At the end of the nineteenth century, physicists believed they had a solid understanding of light and heat. Their equations predicted that a hot object should emit more and more energy at shorter wavelengths, especially in the ultraviolet range. The problem was that the prediction led to an absurd conclusion: a warm stove, a candle, or even the Sun should produce an infinite amount of ultraviolet energy. Reality clearly disagreed. This failure became known as the ultraviolet catastrophe. In 1900, Max Planck proposed that energy is not emitted continuously but in discrete packets, or quanta. His solution matched experimental observations and became one of the first foundations of quantum mechanics, fundamentally changing our understanding of the universe.