Newcomb's Paradox

How do you know which world you are living in? It is a strange burden of proof you are alleging, given today’s general acceptance that local realism isn’t physically tenable.

Also, have you physically demonstrated that a game of rock-paper-scissors can be played in this world for an infinite number of iterations without a winner emerging? How do you propose testing for non-termination?

If one is prepared, for sake of argument, to accept the premmise of an infallible predictor without proof, then it seems especially odd to reject a theoretical solution on the basis that it lacks demonstrable proof.

You are misunderstanding what I am saying. By “world” I am not making any claim about the real world. I am talking about logic here, “world” just mean canvas of facts if you want. I am just saying (1) \land (2) \implies \bot. To show that this is not true is to show that we can have (1) and (2) at the same time without a contradiction. This is what I mean by “world where (1) and (2) are true”.

Are you really arguing there is a chance that Box 2 exists in a superposition of having $1M and having $0?

What relevance is the world “almost” here? Either the predictor is assumed to be infallible, which reduces the pay-off matrix to the diagonal elements, or he isn’t, and all four payoff outcomes are realizable.

Newcomb’s problem is worded in a ‘bait and switch’ fashion, that attempts to blur the distinction between the classical Newcomb problem, in which two boxing is optimal relative to boxes that have definite contents prior to opening them, and the quantum version in the limit of infallibility in which one-boxing is optimal. The unaware reader ends ups conflating quantum and clasical intuitions in a never-ending loop of second-guessing what the predictor predicted.

[quote=“noAxioms, post:339, topic:298”]
I fail to see the relevance of quantum anything in this scenario. Quantum uncertainty doesn’t grant free will, it only grants randomness, not deliberate free choice. Randomness does not yield optimal utility in this scenario. [/quote]

What we are specifically referring to are the remaining diagonal elements of the pay-off matrix when (1) is true. In this situation, if (2) is false, then only only one of those diagonal elements exist in accordance with the Opponent’s prediction, which implies the truth of (3). On the other hand, if (2) is true, then Player has the option of choosing btween the two remaining diagonal elements, implying (3) is false.

Are you asking if Newcomb’s paradox is distinguishable from Wheeler’s Delayed Choice Experiment? Personally, I do not know and am not qualified to make a principled distinction of what is or is not a decohered physical state with a definite history, but I would in ordinary circumstances take both boxes on the assumption that (3) is true.

On the other hand, in terms of qubits of polarised photons, it is possible for a predictor to create a quantum state that encodes only the diagonal outcomes of Newcomb’s pay off matrix.

Also consider Schrodinger’s Overdraft. Is it rational for a poor student to avoid checking his bank-balance, in the hope that his avoidance maintains the possibility of a bank-balance above zero? Obviously his behaviour isn’t rational from our external perspective, but I’m not sure about the rationality from his perspective. I’d urge him to check his balance, but I feel that I can’t give him a good reason why.

Game 2 is structurally identical to Game 3, meaning my argument is structurally identical. Not only is structurally identical, it is literally identical. Why?

Because you set up the causal relations identically between the options a) and b), and the choices of me-me and other-me.

The only difference you made is the way that we signal whether we choose a) or b).

In Game 2, “pressing the b) buttom” is enacted by me picking up a red and a blue box.

In Game 2, “pressing the b) buttom” is enacted by me picking up a blue box.

It doesn’t matter how you “press the button”, how you choose a) or b). What matters are the consequences. In my response to Game 2, I never talked about the mechanism for selecting a) or b). As such, my response to Game 2 can be used for any game where a) and b) are the same choice, but the mechanism is different.

But I very much appreciate your games, because the point to the deeper TB argument. A lot of the time, us TBs will say, “the money is already in Box 2, or already not in Box 2.”

We lean on this physical intuition to help make our point. You have removed the whole element of money being in the boxes. Instead, the boxes are irrelevant, and you are just making a choice, and your choice is correlated with a past choice.

