Reviews of Modern Physics. Four elementary lectures on quantum electrodynamics and quantum field theory , yet containing many insights for the expert. More Read View source View history. This is one of the most difficult aspects of quantum systems to understand. It also means that light can exert pressure as photons slam into an object. It involves two protons — the positively charged particles in an atom — sticking together. While the multiverse is deterministic, we perceive non-deterministic behavior governed by probabilities, because we don't observe the multiverse as a whole, but only one parallel universe at a time. Dual behaviour of matter indicates that the particle displays both particle as well as wave nature.