If measurements on widely separated particles are linked in a way that light-speed communication cannot explain, does that mean something must be travelling faster than light?
It is a reasonable question. Popular accounts of quantum entanglement often speak of an instantaneous connection, then add that nothing can communicate faster than light. Those statements can sound contradictory unless we explain what the experiments actually establish and what ‘something travelling’ would mean.
The distinction matters: an unusual correlation, a controllable signal and a proposed physical explanation are different claims.
What is entanglement?
The Nobel Prize’s account of the 2022 physics award describes entanglement as a shared quantum state of systems that can remain separated. It is not simply a statement that two objects happen to resemble one another.
For a suitable entangled pair, particular measurements give strongly linked outcomes. The relationship depends on the state prepared and on which measurements are made. Entangled particles do not automatically give the same answer for every property or every measurement setting.
An ordinary comparison helps only up to a point. If someone puts a left glove in one box and a right glove in another, opening one tells you what is in the other. No message has to cross the distance. But that example explains only a prearranged correlation; it does not reproduce the full range of quantum correlations tested with different measurement settings.
Bell turned the question into an experiment
John Bell’s 1964 paper made the issue testable. In the relevant class of local hidden-variable models, the statistical relationships between distant outcomes must satisfy mathematical limits called Bell inequalities.
As NIST explains, experimenters choose measurements at two stations, repeat the experiment and compare the relationships between settings and results. Quantum theory predicts that suitably prepared systems can exceed the local-model limits.
This is much stronger than noticing that two matching results occurred. The evidence concerns patterns across many trials and multiple choices of measurement.
Care is needed with the conclusion. Bell tests constrain local hidden-variable explanations under their assumptions, including the relevant independence of measurement choices. They do not rule out every imaginable hidden-variable theory or settle every interpretation of quantum mechanics.
What experiments have shown
In 2015, Hensen and colleagues reported a Bell test using electron spins separated by 1.3 kilometres. Their arrangement addressed the detection and locality loopholes: the problem of selectively detecting a sample and the possibility of ordinary communication between the stations during the relevant measurements.
A separate NIST photon experiment also reported a violation while closing major experimental loopholes. The measurements were arranged so that light-speed communication could not connect the relevant events in time.
These are experimental challenges to a local account of the correlations. ‘Loophole-free’ refers to closing major experimental loopholes; it should not be read as meaning that an experiment depends on no assumptions whatsoever.
Why ‘something must be travelling’ feels compelling
In everyday life, a distant effect normally prompts us to look for a carrier: light, a sound wave, an electrical pulse or a moving object. If the response seems immediate, the obvious question is how fast the carrier travelled.
Entanglement challenges that familiar picture. But a Bell violation does not supply a measured departure time, arrival time and trajectory for a carrier between the particles. Dividing their separation by an assumed zero travel time therefore does not produce a measured speed.
The narrower claim is important: the observed correlations cannot be reproduced by the relevant local models. Concluding that a particular thing travelled between the stations introduces an additional explanatory model.
Why it cannot send a faster-than-light message
NIST’s entanglement explainer emphasises that individual outcomes are unpredictable. A sender cannot simply choose the desired result on one particle and use it to write a message at the other end.
The stronger statement is about the receiver’s statistics. A quantum-steering study distinguishes remote states conditioned on a known measurement result from the unconditioned remote state, which remains unchanged. In ordinary quantum mechanics, changing a local measurement choice cannot by itself make the other observer’s local results reveal that choice.
Call the observers Alice and Bob. Alice chooses between measurements, hoping to encode ‘yes’ or ‘no’. Bob examines his results alone. He cannot decode Alice’s choice from them. They can establish the joint correlations when they compare records using ordinary communication.
Randomness is part of the explanation, but ‘the outcomes are random’ alone is incomplete. The crucial point is that Alice cannot control a detectable change in Bob’s local statistics to transmit her chosen message.
Does no messaging settle the physical question?
It settles an operational question: entanglement alone does not provide a faster-than-light communications channel within standard quantum mechanics. It does not, by itself, decide how every interpretation should describe the shared state or measurement.
The words ‘instantaneous influence’, ‘collapse’ and ‘nonlocality’ need their assumptions stated. An interpretation may describe the physics in one way while another gives a different account of the same experimental statistics. A description should not quietly become a claim that a travelling signal has been detected.
Two shortcuts are therefore unhelpful: ‘we cannot send a message, so there is nothing puzzling here’, and ‘the results are correlated, so a faster-than-light carrier has been measured’. Neither follows from the evidence presented.
What about quantum teleportation?
IBM’s quantum-information course describes teleportation as a protocol using shared entanglement plus two classical bits to transfer a qubit’s state. It does not transport a person or an object.
The receiver needs that classical information to complete the protocol. Teleportation therefore does not turn entanglement into an instantaneous messaging service. Its name is striking; its actual requirements are more informative.
The answer depends on the claim
Have experiments demonstrated entangled correlations incompatible with Bell-local explanations under the relevant assumptions? Yes. Have they measured a material object or controllable message travelling faster than light between the particles? No.
Does that eliminate the deeper question of how nature produces those correlations? No. It identifies the boundary between a reproducible result and the explanation we give it.
Entanglement gives us a reason to question our everyday picture of separated objects. It does not give us a measured speed for an unseen messenger.
Related reading
Editorial notes: evidence and the limits of current understanding
1. Successful predictions and a complete explanation are different claims. Within today’s understanding, quantum mathematics describes entangled correlations remarkably well. That success does not establish that our present account is the final or complete description of physical reality.
2. Scientific conclusions remain open to revision. Neither quantum theory nor relativity should be treated as irrefutable on the authority of a name or an equation. Confidence should reflect reproducible experiments, the assumptions involved and the range in which a theory has been tested. Being open to revision does not make all explanations equally supported: an alternative must account for existing results and, where possible, offer predictions that distinguish it from other accounts.
3. What has not been demonstrated is not the same as what has been ruled out. The Bell experiments discussed here have not measured a carrier travelling faster than light between the particles. This is narrower than a claim that every deeper nonlocal account has been excluded. Equally, leaving a possibility open is not experimental evidence that it occurs. The communication limit and the interpretation of the underlying connection should therefore be discussed separately.
Sources and further reading
- Nobel Prize — Entanglement and the 2022 Physics Prize
- J. S. Bell (1964) — On the Einstein Podolsky Rosen paradox
- NIST — Local realism and Bell tests
- Hensen et al. (2015) — Loophole-free Bell inequality violation over 1.3 kilometres
- NIST — 2015 photon Bell experiment
- NIST — Entanglement and the communication limit
- Smith et al. (2012) — Conclusive quantum steering with superconducting transition-edge sensors
- IBM Quantum Learning — Quantum teleportation
Sources checked on 15 October 2026. This article distinguishes experimental results, standard quantum predictions and interpretive questions; it does not claim to settle every interpretation of quantum mechanics.