[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.63,0:00:09.07,Default,,0000,0000,0000,,Imagine an island where 100 people,
Dialogue: 0,0:00:09.07,0:00:14.15,Default,,0000,0000,0000,,all perfect logicians,\Nare imprisoned by a mad dictator.
Dialogue: 0,0:00:14.15,0:00:18.29,Default,,0000,0000,0000,,There's no escape,\Nexcept for one strange rule.
Dialogue: 0,0:00:18.29,0:00:23.05,Default,,0000,0000,0000,,Any prisoner can approach the guards\Nat night and ask to leave.
Dialogue: 0,0:00:23.05,0:00:26.39,Default,,0000,0000,0000,,If they have green eyes, \Nthey'll be released.
Dialogue: 0,0:00:26.39,0:00:30.34,Default,,0000,0000,0000,,If not, they'll be tossed \Ninto the volcano.
Dialogue: 0,0:00:30.34,0:00:34.10,Default,,0000,0000,0000,,As it happens, \Nall 100 prisoners have green eyes,
Dialogue: 0,0:00:34.10,0:00:36.68,Default,,0000,0000,0000,,but they've lived there since birth,
Dialogue: 0,0:00:36.68,0:00:41.49,Default,,0000,0000,0000,,and the dictator has ensured\Nthey can't learn their own eye color.
Dialogue: 0,0:00:41.49,0:00:43.45,Default,,0000,0000,0000,,There are no reflective surfaces,
Dialogue: 0,0:00:43.45,0:00:46.16,Default,,0000,0000,0000,,all water is in opaque containers,
Dialogue: 0,0:00:46.16,0:00:47.66,Default,,0000,0000,0000,,and most importantly,
Dialogue: 0,0:00:47.66,0:00:50.78,Default,,0000,0000,0000,,they're not allowed \Nto communicate among themselves.
Dialogue: 0,0:00:50.78,0:00:54.75,Default,,0000,0000,0000,,Though they do see each other\Nduring each morning's head count.
Dialogue: 0,0:00:54.75,0:00:59.20,Default,,0000,0000,0000,,Nevertheless, they all know no one would\Never risk trying to leave
Dialogue: 0,0:00:59.20,0:01:02.61,Default,,0000,0000,0000,,without absolute certainty of success.
Dialogue: 0,0:01:02.61,0:01:05.01,Default,,0000,0000,0000,,After much pressure \Nfrom human rights groups,
Dialogue: 0,0:01:05.01,0:01:09.05,Default,,0000,0000,0000,,the dictator reluctantly agrees\Nto let you visit the island
Dialogue: 0,0:01:09.05,0:01:12.46,Default,,0000,0000,0000,,and speak to the prisoners\Nunder the following conditions:
Dialogue: 0,0:01:12.46,0:01:14.55,Default,,0000,0000,0000,,you may only make one statement,
Dialogue: 0,0:01:14.55,0:01:17.86,Default,,0000,0000,0000,,and you cannot tell them \Nany new information.
Dialogue: 0,0:01:17.86,0:01:20.58,Default,,0000,0000,0000,,What can you say \Nto help free the prisoners
Dialogue: 0,0:01:20.58,0:01:24.25,Default,,0000,0000,0000,,without incurring the dictator's wrath?
Dialogue: 0,0:01:24.25,0:01:25.98,Default,,0000,0000,0000,,After thinking long and hard,
Dialogue: 0,0:01:25.98,0:01:31.38,Default,,0000,0000,0000,,you tell the crowd, \N"At least one of you has green eyes."
Dialogue: 0,0:01:31.38,0:01:33.27,Default,,0000,0000,0000,,The dictator is suspicious
Dialogue: 0,0:01:33.27,0:01:37.65,Default,,0000,0000,0000,,but reassures himself that your statement\Ncouldn't have changed anything.
Dialogue: 0,0:01:37.65,0:01:42.40,Default,,0000,0000,0000,,You leave, and life on the island\Nseems to go on as before.
Dialogue: 0,0:01:42.40,0:01:44.66,Default,,0000,0000,0000,,But on the hundredth morning \Nafter your visit,
Dialogue: 0,0:01:44.66,0:01:47.18,Default,,0000,0000,0000,,all the prisoners are gone,
Dialogue: 0,0:01:47.18,0:01:50.88,Default,,0000,0000,0000,,each having asked to leave\Nthe previous night.
Dialogue: 0,0:01:50.88,0:01:53.93,Default,,0000,0000,0000,,So how did you outsmart the dictator?
Dialogue: 0,0:01:53.93,0:01:59.11,Default,,0000,0000,0000,,It might help to realize that the amount\Nof prisoners is arbitrary.
Dialogue: 0,0:01:59.11,0:02:04.18,Default,,0000,0000,0000,,Let's simplify things\Nby imagining just two, Adria and Bill.
Dialogue: 0,0:02:04.18,0:02:06.50,Default,,0000,0000,0000,,Each sees one person with green eyes,
Dialogue: 0,0:02:06.50,0:02:09.74,Default,,0000,0000,0000,,and for all they know, \Nthat could be the only one.
Dialogue: 0,0:02:09.74,0:02:12.31,Default,,0000,0000,0000,,For the first night, each stays put.
Dialogue: 0,0:02:12.31,0:02:15.23,Default,,0000,0000,0000,,But when they see each other \Nstill there in the morning,
Dialogue: 0,0:02:15.23,0:02:17.64,Default,,0000,0000,0000,,they gain new information.
