Brian Greene: Quantum Gravity, Big Bang, Aliens, Life, Death, and Meaning
物理与宇宙学生物与进化音乐与艺术哲学与宗教政治与社会
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AI 智能总结
布莱恩·格林谈量子引力、大爆炸与生命的意义
这是 Lex Fridman 与哥伦比亚大学理论物理学家 Brian Greene 的深度对话。Greene 探讨了量子引力、多元宇宙、时间的本质、外星生命的可能性，以及在一个最终走向热寂的宇宙中如何寻找意义。
量子引力弦理论多元宇宙时间外星生命宇宙学生命意义
Brian Greene 是哥伦比亚大学理论物理学和数学教授，弦理论领域的重要研究者，著有《宇宙的琴弦》《宇宙的结构》《时间的终结》等畅销科普书，是当代最重要的科学传播者之一。
📌 核心观点
- 量子引力与弦理论：Greene 是弦理论的重要倡导者，他解释了为什么统一量子力学和广义相对论是物理学最大的挑战，弦理论提供了一个可能的框架，但目前还缺乏实验验证。
- 多元宇宙：Greene 探讨了多种多元宇宙的可能性——从量子力学的多世界诠释到弦理论的景观，他认为我们的宇宙可能只是无数宇宙中的一个，这对「为什么宇宙的常数恰好适合生命」提供了人择原理解释。
- 时间的本质：Greene 认为时间可能是一种幻觉，物理学的基本方程是时间对称的，「过去」和「未来」的区别可能源于热力学第二定律（熵增），而非时间本身的方向性。
- 外星生命：Greene 认为宇宙中存在其他生命形式的概率极高，但费米悖论（为什么我们没有发现外星文明）是一个深刻的谜题，可能的解释包括文明的自我毁灭或宇宙距离的障碍。
- 生命的意义：在《时间的终结》中，Greene 探讨了在一个最终走向热寂的宇宙中如何寻找意义。他认为意义不需要永恒，人类的创造力、爱和理解本身就是有价值的，即使宇宙最终消亡。
✨ 金句摘录
Greene：时间可能是一种幻觉——物理学的基本方程是时间对称的，「过去」和「未来」的区别可能只是热力学的产物。
Greene：在一个最终走向热寂的宇宙中，意义不需要永恒——人类的创造力和爱本身就是有价值的。
Greene：费米悖论是宇宙中最深刻的谜题之一——如果生命如此普遍，为什么我们如此孤独？
📋 章节目录
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🔑 关键词
dontheoryhumanconsciousnessuniversephysicsstringdimensionsexperiencegoingspaceblackearthdoesnseemsunderstandingphysicalbanggravitytravel
💬 精彩语录
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🎙️ 完整对话（2245 条）
Lex Fridman (00:00.000)
The following is a conversation with Brian Greene,
以下是与布莱恩·格林的对话，
Lex Fridman (00:02.840)
theoretical physicist at Columbia
哥伦比亚大学理论物理学家
Lex Fridman (00:04.900)
and author of many amazing books on physics,
以及许多令人惊叹的物理学书籍的作者，
Lex Fridman (00:08.120)
including his latest, Until the End of Time,
包括他的最新作品《直到时间的尽头》
Lex Fridman (00:11.500)
Mind, Matter, and Our Search for Meaning
心灵、物质和我们对意义的追寻
Brian Greene (00:14.440)
in an Evolving Universe.
在不断发展的宇宙中。
Lex Fridman (00:16.880)
This is the Lex Friedman podcast.
这是莱克斯·弗里德曼的播客。
Brian Greene (00:19.100)
To support it, please check out our sponsors
为了支持它，请查看我们的赞助商
Lex Fridman (00:21.180)
in the description.
在描述中。
Lex Fridman (00:22.420)
And now, here's my conversation with Brian Greene.
现在，这是我与布莱恩·格林的对话。
Lex Fridman (00:27.240)
In your most recent book, Until the End of Time,
在您的最新著作《直到时间的尽头》中，
Brian Greene (00:29.940)
you quote Bertrand Russell from a debate he had
你引用了伯特兰·罗素的一场辩论
Lex Fridman (00:32.620)
about God in 1948.
1948 年关于上帝。
Brian Greene (00:34.880)
He says, quote,
他说，引用，
Lex Fridman (00:37.560)
"'So far as scientific evidence goes,
“‘就科学证据而言，
Brian Greene (00:39.460)
"'the universe has crawled by slow stages
“‘宇宙已经经历了缓慢的阶段
Lex Fridman (00:42.340)
"'to a somewhat pitiful result on this earth,
“‘在这个地球上造成了有点可怜的结果，
Brian Greene (00:45.600)
"'and is going to crawl by still more pitiful stages
“‘并且将会爬行更可怜的阶段
Lex Fridman (00:48.820)
"'to a condition of universal death.
“‘达到普遍死亡的状态。
Brian Greene (00:52.420)
"'If this is to be taken as evidence of purpose,
“‘如果这被视为目的的证据，
Lex Fridman (00:54.980)
"'I can only say that the purpose is one
Brian Greene (00:57.680)
"'that does not appeal to me.
Lex Fridman (00:59.520)
"'I see no reason, therefore,
Brian Greene (01:01.220)
"'to believe in any sort of God.'"
Lex Fridman (01:04.820)
That's quite a depressing statement.
Brian Greene (01:06.980)
As you say, this is a bleak outlook on our universe
Lex Fridman (01:09.900)
and the emergence of human consciousness.
Lex Fridman (01:12.380)
So let me ask, what is the more hopeful perspective
Lex Fridman (01:15.900)
to take on this story?
Brian Greene (01:18.140)
Well, I think the more hopeful perspective
Lex Fridman (01:19.860)
is to more fully understand
Lex Fridman (01:25.060)
what was driving Bertrand Russell to this perspective,
Lex Fridman (01:28.340)
and then to see it within a broader context.
Lex Fridman (01:32.700)
And really, that's, in some sense,
Lex Fridman (01:34.700)
what my book, Until the End of Time, is all about.
Lex Fridman (01:37.500)
But in brief, I would say that there's a lot of truth
Lex Fridman (01:41.740)
to what Bertrand Russell was saying there.
Brian Greene (01:43.700)
When you look at the second law of thermodynamics,
Lex Fridman (01:45.700)
which is the underlying scientific idea
Brian Greene (01:48.140)
that's driving this notion that everything's gonna wither,
Lex Fridman (01:51.660)
decay, fall apart, yeah, that's true.
Brian Greene (01:55.140)
Second law of thermodynamics establishes
Lex Fridman (01:57.240)
that disorder, entropy, in aggregate,
Brian Greene (02:00.900)
is always on the rise.
Lex Fridman (02:02.620)
And that is indeed interpretable
Brian Greene (02:05.980)
as disintegration and destruction
Lex Fridman (02:07.620)
over sufficiently long timescales.
Lex Fridman (02:09.580)
But my view is, when you recognize
Lex Fridman (02:12.460)
how special that makes us,
Brian Greene (02:14.980)
that we are these exquisitely ordered configurations
Lex Fridman (02:18.560)
of particles that only will last for a blink of an eye
Brian Greene (02:22.100)
in cosmological time like terms,
Lex Fridman (02:25.420)
the fact that we're here and we can do what we do,
Brian Greene (02:27.380)
to me, that's just really something
Lex Fridman (02:30.900)
that inspires gratitude and wonder
Lex Fridman (02:34.180)
and a sense of deep purpose
Lex Fridman (02:38.020)
by virtue of being these unique collections of entities
Brian Greene (02:42.100)
that happen to rise up, look around,
Lex Fridman (02:44.640)
and try to figure out where we are
Lex Fridman (02:46.500)
and what the heck we should do with our time.
Lex Fridman (02:48.540)
So it's not that I would disagree with Bertrand Russell
Brian Greene (02:51.740)
in terms of the basic physics and the basic unfolding,
Lex Fridman (02:58.260)
but I think it's really a matter of the slant
Brian Greene (03:00.580)
that you take on what it means for us.
Lex Fridman (03:04.460)
So maybe we'll skip around a bit,
Lex Fridman (03:06.700)
but let me ask the biggest possible question then.
