I don't think so. I only think blue eyed people can leave. Anybody else can have any possible eye colour, they have no way of knowing

that gives us an easy way to measure bullshit in this thread. See which group is having an easier time defending their position - the group that's having a harder time of it must be right

That's might be taken as a suggestion that there is no interference in the world we experience — boundless

I take it as a suggestion that maybe you experience the consequences of interference constantly, as a matter of course, but they're just... normal. They don't look particularly different from anything else you experience.

We live in a quantum world. Quantum IS normal. Everything normal you experience is the consequence of many quantum interactions. So maybe... interference is just happening all the time, and you experience it all the time, and it's just a normal part of this quantum world we're in.

Note however that our experience does seem about definite outcomes without any interference, i.e. our experience suggests to us that there is no interference, period. Of course, it can be wrong. — boundless

Do you have a solid concept of what the experience of interference would be like? What kinds of experiences would you be expecting, if there were interference?

For instance, MWI supporters generally claim that decoherence is enought to have 'classicality'. But IIRC, interference isn't eliminated. The terms relative to interference become very, very small but not zero — boundless

That doesn't seem like a downside to me. Who says interference at classical scales needs to be anything other than very very small?

After all, we've put relatively large objects in superposition...

But how? *sigh*. — AmadeusD

At some level it's going to be fundamental. There's not going to be a deeper "how" sometimes, eventually it's gonna be "because those are the rules".

Like when one object hits another object and the interaction causes both to change speed - equal and opposite reaction, conservation of momentum - the "how" might not really satisfy you. Are you okay with "because that's just how it works"?

don't start at 100. Start at the minimum possible number of blue eyes.

It's gotta be something like 3 or 4 right?

that's my take, for the "guru says nothing" scenario. I have no reason to think that logic doesn't hold all the way to to 100, or any other number

in his defense, he did learn that the logic he laid out doesn't work for 2 blue eyed people, nor 3. I think he's teachable but just impatient. He keeps trying to skip right to the final conclusion without taking his time building up solid premises

So by day 3, all blue eyed people will leave.

I'm assuming this pattern continues up to day 100 — Philosophim

Yes!

green eyed people will be doing the same calculus, but one day behind blue. — Philosophim

Will they?

So, we've established that IF there were only 1 blue eyed person, he'd leave on the first night, right?

"They are all perfect logicians -- if a conclusion can be logically deduced, they will do it instantly. No one knows the color of their eyes. Every night at midnight, a ferry stops at the island. Any islanders who have figured out the color of their own eyes then leave the island"

So, in the case of 2 blue eyed people, let's get into one of their heads. I'm going to be thinking as the blue-eyed person right now:

I see 1 blue eyed person and 198 brown eyed people and 1 green eyed guru. The guru just said she sees someone with blue eyes.

either (a) the blue eyed person I see is the ONLY blue eyed person,
or (b) my eyes are blue as well, and we both have blue eyes..

If (a) is true, the blue eyed guy I see will leave the first night.

<So I wait the first night, wake up second morning, and look around, and I see that the blue eyed guy is still on the island>

So that means (a) isn't true, and (b) must be true, so I can catch the ferry on the second night.

You won't find it odd if you allow me to show you the rest of the logic. Shall I lay out what happens with 2 blue eyed people?

you won't confirm that I had the rules right at this point. — Philosophim

There were no "rules" about how many people can be on the island. It's an island. However many people you want are on the island. I laid out the scenario and told you how many people of each eye color ARE on the island. That's not a rule, that's just a fact. I don't know why you want it to be a "rule" - seems like something you're just actively confusing yourself about.

There are 100 blue eyed, 100 brown eyed, 1 green eyed. That's not a "rule", that's just the scenario.

Those people can't see their own eye color, so they don't know that's the scenario. A blue eyed person thinks it could be the case that there are 99 blue eyed, 101 brown eyed, 1 green eyed, or maybe his eyes are green instead of brown, or maybe his eyes are amber.

If this answer is something like, "Everyone will turn and stare at the two blue eyed people, I'm going to be angry. That's not a logic puzzle, that's a riddle — Philosophim

so you're inventing nonsense to be confused about, and now you're inventing stuff to be angry at.

Try to use logic and think about it. Let me know if you want the answer to this scenario with 2 blue eyed people.

Obviously if the eye color can vary, then in the case where one person could see everyone else did not have blue eyes, they would know they have blue eyes. — Philosophim

So, now imagine this:

2 blue eyed people, 198 brown eyes. Guru says "I see someone with blue eyes". What do you think happens then?

"people" aren't misundedrstanding anything. Only you. Person, singular. You're getting tripped up on literally nothing. You're inventing stuff to be confused about.

I didn't invent this logic puzzle. This isn't mine. This was invented by a smart guy, and many smart people did the puzzle and liked it. People aren't confused, you're confused.

ah I see, I guess I didn't notice when you switched...

But you think if there's 100 blue and 100 brown, and the guru says nothing, they can leave on the 100th day?

Do you think that if there were only 2 blue eyed people, and the guru didn't say anything, they could leave on the second day?

I'm asking you to imagine something. That's it. Either you can, or you can't. If you cannot imagine any different scenario than the one presented, then you will be incapable of understanding the logic of the solution.

Your logic relies on the statement "everyone sees one blue". That's not true if there's one blue eyed person.

I don't even understand what you're asking.

except for the fact that premise B wouldn't be true in that scenario. Are you just refusing to acknowledge that I said that?

If there wer eonly one blue, it wouldn't be true that everyone sees one blue. Right? Do you understand why that is?

I'm asking you to imagine something. Can you do that?

