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.
Boltzmann brains are of interest to physicists, in particular to cosmologists. The idea is that, according to quantum mechanics, there is energy in empty space which can fluctuate, producing particles as it does so. "If you wait long enough then these fluctuations will form, not just a particle here and a particle there, but a whole complex collection of them. A virus, or a little bunny rabbit, or even a functioning human being," explains Sean Carroll, a theoretical physicist at California Institute of Technology. "The idea is that a brain is the simplest thing that can randomly fluctuate into existence and can still be counted as a conscious being." Such a brain is called a Boltzmann brain (after the 19th century physicist Ludwig Boltzmann who studied fluctuations in systems that are made up of many particles, such as gases).
I had never heard of such a thing. More within, including the mind-bending question: what if we are just Boltzmann brains?
(via The Browser)