Lex Fridman (03:09.020)
You said purpose.
Lex Fridman (03:10.260)
So what's the meaning of it all then?
Lex Fridman (03:12.500)
Is there a meaning to life that we can take from this,
Brian Greene (03:17.500)
from this brief emergence of complexity
Lex Fridman (03:22.180)
that arises from simple things
Lex Fridman (03:24.260)
and then goes into a heat death
Lex Fridman (03:26.860)
that is once again returns to simple things
Lex Fridman (03:29.780)
as the march of the second law of thermodynamics goes on?
Lex Fridman (03:33.040)
I think there is,
Lex Fridman (03:33.880)
but I don't think it's a universal answer.
Lex Fridman (03:36.620)
And so I think throughout the ages,
Brian Greene (03:39.340)
there has been a kind of quest for some final way
Lex Fridman (03:44.340)
of articulating meaning and purpose,
Brian Greene (03:47.660)
whether it's God, whether it's love,
Lex Fridman (03:50.540)
whether it's companionship.
Brian Greene (03:51.660)
I mean, many people put forward different ways
Lex Fridman (03:53.700)
of taking this question on,
Lex Fridman (03:56.660)
and there is no one right answer
Lex Fridman (03:59.340)
when you recognize deeply that the universe doesn't care.
Brian Greene (04:05.060)
There is nothing out there that is the final answer.
Lex Fridman (04:08.940)
It's not as though we need a more powerful telescope
Lex Fridman (04:11.860)
and somehow if we can look deeply into the universe,
Lex Fridman (04:14.940)
all will become clear.
Brian Greene (04:17.300)
In fact, the deeper we've looked,
Lex Fridman (04:18.980)
both literally and metaphorically,
Brian Greene (04:21.420)
into the universe and into the structure of reality,
Lex Fridman (04:24.860)
the more it's become clear
Brian Greene (04:27.020)
that we are just a momentary byproduct
Lex Fridman (04:30.700)
of laws of physics that don't have any emotional content.
Brian Greene (04:36.220)
They don't have any intrinsic sense of meaning or purpose.
Lex Fridman (04:39.640)
And when you recognize that,
Brian Greene (04:41.340)
you realize that searching for the universal
Lex Fridman (04:43.860)
for this kind of a question is a fool's errand.
Brian Greene (04:47.680)
Every individual has the capacity to make their own meaning,
Lex Fridman (04:51.820)
to set their own purpose.
Lex Fridman (04:53.700)
And that's not some platitude, that is what we are.
Lex Fridman (04:57.860)
Because there is no fundamental answer,
Brian Greene (04:59.780)
it's what you make of it.
Lex Fridman (05:01.120)
And however much that may sound like a hallmark card,
Brian Greene (05:04.180)
this really is the deep lesson of physics and science
Lex Fridman (05:09.120)
more generally over the past few hundred years.
Brian Greene (05:11.420)
Well, there's some level where you can objectively say
Lex Fridman (05:14.700)
that whatever we've got going on here,
Brian Greene (05:16.340)
it's kind of peculiar.
Lex Fridman (05:18.060)
It's kind of special in terms of complexity.
Lex Fridman (05:23.340)
And maybe you can even begin to measure it
Lex Fridman (05:26.540)
and like come up with metrics
Brian Greene (05:28.900)
where whatever we've got going on on Earth,
Lex Fridman (05:31.560)
these like interesting hierarchical complexities
Brian Greene (05:35.620)
that form more and more sophisticated biological system,
Lex Fridman (05:39.320)
that seems kind of unique
Brian Greene (05:40.760)
when you look at the entire universe,
Lex Fridman (05:45.460)
the observable part that we can see with our tools.
Brian Greene (05:48.460)
I mean, so I have to ask,
Lex Fridman (05:50.620)
as you describe in your book once again,
Brian Greene (05:53.900)
Schrodinger wrote the book,
Lex Fridman (05:55.120)
"'What is Life?' based on a few lectures he gave in 1944."
Lex Fridman (05:59.180)
So let me ask the fundamental question here.
Lex Fridman (06:02.700)
What is life?
Brian Greene (06:04.540)
This particular thing we've got going on here,
Lex Fridman (06:06.820)
this pocket of complexity
Lex Fridman (06:08.260)
that emerged from such simple things?
Lex Fridman (06:10.180)
Yeah, it's a tough question.
Brian Greene (06:11.620)
I asked that question even to Richard Dawkins once,
Lex Fridman (06:15.580)
and I already have my preconceived notion,
Brian Greene (06:18.340)
which he pretty much confirmed,
Lex Fridman (06:20.020)
which is if one could give an answer to that question
Brian Greene (06:24.900)
that allowed you to sort of draw a line in the sand
Lex Fridman (06:28.060)
between the not living and the living,
Brian Greene (06:30.640)
then perhaps we would have the insight that we yearn for
Lex Fridman (06:34.020)
and trying to say, what is so special about life?
Lex Fridman (06:36.460)
But the fact of the matter is, it's a continuum.
Lex Fridman (06:39.260)
There's a continuum from the things
Brian Greene (06:41.180)
that we would typically call nonliving and animate
Lex Fridman (06:44.100)
to the things that we obviously call animate
Lex Fridman (06:46.660)
and full of the currents of life.
Lex Fridman (06:49.780)
Somewhere in there,
Brian Greene (06:51.780)
it is a question of the complexity of the structure,
Lex Fridman (06:55.500)
the ability of the structure to take in raw material
Brian Greene (07:00.300)
from the environment and process it through a metabolism
Lex Fridman (07:04.000)
that allows the structure to extract energy
Lex Fridman (07:07.260)
and to release entropy to the wider environment.
Lex Fridman (07:10.980)
Somewhere in those collections of biological processes
Brian Greene (07:15.100)
is the necessity or the necessary ingredients
Lex Fridman (07:19.540)
and processes for life,
Lex Fridman (07:20.580)
but drawing that line in the sand
Lex Fridman (07:22.600)
is not something that we're able to do,
Lex Fridman (07:25.540)
but I would agree with you.
Lex Fridman (07:27.500)
It's deeply peculiar.
Brian Greene (07:30.940)
It may in fact be unique,
Lex Fridman (07:33.900)
but it may not.
Brian Greene (07:35.000)
It could be that the universe is such
Lex Fridman (07:38.240)
that under fairly typical conditions,
Brian Greene (07:41.020)
a star that's a well ordered source of low entropy energy,
Lex Fridman (07:47.420)
that's what the sun is,
Brian Greene (07:49.120)
together with a planet being bathed
Lex Fridman (07:51.020)
by that low entropy energy,
Brian Greene (07:52.700)
together with a surface that has enough
Lex Fridman (07:55.740)
of the raw constituents that we recognize
Brian Greene (07:59.300)
are fairly commonplace result of supernova explosions
Lex Fridman (08:03.140)
where a star spews forth the result of the nuclear furnace
Brian Greene (08:07.960)
that is the core of a star.
Lex Fridman (08:09.260)
It could be that all you need
Brian Greene (08:11.700)
are those fairly commonplace conditions
Lex Fridman (08:15.020)
and maybe life naturally forms.
Lex Fridman (08:17.020)
Look, the James Webb Space Telescope, right?
Lex Fridman (08:19.400)
It's going up hopefully in December.
Lex Fridman (08:21.780)
And one of the goals of that mission
Lex Fridman (08:23.760)
is to look at atmospheres around distant planets
Lex Fridman (08:26.660)
and perhaps come to some sense of how special
Lex Fridman (08:30.460)
or not life or life as we know it is in the universe.
Brian Greene (08:35.960)
Which part of the story of life,
Lex Fridman (08:39.060)
let's stick to Earth for a second,
Lex Fridman (08:40.700)
do you think is the hardest?
Lex Fridman (08:42.760)
If you were like a betting man,
Lex Fridman (08:45.860)
which part is the hardest to make happen?
Lex Fridman (08:48.460)
Is it the origin of life?
Brian Greene (08:50.180)
Again, we haven't drawn the line where,
Lex Fridman (08:52.500)
as you say, the line between a rock and a rabbit.
