Seasons

Dear Psimagus:

My view of the double-slit experiment is very straightforward. A wave goes through two slits and is diffracted. It interacts with the detector screen in a punctiliar, probabilistic fashion. There is no particle that travels in a continuous trajectory (or several) from the source to the screen. It is true that, once you assume that there is such a particle, you are led to bizarre conclusions; I conclude by reductio ad absurdum that the assumption is false. Other evidence that it is false comes from quantum tunneling, wherein a 'particle' goes from A to B even though there is a region between the two in which the 'particle' cannot exist.
There is currently a whole industry consisting of finding the most bizarre possible interpretations of Quantum Mechanics. There must be twenty or thirty such interpretations by now. If profundity varies directly with distance from common sense, conceptual clarity, and logical consistency, many of these interpretations are extremely profound.
You write, "this interpretation is generally accepted to be unavoidable." I do not think this is so - there are many interpretations of Quantum Mechanics, and debate on these issues continues - but in any event, I am not deeply concerned with what is "generally accepted." I make my own decisions, based on formulations of Quantum Mechanics such as that found on pp. 214-225 of Cohen-Tannoudji, Diu, and Laloe, Quantum Mechanics. If you can derive your views rigorously from such postulates, I will be very impressed, revise my opinions, and apologize for giving you a hard time.

Walk in Beauty, Irina

Dear Psimagus:

I am not opposed to multi-location in principle. I believe that it is possible to give a consistent account of time-travel (though there is no evidence I know of that time-travel actually happens), according to which I could go back in time and shake hands with my earlier self. In such a case, I would be in two places at once. There would not be two of me, however.

IMCO (In My Curmudgeonly Opinion), there is such a thing as identity. It is the relation that each thing bears to itself, and to nothing else. The set {x,y} has one element if and only if x exists and is identical to y. If x exists and y exists but x is not identical to y, then {x, y} has two elements. Is there anything in this paragraph that you disagree with?

Dear Psimagus:

I do not think that quantum entanglement is the same as identity. On the contrary, if 'particle' X has spin up, and 'particle' Y simultaneously has spin down, as often happens in EPR cases, they cannot be the same particle (unless Quantum Mechanics is false). I conclude that even if Irina-1 and Irina-2 are 'entangled' (Ooh, sounds like fun!), they need not be the same person.

Dear Bev:

Here is an interesting (I do not say conclusive) argument about the supposed reducibility of subjective experience to physical qualities (I'll give a citation for it later) :

Let's suppose (for the sake of argument) that someday we develop a complete reduction of inner experience to neurophysiology. That is, for any possible experience, we can specify exactly how brain cells, neuromodulators, etc. must be arranged in order for that experience to occur. Conversely, for any possible arrangement of brain cells, etc., if that arrangement produces a conscious experience, we know what that experience will be.
Now let us imagine a woman (call her "Bevrina") who has been blind from birth. She has never had any visual experience. In particular, Bevrina has never experienced redness. She has, however, studied neurophysiology and completely mastered the subject. In particular, she knows exactly what's going on in people's brains when they experience redness.
But then, she should be able to consult her books and find out what red looks like. For, we have assumed that Science has discovered which subjective experiences go with which brain states.

But isn't there something implausible about the idea that a person who has been blind from birth would be able to find out what red looks like by consulting a book? Can what red looks like be described in words?

If an assumption leads to a false conclusion, that casts doubt on the assumption. The assumption that Science will one day be able to say which inner experiences follow from which neurophysiological states appears to lead to the implausible conclusion that it is possible that a woman blind from birth can learn what red looks like by consulting neurophysiology books. This casts doubt on the assumption.

I see one flaw in that model. She can know what the brain state for red would be, but she would only know what red looks like if there were a way of inducing that same brain state within her own head.

Which is slightly more plausible in one sense, and less in another. We'd need a way to induce any desired brain state in someone.

Dear Ulrike:

You write: "I see one flaw in that model. She can know what the brain state for red would be, but she would only know what red looks like if there were a way of inducing that same brain state within her own head."

Which she presumably can't do, her brain not being capable of entering those states. But why is this a flaw? What is it a flaw in?
I find it quite plausible that "She can know what the brain state for red would be, but she would only know what red looks like if there were a way of inducing that same brain state within her own head." But this does not seem to reveal a flaw in the argument I presented. Rather, it reinforces the argument. The argument runs thus:

Premises:
(1) If there were a complete theory of the relations between brain states and states of subjective experience, then Bevrina could know what red looks like, simply by learning what brain states constituted seeing (or appearing to see) something red, and then using the theory to find out what inner states went with brain states of that kind.
(2) But Bevrina cannot know what red looks like, even though she can learn everything about that aspect of neurophysiology.
Conclusion:
(3) There can be no complete theory of the relations between brain states and states of subjective experience.

