6. From a
reductionist point of view, the identity of generic objects is reducible to some
material or structural characteristics. Therefore, we have to consider two
groups of theories: those that eventually
reduce identity to something material, and those that eventually
reduce identity to something structural.
7. The
theories that reduce identity to
something material presuppose that material objects have some “intrinsic
identity” that is not structural. Because all material objects are composed of
parts, we have to face the paradox of the
ship of Theseus: if we gradually change the components of a complex object,
we end up having a brand-new object with none of its original components. The
original paradox speaks about the mythological ship of Theseus, the first ship
ever built, of which it was said that it was conserved by the Athenians and
maintained over time by changing out the parts that had deteriorated until no
original parts were still in place. If we think that the identity of objects
does not depend on their structure, but on the intrinsic identity of something
material, we must conclude that the complex object has lost its original
identity. The identity of complex objects
depends on the identity of their component objects. Reasoning in this way,
we quickly find ourselves reduced to considering the intrinsic identity of each
subatomic elementary particle.
8. Because we
are discussing the identity of objects as the basis of the personal identity
concept, we must note that we continuously exchange the matter of our body,
literally with every breath we take. A common saying with some scientific
grounding is that in seven years we change all the matter that constitutes our
body. For this reason, reductionists that support this theory have to
acknowledge that despite what we believe, we do not have the same personal
identity that we had seven years ago. This does not mean that our body has grown
older in seven years; this means that we are actually another person, believing that we are the same person only
because we have inherited the memories of the different person who existed
seven years ago with a body constituted of completely different matter from the
one we have today.
9. Even
suspending our judgement about our personal identity, and returning to reasoning
about the identity of the objects, we have to face another problem. The question
comes from the fact that that physics says that
elementary particles have some measurable properties,
but have no intrinsic identity. They are indistinguishable. And if we still
imagine that they may have some hidden
univocal property to which we may anchor their identity, then we are
embracing a theory that cannot contend
with dualist theories on the grounds of unfalsifiability, because it is also
unfalsifiable. Some might think that the identity of a particle can be given by its position in space-time, which
has to be unique. Actually, these are geometric properties that are best suited
to the concept of identity based on structure, discussed next. Keep in mind that
space-time coordinates are not absolute; they are always relative to some
reference system.
10. The fact
that elementary particles are indistinguishable is difficult to accept: our
common sense suggests that each particle has its own position, and as we can
trace its position in space, we can be sure that it has some identity that
persists in time. But modern physics says that reality is much more complicated
than that. We may have successive detections of particles but nothing guarantees
that the particle is the very same as before. The equations to compute the
positions of particles regard them as a wave and give as a result the
probability of all the possible new positions.
Regarding the particle detected in a second place as the very same particle that
was detected in a first place is an arbitrary generalization of our thinking,
but is not based on any physical truth. Quantum physics regards all the
particles as continually appearing and disappearing in a so-called “quantum
foam” of virtual particles. We should think of particles as the localized counterpart of a given energy
packet, not as little material marbles. We can still imagine associating an
identity with each energy packet, but the ground becomes slippery here for an
identity concept based on matter, because these packets are local thickenings of
the total energy of the universe. A good article by Meinard Kuhlmann published
by Scientific American in August 2013
explains these experimental problems:
http://www.scientificamerican.com/article/physicists-debate-whether-world-made-of-particles-fields-or-something-else/
.
Studying the matter at the extremes of our knowledge, we end
up with equations and packets of energy that cannot help in supporting the
concept of identity based on something material. The world is made of particles
no more material than bubbles on the surface of boiling water. This leads us to
regard identity as something that derives from structure.
11. According
to Derek Parfit, your personal identity remains the same (and therefore you
remain you) as long as your psychological traits are sufficiently similar to the
ones you had before. In the reductionist view, these psychological traits are
mapped physically to a configuration of neurons in your brain. So, in this view,
your personal identity depends on the identity of an object that is identified
as something structural: the identity of
a brain with the neuronal configuration that implements your psychological
traits.
12. It is
possible to say that the identity of a brain is based on its
capacity to generate thoughts. We can
say that a brain itself has no identity, but
it acquires an identity only when it is functioning. This can be regarded as
a more abstract level of structural identity, but actually is not based on the
identity of an object, but on a property
of that object that makes it a subject. This will be discussed in more
detail later, once we have seen that the concept of identity when referring to
objects is not a good one to base the concept of personal identity on. Here, we
have to notice that the concept of “functioning brain” has meaning only from a
perspective of sentience, because it expresses the capacity of the brain to generate a mind that we know exists
only by our direct experience, but is not deducible by simple physical
observation: we are able to observe only the physical counterparts of the brain
activity, but the notion that that
activity generates a mind is proven only by our personal direct experience of
our own mind.
