It’s All About Boltzmann, Baby

This… this just might be my new favorite scientific concept.  You’re gonna love this.  What happens when you follow the idea of random coincidence to its infinite extreme.

It was just like this, except I was even more handsome

Remember my story of embarrassment on the soccer field, from the introduction of this article?  I managed to unintentionally kick a soccer ball straight up in just the right trajectory to land on my unsuspecting coach’s head.  While what I accomplished was astoundingly implausible, perhaps nearly impossible even for the most accurate soccer star to do intentionally, it didn’t violate the laws of physics.  As long as you don’t violate physical law, you can do all kinds of strange things if you wait around long enough.  That’s how you can be dealt a royal flush in poker maybe a couple times in your life.  Or you can bonk your soccer coach on the head (and presumably embarrass the hell out of your father) every once in a while.

Now let’s switch gears to the topic that naturally comes to mind after kicking soccer balls at coaches — thermodynamics.  Imagine a room full of gas, say the room you’re sitting in now as you’re reading this.  Chances are very good that the entire room is uniformly filled with gas – that you don’t have a pileup of air on the left side of the room, for example.  Because the little gas molecules are constantly jostling and bumping, they tend to spread out evenly to fill the entire room.  But there’s nothing to stop them from just happening to gather more towards one side of the room, just by random fluctuation.  It could just so happen that every molecule bounces just right, and all of the air in the room huddles down in the corner, leaving a vacuum in the rest of the room.  It’s so astoundingly unlikely that it’ll never happen in your lifetime (nor that of the universe), but it isn’t physically impossible.  In our experience we consider it impossible for all practical purposes, but that’s because we won’t live long enough for something that rare to happen to us.  But what if the universe were infinite?

In a universe filled with an infinite number of rooms filled with room-temperature gas, eventually you’ll stumble across that one room where some rare fluctuation does happen.  One of the trillions of rooms will be “one in a trillion” – in some room somewhere, all the gas will just happen to collect on one side of the room.  In an infinite universe, somewhere a coffee cup spontaneously unmixes the coffee from the creamer.  If our universe is infinite, then any event which isn’t physically impossible will eventually happen.  And so somewhere, out there in that infinite universe, there will be a set of stars that just line up to spell out your name.  Somewhere else, a bunch of random molecules just happen to gather in one spot to create a soccer ball, for a brief moment before dissipating.  And somewhere, out there, eventually, a working conscious brain will form, purely by just the right random fluctuation of just the right molecules.  In an infinite universe, somewhere out there is an exact copy of your brain, spontaneously appearing out of the void, intact with your memories and personality, but unfortunately for this copy, floating free and unprotected in the harshness of space.

"Goo goo what the..."

So the chilling idea is that in an infinite universe, given enough time, random fluctuations will cause spontaneous appearances of just about anything – and what’s really chilling is that a rare few of those spontaneously appearing objects will happen to be conscious – the particles of matter just so happen to assemble together in just the right configuration to form a working brain (be it human, rodent, trilobite, alien, superintelligent computer, whatever).  Obviously the more complex the brain (or object whatsoever), the more rare the fluctuation to cause it, and the less likely it will be to appear.  But we’re talking about an infinite universe, so they’re bound to appear eventually.  These are called “Boltzmann Brains” (or also “Boltzmann Babies”, which I like much better), named for the famous physicist Ludwig Boltzmann, the father of thermodynamics.

Creeped out yet?  Feeling sorry for these poor duplicates of you, doomed to live their short existences out in the void, not safe and sound contained inside a nice warm body on a cozy planet, like you?  Poor random brains, they’re not “real”, like you.  In fact they may not even realize they’re not “real”, having been formed with memories just like yours – as far as they know, they’re real (until they fall apart or are destroyed in the harsh environment).  Don’t be so smug.  Lemmie give it to you straight – in an infinite universe, where anything that is physically possible will eventually happen, there are far more Boltzmann Brains out there than “real” brains – after all, it’s a lot easier for a random fluctuation to piece together a just working brain for a bit than to create an entire solar system that contains a planet that can support life.  And so… since all of these brains don’t know they’re not “real” brains, it’s more likely that you are a Boltzmann Brain, floating through space alone, than a “real” brain.  After all, you wouldn’t know, would you?

"Well SHIT!" *dissolves into the infinite void*

So here’s the creepiest problem, in a nutshell – in an infinite universe, it’s far more likely that you are a Boltzmann Brain, spontaneously formed from a random fluctuation of molecules moving just right and born with complete intact “memories” of the full history of your life up to this point, instead of actually being a living brain inside a body (as you believe).  “But wait”, you ask, “I remember my childhood clearly!  I didn’t just form a few seconds ago!”  Well, if you formed with those memories intact, then you would “remember” them as if they really happened, and you wouldn’t be able to tell the difference.  And a few seconds from now when you dissipate, there won’t be any consciousness left to notice that you’re dissipating.

Why exactly would Boltzmann brains be much more common than actual “real” brains (as we envision ourselves)?  If we assume the universe is infinite in extent and has been around for a while, and entropy is always increasing, then the universe should be heading for a uniform “heat death” state of maximum entropy.  But when we look around, we see a strikingly low amount of entropy – stars, planets, beings like us all exist.  So, he presumed, perhaps we’re existing in a local bubble of lower-entropy fluctuation – throughout the universe, entropy is constantly fluctuating, on a global scale heading ever upward but locally free to dip downwards temporarily.  And larger dips in entropy are much more rare than small dips.  The magnitude of downward fluctuation in entropy needed to make a pocket big enough for our solar system to form, and to last long enough for life to start, is much less likely than a fluctuation big enough to give space for a self-aware brain to form (complete with false memories of a past).  Ergo, the small fluctuations that enable a Boltzmann brain to form are much more likely to happen than a large fluctuation needed to allow our visible universe to form.  So we’re much more likely to be a Boltzmann brain, hallucinating the observable universe we see, instead of actually physically existing the way we think we do.

"We've come to render your cosmological models embarrassing..."

You can imagine how disturbing this must have been to Boltzmann and other physicists of the time, when it was presumed the universe really was infinite.  Since Boltzmann’s time, we’ve made serious advances in understanding the universe – quantum mechanics, the Big Bang, etc.  And the idea of randomness still can imply very strange (yet not against the laws of physics) events can happen.  Quantum tunneling, for instance – it has been calculated that the likelihood that we would be instantly teleported to the surface of Mars is 10^10^51 to 1. — not very likely (in fact astronomically tiny even in the lifetime of our universe), but not strictly impossible.  But we’re beyond believing that Boltzmann Babies could be real, right?  WRONG.  While it’s true that some of the assumptions underlying the original idea are now known not to hold (e.g. the Big Bang that started the universe), the uncomfortable idea of Boltzmann brains is still debated among the cosmologists – all related to the concept of entropy.  You can imagine the similar kinds of uncomfortable conclusions to be made about an infinite supply of universes in a multiverse theory.  In fact the debate rages on among cosmologists today about how to devise theories of the origin of the universe that don’t lead to a proliferation of Boltzmann babies, the thinking being that a theory that can eliminate them is a more realistic model of our universe.  This has led to sober research publications in mainstream physics journals using terms like “freaky observer“, and decrying the presence of Boltzmann Brains as some scourge that must be eliminated.

Weird, eh?  It’s gonna get weirder.

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