Is it true, as Bertrand Russell claimed, that the laws of nature as we know them involve only functional relations between successive states, with no reference to “causes” and “effects”? And if it is true, is that because of all the possible laws of nature, acausal ones turned out to be the ones that are instantiated, or are acausal laws the only ones we’ve ever formulated to model the real world with?
In fact, when using the equations intended to describe the physical world, one most often does have an idea which term is the cause and which term is the effect. For example, in Newton’s Law
everybody intuits that it is the force that causes the acceleration and not vice versa. Or when considering the diffusion of heat
we know that it’s the temperature gradient that drives heat, rather than vice versa. Or in the Schroedinger equation
the Hamiltonian operator drives the evolution, not vice versa.
The question is whether this asymmetry is in the equations themselves or is imposed by a metaphysical intuition of their users.
For equations like the above, we might postulate that the effect is always the term that appears under the highest time derivative. This rule does match my intuition in every case I’ve thought of. One source of confusion, I think, is that philosophers tend to insist on seeing causes and effects as existing at different instances of time. I think it would be closer to the truth to say that cause and effect are always simultaneous. The effect is not the subsequent state, but the time derivative itself, which exists simultaneously with its cause.
Question: is the language of causality inappropriate for relations that don’t involve time derivatives? I’ve been reading John Losee’s Theories of Causality (following its mention on Edward Feser’s blog), and it seems that some philosophers have said this. I do have an intuition that in
it’s the field that’s the effect of the charge density. However, this intuition is not as strong as the other. One could reduce this case to the previous ones by noting that the above is actually the time component of the equation
and the spatial components (Ampere’s Law) have time derivatives in them. However, my intuition was there long before I knew this.
One might ask what I make of this
Would I say that zero is the cause of the magnetic field having no divergence? That would be silly. I suppose one could add a magnetic monopole density to the right hand side and say that the cause of having no divergence is that this density happens to be zero. However, I’m uncomfortable with ascribing real causative power to absences and with irreducible references to couterfactuals (issues that also comes up a lot in Losee’s book). The alternative is to say that being divergenceless is the default for things like the magnetic field, that given its nature it needs an external cause only to explain deviations from this.
Causality is something I’m very interested in but that I’ve only just started thinking about seriously, so I’m going to hold off on making any conclusions, except for the following. It is not clear that asymmetries in physical equations cannot be used to distinguish causes from effects.
Filed under: philosophy of science |