Newcomb's Paradox Needs a Demon • Hacker News Board

Re: Newcomb's Paradox Needs a Demon

#31

Post by vidarh » Thu, Mar 12, 2026, 6:26 PM UTC

malfist wrote: post #29

OskarS wrote: post #15

Earlier quoted context omitted.

> Two boxes is the only choice that makes sense. It is always better than one box. Congratulations on your $1,000. I'll use some of my $1,000,000 I got by nonsensically picking one box to toast in your honor and dedication to logic.

Or your zero dollars if your predictor wasn't quiet as perfect as billed.

But the predictor would need to be almost as bad as pure chance for the odds to tilt away from one box. Unless you think it is materially worse than chance, it's a bad bet.

Re: Newcomb's Paradox Needs a Demon

#32

Post by pinusc » Thu, Mar 12, 2026, 8:38 PM UTC

mcphage wrote: post #21

genshii wrote: post #18

I've been presented with this thought experiment before and I always feel like I'm missing something when other people talk about it. Why would you ever take both boxes? The premise is that the predictor is always right. So whether you take one or both boxes, the predictor would have predicted that choice. We know from the setup that if the predictor said you would take the one box, it will have a million dollars. Th…

> Why would you ever take both boxes? As near as I can tell, it boils down to this: no matter what the predictor has chosen, one you walk into that room, there's more money in both boxes, then there is in one box. But it feels like half an analysis—focusing solely on what you decide, while ignoring the fact that the other side is deciding based on what you think they'll decide. Maybe that's me being unfair, because I…

(To two-boxers) it's not half an analysis because once you walk into the room your choice is causally independent of the demon/AI/alien prediction.

There's something vaguely similar to the fallacy of proposed (Cooperate,Cooperate) solutions to the Prisoner's Dilemma. The arguments go as follows: (1) if we're both rational agents and we have the same information and same payoffs, we will make the same choice; (2) therefore, (Cooperate,Defect) and (Defect,Cooperate) are out of the question; (3) therefore, the only options are (Defect,Defect) and (Cooperate,Cooperate); (4) so I should Cooperate since it gives the better payoff. It seems to follow logically but (1) and (2) are problematic because you can't assume symmetrical solutions and thus eliminate asymmetrical outcomes, because that is essentially the same as saying "what I choose causally affects what my opponent chooses".

In the same way, one-boxing is irrational (for this argument, anyway; I'm undecided myself) because the prediction has already been made, and so your choice to one-box or two-box cannot have any causal relevance to the contents of the boxes. Even a perfect predictor cannot invert the flow of causality.

Re: Newcomb's Paradox Needs a Demon

#33

Post by danbruc » Thu, Mar 12, 2026, 9:32 PM UTC

mcphage wrote: post #21

genshii wrote: post #18

I've been presented with this thought experiment before and I always feel like I'm missing something when other people talk about it. Why would you ever take both boxes? The premise is that the predictor is always right. So whether you take one or both boxes, the predictor would have predicted that choice. We know from the setup that if the predictor said you would take the one box, it will have a million dollars. Th…

> Why would you ever take both boxes? As near as I can tell, it boils down to this: no matter what the predictor has chosen, one you walk into that room, there's more money in both boxes, then there is in one box. But it feels like half an analysis—focusing solely on what you decide, while ignoring the fact that the other side is deciding based on what you think they'll decide. Maybe that's me being unfair, because I…

The thing is, you can not chose once you are in the room. The fact that an [almost] perfect predictor exists implies that your choice must already be fixed at the point in time the predictor makes its prediction. Or the other way around, if you could still choose both options once you are in the room, say by basing your choice on some truly random and therefore unpredictable event like a radioactive decay - at least as far as we know truly unpredictable - then the predictor could not [almost] perfectly predict your choice, i.e. an [almost] perfect predictor can not exist.

So what you really want is to be in a state that will make you chose one box and you want to already be in that state at the time the predictor makes its predictions because the predictor will see this and place the million dollars into the second box. And as we have already said, you can not chose to take two boxes afterwards as that would contradict the existence of the predictor.

Re: Newcomb's Paradox Needs a Demon

#34

Post by xigoi » Thu, Mar 12, 2026, 9:36 PM UTC

GaelFG wrote: post #27

xigoi wrote: post #20

Earlier quoted context omitted.

Assuming that the predictor is always right, there are only two possible scenarios: • You take one box and get $1000000 • You take two boxes and get $1000 The choice seems quite clear to me.

Not from the article : Before you walk in, a supercomputer predicted which choice you'd make, and put $1000000 in the opaque box if it predicted you'd take just the one, or $0 if it predicted you'd take both. So the amount of money in the black box don't change whatever you REALLY pick. Either the predicator would have guessed you'd pick both and there is 0$ in black box, in that case you have interest to take both b…

This is exactly what’s funny about the paradox – we both think that our choice is completely obvious.

My argument is that since the predictor is always right, the situation where you choose two boxes and you get $1001000 simply cannot happen, because then the predictor would’ve predicted your choice and placed nothing in the variable box.

Re: Newcomb's Paradox Needs a Demon

#35

Post by Ethee » Thu, Mar 12, 2026, 10:54 PM UTC

genshii wrote: post #18

I've been presented with this thought experiment before and I always feel like I'm missing something when other people talk about it. Why would you ever take both boxes? The premise is that the predictor is always right. So whether you take one or both boxes, the predictor would have predicted that choice. We know from the setup that if the predictor said you would take the one box, it will have a million dollars. Th…

As a one boxer myself this is the way I see it. The problem is presented as a value proposition, how do I walk out of this room with the most money? This typically prompts people to think of this as a statistics problem, and you genuinely can use statistics to 'solve' this, but that has nothing to do with what seems to be the problems underlying premise. Which is, do you actually believe that the predictor can even make that prediction? I think most people who take things logically at face value (like Veritasium watchers) would accept the premise as it's set up. I think for the two boxers there's some doubt they have about the predictors actual abilities, or they think they can 'outsmart' the predictor. The problem is setup in such a way however that it's fundamentally impossible to outsmart, which is I think what makes this problem so interesting.

