5.2 Derivative dispositions

Energy and force

If we look at physics and at what physics regards as part of its central understanding, we see that one extremely important idea is energy. Physics talks about kinetic energy as energy having to do with motion and potential energy as energy having to do with what would happen if the circumstances were right. If we look at definitions of force and energy which are commonly used to introduce these concepts, we find definitions like

• force: the tendency F to accelerate a mass m with acceleration F/m.
• energy: the capacity E to do work, which is the action of a force F over a distance d, according to E=Fd.
• potential energy field: the field potential V(x) to exert a force given by F= - dV(x)/dx if a test particle is present.

Furthermore, we may see a pattern here:

• potential energy field: the disposition to generate a force, and
• force: the disposition to accelerate a mass, and
• acceleration: the final result.

I take these as examples of two successive derivative dispositions, where the effect of one disposition operating is the generation of another. An electrostatic field potential is a disposition, the manifestation of which--when a charge is present--is not itself motion, but is the presence now of a derivative disposition, namely a force. The manifestation of a force--when acting on a mass--may or may not occur as motion, as that depends on what other forces are also operating on the mass. The production of a force by a field potential does not appear to be something that occurs by means of the rearrangements of microscopic parts. It appears to be more fundamental and almost sui generis. It appears that field potentials, force and action form a set of multiple generative levels. This situation is in need of philosophical inspection.

Admittedly, many physicists and philosophers often manifest here a tendency to say that ‘only potential energy is real’, or conversely perhaps that ‘only forces are real’, or even that ‘only motion is real’, and that in each case the other physical quantities are simply calculational devices for predicting whichever is declared to be real. Please apply a contrary tendency and resist this conclusion. In Section 6.4 I will evaluate such reductionist strategies and discuss the comparative roles of mathematical laws and dispositional properties within a possible dispositional essentialism.

Sequences or levels?

We normally think of energy, force and acceleration as the sequential stages of a process. However, in nature, there is still energy even after a force has been produced, and forces continue to play their roles both during and after accelerations. This means that energy does not finish when force begins, and force does not finish when acceleration begins, but, in a more complicated structure, all three continue to exist even while producing their respective derivative dispositions. The best way I can find to explain this more complicated structure is that of a set of ‘multiple generative levels’. We can think of a ‘level of energy’ as persisting even while it produces forces. Since we take forces as existing even while they produce accelerations, we must allow ourselves to talk of a ‘level of forces’ as existing continuously. The idea of a ‘level’ is a spatial metaphor for what is not itself spatial, but the metaphor still serves to illustrate my argument.