Brian Greene (08:55.900)
That part, is it complex organisms,
Lex Fridman (09:01.180)
like multicellular organisms?
Brian Greene (09:03.260)
Is it crawling out of the ocean
Lex Fridman (09:05.980)
where the fish somehow figured out how to crawl around?
Brian Greene (09:09.380)
Is it then the us homo sapiens,
Lex Fridman (09:12.960)
as we like to think of ourselves special and intelligent?
Lex Fridman (09:17.340)
Or is it somewhere in between?
Lex Fridman (09:18.920)
As you also talk about, again, very hard to know
Brian Greene (09:23.500)
at which point this consciousness emerge.
Lex Fridman (09:28.580)
If you were to sort of took us a survey
Lex Fridman (09:31.940)
and made bets about other Earth like planets in the universe,
Lex Fridman (09:36.380)
where do you think they get stuck the most?
Brian Greene (09:38.660)
Well, I would certainly say if we're gonna go all the way
Lex Fridman (09:40.380)
to conscious beings like ourselves,
Brian Greene (09:42.420)
I would put it at the onset of consciousness,
Lex Fridman (09:45.180)
which again, I think is a continuum.
Brian Greene (09:47.620)
I don't think it is something that you can draw the line
Lex Fridman (09:50.920)
in the sand, but there are obvious circumstances,
Brian Greene (09:53.980)
there are obvious creatures such as ourselves
Lex Fridman (09:56.020)
where we do recognize a certain kind
Brian Greene (09:58.540)
of self reflective conscious awareness.
Lex Fridman (10:01.820)
And if we think about what it would require
Brian Greene (10:05.640)
for a system of living beings to acquire consciousness,
Lex Fridman (10:10.980)
I think that's probably the hardest part because look,
Brian Greene (10:14.700)
take Earth and recognize that weren't for,
Lex Fridman (10:18.780)
some singular event 65 million years ago
Brian Greene (10:21.980)
where this large rock slams into planet Earth
Lex Fridman (10:25.340)
and wipes out the dinosaurs,
Brian Greene (10:27.860)
maybe the dinosaurs would still rule the planet
Lex Fridman (10:31.380)
and they may well have not developed
Brian Greene (10:35.560)
the kind of conscious awareness that we have.
Lex Fridman (10:38.900)
So for billions of years on this planet,
Brian Greene (10:41.580)
there was life that didn't have the kind
Lex Fridman (10:44.460)
of conscious awareness that we have.
Lex Fridman (10:47.180)
And it was an accidental event in astrophysical history
Lex Fridman (10:52.340)
that allowed a mammalian species like us
Brian Greene (10:56.120)
to ultimately be the end product.
Lex Fridman (10:58.260)
And so, yeah, I could imagine there's a lot of life
Brian Greene (11:00.960)
out there, but perhaps none of it's wondering
Lex Fridman (11:04.800)
what's the meaning of life or trying to make sense of it,
Brian Greene (11:08.620)
just going about its business of survival,
Lex Fridman (11:11.260)
which of course is the dominant activity
Brian Greene (11:13.620)
that life on this planet has practiced.
Lex Fridman (11:15.620)
We are a rare exception to that.
Lex Fridman (11:17.900)
And I really appreciate that you lean into
Lex Fridman (11:20.020)
some of these unanswerable questions from me today.
Lex Fridman (11:22.500)
But the, so you think about consciousness,
Lex Fridman (11:25.400)
not as like a phase shift, the binary zero one,
Brian Greene (11:28.420)
you think of it as a continuum that humans somehow
Lex Fridman (11:33.340)
are maybe some of the most conscious beings on Earth.
Lex Fridman (11:37.500)
So you're, so.
Lex Fridman (11:39.140)
I mean, people will dispute that.
Brian Greene (11:40.800)
Yes, I mean, well, and it's a very hard argument.
Lex Fridman (11:43.680)
People will dispute that, rocks probably
Brian Greene (11:45.900)
will stay quiet on the matter.
Lex Fridman (11:47.220)
Maybe not, right?
Brian Greene (11:48.780)
For the moment, they're waiting for their opportunity.
Lex Fridman (11:51.580)
But I agree that, look, even when you and I
Brian Greene (11:57.780)
look at each other, I am not fully convinced
Lex Fridman (12:01.620)
that you're a conscious being, right?
Brian Greene (12:03.560)
I mean, I think that you are.
Lex Fridman (12:04.580)
It's not to me.
Brian Greene (12:05.420)
I mean, your behavior is such that
Lex Fridman (12:07.300)
that's the best explanation for what's going on.
Lex Fridman (12:09.340)
But of course, we're all in the position
Lex Fridman (12:11.460)
of only having direct awareness of our own conscious being.
Lex Fridman (12:16.460)
And therefore, when it comes to other creatures in the world,
Lex Fridman (12:19.820)
we're in a similar state of ignorance
Brian Greene (12:21.700)
regarding what's actually happening inside of their head,
Lex Fridman (12:25.240)
if they have a head.
Lex Fridman (12:26.540)
And so it's hard to know how singular we are,
Lex Fridman (12:30.340)
but I would say based on the best available data
Lex Fridman (12:33.260)
and the best explanations that we can make,
Lex Fridman (12:34.920)
yeah, there is something special about us.
Brian Greene (12:36.580)
I don't think that there are fish walking around
Lex Fridman (12:39.500)
and coming up with existentialism.
Brian Greene (12:43.260)
I don't know that there are dogs walking around
Lex Fridman (12:46.820)
who've developed an understanding
Brian Greene (12:48.260)
of the general theory of relativity.
Lex Fridman (12:49.620)
I mean, maybe we're wrong,
Lex Fridman (12:50.840)
but that seems the best explanation.
Lex Fridman (12:54.140)
What do you think is more special,
Lex Fridman (12:55.700)
intelligence or consciousness?
Lex Fridman (12:57.940)
I think consciousness.
Lex Fridman (12:59.300)
And I think that there's a deep connection
Lex Fridman (13:02.140)
between these ideas.
Brian Greene (13:03.620)
They are distinct, but they're deeply connected.
Lex Fridman (13:06.000)
But look, I mean, to me and to, of course, many philosophers
Brian Greene (13:10.020)
who actually coined a name for this,
Lex Fridman (13:11.320)
the hard problem of consciousness,
Brian Greene (13:13.060)
David Chalmers and others,
Lex Fridman (13:15.460)
as a physicist, I look out at the world
Lex Fridman (13:17.780)
and I see it's particles governed by physical law.
Lex Fridman (13:23.000)
We can name them.
Brian Greene (13:24.620)
We got electrons, we got quarks
Lex Fridman (13:27.800)
that come in various flavors and so forth.
Brian Greene (13:29.920)
We have a list of ingredients that science has revealed
Lex Fridman (13:33.500)
and we have a list of laws that seemingly
Brian Greene (13:36.140)
govern those ingredients.
Lex Fridman (13:37.300)
And nowhere in there is there even a hint
Brian Greene (13:41.300)
that when you put those particles together in the right way,
Lex Fridman (13:45.700)
an inner world should turn on.
Lex Fridman (13:48.260)
And it's not only that there's no hint, it's insane.
Lex Fridman (13:52.060)
I mean, it's ridiculous.
Lex Fridman (13:53.700)
How could it be that a thoughtless,
Lex Fridman (13:56.660)
passionless, emotionless particle,
Brian Greene (14:00.180)
when grouped together with compatriots,
Lex Fridman (14:03.180)
somehow can yield something so deeply foreign
Lex Fridman (14:07.300)
to the nature of the ingredients themselves?
Lex Fridman (14:09.380)
So answering that question,
Brian Greene (14:12.900)
I think is among the deepest
Lex Fridman (14:14.940)
and most difficult questions that we face.
Lex Fridman (14:17.900)
Do you think it is in fact a really hard problem?
Lex Fridman (14:23.500)
Or is it possible, I think you mentioned in your book,
Brian Greene (14:28.100)
that it's just like almost like a side effect.
Lex Fridman (14:30.060)
It's an emergent thing that's like, oh, it's nice.
Brian Greene (14:33.220)
It's like a nice little feature.
Lex Fridman (14:34.940)
Yeah.
