There is a widely circulated (amongst philosophers) argument against the Boltzmann brain hypothesis made on bayesian grounds. Technical, but very interesting. It's being published next year in what's generally regarded as the top academic journal for philosophy: https://philpapers.org/archive/DOGWIA-6.pdf
> As unlikely as it is for a BB to form at all, it’s drastically more unlikely for additional things to simultaneously form around it. And even if additional things did form around the BB, it is not especially likely they will be the kind of stable and sensible objects a brain could even perceive. Therefore, the evidence we have is more likely supposing we are OOs than supposing we are BBs.
which doesn't ring true to me. Assuming that universe is indeed dominated by BBs, it's not at all clear to me that any observations we could possibly make "is more likely supposing that we are OOs". While the number of BBs "with decorations" would be dwarfed by the number of BBs without, it is still entirely feasible that there are many more such BBs than there are OOs.
I also found their argument as to why all observations shouldn't be considered hallucinations (including "over time", "history of" etc) as a matter of probability to be incomprehensible.
It's philosophically gauche but I often like to criticize arguments based on “what if they were right?”...
So for example the ontological argument putatively argues for the existence of a Perfect Being but it would seem to work even if you restricted the domain somewhat to something smaller than “all beings”, and so presumably also argues for the existence of a perfect Toaster.
Similarly here, the claim is that in a BB universe, even though countlessly more brains see the exact same stuff as you, there is something about the Bayesian update factor that you all have where you all still should conclude you are not the Boltzmann Brains and the evidence is never enough.
How do you look at that description, and not conclude that according to that argument, Bayesian reasoning is just strictly wrong? Like everyone (more or less) is “it” and everyone (more or less) says “it’s not me!” and everyone (more or less) is wrong and here is our philosopher dusting their hands saying ‘yep! sounds good, solved the problem!’
> How do you look at that description, and not conclude that according to that argument, Bayesian reasoning is just strictly wrong?
I believe you're conflating epistemics with decision theory. Sure, the measure of all minds experiencing your current mind-state may be dominated by Boltzmann Brains, with observations that do not correspond to any local state of the world, and which will dissipate momentarily.
But, since your decisions as one of those BB's have no effect, you should make decisions based on the fraction of minds-like-you which are living in a persistent world where those decisions have effects which can, in principle, be predicted.
I love that this addresses that probabilistic confirmation is fundamentally intransitive in Bayesian epistemology, and bumps in probability don’t necessarily propagate through multiple probabilistic links (Evidence -> BBU and BBU -> BB doesn’t mean Evidence -> BB).
Really well put-together and careful main line of argumentation IMO
Ludwig Eduard Boltzmann; 20 February 1844 – 5 September 1906) was an Austrian physicist and philosopher.
Boltzmann wrote treatises on philosophy such as "On the question of the objective existence of processes in inanimate nature" (1897). He was a realist. In his work "On Thesis of Schopenhauer's", Boltzmann refers to his philosophy as materialism and says further: "Idealism asserts that only the ego exists, the various ideas, and seeks to explain matter from them. Materialism starts from the existence of matter and seeks to explain sensations from it."
Here's a different way of thinking about it. There are two things that are both very plausible: One - based on your direct personal experience - is that you are a non-boltzmann-brain-human living a normal life on earth. Two - based on well-accepted science - is that it is MUCH more likely for you to be a boltzmann brain than not.
Great; these two things are seemingly inconsistent. Which means one must be false. But if either of these is false, it's surprising! Because one is based on our direct experience of ourselves, as you have pointed out, and the other is based on well-established science. So what's interesting about Boltzmann brain (and similar) is that it shows that one part of our body of knowledge must be false. And this ought to motivate us to investigate exactly what it is that we have wrong.
None of these are even the interesting points. Arguing about whether you or I are a BB is meaningless.
What I want to know is this: will BBs exist in the immeasurably far future? If they will exist, how fast could they possibly think, how long could they last, and what is the limit on their intelligence? Could they comprehend their own existence from first principles? In the short instants that they exist, would they realize how short their life expectancy is?
>Two - based on well-accepted science - is that it is MUCH more likely for you to be a boltzmann brain than not.
We're not each individual BBs (and you're not a lonely BB imagining the rest of us). It's closer to the truth that our entire universe is one big BB that just blipped into existence one moment billions of years ago. If we accept the concept of a Boltzmann Brain at all, then it must be that some configurations of one where parts of the brain are disconnected from each other and each spawns and intelligence... or even just unintelligent matter/machinery. Scale that up to a few billion light years wide, and that's us.
If a BB could exist, it could also represent a type of intelligence that is so foreign to our experience that we wouldn't even recognize it as such, even if it could last long enough for us to encounter and study it.
Very likely BBs can't exist in our current high-stability regime, and only in the post-matter universe where vacuum-decay-style events occur more often would they manifest. I think they're incredibly far future only. As for the type of intelligence, it seems probably that they'd be completely alien to us, yes, as there must be modes of intelligence other than that evolved my social monkeys. Don't expect any of them to be friendly (though, what sort of violence they could hope to commit is beyond me).
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