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In this discussion of whether color experience can be reduced to the physics we have, let us return to the beginning and at least try to agree on why we disagree.
Before I knew about science, I lived in a world which included colored objects. Subjectively I still do. But I have also learned a theory of the world according to which it is made entirely of particles and fields. For the purposes of discussion, we can say that according to this theory, the world consists of particles and fields in a changing spatial configuration. (If quantum mechanics comes up, let us say that it consists of an association of complex numbers with a set of such configurations.)
I expect that we agree that at the fundamental level, this theory does not contain color. So if I am to believe that this theory describes the whole of reality, and if I am to regard my experience of colored objects as part of reality, then the elements of that experience must be identified with complex, non-fundamental entities or properties appearing in the physical theory.
A priori, I regard it as outlandish that color is an arrangement of things in space, or any other such composite property from the physical theory in question. They appear to be radically dissimilar things, as if one were to say that yesterday was the number 2. So when someone says that color is such a property, if they wish to convince me, they must overcome this skepticism and somehow explain how this can be so. I mention this, not to signal that I shall not be moved come what may, but to mention a psychological fact, and to indicate how large the gulf between the one and the other appears to me.
Robin Z, Richard Hollerith, and Silas Barta have all defended the physical reduction of color, as have several others. So I shall examine their positions in turn, and at least try to understand what it is that they are proposing.
Robin Z's most recent statement of her position is here. She says the experience of greenness occurs in the mind, the mind is a product of the operation of the brain, and the ultimate cause of the experience of greenness is usually the incidence of light of a certain wavelength upon the surface of the eye, which produces an unspecified causal sequence resulting ultimately in the experience of greenness.
This explanation does not specify which complex physical entity is the experience of greenness, or how it is that color arises from colorless physics. So it does not help me understand or give me reason to change my view.
An analogy with the figures in a video game is also presented. But described physically, an image on a screen is an arrangement of things in space, so it is not a problem to account for it in terms of a spatially based physics.
In Richard's comments, I cannot find a specific account of what color is physically. There is the assertion that "The state of my brain that corresponds with the blue experience can be a normal, ordinary, conventional physical state", but there is no explanation of what sort of physical thing a "blue experience" might be.
Richard also talks about information processing and model maintaining, so that is probably relevant to his concept of how the reduction is to be achieved, but it is not enough detail for me to work with.
Silas has been more specific. Following Gary Drescher, he refers to the "generated symbols" of the Lisp programming language. Silas says: "To experience blue is to feel your cognitive architecture assigning a label to sensory data."
We can all agree that there is no barrier in principle to providing a physical account of what happens inside a computer when such an operation occurs, though the details may be complicated. For example, in the computers we have, such a process consists of many charged objects changing their locations inside a number of transistors in a certain way.
I have no objection in principle to Silas supposing that an analogous computational process might occur in the human brain. The physical reality there will similarly consist of numerous charged objects moving around, such as ions moving across membranes, in a certain way.
Silas says that the experience of color is how it feels for this to happen. But I still do not see where the color is. Either I am to look for it in the motions of the ions themselves, in which case I do not see it; or I am to look for it in the "feel" of those motions, but I do not know what that means, in terms of the physical theory with which we began.
I therefore conclude that I have not yet been given a reason to think that color can, after all, be found in a colorless physics.
This will probably be my last reply to Mitchell on consciousness or ontology.
It is now very highly probable that my differences with Mitchell in this thread stem from differences over epistemology. Specifically, Mitchell considers it epistemologically satisfactory to adhere to his current position until provided with strong evidence or strong argument against it. The best summary of that position in a few sentences is probably the following passage written by Mitchell less than 36 hours ago to be found in the parent of this comment:
My position is that what Mitchell considers outlandish is a perfectly normal and perfectly satisfactory hypothesis. None of Mitchell's indictments of the hypothesis strike me as actual handicaps in a proper contest among hypotheses (i.e., in a proper epistemological process). If you want a summary in a few sentences of my position (which is the standard position round here) on how hypotheses should be judged, see the first paragraph of something I wrote less than 48 hours ago. I would gladly elaborate on it and how it applies to Mitchell's concerns if anyone is interested. Alternatively, the interested reader could just wait for the top-level submission promised by jimrandomh in a sister to this comment.
