We’re flattered, but enough of the physics envy. It’s embarrassing us all.

A couple of days ago in the Guardian, Timothy Garton Ash highlighted how economics has been dangerously led astray by the baseless assumption that it’s a “hard” science like physics: When economists ignore the human factor, we all pay the price. It’s a convincing and compelling argument, and Garton Ash’s admonition of economists aspiring to the “status, certainty and predictability of physics” should be on the required reading list for all those who study and teach the dismal science.

This misplaced aspiration to reduce exceptionally complex, human issues to simplistic mathematical models, and to adopt the methodology and mindset of the physicist when it’s far from appropriate, is, however, widespread. Physics envy extends well beyond the confines of economics: the green-eyed monster is hardly a stranger in other social sciences. I’m not about to revisit the science wars  — nor am I about to loftily suggest that physics (and, more generally, the physical sciences) is purer-than-pure when it comes to peer review or its ability to sniff out a hoax — but Garton Ash’s article appeared just as I had finished reading a very recent, highly lauded, and exceptionally frustrating example of the misapplication of physics concepts in social science. It seems that, twenty years on from Sokal’s hoax, the social sciences still too often remain in thrall to their physical counterparts.

I can’t quite remember where I first read about Alexander Wendt‘s book, “Quantum Mind and Social Science: Unifying Physical and Social Ontology” but I suspect it was via Twitter (before I retired my account). It’s published by Cambridge University Press (so it’s got their imprimatur of adademic quality), and the reviews at their website are glowing: “a book of speculative grand theorising that is sadly lacking in the social sciences today”; “For most social scientists, all that Wendt takes us through will be a revelation. Wendt’s discussion of this material is just fabulous,”; “The author takes a courageous stance on a number of deep and difficult issues in philosophy of mind.”

Despite the title, I tried to give Wendt’s book the benefit of the doubt. I really did. And, to be fair, at times he does a fairly good job of outlining the history, the underpinnings, and the philosophical ramifications of quantum physics, including such challenging aspects as Bell’s inequalities, the EPR paradox, and entanglement. But there’s this right at the start of the book (p.3):

In this book I explore the possibility that this foundational assumption of social science [that we live in a world of classical physics] is a mistake, by re-reading social science “through the quantum”. More specifically, I argue that human beings and therefore social life exhibit quantum coherence — in effect that we are walking wave functions. I intend the argument not as as an analogy of metaphor, but as a realist claim about what people really are“. (Emphasis mine).

No.

Just no.

This, the central theme of Wendt’s book (which runs to 293 pages excluding references), is demonstrably incorrect. We are not phase-coherent wavefunctions. Phase coherent interference of quantum mechanical pathways is the bedrock of quantum physics. As Feynman put it in the context of the double slit experiment: “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.

If we were indeed walking wavefunctions then all of those quantum mechanical effects that we see at the single particle level would apply to our macroscopic world. And they clearly don’t. One of the very first concepts that physics undergrads (or, indeed, physics A-level students) encounter in their study of quantum mechanics is the de Broglie wavelength. There’s an exceptionally  simple relationship between the quantum mechanical wavelength of a particle/object (λ) and its momentum (p) which goes like this:

λ = h/p

where is Planck’s constant. (Apologies to the physicists who may be reading. You might want to skip forward a bit. There’s a ranty bit towards the end). For a typical human at typical walking speeds, that wavelength is not just negligibly small, it’s utterly beyond negligibly small. I’ll leave you to do the sums. (I’ll note in passing that “de Broglie wavelength” is not an entry in the index of Wendt’s book).

If we were walking wavefunctions of the type Wendt proposes then we would see the same type of interference effects in our everyday life that happen at the single particle level. We would diffract when we walk through doorways. We would be able to tunnel through walls without expending any energy. That blasted cat would indeed be simultaneously dead and alive.

(Edit 07/02/16:: I should clarify that even if humans were phase-coherent wavefunctions, and all other physics remained the same, the probability for tunnelling through a wall would still be unimaginably tiny. However, it’s clear from Wendt’s arguments that all other physics wouldn’t remain the same…)

But we don’t, and it isn’t. And the reason we don’t is exceptionally simple: we live in a world of classical physics. Wendt disputes this: “It has long been assumed that quantum effects wash out statistically, leaving the decohered world described by classical physics as an adequate approximation of macroscopic reality“.  But it’s not an assumption — it’s demonstrably the case that quantum effects “wash out statistically” as the system size/degrees of freedom/temperature increase. A vast amount of experimental data (coupled with an extremely well-developed mathematical framework) clearly shows this. No assumption necessary — there’s oodles of exceptionally strong evidence that demonstrates that human beings do not behave like quantum particles.

Moreover, we spend a great deal of time in undergraduate lectures teaching students to take the appropriate limit so that a quantum problem reduces to the classical situation (or a relativistic problem reduces to a classical scenario). One illuminating example is the case of Planck’s formula for the average energy per mode of blackbody radiation (to which Wendt refers on p.44 of his book) — this reduces to the classical formula (which is simply kT) in the appropriate limit(s). It is beyond misleading to suggest that it is only an “assumption” that quantum effects are washed out in the macroscopic world. There’s enough quantum woo out there from the likes of Deepak Chopra without accomplished academics such as Wendt (and prestigious academic publishers such as Cambridge University Press) adding to it.

Social science is important – it provides key insights into human behaviour and addresses questions that are beyond the scope of the physical sciences. I enjoy interacting and collaborating with my colleagues in social science both at Nottingham and elsewhere and gain a great deal from our discussions. But I’ll be brutally honest. I know for a fact that there are many in the “hard” sciences (and elsewhere) who would argue that the funding of social science is a waste of money and that it could be much better spent elsewhere. Misappropriating ideas from quantum mechanics in an attempt to ride on the coat-tails of the (highly successful) intellectual framework underpinning physics does social science no favours at all.

We physicists still don’t understand what the vast majority of the universe is made up of. So don’t envy us — pity us. And try to follow xkcd’s advice the next time you see “quantum” used outside a physics context…