Physics, Plato and epistemology

In a recent Scientific American article, the late physicist Victor Stenger, along with authors James A. Lindsay and Peter Boghossian argue that, while not acknowledged as such, some interpretations of quantum mechanics are implicitly platonic (with a lower-case p).

We will use platonism with a lower-case “p” here to refer to the belief that the objects within the models of theoretical physics constitute elements of reality, but these models are not based on pure thought, which is Platonism with a capital “P,” but fashioned to describe and predict observations.

The authors suggest that while early 20th century physicists like Einstein, Bohr, Schrödinger, Heisenberg, and Born considered the philosophical implications of their discoveries, after World War II, the next generation of scientists judged this effort unproductive. Most physicists, they say, now agree that observation is the only reliable source of knowledge, and that only testable ideas are useful (hence the falling out of favor of string theory). But the authors also argue that this younger generation of physicists “went ahead and adopted philosophical doctrines, or at least spoke in philosophical terms, without admitting it to themselves.” They justify this, in part, with a reference to physicist David Tong who claims in a 2012 Scientific American article that the particles to which experiments refer are illusions.

Physicists routinely teach that the building blocks of nature are discrete particles such as the electron or quark. That is a lie. The building blocks of our theories are not particles but fields: continuous, fluidlike objects spread throughout space.

This view is explicitly philosophical,” the authors say, “and accepting it uncritically makes for bad philosophical thinking.”

I enjoyed this twist on the partnership of the observable with the abstract – namely their using the mathematics that captures the data to ‘reveal’ a platonic view.  It’s not clear to me that this is a fair characterization of Tong’s observation, but it is an interesting one. The authors do distinguish between realists (those who find the mathematical objects to be representative of reality) and instrumentalists (those who claim that reality just constrains what may be observed, but need not correspond to the mathematical models used) and their critique is mostly aimed at the realists. But the article is largely responding to recent criticisms of philosophy heard from physicists like, Lawrence Krauss and Neil deGrasse Tyson.   The authors suggest that many physicists have chosen a philosophical perspective and that there are problems associated with their not acknowledging this.

The direct, platonic, correspondence of physical theories to the nature of reality, as Weinberg, Tong and possibly Krauss have done, is fraught with problems: First, theories are notoriously temporary. We can never know if quantum field theory will not someday be replaced with another more powerful model that makes no mention of fields (or particles, for that matter). Second, as with all physical theories, quantum field theory is a model—a human contrivance. We test our models to find out if they work; but we can never be sure, even for highly predictive models like quantum electrodynamics, to what degree they correspond to “reality.” To claim they do is metaphysics.

I understand the admonition, but here’s the part in which I am most interested:

Many physicists have uncritically adopted platonic realism as their personal interpretation of the meaning of physics. This is not inconsequential because it associates a reality that lies beyond the senses with the cognitive tools humans use to describe observations.

In order to test their models all physicists assume that the elements of these models correspond in some way to reality. But those models are compared with the data that flow from particle detectors on the floors of accelerator labs or at the foci of telescopes (photons are particles, too). It is data—not theory—that decides if a particular model corresponds in some way to reality. If the model fails to fit the data, then it certainly has no connection with reality. If it fits the data, then it likely has some connection. But what is that connection? Models are squiggles on the whiteboards in the theory section of the physics building. Those squiggles are easily erased; the data can’t be.

(emphasis added)

What is the relationship between those squiggles and reality, or even between the data and the mathematics that turns the data into the signature of an event?  These are questions filled with meaning.  And one of the most important points made is this one:

All of the prominent critics of philosophy whose views we have discussed think very deeply about the source of human knowledge.

Physics is as much concerned with how knowledge is acquired as it is about the nature of physical reality. The senses are extended with the use of detectors – mechanical (and sometimes very large) sensory mechanisms that we’ve learned to build. And this sensory data can only be understood when run through analysis programs that are grounded in mathematics, and whose meaning is expressed mathematically. If the detectors extend the senses, perhaps the mathematics extends cognition.  The fact that the data can now significantly challenge our conceptual abilities should be a fact that contributes to both epistemological discussions and physics discussions. And epistemological discussions inevitably lead to questions about cognition.

Certainly one cannot have a productive discussion about the nature of reality without the data that physics provides. And I agree that this limitation does not apply to other areas of philosophy like ethics, aesthetics, and politics. But epistemology is something to which the sciences can make a contribution, and this may very well spring from philosophers of science.

Here’s another point well taken:

…those who have not adopted platonism outright still apply epistemological thinking in their pronouncements when they assert that observation is our only source of knowledge.

Mathematics consistently raises the question, “what does it mean to know something.” A teacher of mine once lamented the fact that we can’t allow children to rediscover mathematics because there isn’t enough time, because now so much is known. What is it that’s known? The partnership, in physics, of mathematics with observables that lie beyond the range of the senses should fuel epistemological discussions, and not only ones inspired by mathematics and physics, but ones that could also inform them.

There is some interest among physicists about current research in cognitive science. Cosmologist Max Tegmark, for example, has taken an interest in Giulio Tononi’s integrated information theory of consciousness. In a recent TED talk, I believe Tegmark proposed that the only difference between a structure that exists mathematically and one that also exists physically is how the information is instantiated. This is consistent with something that David Deutsch’s once said – that the brain faithfully embodies the mathematical relationships and causal structure of things like a quasars, and does so more and more precisely over time.  He made the following observation about brains and quasars:

Physical objects that are as unlike each other as they could possibly be can, nevertheless, embody the same mathematical and causal structure and do it more and more so over time.

These are thoughts that touch equally on epistemology and the nature of reality.

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