Imagine you’re an isolated brain floating lonely through the vast expanse of the Universe with all your thoughts, memories and perceptions just figments of your imagination. That’s a depressing thought, but not a new one. There’d even be a name for you: you’d be a Boltzmann brain.
How do we actually know that we are not Boltzmann brains? Well, we don’t, but we might as well agree that we are not. “[If you are a Boltzmann brain] then all your ideas about history, your memory, the laws of physics and the rules of logic have all just fluctuated into your brain,” explains Carroll. “And therefore you have no right to believe them because other laws, incorrect laws, could also have fluctuated into your brain. So you can’t simultaneously believe that you’re a Boltzmann brain and have any good reason to believe you’re a Boltzmann brain.”
Paradoxically, this paradox lets us off the hook: there is no point in doing science if we’re not happy to agree that we’re not Boltzmann brains and that our observations about the world are real. “I would advocate to try to come up with theories in which we’re not likely to be Boltzmann brains and then we’re on safe ground,” says Carroll.
Readers? If this is what cosmology has come to, what do you recommend?
See also: The multiverse: Where everything turns out to be true, except philosophy and religion
As if the multiverse wasn’t bizarre enough …meet Many Worlds
But who needs reality-based thinking anyway? Not the new cosmologists
Multiverse cosmology: Assuming that evidence still matters, what does it say?
In search of a road to reality