[jancsika]

I think it's the other way around.

Descartes/Hume are saying that to even bootstrap our understanding of reality, we have a hard dependency on sensory perception. (I mention Hume because he points out that even Descartes' singular ground-truth can't lead anywhere else without linking sensory perception back into the mix.) And when I say "nearly anything" it includes our notions about the laws of physics. (Which, btw, cannot be derived from Descartes' singular ground-truth.)

At best, BB is a restatement of what I wrote with the philosophically irrelevant detail that the BB hypothesis relies on all the same laws of physics we have in common with our universe. But I imagine it's really meant commonly as a weaker claim-- one which takes the laws of physics as epistemological ground-truth to derive an ambiguity about the nature of our reality within that universe.

My speculation is that science-minded people think BB is the most potent thought experiment for the same reason non-musicians might think Pachelbel's Canon in D is the best ever-- they've heard it a lot at places filled with people they admire.

[soulofmischief]

As someone familiar with both Descartes and Boltzmann, I will chime in and say that you're approaching this from an angle of contempt and defensiveness, imagining the Boltzmann brain as an inferior subset of or analogy to long-studied philosophical and metaphysical issues such as ground truth or the evil demon. Instead, I implore you to give benefit of the doubt and attempt to understand the differences.

The Boltzmann brain is not making some grand statement on ground truth or perception. It's not about intrinsics or perception at all. Boltzmann discussed how the universe, even in a state of 100% thermodynamic equilibrium, may spontaneously end up in a state of non-equilibrium, reducing entropy. The Boltzmann brain was a concept developed by others in response to this theory.

In fact, many theories are such that a Boltzmann brain actually has a higher chance of occurring than all of the billions of years of coincidences which led up to me typing this message out to you.

It's purely an argument of entropy and spontaneous symmetry breaking. The sensory and perceptive states described by the Boltzmann brain only serve to illustrate the point, and are not the main subject of the problem.

Don't forget that philosophy was the first science, and viewing people as "science-minded" (and therefore not philosophy-minded) hurts the scientific legitimacy of philosophy, and also only serves to exclude. Many scientists also have deep philosophical grounding. Many also have deep musical grounding. You yourself are exhibiting a lack of domain knowledge regarding the Boltzmann brain, filtering it through your "philosophy-minded" perspective, so maybe we can dispense with these kinds of judgements and focus on the core argument.

The world is not so black and white, and there is no false dichotomy between people who are "science-minded" and "philosophy-minded". Both follow the same exact scientific method of inquiry.

Additionally, "the same reason non-musicians might think Pachelbel's Canon in D is the best ever" comes across as a strawman. Some people might prefer that piece overall, but it's not a crime for someone to enjoy it. But relatively few probably consider it "the best ever".

But also, who cares? Why judge? I have a lot of favorite modern pieces which are technically inferior to most classical pieces. But as a musician, not just an engineer, I consider sensory evocation to be equally as important as technicality.

[sdwr]

Sounds about right, except Pachelbel's Canon actually is the best song ever for non-musicians.

It showcases harmony and contrasting lines in the simplest, punchiest, most pleasing way. It's fundamentally "the good stuff", and untrained ears slurp it up like babies w pats of butter.

[raattgift]

Probably no physicist thinks that Boltzman brains are a potent thought experiment. BBs are short-hand for a problem in combining cosmology and statistical mechanics in a way in which there is a hierarchy of vastly improbable configurations fluctuating into existence out of thermal equilibrium.

Discounting Brain-in-a-Vat (because it's cognitively useless), the problem in a nutshell is that we inhabit a universe which appears (a) to have had a hot dense phase in approximate thermal equilibrium, (b) a future sparse phase in approximate thermal equilibrium, and (c) a whole bunch of structure in between those. Is the structure a fluctuation in (a)? Could (a) be a fluctuation in (b)? These are reasonable questions about which one can ask: is there astrophysical or laboratory evidence available to determine the answers?

One problem is that if (a) (early conditions) is a fluctuation in (b) (late conditions), wherein (a) simply evolves into (c) (complex structure with galaxies and so on) and then (b), what mechanisms could suppress simpler configurations than (a)?

A huge huge huge number of low-entropy Boltzmann brains fluctuating into existence is vastly more likley (on Boltzmann entropy grounds) than an early very-very-very-very-very-low-entropy universe compatible with the standard model of particle physics and the cosmic microwave background and galaxies all over the sky, in which there is a nonzero chance of human brains arising via evolutionary processes.

A tiny change in a Boltzmann brain as it fluctuates into existence could lead to a significant loss of false memory; a tiny change in a maximally-hot maximally-dense phase in the early universe could lead to completely different chemical elements (or none at all).

So Boltzmann brains highlight some metaphysical ratholes one can fall into with respect to the fine-tuning of the (a) state, and have provoked work on how (a) could be so generic an outcome that the evolution of (a)->(c) is "unsurprising". The hard part is coming up with observables which usefully compare a given hypothetical solution and our own sky.

[anon34223879]

I would question the idea of bootstrapping; rather sensory perception is a QC/QA function that confirms the brain's construct of reality.

The only reason we can generally agree on the nature of any object is our common evolution and generally the same sensory ability. (but that isn't universal and differs widely across species)