Great student questions generated from Postulates of Quantum Mechanics reading

In my 3rd year (intro to ) Quantum Mechanics course the first homework assignment I gave them was meant to serve as a mostly gentle review of probability and modern physics as is relevant to the first chapter of Griffiths.

But I also asked them to read an 8-page section of some supplemental notes prepared by Michael Dubson and Steve Pollock at CU-Boulder (they can be found in the “Lecture Notes” folder of the “all course materials EXCEPT assessments” link on this page). These notes talk explicitly about the postulates of quantum mechanics (which Griffiths does not), about postulates in general and they compare and contrast classical and quantum mechanics.

As part of that first homework assignment I asked my students to read these notes and gave them the instructions:

Please write one or two questions that were burning in your brain after you read these pages.

And they gave me some wonderful questions which should provide us with some rich discussion on Monday. Here they are:

  1. I’m very confused how a wavefunction can change instantly after a measurement has been made on it’s position. (note: several variations of this question showed up)
  2. What reasoning did Schrodinger have for writing down his equation? (note: several variations of this question showed up and one student noted that it looked a lot like an equation he had seen in our PDEs course)
  3. Why is gravity proving to be so difficult to incorporate into quantum theory?
  4. Do quantum and classical mechanics agree with each other in predicting the outcomes of physical phenomena at a particular intermediate scale between the quantum scale and the macroscopic scale?
  5. Why does Planck’s constant have that specific value?
  6. Does the wavefunction ever reconstruct itself after being collapsed due to an observation?
  7. How come taking measurements changes the look of the wavefunction? It almost looks like a dirac delta function in the after measurement graph shown.
  8. (edited for brevity) Since real-world sized objects are made up of large quantities of microscopic particles shouldn’t the (quantum) laws and properties that govern the small not also govern the behavior of the large, which are really just big groups of the small? Why would we get different physics looking at many than looking at one?
  9. If x and p are not well-defined for a point particle, how does putting a group of them together suddenly make them defined for the group? how many does it take? Two? Three? Four billion trillion? At what point does a system become macroscopic?
  10. Where did the notion of wave-particle duality originate?
  11. How valid is string theory and a fundamental level?
  12. How does a measurement give the particle a definite position?
  13. How does Psi-squared represent the probability that a particle is at a specific location when we are told that Psi only “carries information about the particle, it is not ‘the particle’ or ‘the position of the particle'”?

Fantastic! Now they’re curious. And I’m not great at establishing a framework that ties together the ideas in a course, but I think that these questions mostly provide that framework and it was them that generated it instead of me. It’s their framework! I am thrilled.

8 Comments on “Great student questions generated from Postulates of Quantum Mechanics reading”

  1. bwfrank says:

    Hey Joss,

    I love this, and you probably aren’t surprised to hear it. I also love how you are thinking about this: Letting student ideas and questions be at least part of the framework for tying together ideas. I imagine some of these questions have come up in the past when you’ve taught it. Any that are new? Any that you are surprised about? Any you thought they would ask , but didn’t?

    I think my favorite question is #2. The reasons is this: It’s only one that says to me, “I’m not even sure why we or anyone else are even considering this stuff? There must have been a good reason to write down that equation, and I want to know what those reasons were” The other questions seem to mostly take QM as truth and ask questions about confusing things or about its implication. Also good questions, but they are different to me.

    Also, can you share the 8-page notes?

    • Joss Ives says:

      Hi Brian,

      Based on previous experience asking for “questions still burning in your brain”, I was pleasantly surprised at how most of these questions indicated genuine curiosity and interest instead of seeming like they were just filling in the required steps in an assignment. I guess I was expecting to mostly see superficial questions, but instead got a whole bunch of questions which will help me make the content more relevant to them. Now I have a better idea of which parts of the classical/quantum divide seem the most odd to them. And can try to frame some of our future discussions using questions that they brought up themselves.

      I really like your point about question number 2.

      I added a link near the top of the post that links to the Colorado materials from which I took the notes in question.

  2. Andy "SuperFly" Rundquist says:

    I really like the 6th and 7th ones. The first one hints at a vocabulary problem with the word collapse, indicating that after a collapse, it’s not a wavefunction anymore. The second one ties in to a previous class, that’s just awesome!

    How will you use this list? Will you go back to it often? Will the students consider the whole thing to belong to them or just their own question?

    Cool stuff, Joss, keep it up!

    • Joss Ives says:

      At the point that they did the reading, the word wavefunction meant very little to them so this was all very interested in terms of seeing how they are using the vocabulary at this early stage.

      I’m really not too sure how I am going to use this list. I think on Monday I’m going to post the list of questions and see if anybody would like to try answering their fellow students’ questions. I will definitely take some time on Monday to talk a bit more about the classical/quantum issues. Some of the questions seem like they will be great for motivating some of the future topics and will try my best to bring them up again at appropriate times.

      Andy that’s an interesting question about the whole list belonging to them collectively or just their own questions belonging to each of them individually. I guess I will just ask them how much ownership they feel for the whole list. That seems like that could be an interesting conversation and something that could help them develop a sense of community around this subject.

      One last thing that I didn’t previously mention was that I like how these are a bunch of conceptually motivated questions (as opposed to mathematically motivated). I think this will help me keep the conceptual ideas of quantum at the forefront instead of losing them behind the mathematics of the subject which is definitely what has happened in the past when this subject in my hands.

  3. Joss Ives says:

    Back with a quick update. We spent 3/4 of an hour talking about these questions. I didn’t do a great job of making it a conversation, it was more like a Q&A. But it was really fun and they seemed to enjoy it and were certainly much more interested than if I had simply prepared a presentation on most of these ideas without first having had them generate their own questions. I would love to repeat something like this in other courses, but have to figure out what sort of resources might help them generate as many great questions as I saw here.

  4. […] of quantum mechanics and some compare/contrast points between classical and quantum mechanics. They generated fantastic questions and we spent a whole period going through these questions and tying the ideas from these questions […]

  5. […] Frank echoed by suggesting I do the same thing I did when I got my Quantum Mechanics class to generate questions based on a reading. Andy Rundquist also suggested I could get them to screencast their interesting discoveries […]

  6. […]  This one goes really well with the student generated question type of pre-class assignment (see Post 1 in this series) and then functions quite similar to the simulation-based pre-class assignments by […]

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