Knowledge of Quantum Hidden Variables Enables Backwards-In-Time Signaling

Avishy Carmi, Eliahu Cohen, Lorenzo Maccone, Hrvoje Nikolić

Research output: Contribution to journalArticlepeer-review


Bell’s theorem implies that any completion of quantum mechanics which uses hidden variables (that is, preexisting values of all observables) must be nonlocal in the Einstein sense. This customarily indicates that knowledge of the hidden variables would permit superluminal communication. Such superluminal signaling, akin to the existence of a preferred reference frame, is to be expected. However, here we provide a protocol that allows an observer with knowledge of the hidden variables to communicate with her own causal past, without superluminal signaling. That is, such knowledge would contradict causality, irrespectively of the validity of relativity theory. Among the ways we propose for bypassing the paradox there is the possibility of hidden variables that change their values even when the state does not, and that means that signaling backwards in time is prohibited in Bohmian mechanics.

Original languageAmerican English
Article number4477
Number of pages10
JournalApplied Sciences (Switzerland)
Issue number10
StatePublished - 14 May 2021


  • Causality
  • Contextuality
  • Hidden variables

All Science Journal Classification (ASJC) codes

  • General Engineering
  • Instrumentation
  • Fluid Flow and Transfer Processes
  • Process Chemistry and Technology
  • General Materials Science
  • Computer Science Applications


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