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Feynman’s legacy — quantum originality

Much has been written about Richard Feynman. Many tributes and books. Feynman wrote some books as well. But the inspiration for this post is an exhibit promoted for Caltech’s 82nd Annual Seminar Day and Reunion Weekend May 16 – 19, 2019.

The Mind’s Eye: Richard Feynman in Word & Image
In work and play, Richard Feynman was a distinctively visual thinker. The Caltech Archives is telling the story of Feynman’s life and physics by exhibiting the notes and artwork through which he shared his vision. Highlights include the diagrams with which Feynman developed his Nobel Prize-winning physics, as well as lecture notes, sketches, and photographs. The exhibit also includes a new virtual reality experience which brings Feynman’s playful spirit to life with one of his favorite autobiographical stories.
Beckman Institute, Beckman Museum, Room 131

And Interesting Engineeering published an article yesterday on Feynman, “An Odd Physicist: What Is Feynman’s Legacy?” (March 9, 2019). The article contains a couple of photos and YouTube videos (and lots of ads) and references to lectures and books.

Richard Phillips Feynman (1918-1988) was one of the most brilliant and original physicists of the 20th century. With an extraordinary intuition, he always sought to address the problems of physics in a different way than others.

Feynman’s technique illustrates his mood quite well. All his colleagues wrote long mathematical formulas whereas Richard Feynman drew, literally, the physical processes that he wanted to study, from which the calculations can be easily made with precise rules.

Currently, the use of Feynman diagrams or the variants of these diagrams is the standard procedure for calculations in the field of physics.

How Feynman approached a topic in physics (among other things) was fascinating. I saw him do this one or twice at Hughes Aircraft when I worked there. I’ve become quite interested in what it means to think like a physicist.

Although Feynman made a great effort to find simple and clear explanations for the students, the most who benefited were the Ph.D. students, professors, and scientists who attended his course because he used a brilliant way to illustrate by example how to think and reason in physics.

If we leave all of Feynman’s aspects aside, his originality is basically his biggest legacy to humanity and future generations.

The laws of physics can often be formulated in many ways, different at first glance until with certain mathematical work; they are shown to be identical. Feynman said that this is a mysterious fact that nobody understands and saw a reflection of the simplicity of nature.

In physics lab at Caltech in the early years of the “red book” The Feynman Lectures on Physics class, we did the double-slit experiment (not the “dim” beam version, as I recall). 

With his pragmatic style, Feynman always entered directly into the heart of the issue, into the audience, and the audience could grasp the problem posed.

A good example of this is when we talk about quantum physics. The whole mystery of quantum can be summed up in the wave/corpuscle duality, and the double-slit experiment contains the basic ingredients for discussing it.

As Feynman stated in The Feynman Lectures on Physics:

In this chapter we shall tackle immediately the basic element of the mysterious behavior in its most strange form. 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. In reality, it contains the only mystery. We cannot make the mystery go away by “explaining” how it works. We will just tell you how it works. In telling you how it works we will have told you about the basic peculiarities of all quantum mechanics. — The Feynman Lectures on Physics, vol III, p. 1-1 (1965).

Other posts which reference Feynman:

Point particles RIP

Infinity and beyond … under the rug

Virtual attraction

Sisyphean hierarchy

EM jumble

“Our main concentration will not be on how clever we are to have found the Law of Gravitation all out, but on how clever nature is to pay attention to it.” — Richard Feynman, The Character of Physical Law


11 thoughts on “Feynman’s legacy — quantum originality

  1. This Scientific American article “Watch Now: Einstein’s Scientific Revolution and the Limits of Quantum Theory – Cosmologist Lee Smolin says that at certain key points, the scientific worldview is based on fallacious reasoning” (by Jim Daley on April 17, 2019) promotes a lecture (and book) by Lee Smolin regarding the completeness of quantum mechanics (quantum theory). The video also may be viewed here.

    “Most of what we do [in science] is take the laws that have been discovered by experiments to apply to parts of the universe, and just assume that they can be scaled up to apply to the whole universe,” Smolin says. “I’m going to be suggesting that’s wrong.”

  2. Another test of the Standard Model is research on the electron electric dipole moment [EDM]. Wiki:

    Within the Standard Model of elementary particle physics, such a dipole is predicted to be non-zero but very small, at most 10−38 e⋅cm, where e stands for the elementary charge. The existence of a non-zero electron electric dipole moment would imply a violation of both parity invariance and time reversal invariance. … More precisely, a non-zero EDM does not arise until the level of four-loop Feynman diagrams and higher. An additional, larger EDM (around 10−33 e⋅cm) is possible in the standard model if neutrinos are Majorana particles.