The only way I can see to impose a quantitative framework upon this disagreement is to construct a Bayesian belief network encompassing all the key propositions in both your argument and my argument, and then we try to find where your probabilistic dependencies are different to mine. But I wonder if that's even necessary.
Here's my reasoning:
Your reasoning is something like:
To come around to your view, I have to deny my second premise. I see three ways you can try to make me do that. First, you can show me a specific way to get color from noncolor - but no-one has shown me that. Second, you can use historical analogy to argue that my intuition is wrong. But in my most recent comment to RobinZ I explained why consciousness is different. Third, you can appeal to consensus: everyone else here thinks we can get color from noncolor somehow. But that consensus can be explained psychologically, culturally and historically.
Like I said, we can set about the laborious task of formalizing all this. But do we need to?
I am going to ignore the parts of Mitchell's comment where Mitchell repeats points I already responded to, which leaves us with one point:
I do not know what you mean by a Bayesian belief network about an argument. I humbly suggest that when you wrote that sentence, you were confused about how a quantitative framework (as you call) or a formal epistemological treatment (as I would call it) would go. Please allow me to give the miminum amount of exposition necessary for present purposes. Although it is a clear improvement over what Mitchell wrote, there might be mistakes in the following exposition because I came to "technical epistemology" after the age of 40 and life circumstances have prevented me from giving it the study it deserves. If Eliezer, Anna Salamon or Steve Rayhawk takes exception to anything I say below, then believe them, not what I say below.
In the gospel according to Jaynes, Pearl, Solomonoff, etc, there is one Bayesian belief network out of all the possible Bayesian belief networks that is the accurate model of reality. If we knew which one it was, we would be able to use it to answer any question about any cause-and-effect relationship that is in principle answerable -- or so it seems to me according to my untutored understanding. Parenthetically, in Causality Pearl opines that systems of equations similar to the structural equation models pioneered by the econometricians are probably a better representation than Bayesian belief networks. Hutter and Schmidhuber I think use Turing machines instead of Bayesian belief networks. Needless to say, if you have a formal model of reality in one representation (Bayesian belief network, say), it is a fairly easy mathematical exercise to put it into a different representation.
So, there is one "objectively true" model of reality, but I do not know which one it is. Consequently, what I have as my model of reality is a distribution over models -- er, to be precise, a distribution over candidates for the One True model. (I think I used the word "hypothesis" in my previous comment, but right now I prefer "candidate model".) By "distribution" I mean a mapping from candidates to real numbers in the interval between 0 and 1. I will refer to these real numbers as probabilities. There are an uncountable number of candidates, and the only way to get the probabilities of the candidates to sum to 1 is if the probabilities of arithmetically longer candidates are geometrically smaller. This is the formal version of Occam's Razor. Why do the probabilities need to sum to 1? Well, the short answer is the Kolmogorov axioms say so. Who made the Kolmogorov axioms God? Cox's theorem did.
Since physics is the study of fundamental reality, when I say "our civilization's standard physical model" I refer to our civilization's standard model of fundamental reality. The word "fundamental" is in there to indicate that "Fairbanks is the capital of Alaska" is not in the model. Our civilization's model of fundamental reality remains informal. To produce a formal model would require more than one generation of scientific effort in my humble estimate. In other words, to get it done would entail some community of scientists working on it till they became experts at the work, which I would think would take at least ten years. Then that first generation of scientists would have to train a second generation. But maybe I am wrong and it would take only one generation of scientific research to produce a formal model sufficiently useful that researchers wielding the model could compete with professional physicists trained the conventional way. (It would be a very cool achievement and parenthetically a potent way to remove human cognitive biases from scientific research it seems to me according to my untutored understanding of formal epistemology).
Even though I do not have a formal model of fundamental reality, my knowledge of formal epistemology which I have attempted to summarize briefly above is still useful because (probabalistically speaking, that is, excluding the freak case where all the air molecules go to one half of the room) any process that produces a true model of reality must approximate the process by which evidence updates a distribution on candidate models of reality outlined briefly above. (In particular, the process of natural selection that produced the scientists that produced our civilization's physical models must approximate the process outlined above.)
Well, that should be enough to correct Mitchell's false or confusing or easily-misinterpreted statements (quoted above) about formal epistemology -- which is the only end for which I have any patience left in this top-level submission by Mitchell.
