Boltzmann Brain: The Rumour That You Just Appeared With a Lifetime of False Memories

Boltzmann Brain is the name of a problem in cosmology. It asks whether a very old, cold, nearly empty universe could create a brain after an extremely long time. That brain would contain memories of family, school, history, and a life that never happened outside it. It would still feel that it lived in a real world because every memory arrived with the brain. The rumour pushes this problem to its hardest conclusion: the reader might be a random brain rather than the result of birth, childhood, and a continuous history.

The story takes its name from Ludwig Boltzmann, an Austrian physicist of the nineteenth century. He studied heat, probability and entropy. Entropy can be explained simply as the amount of disorder in a system. A tidy room has lower entropy than a room where everything has been thrown around. Over time, systems usually move from order toward disorder. The large question for the universe is why its earliest state had enough order to make stars, planets, life and memory. Boltzmann considered whether, in a very large universe, ordered regions could arise randomly as rare fluctuations.