Disembodied brains

Boltzmann’s reasoning, however, was undermined by another, more absurd, conclusion. Rare fluctuations could also give rise to single, momentary brains – self-aware entities that spontaneously arise through random collisions of particles. Such “Boltzmann brains”, the argument goes,  are far more likely to arise than the entire visible universe or even the solar system. An infinity of space would therefore contain an infinitude of such disembodied brains, which would then be the “typical observer”, not us. Can this bizarre vision possibly be real, or does it indicate something fundamentally wrong with our notion of “typicality”? Or is our notion of “the observer” flawed; can thermodynamic fluctuations that give rise to Boltzmann brains really suffice? Or could a futuristic supercomputer even play the Matrix-like role of a multitude of observers? These questions about existence and our place in the universe are akin to those debated by philosophers throughout the ages. Now, for the first time, they are arising in concrete areas of scientific practice. Might a final, asyet-undiscovered theory of quantum gravity reconcile all of these mysteries and, if so,  could deep philosophical thinking pave the way, just as the work of philosophers such as David Hume and Ernst Mach did for Einstein? Drawing the line between philosophy and physics has never been easy. Perhaps it is time to stop trying. The interface is ripe for exploration.  ■