Feynman and what comes next...

As you may be aware of, I am a Feynman aficionado:

1. My scientific motto is a (not so famous) quote of Feynman: "All we do is draw little arrows on a piece of paper - that's all!"
2. My Twitter visual profile is dedicated to him.
3. I love viewing videos of his lectures or his interviews.
4. I regularly go across his written works.
5. I've spotted errata in his Physics Lectures, volume III (Quantum mechanics), most of them typo, but some substantial errors.

Curiously, I discovered him relatively late. When I followed quantum mechanics courses at university (somewhere between 1985 and 1989), my courses didn't refer to his lectures. I consider that as a missing. It was only after I took time to dig deeper into the quantum foundations (after 1996) that I came across his works. Reading his works was so enlightening for my comprehension of the fundamental laws of nature, that there are pieces that I could read tens of times and each time I would learn new things. Or better said: approach known things from a new point of view.

Feynman is deservedly one of the most quoted people (at the Selected Pages section of Wikiquote, he figures along with people like Aristotle, Buddha, Confucius, Einstein, Jesus or Shakespeare...). His words are inspiring and often explain physical truths in plain language, comprehensible to the layman. As for all quotes, there is a caveat: they must not be seen as an absolute truth. Or as Feynman stated it himself: Learn from science that you must doubt the experts.

Very early I was skeptic about one of Feynman's most famous quotes: nobody understands quantum mechanics. This is often requoted in a more or less transformed way (for example Dawkins' version: "If you think you understand quantum mechanics, you don't understand quantum mechanics"). Does this quote have a general and definitive value of truth? Or was it just that Feynman didn't know of anyone who could explain quantum mechanics in an understandable common sense way?

Chapter 1 of Feynman's quantum lectures gives some insight in the reasons of his belief that nobody understands quantum mechanics: "We choose to examine a phenomenon which is impossible, absolutely impossible, to explain in any classical way, and which has in it the heart of quantum mechanics." He goes on to describe the double-slit experiment (with electrons), showing that it is impossible to think of waves alone or of bullets alone (such explanations have been taken over by popular media like that given by "Granddaddy of all Quantum Weirdness"). And Feynman concludes with "No one has found any machinery behind the law. No one can explain any more than we have just explained. No one will give you any deeper representation of the situation." These are terrible sentences when repeated to hundreds of thousands, maybe millions of physics students since 1965. They mark a halt for any further investigation of the subject.

Fortunately, there are inventive unconventional physicists. There were already deeper theoretical representations given by physicists like De Broglie or David Bohm, showing how a particle may be directed by a guiding wave and thus yield all the experimental results of the double slit experiment, but this had never been put to proof during their lifetime with an experimental model.

Today, I think I can safely say that the quote "nobody understands quantum mechanics" is experimentally outdated. Couder and Fort, two French physicists, experimented with bouncing droplets on a liquid subtract and discovered that they exhibited quantum behaviour, without looking for any quantum analogy:

• droplet travelling in its wave,
• diffraction and interference patterns of travelling droplets similar to photon and electron diffraction patterns,
• attraction and repulsion of droplets embedded in their waves,
• symmetric and anti-symmetric orbital motion of droplets.

Visuals presented by Couder are breathtaking. Even if you don't understand french, I highly recommend watching bouncing droplets orbiting around each other (for example at 25:35 of his 2006 presentation).

An upcoming paper of Couder's group in Physical Review Letters even suggests a quantum tunneling analogy with ordinary droplets: "Unpredictable tunneling of a classical wave-particle association", by A. Eddi, E. Fort, F. Moisy, and Y. Couder.

So today, Feynman's defeatist words about nobody understanding quantum mechanics are outdated. Please, experimental physicists, go ahead, be inventive and focus on experiments where ordinary macroscopic individual particles simulate quantum behaviour, polarization, bosonic and fermionic behaviour, inward bound forces, entanglement, quantum erasure, coupling of ordinary particles to their pilot-wave fields (gravitation, electromagnetism). Because all these quantum phenomena may be rationally understood with the help of experimental models. It's just a matter of inventivity. And we "will find someday that, after all, it isn't as horrible as it looks." ~ Feynman's Epilogue to his Lectures on Physics.

Is quantum physics associated with common sense or is it flapdoodle?

I would like to thank those who prompted me on the apparent contradiction between "Common Sense" and "Quantum Physics", calling it an oxymoron.

A few month ago, in a discussion on sci.physics:

"Common Sense" Quantum Physics?
Now THERE is an oxymoron if ever there was one!

And recently, I was prompted by a tweet:

Common sense quantum physics sounds like an oxymoron to me!

Of course, I chose my blogtitle to be suggestive, even a bit provocative. But I wanted it also to be earnest. How is it possible that the most fundamental theoretical framework of nature is not considered as common sense? To me this is sufficient evidence that there is something wrong in our understanding and teaching of Quantum Physics.

My opinion is that our specialized physics education is responsible for that oxymoron. I've got children, one of them who's just got to high school. When they ask me about what I'm doing with my video-clips and I explain to them how quantum systems behave, they grasp it intuitively.

For instance, I'll explain that interference patterns with single particles are obtained because the single particle rides on a wave and that wave directs it at special places on a screen, that's how ordinary particles behave. But I'll never ever explain it through unnecessary hocus pocus quantum flapdoodle.  

All the same, they understand very well that we don't know whether Schrödinger's cat is dead or alive before we've opened the box. I'll never ever tell them that the cat is both dead and alive at the same time. I'll just say that because we don't know whether it is dead or alive, quantum physics has some rules that give odds for each possible result of the observation. That conforms to their perception of reality.

With respect to quantum mechanics, I find classical mechanics concepts like gravity harder to explain. The fact that the sun attracts the earth or that the earth attracts a falling apple is less intuitive than the fundamental quantum principles.

That's what I mean by "ordinary common sense quantum physics" with respect to "educated common sense classical physics".