Lex Fridman Podcast - #42 - Peter Norvig: Artificial Intelligence: A Modern Approach

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The following is a conversation with Peter Norvig.

He’s the Director of Research at Google

and the coauthor with Stuart Russell of the book

Artificial Intelligence, A Modern Approach,

that educated and inspired a whole generation

of researchers, including myself,

to get into the field of artificial intelligence.

This is the Artificial Intelligence Podcast.

If you enjoy it, subscribe on YouTube,

give five stars on iTunes, support on Patreon,

or simply connect with me on Twitter.

I’m Lex Friedman, spelled F R I D M A N.

And now, here’s my conversation with Peter Norvig.

Most researchers in the AI community, including myself,

own all three editions, red, green, and blue,

of the Artificial Intelligence, A Modern Approach.

It’s a field defining textbook, as many people are aware,

that you wrote with Stuart Russell.

How has the book changed and how have you changed

in relation to it from the first edition

to the second to the third and now fourth edition

as you work on it?

Yeah, so it’s been a lot of years, a lot of changes.

One of the things changing from the first

to maybe the second or third

was just the rise of computing power, right?

So I think in the first edition, we said,

here’s predicate logic, but that only goes so far

because pretty soon you have millions of short little

predicate expressions and they can possibly fit in memory.

So we’re gonna use first order logic that’s more concise.

And then we quickly realized,

oh, predicate logic is pretty nice

because there are really fast SAT solvers and other things.

And look, there’s only millions of expressions

and that fits easily into memory,

or maybe even billions fit into memory now.

So that was a change of the type of technology we needed

just because the hardware expanded.

Even to the second edition,

resource constraints were loosened significantly

for the second.

And that was early 2000s second edition.

Right, so 95 was the first and then 2000, 2001 or so.

And then moving on from there,

I think we’re starting to see that again with the GPUs

and then more specific type of machinery

like the TPUs and you’re seeing custom ASICs and so on

for deep learning.

So we’re seeing another advance in terms of the hardware.

Then I think another thing that we especially noticed

this time around is in all three of the first editions,

we kind of said, well, we’re gonna find AI

as maximizing expected utility

and you tell me your utility function.

And now we’ve got 27 chapters where the cool techniques

for how to optimize that.

I think in this edition, we’re saying more,

you know what, maybe that optimization part

is the easy part and the hard part is deciding

what is my utility function?

What do I want?

And if I’m a collection of agents or a society,

what do we want as a whole?

So you touched that topic in this edition.

You get a little bit more into utility.


That’s really interesting.

On a technical level,

we’re almost pushing the philosophical.

I guess it is philosophical, right?

So we’ve always had a philosophy chapter,

which I was glad that we were supporting.

And now it’s less kind of the Chinese room type argument

and more of these ethical and societal type issues.

So we get into the issues of fairness and bias

and just the issue of aggregating utilities.

So how do you encode human values into a utility function?

Is this something that you can do purely through data

in a learned way or is there some systematic,

obviously there’s no good answers yet.

There’s just beginnings to this,

to even opening the doors to these questions.

So there is no one answer.

Yes, there are techniques to try to learn that.

So we talk about inverse reinforcement learning, right?

So reinforcement learning, you take some actions,

you get some rewards and you figure out

what actions you should take.

And inverse reinforcement learning,

you observe somebody taking actions and you figure out,

well, this must be what they were trying to do.

If they did this action, it must be because they want it.

Of course, there’s restrictions to that, right?

So lots of people take actions that are self destructive

or they’re suboptimal in certain ways.

So you don’t wanna learn that.

You wanna somehow learn the perfect actions

rather than the ones they actually take.

So that’s a challenge for that field.

Then another big part of it is just kind of theoretical

of saying, what can we accomplish?

And so you look at like this work on the programs

to predict recidivism and decide who should get parole

or who should get bail or whatever.

And how are you gonna evaluate that?

And one of the big issues is fairness

across protected classes.

Protected classes being things like sex and race and so on.

And so two things you want is you wanna say,

well, if I get a score of say six out of 10,

then I want that to mean the same

whether no matter what race I’m on, right?

Yes, right, so I wanna have a 60% chance

of reoccurring regardless.

And one of the makers of a commercial program to do that

says that’s what we’re trying to optimize

and look, we achieved that.

We’ve reached that kind of balance.

And then on the other side,

you also wanna say, well, if it makes mistakes,

I want that to affect both sides

of the protected class equally.

And it turns out they don’t do that, right?

So they’re twice as likely to make a mistake

that would harm a black person over a white person.

So that seems unfair.

So you’d like to say,

well, I wanna achieve both those goals.

And then it turns out you do the analysis

and it’s theoretically impossible

to achieve both those goals.

So you have to trade them off one against the other.

So that analysis is really helpful

to know what you can aim for and how much you can get.

You can’t have everything.

But the analysis certainly can’t tell you

where should we make that trade off point.

But nevertheless, then we can as humans deliberate

where that trade off should be.

Yeah, so at least we now we’re arguing in an informed way.

We’re not asking for something impossible.

We’re saying, here’s where we are

and here’s what we aim for.

And this strategy is better than that strategy.

So that’s, I would argue is a really powerful

and really important first step,

but it’s a doable one sort of removing

undesirable degrees of bias in systems

in terms of protected classes.

And then there’s something I listened

to your commencement speech,

or there’s some fuzzier things like,

you mentioned angry birds.

Do you wanna create systems that feed the dopamine enjoyment

that feed, that optimize for you returning to the system,

enjoying the moment of playing the game of getting likes

or whatever, this kind of thing,

or some kind of longterm improvement?


