Category: Academics

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Video lectures are the future of learning physics

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I am going to follow up my last post with a topic on the same theme: academic tools.

Video lectures are the future of learning physics.…at least for the lecture medium. The other key component for the future of learning physics will be massive collaboratively edited textbooks and review articles (i.e., Wikipedia+GitHub for physics). I have more thoughts on this for another post. (EDIT: Now posted here.)a   The ability to speed up the rate of playbackDownload a lecture and play it in VLC. Use the ‘[‘ and ‘]’ keys to change playback speed. This is very satisfying, as your whims literally control the pace at which the lecturer goes through the material.b  , or go back over a point you missed without wasting everyone else’s time, is just so much more efficient than a live lecture. Of course, getting answers to questions is crucial and video lectures lack this mechanism of feedback, but this can easily be supplemented with office hours and by taking courses alongside others.

But the real power of video lectures is the ability for everyone to view the very best lectures on any given topic, and moreover for individuals to find lectures that are tailored to their particular expertise. This is just so much better than what is possible when you are restricted to hear lectures from people in the same building. When each course has 100 different versions taught by different lecturers ranked by popularity, and when the best lecturers can improve through targeted feedback from thousands of students, the quality is going to skyrocket.

Perimeter is one of the places leading the way on this. They record all their major lectures (and many of their minor, unimportant talks) and put them all up on the website, for free and fully searchable.… [continue reading]

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Zotero is great, TeX should be better

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If you’re an academic, you should consider using Zotero, a piece of software that manages your library of papers (including PDFs with comments), pulls papers automatically from journal websites, syncs across devices, generates bibtex files, and other cool stuff. (More here.)


Get Zotero

Interestingly, Zotero is evidence that custom built academic software funded by charitable foundations can provide a tremendously positive service to the academic community.

Zotero is a production of the Roy Rosenzweig Center for History and New Media at George Mason University and the Corporation for Digital Scholarship. It has been generously funded by the United States Institute of Museum and Library Services, the Andrew W. Mellon Foundation, and the Alfred P. Sloan Foundation.

I have long said that the single most effective useI wish I had a good econ-market-failure story to tell about why a better version of TeX hasn’t arisen on its own, but I only have a mediocre one: I suspect that in general software is under supplied because of the difficulty of getting people pay for it. First because it’s difficult to prevent people from copying it, and second because online payments are friction-ful, especially without a reputation system in place. (The success of the various App stores is good evidence here.) Academics are a small market, so they can’t rely on the zero marginal cost of software to make up for these problems, even in the most important areas. And academics probably have an unusually high desire for open source software, or at least software that’s not entangled with a single company.a   of ~$1 million for advancing math and physics research would be to hire some software developers for a couple of years and make an enterprise-quality successor to TeX.… [continue reading]

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Ambiguity and a catalog of the actions

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I had to brush up on my Hamilton-Jacobi mechanics to referee a paper. I’d like to share, from this Physics.StackExchange answer, Qmechanic’ clear catalog of the conceptually distinct functions all called “the action” in classical mechanics, taking care to specify their functional dependence:

At least three different quantities in physics are customary called an action and denoted with the letter S.

  1. The (off-shell) action

    (1)   \[S[q]~:=~ \int_{t_i}^{t_f}\! dt \ L(q(t),\dot{q}(t),t)\]

    is a functional of the full position curve/path q^i:[t_i,t_f] \to \mathbb{R} for all times t in the interval [t_i,t_f]. See also this question. (Here the words on-shell and off-shell refer to whether the equations of motion (eom) are satisfied or not.)

  2. If the variational problem (1) with well-posed boundary conditions, e.g. Dirichlet boundary conditions

    (2)   \[ q(t_i)~=~q_i\quad\text{and}\quad q(t_f)~=~q_i,\]

    has a unique extremal/classical path q_{\rm cl}^i:[t_i,t_f] \to \mathbb{R}, it makes sense to define an on-shell action

    (3)   \[ S(q_f;t_f;q_i,t_i) ~:=~ S[q_{\rm cl}],\]

    which is a function of the boundary values. See e.g. MTW Section 21.1.

  3. The Hamilton’s principal function S(q,\alpha, t) in Hamilton-Jacobi equation is a function of the position coordinates q^i, integration constants \alpha_i, and time t, see e.g. H. Goldstein, Classical Mechanics, chapter 10.
    The total time derivative

    (4)   \[ \frac{dS}{dt}~=~ \dot{q}^i \frac{\partial S}{\partial q^i}+ \frac{\partial S}{\partial t}\]

    is equal to the Lagrangian L on-shell, as explained here. As a consequence, the Hamilton’s principal function S(q,\alpha, t) can be interpreted as an action on-shell.

These sorts of distinctions are constantly swept under the rug in classical mechanics courses and textbooks (even good books like Goldstein). This leads to serious confusion on the part of the student and, more insidiously, it leads the student to think that this sort of confusion is normal. Ambiguity is baked into the notation! This is a special case of what I conjecture is a common phenomena in physics:

  • Original researcher thinks deeply, discovers a theory, and writes it down.
… [continue reading]
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Planck, BICEP2, dust, and science news

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The Planck Collaboration has released a paper describing the dust polarization in the CMB for the patch of sky used recently by BICEP2 to announce evidence for primordial gravitational waves. Things look bleak for BICEP2’s claims. See Peter Woit, Sean Carroll, Quanta, Nature, and the New York Times.

