The familiar theories o f physics have the feature that the application o f the theory to make predictions in specific circumstances can be done by means o f an algorithm. We propose a more preciseâ€¦ (More)

We consider notions of physical equivalence of sets of histories in the quantum mechanics of a closed system such as the universe. We show first how the same set of histories can be relabeled inâ€¦ (More)

The world is four-dimensional according to fundamental phy sics, governed by basic laws that operate in a spacetime that has no unique division into space and time. Ye t our subjective experience ofâ€¦ (More)

Usual quantum mechanics requires a fixed, background, spacetime geometry and its associated causal structure. A generalization of the usual theory may therefore be needed at the Planck scale forâ€¦ (More)

SFI WORKING PAPER: 2006-12-056 SFI Working Papers contain accounts of scientific work of the author(s) and do not necessarily represent the views of the Santa Fe Institute. We accept papers intendedâ€¦ (More)

The origin of classical predictability is investigated for the one dimensional harmonic chain considered as a closed quantum mechanical system. By comparing the properties of a family ofâ€¦ (More)

Feynman's sum-over-histories formulation of quantum mechanics is reviewed as an independent statement of quantum theory in spacetime form. It is different from the usual SchrÃ¶dinger-Heisenbergâ€¦ (More)

We consider the no-boundary proposal for homogeneous isotropic closed universes with a cosmological constant and a scalar field with a quadratic potential. In the semiclassical limit, it predictsâ€¦ (More)

From data in the present we can predict the future and retrodict the past. These predictions and retrodictions are for histories â€” most simply time sequences of events. Quantum mechanics givesâ€¦ (More)