Leonard Susskind: Quantum Mechanics, String Theory, and Black Holes
物理与宇宙学AI 与机器学习技术与编程音乐与艺术心理与人性
📋 章节目录
暂无章节信息
🔑 关键词
quantumdonsystemsphysicsmechanicscomputertheoryblacklearningstringintelligencemachinethinkingholesspacebetterbrainequationscomputersclassical
💬 精彩语录
暂无语录
🎙️ 完整对话（1209 条）
Lex Fridman (00:00.000)
The following is a conversation with Leonard Susskind.
以下是与伦纳德·苏斯金德的对话。
Lex Fridman (00:03.080)
He's a professor of theoretical physics
他是一位理论物理学教授
Lex Fridman (00:04.840)
at Stanford University and founding director
斯坦福大学和创始董事
Lex Fridman (00:07.640)
of Stanford Institute of Theoretical Physics.
斯坦福理论物理研究所的教授。
Lex Fridman (00:10.400)
He is widely regarded as one of the fathers
他被广泛认为是父亲之一
Leonard Susskind (00:13.040)
of string theory and in general,
弦理论和一般情况下，
Lex Fridman (00:14.920)
as one of the greatest physicists of our time,
作为我们这个时代最伟大的物理学家之一
Leonard Susskind (00:17.400)
both as a researcher and an educator.
既是一名研究者，又是一名教育家。
Lex Fridman (00:20.400)
This is the Artificial Intelligence Podcast.
这是人工智能播客。
Leonard Susskind (00:23.320)
Perhaps you noticed that the people I've been speaking with
也许你注意到与我交谈过的人
Lex Fridman (00:26.120)
are not just computer scientists,
不仅仅是计算机科学家，
Lex Fridman (00:27.880)
but philosophers, mathematicians, writers,
但是哲学家、数学家、作家，
Lex Fridman (00:30.640)
psychologists, physicists, and soon other disciplines.
心理学家、物理学家，很快还有其他学科。
Leonard Susskind (00:34.240)
To me, AI is much bigger than deep learning,
对我来说，人工智能比深度学习更重要，
Lex Fridman (00:37.400)
bigger than computing.
比计算更大。
Leonard Susskind (00:39.000)
It is our civilization's journey
这是我们的文明之旅
Lex Fridman (00:40.880)
into understanding the human mind
去理解人类的思想
Lex Fridman (00:42.880)
and creating echoes of it in the machine.
并在机器中产生它的回声。
Lex Fridman (00:45.880)
If you enjoy the podcast, subscribe on YouTube,
如果您喜欢播客，请在 YouTube 上订阅，
Leonard Susskind (00:48.800)
give it five stars on iTunes, support it on Patreon,
在 iTunes 上给它五颗星，在 Patreon 上支持它，
Lex Fridman (00:51.840)
or simply connect with me on Twitter
Leonard Susskind (00:53.680)
at Lex Friedman, spelled F R I D M A M.
Lex Fridman (00:57.600)
And now, here's my conversation with Leonard Susskind.
Leonard Susskind (01:02.760)
You worked and were friends with Richard Feynman.
Lex Fridman (01:05.360)
How has he influenced you, changed you
Lex Fridman (01:07.640)
as a physicist and thinker?
Lex Fridman (01:10.160)
What I saw, I think what I saw was somebody
Leonard Susskind (01:13.920)
who could do physics in this deeply intuitive way.
Lex Fridman (01:18.600)
His style was almost to close his eyes
Lex Fridman (01:21.080)
and visualize the phenomena that he was thinking about.
Lex Fridman (01:24.540)
And through visualization, outflank the mathematical,
Leonard Susskind (01:30.520)
the highly mathematical and very, very sophisticated
Lex Fridman (01:34.360)
technical arguments that people would use.
Leonard Susskind (01:37.020)
I think that was also natural to me,
Lex Fridman (01:39.400)
but I saw somebody who was actually successful at it,
Leonard Susskind (01:43.960)
who could do physics in a way that I regarded
Lex Fridman (01:47.760)
as simpler, more direct, more intuitive.
Lex Fridman (01:55.520)
And while I don't think he changed my way of thinking,
Lex Fridman (01:59.080)
I do think he validated it.
Leonard Susskind (02:01.480)
He made me look at it and say, yeah,
Lex Fridman (02:03.080)
that's something you can do and get away with.
Leonard Susskind (02:06.280)
Practically didn't get away with it.
Lex Fridman (02:08.680)
So do you find yourself, whether you're thinking
Leonard Susskind (02:12.000)
about quantum mechanics or black holes
Lex Fridman (02:14.720)
or string theory, using intuition as a first step
Lex Fridman (02:19.400)
or step throughout using visualization?
Lex Fridman (02:22.160)
Yeah, very much so, very much so.
Leonard Susskind (02:24.680)
I tend not to think about the equations.
Lex Fridman (02:27.720)
I tend not to think about the symbols.
Leonard Susskind (02:30.160)
I tend to try to visualize the phenomena themselves.
Lex Fridman (02:34.660)
And then when I get an insight that I think is valid,
Leonard Susskind (02:38.400)
I might try to convert it to mathematics,
Lex Fridman (02:40.360)
but I'm not a natural mathematician.
Leonard Susskind (02:44.400)
I'm good enough at it.
Lex Fridman (02:46.280)
I'm good enough at it, but I'm not a great mathematician.
Lex Fridman (02:49.820)
So for me, the way of thinking about physics
Lex Fridman (02:52.440)
is first intuitive, first visualization,
Leonard Susskind (02:57.760)
scribble a few equations maybe,
Lex Fridman (02:59.680)
but then try to convert it to mathematics.
Leonard Susskind (03:02.980)
Experience is that other people are better
Lex Fridman (03:04.800)
at converting it to mathematics than I am.
Lex Fridman (03:08.000)
And yet you've worked with very counterintuitive ideas.
Lex Fridman (03:12.000)
No, that's true.
Leonard Susskind (03:12.840)
That's true.
Lex Fridman (03:13.680)
You can visualize something counterintuitive.
Lex Fridman (03:15.600)
How do you dare?
Lex Fridman (03:16.440)
By rewiring your brain in new ways.
Leonard Susskind (03:19.920)
Yeah, quantum mechanics is not intuitive.
Lex Fridman (03:22.680)
Very little of modern physics is intuitive.
Lex Fridman (03:26.840)
Intuitive, what does intuitive mean?
Lex Fridman (03:29.480)
It means the ability to think about it
Leonard Susskind (03:31.800)
with basic classical physics,
Lex Fridman (03:33.720)
the physics that we evolved with throwing stones,
Leonard Susskind (03:38.720)
or splashing water, whatever it happens to be.
Lex Fridman (03:44.800)
Quantum physics, general relativity,
Leonard Susskind (03:47.080)
quantum field theory are deeply unintuitive in that way.
Lex Fridman (03:51.160)
But after time and getting familiar with these things,
Leonard Susskind (03:55.200)
you develop new intuitions.
Lex Fridman (03:57.040)
I always said you rewire.
Lex Fridman (03:59.680)
And it's to the point where me and many of my friends,
Lex Fridman (04:04.360)
I and many of my friends,
Leonard Susskind (04:05.680)
can think more easily quantum mechanically
Lex Fridman (04:10.280)
than we can classically.
Leonard Susskind (04:11.520)
We've gotten so used to it.
Lex Fridman (04:13.520)
I mean, yes, our neural wiring in our brain
Leonard Susskind (04:17.240)
is such that we understand rocks and stones and water
Lex Fridman (04:20.400)
and so on.
Leonard Susskind (04:21.240)
We sort of evolved for that.
Lex Fridman (04:22.060)
Evolved for it.
Lex Fridman (04:23.320)
Do you think it's possible to create a wiring
Lex Fridman (04:26.720)
of neuron like state devices that more naturally
Leonard Susskind (04:31.160)
understand quantum mechanics, understand wave function,
Lex Fridman (04:35.880)
understand these weird things?
Leonard Susskind (04:38.120)
Well, I'm not sure.
Lex Fridman (04:39.040)
I think many of us have evolved the ability
Leonard Susskind (04:42.480)
to think quantum mechanically to some extent.
Lex Fridman (04:46.360)
But that doesn't mean you can think like an electron.
Leonard Susskind (04:50.220)
That doesn't mean another example.
Lex Fridman (04:53.600)
Forget for a minute quantum mechanics.
Leonard Susskind (04:55.880)
Just visualizing four dimensional space
Lex Fridman (04:58.660)
or five dimensional space or six dimensional space,
Leonard Susskind (05:02.080)
I think we're fundamentally wired
Lex Fridman (05:05.780)
to visualize three dimensions.
Leonard Susskind (05:08.240)
I can't even visualize two dimensions or one dimension
Lex Fridman (05:11.960)
without thinking about it as embedded in three dimensions.
Leonard Susskind (05:16.040)
If I wanna visualize a line,
Lex Fridman (05:18.280)
I think of the line as being a line in three dimensions.
Leonard Susskind (05:23.000)
Or I think of the line as being a line on a piece of paper
Lex Fridman (05:25.580)
with a piece of paper being in three dimensions.
Leonard Susskind (05:28.160)
I never seem to be able to, in some abstract and pure way,
Lex Fridman (05:33.240)
visualize in my head the one dimension,
Leonard Susskind (05:35.920)
the two dimension, the four dimension, the five dimensions.
Lex Fridman (05:38.840)
And I don't think that's ever gonna happen.
Leonard Susskind (05:41.400)
The reason is I think our neural wiring
Lex Fridman (05:43.600)
is just set up for that.
Leonard Susskind (05:47.000)
On the other hand, we do learn ways
Lex Fridman (05:49.060)
to think about five, six, seven dimensions.
Leonard Susskind (05:52.600)
We learn ways, we learn mathematical ways,
Lex Fridman (05:56.200)
and we learn ways to visualize them, but they're different.
Lex Fridman (06:00.800)
And so yeah, I think we do rewire ourselves.
Lex Fridman (06:04.800)
Whether we can ever completely rewire ourselves
Leonard Susskind (06:07.240)
to be completely comfortable with these concepts, I doubt.
Lex Fridman (06:11.680)
So that it's completely natural.
Leonard Susskind (06:13.560)
To where it's completely natural.
Lex Fridman (06:15.080)
So I'm sure there's somewhat, you could argue,
Leonard Susskind (06:18.160)
creatures that live in a two dimensional space.
Lex Fridman (06:22.400)
Yeah, maybe there are.
Lex Fridman (06:23.560)
And while it's romanticizing the notion of curse,
Lex Fridman (06:28.640)
we're all living, as far as we know,
Leonard Susskind (06:30.040)
in three dimensional space.