But TBism never relied on the money physically (not) being in Box 2. The crux of the TB argument is of the form:

The most decisive choice has already been made in the past, and we cannot change it now in the present (Phase 2). All we do is change our knowledge regarding what likely happened, because our current choice is correlated with the past choice. But knowledge \ne money

This argument is made more intuitive when the $1M is literally lying in Box 2, or literally not lying in Box 2. But it was never necessary, because whether or not the participant has won that $1M has nonetheless already been determined in the past.

Anyways, just to be absolutely clear that I have responded to Game 3, I will paste in Game 3’s rules below, and then my response to Game 2, re-appropriated for Game 3. You will see that with literally no changes, my response to Game 2 still holds. Then at the end of this, I will give you a variation on Newcomb’s Game to show you what I mean above.

Game 3

  1. There is an empty red box and an empty blue box

  2. You are cloned

  3. You are asked to choose between either a) the red box or b) the blue box

  4. The clone is asked to choose between either a) the red box or b) the blue box

  5. The clone is destroyed

  6. If you both chose (a) then you win $1,000,000

  7. If you both chose (b) then you win $1,000

  8. If you chose (a) and your clone chose (b) then you win $0

  9. If you chose (b) and your clone chose (a) then you win $1,001,000

So, again I assume neither of us know we are the clone.

Now, using the same argument as for Game 1, I am assuming no inherent, ethical care for other-me. I only care about what is beneficial to me-me, so any care (if at all) for other-me would merely be an extension of my care for me-me.

So, do I selfishly care about other-me in this scenario?

Well, if I care about other-me, then other-me probably cares about me too. But, one of two things is true:

  1. Other-me has already made their decision, and I cannot impact it.

  2. Other-me will make their decision after me, which means I am the clone and will die, meaning I don’t care about anything anyways.

So, caring about other-me possibly cannot help me-me. Therefore, in this scenario, I neither have selfless nor selfish reasons to care about other-me. That covers any and all reasons to care about other-me, which means I do not need to re-create my matrix above. (I only made it as a matter of clarity in the first section).

So, the possibility space is reduced to this: am I the clone or the non-clone?

If I am the clone, then my actions do not matter to me-me.

If I am not the clone, then it matters. So, I know my clone chose either a) or b), though I have yet to determine the likelihood of which. I can nonetheless evaluate how much I win in either scenario:

My clone picked a) [Option 1]

If I pick a), I get $1M. If I pick b), I get $1,001,000.

My clone picked b) [Option 2]

If I pick a), I get $0. If I pick b), I get $1000.

In both scenarios, me-me picking b) gives me more money than me-me picking a).

We say that me-me picking b) dominates. So, on first thought, I should pick b).

But, my clone would likely think the same! This increases the likelihood that Option 2 is correct. So, does that change anything? Well, choice b) is still better in Option 2, so no… no it does not change anything.

If I could affect the past choice of my clone, then I would want to make it pick a). But I cannot affect the past, I cannot affect the clone. My behavior is indicative of the likely behavior of the past clone. So, if I behave selfishly by picking b), then that is bad news to me-me.

But if I instead go for a), I am not actually changing the past behavior of the clone. If I go for a), I am simply picking the option that will give me less money because it gives me better news.

I do not optimize the niceness of the news my behavior gives me. I do not optimize the optimism of the knowledge I gain. I optimize the actualities around me, I optimize the present/future because I cannot optimize the past.

This is my nature. There are games that punish this nature, and there are games that do not. We do not define rationality based on some games. We define rationality based on truth. We use that truth to create a rational decision theory. Believing in that rational decision theory will usually outperform believing the irrational theory, because alignment with truth happens to usually help in the real world.

And as I’ve argued in an earlier post, these games do not punish me for applying CDT. These games punish me for believing in CDT.

They punish me for my nature/beliefs in the past, and that is why you see non-CDT adherents winning over me in these games. If you look across all real games, then the picture will be different. Truth matters. CDT follows the truth by upholding the unidirectionality of causality, thus properly differentiating between correlation and causation. Applying this will always be better. Believing in this, not always. Sometimes we are punished for our beliefs, even if they are better/rational.

Now, if I have a rational belief, and I know I am about to go into a situation where that belief will harm me, then (if it’s worth it), it will be rational to let go of the rational belief. This is rational adaptation, which I covered in the OP.

