On the odd aspects of how light Really works...

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rjlittlefield
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On the odd aspects of how light Really works...

Post by rjlittlefield »

This is to call to your attention an excellent book:

"QED: The Strange Theory of Light and Matter", Richard P. Feynman.

For many years I had heard about this book, but the title always seemed so far above me that I never even looked at the actual book.

That was a big mistake.

The book is basically an edited recap of four lectures that Feynman prepared and presented for a general public audience, to explain the essential intuitions behind Quantum ElectroDynamics (QED).

Just as a teaser, it covers such interesting aspects as...
  • Light doesn't really reflect off the surface of glass. That's just the aggregate effect of a bunch of scattering off individual electrons within the body of the glass. It seems like off the surfaces because, from a distance, lots of things cancel out to make it look that way.
  • That bit about "from a distance" is important. Close to the body of the glass, there are a lot of non-canceling effects that end up resulting in spatial variations that can be far smaller than the diffraction limit based on photon energy (wavelength). This is what enables near field super-resolution phenomena such as are exploited in the new microscopy technique referenced at "Special slide + reconstruction algorithm = super resolution microscopy".
  • "Total internal reflection" isn't really totally internal. This is addressed in a different way by Wikipedia, but somehow the Wikipedia explanation makes a lot more sense to me after reading Feynman's explanation (and the recent series mentioned at "The Curious Observer's Guide to Quantum Mechanics").
  • "Isn't it wonderful -- you can take a piece of mirror where you didn't expect any reflection, scrape away part of it, and it reflects!" (Feynman himself, quoted from pages 46-47, regarding diffraction gratings.)
Lots of diagrams, no formulas. No math more complicated than arithmetic. Almost entirely conceptual, but tied to observable effects.

I should have read this decades ago!

--Rik

Lou Jost
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Re: On the odd aspects of how light Really works...

Post by Lou Jost »

Feynman was a great explainer, even for basic classical physics. We used his Lectures series as a textbook in introductory physics.

Regarding QED, my favorite part of Feynman's viewpoint is that antiparticles are ordinary particles going backwards in time. When a particle and antiparticle appear to annihilate each other, the two particles are actually both the same individual particle, turning backwards in time at the point of annhilation, emitting photons as it turns backwards.

rjlittlefield
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Re: On the odd aspects of how light Really works...

Post by rjlittlefield »

Lou Jost wrote:
Sun Jun 06, 2021 5:45 am
We used his Lectures series as a textbook in introductory physics.
Me too. In fact, as I write this, there is still a copy prominently visible on my bookshelves.

But somehow the title of the QED book had always warned me off, and the Wikipedia article on "Quantum electrodynamics" did nothing to dispel that warning.

Having now read the book, I consider its title as probably an accidental analog of warning coloration used by a harmless mimic, sort of like seeing a hover fly and thinking "bee".

For me, the most interesting aspect of the QED book is what the Preface describes this way:
If you are planning to study physics (or are already doing so), there is nothing in this book that has to be "unlearned": it is a complete description, accurate in every detail, of a framework onto which more advanced concepts can be atached without modification. For those of you who have already studied physics, it is a revelation of what you were really doing when you were making all those complicated calculations!
I have no objection to simplified models that have to be "unlearned" to make progress. But it's very nice to know that in this case I don't have to.

--Rik

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