The Quantum Landscape 2013
Characterising quantum non-locality using simple physical principles has become a hot topic in quantum foundations of late. In the simpler case of local hidden variable models, the space of allowed correlations can be characterised by requiring that there exists a joint probability distribution over all possible experimental outcomes, from which the experimental probabilities arise as marginals. This follows from Bell’s causality condition. But the existing characterisations of quantum correlations are far from being so straightforward.
I argue that quantum mechanics cannot usefully be extended to a theory of the whole universe, so the task of quantum foundations is to discover that cosmological theory which reduces to quantum mechanics when restricted to small subsystems of the universe. I argue that that cosmological theory will be based on a global notion of physical time which implies the distinction between past, present and future is real and objective. These motivate two examples of novel formulations of quantum theory: the real ensemble formulation and the principle of precedence. Each may imply departure
Having a fundamental spacetime view of physics, appears more justified in attempting to construct a quantum theory of gravity. In this talk, motivated by the latter, a path integral approach is adopted and an attempt to construct a self-consistent realistic histories formulation of quantum theory is presented. After revising the histories viewpoint of classical physics, the quantum case is considered. However, the nature of the probabilities arising from the path integral, leads us to alter the classical picture.
The last few years have seen a spate of operational or information-theoretic
Quantum theory does not define its own landscape. We structure the landscape in response to some contemplated inadequacy of quantum theory. Much foundational work has been motivated by perceived conceptual inadequacies associated with non-locality and the measurement problem. By denying the descriptive function of the quantum state a pragmatist approach may free quantum theory of every conceptual flaw, only to highlight questions we can’t use the theory to address. We should seek to populate the quantum landscape with theories we could use to answer these questions.
We discuss energy diffusion due to spontaneous localization (SL) for a relativistically-fast moving particle. Based on evidence from relativistic extensions of SL we argue that non-relativistic SL should remain valid in the particle rest frame. This implies that calculations can be performed by transforming non relativistic results from the particle rest frame to the frame of the observer. We demonstrate this by considering a relativistic stream of non-interacting particles of cosmological origin and showing how their energy distribution evolves as they traverse the Universe.
I describe some tentative new ideas on modified
versions of quantum theory motivated by the path integral formalism, and on
other generalizations, and comment on possible experimental implications.