Are you even thinking about that?

That’s really going to the philosophical area.

No, I think that’s a really important issue too.

Certainly thinking about that.

I don’t think about that as an AI issue as much.

But as you say, the point is we’ve built this society

and this infrastructure where we say we have a marketplace

for attention and we’ve decided as a society

that we like things that are free.

And so we want all the apps on our phone to be free.

And that means they’re all competing for your attention.

And then eventually they make some money some way

through ads or in game sales or whatever.

But they can only win by defeating all the other apps

by instilling your attention.

And we build a marketplace where it seems like

they’re working against you rather than working with you.

And I’d like to find a way where we can change

the playing field so you feel more like,

well, these things are on my side.

Yes, they’re letting me have some fun in the short term,

but they’re also helping me in the long term

rather than competing against me.

And those aren’t necessarily conflicting objectives.

They’re just the incentives, the direct current incentives

as we try to figure out this whole new world

seem to be on the easier part of that,

which is feeding the dopamine, the rush.


But so maybe taking a quick step back at the beginning

of the Artificial Intelligence,

the Modern Approach book of writing.

So here you are in the 90s.

When you first sat down with Stuart to write the book

to cover an entire field,

which is one of the only books that’s successfully done that

for AI and actually in a lot of other computer science

fields, it’s a huge undertaking.

So it must’ve been quite daunting.

What was that process like?

Did you envision that you would be trying to cover

the entire field?

Was there a systematic approach to it

that was more step by step?

How was, how did it feel?

So I guess it came about,

go to lunch with the other AI faculty at Berkeley

and we’d say, the field is changing.

It seems like the current books are a little bit behind.

Nobody’s come out with a new book recently.

We should do that.

And everybody said, yeah, yeah, that’s a great thing to do.

And we never did anything.


And then I ended up heading off to industry.

I went to Sun Labs.

So I thought, well, that’s the end of my possible

academic publishing career.

But I met Stuart again at a conference like a year later

and said, you know that book we were always talking about,

you guys must be half done with it by now, right?

And he said, well, we keep talking, we never do anything.

So I said, well, you know, we should do it.

And I think the reason is that we all felt

it was a time where the field was changing.

And that was in two ways.

So, you know, the good old fashioned AI

was based primarily on Boolean logic.

And you had a few tricks to deal with uncertainty.

And it was based primarily on knowledge engineering.

That the way you got something done is you went out,

you interviewed an expert and you wrote down by hand

everything they knew.

And we saw in 95 that the field was changing in two ways.

One, we’re moving more towards probability

rather than Boolean logic.

And we’re moving more towards machine learning

rather than knowledge engineering.

And the other books hadn’t caught that way

if they were still in the, more in the old school.

Although, so certainly they had part of that on the way.

But we said, if we start now completely taking

that point of view, we can have a different kind of book.

And we were able to put that together.

And what was literally the process if you remember,

did you start writing a chapter?

Did you outline?

Yeah, I guess we did an outline

and then we sort of assigned chapters to each person.

At the time I had moved to Boston

and Stuart was in Berkeley.

So basically we did it over the internet.

And, you know, that wasn’t the same as doing it today.

It meant, you know, dial up lines and telnetting in.

And, you know, you telnet it into one shell

and you type cat file name

and you hoped it was captured at the other end.

And certainly you’re not sending images

and figures back and forth.

Right, right, that didn’t work.

But, you know, did you anticipate

where the field would go from that day, from the 90s?

Did you see the growth into learning based methods

and to data driven methods

that followed in the future decades?

We certainly thought that learning was important.

I guess we missed it as being as important as it is today.

We missed this idea of big data.

We missed that the idea of deep learning

hadn’t been invented yet.

We could have taken the book

from a complete machine learning point of view

right from the start.

We chose to do it more from a point of view

of we’re gonna first develop

different types of representations.

And we’re gonna talk about different types of environments.

Is it fully observable or partially observable?

And is it deterministic or stochastic and so on?

And we made it more complex along those axes

rather than focusing on the machine learning axis first.

Do you think, you know, there’s some sense

in which the deep learning craze is extremely successful

for a particular set of problems.

And, you know, eventually it’s going to,

in the general case, hit challenges.

So in terms of the difference between perception systems

and robots that have to act in the world,

do you think we’re gonna return

to AI modern approach type breadth

in addition five and six?

In future decades, do you think deep learning

will take its place as a chapter

in this bigger view of AI?

Yeah, I think we don’t know yet

how it’s all gonna play out.

So in the new edition, we have a chapter on deep learning.

We got Ian Goodfellow to be the guest author

for that chapter.

So he said he could condense his whole deep learning book

into one chapter.

I think he did a great job.

We were also encouraged that he’s, you know,

we gave him the old neural net chapter

and said, modernize that.

And he said, you know, half of that was okay.

That certainly there’s lots of new things

that have been developed,

but some of the core was still the same.

So I think we’ll gain a better understanding

of what you can do there.

I think we’ll need to incorporate

all the things we can do with the other technologies, right?

So deep learning started out with convolutional networks

and very close to perception.

And it’s since moved to be able to do more

with actions and some degree of longer term planning.

But we need to do a better job

with representation than reasoning

and one shot learning and so on.

And I think we don’t know yet how that’s gonna play out.

So do you think looking at some success,

but certainly eventual demise,

a partial demise of experts

to symbolic systems in the 80s,

do you think there is kernels of wisdom

and the work that was done there

with logic and reasoning and so on

that will rise again in your view?

