Astronomy 152: Freshman Seminar in Astrophysics
Department of Astronomy, Haverford College
Spring 2004

Welcome

Welcome to the Spring 2004 edition of Astronomy 152: Freshman Seminar in Astrophysics, taught by Froney Crawford (this is the same course as Physics 152). This is a half-credit course intended primarily for prospective physical science majors.

The prerequisites for the course are:

Prerequisite: Physics 105 (or 101) at Haverford (or the Bryn Mawr equivalent).
Co-requisite: Physics 106 (or 102) at Haverford (or the Bryn Mawr equivalent).

The required textbook for the course is Just Six Numbers: The Deep Forces That Shape the Universe by Martin J. Rees.

Instructor Contact Information

Instructor: Fronefield Crawford
Office: Koshland INSC Link 106
Phone: (610) 896-2973
Email: fcrawfor@haverford.edu
Office Hours: Mon 2:00-4:00 p.m., Wed 2:00-4:00 p.m.

Come see me anytime.

Course Description

The advertised purpose of this course is to introduce beginning physical science students to some of the exciting new developmens in astrophysics. The overall theoretical understanding of many of these topics can be expessed in terms of fundamental physics at the level of an introductory course (e.g., Physics 105 and 106), and much of the class will involve the application of fundamental physical principles to various astrophysical phenomena. Since the details of these phenomena are quite complicated, it will be necessary to construct simple models and make judicious approximations. However, this shouldn't be viewed as a limitation of the course; in fact, such activities are precisely what working physicists often do. The picture of physics you may have acquired so far, i.e., a series of "laws" (and corresponding equations) and "problems" to be solved with those laws, is usually very far from the reality of "doing physics." The study of physics is a never-ending series of constructing models to describe physical phenomena and then attempting to apply these models to new situations. Ultimately these models are "wrong" in the sense they invariably fail to properly describe or predict some new phenomenon (this was true for Newton's law of gravitation which was surpassed by Einstein's theory of general relativity, which in turn will have to be generalized to include quantum mechanics). Therefore, the approach in this course will, hopefully, give you a better idea of how physics really works.

The unity of physics (i.e., the interrelation of different areas of physics), is also something that is readily apparent in dealing with complex astrophysical phenomena. This is also a crucial aspect of the study of physics that is often not emphasized in standard courses (for understandable reasons). For example, to understand why stars shine, one needs to invoke thermal and statistical physics, gravitational physics, hydrodynamics, electrodynamics, nuclear physics, scattering theory, quantum mechanics, etc. While we will necessarily make gross simplifications (I assume that you have not yet mastered the above topics!), you should begin to get a feel for how physicists pursue such a problem.

Finally, it is hoped that this course will provide you with insight on how to go about "solving" quite general physical problems. This is also not the standard fare in most courses where you are required to apply restricted techniques to solve a set of restricted problems in, for example, electrodynamics. Physicists, and astrophysicists in particular, often choose problems for study not because they involve applications in a particular branch of physics but rather because they are inherently interesting (or important). They then use those areas of physics that are required to solve "the problem." Of course, this isn't easy, and the present class won't, by any means, make you an expert in doing it. However, any insight you gain here will undoubtedly help you in your future study of physics. Among useful skills are: the ability to look at a complicated problem and "see" the most important feature of it; the ability to build simple models that capture the salient features of a problem; the ability to make approximations; the ability to do simple "back-of-the-envelope" calculations; and the ability to judge what is a reasonable result, (i.e., to know when you've made a mistake).

The text, Just Six Numbers: The Deep Forces That Shape the Universe by Martin Rees, is not a resource for achieving the above goals; in fact, it is intended primarily for the non-technical reader. However, it will provide a backdrop for putting into context the topics listed below. It also will provide examples of the inter-relatedness of physics. Finally, it tells a facinating story of how a few (six) seemingly unrelated quantities have conspired to allow just the kind of Universe that is required to have such creatures as us in it. Some of the discussion seems more philosophical than physical and illustrates Rees's particular take on the subject.

Course Format

In addition to the first, introductory and organizational lecture, there will be seven classes that meet every other Monday evening. A reading assignment will be given in advance (from Rees, your current physics text, and from a few web sources). You will be assigned a few questions and/or problems based on these readings that will be due at the beginning of class. Each class will begin with an introductory lecture that, in addition to the readings, will help set up the topic(s). After a short discussion, there will be a coffee/cookie break during which there will hopefully be more discussion. The remainder of the class will be a workshop in which we will discuss the topic and break up into teams to work on one or two defining problems. The latter will not be typical textbook problems, but rather questions like, "What can we deduce about the mass content of the local universe from the dipole moment in the Cosmic Microwave Background radiation?" and "Why is there a maximum mass of a neutron star, what is this mass, and what happens when this mass is exceeded?" These will entail marshalling information from the readings, your overall knowledge of physics, and your ability to make simplifying models of the systems; in short: "doing physics." Individuals or pairs of students may be called on to lead the discussion on particular topics. One follow-up written question (probably one of the problems discussed in the workshop) may be assigned to be handed in at the beginning of the next class. The only exam will be the final that will be a combination of multiple choice questions and a few, short, back-of-the-envelope problems. While all of this may sound like a lot of work for a half-credit course, the readings will not be excessive, the assignments are short, and the class only meets every other week. However, because of the workshop nature of the course, class attendance is mandatory.

Meeting Times and Schedule

Meetings: Mon 7:30-10:00 p.m. in the Observatory every other week.

Date Mon Jan 19 Mon Feb 2 Mon Feb 16 Mon Mar 1 Mon Mar 15 Mon Mar 29 Mon Apr 12 Mon Apr 26

Topic Introductory Lecture/Workshop Relativity Theory Let's Build a Star Collapsed Stars and Black Holes The Big Bang Dark Matter Structure Formation and the Accelerating Universe Cosmic Rays and Wrapping It All Up

Readings Rees Chapter 1 Selected from physics text Rees Chapter 2-4, and selected from physics text Selected from physics text and web Rees Chapter 5, and selected from physics text and web Rees Chapter 6, and selected from web Rees Chapter 7-8, and selected from web Rees Chapter 9-11, and selected from web

Links to Course Readings

• Active Galaxies and Quasars, NASA web site
• "The Evolution of the Universe", by Peebles et al.
• "Dark Matter in the Universe", by Rubin
• "Quintessential Universe", by Ostriker and Steinhardt
• "Cosmic Rays at the Energy Frontier", by Cronin, Gaisser, and Swordy