 Bell’s investigation generated an ongoing debate on the foundations of quantum mechanics. One important feature of this debate was confirmation that entanglement can persist over long distances, thus falsifying Schrödinger’s supposition of the spontaneous decay of entanglement as two entangled particles separate. (Free space entanglement of photons has been confirmed in experiments between the Canary Islands of La Palma and Tenerife, a distance of 143 km. See Herbst et al 2014.) But it was not until the 1980s that physicists, computer scientists, and cryptologists began to regard the non-local correlations of entangled quantum states as a new kind of non-classical physical resource that could be exploited, rather than an embarrassment for quantum mechanics to be explained away. For a discussion of entanglement — what it is, why it is conceptually puzzling, and what you can do with it, including a simple proof of Bell’s theorem — see the graphic novel Totally Random: Why Nobody Understands Quantum Mechanics (A Serious Comic on Entanglement), Bub and Bub 2018. For further discussion of entanglement as a physical resource, including measuring entanglement, and the manipulation and purification of entanglement by local operations, see “The Joy of Entanglement” by Popescu and Rohrlich in Lo, Popescu, and Spiller 1998, Nielsen and Chuang 2000, or Bub 2016. 