
Boltzmann brain hypothesis discussed in a Dilbert comic strip, April 27, 2009. [5]

Boltzmann brain hypothesis discussed in a Dilbert comic strip, April 27, 2009. [5]

In cosmological thermodynamics, Boltzmann brain problem, or “Boltzmann’s brain” or “Boltzmann’s brain paradox” is an apples and oranges type of puzzle situated by American physicist Andreas Albrecht in 2002 which asks, to the effect, that if the universe began in a low entropy condition, an ordered state, and is now moving or inflating to high entropy final conditions, loosely a disordered state, thus giving directions to the arrow of time, then how does one explain the existence of so many “brains”, modeled as low entropy fluctuations, which are considered as incredibly rare events, in the universe? To a good approximation, the Boltzmann brain problem is a reformulation of the 1858 Spencerian dilemma, albeit in the context of big bang theory.

In this frame of logic, a person or rather a brain is seen as a momentary fluctuation in a field of matter and energy in the inflationary space and time of the expanding universe. [4] The idea of fluctuation-produced hypothetical "Boltzmann Brains" has become a sort of journal writing past time for astrophysicists in recent years, just as the hypothetical Maxwell's demons have been for information theory physicists in the last dozen decades.

Etymology
American physicist Andreas Albrecht stated that the Boltzmann brain paradox was first discussed in his 2002 article “Cosmic Inflation and the Arrow of Time”. [1] In this article, Albrecht states that typical discussions on cosmic inflation start out by presenting a series of cosmological “problems” that appear to be present in the standard big bang model, one being the “flatness problem”, another being the “homogeneity problem.”


Boltzmann's brain fluctuation diagram by American physicist Sean Carroll. [6]

Boltzmann's brain fluctuation diagram by American physicist Sean Carroll. [6]

In a subsection to this article entitled Boltzmann’s Efficient Fluctuation Problem, Albrecht states his first presentation of what is now known as the Boltzmann brain problem:

“Boltzmann worried that if our world really emerged from a random fluctuation, then a strong prediction is made that we exist in the midst of utter chaos. The fact that instead we live in a universe billions of light-years in size which is extremely quite an un-chaotic, and that seems to have room for not just our cozy planet, but many more like it seems to be in blatant contradiction to these predictions.”

Albrecht goes on to argue that cosmic inflation gives a resolution to this so-called problem. He began dubbing the issue the “Boltzmann brain paradox” in 2004.

Boltzmann Brains
In 2006, owing to the over-prevalence of the use of this term "Boltzmann brains', Canadian theoretical physicist Don Page introduced the notation of BB or BBs as shorthand for: [3]

Boltzmann Brains (BB) = hypothetical brains resulting from thermal or vacuum fluctuations.

This notation, similar to Maxwell's demon, has since gained popularity in the astrophysics community. In fact, dueling papers have supposedly appeared in the last few years, replete with references to reincarnation, multiple universes, and death of spacetime, etc., all in attempts to reconcile cherished cosmology theories of big bang and inflation with the second law and human existence. [4]

Difficulties on theory
The entire theory, to note, takes a while to sift though, but the central issue seems to be the mixing of chemistry (reactions) and biology (evolution) together with concepts from statistical mechanics and cosmology (e.g. hydrogen burning, nucleosynthesis, etc.,) to make rather outlandish conclusions. The theme of the debate is similar to the underlying theme to the thermodynamical aspects of the famous creation vs evolution debates, which is that incorrect rephrasing of the standard second law, i.e. "the entropy of the universe tends to a maximum" [Clausius, 1865], which has to do simply with the mathematics of heat transforming into internal work per each heat cycle, into the Boltzmann/Planck second law variation, i.e. “there exists in nature a quantity, called entropy that depends on disorder, which changes always in the same sense in all natural processes” [Planck, 1897], reapplied to the entire universe, which is not technically correct.

References
1. Albrecht, Andres and Sorbo, Lorenzo. (2004). “Can the Universe Afford Inflation?” Arxiv.org, May.
2. Albrecht, Andres. (2002). “Cosmic Inflation and the Arrow of Time”, In: Science and Ultimate Reality: From Quantum to Cosmos. Cambridge University Press, 2004.
3. (a) Page, Don H. (2006). “Return of the Boltzmann Brains”, Phys. Rev. D. 78, 063536.
(b) Page, Don N. (2008). “Is our Universe Likely to Decay within 20 Billion Years?”, Phys. Rev. D. 78, 063535.
4. Overbye, Dennis. (2008). “Big Brain Theory: Have Cosmologists Lost Theirs?”, NYTimes.com, Jan 15.
5. Boltzmann brain hypothesis (Dilbert comic strip), April 27, 2009.
6. Boltzmann’s Brain (fluctuation diagram) by Sean Carroll, California Institute of Technology, NYTimes.com, Jan 14, 2008.

Further reading
● Carroll, Sean M. (2006). “Boltzmann’s Anthropic Brain”, Discover Blogs. Aug 01.
● Linde, Andrei. (2007). “Sinks in the Landscape, Boltzmann Brains and the Cosmological Constant Problem”, Journal of Cosmological and Astroparticle Physics. Jan.
● Gott, J. Richard. (2008). “Boltzmann Brains—I’d Rather See Than Be One”, Arxiv.org.

External links
● Boltzmann brain – Wikipedia.