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Is it enough to get A's in quantum mechanics?

  1. Jan 24, 2013 #1
    Major anxiety!

    I'm in undergrad honors quantum mechanics II. I got an A in honors quantum mechanics I. It was darn hard but I did it. My problem is that I feel like all I'm doing is keeping up, chapter to chapter, topic to topic, without anything really sticking.

    I feel like a total amateur at this, it's making me wonder if I'm good enough to go to grad school for this. I believe I earned my A but at the same time it seems like I can't retain anything I've learn in QM longer than a month. I can build up my conceptual understanding of other areas of physics with examples, like physics brainteasers (like the Flying Circus of Physics). Math is also a strength of mine but I feel like I have nothing to visualize, and I'm a visual learner, so it feels like I'm not retaining enough even though my grades are good.

    Is it supposed to be this way? Will things stick better the second time around in grad school, or does it sound like I don't have what it takes?
  2. jcsd
  3. Jan 24, 2013 #2
    Can you tell us what book you used?

    There is quite a bit of stuff that can be visualized in quantum mechanics. Don't let any grumpy visualization-haters tell you otherwise. However, a lot of it is an abstract kind of visualization.
    You'll probably have a lot of these difficulties if you continue in physics. That's why I ended up going towards math instead, but eventually, I had some of the same difficulties there.

    As a fellow visual-thinker, I can tell you that, so far, I liked Sudbery's book, Quantum Mechanics and the Particles of Nature: An outline for mathematicians (the title is somewhat misleading, since the book is not completely rigorous, perhaps, it just doesn't rely on too much of a physics background). The first three chapters are very good. I'm not sure after that. The best conceptual approach to the Harmonic Oscillator that I have seen is on Baez's website, under seminar notes, but it involves some category theory, which might be somewhat unmotivated if you are not steeped in math, like I am. Another source is The Road to Reality, by Penrose, who is known to be a very visual thinker.

    The funny thing is, I have had the same issues, but rather than studying and then forgetting, what I am doing is learning quantum mechanics S - L - O -W - L -Y, as I put the conceptual pieces together, one by one. You've probaby covered more ground than I have already, but what I have learned (a decent amount, by now), I understand very deeply and easily retain.

    Another thing is that quantum mechanics draws heavily on classical mechanics for its inspiration, so it helps if you understand that very deeply. The go to book for that is V I Arnold's Mathematical Methods of Classical Mechanics, particularly, the later chapters.
  4. Jan 24, 2013 #3
    Using McIntyre's book, it's new. It emphasizes a spin-first approach and seems to de-emphasize parallels to classical mechanics. It was a last-second switch from Shankar. We're going through every chapter of the book, it's intensive, and I would very much like to take things more slowly but I can't. I've had a year-long course in classical mechanics and mathematical methods for physics, got all A's and felt pretty competent with it.

    I feel like I wouldn't have anything to complain about if the course weren't such a break-neck paced course. It is an honors course, am I being too hard on myself?

    Another difficulty is that my book is unique, and the way it teaches things is unique (though it uses Dirac notation), which can make consulting another text tricky because I don't find many other sources that spend near as much time on spin (and especially spin-1/2) systems to teach concepts so many times I've looked for clarity on something in this book and found nothing on Google because this book came out of a special program at Oregon State. (I don't go to Oregon State)
  5. Jan 24, 2013 #4


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    There's more to physics than quantum mechanics. Unless you want to be doing research in high energy physics or hard condensed matter, you don't need to be an expert in quantum mechanics or quantum field theory. You should know all the basics, of course, and you will be tested on it in grad school, but not being able to do something like second quantization on a moment's notice is not going to sink your graduate school career.

    Edit: I should also say that even if you do want to do theoretical high energy physics or hard condensed matter, you will be using the needed techniques so often that they should eventually become second nature to you. It takes time, but if you work with something enough you get the hang of it.
    Last edited: Jan 24, 2013
  6. Jan 25, 2013 #5
    Have you heard of Sakurai's book? I'm not familiar with the book you mention but Sakurai's Modern Quantum Mechanics takes a similar approach, i.e starts off with spin-1/2 systems and doesn't really relate stuff to Classical Mechanics. And it's written in a remarkably clear way, at least I thought so after reading parts of it, having been through Griffiths.

    As far as long term retention goes, just focus on learning what you can for now. You'll probably see this material more than once. Take graduate quantum mechanics as well.
  7. Jan 26, 2013 #6


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    I felt the same way in undergrad QM. I got good grades, but always felt like i wasn't seeing the big picture. In grad school things got better. Grad QM formed a more coherent picture, at least in my mind. I used Gasiorowicz for undergrad quantum and Sakurai for grad quantum.

    Also, you should remember the old saying, "If you think you've understood QM, you haven't understood QM."
  8. Jan 26, 2013 #7


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    Ugh, I also had Gasiorowicz for intermediate quantum. I really didn't like that textbook. I remember trying to do problems from it as practice for exams and I did not find them easy or enlightening! I made a point of not taking that book with me when I went to grad school. It does not surprise me that it doesn't have very good ratings on Amazon!

    TomServo, how are you at linear algebra? Quantum mechanics is basically an application of linear algebra, which is especially easy to see when using Dirac notation. Perhaps your problem is not so much the mathematics but the concepts they're meant to represent? That's a common problem students have with physics, even classical physics. It's not a surprise that quantum can seem extremely hard to grasp conceptually, but do keep at it. If you're good at linear algebra and you can start making connections between the math and the concepts that may help you catch up.
  9. Jan 27, 2013 #8


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    Yes, I agree. It works well as a quick reference later on, but I found it a terrible book to learn from. It reads like a list of equations and the problems gave no insight. I even remember a few problems that were just math problems where the connection to the related physics was never discussed, shown, or implied.
  10. Jan 27, 2013 #9
    I got an A in linear algebra. Unfortunately I took that class about a year and a half before taking quantum!

    I'm not a guy who is happy having things handed down from on high, and I felt like a lot of the math was just "here it is, and it works, so use it and shut up" without anybody stopping to explain.

    But thanks to everybody for their replies, especially the guy who said he felt better after grad school quantum.
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