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Scientific Reports

Testing the speed of “spooky action at a distance” in a tabletop experiment

Luigi Santamaria Amato, Deborah Katia Pallotti, Mario Siciliani de Cumis, Daniele Dequal, Andrea Andrisani, Sergei Slussarenko

Published May 21, 2023• 6 citations
Publisher

Abstract

Nonlocality, probably the principal friction between Quantum Physics and Relativity, disturbed the physicists even more than realism since it looks to originate superluminal signalling, the Einsteinian "Spooky action at a distance". From 2000 on, several tests to set lower bounds of the Spooky action at a distance velocity ([Formula: see text]) have been performed. They are usually based on a Bell Test performed in km long and carefully balanced experimental setups to fix a more and more improved bound making some assumptions dictated by the experimental conditions. By exploiting advances in quantum technologies, we performed a Bell's test with an improved bound in a tabletop experiment of the order of few minutes, thus being able to control parameters otherwise uncontrollable in an extended setup or in long lasting experiments.

DOI
10.1038/s41598-023-35280-8

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Comment on: Testing the speed of the spooky action at a distance in a tabletop experiment. [Sci Rep 13, 8201 (2023)]

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Comment on: Testing the speed of 'spooky action at a distance'

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Spooky Action at a Distance In the context of correlation experiments involving pairs of experiments performed at very nearly the same time in very far-apart experimental regions, Einstein famously said [1], But on one supposition we should in my opinion hold absolutely fast: “The real factual situation of the system S2 is independent of what is done with system S1 which is spatially separated from the former.” This demand is incompatible with the basic ideas of standard (Copenhagen/orthodox) quantum mechanics, which makes two relevant claims: (1) Experimenters in the two labs make “local free choices” that determine which experiments will be performed in their respective labs. These choices are free in the sense of not being predetermined by the prior history of the physically described aspects of the universe, and they are localized in the sense that the physical effects of these free choices are inserted into the physically described aspects of the universe only within the laboratory in which the associated experiment is being performed. (2) These choices of what is done with the system being measured in one lab can (because of a measurement-induced global collapse of the quantum state) influence the outcome of the experiment performed at very close to the same time in the very faraway lab. This influence of what is done with the system being measured in one region upon the outcome appearing at very nearly the same time in a very faraway lab was called “spooky action at a distance” by Einstein, and was rejected by him as a possible feature of “reality.” John Bell's Quasi-classical Statistical Theory Responding to the seeming existence in the quantum world of “spooky actions,” John Bell [2] proposed a possible alternative to the standard approach that might conceivably be able to reconcile quantum spookiness with “reality.” This alternative approach rests on the fact that quantum mechanics is a statistical theory.We already have in physics a statistical theory called “classical statistical mechanics.”

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Nonlocality, probably the principal friction between Quantum Physics and Relativity, disturbed the physicists even more than realism since it looks to originate superluminal signalling, the Einsteinian "Spooky action at a distance". From 2000 on, several tests to set lower bounds of the Spooky action at a distance velocity ([Formula: see text]) have been performed. They are usually based on a Bell Test performed in km long and carefully balanced experimental setups to fix a more and more improved bound making some assumptions dictated by the experimental conditions. By exploiting advances in quantum technologies, we performed a Bell's test with an improved bound in a tabletop experiment of the order of few minutes, thus being able to control parameters otherwise uncontrollable in an extended setup or in long lasting experiments.
In 1989, Eberhard proposed a v-causal model where quantum correlations between entangled particles are established by communications moving at a superluminal speed v_t > c in a preferred frame. In successive years, several experiments established lower bounds for the possible tachyons velocities. In a recent paper, Luigi Santamaria Amato et al. performed an interesting east-west aligned tabletop experiment under the assumption that the preferred frame is the Cosmic Microwave Background (CMB). In that paper, they criticize long-distance experiments but here we show that most of their criticisms are not applicable to long-distance tunnel experiments where the highest lower bound was obtained.
In a recent experiment, Salart et al. addressed the important issues of the speed of hypothetical communication and of reference frames in Bell-type experiments. The authors report that they "performed a Bell experiment using entangled photons" and conclude from their experimental results that "to maintain an explanation based on spooky action at a distance we would have to assume that the spooky action propagates at speeds even greater than the bounds obtained in our experiment", exceeding the speed of light by orders of magnitude. Here we show that, analyzing the experimental procedure, explanations with subluminal or even no communication at all exist for the experiment.
In their well-known paper, Einstein, Podolsky, and Rosen called the nonlocal correlation in quantum entanglement a "spooky action at a distance." If the spooky action does exist, what is its speed? All previous experiments along this direction have locality and freedom-of-choice loopholes. Here, we strictly closed the loopholes by observing a 12 h continuous violation of the Bell inequality and concluded that the lower bound speed of spooky action was 4 orders of magnitude of the speed of light if Earth's speed in any inertial reference frame was less than 10(-3) time the speed of light.
Spooky Action at a Distance In the context of correlation experiments involving pairs of experiments performed at very nearly the same time in very far-apart experimental regions, Einstein famously said [1], But on one supposition we should in my opinion hold absolutely fast: “The real factual situation of the system S2 is independent of what is done with system S1 which is spatially separated from the former.” This demand is incompatible with the basic ideas of standard (Copenhagen/orthodox) quantum mechanics, which makes two relevant claims: (1) Experimenters in the two labs make “local free choices” that determine which experiments will be performed in their respective labs. These choices are free in the sense of not being predetermined by the prior history of the physically described aspects of the universe, and they are localized in the sense that the physical effects of these free choices are inserted into the physically described aspects of the universe only within the laboratory in which the associated experiment is being performed. (2) These choices of what is done with the system being measured in one lab can (because of a measurement-induced global collapse of the quantum state) influence the outcome of the experiment performed at very close to the same time in the very faraway lab. This influence of what is done with the system being measured in one region upon the outcome appearing at very nearly the same time in a very faraway lab was called “spooky action at a distance” by Einstein, and was rejected by him as a possible feature of “reality.” John Bell's Quasi-classical Statistical Theory Responding to the seeming existence in the quantum world of “spooky actions,” John Bell [2] proposed a possible alternative to the standard approach that might conceivably be able to reconcile quantum spookiness with “reality.” This alternative approach rests on the fact that quantum mechanics is a statistical theory.We already have in physics a statistical theory called “classical statistical mechanics.”
We analyze foundational consequences of recently announced loophole free tests of violation of Bell's inequality. We consider two interpretations of these remarkable experiments. By the conventional one Einstein was wrong and Bohr was right, there is spooky action at a distance, quantum realism is incompatible with locality. However, we show that it is still possible to treat quantum mechanics without appealing to nonlocality or denying realism. We hope that this note will attract attention of the experts in quantum foundations and convince them to come with their own comments on the final Bell's test.
In 1964 John Bell proved a theorem2 allowing the experimental test of whether what Einstein derided as “spooky actions at a distance” actually exist. We will see that they do. Bell's theorem can be displayed with a simple, nonmathematical thought experiment suitable for a physics course at any level. And a simple, semi-classical derivation of the quantum theory result can be given for physics students. These entanglement phenomena are today applied in industrial laboratories and are increasingly discussed in the popular literature. Unfortunately, they are also misappropriated by the purveyors of pseudoscience, something physicists have a responsibility to address.3 Students can be intrigued by the quantum strangeness physics has encountered at a boundary of our discipline.