Brian Greene (14:35.780)
Well, I mean, when people use the phrase hard problem,
Lex Fridman (14:38.380)
I mean, they mean in a somewhat technical sense
Brian Greene (14:40.840)
that it's trying to explain something
Lex Fridman (14:44.780)
that seems fundamentally unavailable
Lex Fridman (14:47.660)
to third party objective analysis, right?
Lex Fridman (14:53.180)
I'm the only one that can get inside my head
Lex Fridman (14:55.680)
and I can tell you a lot about what's happening
Lex Fridman (14:57.740)
inside my head right now, it's reflected
Brian Greene (14:59.580)
in what I'm saying, and you can try to deduce things
Lex Fridman (15:02.180)
about what's going on inside my head,
Lex Fridman (15:03.580)
but you don't have access to it in the way that I do.
Lex Fridman (15:06.300)
And so it seems like a fundamentally different
Brian Greene (15:08.100)
kind of problem from the ones that we have successfully
Lex Fridman (15:12.260)
dealt with over the course of centuries in science,
Brian Greene (15:14.240)
where we look at the motion of the moon,
Lex Fridman (15:15.900)
everybody can look, everybody can measure it.
Brian Greene (15:18.300)
We look at the properties of hydrogen
Lex Fridman (15:20.940)
when you shine lasers on it,
Brian Greene (15:22.660)
everybody can look at the data and understand it.
Lex Fridman (15:25.900)
And so it seems like a fundamentally different problem
Brian Greene (15:29.020)
in that sense, it seems like it is hard
Lex Fridman (15:32.340)
relative to the others, but I do think ultimately
Brian Greene (15:35.900)
that the explanation will be, as you recount,
Lex Fridman (15:38.980)
I think that a hundred years from now,
Brian Greene (15:41.140)
or maybe it's a thousand, it's hard to predict
Lex Fridman (15:43.020)
the timescale for developments,
Lex Fridman (15:45.520)
but I think we'll get to a place where we'll look back
Lex Fridman (15:48.420)
and kind of smile at those folks in the 20th century
Lex Fridman (15:53.300)
and before, 21st century and before,
Lex Fridman (15:55.340)
who thought consciousness was so incredibly mysterious
Brian Greene (15:59.340)
when the reality of it is, eh, it's just a thing that happens
Lex Fridman (16:03.820)
when particles come together.
Lex Fridman (16:05.800)
And however mysterious that feels right now,
Lex Fridman (16:10.420)
I think for instance, when we start to build
Brian Greene (16:12.140)
conscious systems, things that you're more familiar with
Lex Fridman (16:15.540)
than I am, when we start to build these artificial systems
Lex Fridman (16:19.420)
and those systems report to us, I'm feeling sad,
Lex Fridman (16:23.220)
I'm feeling anxious, yeah, there's a world going on
Brian Greene (16:25.500)
inside here, I think the mystery of consciousness
Lex Fridman (16:28.580)
will just begin to evaporate.
Brian Greene (16:30.860)
Well, that's, first of all, beautifully put,
Lex Fridman (16:33.460)
and I agree with you completely,
Brian Greene (16:35.220)
just the way you said it, it'll begin to evaporate.
Lex Fridman (16:38.500)
I have built quite a few robots
Lex Fridman (16:41.260)
and have had them do emotion, emotional type things,
Lex Fridman (16:47.220)
and it's immediate that exactly what you're saying,
Brian Greene (16:49.380)
this kind of mystery of consciousness starts to evaporate,
Lex Fridman (16:52.600)
that the kind of need to truly understand,
Brian Greene (16:57.620)
to solve the hard problem of consciousness disappears,
Lex Fridman (17:00.380)
because, well, I don't really care if I understand
Lex Fridman (17:05.060)
what can solve the hard problem of consciousness.
Lex Fridman (17:07.300)
That thing sure as heck looks conscious.
Brian Greene (17:09.660)
I feel like that way when I interact with a dog.
Lex Fridman (17:12.840)
I don't need to solve the problem of consciousness
Brian Greene (17:16.420)
to be able to interact and richly enjoy the experience
Lex Fridman (17:22.740)
with this other living being.
Brian Greene (17:24.380)
Obviously, same thing with other humans.
Lex Fridman (17:26.440)
I don't need to fully understand it.
Lex Fridman (17:27.940)
And there's some aspect, maybe this is a little bit
Lex Fridman (17:31.020)
too engineering focused, but there's some aspect
Brian Greene (17:33.540)
in which it feels like consciousness is just a nice trick
Lex Fridman (17:38.660)
to help us communicate with each other.
Brian Greene (17:41.740)
It sounds ridiculous to say, but sort of the ability
Lex Fridman (17:47.540)
to experience the world is very useful,
Brian Greene (17:51.220)
in a subjective sense, is very useful to put yourself
Lex Fridman (17:55.160)
in that world and to be able to describe the experience
Brian Greene (17:58.340)
to others.
Lex Fridman (17:59.180)
It could be just a social and the merge.
Brian Greene (18:01.840)
Obviously, animals, the sort of more primitive animals
Lex Fridman (18:04.500)
might experience consciousness in some more primitive way,
Lex Fridman (18:08.780)
but this kind of rich, subjective experience
Lex Fridman (18:12.300)
that we think about as humans, I think it's probably
Brian Greene (18:14.540)
deeply coupled with language and poetry.
Lex Fridman (18:17.840)
Yeah, that resonates with my view as well.
Brian Greene (18:20.680)
I mean, there's a scientist, maybe you've spoken to him,
Lex Fridman (18:23.340)
Michael Graziano from Princeton.
Brian Greene (18:25.140)
Yeah, he's developed ideas of consciousness that,
Lex Fridman (18:29.620)
look, I don't think they solve the problem,
Lex Fridman (18:31.620)
but I think they do illuminate it in an interesting way
Lex Fridman (18:34.340)
where basically we are not aware
Brian Greene (18:39.020)
of all the underlying physiochemical processes
Lex Fridman (18:43.060)
that make our brains and our inner worlds
Brian Greene (18:45.900)
tick the way they do.
Lex Fridman (18:48.020)
And because of that dissociation between sensation
Lex Fridman (18:52.220)
and the physics of it and the chemistry of it
Lex Fridman (18:55.140)
and the biology of it, it feels like our minds
Lex Fridman (18:58.900)
and our inner worlds are just untethered,
Lex Fridman (19:00.960)
like floating somewhere in this gray matter
Brian Greene (19:04.640)
inside of our heads.
Lex Fridman (19:06.500)
And the way I like to think of it is like,
Brian Greene (19:08.580)
look, if you were in a dark room, right,
Lex Fridman (19:13.980)
and I had glow in the dark paint on my fingers,
Lex Fridman (19:17.380)
so all you saw was my fingers dancing around,
Lex Fridman (19:20.380)
there'd be something mysterious.
Lex Fridman (19:21.980)
How could those fingers be doing that?
Lex Fridman (19:24.460)
And then you turn on the light, you realize,
Brian Greene (19:25.300)
oh, there's this arm underlying it,
Lex Fridman (19:27.700)
and that's the deep physical connection explains it all.
Lex Fridman (19:30.660)
And I think that's what we're missing,
Lex Fridman (19:32.620)
the deep physical connection between what's happening
Brian Greene (19:35.800)
up here and what is responsible for it
Lex Fridman (19:38.540)
in a physical, chemical, biological way.
Lex Fridman (19:41.420)
And so to me, that at least gives me some understanding
Lex Fridman (19:43.660)
of why consciousness feels so mysterious
Brian Greene (19:46.740)
because we are suppressing all of the underlying science
Lex Fridman (19:51.580)
that ultimately is responsible for it.
Lex Fridman (19:53.540)
And one day we will reveal that more fully,
Lex Fridman (19:55.940)
and I think that will help us tether this experience
Brian Greene (19:59.260)
to something quite tangible in the world.
Lex Fridman (1:00:00.180)
from the laws of physics?
Brian Greene (1:00:01.180)
I do.
Lex Fridman (1:00:02.540)
There is nothing that's not ultimately explainable
Brian Greene (1:00:06.300)
with the laws of physics from this physicalist perspective,
Lex Fridman (1:00:09.460)
which is what I take.
