Quantum mechanics arose from a solution to the black-body radiation problem.
== Theory ===== Spectrum ===Black-body radiation has a characteristic, continuous frequency spectrum that depends only on the body's temperature,  called the Planck spectrum or Planck's law
 In 1935, Einstein and his collaborators Boris Podolsky and Nathan Rosen published an argument that the principle of locality implies the incompleteness of quantum mechanics, a thought experiment later termed the EinsteinPodolskyRosen paradox