13. Because we
discuss the identity of objects in order to use it to define personal identity,
we have to face the problem that because identity based on structure is not
linked to some specific bunch of matter, in principle
we could build many brains having the very same structure and therefore
generate many numerically different minds
with the very same personal identity. Parfit thinks that if your body is
destroyed and then built again in a different place, replicating exactly the
same original structure, your personal identity would be preserved. But if your
body is replicated without destroying the original body, Parfit thinks that the
original personal identity may not be preserved even in the original body. To
avoid the possibility of two physically separated bodies having the same
personal identity, Parfit needs to
introduce a clause that specifies that personal identity is preserved as long as
there exists only a single physical brain at a given time with the required
structural characteristics. This is what Daniel Kolak calls a “metaphysical epicycle”, and it
raises more problems than it solves. This clause implies that the existence
somewhere in space of a copy of myself influences my personal identity, and
therefore that my personal identity is
determined not only by my inner structure, but also by the outer structure of
the world around me.
14. Actually,
this problem also applies when we reason about bare objects. In our daily life,
we know that two identical objects are not really identical: if we could check
them atom-by-atom, we would discover many little differences. Notwithstanding
this, we can imagine having two objects
of macroscopic dimensions, let’s says two salt crystals, that are exactly identical to each
other even when compared at the level of atoms. In this case, we would not
say that because they have the same structure, they have the same identity. We
would make a distinction, talking about “the one on the left” and “the one on
the right”. This means that the outer
environment is playing a part in defining the identity of the two objects.
But if we limit the definition to a finite environment, then recreating a copy
of the environment would once more introduce an ambiguity in the definition. To
avoid definitively any ambiguities in the definition of the identity of an
object, we have to consider an
environment so vast that it is not possible to copy it, to make sure that it is
unambiguous throughout the whole universe. This is the same as the case we
suggested before, in criticizing the concept of identity based on matter, about
the proposal to link the identity of each
elementary particle to its position in space-time. We end up needing to
consider the whole universe in order to define the identity of its elementary
particles.
15. In
accordance with all these considerations, it turns out that the identity of
every object, and therefore, if we are reductionists, the personal identity of
each human being, is determined not only by its inner structure, but also by the
structure of the surrounding environment.
The identity of an object is not an intrinsic property that it has
a priori, but rather it can be defined
unambiguously only by considering the environment containing the object, and to
avoid any ambiguity this environment has to be expanded to include the whole
universe.
16. The parts of the universe to which we assign separate
identities are arbitrary. For
example, two separate islands can be considered to have two different
identities, but if the level of the sea decreases, they can become a single
island, with a different identity than the original two, without any change in
their inner structure. It is just a matter of practical convention to regard
them as two objects instead of a single greater geographical region, or as just
parts of the planet Earth. This also applies to objects that seem more definite,
such as two crystals or two clocks. We are comfortable with this because
objects appear spatially separated.
Actually, this geometrical condition simplifies our communication conventions,
but we could assign them other identities in a different way, without any loss
in terms of physical reality. The reason that it appears natural to assign a
different identity to different objects like two clocks is that each of these
objects may be used to execute the task of keeping time. This task is meaningful
for us, because we are sentient observers who know that some objects can be used
to achieve a goal, but still the fact that we regard the clock as having an
identity is a decision that we make arbitrarily.
17. From a
strictly physical point of view, all
physical objects are temporary structures made of energy packets tossed into the
quantum foam. We have to conclude that
the identity of objects is always
reducible to a communication convention and that it has no absolute meaning. Considering all the objects as
geometrical parts of the whole universe actually defers the problem of the
definition of the identity of objects to the identity of the universe. But
the only way to define the identity of
the whole universe is to describe its inner structure, and
this causes the definition of all the identities to become circular.
18. Once the
concept of identity of objects is lost, even the difference between the concepts
of “type” and “instances” of objects vanishes. The instance of an object can be
regarded as the actualization-with-a-unique-identity of a type definition. Once
the unique identity is deferred to the whole universe, which has no further
container object, this unique identity become useless, and the definition of an
unidentified actualization of the type corresponds with the definition of the
type. It is important to remark that in considering the universe as a whole, I
mean that it has no exchange of information with anything else. If we ever
discover some forces that are inducted by a parallel universe, we should
consider both our universe and the parallel universe, or even a bigger
multiverse, to again be “the whole
universe”. As the concept of identity vanishes when applied to the whole
universe, so also the difference between the theoretical existence of the
universe and the actualization of the universe that we experience vanishes. I
mean that we may think of ourselves as experiencing directly the type of the
universe, instead of the actualization of one instance of that type. This will
be discussed again later when speaking about the General Existential Problem.