From Carl Zetie
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 our limited knowledge about what constraints apply to how universes might form.
If 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.
Other more subtle possibilities exist. There might be merely a countable infinity of distinct actualised universes out of an uncountable infinity of possible universes, just as the infinite set of whole numbers (integers) is an infinitesimal fraction of the real numbers. Alternatively, actual universes might be some special subset of a countable infinity of possible universes. If it turns out that space-time is quantised, this could be the more likely case.
If the multiverse arises from universes spawning further universes, each with slightly different physical constants, the population of universes may explore only a fraction of the possible “ecological niches”, even after infinitely many repetitions.
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You quote Andrei Linde of Stanford University as asking “How do you compare infinities?” The answer, as Georg Cantor demonstrated more than a century ago, is “very carefully”.
Waterford, Virginia, US
