

From Wikipedia https://en.wikipedia.org/wiki/Earliest_known_life_forms

> It's probable that life readily forms given the right conditions

Is this true? It is it also impossible to know?

We haven't been able to reproduce it, so is your argument that we just haven't gotten the conditions correct?

An argument for life being expected is made pretty well in the book "At Home in the Universe" by Stuart Kaufman (spelling?).

We the expected.

The Miller-Urey experiment produced over 20 different amino acids, the building blocks of life.[1] Scientists think the first cells developed from chemically active water droplets.[2] I'd argue we have reproduced it, there just isn't enough time to be sure.

[1] https://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment

[2] https://www.quantamagazine.org/dividing-droplets-could-expla...

Statistically speaking, if it happened on our planet, it can (and likely has or will) happen elsewhere. Given that there are approximately 700 quintillion planets in the observable universe, it seems sensible to expect it to be mathematically possible and even likely that it has also developed elsehwere.

For all we know, there were space fairing civilizations in or around Alpha Centauri. Maybe they were killed in a cataclysmic event a billion years before earth was formed?

> Statistically speaking, if it happened on our planet, it can (and likely has or will) happen elsewhere. Given that there are approximately 700 quintillion planets

But numbers can go as low as they please, statistically speaking. It’s not like “1 in a billion” is the lowest possible probability. What if there are 700 quintillion planets and the probability of life evolving on a planet is 1 in 700 sextillion and we just got really lucky?

It's certainly possible but you've also chained a very specific series of events to explain an observation. Such scenarios are most hygienically reasoned about using a Bayesian quantification and updating of uncertainty. There's a lot we don't know but from what we do know and the observations we've made, life is likely to be extremely rare.

I agree with all of this, but I don't think any of it makes the GP statement true.

It seems likely simply because life came into existence almost as soon as physically possible on earth.

Suppose that life starting is one out of multiple hard steps needed for us to exist. And there's a deadline of perhaps a billion more years before we could never exist, if we didn't occur by then.

Then the early appearance of life is not evidence that life happens easily: all of the hard steps have to happen 'quickly' relative to how long they would 'naturally' take, or we wouldn't exist to observe this history.

I think the paper explains this logic, going by the abstract.

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