[griffzhowl]

Yes, and the idea of Boltzmann brains depends for its credence on those physical principles used to derive it. And those principles in turn depend on the reality (or at least reasonable reliability) of our memories and the whole history of experimental and theoretical development leading to them. So trying to use it as an arugment for philosophical scepticism, or that it's a probable scenario, would be self-defeating, denying its own evidence.

It does give a technically detailed construction for how such a scenrio might come about though, as you say, so it can be interesting to think about.

[jancsika]

Sure. But as I said to another respondent, it's a much weaker claim than those which already exist in the philosophical literature.

That doesn't matter if BB is just a bridge for physicists to a deeper understand of philosophy. But I have a sneaking suspicion that BB is part of a basket of ideas in a kind of bubble category of "Philosophy for the Scientist." Similar to those "101 Jokes for Golfers" books-- I mean, fine, but if those are the only jokes you know you're probably insufferable at parties.

[lazide]

Well, the BB isn’t necessarily a serious proposal.

Rather, when you do the math on all the billion/trillion to one shots that are definitely happening, every second of every day, in physics - and look around at the universe as it appears to exist now and how many of those shots had to play out in a specific way - and then do the math on the probability of a BB spontaneously existing, then it’s really absurd that we aren’t somehow BB’s.

[namaria]

I don't know, I've always seen Boltzman brains like I see Schröedinger's cat. I think it was intended to show the absurdity of certain philosophical interpretations of the data available, but somehow got misapprehended as an argument defending those interpretations. Namely that randomness could somehow spontaneously lead to ordered complexity.

[raattgift]

You seem to have it exactly backwards: we have 200 years of practical evidence in favour of modern fluctuation theory thanks to things like steam turbines. Structure does sponataneously appear in a gas in thermal equilibrium, one can show this in a classroom experiment.

Landau and Lifshitz vol 5 <https://en.wikipedia.org/wiki/Course_of_Theoretical_Physics#...> is the standard textbook. There's an older copy on the Internet Archive <https://archive.org/details/landau-and-lifshitz-physics-text...>. (Having the background of L&L vol 9 makes a classroom demonstration even easier: a small handful of electronic parts for a resistive-capactive low-voltage DC electric dipole, a decent oscilloscope or other apparatus to measure and record fluctuating voltage, and a thermometer).

The probability of an out-of-equilibrium structure spontaneously fluctuating (briefly!) into existence depends on the complexity of the structure, and Boltzmann brains are much much much less complex than the whole Earth, solar system, Milky Way, or the early universe in which these structures' precursors originated. So therefore any theory compatible with statistical physics in which the early low-entropy state of the universe is a fluctuation in a higher-entropy "gas" is imperiled.

For the philosopher or two who wrote comments above in this thread, https://plato.stanford.edu/entries/statphys-Boltzmann/ is probably of interest.

[namaria]

Yes I am familiar with the physics behind what I said. Quoting a university textbook on a philosophical argument is an interesting choice.

I have studied and reflected on the subject and I really think Boltzman brains and Schröedinger cat are thought experiments that go way over the head of their pop sci/undergrad classroom interpretations.

[raattgift]

> Schröedinger [sic]

Schrödinger or Schroedinger: it is just you on HN <<https://duckduckgo.com/?q=%22Schr%C3%B6edinger%22+site%3Anew...> who has used "öe", multiple times.

Boltzmann brains have nothing to do with Schrödinger: statistical mechanics works fully classically, and nobody treats Boltzmann brains in a quantum mechanical way because a Boltzmann brain is an unembodied ephemeral human brain. Natural human brains have a history of being warm and electrically noisy (any quantum features decohere faster than thought), while fluctuated-out-of-equilibrium human brains aren't around long enough to have their temperature measured, nor to produce much electrical noise.

A quantum-mechanical Boltzmann brain emerging from a gas of photons in (cold) equilibrium in which fluctuations take photons out of equilibrium and into the farrrr UV is going to be on the short-lived end of Boltzmann brains: things like annihilations and complicated decay chains will dissolve them away quickly. Which is the point. Boltzmann brains, unlike the bowl of petunias in The Hitchhiker's Guide to the Galaxy, should not have time to compose poetry.

Very hot thermal radiation is what destroys classical Boltzmann brains. They sort-of are a cool spot in an extremely violently hot bubble in an otherwise cold (colder than brains!) gas of almost everywhere uniform temperature.

> Yes I am familiar with the physics ...

> Quoting a university [physics] textbook on a philosophical argument

... which is philosophizing about actual physics ...

> is an interesting choice.

Well, what textbooks or other sources do you rely upon when philosophizing about fluctuation theory? What have you read or taught from?

> pop sci/undergrad classroom interpretations

?