• Question: Explain string theory?

    Asked by seanhanafey to Eoin on 13 Nov 2013.
    • Photo: Eoin O Colgain

      Eoin O Colgain answered on 13 Nov 2013:

      In contrast to usual particle physics theories, string theory puts forward the idea that particles are not fundamental and they merely arise as oscillations (vibrations) of a more fundamental one-dimensional object, a string. Since one of the oscillations of this string corresponds to the quantum of gravity, the graviton, string theory can describe gravity and particle theory in a unified way. So, it may be a step towards unification of forces, including gravity. It is a candidate for the Theory of Everything (TOE).

      Mathematical consistency in string theory tells us that we should have either 26 or 10 ten-dimensional spacetime and not 4. This is a curious feature, since we have not observed extra dimensions.

      Lots of string theorists work on something called the AdS/CFT correspondence, or a generalisation called gauge/gravity duality. If true, this is an extremely deep idea and relates theories WITHOUT gravity to theories WITH gravity. It is being applied to model condensed matter physics and the quark gluon plasma as a calculational tool.

      And as for the status of string theory, very few people fully understand the implications of the theory. Indeed, it is not yet a “theory”, since it does not make concrete predictions, more qualitative statements. The situation is summed up in this cartoon.

      http://xkcd.com/171/

Comments

  • Photo: eadaoinxx

    eadaoinxx commented on :

    !!!!!

  • Photo: Eoin

    Eoin commented on :

    String theory is based on an observation that gravity is already included for free in the theory. If one wants a unified theory, one explaining everything, then this is required. (I can explain more about quantum gravity if there is a related question :)).

    RHIC experiments on heavy ions at Brookhaven found that the Quark-Gluon Plasma, the high energy goo, they produce exhibits something called elliptic flow. This means small (shear) viscosity.

    String theory can explain this result, whereas perturbative QCD (stong nuclear force theory) cannot. There is some progress on getting the same result recently using computer simulations, but string theory got there first.