    To date, no experiment has found a non-zero electron EDM. The Particle Data Group publishes its value as … Here is a list of electron EDM experiments after 2000 with published results

    The Harvard-Yale ACME experiments are referenced in this article “What a Tiny Electron Reveals About the Structure of the Universe” (by Alexey Petrov on January 06, 2019). The article references this Nature article “Improved limit on the electric dipole moment of the electron” (published by the ACME Collaboration on 17 October 2018), and asks the question: “What is the shape of an electron?” The question connects with my post “Point particles RIP.” If an electron has a “shape,” then …

    What replaces the concept of shape in the micro world? Since light is nothing but a combination of oscillating electric and magnetic fields, it would be useful to … [see] how it responds to applied electric and magnetic fields.

    If the shape of an object reflects the distribution of its electric charge, it would also imply that the object’s shape would have to be different from spherical. Thus, naively, the EDM would quantify the “dumbbellness” of a macroscopic object.

    Physicists of the ACME collaboration did not observe the electric dipole moment of an electron — which suggests that its value is too small for their experimental apparatus to detect. This fact has important implications for our understanding of what we could expect from the Large Hadron Collider experiments in the future.

    The article also includes a link to this YouTube video [visualization] “The ACME Search for the Electron EDM” on the ElectronEDM channel (published on Dec 13, 2013), with this description:

    The ACME collaboration explains in simple terms how a precision measurement of the electron can tell us important things about the universe and test the fundamental theories of physics.

  3. In an email on July 31, 2018, I wrote:

    Here’s updated information on where to view the “Feynman: Take the world from another point of view” video.

    I discovered that the video actually is available on YouTube (published on May 10, 2008), where the 1973 interview was split into 4 parts, as follows:

    Here’s a background blurb on the interview (from

    In this clip from a documentary film shot in Yorkshire in 1973, physicist and philosopher Richard Feynman (1918-1988) talks with Fred Hoyle, an accomplished astronomer from the United Kingdom.

    Feynman poses the question: “What, today, do we not consider part of physics, which may ultimately be part of physics?”

  4. [From an email on November 28, 2018]

    One of the books I’m currently reading opens with a Feynman quote:

    I hope you can accept Nature as she is – absurd. Richard Feynman — Ball, Philip. Beyond Weird (p. 3). University of Chicago Press. Kindle Edition.

    Ball discusses Feynman in other places in his book as well, for example:

    In case we didn’t get the point, Feynman drove it home in his artful Everyman style. ‘I was born not understanding quantum mechanics,’ he exclaimed merrily, ‘[and] I still don’t understand quantum mechanics!’ Here was the man who had just been anointed one of the foremost experts on the topic, declaring his ignorance of it.

    What hope was there, then, for the rest of us?

    Feynman’s much-quoted words help to seal the reputation of quantum mechanics as one of the most obscure and difficult subjects in all of science. Quantum mechanics has become symbolic of ‘impenetrable science’, in the same way that the name of Albert Einstein (who played a key role in its inception) acts as shorthand for scientific genius.

    Feynman clearly didn’t mean that he couldn’t do quantum theory. He meant that this was all he could do. He could work through the math just fine – he invented some of it, after all. That wasn’t the problem. Sure, there’s no point in pretending that the math is easy, and if you never got on with numbers then a career in quantum mechanics isn’t for you. But neither, in that case, would be a career in fluid mechanics, population dynamics, or economics, which are equally inscrutable to the numerically challenged.

    No, the equations aren’t why quantum mechanics is perceived to be so hard. It’s the ideas. We just can’t get our heads around them. Neither could Richard Feynman.

    His failure, Feynman admitted, was to understand what the math was saying. It provided numbers: predictions of quantities that could be tested against experiments, and which invariably survived those tests. But Feynman couldn’t figure out what these numbers and equations were really about: what they said about the ‘real world’. — Ball, Philip. Beyond Weird (pp. 6-7). University of Chicago Press. Kindle Edition.

  5. [From another email on November 28, 2018]

    As far as physics and connection with the “real world,” I studied and promoted visualization in my career at Hughes. Particularly as a R&D project. The term has become mainstream, not just in the movie industry. That’s one of the factors in my continued attachment to Feynman’s take. I am impressed with the widespread use of visualization at Caltech and generally in science. So much better than when we were undergrads.