If we take as a premise that "everyone sees at least one blue", then the counterfactual still works: If there is one blue, he would leave on day one. As you pointed out, that the counterfactual is false is irrelevant. — hypercin

If there were only one blue, then it WOULDN'T be true that everyone sees at least one blue.

I'll work my way up to the answer.

Imagine instead that of the 200 people the guru was speaking to, 199 of them had brown eyes and 1 had blue eyes. The guru says "I see someone with blue eyes". What happens next? Can anybody leave then?

all 200 people.

This puzzle isn't trying to trick you with wording. The most natural interpretation of that bit of the text is that ALL of the islanders are there, and that's how you should interpret it.

"Standing before the islanders" - no need to try to think of clever alternate ways of interpreting it, at face value "the islanders" means all of them.

ps I'm sorry for being rude. You getting confused about what "the islanders" meant or the eye colours just seemed... concocted. But if that was all genuine confusions, then rest easy knowing you got it all right.

A. There are 100 blue eyes, 100 brown eyes, and one green eyed elder.
B. However, the islanders do not know that this is the limit of eye color, and their eye colors could be any color under the rainbow. They also don't know the actual number. So even if they see 100 blue eyed individuals, they're own eye color could be blue or anything else.
C. The elder is speaking to all 200 other people on the island, and we're assuming he sees all 200 people, and says, "I see someone with blue eyes".

The only uncertainty that isn't listed here is how many people the elder saw while speaking to everyone — Philosophim

Your paragraph here shows you were pretty adept at getting over most of your self-inflicted confusions. You're right about the setup.

The elder saw all of them and was looking at everyone when she said it. Not any one person. Even while saying it, she knew and could see 100 blue eyed people.

it genuinely seems like you're trying to be confused

yeah, totally, i get it. I get why it seems like you ought not to need the guru. But when none of the proofs work, and you can't even bootstrap the deductive process on n=1 or n=2, then there's nowhere to go from there.

If the argument begins with "everyone can see that there are multiple blue and brown but no one says anything." What is the next step? — unenlightened

For him the next step is just imagining someone says something.

There are established usages of the word 'causation', both in ordinary language and in specialized domains. Capturing these usages in a single, all-encompassing definition has proven to be difficult. To my knowledge, no one definition works perfectly. — SophistiCat

I agree with you, but that's kinda scary isn't it? It's such a fundamentally important concept, to pretty much everything in life, especially philosophy. Without causation there's... nothing. If we didn't live in a causal world, there'd be nothing to experience, sense, or even think. It's so fundamentally important and yet so difficult to even define.

Mind blowing.

I've told you, it's probably not as simple as there being some specific n — Michael

You telling me something doesn't make it true. If the logic works, there's got to be a point at which it works. If there's no n at which the logic works, then... it doesn't work.

The last time you said it was simple, you said that about something you were wrong about. Your overconfidence is...weird. I mean it was weird to begin with, but to use the same overconfident line again, after you know the last time you said it you were wrong, is like... double weird. Why are you doing that? Don't you think that's weird? You've been consistently wrong, I don't know where your arrogance comes from.

If you're right, you should be able to prove it. This is a case of pure deductive reasoning, and I'm quite frankly enjoying it. If you want to throw in the towel, fine, I just... don't even know why you bothered to say anything if you don't want to even try to prove it.

so what number n does it start working at? Not 2. Not 3. Which one?

It is sufficient that all blues know that all blues know that green sees blue.

Shouldn't it work at n=3 then? But we've both agreed it doesn't.

why are you so eager to skip to the end solution without building up working premises first?

There's a pattern here. We proved that it doesn't work for n=2, and because of that, you immediately accepted that it doesn't work for n=3.

For some reason, you didn't apply that to n=4 - for the exact same reason you can reject n=3 if n=2 doesn't work, you can reject n=4 if n=3 doesn't work. And if you can reject n=4, you can reject n=5. And so on. Up to 100.

Your confidence should be shaken. You were so confident about n=2, to the point of even saying "I've already explained it, I can't make it any more simple" - and then we proved you wrong. And you agree that you were wrong about n=2. So... don't you think maybe you should be a little less confident about n=100?

I'm not saying you should immediately reject n=100, but maybe accept that you have a serious burden of proof there, because if n=2 doesn't work, neither does 3, and so on, right?

So don't be so sure. Do the logic. Work it out. Don't just state a conclusion and call it a day, this is a deduction puzzle. I want to see you deduce.

"the blues would have all left on day 3 if there were only 3"

Doesn't that rely on the logic working for n=3?

So I actually think this requires n>=4. — Michael

If you think the logic works for n=4, but the logic relies on a premise that pretty much explicitly says "the logic also works for n=3", then... n=4 can only work if n=3 works, no? And n=3 doesn't work. We both agree n=3 doesn't work. So if n=3 doesn't work, can you rationally say "the blues would have all left on day 3 if there were only 3"? That IS what n=3 is saying. I don't think you can say "the blues would have all left on day 3 if there were only 3". We can't just freely accept that as a deductively valid premise to use in your logic.

The exact same thing as if green were to say "I see blue". — Michael

Okay, so... you wait for day 4, you think "the blues would have all left on day 3 if there were only 3", and then you leave on day 4 as a blue with all the other blues?

so what do you deduce? What's the rest of it? You've only given half a story here. You see 3 blue, 3 brown, 1 green, green says nothing - what do you deduce and how?

okay so you've completely bypassed all of unenlighteneds reasoning now. You're entirely on your own here and nothing you say relies on his logic at all.

So I actually think this requires n>=4.

If I see 3 blue, 3 brown, and 1 green, then everyone knows that everyone knows that green sees blue and brown, and that allows the blues and browns to deduce their own eye colour — Michael

Is that n>=4? Are you talking from the perspective of a blue eyed person? Because that's only n=4 for blue, not for brown.