T-duality and emergence
Tiziana Vistarini · 2019
Extra dimensions play a crucial role in quantum string theory. Postulated mainly for consistency reasons, they turn out to reinforce the theory’s predictive power. Indeed, they crucially contribute to let the theory display the massless spectrum of gauge bosons and chiral fermions of the Standard model. Duality is a type of symmetry that involves a space whose elements are not physical states. Both the transformed and untransformed objects are physical theories. Two distinct physical theories are dual of one another if they produce the same physics, that is, if they have the same physical content. The strategy of introducing compact extra dimensions to increase physical theories’ predictive powers did not originate in the context of string theory. Kaluza-Klein reduction produces the unification of electromagnetism and general relativity by proving that the symmetry group of electromagnetism can be obtained from the five-dimensional compactified gravity.