We do not know yet whether a description in terms of 10 or 11 dimensions is more appropriate for the universe where we live in. But these two possibilities are continuously connected. They are simply different possibilities for the internal geometry. Since the geometry of the internal space is quantum mechanical, asking what its dimension is might not be the right question.

In summary, in a quantum spacetime the dimension might not be a well defined notion. When the space in question is small, it can interpolate continuously between different dimensions.

— Who’s Counting? Is it 10 or 11? (dimensions, that is — M Theory is making me Manic!)

— Prof. Juan Maldacena

— Institute for Advanced Study

2013.08.29 Thursday ACHK