Lex Fridman (06:31.680)
But how do those creatures imagine 3D space?
Leonard Susskind (06:35.600)
Well, probably the way we imagine 4D,
Lex Fridman (06:37.640)
by using some mathematics and some equations
Lex Fridman (06:40.480)
and some tricks.
Lex Fridman (06:44.440)
Okay, so jumping back to Feynman just for a second.
Leonard Susskind (06:48.380)
He had a little bit of an ego.
Lex Fridman (06:52.700)
Yes.
Lex Fridman (06:54.780)
Why, do you think ego is powerful or dangerous in science?
Lex Fridman (07:00.140)
I think both, both, both.
Leonard Susskind (07:02.880)
I think you have to have both arrogance and humility.
Lex Fridman (07:06.500)
You have to have the arrogance to say, I can do this.
Leonard Susskind (07:10.620)
Nature is difficult, nature is very, very hard.
Lex Fridman (07:13.620)
I'm smart enough, I can do it.
Leonard Susskind (07:16.140)
I can win the battle with nature.
Lex Fridman (07:19.020)
On the other hand, I think you also have to have
Leonard Susskind (07:21.020)
the humility to know that you're very likely
Lex Fridman (07:26.460)
to be wrong on any given occasion.
Leonard Susskind (07:29.060)
Everything you're thinking could suddenly change.
Lex Fridman (07:33.300)
Young people can come along and say things
Leonard Susskind (07:35.500)
you won't understand and you'll be lost and flabbergasted.
Lex Fridman (07:39.820)
So I think it's a combination of both.
Leonard Susskind (07:42.620)
You better recognize that you're very limited,
Lex Fridman (07:46.660)
and you better be able to say to yourself,
Leonard Susskind (07:49.280)
I'm not so limited that I can't win this battle with nature.
Lex Fridman (07:53.460)
It takes a special kind of person
Leonard Susskind (07:56.640)
who can manage both of those, I would say.
Lex Fridman (07:59.820)
And I would say there's echoes of that in your own work,
Leonard Susskind (08:03.020)
a little bit of ego, a little bit of outside of the box,
Lex Fridman (08:05.900)
humble thinking.
Leonard Susskind (08:08.260)
I hope so.
Lex Fridman (08:09.580)
So was there a time where you felt,
Leonard Susskind (08:16.500)
you looked at yourself and asked,
Lex Fridman (08:18.080)
am I completely wrong about this?
Lex Fridman (08:19.920)
Oh yeah, about the whole thing or about specific things?
Lex Fridman (08:23.980)
The whole thing.
Lex Fridman (08:24.900)
What do you mean?
Lex Fridman (08:25.900)
Wait, which whole thing?
Leonard Susskind (08:27.060)
Me and me and my ability to do this thing.
Lex Fridman (08:29.960)
Oh, those kinds of doubts.
Lex Fridman (08:31.420)
First of all, did you have those kinds of doubts?
Lex Fridman (08:33.840)
No, I had different kind of doubts.
Leonard Susskind (08:35.940)
I came from a very working class background
Lex Fridman (08:37.940)
and I was uncomfortable in academia for,
Leonard Susskind (08:41.100)
oh, for a long time.
Lex Fridman (08:43.760)
But they weren't doubts about my ability or my,
Leonard Susskind (08:48.020)
they were just the discomfort in being in an environment
Lex Fridman (08:52.740)
that my family hadn't participated in,
Leonard Susskind (08:56.620)
I knew nothing about as a young person.
Lex Fridman (08:58.320)
I didn't learn that there was such a thing called physics
Leonard Susskind (09:00.700)
until I was almost 20 years old.
Lex Fridman (09:02.340)
Yeah, so I did have certain kind of doubts,
Lex Fridman (09:09.560)
but not about my ability.
Lex Fridman (09:11.860)
I don't think I was too worried
Leonard Susskind (09:14.000)
about whether I would succeed or not.
Lex Fridman (09:18.040)
I never felt this insecurity, am I ever gonna get a job?
Leonard Susskind (09:23.080)
That had never occurred to me that I wouldn't.
Lex Fridman (09:27.180)
Maybe you could speak a little bit to this sense
Leonard Susskind (09:29.860)
of what is academia.
Lex Fridman (09:31.720)
Because I too feel a bit uncomfortable in it.
Leonard Susskind (09:37.800)
There's something I can't put quite into words
Lex Fridman (09:40.040)
what you have that's not, doesn't, if we call it music,
Leonard Susskind (09:45.240)
you play a different kind of music than a lot of academia.
Lex Fridman (09:48.520)
How have you joined this orchestra?
Lex Fridman (09:51.960)
How do you think about it?
Lex Fridman (09:54.480)
I don't know that I thought about it
Leonard Susskind (09:56.080)
as much as I just felt it.
Lex Fridman (09:58.240)
Thinking is one thing, feeling is another thing.
Leonard Susskind (10:02.800)
I felt like an outsider until a certain age
Lex Fridman (10:07.100)
when I suddenly found myself the ultimate insider
Leonard Susskind (10:10.740)
in academic physics.
Lex Fridman (10:14.520)
And that was a sharp transition, and I wasn't a young man.
Leonard Susskind (10:19.600)
I was probably 50 years old.
Lex Fridman (10:22.280)
So you were never quite, it was a phase transition,
Leonard Susskind (10:24.960)
you were never quite in the middle.
Lex Fridman (10:27.360)
Yeah, that's right, I wasn't.
Leonard Susskind (10:29.440)
I always felt a little bit of an outsider.
Lex Fridman (10:32.080)
In the beginning, a lot an outsider.
Leonard Susskind (10:37.200)
My way of thinking was different,
Lex Fridman (10:40.440)
my approach to mathematics was different,
Lex Fridman (10:43.040)
but also my social background
Lex Fridman (10:47.160)
that I came from was different.
Leonard Susskind (10:49.320)
Now these days, half the young people I meet,
Lex Fridman (10:51.520)
they're parents or professors.
Leonard Susskind (10:53.020)
That was not my case.
Lex Fridman (10:59.900)
But then all of a sudden, at some point,
Leonard Susskind (11:02.220)
I found myself at very much the center of,
Lex Fridman (11:06.260)
maybe not the only one at the center,
Lex Fridman (11:07.840)
but certainly one of the people in the center
Lex Fridman (11:09.860)
of a certain kind of physics.
Lex Fridman (11:12.220)
And all that went away, it went away in a flash.
Lex Fridman (11:17.700)
So maybe a little bit with Feynman,
Lex Fridman (11:21.780)
but in general, how do you develop ideas?
Lex Fridman (11:24.500)
Do you work through ideas alone?
Lex Fridman (11:26.100)
Do you brainstorm with others?
Lex Fridman (11:27.820)
Oh, both, both, very definitely both.
Leonard Susskind (11:31.400)
The younger time, I spent more time with myself.
Lex Fridman (11:36.580)
Now, because I'm at Stanford,
Leonard Susskind (11:39.460)
because I have a lot of ex students
Lex Fridman (11:44.460)
and people who are interested in the same thing I am,
Leonard Susskind (11:50.840)
I spend a good deal of time, almost on a daily basis,
Lex Fridman (11:54.320)
interacting, brainstorming, as you said.
Leonard Susskind (11:57.360)
It's a very important part.
Lex Fridman (12:00.400)
I spend less time probably completely self focused
Leonard Susskind (12:03.720)
than with a piece of paper
Lex Fridman (12:07.800)
and just sitting there staring at it.
Lex Fridman (12:09.640)
What are your hopes for quantum computers?
Lex Fridman (12:13.320)
So machines that are based on,
Leonard Susskind (12:16.240)
that have some elements of leverage quantum mechanical ideas.
Lex Fridman (12:21.240)
Yeah, it's not just leveraging quantum mechanical ideas.
Leonard Susskind (12:24.840)
You can simulate quantum systems on a classical computer.
Lex Fridman (12:29.840)
Simulate them means solve the Schrodinger equation for them
Leonard Susskind (12:33.200)
or solve the equations of quantum mechanics
Lex Fridman (12:36.640)
or solve the equations of quantum mechanics
Leonard Susskind (12:40.200)
on a computer, on a classical computer.
Lex Fridman (12:43.600)
But the classical computer is not doing,
Leonard Susskind (12:47.400)
is not a quantum mechanical system itself.
Lex Fridman (12:49.760)
Of course it is.
Leonard Susskind (12:50.640)
Everything's made of quantum mechanics,
Lex Fridman (12:52.120)
but it's not functioning.
Leonard Susskind (12:53.280)
It's not functioning as a quantum system.
Lex Fridman (12:56.080)
It's just solving equations.
Leonard Susskind (12:58.560)
The quantum computer is truly a quantum system
Lex Fridman (13:01.840)
which is actually doing the things
Leonard Susskind (13:05.000)
that you're programming it to do.
Lex Fridman (13:07.360)
You want to program a quantum field theory.
Leonard Susskind (13:12.040)
If you do it in classical physics,
Lex Fridman (13:13.680)
that program is not actually functioning in the computer
Leonard Susskind (13:17.600)
as a quantum field theory.
Lex Fridman (13:18.760)
It's just solving some equations.
Leonard Susskind (13:21.760)
Physically, it's not doing the things
Lex Fridman (13:23.720)
that the quantum system would do.
Leonard Susskind (13:27.240)
The quantum computer is really a quantum mechanical system
Lex Fridman (13:30.400)
which is actually carrying out the quantum operations.
Leonard Susskind (13:34.120)
You can measure it at the end.
Lex Fridman (13:36.320)
It intrinsically satisfies the uncertainty principle.
Leonard Susskind (13:40.480)
It is limited in the same way that quantum systems
Lex Fridman (13:44.320)
are limited by uncertainty and so forth.
Lex Fridman (13:47.440)
And it really is a quantum system.
Lex Fridman (13:49.240)
That means that what you're doing
Leonard Susskind (13:51.360)
when you program something for a quantum system
Lex Fridman (13:53.360)
is you're actually building a real version of the system.
Leonard Susskind (13:58.160)
The limits of a classical computer,
Lex Fridman (14:00.440)
classical computers are enormously limited
Leonard Susskind (14:02.920)
when it comes to the quantum systems.
Lex Fridman (14:07.160)
They're enormously limited
Leonard Susskind (14:09.040)
because you've probably heard this before,
Lex Fridman (14:12.240)
but in order to store the amount of information
Leonard Susskind (14:14.960)
that's in a quantum state of 400 spins,
Lex Fridman (14:19.920)
that's not very many, 400 I can put in my pocket,
Leonard Susskind (14:23.040)
I can put 400 pennies in my pocket.