So certainly I think the idea of representation

and reasoning is crucial

that sometimes you just don’t have enough data

about the world to learn de novo.

So you’ve got to have some idea of representation,

whether that was programmed in or told or whatever,

and then be able to take steps of reasoning.

I think the problem with the good old fashioned AI

was one, we tried to base everything on these symbols

that were atomic.

And that’s great if you’re like trying to define

the properties of a triangle, right?

Because they have necessary and sufficient conditions.

But things in the real world don’t.

The real world is messy and doesn’t have sharp edges

and atomic symbols do.

So that was a poor match.

And then the other aspect was that the reasoning

was universal and applied anywhere,

which in some sense is good,

but it also means there’s no guidance

as to where to apply.

And so you started getting these paradoxes

like, well, if I have a mountain

and I remove one grain of sand,

then it’s still a mountain.

But if I do that repeatedly, at some point it’s not, right?

And with logic, there’s nothing to stop you

from applying things repeatedly.

But maybe with something like deep learning,

and I don’t really know what the right name for it is,

we could separate out those ideas.

So one, we could say a mountain isn’t just an atomic notion.

It’s some sort of something like a word embedding

that has a more complex representation.

And secondly, we could somehow learn,

yeah, there’s this rule that you can remove

one grain of sand and you can do that a bunch of times,

but you can’t do it a near infinite amount of times.

But on the other hand, when you’re doing induction

on the integer, sure, then it’s fine to do it

an infinite number of times.

And if we could, somehow we have to learn

when these strategies are applicable

rather than having the strategies be completely neutral

and available everywhere.

Anytime you use neural networks,

anytime you learn from data,

form representation from data in an automated way,

it’s not very explainable as to,

or it’s not introspective to us humans

in terms of how this neural network sees the world,

where, why does it succeed so brilliantly in so many cases

and fail so miserably in surprising ways and small.

So what do you think is the future there?

Can simply more data, better data,

more organized data solve that problem?

Or is there elements of symbolic systems

that need to be brought in

which are a little bit more explainable?

Yeah, so I prefer to talk about trust

and validation and verification

rather than just about explainability.

And then I think explanations are one tool

that you use towards those goals.

And I think it is an important issue

that we don’t wanna use these systems unless we trust them

and we wanna understand where they work

and where they don’t work.

And an explanation can be part of that, right?

So I apply for a loan and I get denied,

I want some explanation of why.

And you have, in Europe, we have the GDPR

that says you’re required to be able to get that.

But on the other hand,

the explanation alone is not enough, right?

So we are used to dealing with people

and with organizations and corporations and so on,

and they can give you an explanation

and you have no guarantee

that that explanation relates to reality, right?

So the bank can tell me, well, you didn’t get the loan

because you didn’t have enough collateral.

And that may be true, or it may be true

that they just didn’t like my religion or something else.

I can’t tell from the explanation,

and that’s true whether the decision was made

by a computer or by a person.

So I want more.

I do wanna have the explanations

and I wanna be able to have a conversation

to go back and forth and said,

well, you gave this explanation, but what about this?

And what would have happened if this had happened?

And what would I need to change that?

So I think a conversation is a better way to think about it

than just an explanation as a single output.

And I think we need testing of various kinds, right?

So in order to know,

was the decision really based on my collateral

or was it based on my religion or skin color or whatever?

I can’t tell if I’m only looking at my case,

but if I look across all the cases,

then I can detect the pattern, right?

So you wanna have that kind of capability.

You wanna have these adversarial testing, right?

So we thought we were doing pretty good

at object recognition in images.

We said, look, we’re at sort of pretty close

to human level performance on ImageNet and so on.

And then you start seeing these adversarial images

and you say, wait a minute,

that part is nothing like human performance.

You can mess with it really easily.

You can mess with it really easily, right?

And yeah, you can do that to humans too, right?

So we.

In a different way perhaps.

Right, humans don’t know what color the dress was.


And so they’re vulnerable to certain attacks

that are different than the attacks on the machines,

but the attacks on the machines are so striking.

They really change the way you think

about what we’ve done, right?

And the way I think about it is,

I think part of the problem is we’re seduced

by our low dimensional metaphors, right?


I like that phrase.

You look in a textbook and you say,

okay, now we’ve mapped out the space

and a cat is here and dog is here

and maybe there’s a tiny little spot in the middle

where you can’t tell the difference,

but mostly we’ve got it all covered.

And if you believe that metaphor,

then you say, well, we’re nearly there.

And there’s only gonna be a couple adversarial images.

But I think that’s the wrong metaphor

and what you should really say is,

it’s not a 2D flat space that we’ve got mostly covered.

It’s a million dimension space

and a cat is this string that goes out in this crazy path.

And if you step a little bit off the path in any direction,

you’re in nowhere’s land

and you don’t know what’s gonna happen.

And so I think that’s where we are

and now we’ve got to deal with that.

So it wasn’t so much an explanation,

but it was an understanding of what the models are

and what they’re doing

and now we can start exploring, how do you fix that?

Yeah, validating the robustness of the system and so on,

but take it back to this word trust.

Do you think we’re a little too hard on our robots

in terms of the standards we apply?

So, you know,

there’s a dance in nonverbal

and verbal communication between humans.

If we apply the same kind of standard in terms of humans,

we trust each other pretty quickly.

You know, you and I haven’t met before

and there’s some degree of trust, right?

That nothing’s gonna go crazy wrong

and yet to AI, when we look at AI systems

or we seem to approach skepticism always, always.

