In string theory, Does a string have a mass?
“A string is simply a one dimensional extended object. However, it is not like just an ordinary string, say a violin string. The energy density along a string in the fundamental string theory is assumed to be a universal constant which is usually denoted as 1/2pa ¢c, where c is the velocity of light and a ¢ is the new fundamental constant characterizing string theory. Thus, even when the string stretches or shrinks, the energy per unit length does not change. In other words, the total mass of a string is essentially determined by its total length. This means that the length of the string in the states with lowest energy is zero, at least classically, and so the masses of these states vanish. If we treat the string quantum-mechanically, we have to take into account quantum fluctuations and therefore we cannot say that the length of the lowest energy states of the string is strictly zero in the classical sense. However, the fact that their masses are vanishing is still valid. It also tur
