Thursday, September 5, 2019

Aristotelian metaphysics and global physics

Too much of the contemporary ontological imagination is guided by the idea that the fundamental physical stuff in the world is discrete particles. Yet this is clearly dubious, since quantum mechanics (on non-Bohmian interpretations) suggests that the world is full of superpositions of states with different numbers of particles, while if discrete particles really exist, there had better be a well-defined number of them. Quantum mechanics instead suggests an ontology of the physical world where there is exactly one entity, “the Global Wavefunction”, whose physical state can be aptly represented as a vector in an infinite-dimensional vector space. And even if we didn’t have quantum mechanics’ vector-based approach on the table, we still wouldn’t be in an epistemic position to know that the right physics is based on particles rather than fields.

An ontology of material objects that composes these objects out of particles is held hostage to a particle-based physics that may well not be true. It would be best if one could work on the ontology of material objects without presupposing an answer to the question whether fundamental physical reality is field-like, vector-like or particle-like. I do not know if this is tenable. If it’s not, then the ontology of material objects needs to be done conditionally: If fundamental physical reality is of this sort, then material objects are like this.

Interestingly, some metaphysical problems may become easier given a non-particulate physical substratum. For instance, one of the hardest problems for a contemporary Aristotelian metaphysics has been the problem of what happens to particles that get incorporated into a substance, in light of the axiom that a substance cannot be composed of substances. But if we do not see fundamental physical reality as made of apparently substantial particles, the problem dissolves.

Today I want to sketch two Aristotelian approaches that take globalized vector- and field-approaches seriously. On the vector- and field-approaches, fundamental physical reality consists of a mere handful of entities: a single vector-like entity or several (hopefully no more than a dozen, and ideally only one) field-like entities. But being Aristotelian, we will think there are at least billions of substances: every organism is a substance. If these substances are to be related to fundamental physical entities, billions of them will have to be related to the same fundamental physical entities.

The ordinary substances on my stories will be organisms. There are billions of them. In addition to the ordinary substances, there are extraordinary substances: one for each of the handful of fundamental physical entities (fields or a vector).

My stories now diverge. On the first story, the billions of ordinary substances each encode and ground local features of the global fundamental physical entities. On a field version of the story, you encode and ground the features that the global fields have where you are located and your dog encodes and grounds the features that the global fields have where your dog is located (I am less clear on how to describe the vector version). This is not enough. For there aren’t enough organisms in the universe to ground all of the richness of the global fundamental physical entities: too much of the universe is lifeless. Thus, I propose that there are additional substances located where the organisms are not, and the features of these substances ground the rest of the features of the global fundamental physical entities. One way to run this story is to say that there is one of these additional substances per global fundamental physical entity, and each grounds the features of its corresponding global fundamental phsyical entity away from organisms. These additional substances are like swiss cheese, with the holes being filled with organisms like people and dogs.

On this version of the Aristotelian story—which can be varied in a number of ways—the global fundamental physical entities are not metaphysically fundamental. They are grounded in the many substances of the world.

On the second story, the global fundamental physical entities are substances. They are global substances. These global substances interact with the ordinary substances (there are many ways to spell out this interaction). We can now identify the matter of an ordinary substance x either with x’s powers and liabilities for interaction with the global substances or with the plurality of these global substances qua interacting with x.

There are many options here. Much detail to be worked out. Some options may be inferior to others, but I doubt in the end we will come to a single clearly best option.


Michael Gonzalez said...

Quick mention: There are Bohmian field theories.

But, a couple of more salient issues:

1) Why suppose that substances cannot be composed of other substances? After all, leaving fundamental physics entirely aside, cells seem to be alive, and therefore must be substances; and yet, we are composed of them.

2) The particle view doesn't come out of nowhere. It is the naturally expected consequence of all the fine-graining we do before we get to fundamental physics. If we can "zoom in" down to the the atom, and still be talking chemistry, then everything is quite particulate in nature, and the least surprising thing would be for those particles to be composed of yet smaller ones (like quarks and electrons and such) which have the properties of the standard model plus some non-local thing.

So, while another story may be true, I don't see why we shouldn't be strongly predisposed to the type of story that naturally seems to follow from the "zooming in" we've done so far -- especially considering that some of the strange, wave/particle sorts of phenomena have already been replicated at the macro scale (e.g. two-slit experiments with droplets of fluid).

3) Is it not strange to speak of the wave-function or vectors as though they were objects? Are they not mere mathematics? It would be like saying that the fundamental components of the world might be "nouns". For sure, they are described using nouns, but nouns aren't things and don't compose any real things. At any rate, this doesn't affect the field view, which made some sense to me and which might be a promising route both for Aristotelians and for physicists in general.

Alexander R Pruss said...

Ad 3: Speaking of the wavefunction or vector as though it were an object is a metonymy. The object is an object that is described by the wavefunction or vector. It's kind of like talking of a soccer ball as a sphere, even though mathematically a sphere is a locus of points equidistant from a center, and a soccer ball is not made of points.

Alexander R Pruss said...

I wonder if fields aren't rather like Aristotelian stuff?