Quantum Waves and Probabilities

Most recent answer: 04/28/2015

Q:
I am an 8th grade science teacher who has regularly used the pre-Bohr planetary-like model of the atom (like most 8th grade science teachers and textbooks) to help students start to understand atomic physics. But in my free time, I have repeatedly tried, and failed, to really understand the quantum theory model of the atom. I guess I have made some progress, but some of it has made me go back and question even what I thought I wasn't a problem, which leads me to my seemingly simple, but really loaded, question here: What is a wavelength? I mean, if electrons and photons can be described as moving in waves, and if the frequency of photon waves determine whether radio/visible light/x-rays/etc. are emitted, but if quantum theory says that these waves are actually just waves of probability, why are some somes parts of the wave more probable and others less probable for the appearance of a photon or an electron, and why do different probabilities turn into x-rays while others into color, etc? I suspect all my ideas are muddled together and I'm not even asking the question in the right way - can anyone help me sort this out about waves? Many thanks!
- monesh (age 45)
Myrtle Beach, SC, USA
A:

Muddled or not, that's an important deep question.

We actually don't really know how the quantum wave, which follows a definite non-random equation, turns into events which only have a probabalistic relation to the wave. That's called the "measurement problem" or more generally the problem of quantum interpretation. (see , )

As for the waves with different wavelengths behaving differently, that's not mysterious. Think of a water wave bouncing off a pattern of rocks. The way the wave bounces will depend on the wavelength. Quantum waves are the same. What's quantum about them is that if their energy is absorbed (in a typical case, at least) it's absorbed in little packets with energy hf, where f is the frequency and h is Planck's constant. The size of those packets determines what sort of chemical changes the light can trigger. The timing of those absorptions is somewhat random. That brings us back to the question of how those random events arise from a deterministic wave equation.

Mike W


(published on 04/28/2015)