Thursday, 14 October 2010

Dancing around the quantum

Quantum theory is an absolutely fundamental foundation of physics. It describes how everything works on a small scale, from atoms to photons of light. It is, arguably the most important part of modern physics. So what do we do when we teach science to children? We ignore it, and start them off with a Victorian picture of the world, which inevitably means that quantum theory will seem strange and confusing when (and if) it is eventually presented. It's as if we first taught kids that the Earth was the centre of the universe, then, later in their education, we said 'Well, actually, that's not really how modern science sees it.'

I believe we ought to bite the bullet and teach the real basics of science including quantum theory in junior school. (This is partly why I wrote Getting Science, which is aimed at primary school teachers who don't have a science background to bring them up to speed on the important stuff.)

I have neither time nor enough of your attention to run through all of quantum physics here, but I wanted to pick up on one point that causes much confusion, leaving some science writers dancing around the issue even today - and that's wave-particle duality.

We introduce light as a wave, then go through this uncomfortable dance saying 'Well, sometimes it's like a wave, but at other times it's like a particle. Strange, huh?' But I'd argue this dance really isn't necessary. Let me quote one of the two greatest physicists of the twentieth century, Richard Feynman:

I want to emphasize that light comes in this form - particles. It is very important to know that light behaves like particles, especially for those of you who have gone to school, where you were probably told something about light behaving like waves. I'm telling you the way it does behave - like particles.

Feynman showed how a quantum particle that has a particular property that varies over time (phase) produces all the effects we experience with light. There is no equivalent which will describe everything light does using waves. Making use of a pure particle description is admittedly quite clumsy sometimes, because wave-like properties emerging from phase are easier described using terms like 'wavelength' - so it is convenient sometimes to use wave models. But if Feynman's right (and who am I to argue with him?) then we ought to be teaching people particles first and explaining the use of a wave model later. We've got the whole thing back to front.

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