And it’s like they have to prove through a lot of hard work

that they’re even worthy of even inkling of our trust.

What do you think about that?

How do we break that barrier, close that gap?

I think that’s right.

I think that’s a big issue.

Just listening, my friend Mark Moffat is a naturalist

and he says, the most amazing thing about humans

is that you can walk into a coffee shop

or a busy street in a city

and there’s lots of people around you

that you’ve never met before and you don’t kill each other.


He says, chimpanzees cannot do that.

Yeah, right.


If a chimpanzee’s in a situation where here’s some

that aren’t from my tribe, bad things happen.

Especially in a coffee shop,

there’s delicious food around, you know.

Yeah, yeah.

But we humans have figured that out, right?

And you know.

For the most part.

We still go to war, we still do terrible things

but for the most part, we’ve learned to trust each other

and live together.

So that’s gonna be important for our AI systems as well.

And also I think a lot of the emphasis is on AI

but in many cases, AI is part of the technology

but isn’t really the main thing.

So a lot of what we’ve seen is more due

to communications technology than AI technology.

Yeah, you wanna make these good decisions

but the reason we’re able to have any kind of system at all

is we’ve got the communication

so that we’re collecting the data

and so that we can reach lots of people around the world.

I think that’s a bigger change that we’re dealing with.

Speaking of reaching a lot of people around the world,

on the side of education,

one of the many things in terms of education you’ve done,

you’ve taught the Intro to Artificial Intelligence course

that signed up 160,000 students.

There’s one of the first successful example

of a MOOC, Massive Open Online Course.

What did you learn from that experience?

What do you think is the future of MOOCs,

of education online?

Yeah, it was a great fun doing it,

particularly being right at the start

just because it was exciting and new

but it also meant that we had less competition, right?

So one of the things you hear about,

well, the problem with MOOCs is the completion rates

are so low so there must be a failure

and I gotta admit, I’m a prime contributor, right?

I probably started 50 different courses

that I haven’t finished

but I got exactly what I wanted out of them

because I had never intended to finish them.

I just wanted to dabble in a little bit

either to see the topic matter

or just to see the pedagogy of how are they doing this class.

So I guess the main thing I learned is when I came in,

I thought the challenge was information,

saying if I’m just, take the stuff I want you to know

and I’m very clear and explain it well,

then my job is done and good things are gonna happen.

And then in doing the course, I learned,

well, yeah, you gotta have the information

but really the motivation is the most important thing

that if students don’t stick with it,

it doesn’t matter how good the content is.

And I think being one of the first classes,

we were helped by sort of exterior motivation.

So we tried to do a good job of making it enticing

and setting up ways for the community

to work with each other to make it more motivating

but really a lot of it was, hey, this is a new thing

and I’m really excited to be part of a new thing.

And so the students brought their own motivation.

And so I think this is great

because there’s lots of people around the world

who have never had this before,

would never have the opportunity to go to Stanford

and take a class or go to MIT

or go to one of the other schools

but now we can bring that to them

and if they bring their own motivation,

they can be successful in a way they couldn’t before.

But that’s really just the top tier of people

that are ready to do that.

The rest of the people just don’t see

or don’t have the motivation

and don’t see how if they push through

and were able to do it, what advantage that would get them.

So I think we got a long way to go

before we were able to do that.

And I think some of it is based on technology

but more of it’s based on the idea of community.

You gotta actually get people together.

Some of the getting together can be done online.

I think some of it really has to be done in person

in order to build that type of community and trust.

You know, there’s an intentional mechanism

that we’ve developed a short attention span,

especially younger people

because sort of shorter and shorter videos online,

there’s a whatever the way the brain is developing now

and with people that have grown up with the internet,

they have quite a short attention span.

So, and I would say I had the same

when I was growing up too, probably for different reasons.

So I probably wouldn’t have learned as much as I have

if I wasn’t forced to sit in a physical classroom,

sort of bored, sometimes falling asleep,

but sort of forcing myself through that process.

So sometimes extremely difficult computer science courses.

What’s the difference in your view

between in person education experience,

which you, first of all, yourself had

and you yourself taught and online education

and how do we close that gap if it’s even possible?

Yeah, so I think there’s two issues.

One is whether it’s in person or online.

So it’s sort of the physical location

and then the other is kind of the affiliation, right?

So you stuck with it in part

because you were in the classroom

and you saw everybody else was suffering

the same way you were,

but also because you were enrolled,

you had paid tuition,

sort of everybody was expecting you to stick with it.

Society, parents, peers.

And so those are two separate things.

I mean, you could certainly imagine

I pay a huge amount of tuition

and everybody signed up and says, yes, you’re doing this,

but then I’m in my room

and my classmates are in different rooms, right?

We could have things set up that way.

So it’s not just the online versus offline.

I think what’s more important

is the commitment that you’ve made.

And certainly it is important

to have that kind of informal,

you know, I meet people outside of class,

we talk together because we’re all in it together.

I think that’s really important,

both in keeping your motivation

and also that’s where

some of the most important learning goes on.

So you wanna have that.

Maybe, you know, especially now

we start getting into higher bandwidths

and augmented reality and virtual reality,

you might be able to get that

without being in the same physical place.

Do you think it’s possible we’ll see a course at Stanford,

for example, that for students,

enrolled students is only online in the near future

or literally sort of it’s part of the curriculum

and there is no…

Yeah, so you’re starting to see that.

I know Georgia Tech has a master’s that’s done that way.

