Robert Oppenheimer's greatest contribution to physics was one that he wanted nothing to do with for the rest of his life. In 1939 Oppenheimer and his student Hartland Snyder published a paper in the same issue of the Physical Review that featured Niels Bohr and John Wheeler's seminal article on the mechanism of nuclear fission (the issue incidentally came out on the same day that Germany attacked Poland). In five short pages Oppenheimer and Snyder laid out the essential characteristics of what we know today as a black hole. Then World War 2 intervened, and the Bohr-Wheeler paper suddenly became very important while the Oppenheimer-Snyder piece was cast on the sidelines.

After the war, general relativity - which until then was considered a backwater of frontier science, more mathematics than physics - was resurrected by a handful of schools in Europe and the US led by pioneers like John Wheeler and Dennis Sciama. Strangely by then, Oppenheimer had lost all interest in the topic. This was attested to by Freeman Dyson who tried to get Oppenheimer interested in his pre-war work on gravitation several times. Each time the master changed the subject and never showed the slightest interest in recent developments in the field. Why did Oppenheimer display such casual indifference to a contribution that may well have gotten him a Nobel Prize had he lived long enough to see it experimentally validated? Because by then, as Dyson puts it,

"Oppenheimer in his later years believed that the only problem worthy of the attention of a serious theoretical physicist was the discovery of the fundamental equations of physics. Einstein certainly felt the same way. To discover the right equations was all that mattered. Once you had discovered the right equations, then the study of particular solutions of the equations would be a routine exercise for second-rate physicists or graduate students."

Oppenheimer and Einstein's view was one that was not alien to many of history's greatest physicists. A search for the fundamental laws was the most important activity a physicist could be engaged in; everything else was best left to lesser minds. Personally I detest this attitude, but for better or worse I think it's been implicitly true throughout the history of physics.

I was reminded of Oppenheimer's story by Chad Orzel's characteristically insightful critique of my previous post. The title of the post makes Orzel's take clear: "Repeat after me: Particle physics is not all of physics". His point is well-taken; particle physicists are behaving like the great questions of their discipline are the only ones that truly count, and therefore if those questions run into a wall then all of physics must be grinding to a halt. This is of course completely false simply based on the everyday work of the majority of the world's physicists which has nothing to do with quantum chromodynamics and Higgs bosons. Orzel gives us just one example of the fact that such views are in a minority by pointing out that the most populated division of the American Physical Society actually consists of condensed matter physicists. Particle physicists clock in at number two, but even then:

"That (number) almost certainly overestimates the number of people working directly on a Theory of Everything. The fact is, the physicists whose work is genuinely in crisis as a result of recent developments (or, more accurately, the lack thereof) are a tiny minority of professional physicists. They’re vastly overrepresented in the media, in large part because wildly speculative stuff about multiple universes is sexy and provides lots of opportunities for stoner-friendly CGI, but if they all got sucked into a black hole tomorrow (thus settling the “firewall” debate for good and all), physics as a whole would continue on with barely a hiccup."

That point about the overrepresentation of theoretical physics in the media is one which I would wildly applaud, especially since I wrote a post bemoaning how this fact misleads the public into thinking that the questions of particle physics are the only exciting ones in the field. In that post I called for a much bigger effort by experimentalists (and yes, by condensed matter experts) in presenting their science to the public.

Having said that, I think that Orzel's post seems to give short shrift to what physics has been about until now, and therefore while I sympathize with his sentiments I suspect that all varieties of physicists will always have a weakness for fundamental laws. The fact is that even if the majority of physicists don't themselves work on fundamental laws, it's hard to deny that philosophically, the history of physics has largely been the search for fundamental laws which mostly manifested themselves under the rubric of "unification".

As long as physics was around its practitioners have tried to find common ground between disparate phenomena. Galileo discovered that Jupiter had moons just like the earth and Venus had phases just like our moon does. Newton's crowning achievement - one that unseated two thousand years of "ethereal" thinking set in motion by Aristotle - was to demonstrate that objects in the heavens obey the same laws followed by objects on earth. Unification continued to be a high water mark in developments that followed. A completely legitimate history of physics can be written simply based on stories about unification, from Faraday and Maxwell's unification of electricity and magnetism to Weinberg and others' unification of the weak and electromagnetic forces.

We know all this, but the reason why unification has featured high on the list of physicists' favorite moments in history is because with unification comes simplification. And this simplification has always been a principal component of the search for fundamental laws. As physicists say only half jokingly, the most fundamental law would be a one-line equation on a cocktail napkin that explains everything. There is something not only greatly pleasing but exceedingly practical in having two equations for two very different phenomena suddenly condensed into one. So it's not just particle physics but all kinds of physicists who have benefited from unified fundamental laws, and it goes without saying that a condensed matter physicist would cherish simplification in his mathematics as much as a particle theorist.

Moving from the realm of the ethereal to the wildly practical for instance, one only needed to have asked physicists working on radar during World War 2 how grateful they were for Maxwell's equations. The fact is that even if condensed matter physicists don't work on fundamental laws themselves, and even if it may be true that their day-to-day work would largely remain unaffected if all the world's string theorists decided to throw in the towel tomorrow and write existentialist novels, it's also equally true that every condensed matter physicist has already benefited from fundamental laws. I would suspect that this remains true regardless of whether or not a condensed matter physicist will personally have her work transformed by the unification of quantum mechanics and general relativity.

Then there are the questions of aesthetics and completeness which most physicists appreciate even though they may not dictate their own work. Condensed matter physicists may well believe in Philip Anderson's dictum that "More is Different" and they may well agree that a purely reductionist approach does not help them crack superconductivity or giant magnetoresistance, but I would strongly suspect that every one of them secretly wishes that there were in fact a direct, simple, fundamental derivation of the properties of ceramic superconductors from the properties of quarks. Just because there does not seem a plausible path from string theory to your pet project does not mean you won't appreciate finding one. Ever since ancient societies started tentatively groping for explanations of physical phenomena, the goal of physics has been to discover the most basic unifying, connected principles of the cosmos. And this was always implicitly true whether or not you were actively involved in the pursuit of such laws.

So I agree with Orzel that the failure to find a theory of quantum gravity would not generally impact the search for a better topological insulator or DNA tweezer. But somewhere, deep down, it would send a troubling message to every kind of physicist; that at its most fundamental level their science is disconnected and incomplete. Such a revelation might deprive only particle physicists of their jobs, but I am thinking it would leave many more physicists with a deep sense of unease and uncertainty about their own work.

Update: Chad Orzel has a response to my post up on his blog. I agree with him that we seem to disagree very little on this topic on a fundamental level. I have criticized the strong reductionist approach myself several times in previous posts, and as a chemist I appreciate how complexity can be as pleasing and important as simplicity.