Classical physics, specifically the Rayleigh-Jeans law, predicted that as an object's temperature increased, the intensity of the light it emitted would increase without limit across all wavelengths. This meant that the object would radiate an infinite amount of energy at very high frequencies (ultraviolet and beyond).

This prediction was fundamentally flawed and led to what was known as the ultraviolet catastrophe. The problem was that it didn't match experimental observations. In reality, the intensity of light emitted by an object reaches a peak at a certain wavelength, and then decreases at higher wavelengths.

This discrepancy led to the development of quantum mechanics, which provided a more accurate explanation for the behavior of light and matter at the atomic level. Planck's quantum theory, which introduced the concept of quantized energy levels, correctly explained the observed distribution of light emitted from heated objects.