My intuition is that quantum physics presents a picture of reality on which fundamental particles rarely if ever exist simpliciter. Most of the time, the world is in a superposition of the particle existing and not-existing, though perhaps with a much heavier weight being given to the one state rather than the other. Perhaps just at the moment of quantum collapse a particle simply exists. But immediately afterwards, there will be some interaction at the tail end of the wavefunction that makes the particle’s “existence” be in a superposition. And superposed existence is not real existence, since superposed existence comes in degrees, while real existence does not (at least not in the relevant sense of “degrees”).
If my intuition is right, then over the past hour, I take it that on a quantum picture at most instants of time no particles of my body were really existing. Maybe occasionally some particles flashed into being due to some collapse, but at most times there weren’t any particles there.
This means that at most times over the past hour one of the following was true:
I didn’t exist
I existed immaterially
I existed materially without having any particles.
Option (1) leads to ethical and theological difficulties. On that view, I am constantly popping in and
out of existence. But if so, then I am constantly dying and being resurrected. And that robs death and resurrection of their deep moral significance.
Option (2) leads to the interesting question whether I always exist immaterially, or only when none of my particles exist. If always, we get a very strong dualism. If sometimes, then we get a very funny semi-dualism: most of the time I’m immaterial.
Option (3) seems to me to be the most plausible. But on option (3), we should not think of material existence as a function of being constituted by particles. The kind of picture of material existence we get from van Inwagen, where living things come into existence by having their constituent particles get caught up in a life is untenable. Perhaps, instead, material existence is a function of having a certain kind of relationship to the wavefunction of the universe (perhaps a relationship of partly constituting or being partly constituted by that wavefunction).
If my argument is right, then Aristotelian metaphysicians should stop worrying very much about the pesky problem of what happens to the identities of fundamental particles when they get incorporated into our bodies. If there are ever any particles at all, then on quantum grounds independent of Aristotelian metaphysics, they are evanescent beings that do not persist long enough—for their existence soon becomes superposed—to cause much of a problem on that score. I suppose it could still be a problem if they come back into existence later. But it is dubious whether the numerically same particles can come back into existence. Indeed, the whole business of the particles “in the body” is so dubious on quantum grounds, that there is little theoretical cost to such seemingly absurd solutions as saying that there are no electrons in the body—for it seems we should anyway think that most of the time there aren’t any electrons in the body.
In the above, I allowed that perhaps when we have the right eigenstate, for a very short time a particle exists. But even that, I think, is dubious. The change from the system being in an eigenstate of particle number and not being in an eigenstate of particle number seems to be a merely quantitative change in the wavefunction, and hence we have little reason to think it corresponds to substantial generation or corruption.
There is one way out of all of the above: to accept a Bohmian interpretation of quantum mechanics. If I am right, then much contemporary metaphysics is being done on the implicit assumption that something like Bohmianism is right. But why assume that?
9 comments:
This is a very original sorites argument. Still it is a sorites.
A couple of thoughts (for whatever they're worth):
1) This sounds sort of like "Flashy" GRW. It does seem to require that wavefunction collapses occur just at the right times and places that chemical, organic, biological, ecological, etc. relations are unaffected. And I really hope it's not "observer" based, since observation is a power of particular physical things (specifically: animate living beings) and if they'd need to already exist and be observing in order for their own constituent particles to exist... that's a serious problem. But, sans observation requirement, you have something like "flashy GRW", which is certainly a live option.
2) I don't think people have "Bohmian" presuppositions; I think the average physicist is operating without presuppositions at all. Hear me out! I think most are in the "shut up and calculate" mindset in the shadow of Bohr, and so do not think at all about the ontology (or what Bell called "the beables") of their theory. Indeed, I deny that they have a theory at all; merely a mathematical formalism that churns out the right predictions. As Tim Maudlin has mentioned, if you ask the average physicist (or consult the average Physics text) about what an "orbital" is and what those shapes are the shape of, there are many answers they could give, or they will often decline to answer at all.
3) With (2) having being said, I do wonder why you wouldn't think that a Bohmian sort of view isn't to be preferred a priori until we had some strong reasons to the contrary. After all, we arrived at "subatomic particle" talk by fine-graining from the things we can see down to things like macro-molecules and organic compounds, then down to molecules, then down to atoms (the "elements" of the periodic table). So, fine-graining which reveals smaller chunks of matter that are in arrangements which sensibly and intuitively coarse-grain back up to the chemical ones, and so on, seem to be prima facie preferable. After all, nothing from the chemical to the organic to the biological, etc., spends most of its time non-existent (only popping into being as required by a mathematical function, which shouldn't have causal powers anyway, and then we're off to the races about what exactly the wave function (a piece of mathematics) represents in the real world, and........ I'll leave that alone for now).
