Infinite Boltzmann Brains


I have finally encountered an idea that is too mind boggling for me to really comprehend. Unsurprisingly, it is from the world of theoretical physics. In a recent paper published in Physics Review D string theorists Claire Zukowski and Raphael Bousso explore the idea of Boltzmann brains.

Boltzmann brains are hypothesized self-aware (conscious) entities that are produced from random fluctuations in the fabric of spacetime. That just means that stochastic fluctuations in the level of entropy (disorder) in the universe could theoretically produce something complex (i.e., a self-aware entity) if given enough time. Apparently brains can theoretically blink into existence.

Physicist Ludwig Boltzmann first demonstrated that this was mathematically probable in the 19th century.

Fortunately for Boltzmann, dominant cosmological models today allow enough time for his brains. Current models suggest that our universe will produce Boltzmann brains post Black Hole Era, before the universe decays out of existence.


Image Credit / Wikipedia

Boltzmann brains are a serious paradox for physicists to explain away. If there is enough time remaining in the life of the universe for essentially infinite number of Boltzmann brains to come into existence, our subjective experience of the universe will be highly unusual. We perceive the universe to have a directionality, or an “arrow of time” and all of our understanding of the physical laws derive from this observation. But if the experience of Boltzmann brains is the usual experience then we must question the universality of our physical theories. This is because in a post “Black Hole Era” universe there will be no distinguishable past and future; there will be no arrow of time.

Zukowski and Bousso are working to resolve this insane paradox. Zukowski stated:

It has to be more likely to be an ordinary observer than a Boltzmann brain

They believe that we have to rely on string theory to resolve the paradox. String theorists believe that our universe is just one of an infinite number of universes within a larger multiverse. In this multiverse, universes are constantly budding off of parent universes and inflating over time. Zukowski and Bousso contend that in this framework there are more universes with a discernible arrow of time than universes without (i.e., more universes decay before the appearance of Boltzmann brains than the opposite situation). This would mean experience like our own, with a discernible arrow of time, should be the dominant experience in the multiverse.

Obviously, this is all theoretical. The multiverse itself has not been empirically demonstrated, and is but one of several competing theories to describe the conditions that caused the big bang.

I suppose it is reassuring to know that if the multiverse does exist, it may not be overrun wit Boltzmann brains that have no concept of entropy?

As bizarre as this is to think about, it is too much for me to comprehend for evolutionary reasons. First, I have no idea how the trillions of atoms that create our conscious experience could possibly assemble randomly, even if given infinite time. Second, how strange would it be to have no concept of the arrow of time? To not have a temporal lineage with which to trace your own existence? You just exist, seemingly out of nowhere. You would have no baring on any direction at all. No possible way to understand your origin. A consciousness produced from nothing.

I’ll clarify that I am not saying the math is wrong. I am not qualified to say. Clearly if it is being taken seriously by physicists the math is something to be concerned about. And incredulity is not a good enough reason to doubt the possibility of such entities. If it is theoretically possible, so be it. I’m just saying it is an idea too bizarre for me to really grasp. I don’t think I’ve encountered a stranger idea.

Thanks physics.

What do you think of Boltzmann brains?  Let Cadell know on Twitter.


About Cadell Last
I am a science educator, freelance science writer, and founder of The Advanced Apes based in Toronto, Ontario. In the past my academic research focused on the evolution, ecology, and behaviour of non-human primates (i.e., chimpanzees, gorillas, ring-tailed lemurs). Currently, my official blog, The Ratchet, can be found via The Advanced Apes and Svbtle. I enjoy exploring recent research in human evolutionary sciences, as well as biology, ecology, astronomy, physics, and computer science. My work has been featured in Scientific American, American Humanist, Richard Dawkins Foundation for Reason and Science, and Jane Goodall Institute of Canada. I am also exploring science popularization in new mediums in collaboration with PBS Digital Studios with an animated YouTube channel. You can contact me on Twitter (@cadelllast) or via email:

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