Summer School 2010.3: Quantum Physics

Summer school continues. Lesson three is available here. Links to previous lessons are maintained below.

13 replies on “Summer School 2010.3: Quantum Physics”

  1. Chad Cloman says:

    A comment about lesson #2, section 4.1, the sentence that begins with “However, if neutrinos exhibit…”: The introduction to the word “neutrino” is in the next paragraph, and this sentence assumes they’ve already been introduced.

  2. Chad Cloman says:

    This thing about explaining the uncertainty principle by stating that a measurement affects the location and/or momentum — I think it just confuses the issue in the same manner that the “solar system” view of an atom is wrong. In my opinion, the measurement effect shouldn’t even be mentioned, because it’s dead wrong but seems to be what many people take away from the discussion.

    Why go to all this effort to explain how it’s impossible to measure the location or momentum without altering the location/momentum, only to immediately state that the uncertainty principle applies even if the measurement didn’t affect the particle? Just state that, if a particle’s position is well-defined then its momentum becomes less-defined, and vice-versa. It’s one of those weird quantum observer things.

    • It is. It’s hard to hit the other angle at this point, although some aspects are needed for the discussion. Heisenberg will return for reinterpretation in lesson six (IIRC; I wrote these in April, and just did some proofreading in June and July); it should gel more easily at that point.

      Lessons 3-9 were outlined in reverse order; I knew where I wanted things to end, and laid out the prerequisites needed to get there. Then I started writing them in numerical order, start to finish. I hope that readers will see the lines building, converging and intertwining by the time it’s all said and done.

  3. nehamilton says:

    The conclusion made in section 5.1 that science and religion are compatible doesn’t seem appropriate. It seems based on a “god of the gaps” argument. Even if the universe is non-deterministic at such small scales, why would one assume that the explanation would now fall under the purview of religion? I realize that the section title implied some degree of non-scientific conjecture, but I don’t understand why it was necessary at all to include something that would veer the article towards pseudoscience.

    • Frankly, I did it because of the amount of flack I’ve gotten in meatspace and on Usenet from some of the zealots who are opposed to science in general. It’s a bit of a tangent, and I debated between whether it should be in or out myself when I was writing it, but I eventually left it in because the topic is so personally irksome to me.

      • badIm says:

        “A deity of your choice” doesn’t really cover off all options. Perhaps being inclusive of the possibly of multiple deity’s as well as alternative dark and light forces including midichlorians. It also leaves room for such laws as “Murphy” and “sh!t happens”.

        A note to the OP, finding a little humor or a small distraction in such a lesson helps the reader relax and use differing view points to absorb the real information. I find this refreshing and in my personal experience of sitting in lectures, stimulates what could otherwise be a very dry presentation. Although I do find on a whole the writing style for these short lessons not to be dry at all.

        Thank you.

    • J_W_W says:

      Personally, I don’t have a problem with including this kind of “God is in the details” kind of conjecture.

      The farther down the quantum rabbit hole you go, the more confusing and …. uncertain… things get.

      And it is a bit disconcerting. If we ever find those answers I truly believe it will be a big a spiritual realization as it will be a scientific one. That’s just my belief, though.

  4. michelcolman says:

    In 5.1, you left out the “many worlds” interpretation: there is an infinite number of universes, and whenever there is a random “choice” between two possibilities, the universes will fork into two different ones. So every possible event does happen in some universe, but we only get to see one of them (with probably different versions of “us” in different universes experiencing the other possible outcomes)

    • J_W_W says:

      I love this explanation. Its absolutely mind bending when you think that there is an infinite number of universes where a thing happens and also an infinite number of universes where a thing does not happen…..

  5. J_W_W says:

    I like the measurement of current and voltage example for explaining the Heisenberg Uncertainty Principle.

    However, I do want to point out that current can be measured without physically attaching it to the circuit through and induction based current meter. Therefore you wouldn’t “touch” the electron.

    Of course the measurement with an induction based current meter would not affect the electron in its particle form, but it would steal energy from the electron in its wave form….. am I working ahead of things. :-)

    • Erf says:

      Sure it would. Reading the current with induction means using the magnetic field caused by the current to create a new current in the measuring device. That new current has its own magnetic field, which will affect the electrons in the original current. (The current will be reduced.) In this way, even for “particle-mode” electrons, the induction device affects the electrons directly. You don’t need wavy electrons for that (although you do need magnetic fields, which get kind of weird in themselves).

    • Chad Cloman says:

      See Blaine, that’s my earlier point. This is misleading because even if you could measure a particle’s velocity/momentum without changing it in any way, you’d still have the uncertainty. But what people take away from the discussion is that the measurement itself is what causes the uncertainty.

Comments are closed.