ABSTRACT
According to the ‘classical’ model of energy transfer that we accepted until early in the twentieth century, hot objects should radiate energy at all wavelengths. There should be large amounts of energy at high frequencies: the ‘ultraviolet catastrophe’. At the end of the nineteenth century, we ‘recognised’ ‘particles’ of matter and ‘particles’ of electricity. For the wave model, we can think of the pattern of wavy lines sometimes used as a decoration around the edge of a plate. If the pattern is to be continuous, if the lines are to join up properly where they meet, there can be only a whole number of waves around the plate and not intermediate fractional waves. One of the outcomes of the rapid development of quantum models in the 1920s was Werner Heisenberg’s formulation of an ‘uncertainty principle’. Low-temperature helium at low pressures remains liquid because the positions of these light atoms remain uncertain for reasons described by the Heisenberg uncertainty principle.
