Astrophysicist and NPR blogger Adam Frank recently summarized a contentious debate in the philosophy of physics and foundational physics communities as follows:
Carbon-nanotube physicists are so deep within the traditional modes of empirical (i.e., data-driven) scientific investigation that they can happily ignore what goes on in the halls of philosophy. But as Krauss’ example shows, cosmologists can push so hard and so far at the boundaries of fundamental concepts they cross over and fall prey to their own unspoken philosophical biases and misconceptions.
Frank does a decent job summarizing some of the more hotheaded points that physicists and their philosophers argue over. But leaving aside the fact that I’m pretty sure “carbon-nanotube physicists” are not a thing (and Frank’s jarring tendency to mix up “its” and “it’s” throughout the article, which is a personal pet peeve–don’t do it!), the claim that scientists who study nano systems don’t need philosophers is false, and insidiously so, for both those scientists and for philosophers of science.
Those of you who know me know this is the basic motivational claim of my dissertation. As I have not, ahem, published (written) that tome in full, let me give you a brief overview and a demonstration that I hope you will find convincing.
Point 1: Nano systems are defined by their scale, and specifically by novel material behaviors that appear at that scale and not at scales above or below it. For instance, the anisotropic metal nanoparticles I like to study exhibit localized surface plasmon resonance and quantum confinement, both scale-dependent properties that I encourage you to read about on Wikipedia (you know you already typed it in your search bar anyway). The carbon nanotubes Frank mentioned are often recognized as the strongest known materials by some measures, as well as having the ability to conduct electricity in a way bulk carbon cannot (Pro-tip: do not attempt to rewire your house with pencil leads) and there’s a whole Wikipedia page devoted just to their potential society-changing applications.
Point 2: Modeling properties of interest in nano systems in order to obtain, systematize, explain or predict that empirical data Frank referred to cannot be done without reference to the scale of the system. Because the properties of interest in nano systems are scale-dependent (Point 1), representations of those properties will in some way refer to scale.
Point 3: It turns out that a lot of material structure changes at the nano scale. The bonding behaviors (strengths, lengths, angles, crystal packing structures) that we model with molecular models and the macroscopic behaviors (ductility, malleability, thermal transport, resistance to cracking) that we model with, well, macroscopic models–sometimes called phenomenological models–are themselves based in the molecular and macroscopic scales. What actually happens at the nano scale is a little different from what happens at these molecular or macroscopic scales, and so
Point 4: Theoretical models of nano systems have to accommodate changes in material behavior based on changes in scale. This means the assumptions of the models referred to in Point 3 have to change when the models are applied to nano systems, and it turns out that a lot of physicists, chemists and materials scientists are struggling with how to systematize and justify the ways in which those changes happen, which leads us to
Point 5: Philosophers of science can help figure out how to systematize and justify those changes. That’s what we are trained to do, to highlight the assumptions being made by a particular model and question the extent to which those assumptions apply, and whether there are better ones out there.
I’m not saying philosophers are the only ones who can do this; but as far as I can tell from reading a lot of nano journals and talking to a lot of nano scientists, it’s not being done by the scientists themselves. Probably because it’s not quite as exciting to scientists, or as grant-money-conducive, as actually making the nano systems or the models themselves. But, let me put it to you this way: I talked to a professor yesterday whose whole job is to built computer models of nano systems. He’s a very smart guy who does good work and figures out valuable information; he spends a lot of time with that empirical data Frank mentioned. He didn’t realize that the capping ligands he was modeling were actually holding together his nanoparticle, and that the ‘bare,’ uncapped gold nanoparticle in his model was an unrealistic system (i.e. not a physically or chemically stable configuration of atoms). Now, it turns out that the bare nanoparticle in the model ends up being a good model of some material properties of interest, and whose job is it to explain why that highly unrealistic artifact of the model ends up working so well to describe phenomena observed in the world? Likewise, pace Frank’s article, whose job is it to explain why a particle-free quantum field fits the definition of “nothing”? Not necessarily the scientist who came up with the model of the nanoparticle or the quantum field, as Frank clearly and concisely argues.
The job of philosophers has always been to monitor and improve reasoning processes–ask yourself if Socrates was doing anything else with his incessant questioning. That job is one that needs to be done in all areas of science (and elsewhere), not just foundational physics. It is not necessarily the job of “carbon-nanotube physicists” to notice that the computational models they use rely on assumptions that are incompatible with reality, if the models are working well; that’s the essence of the empirical mindset to which Frank refers.
When science as a practice arose out of increased specialization and professionalization from “natural philosophy”, some of the kinds of questions that used to get asked in lab drifted down the hall to the philosophy classroom. That’s fine for now, as long as the philosophers who ask the questions keep getting up and walking back down the hall to the labs every now and then to talk to the scientists–and the scientists listen. This is Frank’s point, which is well taken. It just applies more broadly than even he admits.
Still not convinced? Try this additional anecdote on for size (heh). When physicists model material systems, they often talk about “boundary conditions,” which in solid materials often refers to the surface of the material. In bulk materials, the fraction of the atoms in the material that lie on the surface of the material is infinitesimal, and the behavior of those surface atoms thus doesn’t really have much influence on the behavior of the material at large. So it’s okay to ignore boundaries and use macro-scale models to understand, predict, and explain the behavior of materials. But once materials get down to the nano scale, significant proportions of the atoms in the material actually lie on the surface of the material (See chart above). So the behavior of surface atoms can no longer be ignored, because it becomes the dominant behavior of the system.
This fact is responsible for a lot of the interesting properties of nano systems–surface plasmon resonance, quantum confinement, differences in conductivity and catalytic behaviors between nano and macroscopic systems. It is also not only a scientific fact; it is a conceptual fact, the kind that is the province of philosophers over and above scientists. When the “surface” of a material stops being an infinitesimal part of the material and starts being a significant fraction of the matter in the material, what it means to be a surface changes. It turns out, consequently, that our very concepts are scale-dependent. Philosophers of mind and language, who deal with how words refer to parts of the world and how information about those parts of the world are stored in our brains, have to grapple with the implications of problems in the modeling of nano systems just as much as the scientists modeling those systems do. And the fruits of their labors might end up influencing further scientific advances–a standardization, for instance, of the way in which surfaces are computationally modeled at various scales.
The bottom line here is that whatever “carbon nanotube physicists” are, they need philosophers and philosophers need them, no matter what Adam Frank or Lawrence Krauss have to say about it.