6.4 Philosophy of levels

There are some who doubt that we need a philosophy of generative degrees. In all the apparent examples of multiple generative levels given so far, many physicists and philosophers of physics will assert the particular reality of one of the levels and say that the prior levels are only mathematical devices for predicting the behavior of their chosen real level.

For example, some assert in electromagnetic theory that only the field tensors (incorporating the electric and magnetic vector fields) are real and that the vector potential (incorporating the electrostatic potential) is a calculational device with no reality. They note the gauge uncertainties in the vector potential, which for electrostatics is the arbitrariness in setting the level of zero potential energy. Against this, many have said that the scattering of electrons in the Bohm-Aharonov experiment is most succinctly explained in terms of the vector potential, not the field tensor. It turns out that it is loop integrals of the vector potential which carry physical significance. I conclude that there are non-trivial physical and philosophical questions about the relative ‘reality’ of potentials and forces which require, not immediate preferences, but considered responses.

We saw how reductionist tendencies may be manifest in quantum theories. ‘Decoherent history’ accounts of quantum mechanics want to keep the wave function according to the Schrödinger equation. Such accounts deny that macroscopic outcomes occur in reality but only allow them to be approximate appearances. The founders of quantum theory such as Bohr and Wheeler, however, took the opposite view, saying that an electron is only real when it is being observed--when it makes the flash of light at a particular place--not while it is traveling. In their view, the Hamiltonian and wave function are calculational devices and nothing real, having only mathematical reality as portrayed by the mathematical name ‘wave function’.

The views which make prior or later levels into mere mathematical tricks can be critiqued from the point of view of dispositional essentialism. This view encourages us to not invoke arbitrarily mathematical rules for the laws of nature, but, as suggested above, to replace the role of laws with that of the dispositional properties of particular objects. To apply Occam’s criterion, the question is whether it is simpler to have multiple kinds of objects existing (even within multiple generative levels), each with simple dispositions, or simpler to have fewer kinds of existing objects but with more complicated laws governing their operation.

The previous chapter showed many examples of multiple generative levels, each composed of derivative dispositions. The questions of simplicity and adequacy will have to be examined in these cases as well. My conclusion is that the concepts introduced here enable us to take a more comprehensive and universal view of physical dispositions (such as those of potentials and forces or of Hamiltonians and wave functions) that appear to be ad hoc when taken individually. Furthermore, the logic of multiple generative levels is sufficiently general, such that it can be applied to wide range of processes. We can even consider applying it to God.