Bells Theorem

• Metadata
  • Source: https://www.quantamagazine.org/how-bells-theorem-proved-spooky-action-at-a-distance-is-real-20210720/
  • #physics #article
• Proved "spooky action at a distance" is real
• Locality is a physics principle that says

  An event in one part of the world cannot instantly affect what happens far away #til2021

  • It is a bedrock assumption about physics
• In 1935, Albert Einstein and two colleagues showed that quantum mechanics allows for entanglement
  • "spooky action at a distance"
• In 1964, John Stewart Bell demoted locality by proving quantum mechanics can prove outcomes of certain far-apart measurement than any local theory could
• How Bell's theorem showed entanglement is real
  • When two particles are entangled, measuring the properties of one particle affects the property of the other particle regardless of distance
  • Consider the property spin, which can be "up" or "down"
  • Bell's theorem said that the upper bound on the correlations allowed by local hidden variable theories is 67%
    • So if the experiment can break this inequality then something more than locality is the feature of these particles