This piece is a short introduction to the close relation that can be found between ontic structural realism and quantum mechanics. A more detailed commentary on the 'Ontic Structural Realism and the Philosophy of Physics' section of Everything Must Go (by James Ladyman and Don Ross) will follow shortly.
“Current physical mathematics, especially models of quantum entanglement, are thus crucial to motivating OSR.” - Don Ross ( 'Ontic Structural Realism and Economics'
It's very clear to me that almost the entire ontic structural realism (OSR) project is motivated by findings and theories in quantum mechanics (QM). In other words, findings in the micro-world; not in the macro-world. One can immediately conclude from this that OSR certainly has very little to do with “medium-sized dry goods” (as J.L. Austin once put it) – at least as an inspiration.
In that respect, one can happily agree with the ontic structural realists (OSRs) when they say that QM isn't about “entities or objects”. The thing is, I don't really think that many philosophers (or even all educated people) ever did see protons, electrons or even atoms as objects or entities in the everyday sense.
So when a OSR says:
If you want to insist that a electron is an entity of some kind, then please show me something beyond the data and mathematical structure.
We can reply to that by saying:
But who, exactly, would disagree with the "data and maths" bit of your statement? And how strong and detailed do you think the layperson's - and even philosopher's - commitment to thinghood in the quantum domain is?
Indeed how could a layperson offer us more on an electron than a physicist or a philosopher of science? Nonetheless, it's still data about something and maths about something. Otherwise it's pure maths and there would be no real need for the word 'electron' or even for electrons themselves.
In other words, why do all (or most?) OSRs think that the people who disagree with them only have a commitment to medium-sized dry goods in every domain? That is, a commitment to only those objects they can kick?
When Dr Johnson showed Bishop Berkeley that he could kick a rock: the Bishop was unimpressed. I'm not impressed either. And most philosophers aren't.
When the OSR says that science (or physics) doesn't give us objects, we can say that this was something Berkeley has already said. It was something the British Empiricists and various kinds of idealist said. And, indeed, something many scientists have said; at least since the late 19th century.
Isn't it also the case that sections (if small ones) of the educated West have known that the billiard-ball/solar-system model of the atom is a model since, say, the 1930s? They also know that they can't kick atoms. They know that, in a sense, atoms and definitely protons aren't everyday objects or even objects at all. They also know that models are... well, models.
In any case, even more specifically than quantum mechanics (generally) being a prime motivating force for OSR, quantum entanglement specifically seems to loom large in the literature.
Clearly it's the nature of quantum phenomena which are seen as undermining “traditional metaphysics” by OSRs.
Finally, we can object to OSR without having an explicit commitment to the existence of objects/entities in every domain (specifically in QM!). We simply need to say that that there's more than numbers, equations or "structure" in physics generally and even, specifically, in quantum physics.
In the end, then, all this will depend on what the protagonists in this debate take objects to be. After all, the nature of objects (as well as their very existence) has been discussed in metaphysics for over two thousand years.
Individuals in Quantum Mechanics
As said earlier, OSRs get their point across by bringing QM into the debate.
What are said to be “individuals” or objects (though by whom?) are such things as quantum particles and other spacetime points. According to OSR, the reason why they aren't in fact individuals is logical in nature. In that sense, we're talking about the logic of quantum mechanics here.
For any thing (x) in quantum mechanics, we can say that the law of identity doesn't hold for that x. (In symbols: ∀x (x = x).) That is, x isn't identical to x .(In symbols: x ≠ x or ¬(x = x).) Now why is that?
However, it's acceptable to quantify over what OSRs call “non-individual objects”. That is, such an x can be the value of a first-order variable. Despite that, usually objects (even if non-individual) are seen to be the subject of the law of identity. Though perhaps that's only the case if they're - or if they're seen as – substances with intrinsic properties.
How does this claim fit in here? Is it that because some relations are seen as being ontologically on a par with individuals that the latter are seen not to exist? However, claiming that relations are ontologically on a par with individuals isn't the same as claiming that individuals don't exist.
The main point about quantum entanglement isn't that relations somehow constitute particles: it's that physicists attribute exactly the same intrinsic and relational properties to each (pair) of particles. Thus, at a prima facie level, it can be said that it's not really a surprise if OSRs deem relations to be everything.