Lex Fridman (1:00:10.880)
So you got the particles, you got the laws,
Lex Fridman (1:00:13.980)
and you have things that emerge
Brian Greene (1:00:16.180)
from the choreographed motions of those particles.
Lex Fridman (1:00:20.780)
But is that the best language
Lex Fridman (1:00:23.060)
for talking about these emergent qualities?
Lex Fridman (1:00:26.100)
Usually not.
Brian Greene (1:00:27.540)
If I was to take something even more mundane,
Lex Fridman (1:00:30.940)
like a baseball flying through the air,
Brian Greene (1:00:33.180)
if I was to describe it in terms of the quarks
Lex Fridman (1:00:35.680)
and the electrons,
Brian Greene (1:00:36.820)
I'd give you this mountain of data
Lex Fridman (1:00:39.020)
with 10 to the 28 particles
Lex Fridman (1:00:42.340)
and all of their coordinates and spaces
Lex Fridman (1:00:45.300)
a function of time.
Brian Greene (1:00:46.120)
I hand you this mountain of data,
Lex Fridman (1:00:46.960)
you'd be like, I don't know what this is.
Lex Fridman (1:00:49.180)
And then if you really were clever and you're looking,
Lex Fridman (1:00:51.180)
oh, it's a baseball,
Brian Greene (1:00:53.240)
just described in the least economical way possible.
Lex Fridman (1:00:57.060)
It is much more useful and insightful
Brian Greene (1:01:00.240)
to talk about the baseball flying through the air.
Lex Fridman (1:01:01.940)
Similarly, there are things at the macroscopic level
Brian Greene (1:01:05.660)
like human experience and human emotion and human action
Lex Fridman (1:01:09.680)
and the sensation of free will
Brian Greene (1:01:12.660)
that we undeniably all have,
Lex Fridman (1:01:14.780)
even if it itself doesn't have a basis
Brian Greene (1:01:17.420)
in our understanding of the physical world.
Lex Fridman (1:01:19.460)
It's useful to talk about things in this very human language.
Lex Fridman (1:01:24.380)
And so, yes, it's vital to talk about things
Lex Fridman (1:01:26.700)
in the poetic language of human experience,
Lex Fridman (1:01:29.360)
but do not lose sight of the fact, and some people do.
Lex Fridman (1:01:31.820)
They say, oh, it's just an emergent phenomenon.
Brian Greene (1:01:33.880)
Don't lose sight of the fact that emergent phenomena
Lex Fridman (1:01:36.100)
are emerging from this deeper understanding
Brian Greene (1:01:39.840)
that comes from the reductionist account of physical law.
Lex Fridman (1:01:42.820)
And there's a lot of insight to come from that,
Brian Greene (1:01:44.840)
such as the freedom that you thought that you had,
Lex Fridman (1:01:48.580)
the freedom of will that you thought you had.
Brian Greene (1:01:50.340)
It doesn't have a basis in that reductionist account,
Lex Fridman (1:01:53.180)
so it's not real.
Lex Fridman (1:01:56.380)
So speaking of the poetry of human experience,
Lex Fridman (1:01:59.060)
you mentioned the images of the black holes.
Lex Fridman (1:02:01.140)
How did it make you feel a few years ago
Lex Fridman (1:02:03.140)
when that first image came out?
Brian Greene (1:02:04.820)
It's truly amazing.
Lex Fridman (1:02:06.300)
A sense of, well, I guess the feeling was both amazing
Lex Fridman (1:02:11.860)
and there was a little sense of,
Lex Fridman (1:02:14.640)
jealousy is not quite the right word,
Lex Fridman (1:02:17.340)
but a sense of longing.
Lex Fridman (1:02:19.540)
Yeah, I think that's a better word,
Brian Greene (1:02:20.920)
because here's a subject that started with Einstein
Lex Fridman (1:02:25.480)
back in 1915, writes down the equations
Brian Greene (1:02:28.520)
of the general theory of relativity,
Lex Fridman (1:02:30.620)
and then there are scores of individuals over the decades,
Brian Greene (1:02:34.820)
starting with people like Karl Schwarzschild
Lex Fridman (1:02:37.500)
who analyze the equations,
Brian Greene (1:02:38.900)
see the possibility of black holes.
Lex Fridman (1:02:40.340)
People develop these ideas.
Brian Greene (1:02:41.620)
John Wheeler, all these greats of physics.
Lex Fridman (1:02:44.140)
It's still a hypothetical subject.
Brian Greene (1:02:46.460)
It gets closer to reality through observations
Lex Fridman (1:02:48.940)
of the center of our galaxy,
Brian Greene (1:02:50.500)
stars whipping around in a manner
Lex Fridman (1:02:52.400)
that could only really be explained
Brian Greene (1:02:54.620)
by there being a black hole in the center of our galaxy,
Lex Fridman (1:02:56.940)
but it was still indirect.
Brian Greene (1:02:58.780)
To actually have a direct image that you can look at,
Lex Fridman (1:03:03.580)
what a beautiful arc, narrative arc
Brian Greene (1:03:06.180)
from the theoretical to the absolutely established.
Lex Fridman (1:03:10.180)
And that's what we hope will happen with other areas,
Lex Fridman (1:03:13.620)
for instance, string theory, right?
Lex Fridman (1:03:15.140)
I mean, wholly mathematical subject at the outset
Lex Fridman (1:03:18.620)
and still pretty much a wholly mathematical subject today.
Lex Fridman (1:03:22.580)
Yeah, do we long for that image
Brian Greene (1:03:25.900)
where we can look at it and say, string, it's real.
Lex Fridman (1:03:29.500)
I mean, how thrilling, how thrilling to be part
Brian Greene (1:03:33.600)
of that journey, to be part of that step
Lex Fridman (1:03:36.420)
that moves things from the abstract to the concrete.
Brian Greene (1:03:39.040)
Yeah, so like the image of the DNA, the early images
Lex Fridman (1:03:44.240)
of the DNA, for example, but there is something special.
Lex Fridman (1:03:47.520)
So the problem with strings is they're tiny.
Lex Fridman (1:03:50.940)
So it's harder to take a picture in the following sense.
Brian Greene (1:03:54.900)
When you think of a black hole, I mean, you have a swirl
Lex Fridman (1:03:58.000)
of, I guess, what is, I don't even know it's dust,
Brian Greene (1:04:00.960)
whatever light.
Lex Fridman (1:04:02.400)
A careening onto the event horizon.
Lex Fridman (1:04:04.560)
And then there's darkness in the center.
Lex Fridman (1:04:06.680)
And you just imagine, so that picture in particular,
Brian Greene (1:04:10.120)
I guess, is of a gigantic black hole.
Lex Fridman (1:04:13.000)
So you just, I mean, it's terrifying.
Brian Greene (1:04:16.160)
Billions of times the mass of the sun.
Lex Fridman (1:04:17.600)
Yeah, so it's both exciting and terrifying.
Brian Greene (1:04:19.880)
I mean, I don't know where you fall in the spectrum.
Lex Fridman (1:04:22.040)
I think it's exciting at first.
Brian Greene (1:04:24.920)
Like the longer I think about it, every time I think
Lex Fridman (1:04:27.040)
about it, the more terrifying it becomes.
Lex Fridman (1:04:29.280)
So it always starts exciting and then it goes to terrifying.
Lex Fridman (1:04:32.760)
And both are feelings, very human feelings
Brian Greene (1:04:36.160)
that I appreciate.
Lex Fridman (1:04:38.360)
It's like terrified awe.
Brian Greene (1:04:40.600)
Somehow it's still beautiful.
Lex Fridman (1:04:43.080)
It's a good way of saying it.
Lex Fridman (1:04:43.920)
And I think I kind of share that reaction
Lex Fridman (1:04:45.960)
because there is a way in which when you work on this
Brian Greene (1:04:49.040)
subject, like all the time, I teach it, I teach about
Lex Fridman (1:04:52.880)
black holes, write the equations on the blackboard.
Brian Greene (1:04:56.800)
The ideas reside in a very cognitive,
Lex Fridman (1:05:01.800)
I don't know, mathematical portion of the brain,
Brian Greene (1:05:06.440)
or at least for me.
