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Cosmic Bell Test Using Random Measurement Settings from High-Redshift Quasars.

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This cosmic Bell experiment used ancient quasar light to test quantum entanglement. Researchers observed a significant violation of Bell's inequality, challenging local-realist theories billions of years in the past.

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Area of Science:

  • Quantum physics
  • Cosmology
  • Astrophysics

Background:

  • Bell's inequality tests the foundations of quantum mechanics.
  • Previous experiments were vulnerable to 'freedom-of-choice' loopholes.

Purpose of the Study:

  • To perform a Bell test using measurement settings determined by distant, ancient light sources.
  • To close the 'freedom-of-choice' loophole in Bell tests by using high-redshift quasars.

Main Methods:

  • Utilized polarization-entangled photons for the Bell experiment.
  • Employed real-time wavelength measurements of photons from high-redshift quasars (emitted ~7.8 billion years ago) to determine measurement settings.
  • Ensured locality by design.

Main Results:

  • Observed a statistically significant violation of Bell's inequality by 9.3 standard deviations.
  • Achieved a p-value of ≲7.4×10^{-21}, indicating strong evidence against local realism.
  • Excluded local-realist influences from 96% of the spacetime volume of the experiment's past light cone.

Conclusions:

  • The experiment provides strong evidence for quantum mechanics over local realism, extending back billions of years.
  • Demonstrates the viability of using cosmological sources for fundamental physics tests.
  • Significantly reduces the possibility of loopholes in Bell tests by pushing the 'freedom-of-choice' origin to cosmic timescales.