The domains of quantum theory and general relativity overlap in situations where quantum mechanical effects cannot be ignored. In order to deal with this overlap of theoretical domains, there has been a tendency to apply the rules of quantum field theory to the classical gravitational field equations and without much regard for the implications of the whole enterprise. The gravitational version of the asymmetric ageing of identical biological specimens shows that curved spacetime is not dispensable. This result is used to (...) conclude that the particle-based interpretations of quantum gravity are not acceptable. (shrink)

This essay examines some of the arguments in David Deutsch's book The Fabric of Reality , chief among them its case for the so-called many-universe interpretation of quantum mechanics (QM), presented as the only physically and logically consistent solution to the QM paradoxes of wave/particle dualism, remote simultaneous interaction, the observer-induced 'collapse of the wave-packet', etc. The hypothesis assumes that all possible outcomes are realized in every such momentary 'collapse', since the observer splits off into so many parallel, coexisting, but (...) epistemically non-interaccessible 'worlds' whose subsequent branchings constitute the lifeline-or experiential world-series- for each of those proliferating centres of consciousness. Although Deutsch concedes that his 'multiverse' theory is counter-intuitive, he none the less takes it to be borne out beyond question by the sheer observational/predictive success of QM and the conceptual dilemmas that supposedly arise with alternative (single-universe) accounts. Moreover, he claims the theory resolves a range of longstanding philosophical problems, notably those of mind/body dualism, the various traditional paradoxes of time, and the freewill/determinism issue. The essay suggests on the contrary, that Deutsch unwittingly transposes into the framework of presentday quantum debate speculative themes from the history of rationalist metaphysics, often with bizarre or philosophically dubious results, and that he rules out at least one promising rival account, namely Bohm's 'hidden variables' theory. It goes on to consider reasons for resistance to that theory among proponents of the 'orthodox' (Copenhagen) doctrine, and for the strong anti-realist, at times even irrationalist bias that has characterized much of this discussion since Bohr's debates with Einstein about quantum non-locality, observer-intervention, and the limits of precise measurement. Finally, the contrast is pointed out between Deutsch's ontologically extravagant use of the many-worlds hypothesis (akin to certain ideas advanced by speculative metaphysicians from Leibniz down) and those realist modes of counterfactual reasoning- e.g. in Kripke and the early Putnam- which deploy similar arguments to very different causal-explanatory ends. (shrink)

Fritjof Capra's The Tao of Physics, one of several popularizations paralleling Eastern mysticism and modern physics, is critiqued, demonstrating that Capra gives little attention to the differing philosophies of physics he employs, utilizing whatever interpretation suits his purposes, without prior justification. The same critique is applied and similar conclusions drawn, about some recent attempts at relating theology and physics. In contrast, we propose the possibility of maintaining a cogent relationship between these disciplines by employing theological hypotheses to account for aspects (...) of physics that are free from interpretive difficulties, such as the ability to create mathematical structures with extraordinary predictive success. (shrink)

Abstract The historical evolution of the principle of relativity from Galileo to Einstein is briefly traced, and purported difficulties with Einstein's formulation of the principle are examined and dismissed. This formulation is then compared to a precise version formulated recently in the geometrical language of spacetime theories. We claim that the recent version is both logically puzzling and fails to capture a crucial physical insight contained in the earlier formulations. The implications of this claim for the modern treatment of general (...) dynamical symmetries are discussed. (shrink)