Condensed matter is the largest discipline within physics. It has enormous influence on the average person’s daily life. As of next May, it will even underpin our fundamental system of units. Nonetheless, the field flies under the popular radar, routinely upstaged in the press, television, and popular literature by news of astrophysical exotica and the quest for new elementary particles.
The situation originates in the diverse nature of condensed matter, the tendency of researchers to fall back on jargon, and the companion challenge of explaining its depth and meaning in an inspiring way. It’s important that we recognize those issues and broaden the appeal of the field through improved communication, for the good of both the condensed-matter discipline and physics as a whole.
Even among physicists, condensed matter has traveled a long path to acquire stature. Although the first quantum treatments of solids appeared shortly after the formulation of quantum mechanics, condensed matter as a distinct discipline did not really develop until after World War II. Respect was hard-earned, as work on solids and liquids was viewed by many as closer to engineering, metallurgy, and chemistry. (The story is told well in the recent book Solid State Insurrection, by Joseph Martin; see also the article by Martin in Physics Today, January 2019, page 30.) Some argued that the emerging specialty was mundane, lacking profundity compared with nuclear or particle physics. Wolfgang Pauli famously said, “Festkörperphysik ist eine Schmutzphysik”—solid-state physics is the physics of dirt. Murray Gell-Mann dubbed it squalid state.
Around 1970, solid state was replaced by the term condensed matter, a rebranding that was an attempt to show that the field involves much more than traditional solid-state physics. The modern perspective emphasizes that condensed matter encompasses great breadth, focused on identifying and understanding the collective states and excitations that emerge when large numbers of atoms (or electrons or molecules) are brought together. Unfortunately, the name also requires a paragraph of explanation for an average person to understand.
The names of other parts of physics are much more evocative and explanatory. Astrophysics conjures up images of black holes with glowing accretion disks and supernovae, with voiceovers by Carl Sagan explaining that we are all star stuff. Say particle physics and people immediately picture enormous accelerators and detectors, with commentary by Lisa Randall about vibrating strings and rolled-up extra dimensions. Plasma physics gets to the point, whether it makes people think of solar flares, fusion reactors, or glowing plasma ball desk toys.
Rebranding condensed matter as physics of materials might help alleviate the problem. But changing the name won’t help with the biggest challenge: Condensed matter is generally complicated and at the same time so ubiquitous that it blends into the background without sounding inspiring to the public. Consider the concept of reciprocal space. Instead of talking about the positions of particular atoms or electrons, condensed-matter physicists often talk about spatial frequencies, like the number of regularly spaced atoms or the number of cycles of an electronic wavefunction per unit distance. It’s a way of thinking about periodic solids that’s incredibly mathematically powerful. But it is also very far removed from the real-space way that nearly everyone who isn’t a condensed-matter physicist visualizes everything.
Such language issues were summarized neatly last year by the outstanding Quanta science journalist Natalie Wolchover. After the 2017 announcement that researchers at the Laser Interferometer Gravitational-Wave Observatory had won the Nobel, she tweeted in jest, “Thrilled they won, thrilled not to spend this morning speed-reading about some bizarre condensed matter phenomenon.” In the popular press, news of colliding black holes and speculation about stringy multiverses are mainstream, but condensed matter is obscure and byzantine. The large number of condensed-matter physicists out there—about a quarter of physics PhD recipients do their dissertation in condensed matter—tells us that if physics students get over that hump, the subject is intellectually compelling. But most nonscientists just see the barrier.
Condensed matter also faces a perceived shortfall in inherent excitement. Black holes sound like science fiction. The pursuit of the ultimate reductionist building blocks, whether through string theory, loop quantum gravity, or enormous particle accelerators, carries obvious profundity. Those topics are also connected historically to the birth of quantum mechanics and the revelation of the power of the atom, when physicists released primal forces that altered both our intellectual place in the world and the global balance of power.
Compared with this heady stuff, condensed matter can sound like weak sauce: “Sure, they study the first instants after the Big Bang, but we can tell you why copper is shiny.” The inferiority complex that this can engender leads to that old standby: claims of technological relevance (for example, “this advance will eventually let us make better computers”). A trajectory toward applications is fine, but that tends not to move the needle for most of the public, especially when many breathless media claims of technological advances don’t seem to pan out.
It doesn’t have to be this way. It is possible to present condensed-matter physics as interesting, compelling, and even inspiring. Emergence, universality, and symmetry are powerful, amazing ideas. The same essential physics that holds up a white dwarf star is a key ingredient in what makes solids solid, whether we’re talking about a diamond or a block of plastic. Individual electrons seem simple, but put many of them together with a magnetic field in the right 2D environment and presto: excitations with fractional charges. Want electrons to act like ultrarelativistic particles, or act like their own antiparticles, or act like spinning tops pointing in the direction of their motion, or pair up and act together coherently? No problem, with the right crystal lattice. This isn’t dirt physics, and it isn’t squalid.
Sometimes a colleague will ask, Why should we care? What difference does it make if the general public doesn’t know or care about condensed-matter physics? Does it really matter if physics colloquially means only high-energy physics? One response is obviously self-serving: Support often follows excitement. If we can’t explain to the public, to governments, and to funding agencies why our work is important and exciting, then many fewer of us will be able to do it, and the best and most talented students will not join us.
Beyond that, I believe that it’s generally good for people to have a sense of how the world around us works and to appreciate that the technology they rely on isn’t magic but instead the yield of profound intellectual achievement. Some science writers are very gifted and can make aspects of this come alive—see, for example, Wolchover’s recent discussion of strange metals. Some scientists can bridge this divide as well, such as Mark Miodownik and his great book, Stuff Matters. Conveying the richness and depth in the physics of materials to a broad audience is a major challenge, but one worth the effort, whether through our own outreach or by working with science journalists.
Condensed-matter physics contains some amazing tales if told well, and it’s important that we make those stories accessible and give them an audience.