Friday, May 31, 2013

Sharing my ignorance and confusion

There are things that we all wish we knew or we keep forgetting or we should understand but don't. Furthermore, there are things that I read about, think I understand, but then when pressed I don't think that I can explain to others.
Some of these things are so basic it is embarrassing.

Tony Wright had the nice idea that at the UQ condensed matter theory group meeting each member should have a turn saying a topic they don't understand and feel they should. Speakers will be in order of decreasing seniority. Hopefully, then the junior people will not feel so bad. I guess the ultimate goal is to help one another understand these things. It is also to create a culture where people are comfortable asking basic questions.

So here is a list for me in order of increasing profoundness:
  • Why are metals shiny?
  • How do p-n junctions and transistors work?
  • What is the origin of hysteresis in ferromagnets?
  • Why do extremal areas of the Fermi surface determine the frequency of quantum oscillations?
  • How does a Fano resonance between a bound state in the continuum lead to an asymmetric spectral lineshape?
  • Why does the Kondo effect lead to unitary scattering and a phase shift of pi/2?
  • How do you derive Hund's rules?
  • How do you derive Goldstone's theorem?
  • What is the chiral anomaly in quantum field theory? How is it related to edge states and topological order in condensed matter?
I know that I can look up a book and find the "answer". In some cases I have but then I have forgotten the answer. In other cases, I can mouth the words (say the mantra) but somehow there are things I am just not comfortable with, particularly at a deeper level. Sometimes I am comfortable with the maths but not the physics. Other times it is the opposite. Then the urgency of other tasks takes over ....

What are some questions on your list?


  1. Hi Ross,

    Since you've mentioned Hund's rule, I woul like to add the fact that I'm really not confortable with Madelung's rule. For some time I've been going through chemistry papers and really can't find a derivation of this rule, just some heuristical arguments. It is specially disturbing since that are exceptions. I'm not sure about that status of this rules concerning the "making" of the periodic table. Also regarding why are metals shiny there is the fact that gold, caesium and osmiun have their colours atributed to relativistic effects (not so sure about copper). Pekka Pyykko has some nice papers about relativistic effects in chemistry and I suspect Hund's rule is not independet of such considerations.

    1. I don't even know what Madelung's rule is!

    2., the one that the first orbitals to be filled are the lowest n+l,.

      I understand that by using DFT one can derive the orbital filling, but I'm not sure if there is a proof of the rule. Just to comment that since Hund's rule should be hard anyway.

      Cesar Uliana

  2. Your first two points made me feel happy and the rest made me feel sad.

    Expressing ignorance can still make a colleague feel inferior if they don't even understand the question (let alone the answer!). I know some professors who (I believe) try to humble themselves by expressing their ignorances, yet the topics they choose to express ignorance on still intimidates their colleagues/students.

    Being able to formulate a question and assess one's knowledge can still signal a high level of knowledge or intelligence.

  3. Ben Powell had the nice idea, I just thought it was nice too, so remembered to mention it. I think it is a nice idea, and am looking forward to our first attempt at it!

  4. I came across one not so long ago: why is it possible for a liquid to be equilibrium with a vapour at a particular concentration? I did end up working it out, but it took a lot of staring at the floor.