 In a de Sitter vacuum (but not in a Minkowski vacuum), a Boltzmann brain can form via nucleation of non-virtual particles gradually assembled by chance from the Hawking radiation emitted from the de Sitter space's bounded cosmological horizon.One estimate for the average time required until nucleation is around formula_2 years.A typical nucleated Boltzmann brain will, after it finishes its activity, cool off to absolute zero and eventually completely decay, as any isolated object would in the vacuum of space.