At the most basic level, the entire Grabby Aliens idea turns on the deduction that humans "seem early". To quote from The Paper:
we are roughly at least 10% “surprisingly early” for (n, L̄) combinations... And these are all very restrictive limits on planet lifetimes. Modest increases in power n or max lifetime L̄ beyond these values quickly make our rank look quite surprisingly early.
So, taking this at face value, the 10th percentile is a lower bound for how early we are. To be quite blunt, after spending multiple hours digesting the Grabby Aliens material, as a non-expert, I personally feel very unsure what I should believe is the "expected value" for how early we actually are. 10th percentile doesn't seem early enough to demand the Grabby Aliens hypothesis, 1st or 0.1st percentile does.
But the point is that since "Grabby Aliens" is predicated on a probability, our confidence in "Grabby Aliens" should also be a probability. If we're only "10% early", we can't rule out Grabby Aliens, it just seems less likely.
I think the upshot is to not take the the conclusions of the Grabby Aliens model at face value, nor to nitpick details of the model, because the uncertainty and error bars seem so big. But it is an elegant model because it cuts through some of the complexity in a neglected research area, and gives our feeble human brains something interesting to think about.
Example discussion questions:
(a) In The Paper, Hanson et al make the argument that their simple model is a "crude approximation, but its simplicity can let us better understand and apply it". Can you think of other examples from science where simple models have these virtues? What about examples of simple models that failed?
(b) The entire Grabby Aliens argument hinges on the observation that we appear to have come into existence shockingly early in the timeline of the universe. Do you feel like you understand the argument? Do you find it intuitive? If no, are there general facts (e.g. biases) about human cognition you can point to to help explain why it feels unintuitive?
(c) One big assumption ("approximation") of the Grabby Aliens model (that doesn't seem to have been explored in the literature) is that enough civilizations capable of becoming Grabby would in fact do so, with a rate of expansion close to the practical maximum. Is this plausible?
(d) The first Rational Animations video briefly discusses von Neumann probes as an example of how a grabby civilization might be implemented. If a human-created population of AI von Neumann probes were to become Grabby and take over a significant chunk of the universe, would that be good or bad? Under what circumstances?
(e) What implications, if any, does the grabby aliens idea have for discussions about existential risks to humanity (x-risks)? Can you find any flaws in Hanson's argument in "What Is At Stake?"?
Last, if you find "Grabby Aliens" implausible, but "humans are early" plausible, you may be interested in other possible explanations, such as the hypothesis that we're living in a simulation. To help us stay focused, I personally think it would be best to avoid much discussion of "the simulation" at this meetup. That can be a separate meetup if folks find it interesting.