How to get string between two certain strings in Swift?

Where do strings, in string theory, get their tension from?

• I know that the tension is defined as 1/(2*pi*alpha-prime), where alpha prime is the square root of the string length scale (I've seen planck length used). This would mean that the units are reciprocal square root length. Classical tension is force over length, so the reciprocal part kind of makes sense but what's with the square root stuff? Also, I'm getting we're multiplying by 2pi because a string involves a periodic function. Anyways, what I don't get is why these strings have "tension". Is it really "tension" we're speaking of? If it's intrinsic, why is that so? After all, classical tension involves a force.

• Answer:

  In string theory, tension comes from the Nambu-Goto action co-efficient. The action is [math]S_{NG}= - T \int d\tau d\sigma_{proper}[/math] The [math] \int d\tau d\sigma_{proper}[/math] represents the proper area of the string world sheet. [math]T[/math] is the tension having the dimension of action per unit proper area of the world sheet. Nature tries to minimize this action. That's how you get string tension. Edit (As suggested by ) : In ordinary mechanics you have action = [math]\int L dt[/math] For an ordinary relativistic particle this is generalized to [math]S = -mc \int ds[/math] where ds/c is the infinitesimal proper time, [math]ds^2 = (cdt)^2 - dx^2 - dy^2 - dz^2[/math] A relativistic point particle traces out a line in spacetime called worldline. A relativistic string sweeps out an area in spaceitme which is called worldsheet and the action is written as above.