From oscillators to photons to other things

In 1901, Max Planck introduced the quantum hypothesis as an 'act of despair' in order to provide an explanation for the spectrum of blackbody radiation. This for him was a huge step, so new and controversial that he was reluctant to publish it for some time. Little did he realise the full consequences, which reached far beyond blackbody radiation.

In 1905, Einstein proposed that the quantum hypothesis applies not only to oscillators and to the kind of light which they emit, but to the very nature of light itself. He pointed to experiments which provided evidence that light appears to come in individual bundles of energy, or '''photons' of energy hf. Such a quantum of highly concentrated energy could knock electrons out of the surfaces of metals, as quantified in Einstein's theory of the photoelectric effect, which we will deal with in detail in Chapter 13.

Over the next few years came the realisation that quantisation forms a basis for all the fundamental laws of nature. The laws of mechanics discovered by Isaac Newton work very well in the everyday 'household' world because the effect of quantisation is negligible. When we come to 'the world of the very small' of electrons, atoms and molecules, this effect can no longer be ignored; in fact it becomes dominant to the extent that it changes completely the character of natural laws. Mathematical methods had to be developed to represent these laws in the theory of quantum mechanics, which incorporates Newton's laws of classical mechanics as a special case under the conditions of the 'household' world.

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