# QM or Relativity first for self learners?

1. Jan 6, 2004

### Tyro

I decided to expand my knowledge on Physics a little from what I was taught at school, which was mostly classical/Newtonian stuff. I am planning on learning both Quantum Mechanics & Relativity. Which one should I learn first, so that the knowlege from that first subject would help me learn the other? Why is that? (I'm interested in looking out for some of those connections)

My education in Physics stopped at A-level...otherwise known as Year 12. After that, in the engineering degree I was in, you stick mostly to Newtonian stuff, apart from a little relativity in Celestial Mechanics. From what I know, the E3's (Electrical & Electronic Engineers) did QM.

The Physics subject in the A-level examination board I sat for (Cambridge's) did not touch Relativity at all. As for QM, it was very introductory, mostly thermionic emission from ZnO (IIRC) and how various experiments concluded that light had wave-particle duality and delivered its energy in distinct packets, instead of being purely a wave. The syllabus stopped at saying "there is more than meets the eye for light." Literally.

Last edited: Jan 6, 2004
2. Jan 6, 2004

Staff Emeritus
My opinion for what it's worth.

First do special relativity, and do it with the math (Lorentz transformations) and try to get up to Electromagnetism in relativity. I say that because if you can do that it will be pretty assured that you really know four-momentum and energy and can work with them. Besides, covariant EM will come back to haunt you.

Then do basic quantum mechanics. Do this in two stages. First a basic introduction to the ideas, with math, probably as a one dimensional model. Do as many problems as you can. Then start in on a full bore quantum text (but NOT quantum field theory! Stay away from that till you get your quantum legs). You goal here should be to master ket algebra, Hilbert space, eigenvalues, and be able to do (some of) the problems in the Schaum's outline for QM.

Somewhere in here you want to study classical Lagrangean and Hamiltonian dynamics, at least up to poisson bracket gymnastics. Don't waste time on math courses beyond what you know (calculus is important and feeling comfortable with integration by parts will be a big help).

If you've got this far, look around for an online study group in quantum field theory, and good luck!

I haven't mentioned textbooks. They come and go, and others will be able to give you the current faves. I do want to plug "What is Quantum Mechanics? A Physics Adventure" for the basic QM course. I wish it had beeen around when I was starting out.

3. Jan 6, 2004

### Tyro

*Starts taking notes*

How about Feynman? From what I was told by some that he is good, but at times tends to dwell too much on superfluous points.

Otherwise I still have the textbooks from my A-levels (with lots of unread chapters on QM & Relativity...), like Young and Hecht. I've got a Halliday & Resnick at my parent's place too. I could ask them to post it over.

At what stage do you recommend general relativity?

Oh, BTW, we learnt about classical electromagnetism in a very convoluted way. We weren't actually taught Maxwell's laws in an A,B,C,... way like how you're taught Newton's laws (e.g. "This is the first law. This is the second.") Rather we were just exposed to a concept, which may have been a basic Maxwell law, or a corollary. So, should I brush up on classical EM theory as well?

4. Jan 6, 2004

### mmwave

I had such difficulty with QM the first try that I rechose my EE program to avoid all the solid state stuff! Years later I got a BS in physics "for fun" and had to take a course in analytical mechanics using lagrangian and hamiltonians and voila, QM seemed much more tractable. As an EE, the required math was not lacking so I was struggling with both at the same time, in AM the math was a struggle so then in QM there's only the physics to worry about. It's the long way but it was the only way for me. Studying a little probability before tackling QM was helpful too.

5. Jan 7, 2004

### Kalimaa23

I would try and get a good book on EM before you try and take on special relativity. Why? SR is a natural evolution from the work Lorentz & Poincaré did on EM. A good course in EM should give you the feeling "ooh, I see where this is going".