The meaning of the dictum "Shut up and calculate!"

Eugene Shubert

I've seen the famous dictum "Shut up and calculate!" attributed to Paul Dirac and Richard Feynman. More important than the question of who originated the phrase is the remarkable wisdom and purpose of those words in the context of physics.

Please consider the following statements:

"I think it is safe to say that no one understands quantum mechanics. Do not keep saying to yourself, if you can possibly avoid it, 'But how can it possibly be like that?' because you will go down the drain into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that." [1].

"Some of our descriptions of reality ... cannot be related easily to common, everyday experiences. In quantum mechanics for example, weird phenomena such as “superposition” and “entanglement” have no satisfying, intuitive explanations—yet they are described mathematically in ways that make consistently confirmed laboratory predictions and may even be used someday in super-fast computers. There are physicists who claim not to be bothered by this lack of a mental picture; they belong to what some call the 'shut-up-and-calculate' school. So long as the model makes good predictions, who cares?" [2].

"Most physicists consider non-instrumental questions (in particular ontological questions) to be irrelevant to physics. They fall back on Paul Dirac's point of view, later expressed in the famous dictum: 'Shut up and calculate' often (perhaps erroneously) attributed to Richard Feynman." [3].

I would like to tighten up the arguments of Dirac and Feynman a bit in favor of the "shut-up-and-calculate" school. I believe that I'm in perfect agreement with the "shut-up-and-calculate" philosophy. We're not saying that we prefer mathematically difficult axioms above simpler ones. We're saying, shut up, find simpler axioms and prove theorems if you can, but simplistic arguments and fruitless axioms that don't produce any mathematics are of zero worth when compared to axioms that generate mathematical models and predictions in agreement with experiment.

I have assembled some great quotes in a paper that expresses this philosophy admirably. [4]. If you stumble upon or know of any other great quotes along this line, please post them in this thread. I will be inserting the "Shut up and calculate!" quote in "The Axiomatization of Physics - Step 1" eventually, along with this great statement by John von Neumann that I came across just today:

"The sciences do not try to explain, they hardly even try to interpret, they mainly make models. By a model is meant a mathematical construct which, with the addition of certain verbal interpretations, describes observed phenomena. The justification of such a mathematical construct is solely and precisely that it is expected to work." [5].

I wish that the moderators of sci.physics.foundations would openly affirm that mathematical rigor is obviously the smartest approach to physics and that spending time on threads arguing with those who disagree and who offer no axioms that generate a mathematical model, is like being taken on a rabbit trail safari.

Eugene Shubert · Posted: Wed Feb 21, 2007 7:25 pm Post subject:

I've searched the internet a bit more on the meaning of "Shut up and calculate" and have concluded that it originally meant the positive and practical notion that I and many others have ascribed to it [6][7]. I also believe that Feynman was the first notable scientist to turn that expression on its head by using it at least once in a sarcastic context.

I found these statements by Charles Francis, Wojciech Hubert Zurek and N. David Mermin to be very interesting:

"My experience is that string theorists do not even acknowledge that there are questions in foundations of quantum mechanics. The discussion is non-mainstream, because mainstream physicists do not acknowledge the discussion. This is principally a matter of sticking their head in the sand and refusing to look at what they do not understand. And they do it by taking the very precise words of Dirac, that in the quantum domain certain ideas cease to make sense so that we cannot talk about them, and turning it into ‘shut up and calculate’ whereas what they should be doing is working out, equally precisely, what we can talk about, and indeed, how we can talk about it." [8].

"The message seems to be that there is really no problem and that quantum mechanics can be ‘tame’ and confined to the microscopic domain. Indeterminacy and the double-slit experiment are of course discussed, but to prove peaceful coexistence within the elbow room assured by Heisenberg’s principle and complementarity. Entanglement is rarely explored. This is quite consistent with the aim of introductory quantum-mechanics courses, which has been (only slightly unfairly) summed up by the memorable phrase ‘shut up and calculate.’ Discussion of measurement is either dealt with through models based on the Copenhagen interpretation ‘old orthodoxy’ or not at all. An implicit (and sometimes explicit) message is that those who ask questions that do not lend themselves to an answer through laborious, preferably perturbative calculations are ‘philosophers’ and should be avoided." [9].

"Fifteen years ago, I mused in a Reference Frame column on how different generations of physicists differed in the degree to which they thought that the interpretation of quantum mechanics remains a serious problem (Physics Today, April 1989, page 9). I declared myself to be among those who feel uncomfortable when asked to articulate what we really think about the quantum theory, adding that `If I were forced to sum up in one sentence what the Copenhagen interpretation says to me, it would be "Shut up and calculate!" [10].

I also found what seems to be a very credible history oriented website and it essentially says that "Shut up and calculate" originated with Niels Böhr. Naturally, when I read the following quotes, I see and can separate the unfavorable commentary from the actual historical details:

Copenhagen Interpretation (CI)
"This is the granddaddy of interpretations, championed by the formidable Niels Böhr of Copenhagen University. He browbeat all dissenters into submission (with the notable exception of Einstein) at a Brussels conference sponsored by a philanthropist named Solvay in 1927. Böhr thereby stifled the debate for a generation or two.

"The CI stretches the meaning of the word ‘interpretation’. It essentially says, ‘Thou shalt not ask what happens before ye look’. Böhr pointed out that the Schrödinger equation worked as a tool for calculating where the particle would be, except that it 'collapsed' as soon as you looked at the experiment. If anyone asked why this was, he would say, "shut up and calculate" (or words to that effect).

Summary
"In 1927, at the Solvay Conference, Niels Bohr succeeded in constructing an orthodoxy (the Copenhagen interpretation) which allowed physicists to continue building their armoury of quantum mechanical techniques, while avoiding the frightening questions of what actually happens. He simply said that it was meaningless to give a photon spatial attributes until the wavefunction collapse. This developed into the creed of logical positivism, adherents of which argue it is meaningless to discuss anything that cannot produce concrete experimental results. Positivism is still a major factor in the teaching of physics; students are still told to ‘shut up and calculate’ rather than inquire after meaning." [11].

Of course, my interpretation of the Böhr model is that all of the meaning of it is contained in the mathematical formalism and that it is proper to respond to questions outside of that model by saying ‘shut up and calculate’. I also still stand by my clarification of the subject. In essence, "Be quiet and prove a theorem." This is worth repeating. Simplistic arguments and fruitless axioms that don't produce any mathematics are of zero worth when compared to axioms that generate mathematical models and predictions in agreement with experiment.

I deeply respect this philosophy:

When asked whether the algorithm of quantum mechanics could be considered as somehow mirroring an underlying quantum world, Bohr would answer, "There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature." [12].

Eugene Shubert