In May 1935 Einstein, Podolsky and Rosen published their paper arguing that quantum mechanics was incomplete. Over the following months Einstein and Schrödinger exchanged letters about it. Einstein first proposed a ball in one of two closed boxes, then in early August suggested an unstable charge of gunpowder that was as likely as not to explode within a year, which quantum mechanics would describe as both exploded and unexploded at once. The historian David Kaiser has argued the image reflected the rearmament of Europe that year. About a week and a half after receiving that letter, Schrödinger replied with his own version, swapping the gunpowder for a cat. It appeared later that year in his three-part essay “The Present Situation in Quantum Mechanics” in Die Naturwissenschaften, as a critique of the Copenhagen interpretation, not as an endorsement of a half-dead cat. 📷 Image edited for satirical purposes.