Nobody is quite sure what the M stands for - the rumors are either M for “membrane” or for the “mother of all strings."
String Theory refers to two separate theories, the inital one having 26 dimensions and known as Bosonic String Theory (getting it's name from only describing particles known as Bosons) whilst the later one (and the typical definition string theory refers to these days) has 10 dimensions (which is where the supersymmetric variant enters the picture.) They introduced supersymmetry into the picture, hence the term Super String Theory and SuperStrings.
As far as personal belief goes, I find it difficult to understand why they put numbers on the amount of dimensions which potentially exist. Alright, so they calculate, but: It occurs to me that whilst M-Theory and Superstring Theory are on the right track as far as explaining things go (to a degree), I think they limit themselves by saying, "Well there's X number of dimensions." Perhaps those are the only ones perceivable from our pov in physical reality, or the only conclusions we can draw because of our perspective on physical reality. (I believe Brian Green The Elegant Universe said that or similar and it's nice to see people in the field keeping an open mind on things.)
For example, my understanding of Time is that it is a set of dimensions rather than one dimension itself. Which makes me wonder if quantum physicists didn't just assume that Time was one distinct dimension when they began their calculations instead of examining it closer. Combine that with Heterotic String Theory and M-Theory and it bumps the possibilities just a little.
Assume that one proposed explanation of how the 11th dimension exists in M-Theory is that it remains invisible but is always present, and it begs the question: what else aren't we figuring into the equation or seeing just yet?
Enter the recently proposed F-theory, which is formally a 12 dimensional theory. It cites the existence of not one but 2 time co-ordinates. Fancy that, the possibility that we are living in a world with two times.
And onward. John Schwarz of Caltech for one, feels that the final version of M-theory may not even have any fixed dimensional number. So maybe they're getting somewhere after all =)
I haven't done much in quantum and M-Theory apart from personal research from a magical point of view since the online chat I attended with Michio Kaku months ago sadly. It's an avid interest of mine, but nobody seems that interested in discussing it indepthly, or how it relates to magic. Getting to listen to Michio Kaku discuss the breaking developments in the field was amazing though.
And as far as I know, there isn't any equipment which can 'see' or measure "strings" as of yet. Give it time though *nod*
But they can keep quiet for the time being.