Re: Newcomb's Paradox Needs a Demon

#36

Post by mcphage » Thu, Mar 12, 2026, 11:19 PM UTC

pinusc wrote: post #32

mcphage wrote: post #21

Earlier quoted context omitted.

> Why would you ever take both boxes? As near as I can tell, it boils down to this: no matter what the predictor has chosen, one you walk into that room, there's more money in both boxes, then there is in one box. But it feels like half an analysis—focusing solely on what you decide, while ignoring the fact that the other side is deciding based on what you think they'll decide. Maybe that's me being unfair, because I…

(To two-boxers) it's not half an analysis because once you walk into the room your choice is causally independent of the demon/AI/alien prediction. There's something vaguely similar to the fallacy of proposed (Cooperate,Cooperate) solutions to the Prisoner's Dilemma. The arguments go as follows: (1) if we're both rational agents and we have the same information and same payoffs, we will make the same choice; (2) ther…

> that is essentially the same as saying "what I choose causally affects what my opponent chooses".

No, it’s the same as saying “what my opponent thinks I will choose causally affects what my opponent chooses”, which is obviously true. Also, “what my opponent thinks I will choose is positively correlated with what I do choose”, unless my opponent isn’t very good.

Re: Newcomb's Paradox Needs a Demon

#37

Post by mcphage » Thu, Mar 12, 2026, 11:33 PM UTC

danbruc wrote: post #33

mcphage wrote: post #21

Earlier quoted context omitted.

> Why would you ever take both boxes? As near as I can tell, it boils down to this: no matter what the predictor has chosen, one you walk into that room, there's more money in both boxes, then there is in one box. But it feels like half an analysis—focusing solely on what you decide, while ignoring the fact that the other side is deciding based on what you think they'll decide. Maybe that's me being unfair, because I…

The thing is, you can not chose once you are in the room. The fact that an [almost] perfect predictor exists implies that your choice must already be fixed at the point in time the predictor makes its prediction. Or the other way around, if you could still choose both options once you are in the room, say by basing your choice on some truly random and therefore unpredictable event like a radioactive decay - at least…

> So what you really want is to be in a state that will make you chose one box and you want to already be in that state at the time the predictor makes its predictions because the predictor will see this and place the million dollars into the second box.

Here’s the thing: no, I don’t. I’d much rather walk away with the easy million instead of risking it all for an extra thousand.

Re: Newcomb's Paradox Needs a Demon

#38

Post by danbruc » Fri, Mar 13, 2026, 12:39 AM UTC

mcphage wrote: post #37

danbruc wrote: post #33

Earlier quoted context omitted.

The thing is, you can not chose once you are in the room. The fact that an [almost] perfect predictor exists implies that your choice must already be fixed at the point in time the predictor makes its prediction. Or the other way around, if you could still choose both options once you are in the room, say by basing your choice on some truly random and therefore unpredictable event like a radioactive decay - at least…

> So what you really want is to be in a state that will make you chose one box and you want to already be in that state at the time the predictor makes its predictions because the predictor will see this and place the million dollars into the second box. Here’s the thing: no, I don’t. I’d much rather walk away with the easy million instead of risking it all for an extra thousand.

You can only get a thousand - take both boxes - or a million - take only the second box, zero and one million one thousand are not possible - or at least unlikely - because that would require a misprediction by the predictor but we assume an [almost] perfect predictor.

Re: Newcomb's Paradox Needs a Demon

#39

Post by danbruc » Fri, Mar 13, 2026, 12:53 AM UTC

vidarh wrote: post #24

arethuza wrote: post #11

Earlier quoted context omitted.

I would think that the existence of a flawless predictor is probably more likely to indicate that memories of predictions, and any associated records, have been modified to make the predictor appear flawless.

I would say that if we presume memories of everyone involved have been modified, that is an equally strong predictor that we are in a simulation.

Where does this obsession with the simulation hypothesis come from, it has been so widespread in the last years? It is more or less pointless to think about it, it will not get you anywhere. You only know this universe, to some extend, but you have no idea what a real universe looks like and you have no idea what a simulated universe looks like, so you will never be able to tell which kind our universe is.

But what if we discover that our universe is made from tiny voxels or something like that, that will be undeniable evidence, right? Wrong! Who says that real universes are not made of tiny voxels? It could be [1] the other way around, maybe real universes are discrete but their universe simulations are continuous, in which case the lack of tiny voxels in our universe would be the smoking gun evidence for being in a simulation.

[1] This is meant as an example, I have no idea if one can actually come up with a discrete universe that admits continuous simulations, which probably should also be efficient in some sense.

Re: Newcomb's Paradox Needs a Demon

#40

Post by mcphage » Fri, Mar 13, 2026, 1:53 AM UTC

danbruc wrote: post #38

mcphage wrote: post #37

Earlier quoted context omitted.

> So what you really want is to be in a state that will make you chose one box and you want to already be in that state at the time the predictor makes its predictions because the predictor will see this and place the million dollars into the second box. Here’s the thing: no, I don’t. I’d much rather walk away with the easy million instead of risking it all for an extra thousand.

You can only get a thousand - take both boxes - or a million - take only the second box, zero and one million one thousand are not possible - or at least unlikely - because that would require a misprediction by the predictor but we assume an [almost] perfect predictor.

Then I for one choose the million.