Lex Fridman (1:05:08.280)
And it's only when you like sit down and it's quiet
Lex Fridman (1:05:11.920)
and you start to contemplate, wait, wait, wait, wait,
Lex Fridman (1:05:13.680)
this isn't just like a mathematical game.
Brian Greene (1:05:17.160)
There are these monsters out there.
Lex Fridman (1:05:19.400)
Now I don't, not in a sense of I fear for my life,
Lex Fridman (1:05:22.760)
but it's a sense of how extraordinary is this universe.
Lex Fridman (1:05:28.360)
And so it is breathtaking.
Lex Fridman (1:05:30.440)
How powerful nature is.
Lex Fridman (1:05:31.960)
Yeah, how stupendously powerful nature is.
Lex Fridman (1:05:37.280)
And so there is a deep sense of humility
Lex Fridman (1:05:42.120)
that I think this instills if you really allow
Brian Greene (1:05:45.200)
the ideas to sink in.
Lex Fridman (1:05:48.260)
Well, I have to ask about the most stupendously
Brian Greene (1:05:51.440)
powerful thing to have ever happened in our universe,
Lex Fridman (1:05:54.360)
which is the Big Bang.
Lex Fridman (1:05:56.520)
What's up with the Big Bang?
Lex Fridman (1:05:57.880)
So we can, I mean, with gravitational waves,
Brian Greene (1:06:01.360)
the hope is you have more and more accurate measurements
Lex Fridman (1:06:05.040)
of the gravitational waves.
Brian Greene (1:06:06.040)
You can crawl back further and further back in time
Lex Fridman (1:06:08.440)
towards the Big Bang.
Lex Fridman (1:06:10.680)
Do you have a hope that we'll be able to understand
Lex Fridman (1:06:13.440)
the early spark that created our universe?
Brian Greene (1:06:18.080)
Yeah, that and the deep interior of a black hole
Lex Fridman (1:06:23.280)
I think are the biggest mysteries that we hope
Brian Greene (1:06:26.960)
the melding of quantum mechanics and gravity will reveal,
Lex Fridman (1:06:30.720)
will illuminate.
Lex Fridman (1:06:32.440)
And what question could be more captivating
Lex Fridman (1:06:36.960)
than why is there something rather than nothing, right?
Lex Fridman (1:06:39.920)
Why is there a universe at all?
Lex Fridman (1:06:43.240)
And will the theories that we're developing
Lex Fridman (1:06:46.360)
take us to an answer to that?
Lex Fridman (1:06:48.480)
I don't know.
Brian Greene (1:06:49.720)
Even if we truly knew what the Big Bang is,
Lex Fridman (1:06:51.680)
and that's a big question in its own right,
Brian Greene (1:06:53.480)
one would still be left with the question,
Lex Fridman (1:06:55.120)
well, okay, so you've explained the process
Brian Greene (1:06:59.080)
by which a tiny nugget of a universe,
Lex Fridman (1:07:03.560)
a tiny nugget of space time can undergo some kind of growth
Brian Greene (1:07:08.160)
to yield the world around us.
Lex Fridman (1:07:10.080)
But presumably in that explanation,
Brian Greene (1:07:12.920)
you're gonna involve mathematics and some ingredients
Lex Fridman (1:07:16.400)
like quantum fields or matter or energy or something.
Lex Fridman (1:07:21.880)
Where did that stuff come from?
Lex Fridman (1:07:24.680)
Can we get to that level of explanation?
Brian Greene (1:07:26.880)
I don't know, but it is remarkable
Lex Fridman (1:07:29.120)
that if you ask what happened a millionth of a second
Brian Greene (1:07:34.280)
after the Big Bang,
Lex Fridman (1:07:36.040)
it's not really that controversial any longer, right?
Brian Greene (1:07:40.240)
Even though there's a lot of argument in the field
Lex Fridman (1:07:42.760)
and it's very heated right now I should say
Lex Fridman (1:07:45.400)
regarding what is the right theory of the Big Bang?
Lex Fridman (1:07:49.920)
What is the right theory of early universe cosmology
Brian Greene (1:07:53.440)
where I mean early, much earlier
Lex Fridman (1:07:55.000)
than a millionth of a second,
Brian Greene (1:07:56.040)
a lot of dissent, a lot of heated arguments about that.
Lex Fridman (1:08:01.680)
No pun intended.
Brian Greene (1:08:02.680)
Yeah, right, exactly.
Lex Fridman (1:08:04.280)
But you go like a millionth of a second after that
Lex Fridman (1:08:08.160)
and we're on pretty firm ground.
Lex Fridman (1:08:10.080)
Isn't that amazing, right?
Brian Greene (1:08:12.160)
To understand what happened from that point forward.
Lex Fridman (1:08:15.400)
But to go back is controversial.
Lex Fridman (1:08:18.240)
So there is this theory called inflationary cosmology,
Lex Fridman (1:08:21.600)
which I would say has been the dominant paradigm
Brian Greene (1:08:24.560)
since early 1980s.
Lex Fridman (1:08:27.120)
So what does that mean?
Brian Greene (1:08:27.960)
Roughly 40 years now,
Lex Fridman (1:08:28.920)
it's been the dominant cosmological paradigm.
Lex Fridman (1:08:31.400)
And it makes use of a curious feature
Lex Fridman (1:08:33.760)
of Einstein's general theory of relativity,
Brian Greene (1:08:36.000)
his theory of gravity,
Lex Fridman (1:08:37.240)
where Einstein shows us mathematically
Brian Greene (1:08:39.800)
that gravity can not only be attractive,
Lex Fridman (1:08:41.840)
the kind of gravity that we're used to,
Brian Greene (1:08:43.280)
things pulled together, but it can also be repulsive.
Lex Fridman (1:08:47.400)
And that fact is then leveraged by people like Alan Guth
Lex Fridman (1:08:53.200)
and Andre Linde, and at the time Paul Steinhardt
Lex Fridman (1:08:56.240)
and Andreas Albrecht and others to say,
Brian Greene (1:08:58.760)
okay, if we had a little nugget in the earlier universe,
Lex Fridman (1:09:01.400)
which was filled with the stuff
Brian Greene (1:09:03.520)
that yields this repulsive gravity,
Lex Fridman (1:09:05.520)
well, that would have blown everything apart.
Brian Greene (1:09:07.360)
It would cause everything to swell.
Lex Fridman (1:09:09.160)
Beautiful explanation for what the bang
Brian Greene (1:09:11.400)
in the big bang was.
Lex Fridman (1:09:13.040)
And then people mathematically analyze the consequences
Brian Greene (1:09:16.760)
of this idea and they make predictions
Lex Fridman (1:09:19.040)
for tiny temperature differences across the night sky
Brian Greene (1:09:22.680)
that in principle could be measured.
Lex Fridman (1:09:24.840)
You send up balloons, you send up satellites
Brian Greene (1:09:27.120)
with very refined thermometers,
Lex Fridman (1:09:29.920)
and they measured the temperature of the night sky
Lex Fridman (1:09:33.000)
and the statistical distribution
Lex Fridman (1:09:34.800)
of the temperature differences agrees
Brian Greene (1:09:36.440)
with the mathematical predictions.
Lex Fridman (1:09:39.920)
I mean, you just sort of have to stand in awe
Brian Greene (1:09:43.200)
of this insight.
Lex Fridman (1:09:44.560)
So you think, aha, the theory has been established,
Lex Fridman (1:09:48.320)
but scientists are an incredibly skeptical bunch.
Lex Fridman (1:09:54.200)
And some scientists, including one of the people
Brian Greene (1:09:56.640)
who helped develop the theory at the outset,
Lex Fridman (1:09:58.360)
Paul Steinhardt comes along and says,
Brian Greene (1:10:00.960)
well, yeah, this theory has done pretty well so far,
Lex Fridman (1:10:04.120)
but there are aspects of this theory
Brian Greene (1:10:06.480)
that are making me lose confidence.
Lex Fridman (1:10:08.160)
For instance, this theory seems to suggest
Brian Greene (1:10:10.880)
that there might be other universes.
