They are made out of mass, you silly goose. Why are you asking such a stupid question?

Not so fast.

As it turns out, in superstring theory, the masses of fundamental particles are said to scale with the tension of the string. It is not the case that various particles are made out of heavier and lighter strings (like thick and thin wires), and therefore their mass is the "amount of string" present. Instead, the mass is determined by converting the amount of potential energy in the tension (T) of the string into mass using the conversion ,

m = E/c

^{2}

The various masses which accompany each fundamental particle are the various tensions that string takes on dependent on its mode of vibration.

To visualize this, imagine winding a rubber band around the thin part of a doorknob, which is also a circle. If the string has a tension T = 1/alphaprime , (the conventional notation for the string tension), then winding the string once, twice, three times ... around a circle of size R, costs an energy:

This is because the tension is defined as the mass per unit length of the string; and if we wind the string n times around the circle, it has a length which is n times the circumference of the circle. Just as a 9D experimentalist cannot see momentum in the 10th dimension, she also cannot see this string's winding number. Instead, she sees each of the winding states above as new elementary particles in the 9D world, with discrete masses that depend on the size of the compactified dimension and the string tension.

So what are strings made of? Since mass is the tension of the string (and not the "stuff which the string is made of") the question is pushed to the backburner and not answered directly.

We can now ask whether or not the mathematical dilettantes at Princeton ever bother themselves with this ontological question : what substance are these strings composed of?

Further, we might ask whether this question makes any sense at all to begin with.

Your thoughts?