Oftentimes it’s sort of,

they’re creeping in in terms of a master’s program

or sort of further education,

considering the constraints of students and so on.

But I mean, literally, is it possible that we,

you know, Stanford, MIT, Berkeley,

all these places go online only in the next few decades?

Yeah, probably not,

because, you know, they’ve got a big commitment

to a physical campus.

Sure, so there’s a momentum

that’s both financial and culturally.

Right, and then there are certain things

that’s just hard to do virtually, right?

So, you know, we’re in a field where,

if you have your own computer and your own paper,

and so on, you can do the work anywhere.

But if you’re in a biology lab or something,

you know, you don’t have all the right stuff at home.

Right, so our field, programming,

you’ve also done a lot of programming yourself.

In 2001, you wrote a great article about programming

called Teach Yourself Programming in 10 Years,

sort of response to all the books

that say teach yourself programming in 21 days.

So if you were giving advice to someone

getting into programming today,

this is a few years since you’ve written that article,

what’s the best way to undertake that journey?

I think there’s lots of different ways,

and I think programming means more things now.

And I guess, you know, when I wrote that article,

I was thinking more about

becoming a professional software engineer,

and I thought that’s a, you know,

sort of a career long field of study.

But I think there’s lots of things now

that people can do where programming is a part

of solving what they wanna solve

without achieving that professional level status, right?

So I’m not gonna be going

and writing a million lines of code,

but, you know, I’m a biologist or a physicist or something,

or even a historian, and I’ve got some data,

and I wanna ask a question of that data.

And I think for that, you don’t need 10 years, right?

So there are many shortcuts

to being able to answer those kinds of questions.

And, you know, you see today a lot of emphasis

on learning to code, teaching kids how to code.

I think that’s great,

but I wish they would change the message a little bit,

right, so I think code isn’t the main thing.

I don’t really care if you know the syntax of JavaScript

or if you can connect these blocks together

in this visual language.

But what I do care about is that you can analyze a problem,

you can think of a solution, you can carry out,

you know, make a model, run that model,

test the model, see the results,

verify that they’re reasonable,

ask questions and answer them, right?

So it’s more modeling and problem solving,

and you use coding in order to do that,

but it’s not just learning coding for its own sake.

That’s really interesting.

So it’s actually almost, in many cases,

it’s learning to work with data,

to extract something useful out of data.

So when you say problem solving,

you really mean taking some kind of,

maybe collecting some kind of data set,

cleaning it up, and saying something interesting about it,

which is useful in all kinds of domains.

And, you know, and I see myself being stuck sometimes

in kind of the old ways, right?

So, you know, I’ll be working on a project,

maybe with a younger employee, and we say,

oh, well, here’s this new package

that could help solve this problem.

And I’ll go and I’ll start reading the manuals,

and, you know, I’ll be two hours into reading the manuals,

and then my colleague comes back and says, I’m done.

You know, I downloaded the package, I installed it,

I tried calling some things, the first one didn’t work,

the second one worked, now I’m done.

And I say, but I have a hundred questions

about how does this work and how does that work?

And they say, who cares, right?

I don’t need to understand the whole thing.

I answered my question, it’s a big, complicated package,

I don’t understand the rest of it,

but I got the right answer.

And I’m just, it’s hard for me to get into that mindset.

I want to understand the whole thing.

And, you know, if they wrote a manual,

I should probably read it.

And, but that’s not necessarily the right way.

I think I have to get used to dealing with more,

being more comfortable with uncertainty

and not knowing everything.

Yeah, so I struggle with the same,

instead of the spectrum between Donald and Don Knuth.


It’s kind of the very, you know,

before he can say anything about a problem,

he really has to get down to the machine code assembly.


And that forces exactly what you said of several students

in my group that, you know, 20 years old,

and they can solve almost any problem within a few hours.

That would take me probably weeks

because I would try to, as you said, read the manual.

So do you think the nature of mastery,

you’re mentioning biology,

sort of outside disciplines, applying programming,

but computer scientists.

So over time, there’s higher and higher levels

of abstraction available now.

So with this week, there’s the TensorFlow Summit, right?

So if you’re not particularly into deep learning,

but you’re still a computer scientist,

you can accomplish an incredible amount with TensorFlow

without really knowing any fundamental internals

of machine learning.

Do you think the nature of mastery is changing,

even for computer scientists,

like what it means to be an expert programmer?

Yeah, I think that’s true.

You know, we never really should have focused on programmer,

right, because it’s still, it’s the skill,

and what we really want to focus on is the result.

So we built this ecosystem

where the way you can get stuff done

is by programming it yourself.

At least when I started, you know,

library functions meant you had square root,

and that was about it, right?

Everything else you built from scratch.

And then we built up an ecosystem where a lot of times,

well, you can download a lot of stuff

that does a big part of what you need.

And so now it’s more a question of assembly

rather than manufacturing.

And that’s a different way of looking at problems.

From another perspective in terms of mastery

and looking at programmers or people that reason

about problems in a computational way.

So Google, you know, from the hiring perspective,

from the perspective of hiring

or building a team of programmers,

how do you determine if someone’s a good programmer?

Or if somebody, again, so I want to deviate from,

I want to move away from the word programmer,

but somebody who could solve problems

of large scale data and so on.

What’s, how do you build a team like that

through the interviewing process?

Yeah, and I think as a company grows,

you get more expansive in the types

of people you’re looking for, right?

So I think, you know, in the early days,

we’d interview people and the question we were trying

to ask is how close are they to Jeff Dean?

