Re: Can wave/particle duality be avoided?

Hi Paul,

That's a pretty good analogy in some ways. You've picked up on an important aspect of wave behavior: the fact that a single "wave" (your guitar string) can have different effects depending on exactly how you choose to interact with it. This property explains wave-particle duality, rather than avoids it!

In quantum mechanics, you don't talk about either particles or waves directly. The "real thing", the entity, the thing our equations apply to, is called a wavefunction. Wavefunctions very strange things; sometimes you wonder if they only exist on paper. The reason they are strange is that they seem to behave differently if you apply different measurements to them.

Physicists refer to measurements as "operators". An operator is like a question you can ask the wavefunction. For example, if I am given a photon wavefunction, I can ask it "Where are you?" And it will give me some answer, a different one every time, but randomly selected according to some underlying pattern. I can also ask "What is your frequency?", "What is your total spin?", "How are you polarized?", and it will give me answers randomly selected from some underlying pattern. I can never observe the wavefunction directly, I can only ask it these questions. (Another interesting point is that, whenever you ask a question, you are changing the wavefunction's internal patterns, and thus changing the pattern of answers to subsequent questions.) In the double-slit experiment, you might say that the slits only query about the frequency of the photons; the detector-screen ignores the frequency and asks about the position. The wavefunction obliges, and "answers" the slits by behaving with a certain frequency, and "answers" the detector by appearing in a certain position.

With your guitar analogy, you could view the whole string as something like a wavefunction. Two of the questions you can ask this string are "What is your frequency of vibration?" (You could listen to the sound of the string to find out), and "What is the amplitude of the vibrations at, say, the third fret?" (you could touch the string and feel a force). But listening to the string doesn't tell you anything about the behavior of specific points, and touching the string doesn't tell you about the frequency. They are two different "operators" you could apply to the same object. The analogy works pretty well, actually!

The thing we sometimes call "wave particle duality" should really be called "quantum mechanics". It's not mysterious and contradictory at all, if you believe in wavefunctions and quantum operators. If you try to measure your wavefunction's position, you'll be given a position (i.e. a particle); if you measure its frequency, you'll be given a frequency (i.e. a wave). The mathematics and physics behind this is extremely elegant, robust, and accurate in its description of the world. It's not something that needs to be avoided.

I might recommend two books full of interesting quantum mechanics thoughts and analogies: "Quantum Reality" by Nick Herbert, and "Mr Tompkins in Paperback" by George Gamow. Personally, though, I think that quantum mechanics is better appreciated via its mathematical foundations, which can be found in any undergrad quantum mechanics textbooks.

-Ben