Here's The Answer To 'The Hardest Logic Puzzle In The World'
Yesterday, minds were melted by the tale of the "green-eyed dragons."
Today, the answer.
To refresh your memory, here's the curious fable posed by a Harvard handout:
Feeling pretty good about your guess? Scroll down to see the answer!
Are you definitely ready?
Answer: All 100 dragons become sparrows, on the 100th midnight.
Not sure how we got there? io9 has a good explanation, which you can read in detail here.
Basically…
"If you tell a single green-eyed dragon that ‘at least one of you’ has green eyes, that dragon would know instantly and unambiguously that she has green eyes. At midnight she would turn into a sparrow.
“So let's imagine 2 green-eyed dragons staring at one another, after being informed by you that at least one of them has green eyes. Each would look upon the other and, seeing a set of green eyes, think the following: 'Do I have green eyes? I don't know. But if I do not, then this other dragon, upon seeing my non-green eyes, will know instantly and unambiguously that he is the one with green eyes, and at midnight will turn into a sparrow.' Each dragon sits and waits to see what the other does. When, at midnight, neither dragon transforms into a sparrow, each one knows instantly and unambiguously that the other dragon did not leave because it, too, saw a dragon with green eyes. And so, on the second night, each transforms into a sparrow at midnight.
“Let's expand the problem to 3 green-eyed dragons... all three dragons wait for the other two dragons to transform into sparrows on the second midnight. When this does not happen, each of the three dragons concludes instantly and unambiguously that it has green eyes. On the third midnight, all three transform into sparrows.
“Through the process of induction, we conclude that any number of green-eyed dragons, N, will all turn into sparrows on the Nth midnight following your seemingly inconsequential observation.”
Does that make sense to you? Let us know what you got below.
Oh, and remember: if you ever come across an island of perfectly pleasant talking dragons with a weird thing about their eyes, maybe keep any details that might ruin their existence to yourself.
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Wow Wow.
I don't think anything would happen. In the answer you gave for if there were two dragons, the scenario was what would happen IF the other dragon saw I did NOT have green eyes. Neither turns into a sparrow on the first midnight. True enough. BUT...the same thing happens if the other dragon sees that I DO have green eyes! He will not turn into a sparrow on midnight of day one.
So regardless of what he sees or what I see, neither changes into a sparrow.
What am I missing?
While it's an amusing logic puzzle and a fun mental exercise, the answer you have provided is wrong. The correct answer is: There are not enough data to know what will happen.
You have stated that all dragons are unfailingly logical. However, what you have not said is whether all dragons know that the other dragons are also unfailingly logical. On the 100th day, the dragons will all be wondering whether they have green eyes or whether the logic chain was so difficult that the other dragons were not able to follow it (and should have all turned into sparrows the previous night).