
Boltzmann Brain - mmrichter
https://en.wikipedia.org/wiki/Boltzmann_brain
======
RobertoG
'Permutation City' by Greg Egan, a Science Fiction novel, has as one of its
main subject a variation of this idea.

Recommended, it's a very interesting reading.

~~~
aswanson
One of the many promising looking books on my shelf when I get the ever
elusive time.

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Eerie
You know what`s funny? Our entire universe could be a Boltzmann Universe, that
spontaneously appeared just three minutes ago.

Happy Birthday, everyone!

~~~
sevenless
Much more likely the Boltzmann Brain appeared _right now this instant_ and
you, the reader of this, are just hallucinating all of your experiences and
will disappear in another nano-second.

~~~
Eerie
imfinewiththis.jpg

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chriswarbo
Boltzmann's fluctuations are pretty easily defeated by Feynman's argument:
small fluctuations are exponentially more likely than large fluctuations, so
if we make a new observation (e.g. opening a door) the fluctuation hypothesis
predicts that we'll see random noise; yet we don't, we see more ordered
structure. The hypothesis is refuted.

What I find more interesting is if we're a random fluctuation _on a Turing
machine tape_. "Randomness" takes a lot of space to encode in a program, so
smaller (more likely) programs lead to less random, more structured outputs.
This agrees with our observations.

~~~
jessriedel
> Boltzmann's fluctuations are pretty easily defeated by Feynman's argument:
> small fluctuations are exponentially more likely than large fluctuations, so
> if we make a new observation (e.g. opening a door) the fluctuation
> hypothesis predicts that we'll see random noise; yet we don't, we see more
> ordered structure. The hypothesis is refuted.

You've missed the point of Boltzmann brains. No one who studies this stuff
thinks we're a Boltzmann brain. The question is whether we can rule out
theories that _predict_ Boltzmann brains as the numerically dominant observer
with our observations. Indeed, many very popular theories of cosmology (e.g.,
eternal inflation) are in apparent conflict here.

~~~
sullyj3
If boltzmann brains were numerically dominant, then we would expect to be one,
right?

~~~
jessriedel
Maybe. It's highly contested. One popular argument _against_ that claim (which
I agree sounds reasonable on its face) is that it turns out to allow us to
draw some strong conclusions about the universe which, intuitively, should not
be possible to conclude from our armchair (the "presumptuous philosopher").

In the philosophy literature, this often is framed in terms of a choice
between the self-indication assumption or the self-sampling assumption.

[https://en.wikipedia.org/wiki/Self-
sampling_assumption](https://en.wikipedia.org/wiki/Self-sampling_assumption)

[https://en.wikipedia.org/wiki/Self-
indication_assumption](https://en.wikipedia.org/wiki/Self-
indication_assumption)

The canonical reference on this is Bostrom.

[https://www.amazon.com/Anthropic-Bias-Observation-
Selection-...](https://www.amazon.com/Anthropic-Bias-Observation-Selection-
Philosophy/dp/0415883946)

In the physics literature, this has been discussed as the assumption of
"typicality".

[http://journals.aps.org/prd/abstract/10.1103/PhysRevD.75.123...](http://journals.aps.org/prd/abstract/10.1103/PhysRevD.75.123523)
[http://journals.aps.org/prd/abstract/10.1103/PhysRevD.81.123...](http://journals.aps.org/prd/abstract/10.1103/PhysRevD.81.123524)
[http://arxiv.org/abs/0707.4169](http://arxiv.org/abs/0707.4169)
[http://journals.aps.org/prd/abstract/10.1103/PhysRevD.78.023...](http://journals.aps.org/prd/abstract/10.1103/PhysRevD.78.023514)

Hartle and Srednicki's thought experiment involving the Jovians is a form of
the presumptuous philosopher argument.

~~~
iraphael
I also liked this explanation of the Typicality assumption

[http://scientifica.wikia.com/wiki/The_Typicality_Assumption](http://scientifica.wikia.com/wiki/The_Typicality_Assumption)

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drjesusphd
After reading this, The Last Question by Azamov takes on new meaning.

[http://multivax.com/last_question.html](http://multivax.com/last_question.html)

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vog
From the article:

 _> A Boltzmann brain is a hypothesized self aware entity which arises due to
random fluctuations out of a state of chaos._

This is really strange. Years ago I wrote a short story about a similar topic,
without ever having read about the Boltzmann brain:

"History of Everything"

[https://njh.eu/history](https://njh.eu/history)