Lex Fridman (14:27.840)
To be able to simulate the quantum state
Leonard Susskind (14:32.160)
of 400 elementary quantum systems, qubits we call them,
Lex Fridman (14:37.640)
to do that would take more information
Leonard Susskind (14:39.880)
than can possibly be stored in the entire universe
Lex Fridman (14:43.120)
if it were packed so tightly
Leonard Susskind (14:46.560)
that you couldn't pack any more in.
Lex Fridman (14:50.380)
400 qubits.
Leonard Susskind (14:52.240)
On the other hand, if your quantum computer
Lex Fridman (14:54.520)
is composed of 400 qubits,
Leonard Susskind (14:56.320)
it can do everything 400 qubits can do.
Lex Fridman (14:59.420)
What kind of space, if you just intuitively think
Leonard Susskind (15:02.280)
about the space of algorithms that that unlocks for us,
Lex Fridman (15:06.320)
so there's a whole complexity theory
Leonard Susskind (15:08.480)
around classical computers,
Lex Fridman (15:10.080)
measuring the running time of things,
Lex Fridman (15:12.440)
and P, so on, what kind of algorithms
Lex Fridman (15:14.880)
just intuitively do you think it unlocks for us?
Leonard Susskind (15:18.360)
Okay, so we know that there are a handful of algorithms
Lex Fridman (15:22.080)
that can seriously beat classical computers
Lex Fridman (15:25.760)
and which can have exponentially more power.
Lex Fridman (15:28.200)
This is a mathematical statement.
Leonard Susskind (15:29.480)
Nobody's exhibited this in the laboratory.
Lex Fridman (15:32.320)
It's a mathematical statement.
Leonard Susskind (15:33.600)
We know that's true, but it also seems more and more
Lex Fridman (15:37.640)
that the number of such things is very limited.
Leonard Susskind (15:40.320)
Only very, very special problems
Lex Fridman (15:45.080)
exhibit that much advantage for a quantum computer,
Leonard Susskind (15:49.600)
of standard problems.
Lex Fridman (15:52.120)
To my mind, as far as I can tell,
Leonard Susskind (15:53.900)
the great power of quantum computers
Lex Fridman (15:55.600)
will actually be to simulate quantum systems.
Leonard Susskind (15:59.880)
If you're interested in a certain quantum system
Lex Fridman (16:02.760)
and it's too hard to simulate classically,
Leonard Susskind (16:07.360)
you simply build a version of the same system.
Lex Fridman (16:09.840)
You build a version of it.
Leonard Susskind (16:11.100)
You build a model of it
Lex Fridman (16:12.040)
that's actually functioning as the system.
Leonard Susskind (16:14.440)
You run it, and then you do the same thing
Lex Fridman (16:16.880)
you would do to the quantum system.
Leonard Susskind (16:18.500)
You make measurements on it, quantum measurements on it.
Lex Fridman (16:21.820)
The advantage is you can run it much slower.
Lex Fridman (16:26.140)
You could say, why bother?
Lex Fridman (16:27.540)
Why not just use the real system?
Lex Fridman (16:29.580)
Why not just do experiments on the real system?
Lex Fridman (16:32.340)
Well, real systems are kind of limited.
Leonard Susskind (16:33.900)
You can't change them.
Lex Fridman (16:34.780)
You can't manipulate them.
Leonard Susskind (16:36.300)
You can't slow them down so that you can poke into them.
Lex Fridman (16:40.420)
You can't modify them in arbitrary kinds of ways
Leonard Susskind (16:43.420)
to see what would happen if I change the system a little bit.
Lex Fridman (16:48.420)
I think that quantum computers will be extremely valuable
Leonard Susskind (16:55.500)
in understanding quantum systems.
Lex Fridman (17:00.940)
At the lowest level of the fundamental laws.
Leonard Susskind (17:04.340)
They're actually satisfying the same laws
Lex Fridman (17:06.540)
as the systems that they're simulating.
Leonard Susskind (17:09.860)
Okay, so on the one hand, you have things like factoring.
Lex Fridman (17:13.060)
Factoring is the great thing of quantum computers.
Leonard Susskind (17:17.580)
Factoring large numbers, that doesn't seem that much
Lex Fridman (17:20.620)
to do with quantum mechanics.
Leonard Susskind (17:22.580)
It seems to be almost a fluke that a quantum computer
Lex Fridman (17:28.540)
can solve the factoring problem in a short time.
Lex Fridman (17:34.420)
And those problems seem to be extremely special, rare,
Lex Fridman (17:38.520)
and it's not clear to me
Leonard Susskind (17:40.300)
that there's gonna be a lot of them.
Lex Fridman (17:42.740)
On the other hand, there are a lot of quantum systems.
Leonard Susskind (17:45.180)
Chemistry, there's solid state physics,
Lex Fridman (17:47.900)
there's material science, there's quantum gravity,
Leonard Susskind (17:51.020)
there's all kinds of quantum field theory.
Lex Fridman (17:54.540)
And some of these are actually turning out
Leonard Susskind (17:56.780)
to be applied sciences,
Lex Fridman (17:58.100)
as well as very fundamental sciences.
Lex Fridman (18:01.120)
So we probably will run out of the ability
Lex Fridman (18:05.140)
to solve equations for these things.
Leonard Susskind (18:07.960)
Solve equations by the standard methods of pencil and paper.
Lex Fridman (18:11.620)
Solve the equations by the method of classical computers.
Lex Fridman (18:16.380)
And so what we'll do is we'll build versions
Lex Fridman (18:18.740)
of these systems, run them,
Lex Fridman (18:22.120)
and run them under controlled circumstances
Lex Fridman (18:24.280)
where we can change them, manipulate them,
Leonard Susskind (18:26.840)
make measurements on them,
Lex Fridman (18:28.100)
and find out all the things we wanna know.
Lex Fridman (18:30.540)
So in finding out the things we wanna know
Lex Fridman (18:33.640)
about very small systems, is there something
Leonard Susskind (18:38.640)
that we can also find out about the macro level,
Lex Fridman (18:42.080)
about something about the function, forgive me,
Leonard Susskind (18:45.040)
of our brain, biological systems,
Lex Fridman (18:48.080)
the stuff that's about one meter in size
Lex Fridman (18:50.380)
versus much, much smaller?
Lex Fridman (18:53.260)
Well, what all the excitement is about
Leonard Susskind (18:55.200)
among the people that I interact with
Lex Fridman (18:56.880)
is understanding black holes.
Leonard Susskind (18:58.960)
Black holes.
Lex Fridman (18:59.800)
Black holes are big things.
Leonard Susskind (19:02.160)
They are many, many degrees of freedom.
Lex Fridman (19:04.100)
There is another kind of quantum system that is big.
Leonard Susskind (19:08.740)
It's a large quantum computer.
Lex Fridman (19:11.760)
And one of the things we've learned
Leonard Susskind (19:13.140)
is that the physics of large quantum computers
Lex Fridman (19:15.700)
is in some ways similar to the physics
Leonard Susskind (19:17.580)
of large quantum black holes.
Lex Fridman (19:19.740)
And we're using that relationship.
Leonard Susskind (19:22.000)
Now you asked, you didn't ask about quantum computers
Lex Fridman (19:24.780)
or systems, you didn't ask about black holes,
Leonard Susskind (19:28.100)
you asked about brains.
Lex Fridman (19:29.940)
Yeah, about stuff that's in the middle of the two.
Leonard Susskind (19:32.300)
It's different.
Lex Fridman (19:34.060)
So black holes are,
Leonard Susskind (19:36.580)
there's something fundamental about black holes
Lex Fridman (19:39.580)
that feels to be very different than a brain.
Leonard Susskind (19:42.180)
Yes.
Lex Fridman (19:43.300)
And they also function in a very quantum mechanical way.
Leonard Susskind (19:45.980)
Right.
Lex Fridman (19:46.820)
Okay.
Leonard Susskind (19:47.820)
It is, first of all, unclear to me,
Lex Fridman (19:50.620)
but of course it's unclear to me.
Leonard Susskind (19:52.140)
I'm not a neuroscientist.
Lex Fridman (19:55.340)
I have, I don't even have very many friends
Leonard Susskind (19:58.100)
who are neuroscientists.
Lex Fridman (20:00.200)
I would like to have more friends who are neuroscientists.
Leonard Susskind (20:02.580)
I just don't run into them very often.
Lex Fridman (20:05.620)
Among the few neuroscientists
Leonard Susskind (20:07.420)
I've ever talked about about this,
Lex Fridman (20:09.640)
they are pretty convinced
Leonard Susskind (20:12.440)
that the brain functions classically,
Lex Fridman (20:16.740)
that it is not intrinsically a quantum mechanical system
Leonard Susskind (20:20.600)
or it doesn't make use of the special features,
Lex Fridman (20:23.640)
entanglement, coherence, superposition.
Lex Fridman (20:26.460)
Are they right?
Lex Fridman (20:27.380)
I don't know.
Leonard Susskind (20:28.960)
I sort of hope they're wrong
Lex Fridman (20:30.340)
just because I like the romantic idea
Leonard Susskind (20:32.900)
that the brain is a quantum system.
Lex Fridman (20:35.180)
But I think probably not.
Leonard Susskind (20:38.680)
The other thing,
Lex Fridman (20:40.100)
big systems can be composed of lots of little systems.
Leonard Susskind (20:44.180)
Materials, the materials that we work with and so forth
Lex Fridman (20:47.700)
are, can be large systems, a large piece of material,
Lex Fridman (20:52.880)
but they're made out of quantum systems.
Lex Fridman (20:55.140)
Now, one of the things that's been happening
Leonard Susskind (20:57.180)
over the last good number of years
Lex Fridman (21:00.580)
is we're discovering materials and quantum systems,
Leonard Susskind (21:04.720)
which function much more quantum mechanically
Lex Fridman (21:08.220)
than we imagined.
Leonard Susskind (21:09.640)
Topological insulators, this kind of thing,
Lex Fridman (21:12.020)
that kind of thing.
Leonard Susskind (21:13.500)
Those are macroscopic systems,
Lex Fridman (21:15.220)
but they're just superconductors.
Leonard Susskind (21:17.860)
Superconductors have a lot of quantum mechanics in them.
Lex Fridman (21:22.900)
You can have a large chunk of superconductor.
Lex Fridman (21:25.040)
So it's a big piece of material.
Lex Fridman (21:26.780)
On the other hand, it's functioning and its properties
Leonard Susskind (21:29.640)
depend very, very strongly on quantum mechanics.
Lex Fridman (21:32.840)
And to analyze them, you need the tools of quantum mechanics.