And most people were pretty far away,

but we take the ones that were not that far away.

And so we got kind of a homogeneous group

of people who were really great programmers.

Then as a company grows, you say,

well, we don’t want everybody to be the same,

to have the same skill set.

And so now we’re hiring biologists in our health areas

and we’re hiring physicists,

we’re hiring mechanical engineers,

we’re hiring, you know, social scientists and ethnographers

and people with different backgrounds

who bring different skills.

So you have mentioned that you still may partake

in code reviews, given that you have a wealth of experience,

as you’ve also mentioned.

What errors do you often see and tend to highlight

in the code of junior developers of people coming up now,

given your background from Blisp

to a couple of decades of programming?

Yeah, that’s a great question.

You know, sometimes I try to look at the flexibility

of the design of, yes, you know, this API solves this problem,

but where is it gonna go in the future?

Who else is gonna wanna call this?

And, you know, are you making it easier for them to do that?

That’s a matter of design, is it documentation,

is it sort of an amorphous thing

you can’t really put into words?

It’s just how it feels.

If you put yourself in the shoes of a developer,

would you use this kind of thing?

I think it is how you feel, right?

And so yeah, documentation is good,

but it’s more a design question, right?

If you get the design right,

then people will figure it out,

whether the documentation is good or not.

And if the design’s wrong, then it’d be harder to use.

How have you yourself changed as a programmer over the years?

In a way, you already started to say sort of,

you want to read the manual,

you want to understand the core of the syntax

to how the language is supposed to be used and so on.

But what’s the evolution been like

from the 80s, 90s to today?

I guess one thing is you don’t have to worry

about the small details of efficiency

as much as you used to, right?

So like I remember I did my list book in the 90s,

and one of the things I wanted to do was say,

here’s how you do an object system.

And basically, we’re going to make it

so each object is a hash table,

and you look up the methods, and here’s how it works.

And then I said, of course,

the real Common Lisp object system is much more complicated.

It’s got all these efficiency type issues,

and this is just a toy,

and nobody would do this in real life.

And it turns out Python pretty much did exactly

what I said and said objects are just dictionaries.

And yeah, they have a few little tricks as well.

But mostly, the thing that would have been

100 times too slow in the 80s

is now plenty fast for most everything.

So you had to, as a programmer,

let go of perhaps an obsession

that I remember coming up with

of trying to write efficient code.

Yeah, to say what really matters

is the total time it takes to get the project done.

And most of that’s gonna be the programmer time.

So if you’re a little bit less efficient,

but it makes it easier to understand and modify,

then that’s the right trade off.

So you’ve written quite a bit about Lisp.

Your book on programming is in Lisp.

You have a lot of code out there that’s in Lisp.

So myself and people who don’t know what Lisp is

should look it up.

It’s my favorite language for many AI researchers.

It is a favorite language.

The favorite language they never use these days.

So what part of Lisp do you find most beautiful and powerful?

So I think the beautiful part is the simplicity

that in half a page, you can define the whole language.

And other languages don’t have that.

So you feel like you can hold everything in your head.

And then a lot of people say,

well, then that’s too simple.

Here’s all these things I wanna do.

And my Java or Python or whatever

has 100 or 200 or 300 different syntax rules

and don’t I need all those?

And Lisp’s answer was, no, we’re only gonna give you

eight or so syntax rules,

but we’re gonna allow you to define your own.

And so that was a very powerful idea.

And I think this idea of saying,

I can start with my problem and with my data,

and then I can build the language I want for that problem

and for that data.

And then I can make Lisp define that language.

So you’re sort of mixing levels and saying,

I’m simultaneously a programmer in a language

and a language designer.

And that allows a better match between your problem

and your eventual code.

And I think Lisp had done that better than other languages.

Yeah, it’s a very elegant implementation

of functional programming.

But why do you think Lisp has not had the mass adoption

and success of languages like Python?

Is it the parentheses?

Is it all the parentheses?

Yeah, so I think a couple things.

So one was, I think it was designed for a single programmer

or a small team and a skilled programmer

who had the good taste to say,

well, I am doing language design

and I have to make good choices.

And if you make good choices, that’s great.

If you make bad choices, you can hurt yourself

and it can be hard for other people on the team

to understand it.

So I think there was a limit to the scale

of the size of a project in terms of number of people

that Lisp was good for.

And as an industry, we kind of grew beyond that.

I think it is in part the parentheses.

You know, one of the jokes is the acronym for Lisp

is lots of irritating, silly parentheses.

My acronym was Lisp is syntactically pure,

saying all you need is parentheses and atoms.

But I remember, you know, as we had the AI textbook

and because we did it in the nineties,

we had pseudocode in the book,

but then we said, well, we’ll have Lisp online

because that’s the language of AI at the time.

And I remember some of the students complaining

because they hadn’t had Lisp before

and they didn’t quite understand what was going on.

And I remember one student complained,

I don’t understand how this pseudocode

corresponds to this Lisp.

And there was a one to one correspondence

between the symbols in the code and the pseudocode.

And the only thing difference was the parentheses.

So I said, it must be that for some people,

a certain number of left parentheses shuts off their brain.

Yeah, it’s very possible in that sense

and Python just goes the other way.

So that was the point at which I said,

okay, can’t have only Lisp as a language.

Cause I don’t wanna, you know,

you only got 10 or 12 or 15 weeks or whatever it is

to teach AI and I don’t want to waste two weeks

of that teaching Lisp.

So I say, I gotta have another language.

Java was the most popular language at the time.

I started doing that.

