I have recently been introduced to Evolution News; in particular, their opinions on the physicist Sean Carroll. One particular author ― Michael Egnor ― takes umbrance with Carroll’s discussions, discoveries and publications in physics, and this comes up in two of his articles: An Infinite Number of Universes Is More Plausible Than God and Is Sean Carroll a Boltzmann Brain?. Egnor’s goal (stated and inferred) is to declare that the content of methodological naturalism undermines itself, and therefore atheism undermines itself, and he uses Carroll as his sounding board to demonstrate this.
My response will come in two posts: this one, responding to the claim that Carroll’s work on Boltzman brains is “illogical” and my next post about Carroll and the Multiverse. I hope this post introduces you to a new concept in physics; I will have to mention some touching points of physics and philosophy. That’s good news for me, as I’ve tried reading up on the physics involved and the gist of it I think I have, but the nuance is way beyond me (especially the numbers). However, let us start with Boltzman Brains and then the multiverse.
“Boltzman brain” refers, in general, to any idea whereby a brain1 could materialise as an isolated entity2 and, more specifically, to where the materialisation of an isolated brain ― imagining an ordered universe ― in an otherwise chaotic universe is more likely than a universe with order and brains.3, 4
I have my own objection to this, which is that the idea models ‘probability’ on this universe, which it then concludes is (most likely) a fiction. And so, probabilities in other universes (or the speculated ‘real’ universe) is a complete unknown; we don’t know the distribution of probabilities in other universes (if they exist). If one takes the idea that God wrote all the laws to this universe, and therefore they are more or less arbitrary to each universe, we can’t even begin to speculate, and as far as I can tell, nothing in physics allows us to speculate about laws in other universes either. At best, we can speculate the probability that we are Boltzman Brains imagining this universe, but actually existing in another very similar universe.
But, I am not a physicist and I have to just take seriously the fact that physicists take it seriously.
Egnor goes further than this, and uncouples himself from any grounding, like physicists taking the idea seriously.5 Instead, Egnor thinks the Boltzman Brain phenomenon applies across all possible universes ― apparently ignoring that the problem arises when derived from this universe. After this naive rendition of the problem, the author then gets tunnel vision in his philosophy: apparently the Boltzman Brain problem leads to a problem of solipsism and therefore a problem with reliable knowledge, but only in naturalism.
The Boltzman Brain problem is derived from an understanding of our universe, and so applies equally, regardless of whether you are a physicalist, naturalist or metaphysical supernaturalist (i.e. religious). No matter what happens in this universe to convince you of a God, you have to accept you could live in a universe without a God and be deceived because you are actually an hallucinating Boltzman Brain. Solipsism is a challenge to knowledge, no matter what the rest of your philosophies. If you read Descartes, he evaded this problem by simply demanding that it doesn’t apply to religious thinking (as, I suppose, nothing does).
However, Carroll’s work suggests our understanding of this universe should actually imply a much smaller likelihood of Boltzman Brains, which reduces the risk of Boltzman Brain Solipsism. You can’t just dismiss this work, as Egnor does, because the suggestion of a Boltzman brain makes all knowledge meaningless; the very foundation that Boltzman brains are based on ― a sound understanding of the universe we actually navigate ― turns out not to be as powerful as initially thought. I’ll turn to Carroll’s explanation for laymen:
Kim Boddy, Jason Pollack and I have been re-examining how quantum fluctuations work in cosmology, and in a new paper we’ve come to a surprising conclusion: cosmologists have been getting it wrong for decades now. In an expanding universe that has nothing in it but vacuum energy, there simply aren’t any quantum fluctuations at all. Our approach shows that the conventional understanding of inflationary perturbations gets the right answer, although the perturbations aren’t due to “fluctuations”; they’re due to an effective measurement of the quantum state of the inflaton field when the universe reheats at the end of inflation. In contrast, less empirically-grounded ideas such as Boltzmann brains and eternal inflation both rely crucially on treating fluctuations as true dynamical events, occurring in real time — and we say that’s just wrong…This reasoning provides an escape from the Boltzmann brain problem…
We have no reason but brute speculation to entertain the idea of Boltzman Brains.
But the scale of Egnor’s mistake isn’t just his tunnel vision philosophy or naive rendition of the physics, but also the complete misapprehension of how people seriously take problems within knowledge. Solipsism is an old problem, and one that honest investigators simply have to deal with. You are either a hard solipsist who believes they an individual imagining a complex universe and other individuals, else you are a soft solipsist who
didn’t take the blue pill acknowledges they can’t demonstrate otherwise. This creates an ethic within knowledge-seeking of accepting that, at present, we can only learn about the universe we navigate. We have approaches to knowledge, like Deutschian fallibilism (fallibilism as articulated by David Deutsch), which acknowledges that all claims will have at least a grain of inadequacy in them. Humanity creates knowledge at levels of confidence, and any attack on certainty is no attack on knowledge at all.
Egnor imagines a problem whereby good reasons to believe in Boltzman Brains and the implied solipsism leads to a world where all knowledge is meaningless, and therefore Carroll’s pronouncements on Boltzman brains are “illogical”. But, what Carroll is saying is that we have no good reason to accept Boltzman brains; it is a rebuttal to the first platform Egnor is using. Carroll could be wrong, of course, but that is not what Egnor is saying. Egnor is refusing enquiry on the back of what may well be brute speculation, and making a very big deal out of an old philosophical problem, as if no one has addressed it before.
1 “Brain” here is being defined as anything capable of running a simulation it is aware of. If we run far-too-far, intellectually, with this we could allow ‘disembodied consciousness being struck by an electron storm’ as a brain, despite the lack of material involved there. Please note that involves another universe that behaves very differently from our observed and ordered universe.
2 It is not clear whether the statistics that Boltzman alluded to and other have since worked on include the likelihood of a supporting system to allow the brain to consume calories to function. Running with ideas in our own universe and how it functions (which is admittedly a poor starting point in the context of this conversation), that doesn’t make much difference: the lion share of the complexity (and therefore the ‘entropy jump’) is contained in the brain, not the body.
3 Yes, this creates the ‘brain in a vat’ solipsism. Part of Egnor’s point is that naturalism gives us this ‘Boltzman brain’ dilemma, which undermines knowledge-seeking in naturalism ― which he then considers self-defeating. Yes, the standard “we don’t work to certainty” and “we’re trying to understand the universe we navigate” rebuttals do destroy Egnor’s thesis immediately. Yes, the people who would accept Egnor’s thesis without challenge because they already accept the conclusion are the target audience.
4 There are many ways to conclude that reality is more likely to be occupied by Boltzman brains in chaos than an ordered universe. The original has something to do with the vastness of space and massive amounts of matter and the way they move; that has been refined to talk specifically about quantum fluctuations; there is also a multiverse defence, which states that universes of chaos with randomly assembled brains are more abundant than universes of order (as, in the multiverse model, that is the definition of ‘more likely’).
5 It is not an ‘argument from authority’ fallacy to cite the fact that the actual experts in a field take an idea seriously. That is necessarily how knowledge progresses. We stand on the shoulders of giants because we can’t rediscover the universe individually, over and over. That is why it is essential that science has a strict immune system (as all academic fields should).