Perimeter Scholars International now accepting applications

Perimeter Institute runs a fairly unique one-year Master’s program called Perimeter Scholars International (PSI). It’s an intensive crash course in most parts of theoretical physics at PI. Besides the opportunity to take an additional year of courses before deciding on a PhD programs, attending PSI exposes you to the huge range of smart folks at PI. They are now accepting applications, due Feb 1st, for the term starting Fall of 2015.

Anyone who has talked with me about the graduate school process in the US knows I have strong views about how the current system forces students to effectively pick their field before they know enough physics to evaluate the various options, thereby entrenching the popularity of existing fields. (I’m sure I’ll blog about this in the future.) Although PSI is far from my imaginary ideal that would fix the problems as I see them, I think it is still one of the few steps in the correct direction of giving prospective physics PhD students the training they need to evaluate research programs on the merits rather than on prestige. Alas, PSI didn’t exist when I was looking at grad schools. If I were senior physics major in college now I would definitely try to get into this.

Here’s the blurb:

Each year, Canada’s Perimeter Institute for Theoretical Physics recruits approximately 30 exceptional science graduates for an immersive, 10-month physics boot camp: Perimeter Scholars International (PSI). This unique Master’s program seeks not only students with stellar undergraduate physics track records, but also those with diverse backgrounds, collaborative spirit, creativity, and other attributes that will set them apart as future innovators.

Features of the program include:

  • All student costs (tuition, living, travel) are covered, removing financial and/or geographical barriers to entry
  • Students learn from world-leading theoretical physicists – resident Perimeter researchers and visiting scientists – within the inspiring environment of Perimeter Institute
  • Collaboration is valued over competition; deep understanding and creativity are valued over rote learning and examination
  • PSI recruits worldwide: 85 percent of students come from outside of Canada
  • PSI takes calculated risks, seeking extraordinary talent who may have non-traditional academic backgrounds but have demonstrated exceptional scientific aptitude

Here’s the video advertisement which, if nothing else, should convince you that PI is awesome enough to have a publicity department:… [continue reading]

Dimopoulos proposes super lab for small experiments

Savas Dimopoulos gave a talk recently at Perimeter where he proposed building an institute to bring many small-scale, beyond-the-standard-model experiments under one roof. The claim is that experiments testing fundamental physics (new particles, forces, dimensions, etc.) would benefit from being near each other and related theorists than they would from being grouped with experiments using similar techniques but not probing fundamental physics (as they often are now). He starts the talk with some discussion of axions, the LHC, and some recent small-scale experiments. His proposal (“Super-lab”) begins at 1:05:37.

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Links for November 2014

Almost all the links this month are space related. I promise I spend time thinking about other things but…there’s just a lot of cool space-related links on the internet.

  • Video of the night sky with the stars stabilized so you can watch the ground spin around.
  • For several years the ESA worked on a spacecraft that would test the idea of deflecting a comet with a high-speed impactor. It was brilliantly named Don Quijote, with the rash impactor craft “Hidalgo” rushing in to the target with the observation craft “Sancho” watching from a safe distance. Unfortunately, it looks like the project stalled years ago, but a proposed joint NASA-ESA mission Asteroid Impact & Deflection Assessment (AIDA) could carry the torch [PDF] by targeting the asteroid 65803 Didymos. Didymos is actually a binary system, with a large primary asteroid and a smaller secondary asteroid orbiting it. When the impactor strikes the primary (speed ~ 6.25 km/s), it would induce perturbations to the orbit of the secondary observable from Earth. A 2019 launch and 2022 impact date have been chosen so that Didymos will be passing close to the Earth and the impact event will be visible to ground-based radar.
  • Half of all stars are not in galaxies?

    Astronomers have spotted a faint cosmic glow, unseen until now, that may come from stars that float adrift between galaxies. The discovery suggests that as many as half of all stars in the Universe lurk outside galactic boundaries….The stars were probably tossed there when galaxies collided.

    I don’t understand how this is still uncertain given our knowledge of galaxy and structure formation. But in any case, it’s interesting to note that the large majority (85%) of all the stars we see in the night sky are within 1,000 light years of Earth.

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Video lectures are the future of learning physics

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]

Zotero is great, TeX should be better

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]

Ambiguity and a catalog of the actions

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.
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Links for October 2014

  • Total moving face reconstruction“:

    We present an approach that takes a single video of a person’s face and reconstructs a high detail 3D shape for each video frame. We target videos taken under uncontrolled and uncalibrated imaging conditions, such as youtube videos of celebrities. In the heart of this work is a new dense 3D flow estimation method coupled with shape from shading. Unlike related works we do not assume availability of a blend shape model, nor require the person to participate in a training/capturing process. Instead we leverage the large amounts of photos that are available per individual in personal or internet photo collections. We show results for a variety of video sequences that include various lighting conditions, head poses, and facial expressions.

  • What’s changed since the days when theft was worse than murder? I would really love to see whether a “historical economist” (or whatever those are called) could estimate the statistical value of a human life as defined by people’s own revealed preferences. This is the sort of calculation where we infer how much each of us values our own lives based on the amount we are willing to pay to avoid small chances of death. In the US today, the number is about $8 million now, and is surprisingly consistent (within a factor of 2) over many possible inference methods. (Of course, there are exceptions where people effectively pay rates of many billion dollars per life to avoid emotionally salient risks, like terrorism.)

    The Nautilus article gives the misleading impression that society’s changing values are mostly due to moral progress (presumably arising, I guess, from people being persuaded by moral arguments, or from certain societal norms taking hold).

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Approach to equilibrium in a pure-state universe

(This post is vague, and sheer speculation.)

Following a great conversation with Miles Stoudenmire here at PI, I went back and read a paper I forgot about: “Entanglement and the foundations of statistical mechanics” by Popescu et al.S. Popescu, A. Short, and A. Winter, “Entanglement and the foundations of statistical mechanics” Nature Physics 2, 754 – 758 (2006) [Free PDF].a  . This is one of those papers that has a great simple idea, where you’re not sure if it’s profound or trivial, and whether it’s well known or it’s novel. (They cite references 3-6 as “Significant results along similar lines”; let me know if you’ve read any of these and think they’re more useful.) Anyways, here’s some background on how I think about this.

If a pure quantum state \vert \psi \rangle is drawn at random (according to the Haar measure) from a d_S d_E-dimensional vector space \mathcal{H}, then the entanglement entropy

    \[S(\rho_S) = \mathrm{Tr}[\rho_S \mathrm{log} \rho_S], \qquad \rho_S = \mathrm{Tr}_E[\vert \psi \rangle \langle \psi \vert]\]

across a tensor decomposition into system \mathcal{S} and environment \mathcal{E} is highly likely to be almost the maximum

    \[S_{\mathrm{max}} = \mathrm{log}_2(\mathrm{min}(d_S,d_E)) \,\, \mathrm{bits},\]

for any such choice of decomposition \mathcal{H} = \mathcal{S} \otimes \mathcal{E}. More precisely, if we fix d_S/d_E and let d_S\to \infty, then the fraction of the Haar volume of states that have entanglement entropy more than an exponentially small (in d_S) amount away from the maximum is suppressed exponentially (in d_S). This was known as Page’s conjectureD. Page, Average entropy of a subsystem.b  , and was later provedS. Foong and S. Kanno, Proof of Page’s conjecture on the average entropy of a subsystem.c  J. Sánchez-Ruiz, Simple proof of Page’s conjecture on the average entropy of a subsystem.d  ; it is a straightforward consequence of the concentration of measure phenomenon.… [continue reading]