## Quantum Mechanics and rotations

Let me warn you up front that I cannot yet reconcile Feynman’s answers with McMahon’s recipe. Well, this is supposed to be about the doing of math, not just about math itself.

For Feynman, i’m in “Lectures on Physics”, volume III, Quantum Mechanics. For McMahon, i’m using “Quantum Mechanics Demystified.” References to Schiff are to his “Quantum Mechanics”.

We have looked at the following here: if I know that a spin-1 particle is in the Jz state |+>, i.e.

$\left(\begin{array}{l} 1 \\ 0 \\ 0\end{array}\right)$

and I wanted to know: what are possible values of Jx (the x-component of angular momentum)? and with what probabilities would they occur? What we looked at was the relationship between Jz and Jx in a given coordinate system

I want to consider a different question; I want to rotate the coordinate system.
Read the rest of this entry »

## Happenings – 24 March (3) Quantum Mechanics

this is the third post of its kind. as i said in the first happenings post, i had three breakthroughs last weekend: in PCA, controls, and quantum mechanics. the controls was in post (2), the PCA is coming; this is the quantum mechanics.
at the beginning of what is now last weekend, i had a breakthru in quantum mechanics. i found a simple example of one of the things i was trying to calculate. this came from McMahon’s “Quantum Mechanics Demystified”. he is also the author of “Relativity Demystified”. both books have some really excellent examples in them, things not usually found in introductory books. the bad news is, his quantum mechanics (henceforth QM) text is marred by an awful lot of typos. the good news is, it’s cheap.
i can summarize my overall reaction as follows. i just checked for a 2nd edition which might have fixed the typos. there isn’t one. but he does have “quantum field theory demystified” and i’m going to order it, just because he’s the author. i’ll take my chances with typos. i’m expecting to see some informative examples anyway. Read the rest of this entry »

## Happenings – 24 March

Last week’s happenings post was written Saturday. Later that day I had a great idea for controls. At the beginning of this weekend I found a great example in quantum mechanics; and yesterday afternoon I had a breakthrough in PCA / FA. I think I will describe the first two in separate posts; the PCA will show up soon, in sequence. (The quantum mechanics and controls will not be in one big “happenings” post. my primary reason for keeping posts smaller rather than larger is so that the latex translation is of manageable size.)
Last Monday I went to the annual Oppenheimer Lecture at Cal. it was about quantum mechanics, “spooky actions at a distance”. The speaker’s overheads are available on his webpage http://people.ccmr.cornell.edu/~mermin/homepage/spooky-berk.pdf