Alright, so if a Boltzmann Brain is practically impossible, if not physically impossible, why are we even talking about it? For decades, physicists have bashed the idea and debunked it as nonsense. In 2017, for instance, in his paper “Why Boltzmann Brains Are Bad,” physicist Sean Carroll said that Boltzmann Brains are “cognitively unstable: they cannot simultaneously be true and justifiably believed.” As Discover cites, physicist Richard Feynman adopts a softer perspective. He approaches Boltzmann Brains more like a thought experiment than something literal, similar to the famed Schrödinger’s cat puzzle regarding the nature of quantum mechanics.
After all, the person after whom the Boltzmann Brain is named — 19th-century physicist Ludwig Boltzmann — never actually talked about momentarily reduced entropy making brains pop into existence. Boltzmann (the man, not the brain) was a key figure in advancing our understanding of thermodynamics, as ThoughtCo describes. Thermodynamic laws tell us what we’ve been talking about all along, i.e., systems cannot lose or gain energy and move from states of higher to lower order. This is why time flows in one direction — the “arrow of time,” as it’s called — even though, mathematically, there’s nothing preventing time from moving in either direction, as Quanta Magazine explains.
Despite their impracticality, there’s an obvious reason why Boltzmann Brains have stayed in circulation within scientific circles: they’re fun. Frankly speaking, they’re also the kind of goofy topic needed to get lay folks interested in the sciences.
