Abstract Isaac Newton’s theory of gravity seems to postulate action at a distance. Two distant massive bodies act on one another gravitationally instantaneously without a causal mechanism to mediate the action. This paper will argue that a strategy found in the Principia that allows Newton’s theory to be explanatory without providing a causal explanation can be extended to the quantum case. However, while causal action at a distance can be avoided, the explanatory cost of avoiding any form of nonlocality is higher in the quantum case than in the case of Newton’s theory of universal gravitation.
Abstract Isaac Newton’s theory of gravity seems to postulate action at a distance. Two distant massive bodies act on one another gravitationally instantaneously without a causal mechanism to mediate the action. This paper will argue that a strategy found in the Principia that allows Newton’s theory to be explanatory without providing a causal explanation can be extended to the quantum case. However, while causal action at a distance can be avoided, the explanatory cost of avoiding any form of nonlocality is higher in the quantum case than in the case of Newton’s theory of universal gravitation.
Introduction Our concern in this chapter is locality in quantum mechanics (QM). Locality is a heuristic physics principle based on the following propositions. No Action-at-a-Distance All the evidence points to the principle that physical actions, taken within restricted (localized) regions of space and time by observers or other agencies such as systems under observation (SUOs), do not cause instantly observable effects on other SUOs at large distances. This does not apply to mathematical/ metaphysical concepts such as quantum wave functions or correlations, as these are conceptual objects (Scarani et al., 2000). Statements about instantaneous wave function collapse are vacuous (have no empirical significance) and are therefore not an issue of significance in physics. Such statements are an issue to theorists who objectivize wave functions, as in Hidden Variables (HV) theory. Action-at-a-distance is generally regarded as anathema by most physicists. For example, Newton's law of universal gravitation is well known for mathematically encoding action-at-a-distance. There is direct evidence, however, in the form of a letter written by Newton to Bentley, that Newton believed that gravity acting “at a distance through a vacuum without the mediation of anything else” was an absurdity (Newton, 2006). The no action-at-a-distance principle is encoded in quantized detector networks (QDN) by the requirement that labstate preparation and consequent signal detection never occur at the same stage. Causal Transmission All physically observable consequences of local actions taken by an observer or SUO are transmitted by identifiable physical processes, such as electromagnetic waves or neutrinos. There is no such thing as magic or action-at-a-distance . In QDN this proposition is taken into account implicitly in the labstate outcome amplitudes at each stage, as these model how information is propagated from stage to stage. When necessary, the information void can be modeled as if there were fields and/or particles propagating through it, giving scope for different mathematical models, such as Euclidean space, curved spacetime, noncommuting spacetimes, and so on. The structure of the information void is essentially a discussion of whatever modules have to be taken into account between labstate preparation and signal detection.
Introduction Fifty years after the publication of Bell's theorem, there remains some controversy regarding what the theorem is telling us about quantum mechanics, and what the experimental violations of Bell inequalities are telling us about the world. This chapter represents my best attempt to be clear about what I think the lessons are. In brief: There is some sort of nonlocality inherent in any quantum theory, and, moreover, in any theory that reproduces, even approximately, the quantum probabilities for the outcomes of experiments. But not all forms of nonlocality are the same; there is a distinction to be made between action at a distance and other forms of nonlocality, and I will argue that the nonlocality needed to violate the Bell inequalities need not involve action at a distance. Furthermore, the distinction between forms of nonlocality makes a difference when it comes to compatibility with relativistic causal structure. The Bell locality condition is a condition which, if satisfied, renders possible a completely local account of the correlations between outcomes of spatially separated experiments. Bell's theorem tells us that the probabilities that we compute from quantum mechanics do not admit of such an account. Modulo auxiliary assumptions that, in my opinion, should be noncontroversial, this yields the conclusion that there must be something nonlocal about any theory that yields the quantum mechanical probabilities or anything close to them. One way to violate the Bell locality condition – and this is the way that any deterministic theory must do it – is via straightforward action at a distance. However, we should also consider the possibility of a stochastic theorywith probabilistic laws that involve irreducible correlations. The sort of nonlocality inherent in such a theory involves relations between events that are significantly different from causal relations as usually conceived. Perhaps surprisingly, such a theory, unlike its deterministic cousins, need not invoke a distinguished relation of distant simultaneity. This makes a difference for the situation of the two sorts of theories vis-a-vis relativity. Though a deterministic theory can achieve the appearance of being relativistic, at the level of observable phenomena, it can do so only by introducing a preferred foliation and with it a causal structure at odds with relativistic causal structures. Things are otherwise with dynamical collapse theories.
Most physicists currently believe they have the basic description of the universe [though they currently admit 90% to 99% of the universe is in the form of “dark matter” of which they know nothing except it has gravitational attraction]. You should realize in all of science there are only descriptions of how things happen and nothing about why they happen. Newton gave us the formula for how gravity worked, and he made no hypotheses as to what gravity really was, nor through what medium it worked, let alone why it worked. Indeed, he did not believe in “action at a distance”.
It is shown that a recently proposed model for the gravitational interaction in non relativistic quantum mechanics is the instantaneous action at a distance limit of a field theoretic model containing a negative energy field. It reduces to the Schroedinger-Newton theory in a suitable mean field approximation. While both the exact model and its approximation lead to estimates for localization lengths, only the former gives rise to an explicit non unitary dynamics accounting for the emergence of the classical behavior of macroscopic bodies.
This thesis aims to legitimize the inclusion of action at a distance in scientific theories. I approach this task from two angles. In the first part, I show that action at a distance is a genuine metaphysical possibility. To do so, I examine how theorists in the history of science have justified their assumption of locality (and find these justifications inadequate), reconcile action at a distance with scientific explanation and show that it is not a threat to causation. In the second part, I consider an actual instance of action at a distance in nature: quantum nonlocality. Since action at a distance cannot be excluded through reason alone, if experience indicates action at a distance one may call it as such. I argue that action at a distance is the most viable theory by which to interpret quantum nonlocality.
Abstract After forty years of EPR experiments, it appears on the face of the experimental facts that one of the oldest ideas in Physics has been falsified, namely the retarded interaction paradigm, the notion that long range interactions between quanta, or equivalently causal influences between point events, are mediated by physical entities - fields, particles or “causal influences” in general - that travel through space from one point to the other at or below the characteristic velocity, c. A critical examination of this basic idea shows it to be unsatisfactory in all respects. An alternative is then proposed that satisfies both causality and local action, “distributed action”, which is germane to local realist field models of the quanta, where matter and energy extend in space and interact locally and causally at all locations where they overlap. Bell Inequalities cannot be derived in this context because, with distributed fieldfield interactions, spacelike separation of events does not guarantee the fundamental “no influence” assumption from which all the various Bell Inequalities are derived. Distributed action thus explains what appears to us as instantaneous action at a distance. PACS: 03.65.Ud 03.75.-b