3 ms·
Having read QED early on, my understanding is that while treating a windowpane or mirror as a front and back surface is a useful simplification in most cases, i
by braythwayt 8y ago
Having read QED early on, my understanding is that while treating a windowpane or mirror as a front and back surface is a useful simplification in most cases, it is not for interference.
The "sum of the histories" explanation is that light interacts with all of the molecules at every depth, and once the depth becomes larger than the "wavelength," the interactions statistically can el each other out, and the probability of an interference pattern appearing beco,es infinitesimal.
I have also heard that while "sum of the histories" was useful for explaining QED to undergrads, it wasn't an effective way to calculate results and didn't yield any predictions that more math-heavy approaches coukdn't produce, so it was discarded.
For all I know it has been shown to be wrong for some observed phenomena.
Anyhow... Is that explanation the correct "sum of the histories" explanation? And if so, is ot considered useful to think of it in these terms for laypersons who don't want to dive into the math?
- joshvm 8y agoYou can still get interference if the medium is thicker than a wavelength, but it needs to be close. This effect is quite often seen in CCD detectors used in infrared spectroscopy, as well as certain detectors used for visible spectroscopy. It's called etaloning. But as you suggest, in thicker media there's much less chance of it happening. http://www.andor.com/learning-academy/optical-etaloning-in-charge-coupled-devices-technical-article http://www.andor.com/learning-academy/optical-etaloning-in-c...
- abecedarius 8y agoIt sounds like you're thinking of Feynman's popular book QED (which I'd agree ought to be great for people who want an actual idea of what's going on without taking a college course) -- but in chapter 3 he shows how "we can get the correct answer for the probability of partial reflection by imagining (falsely) that all reflection comes from only the front and back surfaces... what is really going on: partial reflection is the scattering of light by electrons inside the glass." This comes from adding up the coherent effects of that scattering -- he wasn't saying the interference goes away (becomes incoherent). It's not my field, but my impression was that path integrals (sum over histories) did initially figure mainly in discovering the Feynman rules for QED, without getting used much directly by others, but later did find more applications.
- braythwayt 8y agoI am most definately speaking of the book.
- abecedarius 8y agoSorry that wasn't friendlier -- I was writing on too little sleep.