The United Nations has proclaimed this year the International Year of Quantum Science and Technology. Official pronouncements about the IYQ tend to emphasize forward-looking technological applications of quantum science, such as computing and cryptography. They nod only obliquely to the reason why 2025 was chosen as the IYQ: that this year is, allegedly, the centennial of the development of quantum mechanics. The UN resolution proclaiming the IYQ, for example, notes that 2025 “coincides” with the anniversary, and the official IYQ website mentions “100 years of quantum mechanics.”
But is 2025 really the 100th anniversary of quantum mechanics? It depends on whom you ask. According to the standard textbook narrative, it was in 1900 that Max Planck proposed the quantum hypothesis—that the magnitude of a physical property was not continuous but a set of discrete, countable units, or quanta. Several publications celebrated the 100th anniversary in 2000.1 But Planck did...