Now, the consideration you raised would seem to support premise (2). But supporting a premise of an argument does not show that there is a flaw in the argument; in fact, supporting a premise of an argument tends to support the conclusion, if the argument is valid.

So if your point discloses a flaw, I would say that it is a flaw in the idea that one can have a complete theory of the relations between brain states and states of subjective experience.

Walk in Beauty, Irina

Irina: the flaw is that your argument presupposes that READING about the brain state CAUSES her to experience the color red. It does not. It causes her to know what her brain state would be TO experience the color red. In order to experience it, she would have to induce that brain state.

The flaw is the jump from "reading about a brain state" to "experiencing that brain state". In your original argument, it appeared that you equated the two.

psimagus: let me put it this way. If someone ever DOES manage to duplicate a human brain with all of its experiences and memory (including body memory) intact using only physical parameters, that might just convince me that there was nothing beyond the physical. Until then, there's not much to discuss.

Small clarification in terms: physical = measurable and consistent (two people measuring it will get the same result).

Ulrike:

Oh, Dear! I did a very poor job of exposition, then! I apologize! The point I was trying to make was exactly the opposite.

The argument was meant to have the form of a reductio ad absurdum (reduction to absurdity). It makes the assumption that we could have a complete theory only to refute that assumption. It refutes it by showing that if it were true, something highly implausible would also have to be true. That highly implausible something is precisely the idea that a person blind from birth could come to know what red looks like by reading a book.

Far from presupposing that reading about a brain state allows you to enter it, the argument presupposes that this is not in general the case! In other words, the argument runs,

IF
(A) : We had a correct theory about the corelation between brain states and subjective experience,
THEN
(B) : Bevrina would be able to learn what red looks like, by reading about this theory.
(Note that "If A then B" does not imply "A")
BUT
(C) : Bevrina CANNOT learn what red looks like by reading about it, just as you say!
THEREFORE,(D) : (A) must be false!

The argument claims that someone who believes (A) ought to conclude (B), but the argument itself does not conclude (B) . On the contrary, the argument uses the falsehood of (B) in order to argue for the falsehood of (A).

I hope this clarifies things.

I disagree with A implying B above. That's like saying we have a theory (gravity) about what happens when an object falls. Reading about this theory means I can experience what it's like to fall from a 100-story building. No.

Or closer to yours: We have a theory for how people walk. Someone born with no legs can read this theory and understand what it feels like to walk.

Your argument requires the assumption that reading and understanding a theory of X is equivalent to experiencing X. Reading about how X works does not tell you how X feels.

My view of the double-slit experiment is very straightforward. A wave goes through two slits and is diffracted. It interacts with the detector screen in a punctiliar, probabilistic fashion. There is no particle that travels in a continuous trajectory (or several) from the source to the screen.

So you think there is no such thing as a photon, and that light only comes in waves? Now that would seem unorthodox these days (though a century ago I agree it was generally accepted.)
Or that it is distinctly wave or particle at one time but not at another? And that that time can be controlled by approaching it with a measuring device? The light, that has left its emitter as a particle, can effectively predict what sort of measuring device it's going to encounter, and configure itself accordingly? Because if you replaced the difraction grating with a photon detector, a photon is exactly what you'd detect.
That wouldn't be duality - it would be some kind of alternating state. An alternation whose primary purpose moreover would appear to be to make the universe more closely align itself to human concerns about "common sense" (or somesuch.) I tend to doubt the universe cares very much about fitting in with our prejudices - it certainly never went out of its way to provide us with a flat earth or an earth-centred solar system when it might have saved us much head-scratching and occasional anguish.

I sadly don't have a copy of Cohen-Tannoudji, Diu, and Laloe, Quantum Mechanics
to hand (I tend to rely on Penrose, Road to Reality for the most part, since it saves so many feet of bookshelf I'd otherwise need to cover a dozen different disciplines - a highly recommended "user guide" to the universe I might add,) but I will see if our library does have it, and check it out if I can (in fact, with a challenge like that, I'm determined to! )

Cohen-Tannoudji, Diu, and Laloe, Quantum Mechanics

Ouch! That's a week's wages on amazon, and I can confidently predict Swansea Library won't have diverted that much of their Mills & Boon budget to a serious subject. I don't suppose you've got a cheaper reference?