Grabby aliens or false vacuum decay bubbles?
Back in 2020-2021 I worked with Robin Hanson et al on a “grabby aliens” model which offered an explanation for why humans are so early in the history of the universe. I recently had the chance to watch Robin’s 2021 presentation to Foresight Institute on grabby civilizations (GCs). In the Q&A session, Adam Brown offered some questions and comments which suggest that the GC model actually works best as a model of false vacuum decay bubbles, which would make the universe increasingly uninhabitable. First, these bubbles, unlike GCs, are naturally devoid of observers, which prevents the self-indication assumption problem of, “Why are we non-GC observers instead of GC observers?” Second, these bubbles naturally propagate at the speed-of-light, so do not require the development of multi-galaxy civilizational expansion technology. Without further ado, what follows is a minimally-edited transcript of the relevant Q&A between Adam Brown and Robin Hanson:
I have a question, but before I get to the question, I want a clarification first. So in your model, we are us, we're not the grabby aliens, despite in your model the grabby aliens vastly outnumber us. So that seems like you're just hypothesizing that.
The key point is, here we are now. We could potentially become aliens for others. But we are not yet grabby; we have not yet reached the stage where we are expanding rapidly and nothing can stop us. But the key assumption is that we might become grabby; and if we do, that would happen within, say, 10 million years. And that means that our date now is close to a date of origin of grabby aliens, because if it happens it would happen soon. That's the key assumption.
But in your model, almost all of the sentient beings that exist are the much larger grabby aliens rather than the earlier civilizations such as ours. So you need to explain why we're not one of those.
We're trying to be agnostic about the ratio between grabby and non-grabby aliens. So there could potentially be all these quiet aliens out there: vast numbers unknown, density unknown. It's hard to say much about them because you can't see them. We're focused on the grabby ones because we can say things about them, but we're agnostic about the relevant ratio there.
But the grabby aliens are occupying large fractions of the universe, so unless they're not sentient, it sounds like they should be more numerous. So of the sentient beings who exist, we're extremely atypical in your model, which seems to be a point against it.
That wouldn't be a crazy conclusion to draw, but you would have to make further assumptions about observers. We're not in our analysis making assumptions about observers. We're not saying that grabby aliens are observers, or that they will produce a density of observers. We're not saying anything about them other than that they make a visible difference, and then you would see them. That's all we're saying.
Let me move on to my next question then, which is perhaps betraying my day job. Let me present an alternative theory for a resolution of the Fermi Paradox that sounds very different from yours but I think ultimately is sort of quite similar. In your grabby alien model, the reason we don't see them is that they excise a large fraction of their future light-cones. Another model is: when civilizations get sufficiently advanced, they run stupid science experiments, and those stupid science experiments cause vacuum decay in the Higgs sector, for example. In this case, there will be a vacuum bubble that will expand out at the speed of light, and really excise the future light-cone of those advanced civilizations. That theory actually has a lot in common with your theory, in the sense that both result in advanced civilizations excising their future light-cones. And all of the evidence that counts in favor of your theory also counts in favor of that theory: all the evidence in terms of the “N-steps in evolution”, the “why are we so early” questions. And it has the additional advantages that you don't need to explain why it expands at the speed of light (because that's just input from theoretical physics that it'll definitely expand at the speed of light if you make a new bubble of a vacuum) and also has the advantage that you don't need to explain why we don't live in one of those bubbles because there's nothing alive in those bubbles — you've destroyed the Higgs vacuum. So there seems to be some sort of commonality between the vacuum decay bubble literature and what you're saying. And it'll be interesting to look back at the bubble nucleation literature in the light of your comments, and see whether they bear on that.