In May 1935 Einstein, Podolsky and Rosen published their paper arguing that quantum mechanics was incomplete. Over the following months Einstein and Schrรถdinger 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, Schrรถdinger replied with his own version, swapping the gunpowder for a cat. It appeared later that year in his three-part essay โThe Present Situation in Quantum Mechanicsโ in Die Naturwissenschaften, as a critique of the Copenhagen interpretation, not as an endorsement of a half-dead cat.
๐ท Image edited for satirical purposes.