Max Tegmark

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On the dimensionality of spacetime (space.mit.edu) Some superstring theories have more than one effective low-energy limit corresponding to classical spacetimes with different dimensionalities. We argue that all but the (3 + 1)-dimensional one might correspond to ‘dead worlds’, devoid of observers, in which case all such ensemble theories would actually predict that we should find ourselves inhabiting a (3 + 1)-dimensional spacetime. With more or less than one time dimension, the partial differential equations of nature would lack the hyperbolicity property that enables observers to make predictions. In a space with more than three dimensions, there can be no traditional atoms and perhaps no stable structures. A space with less than three dimensions allows no gravitational force and may be too simple and barren to contain observers.
As was pointed out by Ehrenfest back in 1917 [4], neither classical atoms nor planetary orbits can be stable in a space with n > 3, and traditional quantum atoms cannot be stable either [5].

Max Tegmark (Wikipedia) Max Erik Tegmark (born 5 May 1967) is a Swedish-American physicist, machine learning researcher and author. He is best known for his book Life 3.0 about what the world might look like as artificial intelligence continues to improve. Tegmark is a professor at the Massachusetts Institute of Technology and the president of the Future of Life Institute.