Leonard Susskind (21:37.380)
If we can go on to black holes
Lex Fridman (21:41.100)
and looking at the universe
Leonard Susskind (21:42.940)
as a information processing system,
Lex Fridman (21:45.140)
as a computer, as a giant computer.
Leonard Susskind (21:46.740)
It's a giant computer.
Lex Fridman (21:48.560)
What's the power of thinking of the universe
Lex Fridman (21:50.900)
as an information processing system?
Lex Fridman (21:52.340)
Or what is perhaps its use
Leonard Susskind (21:55.160)
besides the mathematical use of discussing black holes
Lex Fridman (21:59.740)
and your famous debates and ideas around that
Leonard Susskind (22:02.820)
to human beings,
Lex Fridman (22:06.080)
or life in general as information processing systems?
Leonard Susskind (22:08.800)
Well, all systems are information processing systems.
Lex Fridman (22:13.300)
You poke them, they change a little bit, they evolve.
Leonard Susskind (22:16.740)
All systems are information processing systems.
Lex Fridman (22:18.340)
So there's no extra magic to us humans?
Leonard Susskind (22:22.660)
It certainly feels, consciousness intelligence
Lex Fridman (22:25.020)
feels like magic.
Leonard Susskind (22:26.060)
It sure does.
Lex Fridman (22:26.900)
Where does it emerge from?
Leonard Susskind (22:29.340)
If we look at information processing,
Lex Fridman (22:33.620)
what are the emergent phenomena
Leonard Susskind (22:35.100)
that come from viewing the world
Lex Fridman (22:37.500)
as an information processing system?
Leonard Susskind (22:39.880)
Here is what I think.
Lex Fridman (22:41.940)
My thoughts are not worth much in this.
Leonard Susskind (22:43.540)
If you ask me about physics,
Lex Fridman (22:44.620)
my thoughts may be worth something.
Leonard Susskind (22:46.660)
If you ask me about this,
Lex Fridman (22:48.060)
I'm not sure my thoughts are worth anything.
Lex Fridman (22:50.880)
But as I said earlier,
Lex Fridman (22:53.280)
I think when we do introspection,
Leonard Susskind (22:55.780)
when we imagine doing introspection
Lex Fridman (22:57.500)
and try to figure out what it is
Leonard Susskind (22:58.980)
when we do when we're thinking,
Lex Fridman (23:00.540)
I think we get it wrong.
Leonard Susskind (23:03.500)
I'm pretty sure we get it wrong.
Lex Fridman (23:04.840)
Everything I've heard about the way the brain functions
Leonard Susskind (23:07.260)
is so counterintuitive.
Lex Fridman (23:09.740)
For example, you have neurons which detect vertical lines.
Leonard Susskind (23:14.380)
You have different neurons
Lex Fridman (23:15.620)
which detect lines at 45 degrees.
Leonard Susskind (23:17.880)
You have different neurons.
Lex Fridman (23:19.420)
I never imagined that there were whole circuits
Leonard Susskind (23:21.800)
which were devoted to vertical lines in my brain.
Lex Fridman (23:25.380)
Doesn't seem to be the way my brain works.
Leonard Susskind (23:28.100)
My brain seems to work if I put my finger up vertically
Lex Fridman (23:31.140)
or if I put it horizontally
Leonard Susskind (23:32.220)
or if I put it this way or that way.
Lex Fridman (23:33.380)
It seems to me it's the same circuits.
Leonard Susskind (23:36.220)
It's not the way it works.
Lex Fridman (23:38.860)
The way the brain is compartmentalized
Leonard Susskind (23:41.460)
seems to be very, very different
Lex Fridman (23:43.660)
than what I would have imagined
Leonard Susskind (23:45.580)
if I were just doing psychological introspection
Lex Fridman (23:49.660)
about how things work.
Leonard Susskind (23:51.940)
My conclusion is that we won't get it right that way,
Lex Fridman (23:55.920)
that how will we get it right?
Leonard Susskind (23:59.640)
I think maybe computer scientists will get it right eventually.
Lex Fridman (24:03.220)
I don't think there are any ways near it.
Leonard Susskind (24:04.420)
I don't even think they're thinking about it,
Lex Fridman (24:06.680)
but eventually we will build machines perhaps
Leonard Susskind (24:11.440)
which are complicated enough
Lex Fridman (24:15.040)
and partly engineered, partly evolved,
Leonard Susskind (24:18.340)
maybe evolved by machine learning and so forth.
Lex Fridman (24:21.060)
This machine learning is very interesting.
Leonard Susskind (24:23.500)
By machine learning, we will evolve systems
Lex Fridman (24:26.020)
and we may start to discover mechanisms
Leonard Susskind (24:30.320)
that have implications for how we think
Lex Fridman (24:35.340)
and for what this consciousness thing is all about
Lex Fridman (24:39.500)
and we'll be able to do experiments on them
Lex Fridman (24:42.060)
and perhaps answer questions
Leonard Susskind (24:43.700)
that we can't possibly answer by introspection.
Lex Fridman (24:49.660)
So that's a really interesting point.
Leonard Susskind (24:51.700)
In many cases, if you look at even a string theory,
Lex Fridman (24:55.240)
when you first think about a system,
Leonard Susskind (24:56.780)
it seems really complicated, like the human brain,
Lex Fridman (24:59.620)
and through some basic reasoning
Lex Fridman (25:02.460)
and trying to discover fundamental low level behavior
Lex Fridman (25:07.060)
of the system, you find out that it's actually much simpler.
Lex Fridman (25:10.140)
Do you, one, have you, is that generally the process
Lex Fridman (25:13.580)
and two, do you have that also hope
Leonard Susskind (25:15.580)
for biological systems as well,
Lex Fridman (25:17.920)
for all the kinds of stuff we're studying at the human level?
Leonard Susskind (25:21.740)
Of course, physics always begins
Lex Fridman (25:23.080)
by trying to find the simplest version of something
Lex Fridman (25:25.500)
and analyze it.
Lex Fridman (25:26.560)
Yeah, I mean, there are lots of examples
Leonard Susskind (25:28.420)
where physics has taken very complicated systems,
Lex Fridman (25:33.360)
analyzed them and found simplicity in them for sure.
Leonard Susskind (25:36.980)
I said superconductors before, it's an obvious one.
Lex Fridman (25:39.900)
A superconductor seems like a monstrously complicated thing
Leonard Susskind (25:42.520)
with all sorts of crazy electrical properties,
Lex Fridman (25:45.980)
magnetic properties and so forth.
Lex Fridman (25:48.380)
And when it finally is boiled down
Lex Fridman (25:50.460)
to its simplest elements,
Leonard Susskind (25:52.940)
it's a very simple quantum mechanical phenomenon
Lex Fridman (25:56.100)
called spontaneous symmetry breaking,
Lex Fridman (25:59.260)
and which we, in other contexts, we learned about
Lex Fridman (26:04.820)
and we're very familiar with.
Lex Fridman (26:06.760)
So yeah, I mean, yes, we do take complicated things,
Lex Fridman (26:10.540)
make them simple, but what we don't want to do
Leonard Susskind (26:13.740)
is take things which are intrinsically complicated
Lex Fridman (26:16.540)
and fool ourselves into thinking
Leonard Susskind (26:18.420)
that we can make them simple.
Lex Fridman (26:20.640)
We don't want to make, I don't know who said this,
Lex Fridman (26:22.380)
but we don't want to make them simpler
Lex Fridman (26:23.660)
than they really are, okay?
Leonard Susskind (26:26.740)
Is the brain a thing which ultimately functions
Lex Fridman (26:30.820)
by some simple rules or is it just complicated?
Leonard Susskind (26:35.580)
In terms of artificial intelligence,
Lex Fridman (26:37.780)
nobody really knows what are the limits
Leonard Susskind (26:40.840)
of our current approaches, you mentioned machine learning.
Lex Fridman (26:43.020)
How do we create human level intelligence?
Leonard Susskind (26:44.840)
It seems that there's a lot of very smart physicists
Lex Fridman (26:48.220)
who perhaps oversimplify the nature of intelligence
Lex Fridman (26:51.260)
and think of it as information processing,
Lex Fridman (26:53.660)
and therefore there doesn't seem to be
Leonard Susskind (26:55.180)
any theoretical reason why we can't artificially create
Lex Fridman (27:00.820)
human level or superhuman level intelligence.
Leonard Susskind (27:02.980)
In fact, the reasoning goes,
Lex Fridman (27:04.540)
if you create human level intelligence,
Leonard Susskind (27:07.300)
the same approach you just used
Lex Fridman (27:08.660)
to create human level intelligence
Leonard Susskind (27:10.440)
should allow you to create superhuman level intelligence
Lex Fridman (27:13.740)
very easily, exponentially.
Lex Fridman (27:16.000)
So what do you think that way of thinking
Lex Fridman (27:18.960)
that comes from physicists is all about?
Leonard Susskind (27:22.260)
I wish I knew, but there's a particular reason
Lex Fridman (27:24.180)
why I wish I knew.
Leonard Susskind (27:27.420)
I have a second job.
Lex Fridman (27:30.420)
I consult for Google, not for Google, for Google X.
Leonard Susskind (27:34.860)
I am the senior academic advisor
Lex Fridman (27:39.060)
to a group of machine learning physicists.
Leonard Susskind (27:43.740)
Now that sounds crazy because I know nothing
Lex Fridman (27:45.700)
about the subject.
Leonard Susskind (27:47.780)
I know very little about the subject.
Lex Fridman (27:49.980)
On the other hand, I'm good at giving advice,
Lex Fridman (27:52.180)
so I give them advice on things.
Lex Fridman (27:53.660)
Anyway, I see these young physicists
Leonard Susskind (27:56.300)
who are approaching the machine learning problem.
Lex Fridman (27:58.660)
There is a real machine learning problem.
Lex Fridman (28:00.900)
Namely, why does it work as well as it does?
Lex Fridman (28:03.060)
Nobody really seems to understand
Lex Fridman (28:06.300)
why it is capable of doing the kind of generalizations
Lex Fridman (28:09.460)
that it does and so forth.
Lex Fridman (28:11.640)
And there are three groups of people
Lex Fridman (28:14.980)
who have thought about this.
Leonard Susskind (28:17.460)
There are the engineers.
Lex Fridman (28:19.060)
The engineers are incredibly smart,
Lex Fridman (28:21.580)
but they tend not to think as hard
Lex Fridman (28:23.800)
about why the thing is working
Leonard Susskind (28:26.080)
as much as they do how to use it.
Lex Fridman (28:28.220)
Obviously, they provided a lot of data,
Lex Fridman (28:31.820)
and it is they who demonstrated
Lex Fridman (28:34.060)
that machine learning can work much better
Leonard Susskind (28:35.820)
than you have any right to expect.