If I have The True Belief Network then I don't need to predict cause-and-effect relationships. I just know the full state of the timeless universe. I mean to ask, why is a belief network constrained to representing physical laws and not physical state? After all, my current network has a bit of both...
I did not say it is constrained to represent physical laws, wedrifid.
Could it be that you believe that my use of "cause-and-effect relationship" implies that constraint? If so, I'm not conceding the implication.
I'm not asking you to concede anything. I'm trying to explore your meaning. What would you (or, for that matter, the experts you cite) say is the One True Model? I can imagine various types of mathematical abstractions but aren't sure which kind you are referring to.
The casual reader might be saying to himself, "There goes Hollerith with another long comment about what he is calling formal epistemology. Why doesn't he have the manners to refrain from injecting a long thread on an unrelated topic into Mitchell's article on monads, consciousness, etc?"
Well, two replies to that. First, I say formal epistemology is not unrelated. Mitchell has been writing for many years around these parts on how consciousness presents a problem for standard physics. He has even solicited donations to support him in researching the matter further, saying that it is dangerous to have a singularity without having done that research. So, one of the ways formal epistemology enters naturally into this comment section is that I humbly sumbit that anyone engaged in such a project that Mitchell is engaged in should have as part of his technical background an education in formal epistemology. It leads to crisper thinking, and given how many resources Mitchell is devoting to the project, his dedicating some of those resources to learning formal epistemology is probably a good use of his time (and, oh, by the way, I'm not going to pay anymore attention to his writings on consciousness, ontology, etc, till he does).
Second, now that it has become plain that my mention of formal epistemology might lead to a long thread of conversation, I will indeed move the conversation to this place. It might move back to Less Wrong in the form of a top-level article by me with a title something like Why most people here should probably learn technical epistemology, a.k.a., the math of rationality. This prospective article would cover no ground that Eliezer has not already covered, but when it is important to publicize some point, then it often wins to have more than one voice making that point.
It would be possible for a person to maintain that only the natural numbers exist, and that there is nothing else. They could point to all the things which can be described using natural numbers; and if you insisted that some particular thing was not actually a natural number, but merely had a relationship to the numbers, they would keep returning their focus to the numerical part of the description of everything, and handwave away every other aspect as not really real, or as itself just being another number.
In the discussion of whether color can be reduced to the motions of particles in space, I feel myself to be in a comparable situation. The discussion of color as such repeatedly turns into a discussion of particles in the light source or particles in the brain...
Perhaps someone out there has conducted the subjective experiment of attending to actual color for a moment, and asking themselves afresh whether this thing could "really" be just particles in motion. The first thing to ask yourself is whether this alleged identity derives any impetus at all from the intrinsic nature of particles in motion. If somehow you knew nothing of color experiences or of neuropsychology, would you have any reason to think, in contemplating any assortment of particles circulating in space, that "color" or "the experience of color" was there? I think not. The motivation for the identity comes entirely from the belief that the world in general has already been explained by a physics of this form, and so color (and everything else about consciousness) must, somehow, also reduce to particles in motion. There is nothing in the intrinsic nature of color or the intrinsic nature of particles in motion to make you think that it is even possible for one to be the other.
That is the sort of argument that you have to resort to with someone who thinks that color is particles, or that everything is a number. You have to draw their attention to their actual experience, and make them question from the very beginning whether what they are saying makes sense. But Richard, I have no idea how to do that within these epistemic formalisms you promote, which seem to mostly be good for arriving at the simplest possible causal structure for hidden causes, and say nothing about how to correctly think about appearances as such, or how to ensure that you are placing a thing in the right ontological category.
But can this formal epistemology be the whole of epistemology? What is your formal epistemic basis for thinking that something exists, or that you have experienced blueness, or that 1+1=2?
I look forward to that.
What I called a BBN (it may be a generalization of the standard concept) is a belief system schema constructed to be capable of representing your reasoning and my reasoning. Nodes are propositions and arrows are inferential steps. The schema must contain a node for every proposition that I use and every proposition that you use, and similarly must contain an arrow for every inferential step appearing in the argument of either person. Once we have that diagram, our two arguments may then be represented as each flowing through a portion of it. We arrive at opposite truth values for a common terminal proposition, so the arguments are in contradiction. To resolve the contradiction or at least identify its cause, we move upstream and try to identify where initial conditions differ.
