Tuesday, July 11, 2017

Special Relativity and physicalism

There is, I think, an underexplored argument against physicalism on the basis of Special Relativity and the unity of apperception.

The unity of apperception seems to imply that there is always a non-relative fact of the matter whether two perceptions are co-perceived: whether I am feeling cold at the same time as I am seeing a red cube, say. (Einstein’s own definition of simultaneity presupposes this: he defines the simultaneity of two distant events in terms of the co-perception of light beams from them.) When two perceptions are co-perceived, they are simultaneous. So there must be a non-relative simultaneity in the mind. But it is very unlikely that all co-perceived perceptions are grounded in exactly the same place in the brain. And simultaneity between physical events happening at different locations is always relative. So perceptions aren’t physical events.

I don’t think this is a very strong argument, though. It’s open to the physicalist to say that perceptual time is different from physical time, and perceptual simultaneity need not correspond to physical simultaneity. The best version of physicalism is functionalism. Now imagine embedding a causally isomorphic copy of Napoleon in a universe with four spatial and one temporal dimension, but in such a way that all of the four-dimensional life of Napoleon is realized within the four spatial dimensions, at a single temporal instant. The three spatial dimensions of Napoleon would be realized within three spatial dimensions, and the temporal dimension of Napoleon would be realized within the fourth spatial dimension. All the diachronic causation in the life of our world’s Napoleon becomes simultaneous causation in the new world. All of the life of the Napoleon-copy is then lived at a single instant of physical time, but it has all of the causal richness that Napoleon’s life had, and it is causally isomorphic to Napoleon. It is plausible, then, that the functionalist will say that Napoleon-copy has the same mental life as Napoleon. But Napoleon-copy’s mental life is all at once physically. So the functionalist can say that mental time is not the same as physical time—without budging from physicalism.

Now, I think some people will find this kind of a separation between physical time and mental time to be unacceptable. If so, then they shouldn’t be physicalists. I myself am not a physicalist, but I find the separation between physical and mental time quite plausible. After all, don’t we say that sometimes time runs faster than at other times?


Ward said...

What kind of non-physicalism do you accept ?

IanS said...

I agree with the conclusion, but I’m not so sure about the argument.

It is not clear, pace Kant, that consciousness really is unified. Speaking for myself, I sometimes experience one event as clearly happening before another, and sometimes not. But I rarely experience two events as positively simultaneous. I recall an experiment (sorry, I don’t have a reference) in which people listened to speech with a click sound added. They could report hearing the words and the click, but were unable to say in which syllable the click had occurred.

In the case of feeling cold and seeing red, I’m sometimes attending to one sometimes to the other but rarely to both together. I infer that I’m experiencing both simultaneously, but I don’t directly experience them that way. Hume’s famous ‘bundle’ passage springs to mind (though his point was different).

I doubt that Einstein’s concept of simultaneity of distant events requires conscious perception. Wouldn’t a pair of photon detectors and some electronics suffice?

It seems unlikely that relativity directly limits our ability to experience simultaneity (if indeed we do experience it). No parts of our brains are more than 10^(-9) light-seconds apart. But 10^(-9) seconds is orders of magnitude less than the time scale in which conscious experience changes (say, 10^(-1) seconds).

To model Napoleon as described, you would have to represent time in this world by a space-like dimension in the 5-d world. Arguably, cause-and-effect is intrinsically temporal, so it’s not clear that you could make a ‘causally isomorphic’ model in this way.