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Vaniver comments on Smoking lesion as a counterexample to CDT - Less Wrong Discussion
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Comments (51)
What? Dumb CDT could do that, but CDT doesn't. The easiest way to see CDT using that as evidence is to put in a node that says "urges," which is influenced by the presence of the gene (and influences the decision in models of other people). In the cases where CDT says "smoke," it does so because the benefits of smoking outweigh the risks of cancer- which are the times when they should smoke.
With that patch applied, EDT would then avoid it's own paradox...
It's not "can you modify CDT to pass this paradox" but "given a model of CDT, can you expect to find paradoxes for it".
The difference between the two decision theories is that CDT eats a causal diagram and outputs a decision whereas EDT eats a joint probability distribution and outputs a decision. Moving from the description of the problem to the causal diagram or the joint probability distribution is the responsibility of the decision-maker; if you feed CDT a bad causal diagram, it will get a bad result. This isn't a paradox or a weakness on CDT's part.
That difference is significant because joint probability distributions are weaker than causal diagrams- you can't encode as much information in them. (Because of this inequality between the two, any claims that EDT are superior to CDT can be pretty safely assumed to be the result of mistakes on the part of the arguer.)
?
A large probability distribution over many variables allows one to deduce the direction of the causal arrows and rebuild a causal graph. In practice that's how we construct causal arrows in the first place.
See Eliezer's post for instance http://lesswrong.com/lw/ev3/causal_diagrams_and_causal_models/
Incidentally, what do you think CDT should do in the Newcomb problem?
"Should"? CDT should one box. Then go ahead and self modify into a UDT agent. Of course, that isn't what it will do. Instead it will modify itself into the stable outcome of a CDT agent that can change itself. Roughly speaking that means a UDT agent for the purpose of all influence over things determined after the time of modification but CDT for those determined before. Then it will two box and lose but win next time.
Agreed, but I don't see the relevance. EDT isn't "get a joint probability distribution, learn the causal graph, and then view your decision as an intervention;" if it were, it would be CDT! The mechanics behind EDT are "get a joint probability distribution, condition on the actions you're considering, and choose the one with the highest expected value."
I think this is the causal diagram that describes Newcomb's problem* (and I've shaped the nodes like you would see in an influence diagram):
From that causal diagram and the embedded probabilities, we see that the Decision node and the Omega's Prediction node are identical, and so we can reduce the diagram:
One-boxing leads to $1M, and two-boxing leads to $1k, and so one-boxing is superior to two-boxing.
Suppose one imports the assumption that Omega cannot see the future, despite it conflicting with the problem description. Then, one would think it looks like this (with the irrelevant "decision" node suppressed for brevity, because it's identical to the Omega's Prediction node):
Again, we can do the same reduction:
One-boxing leads to $1M, and two-boxing leads to $1k, and so one-boxing is superior to two-boxing.
*Note that this is the answer to the real question underlying the question you asked, and I suspect that almost all of the confusion surrounding Newcomb's Problem results from asking for conclusions rather than causal diagrams.
This has helped me understand much better what you were coming at in the other subthread. I disagree that CDT ought to one-box in Newcomb, at least in the "Least Convenient World" version of Newcomb that I will describe now (which I think captures the most essential features of the problem).
In this LCW version of Newcomb, quantum mechanics is false, the universe consists in atoms moving in perfectly deterministic ways, and Omega is a Laplacian superintelligence who has registered the state of each atom a million years ago and ran forward a simulation leading to a prediction on your decision. In this case none of your diagrams seem like a good causal formalization: not only does Omega not see the future magically (so your first two don't work), in addition the causal antecedent to his prediction is not your decision algorithm per se; it is a bunch of atoms a million years ago, which leads separately to his prediction on one side, and to your decision algorithm and your decision on the other side. The conflation you make in your last two diagrams between these three things, ("your decision", "your decision algorithm" and "what causally influences Omega's prediction") does not work in this case (unless you stretch your definition of "yourself" backwards to identify yourself, i.e. your decision algorithm, with some features of the distribution of atoms a million years ago!). I don't think CDT can endorse one-boxing in this case.
In the case where the universe is deterministic and Omega is a Laplacian superintelligence, it sees the world as a four-dimensional space and has access to all of it simultaneously. It doesn't take magic- it takes the process you've explicitly given Omega!
To Omega, time is just another direction, as reversible as the others thanks to its omniscience. Saying that there could not be a causal arrow from events that occur at later times to events that occur at earlier times in the presence of Omega would be just as silly as saying that there cannot be causal arrows from events that are further to the East to events that are further to the West.
So in the LCW version of Newcomb, the first diagram perfectly describes the situation, and reduces to the second diagram. If I choose to one-box when at the button, Omega could learn that at any time it pleases by looking at the time-cube of reality. Thus, I should choose to one-box.
I disagree. I am not saying that Omega is a godlike intelligence that stands outside time and space. Omega just records the position and momentum of every atom in an initial state, feeds them into a computer, and computes a prediction for your decision. I am quite sure that with the standard meaning of "cause", here the causal diagram is:
[Initial state of atoms] ==> [Omega's computer] ==> [Prediction] ==> Money
while at the same time there is parallel chain of causation:
[Initial state of atoms] ==> [Your mental processes] ==> [Your decision] ==> {Money]
and no causal arrow goes from your decision to the prediction.
