Car-bird wave-particle duality

Astronomy 10 learning goal M1.1

The "car-bird" story, as an analogy for the wave-particle duality of light. (This expands on an earlier idea from an unknown source.)

Ask the students if they have seen "Encino Man" (Buena Vista Pictures, 1992), starring Brendan Fraser (along with Pauly Shore and Sean Astin). (Of course students have seen it, but depending on their age, they will have either seen this movie in theaters, or on cable.)

Suppose a student unfreezes and befriends Encino Man, and takes him for a ride. Encino Man is startled to see a car, but the student tells him that it's called a "car." Eventually Encino Man understands that most everything else with wheels and driving on roads are cars as well.

Then the student points out and tells Encino Man what a bird is. Encino Man replies that yes, he knows what a bird is, he just didn't know what _you_ called one...and he doesn't appreciate being patronized.

Later, the student takes Encino Man to the airport. Encino Man is fascinated by the rather large "car" driving around at the airport, but to his surprise, it then becomes a "bird" as it takes off into the air! "It's a car-bird!" he exclaims. Of course, he's referring to an airplane, but Encino Man, for lack of a better label, describes it in terms of the characteristics it displays. It behaves like a car, and other times it behaves like a bird, therefore it can be said to have car-bird duality. But an airplane is _not_ literally a car-bird--that's just how it behaves!

A similar analogy can be made with light. For lack of a better label, light is described in terms of the characteristics it displays. It behaves like a wave (it has wavelength and frequency), and other times it behaves like a particle (its amounts of energy are quantized as photons), therefore it can be said to have wave-particle duality. But light is not _literally_ a wave-particle--that's just how it behaves!