Posts Tagged ‘Physics’

Richard Feynman

August 31, 2007

Richard Feynman has been one of my heroes, ever since the end of my freshman year at Harvard. After my last final exam, but before I headed home for the summer, I was able to sit in the beautiful Lowell House library, without any obligations, and just read chapters from his wonderful Lectures on Physics. After that there wasn’t much doubt in my mind about what I wanted to do with my life.

There’s a lot to say about Feynman, but I will restrict myself for now to a couple rather recent items which give a picture of the character of this remarkable man. First, there is this 1981 BBC Interview, recently released to the web, where you can see him briefly discuss a few of the things that were important to him.

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Secondly, if you haven’t read Perfectly Reasonable Deviations From the Beaten Track, the collection of his letters edited by his daughter Michelle Feynman that was published in 2005, you owe it to yourself to do so. I was skeptical at first that a book of letters, even those of Feynman, could be very interesting, but I wound up reading every word.

Let me just give you one example of a pair of letters from 1964:

Dear Professor Feynman,

Dr Marvin Chester is presently under consideration for promotion to the Associate Professorship in our department. I would be very grateful for a letter from you evaluating his stature as a physicist. May I thank you in advance for your cooperation in this matter.

Sincerely,
D.S Saxon
Chairman
Dick: Sorry to bother you, but we really need this sort of thing.
David S.

Dr. D.S. Saxon, Chairman
Department of Physics
University of California, Los Angeles
Los Angeles, California

Dear David:

This is in answer to your request for a letter evaluating Dr. Marvin Chester’s research contributions and his stature as a physicist.

What’s the matter with you fellows, he has been right there the past few years–can’t you “evaluate” him best yourself? I can’t do much better than the first time you asked me, a few years ago when he was working here, because I haven’t followed his research in detail. At that time, I was very much impressed with his originality, his ablity to carry a theoretical argument to its practical, experimental conclusions, and to design and perform the key experiments. Rarely have I met that combination in such good balance in a student. Was I wrong? How has he been making out?

Sincerely yours,
R.P. Feynman

The above letter stands out in the files of recommendations. After this time, any request for a recommendation by the facility where the scientist was working was refused.

Edit: In the comments below, Shimon Schocken recommends Feynman’s “QED.” I thought of this book after finishing this post. It’s an amazing work. In it, Feynman gives a popular account (you don’t need any physics background to follow it) of his theory of quantum electrodynamics, for which he won the Nobel Prize. But it’s a popular account that makes no compromises in its scientific accuracy. The other books recommended in the comments (“Six Easy Pieces” and “Surely You’re Joking”) are also definitely great books, but “QED” is somehow often overlooked, even though it is the book that Feynman himself recommended to those interested in his work.

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Algorithms for Physics

August 14, 2007


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Much of my own work is at the intersection of statistical mechanics and algorithms, in particular understanding and developing new algorithms using ideas originating in statistical mechanics. Werner Krauth also works at the intersection of the two fields, but coming from a very different angle: he is a leading expert on the development and application of algorithms to compute and understand the properties of physical systems.

In his recently published book, “Statistical Mechanics: Algorithms and Computations,” targeted at advanced undergraduates or graduate students, he covers a very wide range of interesting algorithms. To give you an idea of the coverage, I’ll just list the chapters: “Monte Carlo methods,” “Hard disks and spheres,” “Density matrices and path integrals,” “Bosons,” “Order and disorder in spin systems, “Entropic forces,”and “Dynamic Monte Carlo methods.”

Krauth’s presentation is leavened by his humor, and he often uses the results obtained using his algorithms to make surprising points about physics that would otherwise be hard to convey.

I am often asked by computer science or electrical engineering scientists and researchers for good introductions to physics, and particularly statistical mechanics, and I’m now happy to be able to recommend this book.

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Specifying physics explicitly in terms of algorithms, as Krauth does, gives a very concrete basis for understanding concepts that can otherwise seem terribly abstract. Gerald Sussman and Jack Wisdom make this point in the preface of their already classic book (which is available online) “Structure and Interpretation of Classical Mechanics”:

“Computational algorithms are used to communicate precisely some of the methods used in the analysis of dynamical phenomena. Expressing the methods of variational mechanics in a computer language forces them to be unambiguous and computationally effective. Computation requires us to be precise about the representation of mechanical and geometric notions as computational objects and permits us to represent explicitly the algorithms for manipulating these objects. Also, once formalized as a procedure, a mathematical idea becomes a tool that can be used directly to compute results.”

But while Sussman and Wisdom’s book focuses in great detail on classical mechanics, Krauth’s book covers more broadly subjects in classical mechanics, statistical mechanics, quantum mechanics, and even quantum statistical mechanics. Another difference is that Sussman and Wisdom specify their algorithms in executable Scheme code, while Krauth uses pseudo-code. Of course, both choices have their advantages, just as both of these books are worth your time.