    Another factor is general curiosity about what has changed in the last 50 years. That is what I am exploring and journaling on my physics blog. And there has been progress in understanding quantum mechanics (QM) or quantum physics. I’ve encountered a number of physicists or science communicators who have pointed out that there are today many physicists who understand Einstein’s General Theory better than Einstein did. And the same applies to QM and its early founders (including Einstein). As an example, Philip Ball’s book explores how our understanding of quantum coherence/decoherence evolved only recently (quotes below).

    Why it took so long for decoherence to appear as a core concept in quantum mechanics is not easy to say, given that the theoretical tools needed to understand it were around in Bohr’s and Einstein’s day. Perhaps this is simply another instance of how easy it is in this field to overlook the importance of what elsewhere we take for granted. For the crucial factor in understanding quantum decoherence is that ubiquitous entity present but largely ignored in all scientific studies: the surrounding environment. — Ball, Philip. Beyond Weird (p. 206). University of Chicago Press. Kindle Edition.

    One possible reason why it took so long for decoherence to be identified as the mechanism for turning a quantum system ‘classical’ is that the early quantum theorists couldn’t get past an intuition of locality: the idea that the properties of an object reside on that object. This is what entanglement undermines, and yet for many years after the EPR experiment had been proposed and debated there remained a presumption of neat separation between a quantum system and its environment, just as there is in classical physics. It wasn’t until the 1970s that the foundations of decoherence theory were laid by the German physicist H. Dieter Zeh. Even Zeh’s work was largely ignored until the 1980s, when the term ‘decoherence’ was coined. — Ibid, p. 213.

    Ball is not the only writer that I’ve read who notes such progress. Their point is that it takes decades (or longer) for new scientific ideas to get beyond an initial reactionary milieu and establish themselves organically in scientific practice and technology. Noteworthy are those milestones which respected physicists of their day said were impossible. A good example today is quantum computing where scientists and technologists are making that happen in a practical way, regardless of the weirdness.

  6. This Encyclopaedia Britannica article “Richard Feynman, American Physicist” written by James Gleick (May 7, 2019) recaps highlights of the iconic physicist’s life. His unconventional mind. The article includes historic photographs and an excellent YouTube video “Unlikely Leaders — An overview of the life and work of Richard Feynman” [published on Mar 11, 2014] narrated by Dr. Liz Parvin, senior lecturer, faculty of science (physics), The Open University (A Britannica Publishing Partner). The video includes some notable Feynman quotes.

    Feynman remade quantum electrodynamics—the theory of the interaction between light and matter—and thus altered the way science understands the nature of waves and particles. He was co-awarded the Nobel Prize for Physics in 1965 for this work, which tied together in an experimentally perfect package all the varied phenomena at work in light, radio, electricity, and magnetism. The other cowinners of the Nobel Prize, Julian S. Schwinger of the United States and Tomonaga Shin’ichirō of Japan, had independently created equivalent theories, but it was Feynman’s that proved the most original and far-reaching. The problem-solving tools that he invented—including pictorial representations of particle interactions known as Feynman diagrams—permeated many areas of theoretical physics in the second half of the 20th century.

  7. Reference: What Do You Care What Other People Think? Further Adventures of a Curious Character — Richard P. Feynman as told to Ralph Leighton © 1988

    Part 2

    Page 128
    The main thing I learned at that meeting was how inefficient a public inquiry is: most of the time, other people are asking questions you already know the answer to — or are not interested in — and you get so fogged out that you’re hardly listening when important points are passed over.

    Page 214 – 215 [re the “selling” of the shuttle]
    Maybe they [management] don’t say explicitly “Don’t tell me,” but they discourage communication, which amounts to the same thing. It’s not a question of what has been written down, or who should tell what to whom; it’s a question of whether, when you do tell somebody about some problem, they’re delighted to hear about it and they say “Tell me more” and “Have you tried such-and-such?” or they say “Well, see what you can do about it” — which is a completely different atmosphere. If you try once or twice to communicate and get pushed back, pretty soon you decide “To hell with it.”

    So that’s my theory: because of the exaggeration at the top being inconsistent with the reality at the bottom, commuinication got slowed up and ultimately jammed. That’s how it’s possible that the higher-ups didn’t know.

    The other possibility is that the higher-ups did know, and they just said they didn’t know.

