Boltzmann Brains: Are They Taken Seriously by Scientists?

[RyanJones]

How seriously are Boltzmann Brains taken by the scientific community? I understand there is at least some mathematical evidence for their (someday?) existence, but do many physicists think that there is anything worthwhile in examining the issue? Or, is it one of those "how many angels on the head of a pin" questions?

And, if it's not too sci-fi-ey for me to ask, are there any reasonable ideas about what the "anatomy" of a Boltzmann Brain might be?

Thanks. I checked out wikipedia already, but I have no idea what is really true on that site.

 

[berkeman]

Thread closed temporarily for Moderation...

 

[berkeman]

Thread re-opened.

Here is a reply from a physics Mentor who has reviewed your post:

The concept itself is not "taken seriously" in the sense that physicists seriously expect Boltzmann Brains to ever exist, as far as I can see. It's more a sort of test that's used when evaluating cosmological models--i.e., an empirically viable model should not predict that a randomly chosen observer is more likely to be a Boltzmann Brain than an ordinary observer (one whose brain evolved and developed in the ordinary way). See, for example, this paper (Sean Carroll is a co-author):

http://arxiv.org/abs/1308.4686

 

[Chronos]

It's merely a thought experiment of the kind that amuses theoretical physicists at dinner parties. No one takes it seriously.

 

[RyanJones]

Thanks everyone. Even tho the paper is a bit above my head, I really appreciate it. So, the use of a brain in the Boltzmann Brain thought experiment is arbitrary? As in, we could use any object to illustrate the same idea? (A Boltzmann Eye, for example?)

 

[PeterDonis]

So, the use of a brain in the Boltzmann Brain thought experiment is arbitrary?

Not really. The point of using a whole brain is that, at least according to the thought experiment, it could have experiences; so, for example, if we take just one instant of your experience, there would be no way to distinguish it from a Boltzmann Brain having been brought into existence by a quantum fluctuation, and being in the exact same state as your brain at that instant. In other words, a Boltzmann Brain can count as an "observer", at least for an instant.

 

[slatts]

In his "Chance and the Arrow" chapter of his 2003 book The Fabric of the Cosmos, Brian Greene spends about 32 pages trying unconvincingly to argue around the sorry fact that the conventional "reality" of the outside world is, in fact, quite a huge bit less probable (thermodynamically speaking) than the possibility that it's all being imagined by the brain in a vat. In contemporary terms, the latter possibility would, unfortunately, require much less of a quantum fluctuation. I've heard somewhere, probably in Wikipedia, that Boltzmann figured that the distinction between past and future was what we'd now call a tiny quantum fluctuation.

 

[slatts]

Since Boltzmann committed suicide, I've got to add that I've never understood why the most "economical" processes are considered likelier--they're likelier to be well known in a species that communicates, because they can be expressed more rapidly, but, although Occam's Razor may minimize the work of scientists, redundant complications do at least seem to characterize nature in general and biology in particular.

 

[Chronos]

Slatts, I doubt the universe gives a rats ass about probability economy or any other human intellectual construct. We are trying to make sense of it, not it of us.

 

[slatts]

Good point...Sometimes the simpler explanation will be the more correct. Especially with my own level of ignorance, that is what I'm counting on here. (Except on not being a brain in a vat--there I'm going with the vastly more complicated solution...consistency is nice, but who cares?)