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Do we know how many dimensions there are?

Dale Glabach
Physicists claim to have a beautiful and consistent theory of quantum gravity, yet they can't agree on the number of dimensions. Some say 10, and some say 11. Actually, our universe may have both — 10 and 11 dimensions. The classical notion of space-time loses its meaning in quantum theory. It's replaced by a more general concept, a "quantum space-time" where dimension is not a well-defined notion. We know a great deal about certain quantum space-times, which have many precise properties, but dimension is not one of those properties.

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