On the macroscopic scale there appear to be 3 dimensions of space and 1 of time. For instance to locate an event (say meeting a friend), one has to give 4-ordinates. 3 involve space. Distance left-right, distance forward-back and distance up-down. One involves time – for instance 10’clock. This is the classical physics Einsteinian conception of a 4-dimensional space-time (3 spatial dimensional, 1 time dimension).

But the advent of super-string theory has provided evidence for believing in the existence of extra spatial dimensions. The theory requires 11 space-time dimensions to work. But we only see 4. So where are the other 7? The idea is that the other 7 dimensions only have a tiny extension – they are ‘curled up’ so that they warp back on themselves on a microscopic scale – nothing will get very far traveling through them without returning to their starting point. This idea of extra spatial dimensions has percolated through to popular consciousness.

Not so well known however, is the idea that there may be extra *temporal* dimensions as well. Why should all the extra dimensions of string theory be spatial? Perhaps the reason the idea is widely over-looked is that it’s so wacky sounding. If the extra temporal dimensions were curled up like the spatial dimensions of string theory, then traveling through them would return an object to earlier instants in time!

There have been string theorists exploring the possibility of extra time dimensions. It may be that this idea could resolve some of the paradoxes and confusion surrounding quantum mechanics. In quantum physics, things behave as if they occupy more than one state at once. Counter-factual states – ‘what if’s’ or things that *could* have happened strangely interfere with what *did* happen. No one is quite sure what this means. But string theorists Edward Witten and Cumrun Vafa believe that string theory could resolve these puzzles.

Aside from string theory, there are other wacky physics theories which do strange things to time. Cosmologists Stephen Hawking and James Hartle proposed the notion of ‘Imaginary Time’, so-called because of the use of ‘Imaginary’ numbers from mathematics. In fact these numbers are just as real as real numbers and there would be nothing imaginary about this kind of time if it existed. In this theory, the time dimension can behave as if it’s just another dimension of space. The theory was originally intended to deal only with extreme situations such as the beginning of the universe, where the mystery of the origin of time could be resolved by supposing that ordinary time changes into ‘Imaginary Time’. But suppose that there were extra time dimensions existing even today?

More here.