Now, rationally letting go of a rational belief is impossible, unless you change the very pre-conditions for that rational belief. This is what I do with my contract in Version 2 of the Newcomb Game. In the Iterated Version, I do not need to do anything extra, as the pre-conditions are already there. OB-ing is automatically rational in the Iterated Version of the Newcomb Game. No belief of mine needs to be rationally changed in that case.

The equivalent of Version 2 in your Game 2 would be somehow colluding with my clone before we face our dilemmas. But, a mere agreement would not be enough. Mere agreements are only rationally effective IF you will continue to interact with the other party: ie, there needs to be iteration. This is why the business world somewhat functions despite having plenty of psychos.

But in Game 2, one of us will die. There is no iteration, and so there is no rational, selfish reason for adhering to a mere agreement.

We would need to involve a third party and make a contract with them, such that they would sufficiently penalize the survivor for not adhering to the agreement. This would make it selfishly rational to honor the agreement to pick a).

But again, this requires collusive pre-planning! There is no such thing here. All there is, is a past I cannot affect.

So, I pick option b).

A Variation on V1 of the Newcomb Game

We’ve got all the same rules as V1 of the Newcomb Game, except for this:

When the predictor predicts that Bob is an OB, the predictor does not put $1M in Box 2. Instead, the predictor sends $1M into Bob’s bank account.

Bob is prevented from getting a notification of this, of course. He has no idea.

Bob then enters the room, and there is simply $1000 on the table. The predictor explains how it made its prediction about his behavior yesterday, and if the predictor predicted he was an OB, there is an extra $1M in his bank account. If not, there is not.

Of course, in this scenario, being an OB means not grabbing the $1000. Being a TB means grabbing that $1000. The only difference is your means of signalling your choice of OBism v. TBism, and the fact that the $1M has not been physically put into a box. Instead, it’s been put into a bank account.

So, Bob, do you grab the $1000 lying on the table?

Read the rules carefully. You make your choice before the clone.

You are committing the same mistake as explained here.

There are four outcomes to consider:

  1. If your clone chooses (a) and you choose (a), you win $1,000,000
  2. If your clone chooses (a) and you choose (b), you win $1,001,000
  3. If your clone chooses (b) and you choose (a), you win $0
  4. If your clone chooses (b) and you choose (b), you win $1,000

You cannot influence the clone’s choice after the clone has been created, but you can rule out two of the four outcomes by making a choice — and then you ought consider which of the remaining two is most likely.

My reasoning gives me this:

  1. If your clone chooses (a) and you choose (a), you win $1,000,000 (99%)
  2. If your clone chooses (a) and you choose (b), you win $1,001,000
  3. If your clone chooses (b) and you choose (a), you win $0 (1%)
  4. If your clone chooses (b) and you choose (b), you win $1,000

Your reasoning gives you this:

  1. If your clone chooses (a) and you choose (a), you win $1,000,000
  2. If your clone chooses (a) and you choose (b), you win $1,001,000 (1%)
  3. If your clone chooses (b) and you choose (a), you win $0
  4. If your clone chooses (b) and you choose (b), you win $1,000 (99%)

And this is demonstrated by the fact that if there are 200 participants, and if 100 of them are committed red-boxers, and if 100 of them are committed blue-boxers, and if the clones agree with their original 99% of the time, then we could expect on average:

  1. 99 red-boxers will win $1,000,000
  2. 99 blue-boxers will win $1,000
  3. 1 red-boxer will win $0
  4. 1 blue-boxer will win $1,001,000

You want to phrase this as the game “rewarding irrationality”, which makes no sense. In the context of this game, the rational choice is the choice that is most likely to maximise your reward, which is proven to be red-boxing and not blue-boxing.

Yes, it is, but if your reasoning is sound then you should be able to use it to justify your choice in Game 3 without reference to Game 2.

I don’t need Game 2 to show that my reasoning is sound in Game 3, and I don’t need Game 3 to show that my reasoning is sound in Game 2. The comparison is simply an additional tool to further support my reasoning.

