String theorists postulate at least 11 dimensions.
Then again, I'm one of those who thinks string theory isn't even wrong.
FWIW, my layman’s take on “string theory” is that it provides (among other things) a mathematical system where there is no such thing as a “point.” The smallest unit is not a dimensionless point, but a “string.” Having the smallest entity have a size eliminates the absurd mathematical result when size is driven to zero.
Yes, 11 dimensions, sometimes 12.
Sting theory does appear to be one of the more exotic mathematical exercises to come down the pike. It recognizes the need for "extra" dimensions beyond the 4D of ordinary experience. What is striking to me, however, is string theory's propagation of additional spatial dimensions. (IIRC, it calls for only one extra temporal dimension.) These new-found spatial dimensions are said to be curled up unto themselves and are incredibly teensy — less than Planck length in size. Right there, one knows that they would be physically indetectable on the basis of direct observation in principle. Which kind of puts string theory in the same boat as multi-world cosmological theories: There is no known way to validate or disprove the existence of e..g., "other" worlds, or "other dimensions" in this case.
But the string theorists are all pros, and I am but an amateur. So what do I know? Still, I'm happy the string theorists are happy with their work, and look forward to hearing about any progress they are making.
zeugma, I highly recommend Wesson's article, Time as an Illusion. Here's the abstract from the article:
We review the idea, due to Einstein, Eddington, Hoyle and Ballard, that time is a subjective label, whose primary purpose is to order events, perhaps in a higher-dimensional universe. In this approach, all moments in time exist simultaneously, but they are ordered to create the illusion of an unfolding experience by some physical mechanism. This, in the language of relativity, may be connected to a hypersurface in a world that extends beyond spacetime. Death in such a scenario may be merely a phase change.If nothing else, the article will likely give you something new to think about!
Anyhoot, Wesson developed a 5-dimensional model of the universe that posits a fifth "time-like" dimension, which operates as an extra-cosmic hypersurface. In this particular article, Wesson points out the many ways in which our perception of time may well be a mainly subjective construct.
Fun stuff to think about!
Thanks so much for writing, zeugma!