Wave-Particle Duality
Quantum and Nuclear | Light Sound and Waves

A bit of philosophy?

Teaching Guidance for 11-14 Supporting Physics Teaching

Thoughts from Richard Feynman

One distinction that is made by philosophers about the nature of science is in terms of it being a positivist or realist activity.

Positivists see the role of science as developing theories that successfully account for empirical measurements. Questions such as But what is really there? are of no interest to positivists. On the other hand, realists see the role of science as being one of discovering what the physical world is actually like.

In the realms of quantum theory, light is considered to have both wave-like and chunks of energy properties, which goes against expectations developed from direct experience of the natural world. In the natural world we expect that things are either one (waves) or the other (chunks of energy).

Richard Feynman, in the introduction to his book, QED: The strange theory of light and matter, has something to say on matters of this kind: There is this possibility: after I tell you something, you just can't believe it. You can't accept it. You don't like it. It's a problem that physicists have learned to deal with: they've learned to realise that whether they like a theory is not the essential question. Rather it is whether or not the theory gives predictions that agree with experiment. The theory of QED describes nature as absurd from the point of view of common sense. And it agrees fully with experiment. So I hope you can accept Nature as she is… absurd.

Thus Feynman argues that the quantum view of the world doesn't seem to make sense in relation to common experience. However, this is not what counts. He takes a straight positivist point of view in stating that what matters is whether or not the theory gives predictions that agree with experiment.

In typical Feynman fashion he goes further:

It is my task to convince you not to turn away because you don't understand it [the theory of QED]. You see my physics students don't understand it either. That is because I don't understand it. Nobody does.

These are not just points of abstract philosophy, but are of importance in thinking about teaching and learning in this area. If you and your students think that the wave/photon ideas are somewhat strange, then you are in the very good company of Feynman. You are exactly right in your thinking and this is a message that is worth sharing with students.

Feynman would probably agree that thinking about light as waves allows us to predict where the light is likely to arrive, while the photon story tells us about how the energy is being shifted.

Wave-Particle Duality
is partly explained by the
is exhibited by Electron Photon

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