Lex Fridman (1:10:13.360)
Like, how do you make sense of a theory
Lex Fridman (1:10:15.280)
that suggests there are other universes?
Lex Fridman (1:10:16.880)
Or there are others who come along and say,
Brian Greene (1:10:18.920)
this theory seems to talk about length scales
Lex Fridman (1:10:23.240)
that are minuscule even by the so called Planck length,
Brian Greene (1:10:26.680)
the sort of shortest length that we can imagine
Lex Fridman (1:10:29.360)
making sense of in a theory of quantum gravity.
Lex Fridman (1:10:31.840)
How do you make sense of that?
Lex Fridman (1:10:33.440)
And so on and so forth, they develop a list of things
Brian Greene (1:10:36.720)
that they consider to be chinks
Lex Fridman (1:10:38.560)
in the inflationary cosmological theory's armor.
Lex Fridman (1:10:42.600)
And they develop other ideas,
Lex Fridman (1:10:44.120)
which they claim yield the same predictions
Brian Greene (1:10:47.560)
as inflationary cosmology
Lex Fridman (1:10:48.640)
for those temperature differences across space,
Lex Fridman (1:10:50.440)
but don't suffer from these problems.
Lex Fridman (1:10:52.840)
And then the inflationary cosmology folks say,
Brian Greene (1:10:55.160)
no, no, no, hang on.
Lex Fridman (1:10:56.720)
Your theory suffers from different problems.
Lex Fridman (1:10:59.920)
And so the arguments goes, it's a healthy debate.
Lex Fridman (1:11:02.600)
Talk about real debates in science.
Lex Fridman (1:11:05.120)
So when you ask what's up with the Big Bang,
Lex Fridman (1:11:07.800)
I don't know right now.
Brian Greene (1:11:09.920)
If you would have asked me five years ago,
Lex Fridman (1:11:12.760)
maybe even less than that, three or four years ago,
Brian Greene (1:11:15.160)
I've said, look, inflationary cosmology has some issues,
Lex Fridman (1:11:19.080)
but the package of explanations it provides is so potent
Lex Fridman (1:11:23.560)
and the issues that beset it are seemingly solvable to me
Lex Fridman (1:11:29.080)
that I would imagine it's going to in the end, win out.
Brian Greene (1:11:32.920)
I would still say that today,
Lex Fridman (1:11:34.200)
but I wouldn't say it as loudly.
Brian Greene (1:11:36.200)
I wouldn't say it as confidently.
Lex Fridman (1:11:38.800)
I think it's worth thinking about alternate ideas
Lex Fridman (1:11:42.120)
and it could be the case that the paradigm
Lex Fridman (1:11:44.280)
at some point shifts.
Brian Greene (1:11:46.840)
Does dark matter and dark energy fit into the shifting
Lex Fridman (1:11:50.480)
of the explanations for those?
Brian Greene (1:11:52.520)
Yeah, certainly.
Lex Fridman (1:11:53.360)
So dark energy has in the inflationary theory
Brian Greene (1:11:58.440)
is kind of a big mystery.
Lex Fridman (1:12:00.200)
So dark energy is the observational realization
Brian Greene (1:12:05.600)
in the last 20 years
Lex Fridman (1:12:06.800)
that not only is the universe expanding,
Brian Greene (1:12:09.440)
it's expanding ever more quickly.
Lex Fridman (1:12:11.520)
Something is still pushing things outward.
Lex Fridman (1:12:15.080)
And the explanation is that there's like a residual version
Lex Fridman (1:12:18.320)
of the repulsive gravity from the early universe,
Lex Fridman (1:12:20.560)
but it's such a strange number.
Lex Fridman (1:12:23.000)
When you write that amount of dark energy
Brian Greene (1:12:25.600)
using the relevant units in a theory of quantum gravity,
Lex Fridman (1:12:29.080)
it's a decimal point followed by like 120 zeros
Lex Fridman (1:12:33.040)
and then a one.
Lex Fridman (1:12:34.640)
We're not used to those kinds of numbers in physics.
Brian Greene (1:12:38.280)
We're used to a half, one, pi, e squared to two.
Lex Fridman (1:12:44.960)
Those are the kinds of fundamental numbers
Brian Greene (1:12:46.720)
that emerge in our explanations of the world.
Lex Fridman (1:12:49.840)
And we look at this bizarre number,
Brian Greene (1:12:51.920)
decimal point, all these zeros and a one,
Lex Fridman (1:12:53.720)
we say something's wrong there.
Lex Fridman (1:12:56.200)
Like where would that number have come from?
Lex Fridman (1:12:59.600)
And now there are people who suggest resolution to it.
Lex Fridman (1:13:01.800)
So it's not like we're totally in the dark on it,
Lex Fridman (1:13:03.600)
but those people like Paul Steinhard
Brian Greene (1:13:06.680)
who have alternate cosmological theories,
Lex Fridman (1:13:09.120)
cyclic cosmologies as they call it,
Brian Greene (1:13:11.160)
claim that they have a more natural explanation
Lex Fridman (1:13:14.480)
of the dark energy,
Brian Greene (1:13:15.880)
that it naturally feeds into a cyclical process
Lex Fridman (1:13:19.360)
that is their cosmological paradigm.
Lex Fridman (1:13:22.760)
So yeah, if the cosmology should change,
Lex Fridman (1:13:26.240)
it's conceivable our view of dark energy
Brian Greene (1:13:29.200)
may change from deeply mysterious
Lex Fridman (1:13:31.480)
to deeply integrated into a different paradigm.
Brian Greene (1:13:34.240)
That is possible.
Lex Fridman (1:13:35.560)
I think it's Roger Penrose that think
Brian Greene (1:13:37.440)
that information can bleed through
Lex Fridman (1:13:39.480)
from before the Big Bang to the after the Big Bang.
Brian Greene (1:13:42.440)
Is the Big Bang like a full erasure of the hard drive
Lex Fridman (1:13:46.880)
or is there some information that could bleed through?
Brian Greene (1:13:48.920)
Yeah, I mean, so Roger is among the most creative thinkers
Lex Fridman (1:13:54.040)
of the last 100 years,
Brian Greene (1:13:55.760)
rightly won the Nobel Prize for his insights
Lex Fridman (1:13:59.280)
into singularities in space time
Brian Greene (1:14:02.000)
that we know to afflict our mathematical solutions
Lex Fridman (1:14:06.480)
of black holes in the Big Bang and so forth.
Lex Fridman (1:14:08.120)
And he has an enormously fertile imagination.
Lex Fridman (1:14:13.400)
And I mean that in the most positive sense.
Lex Fridman (1:14:16.320)
And so he has put forward this idea,
Lex Fridman (1:14:19.640)
this conformal cyclic cosmology,
Brian Greene (1:14:21.880)
I think is the official title,
Lex Fridman (1:14:23.760)
although I could be getting that wrong.
Brian Greene (1:14:26.280)
I can't say that I've studied it.
Lex Fridman (1:14:27.920)
I have seen lectures on it.
Brian Greene (1:14:30.280)
I don't find it convincing as yet.
Lex Fridman (1:14:33.240)
It feels like it's being built to find a solution
Brian Greene (1:14:38.720)
as opposed to sort of more naturally emerging.
Lex Fridman (1:14:42.200)
Maybe Roger would say otherwise.
Lex Fridman (1:14:43.920)
And I don't mean to in any way
Lex Fridman (1:14:47.040)
cast aspersions on the work.
Brian Greene (1:14:48.440)
It's vital and interesting and people are thinking about it.
Lex Fridman (1:14:51.400)
I don't consider it as close a competitor
Brian Greene (1:14:55.400)
to say the inflationary theory as for instance,
Lex Fridman (1:14:58.080)
the stuff that Paul Steinhardt has put forward.
Lex Fridman (1:15:00.840)
But again, you've got to keep an open mind
Lex Fridman (1:15:04.120)
in this business when there's so much
Brian Greene (1:15:06.320)
that we don't yet understand.
Lex Fridman (1:15:07.680)
I mean, it is wild to think
Brian Greene (1:15:08.800)
that information could survive something like that.
Lex Fridman (1:15:10.880)
Just like it is wild to imagine
Brian Greene (1:15:13.320)
that information could escape a black hole, for example.
