
Boltzmann brain - danabramov
http://en.wikipedia.org/wiki/Boltzmann_brain
======
Dn_Ab
The best explanation for this paradox and one that should be especially
convincing to computer scientists is that the kolmogorov complexity of any
brain aware enough to have consistent memories is higher than the universe
which contains it. A Boltzmann brain might not be impossible but it is far,far
less likely than arbitrary universes occurring as fluctuations. It makes sense
if you think about it. It's also consistent with the fact that 17th century
mathematics could make so much headway unravelling the laws of physics and
we're still fumbling trying to understand bacteria.

Suppose you were playing with procedural generation. Which would be harder: a
procedural universe, a procedural universe with a generated AI able to
interact with it or an isolated AI which has learned to act optimally in some
arbitrary but specific universe? It is not clear that the last program, meant
to represent a Boltzmann Brain with a memory of interactions with the universe
is any less difficult than the one with the complex generated AI. The isolated
AI might be even harder since a dumb algorithm could, given enough time and
feedback, produce something fairly intelligent.

So it would take more bits to describe a brain with your specific memories
than to specify a universe which _could_ end up with someone similar to you
and easiest of all is the program which generates all possible universes.
Schmidhuber goes into this here:
[http://www.idsia.ch/~juergen/computeruniverse.html](http://www.idsia.ch/~juergen/computeruniverse.html).

Even if the universe is not some automaton, the argument is still valid.
Shorter programs are more likely and a program specifying you with memories of
being embedded in some specific universe requires more bits than evolving a
universe which has the laws required to support and eventually evolve someone
like you.

~~~
Symmetry
I approve of you giving this some thought, but entropy doesn't care about
Kolmogorov complexity at all. A box full of helium where exactly half of the
helium is on one side and half is on the other is not appreciably more likely
than one where there are 17 more helium atoms on one side the box than on the
other despite requiring less bits to describe.

The regions of the Canonical Ensemble corresponding to a "A Brain" are much
smaller than those corresponding to "A brain that's inside a body". And the
incompressibility of phase space means that it's therefor proportionally less
likely in the steady state. Just be very glad that the universe we live in is
such that we seem due for a Big Crunch or Big Rip before getting anywhere near
steady state.

EDIT: A little bit of help for the intuition. In a long run steady state
universe pretty much all matter is going to be inside black holes. Sometimes
you get a spontanious particle/anti-particle pair forming near the radius and
one happens to escape. The odds of this happening enough times to accumulate a
brain's worth of mass outside a black hole are staggeringly unlikely. Each
additional brain's worth of mass decreases the odds exponentially. So I hope
you can see that an entire solar system's worth of mass forming outside a
black hole is so unimaginably unlikely that it dwarfs the unimaginable
unlikely-hood of some mass happening to assemble into a brain.

~~~
schiffern
>A box full of helium where exactly half of the helium is on one side and half
is on the other is not appreciably more likely than one where there are 17
more helium atoms on one side the box than on the other despite requiring less
bits to describe.

Plus, how does one decide which information is counted ("which of two distinct
volumes the atoms occupy") and which information is not ("full position &
velocity of every particle constrained only by uncertainty")?

Because if we don't make that [artificial] distinction, each box has exactly
the same amount of information.

------
exratione
Also worth considering is Dust Theory, from the inventive mind of Greg Egan,
which adds a simulation layer and time/space independence to the Boltzmann
paradox.

[http://schwitzsplinters.blogspot.com/2009/01/dust-
hypothesis...](http://schwitzsplinters.blogspot.com/2009/01/dust-
hypothesis.html)

And the FAQ for those who have read Permutation City:

[http://gregegan.customer.netspace.net.au/PERMUTATION/FAQ/FAQ...](http://gregegan.customer.netspace.net.au/PERMUTATION/FAQ/FAQ.html)

------
gajomi
This is pretty silly. The ``paradox'' only arises because of a confused notion
an apparent incongruity between the second law of thermodynamics and the
subjective perception that complex "things" in the universe
(rivers,trees,people) are highly organized. The second law makes a precise
statement about the evolution of closed thermodynamics systems. The latter
observation is only a vague sentiment without an exact statement, and is at
any rate concerned with open systems to which the second law of thermodynamics
does not apply. So there is no paradox.

Addendum: So I made my way through to some of the references, where one can
find all these papers by respected cosmologists (I am not a cosmologist, but I
have heard of these people and get the sense they that are the real deal).
Anyway, it would seem that the term "Boltzmann brain" refers to a technical
problem associated with the growth rate of the creation of metastable states
from fluctuations during inflation (an actual particle physicist should feel
free to chime in). This article appears to hijack the associated buzzword to
advance a philosophical discussion around the ``paradox''. It is worth
pointing out that none of these cosmology articles are referenced inline in
the text. Who are these people and why are they writing this?

~~~
ubernostrum
(I am not a cosmologist or particle physicist, but my thesis did require me to
delve into both, and was defended in front of someone who _was_ a particle
physicist)

It doesn't require confusions about the second law.

It _does_ require some very specific conditions which may not obtain in the
actual universe. It requires, for example, that the universe can eventually
reach thermodynamic equilibrium, that the universe in this state can persist
over incredibly long time periods, that at least some types of particles are
stable enough to exist over such a time range, etc.

And then starts considering whether situations that we normally associate with
states where free energy and the ability to do work exist could arise
occasionally as a result of random collisions of particles, possible quantum
effects, etc.

The key is that the second law is statistical in nature. It describes a
tendency, wherein macroscopic entropy-decreasing events in a closed system are
merely incredibly improbable. Or, more simply: entropy-decreasing events can
occur, they are just so improbable/rare compared to entropy-increasing events
that we should expect not to observe them.

In that context, the Boltzmann brain and other strange things are at least not
outright impossible.