Lex Fridman (28:37.380)
The machine learning systems are systems.
Leonard Susskind (28:40.180)
The system's not too different
Lex Fridman (28:41.940)
than the kind of systems that physicists study.
Leonard Susskind (28:44.900)
There's not all that much difference
Lex Fridman (28:46.740)
between quantum, in the structure of mathematics,
Leonard Susskind (28:51.540)
physically, yes, but in the structure of mathematics,
Lex Fridman (28:54.480)
between a tensor network designed
Leonard Susskind (28:57.660)
to describe a quantum system on the one hand
Lex Fridman (29:01.420)
and the kind of networks that are used in machine learning.
Lex Fridman (29:05.100)
So there are more and more, I think,
Lex Fridman (29:08.940)
young physicists are being drawn
Leonard Susskind (29:10.940)
to this field of machine learning,
Lex Fridman (29:12.820)
some very, very good ones.
Leonard Susskind (29:15.100)
I work with a number of very good ones,
Lex Fridman (29:16.820)
not on machine learning, but on having lunch.
Lex Fridman (29:20.380)
On having lunch?
Lex Fridman (29:21.300)
Right.
Leonard Susskind (29:22.460)
Yeah.
Lex Fridman (29:23.860)
And I can tell you they are super smart.
Leonard Susskind (29:27.620)
They don't seem to be so arrogant
Lex Fridman (29:30.540)
about their physics backgrounds
Leonard Susskind (29:32.020)
that they think they can do things that nobody else can do.
Lex Fridman (29:35.100)
But the physics way of thinking, I think,
Leonard Susskind (29:37.460)
will add great value to,
Lex Fridman (29:41.780)
or will bring value to the machine learning.
Leonard Susskind (29:43.980)
I believe it will.
Lex Fridman (29:45.740)
And I think it already has.
Leonard Susskind (29:47.980)
At what time scale do you think
Lex Fridman (29:50.500)
predicting the future becomes useless
Leonard Susskind (29:53.180)
in your long experience
Lex Fridman (29:55.340)
and being surprised at new discoveries?
Leonard Susskind (29:57.680)
Well, sometimes a day, sometimes 20 years.
Lex Fridman (30:03.480)
There are things which I thought
Leonard Susskind (30:07.040)
we were very far from understanding,
Lex Fridman (30:09.840)
which practically in a snap of the fingers
Leonard Susskind (30:12.420)
or a blink of the eye suddenly became understood,
Lex Fridman (30:17.440)
completely surprising to me.
Leonard Susskind (30:21.220)
There are other things which I looked at and I said,
Lex Fridman (30:24.120)
we're not gonna understand these things for 500 years,
Leonard Susskind (30:27.320)
in particular quantum gravity.
Lex Fridman (30:29.280)
The scale for that was 20 years, 25 years.
Lex Fridman (30:32.840)
And we understand a lot
Lex Fridman (30:33.800)
and we don't understand it completely now by any means,
Lex Fridman (30:35.920)
but I thought it was 500 years to make any progress.
Lex Fridman (30:40.780)
It turned out to be very, very far from that.
Leonard Susskind (30:42.960)
It turned out to be more like 20 or 25 years
Lex Fridman (30:45.200)
from the time when I thought it was 500 years.
Lex Fridman (30:48.400)
So if we may, can we jump around quantum gravity,
Lex Fridman (30:51.940)
some basic ideas in physics?
Lex Fridman (30:53.720)
What is the dream of string theory mathematically?
Lex Fridman (30:59.280)
What is the hope?
Lex Fridman (31:00.120)
Where does it come from?
Lex Fridman (31:01.440)
What problem is it trying to solve?
Leonard Susskind (31:03.560)
I don't think the dream of string theory
Lex Fridman (31:05.000)
is any different than the dream
Leonard Susskind (31:06.540)
of fundamental theoretical physics altogether.
Lex Fridman (31:09.560)
Understanding a unified theory of everything.
Leonard Susskind (31:12.680)
I don't like thinking of string theory
Lex Fridman (31:15.040)
as a subject unto itself
Leonard Susskind (31:17.320)
with people called string theorists
Lex Fridman (31:19.440)
who are the practitioners
Leonard Susskind (31:21.560)
of this thing called string theory.
Lex Fridman (31:24.120)
I much prefer to think of them as theoretical physicists
Leonard Susskind (31:28.160)
trying to answer deep fundamental questions about nature,
Lex Fridman (31:32.060)
in particular gravity,
Leonard Susskind (31:33.400)
in particular gravity and its connection
Lex Fridman (31:35.040)
with quantum mechanics,
Lex Fridman (31:38.040)
and who at the present time find string theory
Lex Fridman (31:41.320)
a useful tool rather than saying
Leonard Susskind (31:44.520)
there's a subject called string theorists.
Lex Fridman (31:46.440)
I don't like being referred to as a string theorist.
Leonard Susskind (31:48.680)
Yes, but as a tool, is it useful to think about our nature
Lex Fridman (31:54.080)
in multiple dimensions, the strings vibrating?
Leonard Susskind (31:57.500)
I believe it is useful.
Lex Fridman (31:59.040)
I'll tell you what the main use of it has been up till now.
Leonard Susskind (32:02.120)
Well, it has had a number of main uses.
Lex Fridman (32:03.920)
Originally, string theory was invented,
Lex Fridman (32:06.360)
and I know that I was there.
Lex Fridman (32:07.520)
I was right at the spot
Leonard Susskind (32:08.960)
where it was being invented literally,
Lex Fridman (32:13.080)
and it was being invented to understand hadrons.
Leonard Susskind (32:16.960)
Hadrons are subnuclear particles,
Lex Fridman (32:19.120)
protons, neutrons, mesons,
Lex Fridman (32:21.960)
and at that time, the late 60s, early 70s,
Lex Fridman (32:28.580)
it was clear from experiment
Leonard Susskind (32:30.120)
that these particles called hadrons could vibrate,
Lex Fridman (32:33.680)
could rotate, could do all the things
Leonard Susskind (32:36.800)
that a little closed string can do,
Lex Fridman (32:39.640)
and it was and is a valid and correct theory of these hadrons.
Leonard Susskind (32:47.920)
It's been experimentally tested, and that is a done deal.
Lex Fridman (32:53.940)
It had a second life as a theory of gravity,
Leonard Susskind (32:56.240)
the same basic mathematics,
Lex Fridman (32:58.100)
except on a very, very much smaller distance scale.
Leonard Susskind (33:02.360)
The objects of gravitation are 19 orders of magnitude
Lex Fridman (33:07.360)
or orders of magnitude smaller than a proton,
Lex Fridman (33:10.080)
but the same mathematics turned up.
Lex Fridman (33:12.000)
The same mathematics turned up.
Lex Fridman (33:14.300)
What has been its value?
Lex Fridman (33:15.980)
Its value is that it's mathematically rigorous in many ways
Lex Fridman (33:20.720)
and enabled us to find mathematical structures
Lex Fridman (33:27.040)
which have both quantum mechanics and gravity.
Leonard Susskind (33:30.120)
With rigor, we can test out ideas.
Lex Fridman (33:34.080)
We can test out ideas.
Leonard Susskind (33:35.160)
We can't test them in the laboratory.
Lex Fridman (33:37.240)
They're 19 orders of magnitude too small
Leonard Susskind (33:39.840)
are things that we're interested in,
Lex Fridman (33:41.280)
but we can test them out mathematically
Lex Fridman (33:43.160)
and analyze their internal consistency.
Lex Fridman (33:47.800)
By now, 40 years ago, 35 years ago, and so forth,
Leonard Susskind (33:53.720)
people very, very much questioned the consistency
Lex Fridman (33:57.120)
between gravity and quantum mechanics.
Leonard Susskind (33:59.240)
Stephen Hawking was very famous for it, rightly so.
Lex Fridman (34:02.840)
Now, nobody questions that consistency anymore.
Leonard Susskind (34:05.840)
They don't because we have mathematically precise
Lex Fridman (34:09.240)
string theories which contain both gravity
Lex Fridman (34:12.680)
and quantum mechanics in a consistent way.
Lex Fridman (34:15.760)
So it's provided that certainty that quantum mechanics
Lex Fridman (34:21.280)
and gravity can coexist.
Lex Fridman (34:22.840)
That's not a small thing.
Leonard Susskind (34:24.160)
It's a very big thing.
Lex Fridman (34:25.000)
It's a huge thing.
Leonard Susskind (34:25.840)
Einstein would be proud.
Lex Fridman (34:27.240)
Einstein, he might be appalled.
Leonard Susskind (34:28.800)
I don't know.
Lex Fridman (34:29.640)
He didn't like it.
Leonard Susskind (34:30.460)
He didn't like it.
Lex Fridman (34:31.300)
He might not be appalled, I don't know.
Leonard Susskind (34:32.920)
He didn't like quantum mechanics very much,
Lex Fridman (34:34.560)
but he would certainly be struck by it.
Leonard Susskind (34:37.680)
I think that may be, at this time,
Lex Fridman (34:40.060)
its biggest contribution to physics
Leonard Susskind (34:42.000)
in illustrating almost definitively
Lex Fridman (34:45.360)
that quantum mechanics and gravity
Leonard Susskind (34:46.800)
are very closely related
Lex Fridman (34:48.640)
and not inconsistent with each other.
Leonard Susskind (34:51.000)
Is there a possibility of something deeper,
Lex Fridman (34:53.840)
more profound that still is consistent with string theory
Lex Fridman (34:58.840)
but is deeper, that is to be found?
Lex Fridman (35:03.120)
Well, you could ask the same thing about quantum mechanics.
Lex Fridman (35:04.900)
Is there something?
Lex Fridman (35:05.740)
Exactly.
Leonard Susskind (35:06.560)
Yeah, yeah.
Lex Fridman (35:07.400)
I think string theory is just an example
Leonard Susskind (35:09.060)
of a quantum mechanical system
Lex Fridman (35:11.000)
that contains both gravitation and quantum mechanics.
Lex Fridman (35:16.600)
So is there something underlying quantum mechanics?
Lex Fridman (35:19.760)
Perhaps something deterministic.
Leonard Susskind (35:21.560)
Perhaps something deterministic.
Lex Fridman (35:23.920)
My friend, Ferad Etouf, whose name you may know,
Leonard Susskind (35:27.360)
he's a very famous physicist.
Lex Fridman (35:29.600)
Dutch, not as famous as he should be, but...
Leonard Susskind (35:33.820)
Hard to spell his name.
Lex Fridman (35:35.160)
It's hard to say his name.
Leonard Susskind (35:36.280)
No, it's easy to spell his name.
