Amanda Gefter repeats a common fallacy about infinite universes: the assumption that "everything that can happen will happen - an infinite number of times" (6 March, p 28). There are many-possibly infinitely many - ways that this might not be true, given rnour limited knowledge about what constraints apply to how universes might form.rnIf the fundamental constants that characterise a universe can vary continuously - if they are strictly "real" numbers - there would be an uncountably infinite number of configurations of physical laws and no two universes need contain the same families of fundamental particle, let alone be replicas of each other.
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