String theory & Tachyons
String theory and gravity
RELATIVISTIC quantum field theory – the theory thatunifies special theory of relativity and quantum mechanics– has been extremely successful in providing adescription of elementary particles and their strong,weak and electromagnetic interactions. The currentlyaccepted theory of elementary particles, known as the‘standard model’, works extremely well in explainingall the observed experimental phenomena involvingelementary particles. The notable exception is the discoveryof neutrino mass; according to the standardmodel the neutrinos are massless, but recent experimentssuggest that neutrinos have mass. This, however,can be easily accommodated using minor modificationof the standard model within the framework of quantumfield theory.However, the techniques of quantum field theory, atleast its perturbation expansion that has been so successfulin the context of particle physics, do not seem towork for quantizing gravity. If we quantize gravity usingthe standard techniques of perturbative quantumfield theory, we encounter a new kind of particle,known as the graviton, which mediates gravitationalinteraction just as photons mediate electromagnetic interactionin quantum electrodynamics.
