Light: A Very Short Introduction by Ian A. Walmsley

Author:Ian A. Walmsley
Language: eng
Format: epub
ISBN: 9780199682690
Publisher: OUP Oxford
Published: 2015-07-20T04:00:00+00:00

This suggests that to look for such effects you should use either very light particles or very cold ones that are moving very, very slowly. Such effects can be observed. Figure 24 shows an interference pattern made using a double-slit-like interferometer, but using molecules instead of light. The implications of this are mind-boggling. If you think of a molecule as just a very light particle, then you cannot explain the pattern, because you consider that it must have passed through one slit or the other. However, the idea that a particle with mass could be so delocalized as to have passed effectively through both slits to interfere with itself is astounding and beggars belief.

If material objects also behave as waves, then, Erwin Schrödinger conjectured, surely there must be a wave equation describing their behaviour. Where to start looking for such a thing? He took the equation that Hamilton had developed, by means of his optical analogy, to describe how the ‘action’ of a particle evolved. A simple addition to this equation, involving Planck’s constant, moulded it into one that described wave motion. This was the origin of Schrödinger’s famous ‘wave function’. The wave function has a number of properties very analogous to optical waves, including interference and diffraction, but nonetheless refers to things that in the language of pre-quantum physics are palpably particles possessing mass and weight. As a consequence, there are still questions as to what the wave function actually describes. Is it the actual particle itself, or is it a sort of shorthand for what we know about the particle?

24. An interference pattern made using molecules passing one at a time through a tiny version of Young’s apparatus—two very small slits separated by billionths of a metre.

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