Explaining Quantum Mechanics to My Daughter

My daughter saw an article in the student newspaper at her university about the recent result on neutrino oscillations from the MINOS experiment. She thought the write up in the newspaper was dumbed down and asked me what I thought about it. In an uncharacteristly sarcastic moment I wrote back.

Yes, but are you surprised that it is dumbed down? Would you like me to explain in its fully gory detail? It turns out that eigenstates of flavor are not eigenstates of mass, so when a neutrino is produced in a weak interaction it is a mixture of mass eignstates. As the neutrino propagates the mass eigenstates evolve in time at a different rates so the relative strength of the two or three eigenstates changes with time and the probability of observing any particular flavor eigenstate therefore evolves with time.

I did my dissertation on neutrino oscillations and I also worked on B meson oscillation measurments. These are a fascinating quantum phenomena that that can be explained quite nicely using the quantum mechnics from a sophmore level university modern physics class, but first you have to learn about eigenvalues and eigenstates. There are classical analogs to the quantum oscillation like the normal modes of coupled oscillators, but I do not find them quite satisfactory. The normal mode of an oscillator just does not seem as fundamental as the flavor of a neutrino. The role of eigenvalues and eigenstates to quantum mechanics is so fundamental that one cannot even discuss quantum mechanics without them.

I have trouble explaining how exciting I find this physics to people who have not studied quantum mechanics.

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6 Responses to “Explaining Quantum Mechanics to My Daughter”

  1. Guess Who Says:

    Ooops. This time, not a spelling error so much as word choice. You used dumber instead of dumbed… Geez

  2. Fixed.

    No comment on being featured in the blog? No complaints about my sarcasm?

  3. Guess Who Says:

    No comment on the fact that the post I made was more like Mommy than like you?…

  4. Yes, I agree that it is difficult to appreciate the significance without having had quantum mechanics, or linear algebra at the very least (eigenvalues and eigenstates show up there). Standard language can communicate these physical facts only imprecisely, just as math cannot capture emotions.

    And heck, even as a physicist, I appreciate “watered down” explanations of work outside of my specialty from way back when. I know what it’s like to slog through a PRL paper. Just because they’re short doesn’t mean they’re easy!

  5. It is just the eigenvalues but that in quantum mechanics the only allowed value of an observable is the eigenvalue. In graduate quantum mechanics my professor made the first exam an oral exam, and he worked so hard to get me to say that I could observe some other value than an eigenvalue. I wouldn’t be budged. That is probably part of why I still remember it.

    PRLs are hard to read because they are short. How much can I leave out and still get my point across?

  6. Guess Who Says:

    I must say, I feel like there has to be some middle ground between the incredibly simplistic explanation given in our school paper and the rather arcane explanation you gave. I noted your sarcasm, but just thought it was your typical quantum physicist response to us lowly people. You DO have a tendency to be that way, especially when it comes to subatomic particles. But, fear not; next time you come to me with a question about upper-level biology, I will spare no sarcasm in my response to you. I have learned well from the master.

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