Even if you go so far as to interpret the wave-collapsing measurement in Quantum Mechanics as necessarily being conscious perception by a lifeform (which is not the normal stance), then the wave function of those $1M has already been collapsed (not that it was in a superposition in the first place), because the predictor had to grab those $1M and stuff them in the Box 2. Or maybe the predictor’s assistant. Or, alternatively, the predictor had to grab a fistful of air, and stuff it into Box 2. Doesn’t matter.

Researches hit a record of putting 6,100 qubits in a superpositional state in 2026 (source). That’s 6,100 atoms.

In a SINGLE dollar bill, there is roughly 10^{22} to 10^{23} atoms. (source)

You are engaging in deepity here, my friend. There is no wiggle room. There is absolutely no reason to think quantum shenanigans are happening in this thought experiment. We live in the macroscopic world, not the nanoscopic world.

You are basically saying, “If we violate the laws of physics, then one-boxing works!” Okay great, you just said one-boxing doesn’t work then. You’re a two-boxer, just say that.

This was the smartest thing you said in your post.

Blah-blah-blah. If those qubits are going to determine whether the $1M is in Box 2, THEY HAVE TO BE ENTANGLED WITH THE $1M. But that would require putting ONE FUCKING MILLION DOLLARS INTO A SUPERPOSITION.

If you have way to do that, please let me know, and we won’t be millionaires, we’ll be trillionaires.

There is no getting around that, because the crux of the the Newcomb Problem is that the $1M has ALREADY been (or not been) administered to the participant. The only way to make that administering go into a superpositional state is to make the actual $1M go into a superpositional state. Impossible with our current physics.

Oh true! I didn’t read carefully enough, I’ll need to go back to the games. I have some stuff to do right now so I’ll need to come back to you on this.

I’m not arguing against decoherence, nor have I mentioned consciousness or other woo. I’m referring to the Heisenberg-von Neumann cut.

We’re wading into conflicting interpretations of the wave function with respect to an imcomplete theory of QM that remain unresolved, and that in the context of Newcomb’s paradox play out in terms of different underlying premises that lead to the same conclusion.

Then we are thinking of the problem the same way, but differ in our conclusions for some reason.

Also consider the game-logic of roguelike single-player video games; the video games whose game-logic generates a world, typically a dungeon, on-the-fly around a player in in response to their actions; only after the player opens a treasure chest does the game decide its contents. Likewise, it is trivial to program an “infallible opponent” whose response to the player’s choice is the appropriate diagonal of the pay-off matrix.

(Vibe-code Newcomb’s infallible predictor in Nethack, anyone?).

However, the deeper question is how feasible it is to coherently generate an entire world lazily and on-the-fly in response to the player’s actions.

There’s an obvious reason as to why complicated game worlds are designed and implemented in advance of the player arriving, namely to minimise the computational complexity required to ensure that the world grows coherently.

One-off infallible predictors are easy to implement, but the computational complexity required to ensure coherence escalates quickly the bigger the world gets, to the point that I would guess that pure coherent lazy world-generation isn’t merely complex, but generally non-computable.

The feasibility of a near-perfect predictor isn’t really relevant to the problem. It could be magic, it could be Uatu, the near-omniscient Watcher from Marvel comics, it could be a computer that simulated your brain, or it could be an exact biological copy of you from the moment you entered the room.

For the sake of the thought experiment you just assume that there is a near-perfect predictor. In 99% of cases it will correctly predict your choice. In this scenario, what should a rational agent do?

only after the player opens a treasure chest does the game decide its contents. Likewise, it is trivial to program an “infallible opponent” whose response to the player’s choice is the appropriate diagonal of the pay-off matrix.

Yeah but here, there is no prediction.

If the predictor in Newcomb says: “I program the (magical) appearance of the million if and when the player take only one box, and I program the non-appearance of the million if and when the player take two boxes.” Then I guess that’s a game master but not a predictor.

Here’s how I see things.

(1) is basically “If the predictor predicts X then X will happen” but if “X will happen” then we can’t have (2). So the only way is that the predictor never actually makes a prediction.

This messes up the original setting, how can we have the boxes in front of the player already properly filled? To fix that, you say the content of the boxes is “undetermined”, this would be rejecting (3).