Lex Fridman (35:37.520)
Apostrophe, he's the only person I know
Leonard Susskind (35:39.240)
whose name begins with an apostrophe.
Lex Fridman (35:42.040)
And he's one of my heroes in physics.
Leonard Susskind (35:44.280)
He's a little younger than me,
Lex Fridman (35:45.160)
but he's nevertheless one of my heroes.
Leonard Susskind (35:47.640)
Etouf believes that there is some substructure to the world
Lex Fridman (35:52.640)
which is classical in character,
Leonard Susskind (35:55.640)
deterministic in character,
Lex Fridman (35:58.040)
which somehow by some mechanism
Leonard Susskind (36:00.520)
that he has a hard time spelling out
Lex Fridman (36:03.840)
emerges as quantum mechanics.
Leonard Susskind (36:07.400)
I don't.
Lex Fridman (36:08.240)
The wave function is somehow emergent.
Leonard Susskind (36:10.680)
The wave function, not just the wave function,
Lex Fridman (36:13.080)
but the whole thing that goes with quantum mechanics,
Leonard Susskind (36:16.760)
uncertainty, entanglement, all these things,
Lex Fridman (36:19.760)
are emergent. So you think quantum mechanics
Lex Fridman (36:22.680)
is the bottom of the well?
Lex Fridman (36:23.800)
Is the...
Leonard Susskind (36:25.600)
Here I think is where you have to be humble.
Lex Fridman (36:30.120)
Here's where humility comes.
Leonard Susskind (36:31.440)
I don't think anybody should say anything
Lex Fridman (36:33.440)
is the bottom of the well at this time.
Leonard Susskind (36:36.360)
I think we can reasonably say,
Lex Fridman (36:40.960)
I can reasonably say when I look into the well,
Leonard Susskind (36:44.200)
I can't see past quantum mechanics.
Lex Fridman (36:47.240)
I can't see past quantum mechanics.
Leonard Susskind (36:50.480)
I don't see any reason for there to be anything
Lex Fridman (36:52.800)
beyond quantum mechanics.
Leonard Susskind (36:55.040)
I think Etouf has asked very interesting
Lex Fridman (36:58.200)
and deep questions.
Leonard Susskind (36:59.240)
I don't like his answers.
Lex Fridman (37:01.960)
Well, again, let me ask,
Leonard Susskind (37:03.720)
if we look at the deepest nature of reality
Lex Fridman (37:06.560)
with whether it's deterministic
Leonard Susskind (37:09.320)
or when observed as probabilistic,
Lex Fridman (37:13.080)
what does that mean for our human level
Lex Fridman (37:16.960)
of ideas of free will?
Lex Fridman (37:18.320)
Is there any connection whatsoever
Leonard Susskind (37:21.560)
from this perception, perhaps illusion of free will
Lex Fridman (37:24.700)
that we have and the fundamental nature of reality?
Leonard Susskind (37:27.760)
The only thing I can say is I am puzzled by that
Lex Fridman (37:31.400)
as much as you are.
Leonard Susskind (37:32.680)
The illusion of it.
Lex Fridman (37:33.520)
The illusion of consciousness,
Leonard Susskind (37:36.080)
the illusion of free will, the illusion of self.
Lex Fridman (37:39.980)
Does that connect to?
Lex Fridman (37:43.380)
How can a physical system do that?
Lex Fridman (37:45.380)
And I am as puzzled as anybody.
Leonard Susskind (37:48.820)
There's echoes of it in the observer effect.
Lex Fridman (37:51.980)
So do you understand what it means to be an observer?
Leonard Susskind (37:55.340)
I understand it at a technical level.
Lex Fridman (37:57.700)
An observer is a system with enough degrees of freedom
Leonard Susskind (38:00.480)
that it can record information
Lex Fridman (38:02.280)
and which can become entangled
Leonard Susskind (38:03.980)
with the thing that it's measuring.
Lex Fridman (38:05.740)
Entanglement is the key.
Leonard Susskind (38:07.300)
When a system which we call an apparatus or an observer,
Lex Fridman (38:12.020)
same thing, interacts with the system
Leonard Susskind (38:15.180)
that it's observing, it doesn't just look at it.
Lex Fridman (38:19.100)
It becomes physically entangled with it.
Lex Fridman (38:21.540)
And it's that entanglement which we call an observation
Lex Fridman (38:24.460)
or a measurement.
Lex Fridman (38:26.480)
Now, does that satisfy me personally as an observer?
Lex Fridman (38:32.520)
Yes and no.
Leonard Susskind (38:33.360)
I find it very satisfying
Lex Fridman (38:34.300)
that we have a mathematical representation
Leonard Susskind (38:36.680)
of what it means to observe a system.
Lex Fridman (38:40.340)
You are observing stuff right now, the conscious level.
Lex Fridman (38:44.300)
Do you think there's echoes of that kind of entanglement
Lex Fridman (38:48.100)
in our macro scale?
Leonard Susskind (38:49.420)
Yes, absolutely, for sure.
Lex Fridman (38:52.200)
We're entangled with,
Leonard Susskind (38:53.780)
quantum mechanically entangled with everything in this room.
Lex Fridman (38:56.740)
If we weren't, then it would just,
Leonard Susskind (38:59.860)
well, we wouldn't be observing it.
Lex Fridman (39:03.140)
But on the other hand, you can ask,
Lex Fridman (39:05.620)
do I really, am I really comfortable with it?
Lex Fridman (39:10.260)
And I'm uncomfortable with it in the same way
Leonard Susskind (39:12.540)
that I can never get comfortable with five dimensions.
Lex Fridman (39:15.300)
My brain isn't wired for it.
Lex Fridman (39:18.860)
Are you comfortable with four dimensions?
Lex Fridman (39:21.380)
A little bit more,
Leonard Susskind (39:22.620)
because I can always imagine the fourth dimension is time.
Lex Fridman (39:26.340)
So the arrow of time, are you comfortable with that arrow?
Lex Fridman (39:29.980)
Do you think time is an emergent phenomena
Lex Fridman (39:31.980)
or is it fundamental to nature?
Leonard Susskind (39:33.680)
That is a big question in physics right now.
Lex Fridman (39:37.560)
All the physics that we do,
Leonard Susskind (39:40.160)
or at least that the people that I am comfortable
Lex Fridman (39:42.800)
with talking to, my friends, my friends.
Leonard Susskind (39:49.400)
No, we all ask the same question that you just asked.
Lex Fridman (39:51.880)
Space, we have a pretty good idea is emergent
Lex Fridman (39:55.240)
and it emerges out of entanglement and other things.
Lex Fridman (40:00.240)
Time always seems to be built into our equations
Leonard Susskind (40:03.920)
as just what Newton pretty much would have thought.
Lex Fridman (40:06.680)
Newton, modified a little bit by Einstein,
Leonard Susskind (40:09.140)
would have called time.
Lex Fridman (40:12.000)
And mostly in our equations, it is not emergent.
Leonard Susskind (40:19.200)
Time in physics is completely symmetric,
Lex Fridman (40:21.560)
forward and backward.
Leonard Susskind (40:22.400)
Right, it's symmetric.
Lex Fridman (40:23.400)
So you don't really need to think about the arrow of time
Leonard Susskind (40:27.300)
for most physical phenomena.
Lex Fridman (40:29.240)
For most microscopic phenomena, no.
Leonard Susskind (40:33.400)
It's only when the phenomena involve systems
Lex Fridman (40:35.640)
which are big enough for thermodynamics to become important,
Leonard Susskind (40:38.960)
for entropy to become important.
Lex Fridman (40:41.680)
For a small system, entropy is not a good concept.
Leonard Susskind (40:47.960)
Entropy is something which emerges out of large numbers.
Lex Fridman (40:52.840)
It's a probabilistic idea or it's a statistical idea
Lex Fridman (40:56.600)
and it's a thermodynamic idea.
Lex Fridman (40:58.500)
Thermodynamics requires lots and lots
Lex Fridman (41:00.840)
and lots of little substructures, okay?
Lex Fridman (41:04.120)
So it's not until you emerge at the thermodynamic level
Leonard Susskind (41:09.680)
that there's an arrow of time.
Lex Fridman (41:11.720)
Do we understand it?
Leonard Susskind (41:13.560)
Yeah, I think we understand better
Lex Fridman (41:15.800)
than most people think they have.
Leonard Susskind (41:17.160)
Most people say they think we understand it.
Lex Fridman (41:19.360)
Yeah, I think we understand it.
Leonard Susskind (41:21.280)
It's a statistical idea.
Lex Fridman (41:23.900)
You mean like second law of thermodynamics,
Lex Fridman (41:26.400)
entropy and so on?
Lex Fridman (41:27.240)
Yeah, take a pack of cards and you fling it in the air
Lex Fridman (41:29.720)
and you look what happens to it, it gets random.
Lex Fridman (41:32.480)
We understand it.
Leonard Susskind (41:33.400)
It doesn't go from random to simple.
Lex Fridman (41:36.200)
It goes from simple to random.
Lex Fridman (41:38.600)
But do you think it ever breaks down?
Lex Fridman (41:41.820)
What I think you can do is in a laboratory setting,
Leonard Susskind (41:46.180)
you can take a system which is somewhere intermediate
Lex Fridman (41:49.020)
between being small and being large
Lex Fridman (41:53.080)
and make it go backward.
Lex Fridman (41:56.080)
A thing which looks like it only wants to go forward
Leonard Susskind (41:59.560)
because of statistical mechanical reasons,
Lex Fridman (42:01.640)
because of the second law,
Leonard Susskind (42:03.920)
you can very, very carefully manipulate it
Lex Fridman (42:07.120)
to make it run backward.
Leonard Susskind (42:09.100)
I don't think you can take an egg, a Humpty Dumpty
Lex Fridman (42:11.400)
who fell on the floor and reverse that.
Lex Fridman (42:15.000)
But you can, in a very controlled situation,
Lex Fridman (42:18.480)
you can take systems which appear to be evolving
Leonard Susskind (42:22.760)
statistically toward randomness,
Lex Fridman (42:25.360)
stop them, reverse them, and make them go back.
Lex Fridman (42:29.280)
What's the intuition behind that?
Lex Fridman (42:30.800)
How do we do that?
Lex Fridman (42:31.940)
How do we reverse it?
Lex Fridman (42:33.520)
You're saying a closed system.
Leonard Susskind (42:35.600)
Yeah, pretty much closed system, yes.
Lex Fridman (42:38.320)
Did you just say that time travel is possible?
Leonard Susskind (42:41.600)
No, I didn't say time travel is possible.
Lex Fridman (42:44.080)
I said you can make a system go backward.
Leonard Susskind (42:45.960)
In time.
Lex Fridman (42:46.800)
You can make it go back.
