## Posts

## Comments

**david_d**on Where Experience Confuses Physicists · 2008-04-26T15:40:54.000Z · score: 1 (1 votes) · LW · GW

So out of curiosity, how much longer is the cutesy analogy thing going to go on for?

**david_d**on Identity Isn't In Specific Atoms · 2008-04-19T15:25:06.000Z · score: 5 (5 votes) · LW · GW

*If that still doesn't work, read an actual book on quantum mechanics. Feynman's QED is a great place to start..*

Since I was pretty much lost after the first few posts in this series, this is exactly what I am doing. I've gone through the first 2 chapters, and what has surprised me is that at least one part of it (explaining why light "bends" when it goes through a material with a different refractive index) has been MORE intuitive to me than the "classical" explanation. The explanation (or shall I say, analogy) I have always heard is that light is like a bunch of soldiers that "want" to stay in line, so when they hit a patch of mud (i.e. when they have to move slower) they change direction. Another explanation I have been given (which is a bit closer to the QED one) is that light "wants" to get from point A to point B as fast as possible, so it "chooses" the path through the glass (or whatever) that will accomplish this.

The QED explanation (i.e. all of the fastest paths tend to have similar phases so they do not cancel each other out like the slower ones do) was much more satisfying.

FWIW, learning about amplitudes in terms of complex numbers before I started reading the book really helped me grok the arrows that Feynman uses. Otherwise, it would probably take my brain a few steps to keep the "amplitude arrows" and the "possible path of the photon arrows" separate.

Anyway, if anybody reading these posts are as lost as me, I would strongly recommend the QED book.

**david_d**on Joint Configurations · 2008-04-11T21:32:06.000Z · score: 0 (0 votes) · LW · GW

So you calculate events for photons that happen in parallel (e.g. one photon being deflected while another is deflected as well) the same way you would for when they occur in series (e.g. a photon being deflected, and then being deflected again)? It seems that in both cases you are multiplying the original configuration by -1 (i.e. i * i).

FWIW, my first instinct when I saw the diagram was to assume 2 starting configurations, one for each photon, though I guess the point of this post was that I can't do stuff like that. In fact, when I did the math that way, I came up with the photons hitting different detectors twice as much as when they both hit the same one.

I think I'll be picking up the Feynman book.....