Physics (6)562: Statistical Mechanics
Prof. Christopher L. Henley
Syllabus 1/22/2014
CLH can be reached as clh@ccmr.cornell.edu or by phone (better for iterating questions) at 255-5056, including most evenings. Physically in 531 Clark (office hours TBA,
but temporarily 3–4 PM on M-Tu 1/28-1/29).
Our T.A. is Yu-Dai Tsai (yt444@cornell.edu, office hours TBA).
Statistical mechanics
Even I am not quite sure what statistical mechanics is; a one line version is the systematic, quantitative study of macroscopic, collective behaviors emergent from well-defined
microscopic laws of motion, in the limit of large numbers. Sethna’s text is not the best
reference for technical details, but I wanted a less formalistic treatment and a broad, contemporary notion of what stat mech encompasses; in many places, we’ll go a bit beyond
it. This text prioritizes the “why”, demystifying the subtle and still arguable foundations of
the subject, but my own predilection is the “how”: to provide “tools” that will help you in
your graduate careers, whether you do condensed matter experiment, high energy theory,
astrophysics, biophysics, or even finance.
Prerequisites:
This is one of the four core introductory courses that all grads in Physics are expected
to take, unless they already took an equivalent course or learned this material on their
own. The expected audience has taken undergraduate intermediate mechanics, quantum
mechanics, and thermodynamics. But each of these three topics really matters only in
one of the 13 units. So if you have a non-standard background or are from a non-physics
graduate field, you can probably get by, but please consult me during the first week.
Grading weights (and description of activities):
Physics 6562 is grades only (no S/U option)
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Homework
Participation
Midterm(s)
Final project
Weekly
35-40%
Daily
10-15%
in-class and take-home? 25%
in stages
25%
Homework: weekly, and (initially at least) due Weds. in class. (Ask then if you want a
short extension.)
Participation: mainly, daily “teaser questions” about the upcoming topic. Credit in this
category based on whether you do it, not how correct it is.
Midterm exam: Last year we did an in-class 45-minute exam plus a short take-home
exam. (If one of these is canceled, the net midterm grade weight will go from 25% down
to 15% and the remainder reassigned to the other categories.)
Final project: a final paper of 2500 words, with draft due ∼ 5 weeks before the end of
term, for peer review by fellow students. May include a presentation to others in class; a
small part of this grade may depend on other students in the course. The term paper project
involves numerous stages in an attempt to space the work load more evenly.
Academic integrity
As in any course, Cornell’s academic integrity policies apply:
http://cuinfo.cornell.edu/Academic/AIC.html).
The items most pertinent to this course all boil down to don’t present as your work, something that isn’t.
• Teaser questions: Do not write notes from the discussion in class, in the place reserved
for your explanation pre-class.
• Homeworks: You are encouraged to work in groups, or ask senior students’ advice
(preferably after initially sketching all steps on your own). But write up answers privately;
copying verbatim is a violation. Do not consult answer keys from previous years, from
the back of the textbook, or anywhere online, before completing your write up. Please
acknowledge (on the homework paper) those you collaborated with, and cite sources you
used (apart from the course notes and texts).
• Term papers: no copying from sources (sometimes paraphrasing a source is still plagiarism). No re-using a previously written paper. (I reserve the right to apply coincidencedetecting software and/or to require papers to be archived in Turnitin.)
• Exams: no collaboration or communications; no unauthorized use of sources. (Includes take-home, open book exams.)
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Outline
(I’ve grouped the material into two-week chunks; dates are unlikely to be exact.)
Chapters 1–2
Chapters 3–6
Chapter 7
Chapter 8∗
Chapter 9∗
Chapter 10–11∗
Chapter 12–13∗
Overview, random walks
Core: temperature, phase space, entropy, free energy
Quantum stat mech (fermion and boson systems)
Calculation and lattice models
Models, broken symmetries
Correlations; first-order transitions
Continuous transitions, critical phenomena, R.G.
2 weeks
3.5 weeks
1.5 weeks
1 week
1 week
2 weeks
2.5 weeks
“Chapter” refers to the required text, Statistical Mechanics: Entropy, Order Parameters,
and Complexity, by James P. Sethna.
(∗ ) Order of these lectures might be rearranged to follow Statistical Mechanics of Phase
Transitions by J. M. Yeomans, the supplementary text we’ll use during the second half.
Books
Official texts
James P. Sethna, Statistical Mechanics: Entropy, Order Parameters, and Complexity (Oxford University Press, 2006).
Required. (Copies have been ordered by the bookstore. Note Sethna has placed a pdf
version on his website.)
This book was written specifically for Physics ’562, and I’ll try and stick close to it.
This text, unlike most, tries hard to explain everything verbally and intuitively. The exercises are particularly popular, and educational to read through all of them.
J. M. [Julia] Yeomans, Statistical Mechanics of Phase Transitions (Oxford University Press,
1992).
“Recommended” text. The bookstore probably has some copies.
To be used for the portion of the course (after spring break) about lattice models and
critical phenomena; I’ll do that more thoroughly than the Sethna text , but I don’t yet know
how much time is available or whether I’ll follow Yeomans. This is a short (153 pp) and
cheap ($20 for “like new” copies this month!) text, and is outstanding if you want a serious
yet elementary introduction to the renormalization group.
Other books
Disclaimer: I am surprisingly ill-read in these textbooks.
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* Mehran Kardar, Statistical Physics of Particles (Cambridge University Press, 2007). This
is the other contemporary textbook besides Sethna’s, not overly encumbered by quantum
mechanics, but formalistic for my taste and (some say) terse. Kardar was used recently
as the text for ’562 (for 3–4 years by Prof. Eun-Ah Kim), and is your first stop to find a
“second opinion”. A few sections of my lectures will be based on Kardar.
* R. K. Pathria, Statistical Mechanics (1972; 3rd ed, with Paul D. Beale, 2011). This
became, over the past 40 years, the most popular text for this course. It has grown quite
voluminous: I imagine you can find everything you want here, and unfortunately much
more.
Kerson Huang, Statistical Mechanics (1963; 2nd ed., 1987). Pathria and Huang are the
textbooks that older generations learned from (Huang, in my case). Both have lots of
quantum stat mech; both added sections about critical phenomena in revisions, since their
respective first editions predated the renormalization group. (Both Pathria and Huang, I
read, are poets in their native languages, but the texts are hardly poetic; you’ll have more
fun reading States of Matter by David L. Goodstein.)
F. Reif, Fundamentals of statistical and thermal physics (1965). This is the gold standard
for the undergraduate course you should have taken before this.
I know several other texts which are well-known and/or not bad, yet I see no reason to point
you to them. Note in general that “Statistical Mechanics” carried a different connotation
in mid-20th century, encompassing what we’d call the condensed-matter physics of manyparticle quantum systems, e.g. in the Feynman or Landau & Lifshitz texts of that title.
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