~~~
gajomi
I think I completely agree with you. As you point out, one expects that there
is a small but finite probability to have Boltzmann brain-like things pop up
in the universe. And if it did happen it would violate the second law, which
is making a statistical statement.

So my problem with the article (perhaps your comment should help to clarify)
is that it attempts to start a discussion, involving some kind of anthropic
principle/natural selection to resolve a paradox that doesn't exist in the
first place. The body of the article states:

>The usual resolution of the Boltzmann brain paradox is that we and our
environment are the products of a long process of natural selection, which can
produce complex and improbable outcomes without violating the laws of
thermodynamics.

>The Boltzmann brain paradox is that any observers (self-aware brains with
memories like we have, which includes our brains) are therefore far more
likely to be Boltzmann brains than evolved brains, thereby at the same time
also refuting the selection-bias argument. If our current level of
organization, having many self-aware entities, is a result of a random
fluctuation, it is much less likely than a level of organization which only
creates stand-alone self-aware entities.

The authors of this article somehow turn a correct argument of the expectation
value of the number of Boltzmann brains in an ensemble of universes to a claim
that most brains in these universes must be Boltzmann brains. They do this
without mentioning at all how to calculate the probability of non-Boltzmann
brains (assuming the distinction is even valid). TO deal with the feeling of
existential anxiety that they are left with at the worry they might be
Boltzmann brains they then invoke a natural selection+ anthropic principle
argument.

As far as I can tell has very little to do with the concept as it was
introduced by the cosmologists.

~~~
ubernostrum
I suspect, but cannot be sure, that a lot of the handwaving about the second
law is due to the common misconception that evolution somehow violates the
second law.

It's unfortunate but common, especially among people who refuse to accept
evolution, so I'm not surprised to see it being mentioned.

------
JonnieCache
Here's a Sean Carroll article on the subject:
[http://www.preposterousuniverse.com/blog/2006/08/01/boltzman...](http://www.preposterousuniverse.com/blog/2006/08/01/boltzmanns-
anthropic-brain/)

here's another one, linking the higgs field to the cosmological entropy
problem: [http://www.preposterousuniverse.com/blog/2013/08/22/the-
higg...](http://www.preposterousuniverse.com/blog/2013/08/22/the-higgs-boson-
vs-boltzmann-brains/)

(that second one is a bit whacky...)

~~~
tobias2014
Peter Woit also has some material on this :)

[http://www.math.columbia.edu/~woit/wordpress/?s=boltzmann+br...](http://www.math.columbia.edu/~woit/wordpress/?s=boltzmann+brain)

as does Luboš Motl: Boltzmann brains: popular misconceptions
[http://motls.blogspot.de/2008/08/boltzmann-brains-trivial-
mi...](http://motls.blogspot.de/2008/08/boltzmann-brains-trivial-
mistakes.html)

------
cma
Taking the argument further, it seems more likely that you are a Boltzmann
half-brain, with the other hemisphere's input arriving randomly.

------
negamax
It must be noted that we evolved the way we did because nature have selection
functions interwoven in it. Self awareness (consciousness) is still a tricky
subject to grasp. People think of Infinite Loop Apple's office name as play on
programming. But I am pretty sure it's play on thinking.

------
kineticfocus
He was definitely ahead of his time... "Mathematicians Solve 140-Year-Old
Boltzmann Equation"(2010)
[http://www.sciencedaily.com/releases/2010/05/100513162755.ht...](http://www.sciencedaily.com/releases/2010/05/100513162755.htm)

------
codecrusade
I have some observations on this.

1\. The universe we observe is interpreted by a brain(or conscious entity)

2\. There is no proof if the universe is real or fake(Any proof for its
existence if all brains are destroyed?)

3\. Existence of the universe seem to be a property of the conscious mind

4\. There is no probability theory in this realm. Even Randomness is an
attribute of existence which itself is under question

5\. It is impossible to prove if there is only one conscious mind or there are
several(what if all men are fake)

6\. Since the physical brain is part of the universe which again depends on
its own conscious perception, we have a total breakdown. One possibility is
resort to Godel and suggest that consciousness exists outside the
physical/energy plane.

7\. Therefore what are we talking about (super mario questions his own origins
on an 8 pixel screen)

~random

------
miga
Even with a knowledge of psychology, I'm sure few people realize nightmare of
such vision.

Please, consider that many geniuses feel deprived and stressed
([http://en.wikipedia.org/wiki/Gifted_At-
Risk](http://en.wikipedia.org/wiki/Gifted_At-Risk)). It would be unwise to
assume that these problems would not arise for a brain without access to
culture and society. What is a Boltzmann Brain, if not an isolated genius?

To be such an isolated and self-aware brain might be a scary experience, if we
were ever to record it.

Or impoverished one, if it lacked emotions.

------
vog
Loosely related: Some time ago I wrote a fictional story "History of
Everything" about a "overlord of chaos" which is roughly similar to the
Boltzmann brain, at least in its basic idea:

[http://profv.de/history/](http://profv.de/history/)

However, I never thought that this strange idea could ever be part of a
serious scientific discussion, let alone that such a discussion already
happened more than a century ago.

------
will_brown
As a first time introduction, my brain instantly related the Boltzmann brain
concept to Spontaneous Generation
([http://en.wikipedia.org/wiki/Spontaneous_generation](http://en.wikipedia.org/wiki/Spontaneous_generation)).
Oddly, Ludwig Boltzmann lived during the time the Spontaneous Generation
theory was discredited after being a widely accepted theory for 2 millennia.

