Complexity and Emergence – Essential Physics for Our Troubled Times

Lars English, Dickinson College

Times have been changing in physics. No, I’m not talking about string theory, multiverses, dark matter, or any other buzzwords in the news lately. Something more fundamental is happening. There is a new mindset that challenges old assumptions, and its implications arguably extend far beyond the discipline. But to appreciate just how much things have shifted, and why it matters, it is useful to start with a brief history.

The story of physics begins in earnest with Isaac Newton. His formulation of mechanics in the late 17th century commonly marks the birth of our discipline. In fact, classical mechanics (as it’s now called) proved so successful, so durable, that the first and second revolutions had to await the early 20th century. First came the sudden appearance of Einstein’s theory of relativity, and then the gradual arrival of quantum mechanics. In the late 1940s and 50s, a third paradigm shift unfolded in the form of the first quantum field theory, which would culminate in the standard model of particle physics. Now we are in midst of what feels like a forth paradigm shift — towards complexity and emergence — one that can perhaps trace its early beginnings to the chaos theory of the 1970s.

But let’s go back to Newton for a second. Ever since his famous deduction of the mathematics of gravity, physicists have appreciated the power of simplicity. Newton had considered interactions between only two objects at a time — earth and moon, or earth and apple. Such “two-body” problems are usually mathematically tractable, and this explains their appeal in physics. Physicists kept coming back to them again and again. In the 1920s, for instance, the young quantum wave mechanics trained its sight on a single electron around a single proton — aka hydrogen. In the 1940s, it was the electron and the photon. What all these advances shared in common was the “divide-and-conquer” strategy. It was an approach that isolated only a few parts in order to ferret out some of the general laws that govern them, only to then use those laws in more complex situations. One could label this strategy reductionist, but it has been highly successful in physics over the centuries.

Now, however, the limitations of this kind of approach are becoming increasingly apparent. The strategy of breaking things apart, studying the parts in isolation, and from there reconstructing the whole, does not work well on a broad range of new and important problems. These range from making sense of shape-memory alloys, to designing the electromagnetic metamaterials used in cloaking; from understanding the next generation of high-temperature superconductors, to investigating the weird topological excitations that could form the basis for quantum computers. Then there are problems somewhat outside of physics proper that are attracting many physicists, like studying the robustness or fragility of the nation’s electrical grid.

Such modern problems share a couple of common features that preclude a reductionist approach, such as nonlinearity, feedback, and self-organization. They typically involve a large number of strongly interacting parts (more than just two). By tackling such problems, physicists have had to simultaneously cultivate a new mindset that recognizes as a central theme the possibility of emergence, namely the notion that the whole cannot be understood through its parts alone.

I think it is fair to say that most physicists tend to be pragmatic, non-ideological people, and from a practical standpoint, the reductionist strategy works well for certain types of scientific problems, and not so well for others. Yes, physics is now busy crafting an alternative framework going by the name of emergence, but this is motivated by a desire to understand nature in its full complexity and manipulate it. Meanwhile, however, reductionism has long left the exclusive realm of physics and made its way into the larger society, where it continues to derive power from its close former association with physics.

Here is the problem. Reductionism turned philosophy, devoid of scientific context, encourages an unrealistic expectation and a dangerous intellectual overreach in its followers. Once adopted, it has a way of spreading out in all directions to infect one’s thinking. How?

Reductionism says that nothing fundamentally novel can happen when the parts of a system assemble to form the whole. It asserts that the behavior of the whole is already contained in the properties of the isolated parts. Moreover, the laws governing the parts can allegedly also be used to derive the rules operating at the system level, at least in principle. Within this old paradigm, then, the science discovered by microbiologists about DNA transcription and protein production in cells is already fully contained within the laws of quantum mechanics. High-level cognitive function can ultimately be reduced to our genes. Consciousness is a by-product of the firing of neurons — the list goes on.

