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from the out-with-the-old-priors-and-in-with-the-new dept.
New Theory Concludes That the Origin of Life on Earth-Like Planets Is Likely:
Does the existence of life on Earth tell us anything about the probability of abiogenesis — the origin of life from inorganic substances — arising elsewhere? That's a question that has confounded scientists, and anyone else inclined to ponder it, for some time.
A widely accepted argument from Australian-born astrophysicist Brandon Carter argues that the selection effect of our own existence puts constraints on our observation. Since we had to find ourselves on a planet where abiogenesis occurred, then nothing can be inferred about the probability of life elsewhere based on this knowledge alone.
[...] However, a new paper by Daniel Whitmire, a retired astrophysicist who currently teaches mathematics at the U of A, is arguing that Carter used faulty logic. Though Carter's theory has become widely accepted, Whitmire argues that it suffers from what's known as "The Old Evidence Problem" in Bayesian Confirmation Theory, which is used to update a theory or hypothesis in light of new evidence.
[...] As he explains, "One could argue, like Carter, that I exist regardless of whether my conception was hard or easy, and so nothing can be inferred about whether my conception was hard or easy from my existence alone."
In this analogy, "hard" means contraception was used. "Easy" means no contraception was used. In each case, Whitmire assigns values to these propositions.
Whitmire continues, "However, my existence is old evidence and must be treated as such. When this is done the conclusion is that it is much more probable that my conception was easy. In the abiogenesis case of interest, it's the same thing. The existence of life on Earth is old evidence and just like in the conception analogy the probability that abiogenesis is easy is much more probable."
Journal Reference:
Daniel P. Whitmire. Abiogenesis: the Carter argument reconsidered [open], Int J Astrobio, 2022. DOI: 10.1017/S1473550422000350
(Score: 2) by Immerman on Wednesday October 05 2022, @08:11PM (2 children)
You just repeated my point with different words.
There were never any probabilities attached to "easy" - only that it's easier than "hard", so relabeling them as "very unlikely" and "extremely unlikely" changes nothing.
We know little about *how* easy it was for life to arise here, but we do know that it probably *was* easy, compared to most places.
And given that, it seems reasonable to assume that most planets like ours were similarly "easy" for life to get started on - whatever that means. A big moon is really the only characteristic Earth has that we don't have reason to believe are also common elsewhere. (And we have only very limited evidence from which to conclude that it might be rare)
Meanwhile - we know that life not only arose here, it did so almost as soon as liquid water existed on the surface. Which strongly hints that either it was *very* easy to life to start here, or it originated elsewhere.
Basically - if the odds of life arising are equivalent to rolling a die to get a million 1's in a row - then it *might* happen within the first million throws, but it's far more likely to require countless trillions of throws before it happens. And the safe bet is that it took a fairly "typical" number of throws in our case.
(Score: 2) by maxwell demon on Thursday October 06 2022, @04:46AM (1 child)
So you're trying to get out by redefining words? Sorry, "easy" has a meaning. And that meaning is not "all other options are even harder."
And the point remains that we can't say anything about the probability of finding life on other planets, which was Carter's point. We still can't tell because we don't know the probability life had on earth. So even in the unlikely case that Whitmire really meant it in the way you are now claiming, he's still wrong in telling Carter wrong, just for different reasons.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by Immerman on Thursday October 06 2022, @01:52PM
"Easy" and "hard" are a inherently relative concepts that can easily both be applied to the same task based on context:
To someone playing in a sandbox, moving a few dozen more cubic yards of sand is hard, while to someone operating a river dredge, it's so easy it's barely worth mentioning.
An "easy" Olympic figure skating performance is going to be nearly impossible for most skaters.
And when it comes to creating life - "easy" and "hard" are likely to mean very different things that they do for making bread.