Saturday, May 2, 2020

Relativity, brains and the unity of consciousness

I was grading undergraduate metaphysics papers last night and came across a very interesting observation in a really smart student’s paper on Special Relativity and time (I have the student’s permission to share the observation): different parts of the brain have different reference frames, and so must experience time slightly differently.

Of course, the deviation in reference frames is very, very small. It comes from such facts as that

  • the lower parts of the brain are closer to a massive object—the earth—which causes a slight amount of time dilation, and

  • we are constantly wobbling our heads in a way that makes different parts of the brain move at different speeds relative to the earth.

Does such a small difference matter? As I understand their argument, my student thought it would make the A-theory less plausible. For it makes it questionable whether we can say that we really perceive the true objective now in the way that A-theorists would want to say we do. That’s an interesting thought.

I also think the line of thought might create a problem for someone who thinks that mental states supervene on physical states. For consider the unity of consciousness whereby we are aware of multiple things at once. If the consciousness of these different things is partly constituted by different chunks of the brain, then it seems that what precise stream of consciousness we have will depend on what reference frame we choose. For instance, I might hear a sound and feel a pinch at exactly the same moment in one reference frame, but in another reference frame the sound comes before the feeling, and in other the feeling comes before the sound. But that seems wrong: the precise stream of consciousness should not depend on the reference frame.

This shows that if the order of succession within the stream of consciousness does not depend on the reference frame (and it is plausible that it does not), then the precise stream of conciousness cannot supervene on physical states. This is clear if there is no privileged reference frame in the physical world. But even if there is a metaphysically privileged reference frame as A-theorists have to say, it seems reasonable to say that this frame is “metaphysical” rather than “physical”, and hence a dependence of consciousness on this frame is not a case of supervenience of mind on the physical.

Here is what I think we should say: If the A-theory is true, then the mind somehow catches on to the absolute now. If the B-theory is true, then the mind has its own subjective timeline, which is not the timeline of the brain or any part of it.

I think a really careful materialist might be able to affirm the latter option, by analogy to how in a modern digital computer, even though at the electronic hardware level there is analog time (perhaps itself an approximation to some frothy weird quantum time), synchronization of computation to clock ticks results in the possibility of abstracting a precisely defined discrete time that “pretends” that all combinatorial logic happens instantaneously. Roughly speaking, the assembly language programmer works with respect to the discrete time, while the FPGA programmer works primarily with respect to the discrete time but has to constantly bear in mind the constraints that come from the underlying analog time. However, the correspondence between the two levels of time is only vague. Similarly, I think that it is likely that the connection between the mind’s timeline and the physical timelines is going to suffer from vagueness (though perhaps only epistemic). How philosophically happy a materialist would be with such a view is unclear, and there is a serious empirical assumption here for the materialist, namely that the brain has a global synchronizing process similar to a microprocessor’s or FPGA’s synchronizing clock. I doubt that there is, but I know very little of neuroscience.


Martin Cooke said...

Hi again Alex, regarding your "it makes it questionable whether we can say that we really perceive the true objective now in the way that A-theorists would want to say we do," I think that it might do the opposite.

Presentists like myself say that the true objective now is just this present moment. Clearly it is something that includes perceptions, and those perceptions are measured by psychologists as taking times longer than those relativistic differences. So, this observation of your student's does not make that situation any worse for us.

However, a bigger problem for us is the way that relativity makes spacetime seem real. And this observation of your student's might actually help with that problem. Presentists have an answer to the problem of perceptions taking times: the perception is primary, the measurements are secondary, involving a mathematical dimension that is not a real dimension. Since that dimension of measurements is not real, its relativistic aspects have nothing to say about the reality of spacetime.

Alexander R Pruss said...


The perceptions take times longer than the relativistic differences, but there will still be starts and ends to the perceptions. And it will be metaphysically possible to have a case where the starts of two perceptions are sufficiently close together in time that, given supervenience on the physical, which perception comes first will depend on the reference frame.

"Presentists have an answer to the problem of perceptions taking times: the perception is primary, the measurements are secondary": Note that this solution will only work given some form of non-physicalism. So we may still have an interesting argument that if the A-theory is true, physicalism is false.

IanS said...

I’m not so sure that there is a ‘precise stream of consciousness’. Maybe there are loosely related parallel streams. I recall reading about an experiment in which subjects listened to speech with added clicks. They were able to say in which word a click had occurred, but not in which syllable.

To be sure, we force our experiences onto a single timeline (or at least we try to) when we recall or recount them. But do we really experience them that way? It’s not so easy to tell by introspection: if you try to catch yourself experiencing something, you experience the ‘trying to catch’ and lose the ‘experiencing something’. But how else could you tell? It’s like a dog chasing its tail.

Alexander R Pruss said...


I share your worry.

Frank De Silva said...

Hi Alex I wrote a paper many years ago on this subject you can find it here
same thing but less physics

Perception is a continuous experience that exists at every instant, across a set of
simultaneous events in the brain. Special relativity physics states that there can be nothing physical, that
connect simultaneous events. As such, perception cannot be physical but non-physical or dualistic. This argument is analysed further, and a new concept called Concept A is introduced. With the aid of Concept A, free will is explained.