What is the black body problem?

The black body problem refers to the challenge in physics of understanding how an idealized object, known as a black body, absorbs all incident electromagnetic radiation and re-emits it as thermal radiation. Classical physics, particularly through Rayleigh-Jeans law, failed to explain the observed spectrum of black body radiation, leading to the "ultraviolet catastrophe." The resolution came with Max Planck's introduction of quantized energy levels in 1900, laying the groundwork for quantum theory. This marked a significant shift in understanding electromagnetic radiation and energy distribution.