The existence and importance of intrinsic natures
the basic entities of physics, in and of themselves, beyond their behavior? What are their intrinsic natures? (Analogously, what are the chess pieces made of? What is the universe's hardware?) Physics can, in principle, tell me how a physical entity affects the rest of the world - that is, other physical entities - but I am not asking about a relationship. I am asking about a physical entity in isolation.
Since physics is only concerned with relationships, I must look elsewhere for an answer.
At this point, the diehard physicalist has a possible rebuttal: that there are no
intrinsic natures. In this worldview, the basic entities of physics simply are
the sums of their causal properties, and have no further reality or structure. The universe has no underlying hardware; it's "relations all the way down", and the relationships describable by physics are the only things that exist.
Is this claim reasonable? First of all, note that it is a metaphysical
claim. If they exist, intrinsic natures have no effect on physics; therefore, no argument for or against their existence can come from physics. On metaphysical grounds, the only obvious argument against their existence is Occam's Razor. So what are some metaphysical arguments for
One argument is that fundamental non
-relational entities are necessary to avoid circularity or infinite regress. A relation involves "things" that are being related; a worldview that consists entirely of relations is structurally unsound. Just as mathematical theories need undefined terms, so does physics.
There are many possible ways of turning some things hitherto regarded as 'real' into mere laws concerning the other things. Obviously there must be a limit to this process, or else all the things in the world will merely be each other's washing.
Another argument is that the claim, "relationships describable by physics are the only things that exist", is extremely
strong. It seems indistinguishable from Max Tegmark's mathematical universe hypothesis, which claims that mathematics not only describes the universe, but is
the universe: a claim that most people find unpalatable. Mathematics is merely an abstraction, a framework. (As Alfred Korzybski phrased it, "the map is not the territory".) It describes rules for interactions, but says nothing about their instantiation,
or a "current state of affairs". If Tegmark is correct, then what distinguishes abstract mathematical structures - for example, the theory of inaccessible cardinals, which do not seem to exist in the "real world" - from concrete ones (ones that actually exist)?
Even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and makes a universe for them to describe? The usual approach of science of constructing a mathematical model cannot answer the question of why there should be a universe for the model to describe. Why does the universe go to all the bother of existing?
The natural answer to these questions is "intrinsic natures": the properties of the universe that ground reality, and that mathematics does not describe (whatever these may be). But this option is not available to someone who metaphysically declares that all properties are "observable" properties.
The diehard physicalist has another possible rebuttal. Assuming that intrinsic natures do exist, why should we care about them? By definition, they have no causal power, at least in the usual sense. (To use the chess analogy: even though the rules of chess do not depend on their implementation, some kind
of implementation is necessary to play the game.) It seems idle to speculate about things that have no observable effects on the world.
Of course, the same objection can be raised against the entirety of metaphysics, and philosophy in general. As useful as it is, science has no handle on the really big questions: the nature of knowledge, the nature of reality, why there is something rather than nothing. These topics are arguably of supreme importance, so saying that you simply don't care
about them is very odd.
Another good reason to care about intrinsic natures is that consciousness is
intrinsic, as I will now show - thereby settling the questions of existence and importance in one fell swoop.
Consciousness is intrinsic
Why is consciousness (as previously defined) intrinsic, in a sense that precludes any description by physics?
First, consciousness cannot be something relational, because it can be imagined in isolation.
It exists by definition, and in the unfalsifiable solipsistic worldview, nothing else does. If consciousness were a relationship describable by physics, then its existence would entail
the existence of things that were being related - namely, physical entities outside of consciousness. But such an entailment is impossible, because the language of physics is compatible with solipsism; the laws of physics can be expressed entirely within
consciousness, which makes consciousness itself "too big" for physics to describe it. Fortunately, less formal languages (such as English) can express things that physics cannot. Otherwise, the field of metaphysics would not exist.
The reason why our sentient, percipient and thinking ego is met nowhere within our scientific world picture can easily be indicated in seven words: because it is itself that world picture. It is identical with the whole and therefore cannot be contained in it as a part of it.
Second, again by definition, consciousness tells me that something specific
- for example, the appearance of typing on a keyboard - is actually happening at this moment.
This is a statement that no laws of physics can ever imply, because the laws of physics are constant. As discussed earlier, physics defines a set of rules, but says nothing about an instantiation
of those rules, or "current state of affairs". (Peter Hankins calls it "haecceity": the particularity and actuality of experience, which are unavoidably absent in any general, abstract theory.) Consciousness is concrete in a way that physics is not, which makes it a strong candidate for the universe's underlying "hardware", or Stephen Hawking's "fire" - the properties of the universe that ground reality, and that mathematics does not describe.
Explaining the intuition
Let me revisit the man who has been blind from birth. Without experiencing it himself, he cannot know what vision "is". He can learn about its mathematical aspects - the behavior of light, and so on - but all of this knowledge is abstract, ultimately reducible to relationships between undefined terms.
Since the interpretations of these terms are irrelevant to mathematics (just as intrinsic natures are irrelevant to physics), the interpretations must be based on concrete non
-mathematical knowledge. The only source of such knowledge is consciousness. But the blind man's consciousness has never contained visual information, so his interpretations will be different from those of a sighted person; for example, his interpretation of a "point" in space, if points are treated as basic. Even if two people use the same model of physics, their interpretations can (and arguably must) differ.
When the blind man's condition is cured, he does not discover a new physical law. Rather, he learns about something that no abstract theory can ever capture: the reality
or intrinsic nature
of vision, as a content of consciousness. This affects his interpretations
of physical laws. The information that he acquires is not physical, but metaphysical. Rather than having a "map" of vision, he now knows the "territory": a part of reality that was previously inaccessible to him.
This also explains the strange intuition - "the zombic hunch", in Daniel Dennett's words - that someone could be physically identical to a conscious person without
being conscious. This is as nonsensical as the idea that a computer program could run without any hardware to implement it, but it seems
plausible because it contains a grain of truth. Physical descriptions inevitably leave out intrinsic qualities, and the only glimpse of these qualities comes from consciousness. Hence the belief (held by Edward Witten, for example) that science can address many aspects of cognition, but not this
People have called it "the most familiar and most mysterious aspect of our lives" (Max Velmans & Susan Schneider), "the most important topic in the philosophy of mind" (David Chalmers), and "just about the last surviving mystery" (Daniel Dennett). Physicalists say that it can be explained by physics. If by "it", they mean something like "wakefulness" or "attentiveness", then they are probably right. If they mean "consciousness" as previously defined, then they are probably wrong. This
meaning of consciousness is tied to the nature of reality, which places it outside the scope of physics.
Is consciousness precisely what I mean by "intrinsic nature"? Does everything in the universe have some form of consciousness (a view known as "panpsychism")? If the universe is some kind of simulation, and if consciousness is its hardware, does consciousness have causal power "outside" the simulation (in the same sense that a chess piece's implementation does not affect the game, but does affect the world outside the game)? These are questions for philosophers, not for physicists.