The logical conclusion of such a mindset is that ultimately there are only the elementary particles and the laws they obey. Ultimately, we are all just collections of myriad particles that move about in random fashion, collide with one another and interact via fields that are themselves comprised of particles. All the rest can be reconstructed from this layer of reality, and since this layer does not contain any deeper meaning, such meaning is also absent at any other layer. We are left with a sweeping scientific materialism.

The great physicist Philip Anderson once lamented that molecular biologists “seem determined to reduce everything about the human organism to ‘only’ chemistry, from the common cold to all mental disease to the religious instinct.” It is indeed a fundamentally nihilistic view of the world. If science demands reductionism, and reductionism implies materialism and nihilism, do we really want to place our trust in science? It is a fair question — some of the broader science skepticism may be attributable to a rejection of such implications.

Things look no better when we transport the reductionist mindset into the arena of sociology. Here it nudges us to entertain and nurture a suspicion that the reason certain societies happen to be presently wealthy or poor must be traceable back to the individuals making up these societies. It furthers precisely the “cultural” or “ignorance” hypotheses of wealth and poverty that Daron Acemoglu and James Robinson reject in their recent book Why Nations Fail as poor predictors of the future. Such hypotheses usually go hand in hand with ethnic or racial prejudice, and they deceptively insinuate that the status-quo is somehow preordained, unchangeable and genetic.

In philosophy this is referred to as the fallacy of composition, and in physics we encounter some of the most dramatic illustrations that expose this type of fallacy. Think of diamond and graphite — two substances entirely composed of carbon atoms. While their microscopic composition is exactly the same, their macroscopic properties are nothing alike. Anything you could measure about them — mechanically, optically, electrically, thermally, acoustically — would all be vastly different. There is no overlap. Nevertheless, if you burned a piece of graphite and a piece of diamond, the carbon dioxide you get would be indistinguishable. This example (and many others within material science) gives us a glimpse of emergence as articulated in the physical sciences.

The central premise of emergence is that the whole is qualitatively more than the sum of its parts. Much more important than mere composition is structure, organization, or architecture — things that transcend the individual parts. Furthermore, the architecture acts back on the individual parts and affects their behavior — a phenomenon sometimes called downward control. In the graphite versus diamond example, it is the layered honeycomb structure of graphite that nudges the individual carbon atoms to manifest certain electron states, whereas the tetrahedral diamond structure forces carbon electrons into different orbitals. At the same time, of course, the whole cannot demand of its parts what these are not somehow capable of doing. We can speak of a kind of bi-directionality and a co-emergence between levels.

What are the larger implications that follow from the limits of reductionism that are now increasingly appreciated in physics? In a nutshell, the emergence revolution saves us from all kinds of ominous implications that strict reductionism demands. We attain a flexibility of mind where we can admire the wondrous world of sub-atomic particles while not immediately thinking that everything reduces to it. We don’t see science as a hierarchical ladder with a bottom (the “fundamental”) and a top (the “derivative” and “applied”), but as an interweaving tapestry. We avoid a scientific materialism — all-encompassing in scope — that denies among other things the reality of consciousness and human agency. We stay clear of racist or sexist narratives so pervasive in human thinking, as we appreciate the larger feedback loops ever-present in society. We can easily acknowledge stereotype threat as a functioning mechanism with causal powers (i.e., the well-established effect where the mere awareness of a societal stereotype against you suppressed your performance). We can understand gender as a social construct without then going to the extreme of rejecting chromosomes.

In short, emergence is an indispensable idea for our troubled times. It allows us to avoid conceptual extremes in an intellectually honest way. Physics can no longer be enlisted as an ally by opponents to these ideas. Much of physics has become a proponent of emergence, and physicists have put their own distinctive stamp on it. The result will be novel materials, yes, but the ramifications will go far beyond the practical applications. We would do well to take note.

english@dickinson.edu

These contributions have not been peer-refereed. They represent solely the view(s) of the author(s) and not necessarily the view of APS.