silence and looping, which is discussed explicitly in the paper

I confess to having downloaded the paper recently and not given it more attention than was necessary to satisfy my usual habit of having primary sources at hand. I've gone back and read it more carefully, but it probably deserves still longer scrutiny.

(Welcome to Less Wrong, by the way. I don't suppose you need to post an introduction, seeing as you have your own Wikipedia page. Nice to be chatting with you here!)

However, I'm not seeing where this is discussed explicitly, other than (this is perhaps what you mean) under the general heading of using "quantized stimulus parameters" as input to the GLUT-generating process. I grant that this does adequately deal with the most crude timing attacks imaginable.

There do seem to me to be other, more subtle attacks which - according to my earlier argument that, if you have to go back to the drawing board each time such an attack is found, leave the GLUT critique of behaviourism ineffective - would still prove fatal. For instance we can consider teachability of the GLUT, to uncover an entire class of attacks.

Suppose there is some theoretical concept, unknown to the putative human programmers of the GLUT (or perhaps we should call them conversation-authors, as the programming involved is minimal), but which can be taught to someone of normal intelligence. I don't want to restrict my argument to any particular domain, but for illustrative purposes let's pick the phenomenon of lasing light. This is a reasonable example, since the GLUT concept would have been implementable as early as Babbage's time and the key insights date from Einstein's.

In this scenario, the GLUT's interviewer choses as his conversation topic the theoretical background needed to build up to the concept of lasing light. The test comes when she (gender picked by flipping a coin) asks the GLUT to make specific predictions about a given experimental setup that extrapolates relevant physical law into a domain not previously discussed, but where that law still applies.

By my earlier stipulation, the GLUT's builders must discover, in the process of building the GLUT, the physical law of lasing light. They must also prune the conversation tree of "wrong" predictions, since that would alert the interviewer to the fact that the GLUT was "faking" understanding up to the point of the experimental test; this rules out the builders merely "covering all (conversational) bases". They must truly understand the phenomenon themselves.

(One may object that it would take an inordinately long time to teach a person of merely normal intelligence about a phenomenon such as lasing light. But we have earlier stipulated that the length of the test can be extended to human lifespans; that is surely enough for a person of normal intelligence to eventually get there.)

We are led to what is (to me at least) a disturbing conclusion. The building of a GLUT entails the discovery by the builders of all experimentally discoverable physical laws of our universe that can be taught a person of normal intelligence in a reasonable finite lifespan.

I'm not a professional philosopher, so possibly this argument has holes.

Nevertheless it seems to me that this unpalatable conclusion points to one primordial flaw in the GLUT argument: it goes counter to the open-ended nature of the optimization process known as intelligence. You cannot optimize by covering all bases, for the same reason that a theory that can explain all conceivable events has no real content.

The original paper tried to anticipate this objection by offering as a general defense the stipulation that the GLUT should simulate a "desert island" type of castaway, so that the GLUT would be dispensed of the capacity to converse fluently about current events. But the objection is more general and its force becomes harder to avoid if the duration of the test is extended greatly: we need to imagine that the GLUT can be brought up to date with current events, and afterwards respond appropriately to them, as would a person of normal intelligence. This requires the GLUT builders to anticipate the future with enough precision to prune "inappropriate" responses, and so the defense that the builders would "cover all bases" is untenable.

The domain of physical law is the one where the consequences of the teachability test are brought into sharpest focus, but I suspect that "merely social" tests of the GLUT in everyday life would very quickly expose its supposed intelligence as a sham.

Behaviourism, or God-like GLUT builders: pick your poison.

Ok, basic confusion here. ...obviously...

Tut, tut. Assuming the confusion you claim to see is mine: you don't get to tell me that my objection to an intuition pump is incoherent, you are required to show that it is incoherent, and it is preferable to avoid lullaby language in such argumentation.

Yes, the question "what is your index" exposes the GLUT as a confused intuition pump. I am at present looking at the Ned Block (1981) paper Psychologism and Behaviorism which (as best I could ascertain) is the original source for the GLUT concept. It makes a similar claim to yours, namely that "for a Turing Test of any given length, the machine could in principle be programmed in just the same way to pass a Turing Test of that length".

But sauce for the goose is sauce for the gander: for a GLUT of any size, there is a Turing Test of sufficient duration that exposes the GLUT as not conscious, by looping back to the start of the conversation! This shows that the argument from a necessarily finite index does have force to counter the GLUT as an intuition pump.

It is flawed in other ways. You can't blame Ned Block who at the time of writing that paper can't have spent a lot of time on IRC, but someone with that experience would tell you that indexing on character strings wouldn't be enough to pass a 1-hour Turing test: the GLUT as originally specified would be vulnerable to timing attacks. It wouldn't be able to spontaneously say something like "You haven't typed anything back to me for thirty minutes, what's wrong?"

"OK", a GLUT advocate might reply, "we can in principle include timings in the index, to whatever timing resolution you are capable of detecting".

It's tempting to grant this "in principle" counter-objection, especially as I don't have the patience to go to the literature and verify that the "timing attack" objection hasn't been raised and countered before.

But the fact that the timing attack wasn't anticipated by Ned Block is precisely what shows up the GLUT concept as a faulty intuition pump. You don't get to "go back to the drawing board" on the GLUT concept each time an attack is found and iteratively improve it until its index has been generalized enough to cover all possible circumstances: that is tantamount to having an actual, live, intelligent human sit behind the keyboard and respond.