What is the difference between m-theory and the original string theory?

Question

What is the difference between m-theory and the original string theory?

Answer 1

There were two string theory revolutions, but I will assume you are talking about the second revolution.  Well, string theory kind of evolved depending on what parameters you changed or kept.  Eventually, there were many theories that had different parameters, but all still worked.  This is a bad thing.  2+2 does not equal a whole bunch of different things.  However, M-Theory comes along and says that all the different string theories are actually part of the same theory.  I am not too sure on how they are the same theory, but I believe it has to do with external conditions determine the specific parameters that differ.  Hope this answers your question.

Answer 2

Simply put, M-theory is a way of trying to unify a whole family of superstring theories, or classes of theories.  Another oversimplification is that the brane theories extend the fundamental entity into more than a single dimension.  But you have lots of concepts to learn which are common to all the theories, before you need to worry about the differences.

Answer 3

11 dimensional string theory, (and 26 dimensional M theory), has not produced anything.

It is possible that the extra 7 dimensions of space in string theory, (that are not perceived), are mathematical deception that first appeared with 5 dimensional Kaluza-Klein Theory.

String theory is possibly deception involving adding dimensions of space to the already existing 3 dimensions of space one dimension at a time at 90 degree angles to the previous dimension.

That string theory is possibly invalid is stated at the end of the wikipedia article on string theory.