String theory
In 1957 Hugh Everett described his "Relative state" interpretation.  Everett maintained that the wavefunction does not collapse, and since all matter and interactions are presumed to be built up from quantum waveparticles, all possible variations of the quantum field—indicated by the mathematical equations—are real and simultaneously occurring but different courses of history.  By this interpretation, whatever interacts with the field joins the field's state that is relative to the observer's state—itself a waveform in its own quantum field—while the two simply interact in a universal waveform never collapsing.  By now, many physicists' interpretation of the apparent transition from the quantum to the classical realms is not wavefunction collapse, but quantum decoherence.