Introduction
“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.
Quantum
Entanglement
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.
Opposite
Spin
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.
Take
leptons.
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?
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