Posted by: reformedmusings | April 18, 2012

Quantum Electrodynamics (QED) – A great primer

I’ve been buried under a mountain of stuff for a while now. After this last weekend, things lightened up quite a bit. So, I decided to both entertain and exercise my brain by reading on one of my favorite subjects – physics.

My choice of specific topic started rather oddly. I engaged in a discussion over at Wes White’s blog on evolution, the Bible, and our Westminster Standards. In seeking some specific examples of how scientific “facts” change over time, sometimes radically, I came across an article called “The complicated history of simple scientific facts” by Chris Lee. While interesting and somewhat entertaining, Lee seemed to end with the conclusion that light (i.e., electromagnetic energy of any frequency) is fundamentally a wave. My first thought was that this wasn’t the case. Quantum electrodynamics (QED) showed that light consisted of particles commonly known as ‘photons’. Drs. Richard Feynman, Julian Schwinger and Sin-itero Tomonaga won the Nobel Prize for physics in 1965 for their work in QED. That’s a long time ago.

One thing led to another, and I ended up picking up a copy of Feynman’s outstanding introduction to QED, QED: the strange theory of light and matter. The book compiles a 4-lecture series that Feynman gave at UCLA in the early 80’s. Dr. Feynman’s goal was to make QED accessible to folks with minimal technical background, and I believe that he succeeded marvellously.

Any history that I provide here would be woefully inadequate next to what Feynman does in the book. When I went to high school and college, light was treated either a wave or a particle, depending on the problem or phenomenon at hand. Light refracts, diffracts, reflects, produces interference patterns, etc., like a wave. Indeed, one of the initial successes in quantum mechanics produced Schrödinger’s wave equation. Cool, but…

Light also behaved as a particle. The photo-voltaic effect can only be produced if light was a particle. Also, very sensitive photo-multipliers proved that very, very dim light produced the same amplitude of response as brighter light, but that they “ticked” more slowly. That sounds remarkably like fewer particles hitting the detector rather than a continuous wave.

Even worse, it turns out that electrons, which we know are particles of matter, exhibit strangely wave-like behavior in the double-slit experiment:

That’s enough to hurt anyone’s head, and it’s not even the whole story. Feynman takes the double-slit experiment to the next level, and in the process shows that QED accurately handles the strangest phenomena. In addition, other problems couldn’t be solved with classic quantum mechanics, including the Lamb Shift. Enter Feynman diagrams, the Dirac-Feynman path integral formalism, and QED. Feynman maintains, and demonstrates, that QED handles all known physics problems except nuclear and gravity, and they’re currently working to extend QED to the analysis of atomic nuclei.

At its core, QED made key “corrections” or “improvements” to quantum mechanics and brought a new methodology to the fight. QED definitively demonstrates that all the wave-like properties of light can be explained by treating light as a particle, the photon, in interaction with electrons. In fact, every observed electromagnetic phenomenon can be modelled and analyzed with some combination of just three analytical pieces: a photon moving from point to point, an electron moving from point to point, and an electron interacting with a photon. Sounds incredibly simple, but the devil is in the calculations. Even with superc0mputers, we can only analyze very simple situations.

QED has been tested in the laboratory to extreme levels and it has successfully met all challenges. But, there’s a catch. You knew there was. QED only produces probabilities (actually, amplitudes that convert to probabilities). So, you don’t know anything exactly, but only what’s most probable. Einstein famously criticized quantum mechanics for this in his quote: “As I have said so many times, God doesn’t play dice with the world.” OTOH, ya gotta pay to play.

The quantum world hurts your head. It makes no logical sense to our human brains. As Feynman says in his introduction when answering the question if the audience will understand his lectures,

“No, You’re not going to be able to understand it…You see, my physics students don’t understand it either. That is because I don’t understand it. Nobody does.”

The math works, but no human knows why.

Feynman presents a host of examples, some from everyday life, others esoteric, that QED correctly models and he tells you in general how it’s done. As a bonus, in the fourth lecture he covers the extension of QED to nuclear particles. But Feynman doesn’t explain the underlying physical phenomenology, because no one knows how the world works at that level. We don’t even have a bad guess.

God created an amazing world, richer than anyone can even imagine. Physics attempts to explain and model that world using mathematics as its language, and in doing so, brings out a level of beauty that few ever see or appreciate. QED takes us to incredible vistas, which Dr. Feynman ably presents to a somewhat casual audience with good humor and keen insights. Our lack of understanding of the underlying phenomenology which QED models, however, keeps us humbly aware of our dependence on our Creator in whom we live and move and have our very being (Acts 17:28).

I highly recommend Feynman’s primer on QED to anyone interested in exploring some of the wonders that we see every day but rarely consider.

Addendum:

QED handles subatomic interactions incredibly well, and these interactions produce visible phenomenon in common observation (e.g., partial reflections in glass). Einstein’s relativity handles gravity in the larger universe equally well. However, relativity has an Achilles Heel – the black hole. When the relativity equations are solved for the center of a black hole, gravity goes to infinity – an impossibility in the physical world. An attempt was made to combine QED and relativity for two reasons: 1) to provide a smooth continuity between the subatomic, electromagnetic realm and the gravitational realm; and 2) to resolve the infinity in the relativity calculations.

The result was a colossal failure. The resultant equations produced not just one infinity value, but an endless series of infinities. So as I write this, we have no idea how to model a transition between the subatomic, electromagnetic world governed by photon exchanges between electrons and the larger universe held together by gravity. We have a great deal yet to learn.

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