> The Great Filter isn't a thing! There is no Fermi paradox!
Just spent the time to read this whole paper, I think you're misstating some of the claims. A lot of people seem to be confused as to what is stated by the Great Filter/Fermi paradox/Drake equation.
First, let's define some terms (from wikipedia!): "The Great Filter, in the context of the Fermi paradox, is whatever prevents non-living matter from undergoing abiogenesis."
To be clear, the Great Filter is a solution to the Fermi paradox. If the Great Filter is true, then there is no paradox. The statement that there is no Fermi paradox is not the same as saying there is no Great Filter.
This paper suggests that there is a huge amount of uncertainty in $f_l$ and it actually can be quite small, meaning that it is not unlikely that we would see no alien life. (I won't comment on their choice of log-uniform priors, which does not seem intrinsically justified and lets them get much smaller results than if they had just picked uniform)
But that is the Great Filter argument! If there is a great filter, that would be a reason why $f_l$ would be lower and the fermi paradox doesn't occur. The paper never suggests that there is no great filter.
Now contextualizing to this discovery. If there is life on Venus, that changes our estimate of $f_l$, reducing our uncertainty and increasing the posterior probability mass towards life developing, which means that the fact that we haven't seen life must push the probability of development beyond that stage down or our current state of affairs is more unlikely than it was before.
Okay, you're right to say I shouldn't say "there is no Great Filter!" and I was fast and a bit too punchy with claims. What I want to say is "Nick Bostrom's Great Filter argument is not a cause for fear!" (https://nickbostrom.com/extraterrestrial.pdf).
> First, let's define some terms (from wikipedia!): "The Great Filter, in the context of the Fermi paradox, is whatever prevents non-living matter from undergoing abiogenesis."
I think you ended this sentence early. Wikipedia continues that sentence "...from undergoing abiogenesis, in time, to expanding lasting life as measured by the Kardashev scale."
In the context of the Fermi Paradox ("where are they?"), Bostrom is saying that he hopes the Great Filter is "whatever prevents non-living matter from undergoing abiogenesis" ($f_l$), but it might not be. The Great Filter might be a thing that is ahead of us, says he. And, yeah, the prior that it isn't abiogenesis is higher if we find life in our backyard.
So, you're right, finding life on Venus reduces some uncertainty with $f_l$ and pushes some of the probability mass down the Drake equation, which remains a chain of expected value multiplications, which is a bad way to combine probability distributions.
Bostrom's whole argument is predicated on the proposition that the galaxy "should be" teeming with life, and if the argument that it "should be" teeming with life is bogus (boiling down bathtub curved or otherwise not-normally distributed probability distributions to means/point estimates and then multiplying them, even if we had $f_l$ nailed down exactly), then I think that's a win for not worrying about Bostrom's argument so much.
But you are right, it's hard to say "don't worry about it!" if I don't well and clearly define what "it" is, or worse, define it wrong ("the great filter!"). Thanks for pushing this into better clarity.
> Drake equation, which remains a chain of expected value multiplications, which is a bad way to combine probability distributions.
Perhaps the paper wants to say that the problem with the Drake equation is intrinsic to multiplying expected probability, but what they're really doing is laundering their great filter assumptions upwards in the Bayesian hierarchy (ie. into their prior distribution hyperparameters and choice of distribution)
ie. they are still using expected values, they're just using them
This discovery would totally undermine the thesis of this paper. Here's the paper:
> While the analysis above required us to make our own judgment calls about how to represent the state of scientific uncertainty for each of these parameters, our qualitative result is robust to many of these assumptions and can be driven by our claimed uncertainty in f_l alone
This is much less impressive than it sounds. What this means is that if we could verify there is alien life on Venus that independently evolved, then the prior they have for f_l is massively off and their claimed uncertainty is way off. Using a log-uniform + the lowest estimate for f_l they can find in the literature already explains most of their results, not the mere process of multiplying expected probabilities.
> So, you're right, finding life on Venus reduces some uncertainty with $f_l$ and pushes some of the probability mass down the Drake equation, which remains a chain of expected value multiplications, which is a bad way to combine probability distributions.
The only reason they get such a low result is because they push a lot of the probability mass of $f_l$ super super super super far to the left. By their model, the probability that $f_l$ is less than 0.0001 is something like 42%... if we discovered independently evolved life on venus that would shift extremely far to the right and change their results completely.
Just spent the time to read this whole paper, I think you're misstating some of the claims. A lot of people seem to be confused as to what is stated by the Great Filter/Fermi paradox/Drake equation.
First, let's define some terms (from wikipedia!): "The Great Filter, in the context of the Fermi paradox, is whatever prevents non-living matter from undergoing abiogenesis."
To be clear, the Great Filter is a solution to the Fermi paradox. If the Great Filter is true, then there is no paradox. The statement that there is no Fermi paradox is not the same as saying there is no Great Filter.
This paper suggests that there is a huge amount of uncertainty in $f_l$ and it actually can be quite small, meaning that it is not unlikely that we would see no alien life. (I won't comment on their choice of log-uniform priors, which does not seem intrinsically justified and lets them get much smaller results than if they had just picked uniform)
But that is the Great Filter argument! If there is a great filter, that would be a reason why $f_l$ would be lower and the fermi paradox doesn't occur. The paper never suggests that there is no great filter.
Now contextualizing to this discovery. If there is life on Venus, that changes our estimate of $f_l$, reducing our uncertainty and increasing the posterior probability mass towards life developing, which means that the fact that we haven't seen life must push the probability of development beyond that stage down or our current state of affairs is more unlikely than it was before.
Does that make sense?