Leonard Susskind (42:48.040)
You can make it reverse its steps.
Lex Fridman (42:49.520)
You can make it reverse its trajectory.
Leonard Susskind (42:51.520)
Yeah.
Lex Fridman (42:52.400)
How do we do it?
Lex Fridman (42:53.240)
What's the intuition there?
Lex Fridman (42:54.640)
Does it have, is it just a fluke thing
Leonard Susskind (42:58.720)
that we can do at a small scale in the lab
Lex Fridman (43:00.840)
that doesn't have?
Leonard Susskind (43:01.680)
Well, what I'm saying is you can do it
Lex Fridman (43:02.840)
a little bit better than a small scale.
Leonard Susskind (43:05.260)
You can certainly do it with a simple, small system.
Lex Fridman (43:10.480)
Small systems don't have any sense of the arrow of time.
Leonard Susskind (43:14.240)
Atoms, atoms are no sense of an arrow of time.
Lex Fridman (43:20.580)
They're completely reversible.
Leonard Susskind (43:22.380)
It's only when you have, you know,
Lex Fridman (43:24.440)
the second law of thermodynamics
Leonard Susskind (43:25.880)
is the law of large numbers.
Lex Fridman (43:28.480)
So you can break the law because it's not
Leonard Susskind (43:30.800)
a deterministic law. You can break it,
Lex Fridman (43:31.640)
you can break it, but it's hard.
Leonard Susskind (43:33.880)
It requires great care.
Lex Fridman (43:36.080)
The bigger the system is, the more care,
Leonard Susskind (43:38.480)
the more, the harder it is.
Lex Fridman (43:40.760)
You have to overcome what's called chaos.
Lex Fridman (43:43.880)
And that's hard.
Lex Fridman (43:45.600)
And it requires more and more precision.
Leonard Susskind (43:47.660)
For 10 particles, you might be able to do it
Lex Fridman (43:50.080)
with some effort.
Leonard Susskind (43:54.000)
For a hundred particles, it's really hard.
Lex Fridman (43:56.760)
For a thousand or a million particles, forget it,
Lex Fridman (43:59.340)
but not for any fundamental reason,
Lex Fridman (44:01.220)
just because it's technologically too hard
Leonard Susskind (44:03.720)
to make the system go backward.
Lex Fridman (44:08.320)
So, no time travel for engineering reasons.
Leonard Susskind (44:13.440)
Oh, no, no, no, no.
Lex Fridman (44:15.280)
What is time travel?
Lex Fridman (44:16.880)
Time travel to the future?
Lex Fridman (44:19.280)
That's easy.
Leonard Susskind (44:20.400)
You just close your eyes, go to sleep,
Lex Fridman (44:22.400)
and you wake up in the future.
Leonard Susskind (44:23.480)
Yeah, yeah, a good nap gets you there, yeah.
Lex Fridman (44:25.960)
A good nap gets you there, right.
Lex Fridman (44:27.400)
But reversing the second law of thermodynamics,
Lex Fridman (44:32.280)
going backward in time for anything that's human scale
Leonard Susskind (44:36.760)
is a very difficult engineering effort.
Lex Fridman (44:40.000)
I wouldn't call that time travel
Leonard Susskind (44:41.440)
because it gets too mixed up
Lex Fridman (44:43.040)
with what science fiction calls time travel.
Leonard Susskind (44:46.040)
This is just the ability to reverse a system.
Lex Fridman (44:51.040)
You take the system and you reverse the direction
Leonard Susskind (44:55.680)
of motion of every molecule in it.
Lex Fridman (44:58.280)
That, you can do it with one molecule.
Leonard Susskind (45:00.940)
If you find a particle moving in a certain direction,
Lex Fridman (45:03.500)
let's not say a particle, a baseball,
Leonard Susskind (45:06.700)
you stop it dead and then you simply reverse its motion.
Lex Fridman (45:10.960)
In principle, that's not too hard.
Lex Fridman (45:12.840)
And it'll go back along its trajectory
Lex Fridman (45:15.240)
in the backward direction.
Leonard Susskind (45:16.440)
Just running the program backwards.
Lex Fridman (45:18.200)
Running the program backward.
Leonard Susskind (45:19.480)
Yeah. Okay.
Lex Fridman (45:20.460)
If you have two baseballs colliding,
Leonard Susskind (45:22.400)
well, you can do it,
Lex Fridman (45:23.520)
but you have to be very, very careful to get it just right.
Leonard Susskind (45:28.760)
If you have 10 baseballs, really, really, better yet,
Lex Fridman (45:32.400)
10 billiard balls on an idealized,
Leonard Susskind (45:36.200)
frictionless billiard table.
Lex Fridman (45:38.840)
Okay, so you start the balls all on a triangle, right?
Lex Fridman (45:41.800)
And you whack them.
Lex Fridman (45:43.440)
Depending on the game you're playing,
Leonard Susskind (45:44.640)
you either whack them or you're really careful,
Lex Fridman (45:46.000)
but you whack them.
Lex Fridman (45:48.280)
And they go flying off in all possible directions.
Lex Fridman (45:51.520)
Okay, try to reverse that.
Leonard Susskind (45:54.720)
Try to reverse that.
Lex Fridman (45:55.680)
Imagine trying to take every billiard ball,
Leonard Susskind (45:57.680)
stopping it dead at some point,
Lex Fridman (46:00.320)
and reversing its motion
Lex Fridman (46:01.680)
so that it was going in the opposite direction.
Lex Fridman (46:04.200)
If you did that with tremendous care,
Leonard Susskind (46:07.340)
it would reassemble itself back into the triangle.
Lex Fridman (46:11.500)
Okay, that is a fact.
Lex Fridman (46:14.520)
And you can probably do it with two billiard balls,
Lex Fridman (46:16.860)
maybe with three billiard balls if you're really lucky.
Lex Fridman (46:19.920)
But what happens is as the system
Lex Fridman (46:21.840)
gets more and more complicated,
Leonard Susskind (46:23.160)
you have to be more and more precise
Lex Fridman (46:26.120)
not to make the tiniest error,
Leonard Susskind (46:27.880)
because the tiniest errors will get magnified
Lex Fridman (46:30.960)
and you'll simply not be able to do the reversal.
Lex Fridman (46:34.920)
So yeah, but I wouldn't call that time travel.
Lex Fridman (46:38.560)
Yeah, that's something else.
Lex Fridman (46:39.680)
But if you think of it, it just made me think,
Lex Fridman (46:43.240)
if you think the unrolling of state
Leonard Susskind (46:46.980)
that's happening as a program,
Lex Fridman (46:49.840)
if we look at the world,
Leonard Susskind (46:52.860)
silly idea of looking at the world as a simulation,
Lex Fridman (46:56.440)
as a computer.
Lex Fridman (46:59.080)
But it's not a computer, it's just a single program.
Lex Fridman (47:03.200)
A question arises that might be useful.
Lex Fridman (47:06.320)
How hard is it to have a computer that runs the universe?
Lex Fridman (47:11.320)
Okay, so there are mathematical universes
Leonard Susskind (47:18.300)
that we know about.
Lex Fridman (47:20.040)
One of them is called anti de Sitter space,
Leonard Susskind (47:22.840)
where we, and it's quantum mechanics,
Lex Fridman (47:28.520)
I think we could simulate it in a computer,
Leonard Susskind (47:32.240)
in a quantum computer.
Lex Fridman (47:34.140)
Classical computer, all you can do is solve its equations.
Leonard Susskind (47:36.600)
You can't make it work like the real system.
Lex Fridman (47:39.160)
If we could build a quantum computer, a big enough one,
Leonard Susskind (47:41.600)
a robust enough one, we could probably simulate a universe,
Lex Fridman (47:49.880)
a small version of an anti de Sitter universe.
Leonard Susskind (47:52.880)
Anti de Sitter is a kind of cosmology.
Lex Fridman (47:57.680)
So I think we know how to do that.
Leonard Susskind (48:00.100)
The trouble is the universe that we live in
Lex Fridman (48:02.340)
is not the anti de Sitter geometry,
Leonard Susskind (48:04.840)
it's the de Sitter geometry.
Lex Fridman (48:07.320)
And we don't really understand its quantum mechanics at all.
Lex Fridman (48:11.120)
So at the present time,
Lex Fridman (48:12.120)
I would say we wouldn't have the vaguest idea
Lex Fridman (48:14.000)
how to simulate a universe similar to our own.
Lex Fridman (48:18.020)
No, we can ask, could we build in the laboratory
Leonard Susskind (48:21.120)
a small version, a quantum mechanical version,
Lex Fridman (48:27.720)
the collection of quantum computers
Lex Fridman (48:29.620)
and tangled and coupled together,
Lex Fridman (48:32.880)
which would reproduce the phenomena that go on in the universe,
Leonard Susskind (48:38.120)
even on a small scale.
Lex Fridman (48:40.400)
Yes, if it were anti de Sitter space,
Leonard Susskind (48:43.060)
no, if it's de Sitter space.
Lex Fridman (48:44.680)
Can you slightly describe de Sitter space
Lex Fridman (48:47.400)
and anti de Sitter space?
Lex Fridman (48:48.640)
Yeah.
Lex Fridman (48:49.860)
What are the geometric properties of?
Lex Fridman (48:51.400)
They differ by the sign of a single constant
Leonard Susskind (48:54.860)
called the cosmological constant.
Lex Fridman (48:57.960)
One of them is negatively curved,
Leonard Susskind (49:01.760)
the other is positively curved.
Lex Fridman (49:04.840)
Anti de Sitter space, which is the negatively curved one,
Leonard Susskind (49:08.260)
you can think of as an isolated system
Lex Fridman (49:11.360)
in a box with reflecting walls.
Leonard Susskind (49:14.620)
You could think of it as a system
Lex Fridman (49:16.200)
of quantum mechanical system isolated
Leonard Susskind (49:19.240)
in an isolated environment.
Lex Fridman (49:21.800)
De Sitter space is the one we really live in.
Lex Fridman (49:23.740)
And that's the one that's exponentially expanding,
Lex Fridman (49:26.880)
exponential expansion, dark energy,
Leonard Susskind (49:30.040)
whatever we wanna call it.
Lex Fridman (49:31.520)
And we don't understand that mathematically.
Lex Fridman (49:35.880)
Do we understand?
Lex Fridman (49:36.960)
Not everybody would agree with me,
Lex Fridman (49:38.200)
but I don't understand.
Lex Fridman (49:39.560)
They would agree with me,
Leonard Susskind (49:40.600)
they definitely would agree with me
Lex Fridman (49:41.920)
that I don't understand it.