    Page 237
    For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled.

    EPILOGUE: The Value of Science

    Page 248 [re “the open channel”]
    It is our responsibility to leave the people of the future a free hand. … [Otherwise] we will doom humanity for a long time to the chains of authority … It has been done so many times before.

    It is our responsibility as scientists, knowing the great progress which comes from a satisfactory philosophy of ignorance … to teach how doubt is not to be feared but welcomed and discussed; and to demand this freedom as our duty to all coming generations.

  8. Wired > “Even Huge Molecules Follow the Quantum World’s Bizarre Rules by Sophia Chen (09.23.2019) – A record-breaking experiment shows an enormous molecule is also both a particle and a wave – and that quantum effects don’t only apply at tiny scales.”

    … at what size do quantum effects no longer apply? How big can something be and still behave like both a particle and a wave? Physicists have struggled to answer that question because the experiments have been nearly impossible to design.

    Now, Arndt [a physicist at the University of Vienna, Austria] and his team have circumvented those challenges and observed quantum wave-like properties in the largest objects to date – molecules composed of 2,000 atoms, the size of some proteins. The size of these molecules beats the previous record by two and a half times. To see this, they injected the molecules into a 5-meter-long tube. When the particles hit a target at the end, they didn’t just land as randomly scattered points. Instead, they formed an interference pattern, a striped pattern of dark and light stripes that suggests waves colliding and combining with each other. They published the work today in Nature Physics.

    By looking for wavelike behavior in progressively larger objects, Arndt wants to understand how quantum mechanics transitions into the world we normally perceive. To that end, some physicists propose theories such as the continuous spontaneous localization model, which modifies the math of standard quantum mechanics to suggest that larger objects stay in a wavelike state for shorter times. The results of this experiment restricts the likelihood of some of these theories, says Arndt.

    I need a physicist to explain how their experimental setup works like “a dressed-up version of the famous double-slit experiment.” And their incredible control of alignment and spurious vibration and heat to maintain coherence.

  9. And speaking of the double-slit experiment as witness to the “heart of quantum mechanics” (Feynman), here’s another article by Paul Sutter: “Is It a Wave or a Particle? It’s Both, Sort Of” (September 30, 2019). The article has some useful visualizations.

    Image: Light behaves as both particles and waves at the same time, and scientists have been able to observe this duality in action using an ultrafast electron microscope. The wave nature is demonstrated in the wavy upper portion, while the particle behavior is revealed below, in the outlines showing energy quantization. (Image: © Fabrizio Carbone/EPFL)

    Video: Is light a wave or a particle?

    Video: The Mysterious quantum nature of light survives space trips [delayed-choice experiment in space]

    Video: Is matter a wave or a particle?

    Sutter recaps the essential notions of a particle and a wave. A particle is a localized object which can “bounce” off other objects. A wave is not localized – it’s spread out. Waves wiggle and interfere with each other rather than bounce off each other. “Both waves and particles are described by very, very different sets of mathematical equations.”

    So, different kinds of physics experiments were revealing different kinds of properties of light. Sometimes, light acted like a wave, and sometimes, light acted like a particle. Which was it? The answer is that it’s both.

    Then Louis de Broglie proposed that matter particles have a wavelength. And later the double-slit experiment with an electron beam exhibited interference. [1]

    In the deep mathematics of quantum mechanics, an electron (an electron’s wave function) is “a [delocalized] wave of probability representing all the possible places where a particle might be the next time we go looking for it” or “a cloud of where it might be” – something which can interfere with itself (as in the double-slit experiment).

    Sutter jokes about being careful not to throw ourselves through narrow slits. But he doesn’t discuss the experiments which explore how far we can go with the size of particles in double-slit experiments, as noted in my previous comment about 2000-atom molecules. That limit is being explored.

    Why can’t we beam golf balls, baseballs, tennis balls, etc., and demonstrate interference?

    The Wired article hints at the difficulty of maintaining the molecules in a coherent state. Tricky.

    “It’s surprising that this works in the first place,” says Timothy Kovachy of Northwestern University, who was not involved in the experiment. It’s an extremely difficult experiment to pull off, he says, because quantum objects are delicate, transitioning suddenly from their wavelike state to their particle-like one via interactions with their environment. The larger the object, the more likely it is to knock into something, heat up, or even break apart, which triggers these transitions. To maintain the molecules in a wave-like state, the team clears a narrow path for them through the tube, like police cordoning off a parade route. They keep the tube in a vacuum and prevent the entire instrument from wobbling even the slightest bit using a system of springs and brakes. The physicists then had to carefully control the molecules’ speed, so they don’t heat up too much. “It’s really impressive,” says Kovachy.

