Category Archives: work

A Farewell to Black Holes

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Yesterday here at USC was my last lecture in the class about black holes (see also here). We’ve got to move on to other topics (Cosmology, Einstein’s equations, etc) and so cannot do any more. It was a fun last lecture though. I pulled together a few scraps of things I did not finish in the previous lecture (such as the extraordinarily high percentage of binding energy per unit rest mass you can extract with rotating black hole orbits – just what you need to power things like quasars) and then finished with:

  1. A taste of Hawking radiation, the Bekenstein-Hawking entropy and the wonderful and beautiful subject of black hole thermodynamics that opens up when you combine gravity with quantum mechanics*, followed by…
  2. A quick discussion of the Penrose process for extracting energy from rotating black holes. (I’m sure that all (past, present or future) super-advanced civilizations must be using them as the ultimate emissions-free means of generating energy for heating their homes and so forth. No, really.)

*Of course, all undergraduates commonly hate it when you dare bring in stuff from other classes, so to […] Click to continue reading this post →

Potato, Moon

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roast potato

There’s really nothing like a sweet potato roasted in the heart of a wood fire. A wood fire lit out under a clear big sky with a full moon. After a long day of hiking. A day of hiking in the desert on a super hot day of vivid blue, brown, and gold. Delicious flavours, textures and colours.

I spent most of last week on retreat in Death Valley. It was Spring break, and I was […] Click to continue reading this post →

Lighting Up Field Theory

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Sidney Coleman lecturingI got an email from one of the group’s graduate students today*, pointing to an archive of videos of lectures by the great Sidney Coleman. He’s doing quantum field theory. This makes this a marvelous resource, in principle, and so I thought I’d share them with you. They are here.

I wonder: are these the lectures that Jacques Distler has mentioned attending a few times in the past on his blog? This was the 1975-1976 year, a graduate course. I wonder if anyone (else) I know was in that class room…

[Update: I learned from the discussion over on Jonathan Shock’s site that there are some partial lecture notes from the course here, by Bryan Gin-ge Chen, based on notes by Brian Hill. He’s looking for help on completing the project, so get in touch if you want to help out..]

I’ve never seen Coleman in action before, and so I was immediately rather curious, […] Click to continue reading this post →

Categorically Not! – Puzzles!

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The next Categorically Not! is on Sunday March 9th (upcoming). The Categorically Not! series of events that are held at the Santa Monica Art Studios, (with occasional exceptions). It’s a series – started and run by science writer K. C. Cole – of fun and informative conversations deliberately ignoring the traditional boundaries between art, science, humanities, and other subjects. I strongly encourage you to come to them if you’re in the area. Here is the website that describes past ones, and upcoming ones. See also the links at the end of the post for some announcements and descriptions (and even video) of previous events.

The theme this month is Puzzles! Here’s the description from K C Cole:

What isn’t a puzzle? The universe, life and everything are essentially puzzles that, to borrow from Einstein, “beckon like a liberation.” Designing buildings, choreographing dances, cooking meals and getting along with other people all involve solving puzzles (as, of course, does figuring out what’s right in front of your eyes—not to mention putting together a program such as Categorically Not!) A love of puzzles and the challenge of solving them is deeply embedded in human nature.

Categorically Not! - Puzzles! - Speakers

Gwen Roberts, Scott Kim, Gavin Scott.

Our March 9th Categorically Not! features puzzlemaster Scott Kim, who’s […] Click to continue reading this post →

Beyond Einstein: Fixing Singularities in Spacetime

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Not long ago David Morrison (UCSB) came to the mathematics department here at USC to give a colloquium.

David Morrison Colloquium at USC

This was a treat for me for many reasons. Here are three:

  1. It’s always good to see Dave. He’s one of the people I’ve known in the field was since my very first postdoc when I was learning to survive in the big bad world on my own after graduate school. I mostly could not understand a word he or anyone there else said in those days (IAS Princeton, right in the belly of the

[…] Click to continue reading this post →

Tales From the Industry XVII: Jump Thoughts

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A commenter asked how the aforementioned movie viewing and panel discussion went on Friday (movie: Jumper), and so I thought expand a bit on the answer I gave:
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It went very well. We were at the School of Cinematic Arts, at USC. We had a full house in the Norris Theatre, which was great to see. Most of the audience was students from the SCA, I think, with some of the faculty present, and people from the film’s parent studio, and several others. For the panel, present were two of the film’s producers, the visual effects supervisor, costume supervisor, production designer… basically, the perfect people to have a discussion with about the physics! I won’t try to list all names since I did not catch all of them and don’t want to mis-credit people for being there who weren’t.