This is how Ladyman and Ross put their position:
“... quantum particles appear sometimes to possess all the same intrinsic and extrinsic properties. If two electrons really are two distinct individuals, and it is true that they share all the same properties, then it seems that there must be some principle of individuation that transcends everything that can be expressed by the formalism in virtue of which they are individuals.” (page 148)
This means that everything that's true of a must also be true of b simply because a and b are entangled. (In symbols: (x) (y) (F) (x = y ⊃. F (x) ≡ F (y).) Such entanglement effectively means that a and b can't been disentangled or taken as two objects.
To put more meat on this bone of quantum entanglement, it can be said that if we take two fermions (such as electrons), the spin of a (in any given direction) is the “opposite” of the spin of b. a has spin in relation to b and b has spin in relation to a. Indeed a and b simply don't have spin when taken on their own. It's also said that a and b are given the same spatial wave-function when they're both in the first orbit of an atom.
Again, it's as if a and b are one. Or, at the very least, they can't be taken independently. Of course it can now be said that if a and b can never be taken independently, then in what sense are they individuals? Perhaps it can either be said that a and b are as one (i.e., they constitute one object) or that they aren't individuals/objects in the first place. That is, every individuation of a will include an individuation of b. Or, alternatively, it can be said that there can be no independent individuation of either a or b.
Ladyman and Ross argue that relations are fundamental when it comes to fermions. They believe that fermions don't have intrinsic properties – they only have relational properties. (This is also called “contextual individuality” in the literature and can also applied to all spacetime points, not just to fermions.)
Having opposite spin is clearly a relational predicate because of the word “opposite” - opposite to what?
In this case it's fermions which have opposite spin when they're in what's called the “singlet state”.
However, a problem for OSR can immediately be spotted here.
The relational property [opposite spin] can be summed up in Leibnizian logic by the term “irreflexive relation”, which is symbolised aRb (with the R symbolising “opposite spin”). However, what about a and b – the relata – themselves! Surely a and b (electrons, for example) have to be seen as individuals of some kind.
It's certainly true that when it comes to both a and b having the property opposite spin, then clearly that property is relational – indeed fundamentally relational. Thus the property is relational and (it can be argued) it's also more important than both a and b. It's certainly more important (or fundamental) than any seemingly intrinsic properties (which are rejected, by definition, by OSRs).
Again, are relational properties fundamental? This is an important question because some metaphysicians haven't seen relational properties as bona fide properties at all. Such metaphysicians don't believe that relational properties are genuine properties of objects or entities. OSRs, on the other hand, are going in the opposite direction to this.
Another question that can be asked here is:
Can relational properties individuate individuals/particles/things?
What we have here is a chicken-or-egg situation.
On the one hand it can be argued that it is individuals (or a and b) that give individuality to the relations. On the other hand it can be said that relations give individuality to individuals.
Is that a difference that makes a difference?
Perhaps the individuality of a and b is the sum of both intrinsic and relational properties. In any case, a and b are bound to have some relational properties; whether that's opposite spin or bigger/smaller than x.
On the other hand it can be argued that an individual wouldn't have the relational properties it has without also having what can be called intrinsic - or even essential - properties. At the very least, individuals must have properties which are over and above their relational properties in order to have those relational properties in the first place!
... and finally intuitions...
There's a lot of intuition-talk from Ladyman, Ross and other OSRs.
Are they referring to our intuitions about the causes of World War Two or the existence of aliens? Not really; when you scratch the surface, it seems that OSRs are talking about our intuitions regarding quantum phenomena.
I have zero intuitions about leptons. I would suggest that no one really has intuitions about leptons. Perhaps people have intuitions about God, cats and thermostats; but leptons? Surely not.
I've also heard talk about our intuitions regarding such things as “intrinsic donkeyhood” (chose your own xhood).
Who on earth has intuitions about a deeply metaphysical notion such as intrinsic donkeyness, let alone about intrinsic atomness or electronness? It's a metaphysical technical term or notion. Therefore what has intrinsic donkeyhood got to do with intuitions?