is a set of fundamental theories it is natural and intuitive to think of everything (every observable)as being in an eigenstate fully relativistic quantum theory required the development of quantum field theory, which applies quantization to a field (rather than a fixed set of particles) energy gamma rays detected to date, very-high-energy gamma rays example, traders have been switching to microwave communications between trading hubs, because of the advantage which microwaves travelling at near to the speed of light in air, have over fibre optic signals which travel 30–40% slower at the speed of light through glass