Teleportation physics aside for a moment, I’m very impressed with how they realized […] Click to continue reading this post →

Mass Matters

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Well, only four weeks and change behind us in this course, and… the class (see here and here) is ready to understand this wonderful equation:

the schwarzschild solution

and all that it implies. What is it? It encodes the shape of spacetime around a spherical blob of mass of total mass M. No, don’t worry too much about the details, since this is not a lecture about General Relativity….. it is just nice (I hope) every now and again to get a look at the sorts of things we use in our day to day work. This “warped” spacetime encodes what we interpret as the gravitational field (in the old Newtonian language) due to a spherical (or, to a good approximation, almost spherical) mass. Like the sun, or the earth, or that tennis ball in the corner there*. It is an exact solution […] Click to continue reading this post →

Friday Night Wanderings

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It was one of those Friday nights when I was in the mood to get out of the house, but not entirely sure what to get out to. “Out” was more important than “where”, you see. Wanted to do a bit of thinking and to relax and let the heavy week of too many meetings fall away from my shoulders.

In the end, I did a combination of things. After my mood, followed by my at charlie o’s. John Beasley, Nolan Shaheed, Dave Carpenter, Roy McCurdytrajectory, turned away from Pasadena (where I was planning to see Persepolis, as was my original plan – I’ll do it later… really want to see that film) at about 10:30pm I arrived in the Valley and hung out at Charlie O’s which is one of the more happening of the neighbourhoody jazz clubs in LA. (Sadly, in this context, “happening” by LA late night standards means that there’s more than about nine people present.)

There’s always something on each night and you can just walk in and sit at the bar to […] Click to continue reading this post →

Equivalence

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equivalence principle

Well, Tuesday was a big day in class. We reached a landmark – the introduction of one of my very favourite thoughts of the 20th Century: the Equivalence Principle. This is the realization of Einstein’s that there’s something profoundly odd about Newtonian mechanics and Newtonian gravity that hints at something deeper.

Quick reminder from high school (just two formulae, please bear with me): You know […] Click to continue reading this post →

Bookcases

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While the wonderful downpour carries on outside (the whole of Southern California is in the grips of a powerful storm), I’ll continue with the discussion of the re-invigoration of the study that I started a short while ago…

study project - plane
(One of my all-time favourite wood-working tools. The good old-fashioned plane. Planing a bit of wood is jolly good therapy too.)

One of the main things I envisioned, and put into my sketches, was lots of space for books. Lots. I wanted big bookcases that fit the room, and so I planned a simple but robust design that stretched them eight feet from the floor to the ceiling. Of course, I wanted to make them myself – Building them myself would be more fun and much […] Click to continue reading this post →

Lecture One

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lecture notes

So it is that time. A new semester is upon me, and a totally new course to deliver. Today was my first day back on campus after the break (at least during a regular working day).

Sunday saw me sitting down (in the newly completed study) thinking about how I was going to structure the course. This usually has me sitting with the textbook, a pen, a hand drawn calendar on a big sheet of paper, and a frown on my face trying to figure out roughly what topics I will cover, how many lectures I will devote to each, how many class worksheets (see earlier post) I might have, when the midterms will be, and so forth.

What I am teaching? Why, only one of my most favourite topics to teach in the entire […] Click to continue reading this post →

In Which I Fail Physics 101…

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… but pass it on a retake!

While quickly building an ad hoc washing line pulley assembly from a bag of hooks, eyes, and pulleys, and a 2×4, I put this together at first (blotted out some background for privacy of myself and neighbours – click for larger view):

bad design

Huh. Does not want to hang level. Why? A tenth of a second after the thought, I burst out laughing loudly at my error. Ironic since I love teaching about pulleys in basic physics, and for some reason students are scared of pulleys. (Not as scared as they are of torque (why?), but scared nonetheless. I try to help them overcome those fears.) I made an obvious mistake. (Do you see it?)
[…] Click to continue reading this post →