I have only taken a few college physics courses, and I have watched some videos about string theory. I would like to get excited about M-theory, but I have always wondered, why there wouldn't be an infinite number of ways to unite the forces, in which case M-theory is just one possibility amongst an infinite number of possibilities. String theory or M-theory is one mathematical "mechanism" which unites all the forces, Garret Lisi's theory is another "mechanism" which unites the forces into a coherent mathematical structure. This means that there are at least 2 mathematical mechanisms of uniting the forces. But, why stop at an arbitrary number like 2? What evidence do we have that there are not literally an infinite number of ways to unite the forces? All you need is to propose some mathematical "mechanism" which allows the forces to be compatible, and with math being infinite like it is, I see no reason why there would not be an infinite number of ways which can unite the forces. If this is the case, it would seem very premature to get excited about any individual theory, when there are infinite possibilities. If it were possible to mathematically prove, or establish boundaries on the type or number of mechanisms, then it might be possible to show that M-theory is the only possible way to mathematically unite the forces, which would essentially be a mathematical proof that M-theory is true, since we obviously assume our universe must obey the laws of math. One way to do this would be to mathematically prove that any method of mathematically uniting the forces would necessarily make use of strings or banes. This would allow us to know for a fact that our universe is made up of strings, even though they are too small to see. Can you give any information about the points I raised above? And just to simplify, my main question is: What mathematical research has been done on the number of "mechanisms" which can unite the forces?