Emperor's New Clothes

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来自 Princeton University 的课程

Networks Illustrated: Principles without Calculus

43 个评分

Princeton University

Networks Illustrated: Principles without Calculus

43 个评分

What makes WiFi faster at home than at a coffee shop? How does Google order its search results from the trillions of webpages on the Internet? Why does Verizon charge $15 for every GB of data we use? Is it really true that we are connected in six social steps or less? These are just a few of the many intriguing questions we can ask about the social and technical networks that form integral parts of our daily lives. This course is about exploring the answers, using a language that anyone can understand. We will focus on fundamental principles like “sharing is hard”, “crowds are wise”, and “network of networks” that have guided the design and sustainability of today’s networks, and summarize the theories behind everything from the social connections we make on platforms like Facebook to the technology upon which these websites run. Unlike other networking courses, the mathematics included here are no more complicated than adding and multiplying numbers. While mathematical details are necessary to fully specify the algorithms and systems we investigate, they are not required to understand the main ideas. We use illustrations, analogies, and anecdotes about networks as pedagogical tools in lieu of detailed equations. All the features of this course are available for free. It does not offer a certificate upon completion.

从本节课中

Viral Videos on YouTube

What does it take for a video to become "viral" on YouTube? In this lesson, we will take a look at some of the key factors and models that have been used to explain this phenomenon. At the core is the notion of information cascade in a network, which is the counterpart to the wisdom of crowds.

YouTube timeline4:50

Viral style and video recommendation7:36

Defining "viral"3:18

Information cascade & sequential decision making8:24

Number-Guessing Thought-Experiment3:11

First, second, and third "guessers"7:36

Analyzing cascades: Part I13:21

Analyzing Cascades: Part II10:25

Emperor's New Clothes4:34

Considerations5:14

与讲师见面

Christopher Brinton
Lecturer
Electrical Engineering
Mung Chiang
Professor
Electrical Engineering

So we've just seen how easy it is to

start a cascade, of course, depending on the situation.

And the question now is how long will a cascade last?

Well, it'll last forever unless there's some kind of a

disturbance, which really translates to a release of private signals.

So people saying what their private signals

are and telling the public what the private

signals are, so that it's not just the

public actions that are available when making, guesses.

And how many such disturbances do we need?

Well, even a few will often suffice, because they all

know that they're playing follow the leader, so to speak,

just to maximize the, the chance of them being correct,

and they all know how the cascade started if they're rational.

And, therefore, if they can recompute a probability

based on a private signal, that it's now

more probable that something else was the case,

you can quickly reverse or end the cascade.

So this is the counterpart of information cascade

which is called the Emperor's New Clothes effect.

And this name arises from the 19th-century short story in which a

vain emperor, or this guy right here in the picture, is told

that his new clothing is of the finest, best suit of fabric

that is invisible only to those who are unfit for their positions.

In reality, of course, he's actually not wearing any clothes

at all, but, while everybody plays along, which are their public

actions to just not say anything and just assume they

can see his, clothing, including the Emperor himself who plays along.

Because nobody wants to see him quote

unquote, unfit, which is what their private

signals are telling them because really they

just see the guy walking around naked.

Because he's not wearing any clothes but they

don't want to seem like they're unfit for their positions.

Then it only takes one kid to shout out, hey, he's not wearing anything at all.

So, one person, maybe here, who doesn't understand what it

means to be unfit for a position, just to say, hey,

you know, you're not wearing any clothes until everybody becomes

more confident that he is, in fact, not wearing any clothes.

And then the cascade can break.

So how do we break a cascade?

Going back to our number-guessing thought experiments,

suppose the cascade of ones has started.

So we'll say the first two people have guessed and they started

a cascade of ones, so there's some cascade of ones to three maybe.

And, this is, the board, what people have written down.

So, all ones so far.

Now, then the next person comes up to the board.

Suppose the person is shown the private signal of zero, right?

So, the person sees that he gets the private signal of zero.

And, he knows that some cascade has been triggered.

He wants to see, maybe, if he can end the cascade.

Not with himself because even though he sees a private signal of

zero, remember it's still in his best guess to guess a one.

And so, but then he shouts out that he got

a zero, and he said my private signal was a zero.

So now, when the next person comes along, so this is the next person

in line, suppose the next person is now shown another private signal of zero.

So now, this next person can say, okay, well I know

that the person before me had a private signal of zero.

And now I know that I have a private signal of zero.

And then he thinks back to how the cascade was generated in the first place.

The cascade started with the first two people, okay?

In the best-case scenario, they both saw a private signal of a one, right?

And then therefore wrote it and started the cascade.

That is the only case that's comparable, now, to the chance that zero

is the correct answer, because that would be seeing two private signals of one.

Now these people have two private signals of zeros.

But additionally, you know, obviously, that the first person had a

private signal of one, or else he wouldn't have written one.

The second person may not have had a private signal of one at all.

So now you have a case where you can

only know for sure that there was one private signal

of one, right in the beginning, but now you

have two private signals of zero here that you know.

So, therefore, this person's now going to

guess zero, because that's more likely now.

And therefore is breaking the cascade.

So there's a cascade here and now there's no cascade.

And the reason that the cascade broke was that this person shouted the zero.

So, remember, a cascade represents only what happened with

a few people right around the time it started.

That's the key point.

If everybody knows that, which in this case,

if they're all rational, they could figure that

out, another block of a few people, may be able to break it, we show here.

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