And then I said, it’s really hard to have a one to one

correspondence between the pseudocode and the Java

because Java is so verbose.

So then I said, I’m gonna do a survey

and find the language that’s most like my pseudocode.

And it turned out Python basically was my pseudocode.

Somehow I had channeled Guido,

designed a pseudocode that was the same as Python,

although I hadn’t heard of Python at that point.

And from then on, that’s what I’ve been using

cause it’s been a good match.

So what’s the story in Python behind PyTudes?

Your GitHub repository with puzzles and exercises

in Python is pretty fun.

Yeah, just it, it seems like fun, you know,

I like doing puzzles and I like being an educator.

I did a class with Udacity, Udacity 212, I think it was.

It was basically problem solving using Python

and looking at different problems.

Does PyTudes feed that class in terms of the exercises?

I was wondering what the…

Yeah, so the class came first.

Some of the stuff that’s in PyTudes was write ups

of what was in the class and then some of it

was just continuing to work on new problems.

So what’s the organizing madness of PyTudes?

Is it just a collection of cool exercises?

Just whatever I thought was fun.

Okay, awesome.

So you were the director of search quality at Google

from 2001 to 2005 in the early days

when there’s just a few employees

and when the company was growing like crazy, right?

So, I mean, Google revolutionized the way we discover,

share and aggregate knowledge.

So just, this is one of the fundamental aspects

of civilization, right, is information being shared

and there’s different mechanisms throughout history

but Google has just 10x improved that, right?

And you’re a part of that, right?

People discovering that information.

So what were some of the challenges on a philosophical

or the technical level in those early days?

It definitely was an exciting time

and as you say, we were doubling in size every year

and the challenges were we wanted

to get the right answers, right?

And we had to figure out what that meant.

We had to implement that and we had to make it all efficient

and we had to keep on testing

and seeing if we were delivering good answers.

And now when you say good answers,

it means whatever people are typing in

in terms of keywords, in terms of that kind of thing

that the results they get are ordered

by the desirability for them of those results.

Like they’re like, the first thing they click on

will likely be the thing that they were actually looking for.

Right, one of the metrics we had

was focused on the first thing.

Some of it was focused on the whole page.

Some of it was focused on top three or so.

So we looked at a lot of different metrics

for how well we were doing

and we broke it down into subclasses of,

maybe here’s a type of query that we’re not doing well on

and we try to fix that.

Early on we started to realize that we were in an adversarial

position, right, so we started thinking,

well, we’re kind of like the card catalog in the library,

right, so the books are here and we’re off to the side

and we’re just reflecting what’s there.

And then we realized every time we make a change,

the webmasters make a change and it’s game theoretic.

And so we had to think not only of is this the right move

for us to make now, but also if we make this move,

what’s the counter move gonna be?

Is that gonna get us into a worse place,

in which case we won’t make that move,

we’ll make a different move.

And did you find, I mean, I assume with the popularity

and the growth of the internet

that people were creating new content,

so you’re almost helping guide the creation of new content.

Yeah, so that’s certainly true, right,

so we definitely changed the structure of the network.

So if you think back in the very early days,

Larry and Sergey had the PageRank paper

and John Kleinberg had this hubs and authorities model,

which says the web is made out of these hubs,

which will be my page of cool links about dogs or whatever,

and people would just list links.

And then there’d be authorities,

which were the page about dogs that most people linked to.

That doesn’t happen anymore.

People don’t bother to say my page of cool links,

because we took over that function, right,

so we changed the way that worked.

Did you imagine back then that the internet

would be as massively vibrant as it is today?

I mean, it was already growing quickly,

but it’s just another, I don’t know if you’ve ever,

today, if you sit back and just look at the internet

with wonder the amount of content

that’s just constantly being created,

constantly being shared and deployed.

Yeah, it’s always been surprising to me.

I guess I’m not very good at predicting the future.

And I remember being a graduate student in 1980 or so,

and we had the ARPANET,

and then there was this proposal to commercialize it,

and have this internet, and this crazy Senator Gore

thought that might be a good idea.

And I remember thinking, oh, come on,

you can’t expect a commercial company

to understand this technology.

They’ll never be able to do it.

Yeah, okay, we can have this.com domain,

but it won’t go anywhere.

So I was wrong, Al Gore was right.

At the same time, the nature of what it means

to be a commercial company has changed, too.

So Google, in many ways, at its founding

is different than what companies were before, I think.

Right, so there’s all these business models

that are so different than what was possible back then.

So in terms of predicting the future,

what do you think it takes to build a system

that approaches human level intelligence?

You’ve talked about, of course,

that we shouldn’t be so obsessed

about creating human level intelligence.

We just create systems that are very useful for humans.

But what do you think it takes

to approach that level?

Right, so certainly I don’t think

human level intelligence is one thing, right?

So I think there’s lots of different tasks,

lots of different capabilities.

I also don’t think that should be the goal, right?

So I wouldn’t wanna create a calculator

that could do multiplication at human level, right?

That would be a step backwards.

And so for many things,

we should be aiming far beyond human level

for other things.

Maybe human level is a good level to aim at.

And for others, we’d say,

well, let’s not bother doing this

because we already have humans can take on those tasks.

So as you say, I like to focus on what’s a useful tool.

And in some cases, being at human level

is an important part of crossing that threshold

to make the tool useful.

So we see in things like these personal assistants now

that you get either on your phone

or on a speaker that sits on the table,

you wanna be able to have a conversation with those.

And I think as an industry,

we haven’t quite figured out what the right model is

for what these things can do.

