# Fifth force in string theory [closed]

I can't seem to get a clear description of what the "fifth force" in string theory is. What is the fifth force in string theory? What does it do? What mediates it?

## closed as too broad by Brandon Enright, JamalS, Floris, John Rennie, DanuDec 29 '14 at 11:21

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• When you compactify 11-dimensional $M$-theory on a circle to get string theory, there's a moduli field called the dilaton which is produced. This is responsible for setting the string coupling. That's perhaps a bit of a cop-out, but it's one of the easiest moduli fields to visualize in my experience. – Edward Hughes Dec 29 '14 at 13:20