The tension between quantum entanglement and relativistic causality has persisted fornearly a century. Bell inequality violations demonstrate correlations inexplicable by localhidden variables, yet relativity prohibits faster-than-light causal inuences. We dissolvethis tension through causal eliminativism: causation does not exist in fundamental physics.Three results follow: (1) Bell correlations are derivable as atemporal relational constraintswithout causation; (2) relativity prohibits superluminal causation, which does not exist,not superluminal correlation, which does; (3) the measurement problem disappears whenreconceived as constraint activation rather than causal collapse. The 90-year problem wasan artifact of imposing causal categories onto an acausal world. We survey the neo-Russelliantradition supporting this move, address the measurement problem's standard formulation(Maudlin 1995), and demonstrate concrete applications to the Wigner's friend scenario andBell's theorem premises.
The tension between quantum entanglement and relativistic causality has persisted fornearly a century. Bell inequality violations demonstrate correlations inexplicable by localhidden variables, yet relativity prohibits faster-than-light causal inuences. We dissolvethis tension through causal eliminativism: causation does not exist in fundamental physics.Three results follow: (1) Bell correlations are derivable as atemporal relational constraintswithout causation; (2) relativity prohibits superluminal causation, which does not exist,not superluminal correlation, which does; (3) the measurement problem disappears whenreconceived as constraint activation rather than causal collapse. The 90-year problem wasan artifact of imposing causal categories onto an acausal world. We survey the neo-Russelliantradition supporting this move, address the measurement problem's standard formulation(Maudlin 1995), and demonstrate concrete applications to the Wigner's friend scenario andBell's theorem premises.
We propose that causation does not exist in the physical worldbut explanationdoes. Our framework distinguishes two structures often conated: derivation (the-orems follow from axioms) and causation (events produce other events). Physicsretains the former while eliminating the latter. Beginning from constraint axiomsempirically discovered structures that cannot themselves be derivedwe show thatapparent causal claims become theorems: synchronization, phase transitions, andmeasurement outcomes are derivable from constraint geometry, not produced bycausal mechanisms. The quantum measurement problem dissolves because col-lapse presupposes causation; what remains is constraint satisfaction. Entanglementis correlation constraint, not action at a distance. Spacetime emerges as a perspec-tival feature of embedding within atemporal constraint structure. We situate thisframework relative to Adlam's constraint-based laws, Rovelli's relational quantummechanics, and ontic structural realism. The methodological principle is: axiomscannot be causally explained (this would require prior causes), but theorems can bederived from them. Explanation terminates not in deeper causes but in empiricallydiscovered constraint structures.
Two statements in physics are frequently conflated: that nothing can travel faster than light, and that two entangled particles behave as if "instantaneously" connected regardless of their separation. This paper addresses both questions together: whether a faster-than-light particle could exist and, if so, whether it would count as matter; and whether quantum entanglement actually violates the light-speed limit. Starting from the energy–velocity relation of special relativity, it is shown that massive particles cannot reach the speed of light, and the properties of hypothetical tachyons (imaginary mass, absence of a rest frame and violation of causality) are examined. Using the singlet state, the non-separability, reduced state and correlation properties of entanglement are derived, and the quantum violation of the CHSH inequality up to 2√2 is computed. Finally, via the no-signaling theorem, it is shown that entanglement produces non-local correlations without permitting superluminal communication. In conclusion, nature accommodates non-local correlations without allowing any object to travel faster than light.
In his seminal paper, Bell [Physics Physique Fizika 1, 195 (1964)] considers the correlations that result from space-like separated measurements on a pair of entangled particles. He uses relativity theory to motivate the Bell causal structure, then shows the existence of quantum correlations that cannot be explained classically within this causal structure. Classical explanations of such quantum correlations are possible in alternative causal structures, for instance, those that allow superluminal causal influences, but, as shown in [New Journal of Physics 17 033002 (2015)], all such alternative explanations require fine tuning (causation without correlation). Here we discuss the existence of spurious quantum correlations --- correlations that look quantum in one causal structure, but have a natural classical explanation in another. More precisely, there are causal structures that admit non-classical quantum correlations, but for which the same correlations have a classical explanation in another causal structure without fine tuning. The realisation in the other causal structure can also be achieved without breaking any natural constraints on the causal structure that follow from relativity theory. However, similarly to non-classical quantum correlations in the Bell causal structure, we find other causal structures with non-classical quantum correlations that do not have a classical causal explanation in any alternative causal structure without fine tuning.
In light of a recent reformulation of Bell's theorem from causal principles by Wiseman and the author, I argue that the conflict between quantum theory and relativity brought up by Bell's work can be softened by a revision of our classical notions of causation. I review some recent proposals for a quantum theory of causation that make great strides towards that end, but highlight a property that is shared by all those theories that would not have satisfied Bell's realist inclinations. They require (implicitly or explicitly) agent-centric notions such as "controllables" and "uncontrollables", or "observed" and "unobserved". Thus they relieve the tensions around Bell's theorem by highlighting an issue more often associated with another deep conceptual issue in quantum theory: the measurement problem. Rather than rejecting those terms, however, I argue that we should understand why they seem to be, at least at face-value, needed in order to reach compatibility between quantum theory and relativity. This seems to suggest that causation, and thus causal structure, are emergent phenomena, and lends support to the idea that a resolution of the conflict between quantum theory and relativity necessitates a solution to the measurement problem.
We begin with a brief summary of issues encountered involving causality in quantum theory, placing careful emphasis on the assumptions involved in results such as the EPR paradox and Bell's inequality. We critique some solutions to the resulting paradox, including Rovelli's relational quantum mechanics and the many-worlds interpretation. We then discuss how a spacetime manifold could come about on the classical level out of a quantum system, by constructing a space with a topology out of the algebra of observables, and show that even with an hypothesis of superluminal causation enforcing consistent measurements of entangled states, a causal cone structure arises on the classical level. Finally, we discuss the possibility that causality as understood in classical relativistic physics may be an emergent symmetry which does not hold on the quantum level.
Non-classical correlations resulting from entangled quantum systems have sparked debates about the compatibility of quantum theory and relativity, and about the right way to think about causation. Key to a causal theory is that superluminal signalling is forbidden, which holds in quantum theory. In Bell scenarios, relativistic causality principles like no superluminal signalling are often assumed to follow from the standard no-signalling constraints on correlations. We explore the connections between a range of relativistic principles, including no superluminal signalling and no causal loops, and constraints on correlations that can arise with arbitrary interventions, within multi-party Bell scenarios. This includes standard no-signalling conditions and proposed relaxations allowing phenomena like jamming, where it was suggested that superluminal signalling and causal loops remain impossible. Using our recent framework combining relativistic principles with causal modelling, we show that any theory (classical or non-classical) allowing jamming must rely on causal fine-tuning and superluminal causal influences. Additionally, we show that jamming theories can lead to superluminal signalling in certain situations, highlighting limitations for their physicality. However, we identify cases where jamming correlations avoid superluminal signalling under general interventions, demonstrating that standard no-signalling constraints are not necessary for this purpose. We also show that these constraints are insufficient to rule out superluminal signalling and are neither necessary nor sufficient for ensuring no causal loops under general interventions. Finally, we derive necessary and sufficient conditions for ruling out superluminal signalling and operationally detectable causal loops, solidifying our understanding of relativistic causality principles in information processing tasks in space-time.