In other words, to imagine a world in which most particles don't exist most of the time, and yet my DNA and enzymes and neuro-transmitter substances are all made of particles... it just isn't the natural way to proceed. It's fine if something required it; but Neo-Bohmian approaches seem quite fine without it. Why not pursue them?
Basically, I think that if we confine our ontology to particles, flashiness is the best we can hope for.
On reflection, I think Option (1) is not very plausible on the flashy picture, either. For while there may be times when some of our particles flash into existence, the particles that flash into existence will be a very, very small portion of us. Even at those times, most of our body will be in superpositions that preclude particle existence.
I do think Bohmianism should be taken seriously. I particularly like Bell's variant that has an indeterministic dynamics but perfectly defined particle positions. But Bohmianism is just one family of interpretations among many, and so I don't attach a credence to it greater than 1/2.
From my Aristotelian point of view, things do look different than for you. I am much more confident of the existence of living things than of their organic parts, and of their organic parts than of their inorganic parts, and so on. As I go to the microlevel, I wouldn't be surprised to find it's all just got some sort of "virtual existence".
I suppose I can see that, and I do find Aristotelianism generally appealing. But, could "virtual existence" really be the substrate of actual existence? That's part of the problem I have with many approaches to QM. They seem to say that none of the smallest parts of things that we know to exist (including us) actually do exist.
Besides, what do we do with all the evidence substantiating our models of things like DNA, cell structure and function, macro-molecules (like enzymes), and the elements? If we postulate these things, and then the predictions we make based on them come true, how do we deny their existence?
So on a non-Bohmian interpretation, is the impression of physical persistence/continuity an illusion like motion pictures?
Steve: On a "flashy" view, like the one Pruss seems to be endorsing, it seems to me the answer is yes. But then the question is what is it an illusion to? Unless you accept the idea of non-physical objects that can be deluded, you're stuck thinking that just enough underlying reality is present at just the right times throughout our lives that we can exist and function and be deluded.
To that I say the manifest image of fully-formed beings, made up of smaller and smaller parts, who have confirmed the QM formalism in experiments done with real machines in real laboratories strongly recommends a view like the Bohmian one until we are given some actual reason to the contrary. It should enjoy privileged status above anything which would make the manifest image an illusion.
Alex,
If our bodies, and the macroworld around us, are mostly in a state of superposition, what accounts for the impression of persistence/physical continuity?
Steve:
Maybe this: We don't observe uncollapsed states. Whenever we are observing, we are observing collapsed states.
Michael:
I am not saying that there is massive illusion here. Even if there aren't particles, it may be true that the wavefunction is most of the time highly localized. If the wavefunction is one that represents fist particles as present to a degree of 0.999999999999 at the end of my arm, that's enough to make my perception of the fist correct.
Compare this: If it turns out that physical reality is made of fields rather than particles, that doesn't mean our perception of the world around is an illusion, just as when it turned out that most of the "solid" tables and chairs was vacuum, that didn't mean that our perception of the world was an illusion.
Pruss: This way of phrasing it, "...enough to make my perception of the fist correct", seems HIGHLY misleading. I'm not concerned with whether my impression that there is a fist there is "correct" in some mathematical sense. I'm concerned with whether I can see my fist there in front of me. As an illustration, imagine that we are actually in the Matrix (though I think that is conceptually incoherent). When the program version of me closes its eyes, I have the impression of having closed eyes (the tactile and visual experience that one ought to have when their eyes are closed). This corresponds quite accurately with the fact that my real eyes are in fact closed. But it does nothing to take me out of the Matrix.
It is a fundamental part of our conceptual scheme that we actually see our fist at the end of our arm; not that we have some hallucination which corresponds very well with reality. ESPECIALLY not that we have an impression which corresponds to a mathematical fact to 0.9999999% or any other percentage. I just think this whole approach is wrong-headed and stands all-too-firmly in the shadow of Descartes. Only in his shadow can QM interpretations involving "observation" make any sense, and likewise for views that compare our "perception" with a probability distribution in the wave-function (a purely mathematical object, if it is anything at all).
As to fields: Our perception of the world is not that it is made of particles, but rather that it is made of ordinary objects. I think this perception is accurate whether a field theory or a particle theory is the underlying story. As long as they coarse-grain out to molecules that are chemically bonded and arranged in ways that yield the textures, rigidities, colors, etc which we directly engage with via our perceptual powers, I'm all set.
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