Quantum paths cross again

The letters QED stand for quod erat demonstrandum, which, in English, means “that which was to be demonstrated.” The abbreviation graces the ends of proofs, or so I’ve been told. My math homework, however, has yet to produce the innovations worthy of this signature. We had a joke in high school Latin class that QED could be used in place of “duh.” QED, we’ve already proven that.

My favourite bookstore – so far – is Raven Used Books, on the outskirts of Harvard Square in Cambridge, Massachusetts. The science section is along a little sliver of the back wall, and runs from the floor nearly to the ceiling. What it lacks in size it makes up for in neatly alphabetized sections and books that are beautiful inside and out. Once, when perusing the Feynman shelf – the second most famous physicist of the 21st century gets his own shelf – I came across a thin, black hardcover with a plastic case in place of the original book jacket. The title was embossed on the spine, three silver capital letters, arranged in a familiar sequence. But it turns out that QED has a second meaning: quantum electrodynamics.

In 1965, Richard Feynman won the Nobel Prize for his work in QED, a quantum field theory of electromagnetic force. In English, that means that the very building blocks of matter exist on a much smaller scale than that in which people do, and their interactions are governed by forces other than gravity, and must be analyzed by means other than Newtonian, “old-school” physics. The interactions of these particles together happen to be more complex than that of the particles by themselves, and Feynman’s QED was a final step in figuring them out.

But neither the lexicon of physics nor that of laymen, or even that of pure math, can adequately describe Feynman’s landmark contribution to our understanding of the quantum world.

Thumbing through the thin volume, the Feynman diagrams jump out – squiggly stick-figure-like illustrations of the interactions between electrons and positrons that have worked their way into modern physics and popular science paraphernalia alike.

Feynman was not the only person to demonstrate the interactions of quantum particles in electromagnetic fields, but his was the only proof to be accompanied by – no, based around – drawings. The discovery was made simultaneously by both Juliann Schwinger and Sin-Itiro Tomanga, contemporaries of Feynman with whom he shared the million-dollar prize. The same conclusion had been arrived at three separate times, by two very distinct methods.

That seems to be the thing about scientific innovations: the same phenomenon can be discovered more than once, or by many people at the same time. Schwinger and Tomanga’s proofs may have ended with the same three final letters, but the dots and squiggles that supported Feynman’s identical conclusion were absent from their work.

Science is not a cookbook, or a loop of if/else statements. It’s not a dogma, and there isn’t one golden archetype. No “this is how to do experiments” or “this is how to get to the final product.”

As my mom tells me whenever I am being particularly stubborn or arrogant (or both): “Many solutions to the same problem.” And she’s right; there’s no way to argue with that. So usually the best I can do is surrender.

I always respond by leaving my self-righteous mood as intact as possible: “Well, duh.”

Shannon Palus’s column will be back again next semester. Until then, tell her what you’ve QED-ed at plusorminussigma@mcgilldaily.com