In the comments, Peter Woit criticizes the asymmetric way the whole story is likely to be reported:

I think it’s completely accurate at this point to say that BICEP2 has provided zero evidence for primordial gravitational waves, instead is seeing pretty much exactly the expected dust signal.

This may change in the future, based on Planck data, new BICEP2 data, and a joint analysis of the two data sets (although seeing a significant signal this way doesn’t appear very likely), but that’s a separate issue. I don’t think it’s fair to use this possibility to try and evade the implications of the bad science that BICEP2 has done, promoted by press conference, and gotten on the front pages of prominent newspapers and magazines.

This is a perfectly good example of normal science: a group makes claims, they are checked and found to be incorrect. What’s not normal is a massive publicity campaign for an incorrect result, and the open question is what those responsible will now do to inform the public of what has happened. “Science communicators” often are very interested in communicating over-hyped news of a supposed great advance in science, much less interested in explaining that this was a mistake. Some questions about what happens next:

1. Will the New York Times match their front page story “Space Ripples Reveal Big Bang’s Smoking Gun” with a new front page story “Sorry, these guys had it completely wrong?”

… [continue reading]
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Grade inflation and college investment incentives

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Here is Raphael Boleslavsky and Christopher Cotton discussing their model of grade deflation in selective undergraduate programs:

Grade inflation is widely viewed as detrimental, compromising the quality of education and reducing the information content of student transcripts for employers. This column argues that there may be benefits to allowing grade inflation when universities’ investment decisions are taken into account. With grade inflation, student transcripts convey less information, so employers rely less on transcripts and more on universities’ reputations. This incentivises universities to make costly investments to improve the quality of their education and the average ability of their graduates. [Link. h/t Ben Kuhn.]

I’ve only read the column rather than the full paper, but it sounds like their model simply posits that “schools can undertake costly investments to improve the quality of education that they provide, increasing the average ability of graduates”.

But if you believe folks like Bryan Caplan, then you think colleges add very little value. (Even if you think the best schools do add more value than worse schools, it doesn’t at all follow that this can be increased in a positive-sum way by additional investment. It could be that all the value-added is from being around other smart students, who can only be drawn away from other schools.) Under Boleslavsky and Cotton’s model, schools are only incentivized to increase the quality of their exiting graduates, and this seems much easier to accomplish by doing better advertising to prospective students than by actually investing more in the students that matriculate.

Princeton took significant steps to curb grade inflation, with some success. However, they now look to be relaxing the only part of the policy that had teeth.… [continue reading]

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Literature impressions

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I have often been frustrated by the inefficiency of reading through the physics literature. One problem is that physicists are sometimes bad teachers and are usually bad writers, and so it can take a long time of reading a paper before you even figure out what the author is trying to say. This gets worse when you look at papers that aren’t in your immediate physics niche, because then the author will probably use assumptions, mathematical techniques, and terminology you aren’t familiar with. If you had infinite time, you could spend days reading every paper that looks reasonably interesting, but you don’t. A preferred technique is to ask your colleagues to explain it to you, because they are more likely to speak your language and (unlike a paper) can answer your questions when you come up against a confusion. But generally your colleagues haven’t read it; they want you to read it so you can explain it to them. I spend a lot of time reading papers that end up being uninteresting, but it’s worth it for the occasional gems. And it seems clear that there is a lot of duplicated work being done sorting through the chaff.

So on the one hand we have a lengthy, fixed document from a single, often unfamiliar perspective (i.e. the actual paper in a different field) and on the other hand we have a breathing human being in your own field who will patiently explain things to you. An intermediate solution would be to have a few people in different fields read the paper and then translate the key parts into their field’s language, which could then be passed around.… [continue reading]

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Citation indices do not avoid subjectivity

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Peter Higgs used his recent celebrity to criticize the current academic job system: “Today I wouldn’t get an academic job. It’s as simple as that. I don’t think I would be regarded as productive enough.” In this context, it was argued to me that using citation count, publication count, or some other related index during the hiring process for academics is a necessary evil. In particular, single academic job openings are often deluded with dozens or hundreds of applications, and there needs to be some method of narrowing down the search to a manageable number of applicants. Furthermore, it has been said, it’s important that this method is more objective rather than subjective.

I don’t think it makes sense at all to describe citation indices as less subjective measures than individual judgement calls. They just push the subjectivity from a small group (the hiring committee) to a larger group (the physics community); the decision to publish and cite is always held by human beings. Contrast this to an objective measure of how fast someone is: their 100m dash time. The subjectivity of asking a judge to guess how fast a runner appears to be going as he runs by, and the possible sources of error due to varying height or gait, are not much fixed by asking many judges and taking an “objective” vote tally.

Of course, if the hiring committee doesn’t have the time or expertise to evaluate the work done by a job applicant, then what a citation index does effectively do is farm out that evaluative work to the greater physics community. And that can be OK if you are clear that that’s what you’re doing.… [continue reading]