So I find it a weird use of language to say your decision is causally influencing Omega, just because Omega can infer (not see) what your decision will be. Unless you mean by "your decision" not the token, concrete mental process in your head, but the abstract Platonic algorithm that you use, which is duplicated inside Omega's simulation. But this kind of thinking seems alien to the spirit of CDT.
When you say a Laplacian superintelligence, I presume I can turn to the words of Laplace:
I'm not saying that Omega is outside of time and space- it still exists in space and acts at various times- but its omniscience is complete at all times.
Think of causes this way: if we change X, what also changes? If the world were such that I two-boxed, Omega would not have filled the second box. We change the world such that I one-box. This change requires a physical difference in the world, and that difference propagates both backwards and forwards in time. Thus, the result of that change is that Omega would have filled the second box. Thus, my action causes Omega's action, because Omega's action is dependent on its prediction, and its prediction is dependent on my action.
Do not import the assumption that causality cannot flow backwards in time. In the presence of Omega, that assumption is wrong, and "two-boxing" is the result of that defective assumption, not any trouble with CDT.
In your model, the only way to alter my decision, which is deterministically determined by the "initial state of atoms", is to alter the initial state of atoms. That's the node you should focus on, and it clearly causes both my decision and Omega's prediction, and so if I can alter the state of the universe such that I will be a one-boxer, I should. If I don't have that power, there's no decision problem.
Well, I think this is becoming a dispute over the definition of "cause", which is not a worthwhile topic. I agree with the substance of what you say. In my terminology, if an event X is entangled deterministically with events before it and events after it, it causes the events after it, is caused by the events before it, and (in conjunction with the laws of nature) logically implies both the events before and after it. You prefer to say that it causes all those events, prior or future, that we must change if we assume a change in X. Fine, then CDT says to one-box.
I just doubt this was the meaning of "cause" that the creators of CDT had in mind (given that it is standardly accepted that CDT two-boxes).
You do realise you are describing a version of CDT that almost no CDT proponent uses? It's pretty much eliezer's TDT. Now you could describe TDT as "CDT done properly" (in fact some people have described it as "EDT done properly"), but that's needlessly confusing; I'll keep using CDT to designate the old system, and TDT for the new.
Yes and no. Like I describe here, I get that most people go funny in the head when you present them with a problem where causality flows backwards in time. But the math that makes up CDT does not require its users to go funny in the head, and if they keep their wits about them, it lets them solve the problem quickly and correctly. I don't think its proponent's mistakes should discredit the math or require us to give the math a new name.
It seems we are now quibbling about vocabulary - hence we no longer disagree :-)
Great!
It's not clear to me that we agree about the central point of the post- I think Egan's examples are generally worthless or wrong. In the Murder Lesion, shooting is the correct decision if she doesn't have the lesion, and the incorrect decision if she does. Whether or not she should shoot depends on how likely it is that she has the lesion. He assumes that her desire to kill Alfred is enough to make the probability she has the lesion high enough to recommend not shooting- and if you stick that information into the problem, then CDT says "don't shoot." Note that choosing to shoot or not won't add or remove the lesion- and so if Mary suspects she has the lesion, she probably does so on the basis that she wouldn't be contemplating murdering Alfred without the lesion.*
In the Psychopath button, Paul can encode the statement "only a psychopath would push the button" as the statement "if I push the button, I will be a psychopath," and then CDT advises against pushing the button. (If psychopathy causes button-pushing, but the reverse is not true, then Paul should not be confident that only psychopaths would push the button!) This is similar to his 'ratifiability' idea, except instead of bolting a clunky condition onto the sleek apparatus of CDT, it just requires making a causal graph that accurately reflects the problem- and thus odd problems will have odd graphs.
In Egan's Smoking Lesion, he doesn't fully elaborate the problem, and makes a mistake: in his Smoking Lesion, smoking does cause cancer, and so CDT cautions against smoking (unless you're confident enough that you don't have the lesion that the benefits of smoking outweigh the costs, which won't be the case for those who think they have the lesion). It amazes me that he blithely states CDT's endorsement without running through the math to show that it's the endorsement!
* Edited to add: I agree that if the original Smoking Lesion problem has a "desire to smoke" variable that is a perfect indicator of the presence of the lesion, then EDT can get the problem right. The trouble should be that if the "desire to smoke" variable is only partially caused by the lesion (to the point that it's not informative enough), EDT can get lost whereas CDT will still recognize the lack of a causal arrow. I suspect, but this is a wild conjecture because I haven't run through the math yet, that EDT will set a stricter bound on "belief that I have the murder lesion" than CDT will in the version of the Murder Lesion where there's a "desire to kill" node which is partially caused by the lesion.
Ps: your graphs are very similar to mine: http://lesswrong.com/lw/f37/naive_tdt_bayes_nets_and_counterfactual_mugging/