Dialogue: 0,0:02:17.64,0:02:22.27,Default,,0000,0000,0000,,Adria realizes that if Bill had seen\Na non-green-eyed person next to him,
Dialogue: 0,0:02:22.27,0:02:24.23,Default,,0000,0000,0000,,he would have left the first night
Dialogue: 0,0:02:24.23,0:02:28.21,Default,,0000,0000,0000,,after concluding the statement \Ncould only refer to himself.
Dialogue: 0,0:02:28.21,0:02:32.32,Default,,0000,0000,0000,,Bill simultaneously realizes \Nthe same thing about Adria.
Dialogue: 0,0:02:32.32,0:02:34.34,Default,,0000,0000,0000,,The fact that the other person waited
Dialogue: 0,0:02:34.34,0:02:39.12,Default,,0000,0000,0000,,tells each prisoner his\Nor her own eyes must be green.
Dialogue: 0,0:02:39.12,0:02:42.28,Default,,0000,0000,0000,,And on the second morning, \Nthey're both gone.
Dialogue: 0,0:02:42.28,0:02:44.53,Default,,0000,0000,0000,,Now imagine a third prisoner.
Dialogue: 0,0:02:44.53,0:02:48.80,Default,,0000,0000,0000,,Adria, Bill and Carl each see \Ntwo green-eyed people,
Dialogue: 0,0:02:48.80,0:02:53.90,Default,,0000,0000,0000,,but aren't sure if each of the others\Nis also seeing two green-eyed people,
Dialogue: 0,0:02:53.90,0:02:55.51,Default,,0000,0000,0000,,or just one.
Dialogue: 0,0:02:55.51,0:02:57.82,Default,,0000,0000,0000,,They wait out the first night as before,
Dialogue: 0,0:02:57.82,0:03:01.07,Default,,0000,0000,0000,,but the next morning, \Nthey still can't be sure.
Dialogue: 0,0:03:01.07,0:03:03.80,Default,,0000,0000,0000,,Carl thinks, "If I have non-green eyes,
Dialogue: 0,0:03:03.80,0:03:06.98,Default,,0000,0000,0000,,Adria and Bill were just \Nwatching each other,
Dialogue: 0,0:03:06.98,0:03:09.70,Default,,0000,0000,0000,,and will now both leave \Non the second night."
Dialogue: 0,0:03:09.70,0:03:12.47,Default,,0000,0000,0000,,But when he sees both \Nof them the third morning,
Dialogue: 0,0:03:12.47,0:03:16.23,Default,,0000,0000,0000,,he realizes they must \Nhave been watching him, too.
Dialogue: 0,0:03:16.23,0:03:19.28,Default,,0000,0000,0000,,Adria and Bill have each \Nbeen going through the same process,
Dialogue: 0,0:03:19.28,0:03:22.30,Default,,0000,0000,0000,,and they all leave on the third night.
Dialogue: 0,0:03:22.30,0:03:24.26,Default,,0000,0000,0000,,Using this sort of inductive reasoning,
Dialogue: 0,0:03:24.26,0:03:28.88,Default,,0000,0000,0000,,we can see that the pattern will repeat\Nno matter how many prisoners you add.
Dialogue: 0,0:03:28.88,0:03:31.90,Default,,0000,0000,0000,,The key is the concept \Nof common knowledge,
Dialogue: 0,0:03:31.90,0:03:34.54,Default,,0000,0000,0000,,coined by philosopher David Lewis.
Dialogue: 0,0:03:34.54,0:03:38.94,Default,,0000,0000,0000,,The new information was not contained\Nin your statement itself,
Dialogue: 0,0:03:38.94,0:03:42.95,Default,,0000,0000,0000,,but in telling it to everyone \Nsimultaneously.
Dialogue: 0,0:03:42.95,0:03:46.68,Default,,0000,0000,0000,,Now, besides knowing at least one\Nof them has green eyes,
Dialogue: 0,0:03:46.68,0:03:51.09,Default,,0000,0000,0000,,each prisoner also knows \Nthat everyone else is keeping track
Dialogue: 0,0:03:51.09,0:03:54.32,Default,,0000,0000,0000,,of all the green-eyed people they can see,
Dialogue: 0,0:03:54.32,0:03:58.79,Default,,0000,0000,0000,,and that each of them \Nalso knows this, and so on.
Dialogue: 0,0:03:58.79,0:04:00.84,Default,,0000,0000,0000,,What any given prisoner doesn't know
Dialogue: 0,0:04:00.84,0:04:04.32,Default,,0000,0000,0000,,is whether they themselves are one\Nof the green-eyed people
Dialogue: 0,0:04:04.32,0:04:06.43,Default,,0000,0000,0000,,the others are keeping track of
Dialogue: 0,0:04:06.43,0:04:12.57,Default,,0000,0000,0000,,until as many nights have passed\Nas the number of prisoners on the island.
Dialogue: 0,0:04:12.57,0:04:17.10,Default,,0000,0000,0000,,Of course, you could have spared\Nthe prisoners 98 days on the island
Dialogue: 0,0:04:17.10,0:04:21.49,Default,,0000,0000,0000,,by telling them at least 99 of you\Nhave green eyes,
Dialogue: 0,0:04:21.49,0:04:26.25,Default,,0000,0000,0000,,but when mad dictators are involved,\Nyou're best off with a good headstart.