This process will most likely require one to state opinions regarding certain implicit premises, used by the other person, which did not even play a role in one's own argument, as well as to express differing opinions about the arrows, i.e., about the implications of one proposition for the truth of another. One of us may regard the truth of B as independent of the truth of A, whereas the other would say that if A is true, then B is definitely false - or probably false. It is merely a formal process meant to guarantee that the sources of disagreement are mutually understood, something which should happen anyway if the disagreement has developed in a lucid and orderly fashion.
I'm concerned that you want to dive down an explanatory hole with no bottom. Suppose we say: okay, the particles are colored; or space is colored; or otherwise, beneath the objects we perceive to be colored, there are colors. Won't you want those colors explained too?
When I emphasize that the building blocks of physical ontology have no color, I'm not saying that everything would be solved if only they did. But if you start out without color, and your only way to make bigger things is through spatial and causal aggregation, color will not appear by itself - that is the message.
Certain properties can be described counterfactually - does that help? For instance, "fragility" can be a property of an object that never in fact breaks, as long as it would have been disposed to break under a greater proportion of conditions than many comparable objects. An object is a certain color if it is disposed to reflect light of one wavelength as light of a certain wavelength, which may be different from the original. An object can have this property even if it spends its lifetime in the dark.
The physical property to which you refer is deemed color only because it can induce an experience of color. And the experience of color can occur without that specific external stimulus. So the true nature of color must be sought within the brain.
Here is the confusion underlying this whole mess. There are three types of things which color can apply to: objects, light, and experiences. These are related causally: blue objects cause blue light which causes blue experiences; and evidentially: a blue experience is evidence that there was blue light, which is evidence that there was a blue object. However, color as it applies to objects, light, and experiences are three separate entities with different reductions. We use them interchangeably because the causal and evidential relationships allow them to substitute for eachother in almost all contexts.
If you start with one of blue objects, light, or experience clearly defined, then you can use that definition plus the causal/evidential relationships to define the other two. The natural way to define them is to define all three only in relation to eachother - ie, refer only to the entire structure, and depend on the ability to compare the color of reference objects/light/experiences to keep the definition stable. Fortunately, some discoveries from physics have enabled a simple physical description of blue light. Blue light is any light made predominately of photons with a wavelength close to 470nm. Based off that definition, a blue object is one that reflects or produces blue light, and a blue experience is one involving some particular set of neurons which I identify by their causal relationship to blue light. But stimulating these neurons without using light still makes a blue experience, and I could in principle identify those neurons some other way - for example, if I were to discover that protein X is found only in blue-experience neurons, then I could define a blue experience as an experience involving neurons containing protein X, and then define blue light and objects based on that.
There are some other strange entities which can have color because of causal relations, too. For example, the number 255 (#0000FF) is blue because it causes blue photons to be produced when written in the right part of a CSS file.
I don't think you understand the nature of the exercise. Let me return to the example of temperature.
Temperature exists. I say this without qualm - I am an engineer working on thermal issues in electronic packaging, dealing with temperature is my profession. However, temperature is nowhere described in the most current theories of particle physics. Instead, we find that in certain special cases, we can relate certain properties of the distribution of particles to a summarizing parameter in different locations in space, and that if we analyze the behavior of the particles in time this implies certain patterns in the development of the field corresponding to our parameter. These patterns are identical to those observed regarding temperature distributions, and indeed predict in great detail the physics of temperature - even explaining when these physics 'break down'. We therefore conclude that we have discovered a reductive explanation of temperature.
The exact same story may be told about semiconductors, about conductors, about electricity and magnetism, about weather, about chemistry, about sound, and about light. We find a phenomenon associated with certain conditions, and we can relate the nature of that phenomenon to the underlying physics. We further prove this relation constitutes the innate nature of the phenomenon by examining edge cases - very thin conductors, chemistry in extreme conditions, light passing through a fine grating - and observing that the higher-level physics (of electrical conduction, of chemistry, of optics) break down just in the way which the lower level physics predicts.
