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PaperclipPerfector  3mo ago (text post)   3120 thread views

Small-Scale Question Sunday for August 11, 2024

Do you have a dumb question that you're kind of embarrassed to ask in the main thread? Is there something you're just not sure about?

This is your opportunity to ask questions. No question too simple or too silly.

Culture war topics are accepted, and proposals for a better intro post are appreciated.

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Alice, Bob and Carol live in the Soviet Union during Stalin's regime. Alice hates Stalin and wishes him dead. But Alice has never read a column or editorial which was even mildly critical of Stalin (Stalin controls Pravda), and also knows that everyone who criticises Stalin in any capacity immediately vanishes to the gulag, never to be heard from again. For fear of this happening to her, Alice never criticises Stalin in front of Bob and Carol. Unbeknownst to Alice, Bob and Carol also hate Stalin, but have performed exactly the same risk calculus and decided never to publicly criticise Stalin. Hence conversations between Alice, Bob and Carol consist of three people loudly, conspicuously praising Stalin and successfully deceiving the others that they sincerely admire Stalin and think he's the bee's knees - but all three of them hate him and erroneously believe that they're the only one of the three to think so.

This much makes sense to me, but beyond this it gets tough for me. This sounds like "everyone knows Stalin sucks, but everyone doesn't know that everyone knows Stalin sucks". But let's say everyone did know that everyone knows Stalin sucks. Why is that not common knowledge already? Why is it important that everyone knows that everyone knows that everyone knows that Stalin sucks?

I think the answer is roughly the same as that to my favorite riddle: https://xkcd.com/blue_eyes.html

So I'm a few days late, but I'm struggling with the riddle. I can't get it to work out in my head.

I know the answer is that all n blue-eyed people leave on the nth ferry. I understand why that works for low values of n, and how it builds on itself, as each blue-eyed person expects the (n-1) scenario to play out, and then when it doesn't they realize they have blue eyes.

But at some point, everyone can see multiple blue-eyed people. And everyone can see that everyone else can see multiple blue-eyed people. At that point I can't see how the Guru has provided anyone with any new information or any new common knowledge. Nor has the empty outbound ferry on Day 1. So I don't understand how all the blue-eyed people know to leave on Day 100.

The note provides the inductive base case.

(blue, brown, note falls from the sky saying someone has blue eyes)

(1, 0, False): No information on their eyes. They never leave.

(1, 0, True): No one else could possibly have blue eyes. They leave on day 1.

(1, 1, False): Same as (1, 0, False). No one leaves.

(1, n, False): Same as (1, n-1, False). No on leaves.

(2, 0, True): On day 1, each reasons that if they are brown in (1, 1, True), the other person will leave. The other person doesn't leave. They each leave on day 2.

(n, 0, True): On day n-1, each reasons that if they are brown in (n-1, 0, True), the other n-1 people will leave on day n-1. This doesn't happen. All n people leave on day n.

(2, 0, False): On day 1, each reasons that whether they are blue or brown in (1, 1, False), the other person will never leave. The other person does not leave. This gives no information. No one ever leaves.

Etc

To throw another explanation into the arena: Alice, Bob and Carol currently hate Stalin but each thinks they are alone, so they don't rebel. If Alice found a credible note saying "Bob hates Stalin. Carol hates Stalin." Then she has learned a little, but her options don't increase all that much.

  • She can't try to convince Bob to form a rebellion. Since Bob hasn't gotten a note, he will just assume Alice is an agent trying to catch Bob doing something bad. (Haven't dictatorial regimes employed snitches? Sounds familiar right?)
  • She can't really tell Bob: "I know you hate Stalin." Like before, Bob will assume she is an agent. After all, Bob thinks he's the only one opposing Stalin! (Don't governments deploy sting operations to catch detractors? Glowies etc.)
  • She could try to be honest and vulnerable with Bob and say "I hate Stalin." This is actually risky. I can't search for it now and probably couldn't find it - a blog post about how these scenarios, and expectations, affect friendships. Since the social norm is to report your friends who hate Stalin, then Alice's admission is like saying: "Report me." Bob can maybe reason that Alice expects to be safe telling her friend Bob this. Or in other words, Alice has accused Bob of hating Stalin. This would freak Bob the fuck out. I know I would freak out if one of my friends said they were into ISIS or some kind of terrorist group.

Anyways, the above bullet points are just Alice's thought process. In reality, Bob also got a note saying "Alice hates Stalin. Carol hates Stalin." And Carol also got a similar note. The problem, hopefully you see, is that the notes are secret.

Why is it important that everyone knows that everyone knows that everyone knows that Stalin sucks?

Because without that, Alice, Bob and Carol are individually carrying out a risk calculus under the assumption that each of them is the only one who hates Stalin. If you hate Stalin and everybody else loves him, the expected payoff for publicly criticising him is that you are shipped off to the gulag. Thus everyone in the society is incentivised not to criticise Stalin, and he remains in power.

But when it becomes common knowledge, the payoff matrix changes: if I hate Stalin and I know that everybody else does too, the expected payoff for publicly criticising him is that it creates a chain reaction culminating in Stalin being forced out. Common knowledge that Stalin is widely despised is the only thing that can incentivise a self-interested agent in the system (an agent concerned with self-preservation) to act to change the system from within.

The scenario I'm describing above is a pretty quintessential Moloch trap. From outside the system, it's obvious that it's in Alice, Bob and Carol's best interest to rise up and overthrow Stalin. From within the system, none of them have any good reason to believe that attempting to overthrow Stalin would end in any other way than being immediately shipped off to the gulag or executed; hence, they all keep their heads down and the system endures.

L1: Everyone knows Stalin sucks. But they don't know that everyone knows this, so they don't think a rebellion could succeed.

L2: Everyone knows that everyone knows Stalin sucks. But they don't know that everyone knows this, so for all they know everyone else is on L1 and doesn't think a rebellion could succeed, so people expect other people to steer clear of a rebellion due to erroneously not thinking it could succeed, causing it to fail.

L3: Everyone knows that everyone knows that everyone knows Stalin sucks. But they don't know that everyone knows that, so for all they know everyone else is on L2 and expects rebellions to fail, so people expect other people to steer clear of a rebellion due to erroneously thinking that others will steer clear of it due to erroneously not thinking it could succeed, causing it to fail.

Etcetera.

On the other hand, L∞: A trusted newspaper says that everyone agrees Stalin sucks. Now there's no even hypothetical-within-a-hypothetical possibility that somebody might think a rebellion has no chance.

Well typically in most dictatorships there is a cohort of between ten and seventy percent of the population that genuinely do support the regime for ideological or materialistic reasons. And those people are usually the ones holding the guns. Stalin is actually kind of an outlier in the ratio of sheer fear to genuine support. Also, you don’t have to be a genuine hardline supporter of the regime to rat somebody else out to save yourself.

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