Post a Comment On: Backreaction

With somewhat of a delay, here is my annual summary of the Edge annual question. In 2012 the smart people were asked
What is your favorite deep, elegant, or beautiful explanation?
As every year half of the respondents used the opportunity to promote their own research. This year they may be forgiven, for they were likely drawn to their research because they found it elegant or beautiful. A notable exception is experimental psychologist Bruce Hood who nominated Fourier's theorem because "psychology ... is rarely elegant."

Some of his colleagues see this differently though. David M. Buss, for example thinks "Sexual Conflict Theory" is an elegant explanation for what he is concerned: "Men are known to feign long-term commitment, interest, or emotional involvement for the goal of casual sex, interfering with women's long-term mating strategy," he writes. He'd better learn string theory to explain everything.

Psychologist Mahzarin Banaji offers "Bounded Rationality," the insight that human beings are not "smart enough [to behave] in line with basic axioms of rationality." The inexistant rational person would say if the subject of your study doesn't behave as your axioms say, you should conclude that you've used the wrong axioms. More replies from the psychological side are that of Emily Pronin, who finds it beautiful that "Human beings are motivated to see themselves in a positive light," and that of Joel Gold who likes Freud's elegant discovery of the unconscious.

Nathan Myhrvold explains that the scientific method "it is the ultimate foundation for anything worthy of the name "explanation,"" and is, surprisingly, the only one to name the scientific method. The double helix and natural selection, as one could expect, appear various times.

Needless to say, the physicists had a large selection of answers to choose from. As Leonard Susskind wrote in his reply "That's a tough question for a theoretical physicist; theoretical physics is all about deep, elegant, beautiful explanations; and there are just so many to choose from." He chose to nominate Boltzmann's explanation of the second law of thermodynamics because his "favorites are explanations that that get a lot for a little." A good choice.

Anton Zeilinger names Einstein's 1905 proposal that light consists of energy quanta, Raphael Bousso on similar reasoning goes for quantum theory, and Satyajit Das for Heisenberg's uncertainty principle.

Steve Giddings and Roger Highfield nominate Einstein's insight that gravity is curvature of spacetime, Lee Smolin's favorite elegant explanation is the principle of inertia, and Sean Carroll, close by, names the universality of gravity. Stephon H. Alexander, always unpredictable, goes for particle creation in time dependent gravitational fields. (Which, incidentally, was the topic of my master's thesis.)

Lawrence M. Krauss goes for electromagnetism, Eric Weinstein favors the deep insight that quantum theory is "actually a natural and elegant self-assembling body of pure geometry that ha[s] fallen into an abysmal state of pedagogy putting it beyond mathematical recognition," Timo Hannay's favorite is QED, Laurence C. Smith goes for continuity equations, Lisa Randall nominates the Higgs mechanism, and Garrett Lisi names a theory of everything that does not yet exist - who knows what might have been on his mind.

Marcelo Gleiser and Bruce Parker nominate atomism. Gregory Benford and Peter Woit reasonably find beauty in the unreasonable effectiveness of mathematics, and Shing-tung Yau, (Co-author of The Shape of Inner Space) keeps it simple and elegant with "A Sphere."

Max Tegmark is as always entertaining:
"My favorite deep explanation is that our baby universe grew like a baby human — literally. Right after your conception, each of your cells doubled roughly daily, causing your total number of cells to increase day by day as 1, 2, 4, 8, 16, etc. Repeated doubling is a powerful process, so your Mom would have been in trouble if you'd kept doubling your weight every day until you were born... Crazy as it sounds, this is exactly what our baby universe did according to the inflation theory pioneered by Alan Guth and others..."The reason to capitalize Mom is that it stands for God in this creation myth. And I guess the navel of the universe lies at MIT.

Jeremy Bernstein, interestingly enough, names the Planck scale as a limit to measurement of time (and space I want to add), which we recently discussed here. Bernstein however credits this insight to Freeman Dyson.

Freeman Dyson himself thinks it is elegant that general relativity remains unquantized and, repeating earlier statements of his, he "propose[s] as a hypothesis... that single gravitons may be unobservable by any conceivable apparatus." I very much like his reply, because I keep using a fairly old quote from Dyson on my slides to enter into an explanation why the detection of gravitons isn't equivalent to evidence for quantum gravity. So now I can use a newer quotation.

Frank Wilczek offers a very good answer: Simplicity, which he thinks of as the length of an algorithm: "Description length is actually a measure of complexity, but for our purposes that's just as good, since we can define simplicity as the opposite—or, numerically, the negative—of complexity." I like his answer because it touches on the question what we actually mean with elegance.

This underlying big question mark is raised also by Rebecca Newberger Goldstein: "Where do we get the idea — a fantastic idea if you stop and think about it — that the beauty of an explanation has anything to do with the likelihood of its being true?" An excellent point that we explored in my post "Is Physics cognitively biased?"

On that note, Frank Tipler favors parallel universes, Andrei Linde thinks "the inflationary multiverse" is a beautiful explanation for everything, and Martin Rees also nominates the multiverse.

Another noteworthy physicist's reply is that of Seth Lloyd, who made the effort to write up the demonstration SU(2) being a double cover of SO(3).

My award for the most bizarre reply goes to Dave Winer who thinks it is elegant that his computer screen "has the time in the upper-right corner."

The most interesting reply I found that from Barry C. Smith who summarizes it as "Lemons are Fast" and explains "When asked to put lemons on a scale between fast and slow almost everyone says 'fast', and we have no idea why." I'm not sure exactly what is elegant about this, but interesting it is without doubt.

For me the most insightful reply was that of Tania Lombrozo who writes:"Metaphysical half-truths... realism, the existence of other minds, causation... These explanations are so broad and so simple that we let them operate in the background, constantly invoked but rarely scrutinized. As a result, most of us can't defend them and don't revise them. Metaphysical half-truths find a safe and happy home in most human minds.

[T]he depth, elegance, and beauty of our intuitive metaphysical explanations can make us appreciate them less rather than more. Like a constant hum, we forget that they are there."
And the shortest reply is that by Katinka Matson who nominates Occam's Razor.

My nomination for the most beautiful and elegant explanation would have been the variational principle (about whose elegance I wrote here), close to David Dalrymple's reply that named the principle of least action.

Anybody else has the impression that list is getting longer every year? Do they just write more or are there actually more names on the list?

The question that I would like to ask all the smart people is this: If everybody on the planet would read your reply (or have it read to) what would you want to tell them?