We haven't finished the job of reducing subjective phenomena to their fundamental physics, but what we've accomplished so far looks like what we observed in all the previous cases: the normal patterns break down in edge cases (e.g. brain damage) and the science of the underlying phenomenon predicts certain aspects of the phenomenon in very, very special cases (e.g. autonomic nervous reflexes? I'm not a neuroscientist).
This is strong evidence that the entire thing is reducible, and therefore that the phenomenon of color perception can be found in a physics with no explicit color.
I had thought you were someone else, thus the wrongly gendered pronouns, but I know who you are now.
The world can be divided into what goes on in the consciousness of some individual (e.g. yourself), and everything else, some very small part of which will play a role in causing the experience of that individual. Until this point, all naturalistic reductions have consisted of replacing one theory about everything-else with another theory about everything-else, or in otherwise adjusting the overall theory. Since everything-else is known (if you can call it that) only indirectly, by means of its effects on the consciousness of that individual, we have been free to suppose anything about it (that it consists of atoms in the void, that it consists of pure space-time geometry, that it consists of registers in the universal Turing machine), so long as its predicted causal outputs match up with appearances.
But when the time comes to account for appearances themselves, this absolute freedom to hypothesize no longer applies. There must be some fidelity to the appearance of appearances (to use an awkward phrase) in your theory of what they are.
I am quite happy to assert that there is no color in a colorless physics because the range of things you can get out of such a physics is so straightforward to describe. Everything reduces to causal interactions among localized quantitative properties, and so the possible higher-order entities are those you can build out of quantity, space, and causality. It's thoroughly unmysterious. What is mysterious is to suggest that you will get colored objects spontaneously showing up as well, like the ghost of Mickey Mouse hovering above the equations.
None of this is meant to suggest that neuroscience will cease to make progress in producing a causal, analytical and physical account of human consciousness. On the contrary, that progress is going to highlight ever more strongly the ontological mismatch between appearance and physical theory, and will ultimately show us what the correct physical ontology is, if we can avoid clinging to a particular reification or visualization of what the formalism is about. Celia Green writes (Chapter 7 here) that
The step after that is to reinsert the phenomenological ontology into the physical ontology, which is what this article is about.
Don't sweat it -- I honestly don't care in the slightest.
I will have to agree with rhollerith_dot_com here -- you are treating as absurd a thesis we consider ordinary. And I think it's actually worse than that: you are treating as absurd a theory which you explicitly state you would not treat as absurd in any other context. That's not just strange -- that's downright reckless.
Now, you would be justified in being this reckless if you had a substantial amount of evidence to support your idea. We accept quantum mechanics, which is downright strange relative to the Middle-World of our day-to-day experience, but we accept it because it's been proven sixteen ways to next Sunday. But in support of your thesis that human consciousness must be analyzed differently to every other phenomenon in the universe, you have ... the naive sensation of indivisibility in the subjective experience of color.
That's not evidence. That's the phenomenon that needs explaining. And given all the myriad ways in which consciousness fails -- all the errors it makes in analyzing the physical world -- there is no sense in which subjective sensation can ever be a fitting element in a fundamental Theory Of Everything the way you seem to be proposing.
Heh, I was kind of scratching my head at it though. "Wait, did I miss something about Robin Z?"
Only the degree of my indifference to pronouns!
But I did explain why. We have some direct knowledge of consciousness. We have no direct knowledge of what's outside it. Therefore we are not as free to theorize about what consciousness really is; we must at least acknowledge what is there. That includes color, and so theories of nature which don't include color are ultimately untenable, even if they can have interim value as heuristic partial theories.
And by the way, indivisibility of color is not the problem. It is the failure to actually produce color by piling up lots of noncolor.
So far as I can determine, you have not understood anything I or any other physicalist has said. I cannot see any value in spending any further time on this discussion.
A small note (no need to respond): my account as constructed so far is consistent with what Silas has proposed, a proposal I am inclined to accept.
A second small note (again, no need to respond): the analogy to the videogame was not an analogy to the visual output of the console as seen on the television, but to the internal representation within the program. So far as I can ascertain, the distinction is probably moot with regards to your reply.
The confusion in this debate has nothing to do with color or experience; it's about how ontologies and definitions are (or should be) structured. Rather than try to give an incomplete explanation here, I'll write a top-level post to cover the topic properly (probably in about a week)