Lex Fridman (49:44.720)
What about, is there an understanding of the birth,
Lex Fridman (49:48.480)
the origin, the big bang?
Lex Fridman (49:50.320)
So there's one problem with the other.
Lex Fridman (49:51.800)
No, no, there's theories.
Leonard Susskind (49:53.160)
There are theories.
Lex Fridman (49:55.840)
My favorite is the one called eternal inflation.
Leonard Susskind (49:58.980)
The infinity can be on both sides,
Lex Fridman (50:00.680)
on one of the sides and none of the sides.
Lex Fridman (50:02.600)
So what's eternal infinity?
Lex Fridman (50:05.520)
Okay.
Leonard Susskind (50:09.480)
Infinity on both sides.
Lex Fridman (50:13.040)
Oh boy.
Leonard Susskind (50:13.920)
Yeah, yeah, that's.
Lex Fridman (50:15.480)
Why is that your favorite?
Lex Fridman (50:16.520)
Because it's the most just mind blowing?
Lex Fridman (50:21.520)
No.
Leonard Susskind (50:22.360)
Because we want a beginning.
Lex Fridman (50:23.200)
No, why do we want a beginning?
Leonard Susskind (50:26.800)
In practice there was a beginning, of course.
Lex Fridman (50:28.380)
In practice there was a beginning.
Lex Fridman (50:31.280)
But could it have been a random fluctuation
Lex Fridman (50:36.800)
in an otherwise infinite time?
Leonard Susskind (50:39.320)
Maybe.
Lex Fridman (50:41.320)
In any case, the eternal inflation theory,
Leonard Susskind (50:45.840)
I think if correctly understood,
Lex Fridman (50:47.280)
would be infinite in both directions.
Lex Fridman (50:50.680)
How do you think about infinity?
Lex Fridman (50:52.840)
Oh God.
Leonard Susskind (50:53.960)
So, okay, of course you can think about it mathematically.
Lex Fridman (50:57.520)
I just finished this discussion with my friend Sergei Brin.
Lex Fridman (51:01.480)
How do you think about infinity?
Lex Fridman (51:02.800)
I say, well, Sergei Brin is infinitely rich.
Lex Fridman (51:07.960)
How do you test that hypothesis?
Lex Fridman (51:09.360)
Okay.
Leonard Susskind (51:12.000)
Such a good line.
Lex Fridman (51:13.240)
Right.
Leonard Susskind (51:15.400)
Yeah, so there's really no way
Lex Fridman (51:17.160)
to visualize some of these things.
Leonard Susskind (51:20.240)
Yeah, no, this is a very good question.
Lex Fridman (51:22.360)
Does physics have any,
Lex Fridman (51:24.680)
does infinity have any place in physics?
Lex Fridman (51:27.360)
Right.
Leonard Susskind (51:28.200)
Right, and all I can say is very good question.
Lex Fridman (51:35.840)
So what do you think of the recent first image
Lex Fridman (51:39.400)
of a black hole visualized from the Horizon Telescope?
Lex Fridman (51:43.040)
It's an incredible triumph of science.
Leonard Susskind (51:45.680)
In itself, the fact that there are black holes
Lex Fridman (51:47.740)
which collide is not a surprise.
Lex Fridman (51:50.620)
And they seem to work exactly
Lex Fridman (51:52.640)
the way they're supposed to work.
Lex Fridman (51:54.760)
Will we learn a great deal from it?
Lex Fridman (51:57.040)
I don't know, we might.
Lex Fridman (52:00.160)
But the kind of things we'll learn
Lex Fridman (52:01.300)
won't really be about black holes.
Lex Fridman (52:05.240)
Why there are black holes in nature
Lex Fridman (52:09.500)
of that particular mass scale and why they're so common
Leonard Susskind (52:12.780)
may tell us something about the structure,
Lex Fridman (52:15.680)
evolution of structure in the universe.
Lex Fridman (52:18.440)
But I don't think it's gonna tell us
Lex Fridman (52:19.520)
anything new about black holes.
Lex Fridman (52:22.000)
But it's a triumph in the sense
Lex Fridman (52:23.620)
that you go back 100 years
Lex Fridman (52:25.420)
and it was a continuous development,
Lex Fridman (52:28.200)
general relativity, the discovery of black holes,
Leonard Susskind (52:31.480)
LIGO, the incredible technology that went into LIGO.
Lex Fridman (52:37.600)
It is something that I never would have believed
Leonard Susskind (52:43.120)
was gonna happen 30, 40 years ago.
Lex Fridman (52:47.760)
And I think it's a magnificent structure,
Leonard Susskind (52:51.840)
magnificent thing, this evolution of general relativity,
Lex Fridman (52:59.680)
LIGO, high precision, ability to measure things
Leonard Susskind (53:03.980)
on a scale of 10 to the minus 21.
Lex Fridman (53:07.680)
So, astonishing.
Lex Fridman (53:09.400)
So you're just in awe that this path
Lex Fridman (53:12.800)
took us to this picture.
Lex Fridman (53:14.780)
Is it different?
Lex Fridman (53:17.480)
You've thought a lot about black holes.
Lex Fridman (53:19.840)
How did you visualize them in your mind?
Lex Fridman (53:23.560)
And is the picture different than you've visualized it?
Leonard Susskind (53:26.240)
No, it's simply confirmed.
Lex Fridman (53:30.000)
It's a magnificent triumph to have confirmed
Leonard Susskind (53:32.720)
a direct observation that Einstein's theory of gravity
Lex Fridman (53:37.320)
at the level of black hole collisions actually works
Leonard Susskind (53:42.380)
is awesome, it is really awesome.
Lex Fridman (53:45.600)
I know some of the people who are involved in that.
Leonard Susskind (53:48.160)
They're just ordinary people.
Lex Fridman (53:49.960)
And the idea that they could carry this out,
Leonard Susskind (53:54.440)
I just, I'm shocked.
Lex Fridman (53:56.460)
Yeah, just these little homo sapiens?
Leonard Susskind (53:59.360)
Yeah, just these little monkeys.
Lex Fridman (54:00.960)
Yeah, got together and took a picture of...
Leonard Susskind (54:04.800)
Slightly advanced limer's, I think.
Lex Fridman (54:08.540)
What kind of questions can science not currently answer
Lex Fridman (54:11.320)
but you hope might be able to soon?
Lex Fridman (54:13.460)
Well, you've already addressed them.
Lex Fridman (54:15.080)
What is consciousness, for example?
Lex Fridman (54:17.020)
You think that's within the reach of science?
Leonard Susskind (54:19.400)
I think it's somewhat within the reach of science,
Lex Fridman (54:21.640)
but I think that now I think it's in the hands
Leonard Susskind (54:23.680)
of the computer scientists and the neuroscientists.
Lex Fridman (54:27.120)
Not a physicist, with the help.
Leonard Susskind (54:29.520)
Perhaps at some point, but I think physicists
Lex Fridman (54:31.720)
will try to simplify it down to something
Leonard Susskind (54:34.640)
that they can use their methods
Lex Fridman (54:36.320)
and maybe they're not appropriate.
Leonard Susskind (54:38.560)
Maybe we simply need to do more machine learning
Lex Fridman (54:43.560)
on bigger scales, evolve machines.
Leonard Susskind (54:47.800)
Machines not only that learn
Lex Fridman (54:49.360)
but evolve their own architecture.
Leonard Susskind (54:51.320)
As a process of learning, evolve in architecture.
Lex Fridman (54:54.300)
Not under our control, only partially under our control,
Lex Fridman (54:56.960)
but under the control of machine learning.
Lex Fridman (55:00.320)
I'll tell you another thing that I find awesome.
Leonard Susskind (55:03.200)
You know this Google thing that they taught
Lex Fridman (55:05.640)
the computers how to play chess?
Leonard Susskind (55:07.480)
Yeah, yeah.
Lex Fridman (55:08.320)
Okay, they taught the computers how to play chess,
Leonard Susskind (55:10.680)
not by teaching them how to play chess,
Lex Fridman (55:12.440)
but just having them play against each other.
Leonard Susskind (55:14.400)
Against each other, self play.
Lex Fridman (55:15.400)
Against each other, this is a form of evolution.
Leonard Susskind (55:18.800)
These machines evolved, they evolved in intelligence.
Lex Fridman (55:25.600)
They evolved in intelligence
Leonard Susskind (55:27.400)
without anybody telling them how to do it.
Lex Fridman (55:30.880)
They were not engineered, they just played
Leonard Susskind (55:33.240)
against each other and got better and better and better.
Lex Fridman (55:36.040)
That makes me think that machines can evolve intelligence.
Lex Fridman (55:43.500)
What exact kind of intelligence, I don't know.
Lex Fridman (55:46.580)
But in understanding that better and better,
Leonard Susskind (55:49.020)
maybe we'll get better clues as to what goes on
Lex Fridman (55:52.260)
in our own intelligence.
Lex Fridman (55:53.100)
What life in intelligence is.
Lex Fridman (55:55.220)
Last question, what kind of questions can science
Lex Fridman (55:58.700)
not currently answer and may never be able to answer?
Lex Fridman (56:01.820)
Yeah.
Leonard Susskind (56:02.660)
Yeah.
Lex Fridman (56:05.620)
Is there an intelligence out there
Lex Fridman (56:07.300)
that's underlies the whole thing?
Lex Fridman (56:09.260)
You can call them with a G word if you want.
Lex Fridman (56:11.980)
I can say, are we a computer simulation with a purpose?
Lex Fridman (56:18.960)
Is there an agent, an intelligent agent
Lex Fridman (56:22.560)
that underlies or is responsible for the whole thing?
Lex Fridman (56:27.180)
Does that intelligent agent satisfy the laws of physics?
Lex Fridman (56:30.560)
Does it satisfy the laws of quantum mechanics?
Lex Fridman (56:32.600)
Is it made of atoms and molecules?
Leonard Susskind (56:34.460)
Yeah, there's a lot of questions.
Lex Fridman (56:36.560)
And I don't see, it seems to me a real question.
Leonard Susskind (56:42.080)
It's an answerable question.
Lex Fridman (56:43.500)
Well, I don't know if it's answerable.
Leonard Susskind (56:44.800)
The questions have to be answerable to be real.
Lex Fridman (56:49.300)
Some philosophers would say that a question
Leonard Susskind (56:52.240)
is not a question unless it's answerable.
Lex Fridman (56:55.580)
This question doesn't seem to me answerable
Leonard Susskind (56:58.300)
by any known method, but it seems to me real.
Lex Fridman (57:05.140)
There's no better place to end.
Leonard Susskind (57:07.180)
Leonard, thank you so much for talking today.
Lex Fridman (57:08.660)
Okay, good.
🔗 相关节目