If I promise to avoid "infinity", and to keep the "Schröding-cat" in its box, perhaps I could toss a thought into the mix.
If we take “M” theory as perhaps being the most promising variety of string theory, and David Deutsch’s version of the multiverse (The Fabric of Reality, Penguin Books, 1998) as being perhaps the best explained multiverse theory, the nature of my question will emerge clearly.
String theory requires both extra dimensions and multiple universes. M theory involves 11 dimensions. We are told that 7 of these need to be rolled up so tightly that we cannot detect them. This is why we cannot observe them.
On the other hand trillions of universes occupy the same space with such precision of positioning that individual photons, in different universes, can interfere with one another, yet we cannot observe these universes and they are not rolled up. Why, then do the extra dimensions need to be rolled up to avoid detection?
