physics

Trying to learn modern physics from popularizations is like trying to learn to dance by watching the shadows flit by under the closed door of a ballet school.

—John Baez, 22 Jan 2003 email message to sci.physics.research.

9 September 2003
A pedestrian learns Physics

After years of reading popular books and newspaper articles about modern physics with little true understanding, I've decided to try to actually learn something about relativity, quantum mechanics, gravitation, black holes, cosmology, string theory, or whatever else "modern physics" might be.

Hopefully someone like me, trained as a computer scientist or mathematician, will find something useful in these notes, wherein I'll try to keep track of each step I take, trying to learn physics.

I'm writing this sentence on Day Zero—9 September 2003, in the full knowledge that I know nothing about physics, or nearly so. We'll see how far I can get.

Four months later—Notes added 6 January 2004.

Not really knowing where to begin, I started off by trying to learn General Relativity. I started with the book A first course in general relativity, by Bernard F. Schutz. But I found that just getting an understanding of special relativity and tensors was a more reasonable first goal. Thankfully, the Schutz book turned out to be a good resource for that, too.

Here are my notes, "A Pedestrian Learns Modern Physics." I can't imagine why anyone would want to read them—a person would be better off just reading the Schutz book, instead—but here they are, split into separate chunks, in any case:

Part I (18 pages, PDF, 3Mb)

Chapter 1: Warning.
Chapter 2: Introduction.
Books. The "problem book." An awful shock.
Chapter 3: What do you mean, "set the velocity of light equal to one?"
Unit conversions. Planck's constant.

Part II (21 pages, PDF, 3Mb)

Chapter 4: Proper time.
Differentials. Twin paradox. Four velocity.
Chapter 5: Spacetime.
The postulates. Fun with spacetime diagrams. The pole in the barn. Hyperbolic detour—relative velocity.

Part III (60 pages, PDF, 8.5Mb)

Chapter 6: Vector analysis in special relativity.
Vectors. Accelerating spaceships. Energy and momentum. Doppler shift. Compton scattering. Inverse Compton scattering. Eight week assessment. Precis. What next?
Chapter 7: Tensors in special relativity.
One forms. Transformation rules. The gradient. General tensors. The outer product. Index gymnastics. The trapdoor—Tensor differentiation.

Part IV (11 pages, PDF, 1.9Mb)

Chapter 8: Perfect fluids in special relativity.
Fluids. Flux. The stress energy tensor T, and what MTW and the "problem book" have to say about it. Conservation of energy-momentum.

Part V (18 pages, PDF, 2.64Mb)

Chapter 9: Curvature, I

The notes in this chapter are incomplete, but I thought I would put them up here on the web site when I realized I might never come back to finish them.
``The happiest thought of my life.'' Gravitational redshift. The equivalence principle. No global inertial frames. Curvilinear coordinates. The Jacobian. Christoffel symbols. The covariant derivative.