But your (3) is actually that the predictor makes a prediction. In which case, you’re undermining the idea of an ‘infallible predictor’ by rejecting (3) in my opinion but I guess it’s possible.

Two box, if we are referring to the classical scenario, one box if we are referring to a probabilistic version of the quantum scenario.

Counterfactual definiteness amounts to probabilistic independence between Player’s action and Oppoents prediction when conditioned on the presence of box B on the table.

Why?

If there are 200 participants, and if 100 of them are committed one-boxers, and if 100 of them are committed two-boxers, and if the prediction is accurate 99% of the time, then we could expect on average:

  1. 99 one-boxers will win $1,000,000
  2. 99 two-boxers will win $1,000
  3. 1 one-boxer will win $0
  4. 1 two-boxer will win $1,001,000

If you one-box then you will almost certainly be in category (1) and if you two-box then you will almost certainly be in category (2). It is better to be in category (1) than in category (2). Therefore, it is rational to one-box.

The prima facie good reason to two-box is demonstrated to be misguided given the above.

1 Like

Your disjunction — either Event 2 ontically determines Event 1 (retrocausation) or it merely epistemically determines Event 1 (sad news) — is sharply posed, but I think it is a false dichotomy. It assumes that the agent’s epistemic situation during Phase 2 is purely speculative: you survey a world that is already fixed, form beliefs about it, and then decide how to act in light of those beliefs. Under that picture, learning about the box contents and bringing about changes in the world can never coincide in the same cognitive act. So either your choice reaches back and changes the box, or it merely delivers news of what’s already there.

But the deliberating agent is not a spectator of their own situation. They are exercising what Anscombe, drawing on Aquinas, calls practical knowledge. Practical knowledge is “the cause of what it understands,” unlike speculative knowledge, which “is derived from the objects known” (Intention, §48). When the agent deliberates well and concludes “I ought to one-box,” this is not a speculative discovery about an independently fixed world, nor is it an attempt to retroactively alter the past. It is a practical determination that is simultaneously self-knowledge and, given the predictor’s sensitivity to the agent’s rational grounds, world-knowledge. The agent comes to know the content of the opaque box not by peering into it but by working out what they ought to do. Their deliberation is the rational ground from which the predictor’s action already flowed.

This is also what exposes the deep conceptual difficulty in the two-boxer’s Phase 2 stance (and why the problem has remained so controversial). The two-boxer treats their own deliberation as speculative. They survey a world they take to be fixed independently of their reasoning, and try to optimize against it. But the Newcomb setup has arranged things so that the world is not fixed independently of their reasoning. The predictor has made the agent’s practical knowledge causally efficacious with respect to the very facts the agent is deliberating about. To adopt the spectatorial stance (i.e. to think “the box is filled or empty, nothing I reason now can change that”) is to misidentify the kind of knowledge one is exercising.

So the determination is neither merely epistemic (“sad news”) nor “ontically retrocausal.” It is the distinctive determination that practical knowledge has with respect to what it understands. The agent, in deliberating well, is the rational cause of their action and the predictor, being sensitive to that rational causation, has already ensured that the world answers to it.

But the Newcomb setup has arranged things so that the world is not fixed independently of their reasoning

It is fixed, the million is already in the box or not. The reasoning in the room doesn’t change anything and is at most mere evidence. The reasoning/rational profile outside the room has been fixed too

Yes, indeed, the reasoning doesn’t change the already determined content of the box. I have already acknowledged that much. But the content of the box was determined by the predictor in accordance with their foreknowledge of the agent’s ultimate decision. So, it is not independent of their reasoning, unless the predictor is very bad at their job.

Simple question:

The player in the room after much deliberation arrives at the conclusion that they should TB and takes two boxes. After opening, they realize they got $1,000 total.

What would have happened if after the deliberation, the player changed their mind and took one box? What would they win?

That depends what it is that the predictor tracks. In usual statements of the Newcomb problem, the predictor tracks what it is that the agent is foreseen to ultimately decide to do after deliberating. So, in the counterfactual case where the agent would have initially decided to tow-box, changed their mind in the last minute, and then taken just one box, the predictor would have foreseen all of this and the agent would have earned $1,000,000.