We make a brief historical revision of action-at-a-distance in quantum mechanics. Non-locality has been mostly related to systems of two particles in an entangled state. We show that this effect is also apparent in some experiments with individual particles. An easily performed experiment in this regard is introduced.
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.
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.
This chapter explores intuition in the context of phenomena that involve action at-a-distance – the transmission of a force or effect by no known physical means. Because they contradict the laws of physics, they defy reason and commonsense. Nowadays, though, action-at-a-distance is known as nonlocality. And, following experiments confirming quantum entanglement in the 1980s, nonlocality is accepted as a scientific fact. Moreover, because the individual particles in particle pairings appear to act is if they instantly ‘know’ what is happening to each other and display an unconditional, unbreakable union, some physicists characterize this bond as ‘passion at-a-distance’. In short, quantum entanglement is not only seen as fundamental to understanding the physical universe but is also thought integral to the question of consciousness – and may provide a new explanation for group intuitions.
Einstein became bothered by quantum mechanical action at a distance within two years of Schrödinger's introduction of his eponymous wave equation. If the wave function represents the "real" physical state of a particle, then the measurement of the particle's position would result in the instantaneous collapse of the wave function to the single, measured position. Such a process seemingly violates not only the Schrödinger equation but also special relativity. Einstein was not alone in this vexation; however, the dilemma eventually faded as physicists concentrated on using the Schrödinger equation to solve a plethora of pressing problems. For the next 30 years, wave function collapse, while occasionally discussed by physicists, was primarily a topic of interest for philosophers. That is, until 1964, when Bell introduced his famous inequality and maintained that its violation proved that quantum mechanics and, by implication, nature herself are nonlocal. Unfortunately, this brought the topic back to mainstream physics, where it has remained and continues to muddy the waters. To be sure, not all physicists are bothered by the apparent nonlocality of quantum mechanics. So where have those who embrace quantum nonlocality gone wrong? I argue that the answer is a gratuitous belief in the ontic nature of the quantum state.
Erwin Schrodinger first used the phrase “quantum entanglement” in 1935 to describe a mechanical phenomenon at the quantum level where two (or more) particles’ quantum states must be defined in relation to one another even if they may be geographically apart. This paradoxical event has confounded us for a very long time. Entangled particle behavior appears to be mysterious, illogical, and akin to sorcery at work. The successful and dependable principle of locality has led us to the achievements of twentieth-century physics. However, some theorists may doubt the locality itself due to the “spooky” and nonlocal effects of the local laws of quantum theory. Could there truly be an instant connection between two subatomic particles located on the extreme edges of the universe? Is there a theory that predicts such a relationship that is fundamentally faulty or lacking? Are the outcomes of the experiments that show this connection being read incorrectly? These questions challenge our most fundamental understanding of space and time. The universe is currently being disassembled by modern physics, and it will never be the same. Utilizing cutting-edge technology, quantum entanglement will have a positive impact on society. The history of quantum entanglement is outlined in this work, along with several hypotheses regarding the puzzling behavior of entangled particles. Quantum entanglement may also be an instance of nonlocality in action, in which what occurs in one location affects what occurs in another. Entanglement can also be compared to a situation in which a light switch is used to control two (or more) light bulbs, causing them to turn on at the same time when the switch is switched on. The key question is whether one of the aforementioned theories actually accounts for the odd behavior of entangled particles, in which case experimental evidence would unquestionably support the theory.