Consider the very cool and very interesting idea of a Boltzmann brain. The idea is simple to grasp. Instead of a sentient brain that processes information emerging through evolutionary adaptive processes, a Boltzmann brain just spontaneously appears, formed from an available cosmic soup of matter and energy.
I like to use the term ‘cosmological swampwoman’ — probably because it makes me feel like I might have some of the intellectual prowess of Boltzmann (An illusion to be sure, but what harm is there in a little coddling of the ego? Don’t answer that). Mostly because the Boltzman brain concept has a lot in common with the philsophical thought-experimental concept of a swampman: a humanlike organism that just spontaneously materialises sans-evolutionary processes in a primordial swamp (usually due to the addition of lightning.)
The swampman thought experiment is due to Donald Davidson. It is about knowledge (so it’s an epistemological though experiment) but that’s not the part of the thought experiment I am interested in. I just want the part where swampman — sorry, swampwoman — comes into existence nearly instantaneously when lightning strikes a primordial swamp.
Swampwoman’s brain (we’re giving her one so she can amulate and learn medical science and stuff) is pretty darn close to a Boltzmann brain. Exactly a Boltzmann brain, in fact, if the Boltzmann brain emerges in some very tiny amount of time (say a fraction of a second after the lightning strike.) We’re not going to quibble about the number of milliseconds involved. The point is that the swampwoman and her brain just materialise out of the stuff in the swamp — Kerpoof! (Kersplat??). There are no evolutionary adaptive processes involved. She’s just really ‘lucky’.
Boltzmann brains are extraordinarily statistically unlikely. However, extreme statistical unlikelihood is not the same thing as metaphysical impossibility. Metaphysical impossibility is probably much harder to get than extreme statistical unlikelihood, as is physical impossibility. (There are various differences between these depending upon how one characterises and defines the physical world but that is not something I will discuss here. We have our hands full with swampwoman and her brain.)
One needs very strong universal (or multiversal — depending upon one’s scope of application) natural nomic constraints (roughly — natural laws) to get metaphysical impossibility when the possibility being posited is not something analytically illogical and incommensurate like, say, a spherical cube.
How one could ever prove such natural nomic constraints apply at a multi-verse scope is difficult to say. Is such a proof impossible? If one is a finite information processing entity then very probably. (For example: would gravity and the speed of light be the same in the next universe? How would one ever know? The existing universe is our strongest hint, but it by no means provides enough evidence to be even close to certain. It is a huge open question in philosophy and physics.)
There is something important to note at this point (No — it’s not about my ego. Well — maybe it is — but, be nice). There is a mathematical relationship — and a statistico-mathematical relationship — between the degree of heterogeneity of natural kinds in the energy and matter and the statistical likelihood of the occurrence of a Boltzmann brain or cosmological swampwoman.
In other words — the constituents of the swamp matter matters. Specifically — how swampy it is, where degree of swampiness is the degree of different constituents, or the degree of their natural kind heterogeneity.
Whether it is a cosmological metaphorical swamp, or an actual down-to-earth stinky swamp, the idea is that the degree of heterogeneity of the natural kinds (how many different atomic and chemical constituents) in the swamp makes a difference to the likelihood of the occurrence of the Boltzmann swampwoman brain (BSB from here on since I am lazy, and — you can remember one acronym, can’t you? You can forget it again along with this post in 2 minutes).
The less different kinds of mess in the swamp, the less likely it is to produce a BSB.
I do not endorse the thesis that conceivability entails possibility (whether metaphysical, logical, or conceptual). However, I am not convinced that a Boltzmann brain would with 100% certainty never happen in our evolved big-bang initiated universe. It is metaphysically and probably physically conceivable.
If you wish to deny Boltzmann swampwoman brains, then there is tougher challenge to face: a subtly different idea. Here’s the quasi-thought-experiment…
Say spacetime is infinite and the big bang was just one token instance of the natural kind ‘big bang’, of which there have been infinite instances (no need to get into transfinites — just infinity will do). So we can effectively say that there was no beginning (so we’re already both agreeing and disagreeing with the Jesuits). So now posit that we are at time t, and that at no prior time t-n has any Boltzmann brain ever spontaneously occurred.
Are you now willing to say that there will — with 100% certainty — never be a Boltzmann brain ever occur at any time t+n? Because that is a very strong claim that requires more than just the observation that complex sentient organismic systems that we are aware of all emerged via cosmological and biological evolution. Presumably it means that you believe the following to be a (multi-)universal natural nomic constraint:
H1 Information processing brains can only come to exist via emergence qua cosmological and then (biological or other) evolutionary processes.
I do not endorse this very strong stipulation. I can bring myself to endorse only the following compound proposition:
P1 All token instances of information processing brains that we know of came to exist via evolutionary processes, but this does not make the spontaneous appearance of a Boltzmann swampwoman (non-evolved) brain impossible given infinite spacetime with heterogeneous, complex, and chaotic structures, dynamics, and information processing.
It is probably still staggeringly unlikely — but with the scale of the known universe (having 100 billion and 200 billion galaxies) I doubt it is impossible. Galaxies are really enormous and full of mind-bendingly huge amounts of dynamically interacting heterogeneous stuff. As such I suspect it is metaphysically and physically possible that there could have been multiple swampwoman (spontaneous or instantaneousness) Boltzmann brains, and there could have been even more non-swampwoman (slow-forming) Boltzmann brains. Even the instantaneous one seems undeniably metaphysically possible. It has a non-prohibitive conceivability. As for what such a brain would look like and how and what it would think and do: the mind boggles