    And if the wavelength is too small to measure:

    Related post > Eigen what?

    [3] At the macroscopic level, every object (rather than a dynamic system of objects) may be viewed as in its own “eigenstate.” A baseball, for example, is in a state of composite quantum decoherence. All its (emergent) properties appear definite. No quantum behavior is observable — there are no coherent aggregates (as in lasers and superconductors). And the de Broglie wavelength of a baseball is too small to ever measure (~10^–34 m).


    [1] And the whole basis of modern transmission electron microscopes in fact depends on the waviness of electrons (so-called point particles) – that the wavelength of electrons is smaller than light.

    Wiki >

    Transmission electron microscopes are capable of imaging at a significantly higher resolution than light microscopes, owing to the smaller de Broglie wavelength of electrons. This enables the instrument to capture fine detail—even as small as a single column of atoms, which is thousands of times smaller than a resolvable object seen in a light microscope.

    Wiki > Matter wave

    Schrödinger’s quantum mechanical waves are conceptually different from ordinary physical waves such as water or sound. Ordinary physical waves are characterized by undulating real-number ‘displacements’ of dimensioned physical variables at each point of ordinary physical space at each instant of time. Schrödinger’s “waves” are characterized by the undulating value of a dimensionless complex number at each point of an abstract multi-dimensional space, for example of configuration space.

    Wiki > Quantum coherence

    In quantum mechanics, all objects have wave-like properties (see de Broglie waves). For instance, in Young’s double-slit experiment electrons can be used in the place of light waves. Each electron’s wave-function goes through both slits, and hence has two separate split-beams that contribute to the intensity pattern on a screen. … This ability to interfere and diffract is related to coherence (classical or quantum) of the waves produced at both slits.

  10. Here’s a useful resource for “patterns that explain the universe.”

    • Science Focus > “A beginner’s guide to Feynman diagrams” by Brian Clegg (November 1, 2021) – In this extract from Ten Patterns That Explain The Universe, science writer Brian Clegg explains how Richard Feynman’s eponymous diagrams not only illustrate complex particle interactions, but can make calculations easier, too.

    (quote) … nearly every electromagnetic interaction – which means nearly every interaction of matter not involving gravity – is the result of a matter particle emitting a photon, or a matter particle absorbing a photon, or both.

  11. Here’s some past commentary on the Two-Slit Experiment which entails distinguishing between “immaterial information” [of the wave function] and material particles. And the influence of the first on the latter – taken as a metaphysical mystery. I am not sure if the drift is simply saying that mathematics is not reality (i.e., that mathematical representation is not reality or that mathematical representation is an approximation – or characterization – of reality). And versus Sean Carroll’s claim that the wave function is real (and goes through both slits).

    On Caltech’s Science Exchange, this article (below) was noted under Dive Deeper as a “Read More” link for Caltech’s post “What Is Superposition and Why Is It Important?” (2022).

    • The Information Philosopher > “The Two-Slit Experiment and ‘One Mystery’ of Quantum Mechanics” by Bob Doyle (Likely years ago)

    “... the probability amplitude ψ is pure information.”

    The two-slit experiment demonstrates better than any other experiment that a quantum wave function ψ is a probability amplitude that can interfere with itself, …

    Light waves are often compared to water waves, as are quantum probability waves, but this latter is a serious error. Water waves and light waves (as well as sound waves) contain something substantial like matter or energy. But quantum waves are just abstract information – mathematical possibilities. As Paul Dirac tells us, quantum wave functions are not substances.

    The wave function ψ is determined by solving the Schrödinger equation given the boundary conditions of the measuring apparatus (the container). We will see that the thing that goes through both slits is only immaterial information – the probability amplitude wave function ψ (t) if we solve the time-dependent Schrödinger equation.

    We shall see below that the idea of the light wave “collapsing” instantaneously to become a particle was first seen by Einstein in 1905. This is a mistake, one still widely taught.

    (caption) Feynman’s path integral formulation of quantum mechanics suggests the answer. His “virtual particles” explore all space (the “sum over paths”) as they determine the variational minimum for least action, thus the resulting probability amplitude wave function can be said to “know” which holes are open.

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