# Which cosmological models support the Boltzmann Brain Paradox?

In this article, they mention that the Boltzmann Brain paradox is supported by 'the best cosmological models.'

• Sean Carroll (an author of the paper) discusses this particular paper on his blog, and has written at length about Boltzmann brains elsewhere. Possibly you could find an answer by narrowing your searches to that. But the short answer is any cosmological model predicting a lifetime of the universe that is sufficiently long for Boltzmann brains to form. This includes the standard ($\Lambda$CDM or concordance) model which predicts an infinite lifetime for the universe (neglecting the whole Higgs issue). – Michael Brown Sep 5 '13 at 23:00

A model that supports it is a deSitter patch as a closed system with a finite-dimensional Hilbert space, per the abstract of "DeSitter space without dynamical quantum fluctuations", a paper evolved between 2014 and 2016 by Carroll, Boddy, and Pollack, which is available free on Arxiv and includes further references. (I didn't post it as a link because of reported problems with link rot, but you can copy and paste it from PSE.)

The quantum theory used in their interpretation is the Many-Worlds interpretation. The main purposes of CBP's paper are circumvention of the Boltzmann brain problem, as well as circumvention of the future eternality usually characteristic of field-based inflation: CBP provide several scenarios that would greatly reduce, but not completely eliminate, both "problems".

• @ Martin: Sorry for a transposition (now corrected) in CBP's title; try it again if it didn't come up. – Edouard Feb 27 '18 at 16:18

I am no physicist more of an enthusiast the way I understand this is.

There is this thing called Quantum fluctuations which makes two particles from the vacuum of space, its like it borrows energy to create these particles that then immediately annihilate and since the sum of energy before and after is 0 universe remains happy.

There is this idea that universe is infinite and that time does not have beginning nor end, and there is this thing called entropy that is increasing since there are more ways to be in higher entropy than lower and that eventually universe will distribute itself evenly and it will be cold and dark and it's all even in about one google years.

However Quantum fluctuations would still continue and they would sometimes create more than 2 particles that immediately annihilate but 4 and sometimes 6... and since we are talking about infinite time they would eventually fluctuate more complex things like actual stuff, that can be as complex as you want it's just a matter of time.

Now that probability of complex thing coming into existence based on how much entropy has to go lower and our universe is less likely to be fluctuated into existence than functional human brain with all your memories since brain is smaller and requires entropy to go down less.

I have listened to this in one of audio books

Here are some references:

https://en.wikipedia.org/wiki/Boltzmann_brain

https://en.wikipedia.org/wiki/Multiverse

https://en.wikipedia.org/wiki/Temporal_finitism

• That's an interesting idea. They can literally pop out of nowhere – Martin Sep 8 '15 at 19:39
• @Martin yeah, kinda creepy. – Matas Vaitkevicius Sep 8 '15 at 21:46