Quantum Entanglement & Spooky Action at a Distance

Caption notes

Veritasium uses a pair of entangled particles and three randomly selected measurement directions to make “did the particles agree on their answers beforehand?” calculable. For the video’s idealized spin-1/2 singlet and particular three-direction geometry, each side chooses its setting uniformly and independently, with those choices also independent of any preassigned responses. Local preassigned responses and perfect opposite results for matching directions then imply opposite outcomes in at least 5/9 of the nine equally weighted setting combinations; the quantum prediction for this geometry is 1/2. The useful move is to compare the statistical possibilities allowed by assumptions, rather than merely marvel at distant correlations. Read the video’s claim that “hidden information” is ruled out with the locality and measurement-independence conditions attached, and read “more than 5/9” as “at least 5/9.” This does not exclude every hidden-variable theory, nor do all entangled states have opposite same-direction outcomes. The closing distinction is why the correlations cannot send faster-than-light messages: either side alone still sees random results, and the correlation becomes visible only when the two records are compared.