And we’re aiming towards,

well, you just have a conversation with them

the way you can with a person.

But we haven’t delivered on that model yet, right?

So you can ask it, what’s the weather?

You can ask it, play some nice songs.

And five or six other things,

and then you run out of stuff that it can do.

In terms of a deep, meaningful connection.

So you’ve mentioned the movie Her

as one of your favorite AI movies.

Do you think it’s possible for a human being

to fall in love with an AI assistant, as you mentioned?

So taking this big leap from what’s the weather

to having a deep connection.

Yeah, I think as people, that’s what we love to do.

And I was at a showing of Her

where we had a panel discussion and somebody asked me,

what other movie do you think Her is similar to?

And my answer was Life of Brian,

which is not a science fiction movie,

but both movies are about wanting to believe

in something that’s not necessarily real.

Yeah, by the way, for people that don’t know,

it’s Monty Python.

Yeah, it’s been brilliantly put.

Right, so I think that’s just the way we are.

We want to trust, we want to believe,

we want to fall in love,

and it doesn’t necessarily take that much, right?

So my kids fell in love with their teddy bear,

and the teddy bear was not very interactive.

So that’s all us pushing our feelings

onto our devices and our things,

and I think that that’s what we like to do,

so we’ll continue to do that.

So yeah, as human beings, we long for that connection,

and just AI has to do a little bit of work

to catch us in the other end.

Yeah, and certainly, if you can get to dog level,

a lot of people have invested a lot of love in their pets.

In their pets.

Some people, as I’ve been told,

in working with autonomous vehicles,

have invested a lot of love into their inanimate cars,

so it really doesn’t take much.

So what is a good test to linger on a topic

that may be silly or a little bit philosophical?

What is a good test of intelligence in your view?

Is natural conversation like in the Turing test

a good test?

Put another way, what would impress you

if you saw a computer do it these days?

Yeah, I mean, I get impressed all the time.

Go playing, StarCraft playing, those are all pretty cool.

And I think, sure, conversation is important.

I think we sometimes have these tests

where it’s easy to fool the system, where

you can have a chat bot that can have a conversation,

but it never gets into a situation

where it has to be deep enough that it really reveals itself

as being intelligent or not.

I think Turing suggested that, but I think if he were alive,

he’d say, you know, I didn’t really mean that seriously.

And I think, this is just my opinion,

but I think Turing’s point was not

that this test of conversation is a good test.

I think his point was having a test is the right thing.

So rather than having the philosophers say, oh, no,

AI is impossible, you should say, well,

we’ll just have a test, and then the result of that

will tell us the answer.

And it doesn’t necessarily have to be a conversation test.

That’s right.

And coming up a new, better test as the technology evolves

is probably the right way.

Do you worry, as a lot of the general public does about,

not a lot, but some vocal part of the general public

about the existential threat of artificial intelligence?

So looking farther into the future, as you said,

most of us are not able to predict much.

So when shrouded in such mystery, there’s a concern of,

well, you start thinking about worst case.

Is that something that occupies your mind, space, much?

So I certainly think about threats.

I think about dangers.

And I think any new technology has positives and negatives.

And if it’s a powerful technology,

it can be used for bad as well as for good.

So I’m certainly not worried about the robot

apocalypse and the Terminator type scenarios.

I am worried about change in employment.

And are we going to be able to react fast enough

to deal with that?

I think we’re already seeing it today, where

a lot of people are disgruntled about the way

income inequality is working.

And automation could help accelerate

those kinds of problems.

I see powerful technologies can always be used as weapons,

whether they’re robots or drones or whatever.

Some of that we’re seeing due to AI.

A lot of it, you don’t need AI.

And I don’t know what’s a worst threat,

if it’s an autonomous drone or it’s CRISPR technology

becoming available.

Or we have lots of threats to face.

And some of them involve AI, and some of them don’t.

So the threats that technology presents,

are you, for the most part, optimistic about technology

also alleviating those threats or creating new opportunities

or protecting us from the more detrimental effects

of these new technologies?

I don’t know.

Again, it’s hard to predict the future.

And as a society so far, we’ve survived

nuclear bombs and other things.

Of course, only societies that have survived

are having this conversation.

So maybe that’s survivorship bias there.

What problem stands out to you as exciting, challenging,

impactful to work on in the near future for yourself,

for the community, and broadly?

So we talked about these assistance and conversation.

I think that’s a great area.

I think combining common sense reasoning

with the power of data is a great area.

In which application?

In conversation, or just broadly speaking?

Just in general, yeah.

As a programmer, I’m interested in programming tools,

both in terms of the current systems

we have today with TensorFlow and so on.

Can we make them much easier to use

for a broader class of people?

And also, can we apply machine learning

to the more traditional type of programming?

So when you go to Google and you type in a query

and you spell something wrong, it says, did you mean?

And the reason we’re able to do that

is because lots of other people made a similar error,

and then they corrected it.

We should be able to go into our code bases and our bug fix


And when I type a line of code, it should be able to say,

did you mean such and such?

If you type this today, you’re probably going to type

in this bug fix tomorrow.

Yeah, that’s a really exciting application

of almost an assistant for the coding programming experience

at every level.

So I think I could safely speak for the entire AI community,

first of all, for thanking you for the amazing work you’ve

done, certainly for the amazing work you’ve done

with AI and Modern Approach book.

I think we’re all looking forward very much

for the fourth edition, and then the fifth edition, and so on.

So Peter, thank you so much for talking today.

Yeah, thank you.

My pleasure.