Lex Fridman (1:15:16.560)
It just seems like by construction,
Brian Greene (1:15:20.160)
these things are supposed to not bleed out anything.
Lex Fridman (1:15:24.160)
But one of the challenges in all of these theories
Brian Greene (1:15:25.840)
is when we talk about a singularity,
Lex Fridman (1:15:27.640)
has this real sexy term, the singularity.
Lex Fridman (1:15:30.200)
But a singularity is in more ordinary language,
Lex Fridman (1:15:35.560)
a physical system where the mathematics breaks down.
Brian Greene (1:15:39.760)
It's nonsensical.
Lex Fridman (1:15:41.080)
It's like taking one divided by zero.
Lex Fridman (1:15:42.800)
You put that into a calculator and it says E error, right?
Lex Fridman (1:15:45.640)
It does not make sense, doesn't compute.
Lex Fridman (1:15:48.240)
And so it's very hard to make definitive statements
Lex Fridman (1:15:53.240)
about things like the Big Bang or about black holes
Brian Greene (1:15:56.160)
until we cure the mathematical singularities.
Lex Fridman (1:15:59.840)
And there are some who claim that in certain regimes,
Brian Greene (1:16:03.160)
the singularities have been cured.
Lex Fridman (1:16:05.800)
I don't by any means think that there's consensus
Brian Greene (1:16:08.560)
on these ideas.
Lex Fridman (1:16:09.560)
So when one talks about information sort of bleeding
Brian Greene (1:16:12.560)
through the Big Bang, you've really got to make sure
Lex Fridman (1:16:15.000)
that the equations have no singularity.
Brian Greene (1:16:16.840)
You talk about cyclic cosmology,
Lex Fridman (1:16:18.240)
you've got to make sure that the equations
Brian Greene (1:16:20.040)
don't have any singularities as you go from, say,
Lex Fridman (1:16:22.080)
one cycle to the next.
Brian Greene (1:16:23.680)
Now, some of the proponents of these theories claim
Lex Fridman (1:16:25.640)
that they have resolved these issues.
Brian Greene (1:16:27.520)
I don't think that there's a general sense
Lex Fridman (1:16:30.160)
that that is the case as yet, but it could be that,
Brian Greene (1:16:32.920)
look, life is so short that I haven't had the time
Lex Fridman (1:16:36.360)
to deeply delve into all the mathematical intricacies
Brian Greene (1:16:39.000)
of all the ideas that have been put forward.
Lex Fridman (1:16:40.760)
If I did that, I'd never do anything else.
Lex Fridman (1:16:42.720)
But that's what the issue is.
Lex Fridman (1:16:44.200)
And of course, it's just math.
Brian Greene (1:16:45.880)
There may be holes.
Lex Fridman (1:16:47.240)
There may be gaps in our understanding
Brian Greene (1:16:52.920)
in the way we're modeling physical reality.
Lex Fridman (1:16:55.160)
Well, that's the point.
Brian Greene (1:16:56.000)
In fact, when you said, I was about to jump in
Lex Fridman (1:16:57.480)
and say modeling, but you got there first,
Lex Fridman (1:16:59.360)
and it's exactly the right point.
Lex Fridman (1:17:02.000)
We're talking about the universe here, right?
Lex Fridman (1:17:04.640)
And how do you talk about the universe
Lex Fridman (1:17:06.960)
with a straight face, mathematically?
Lex Fridman (1:17:09.000)
And the way you do it is you simplify,
Lex Fridman (1:17:12.080)
you throw away those characteristics of the universe
Brian Greene (1:17:14.680)
that you don't think are vital to a full understanding.
Lex Fridman (1:17:18.520)
And so we're gonna get to a point people are starting to
Brian Greene (1:17:21.560)
where we've got to go beyond those simplifications.
Lex Fridman (1:17:24.800)
And so cosmology has for a long time modeled the universe
Brian Greene (1:17:29.360)
in the most simplest terms, homogeneous, isotropic.
Lex Fridman (1:17:33.320)
It has just a few parameters that describe it,
Brian Greene (1:17:35.920)
the average density of mass and energy and so forth.
Lex Fridman (1:17:38.560)
We have to go beyond those simplifications,
Lex Fridman (1:17:40.360)
and that will require putting these things on computers.
Lex Fridman (1:17:43.400)
We're not gonna be able to do calculations there.
Lex Fridman (1:17:45.200)
So much as astrophysics has gone beyond many simplifications
Lex Fridman (1:17:49.640)
to now give really detailed simulations of star systems
Lex Fridman (1:17:53.280)
and galaxies and so forth,
Lex Fridman (1:17:54.880)
we're gonna have to do that with cosmology,
Lex Fridman (1:17:56.880)
and people are starting to do that today.
Lex Fridman (1:17:59.120)
Yeah, I've seen some interesting work on simulation,
Brian Greene (1:18:02.880)
most simulation cosmology, by the way, is just awesome.
Lex Fridman (1:18:05.760)
But just like simulation of the early formation
Brian Greene (1:18:08.720)
of our solar system to understand how the like the Oort cloud
Lex Fridman (1:18:12.960)
and just, I don't know, the whole of it,
Lex Fridman (1:18:16.520)
how Earth came to be, like how Jupiter just protects us.
Lex Fridman (1:18:22.600)
And then there's like weird like moons and volcanoes
Lex Fridman (1:18:28.160)
and like modeling all of that,
Lex Fridman (1:18:30.600)
the formation of all of that is fascinating.
Brian Greene (1:18:34.440)
Because that naturally is the question
Lex Fridman (1:18:37.120)
of how does life emerge on these kinds of rocks?
Lex Fridman (1:18:41.200)
How does a rock become a rabbit?
Lex Fridman (1:18:44.520)
But speaking of models,
Brian Greene (1:18:47.440)
there's an equation called the Drake equation.
Lex Fridman (1:18:50.360)
We were talking about life.
Brian Greene (1:18:52.720)
Have to ask, at the highest level first,
Lex Fridman (1:18:56.360)
when you look out there,
Lex Fridman (1:18:58.040)
how many alien civilizations do you think are out there?
Lex Fridman (1:19:01.240)
Well, zero, one, or many?
Lex Fridman (1:19:04.640)
So if you say civilization,
Lex Fridman (1:19:08.200)
I would bring my number way down.
Brian Greene (1:19:12.480)
It could be zero.
Lex Fridman (1:19:15.000)
If you talk about life, I think it could be many.
Brian Greene (1:19:20.520)
As we were saying before,
Lex Fridman (1:19:21.800)
I think the move from life to consciousness,
Brian Greene (1:19:25.840)
the kinds of beings that would build
Lex Fridman (1:19:27.480)
what we would recognize as a civilization,
Brian Greene (1:19:30.720)
that may be extraordinarily rare.
Lex Fridman (1:19:34.240)
I hope it's not.
Brian Greene (1:19:36.080)
You know, as a kid, I loved Star Trek.
Lex Fridman (1:19:38.080)
I just loved the idea that we would be part
Brian Greene (1:19:40.560)
of some universal community where,
Lex Fridman (1:19:43.680)
look, experience on planet Earth
Brian Greene (1:19:46.000)
suggests it doesn't always go so well
Lex Fridman (1:19:48.120)
when groups who are separated try to come together
Lex Fridman (1:19:50.880)
and live in some larger collective.
Lex Fridman (1:19:53.760)
But again, as an optimist,
Lex Fridman (1:19:55.920)
how amazing would it be to converse
Lex Fridman (1:19:57.920)
with an alien civilization and learn
Lex Fridman (1:19:59.800)
what they've figured out about physics and cosmology
Lex Fridman (1:20:03.600)
and compare notes and learn from each other
Lex Fridman (1:20:06.960)
in some wonderful way?
Lex Fridman (1:20:09.280)
I love that idea.
Lex Fridman (1:20:10.480)
But if you ask me the likelihood of it,
Lex Fridman (1:20:13.800)
I would err on saying it may be so improbable
Brian Greene (1:20:18.560)
that the conditions conspire to allow life
Lex Fridman (1:20:21.680)
to move to this place of consciousness
Brian Greene (1:20:24.680)
that it might be rare.
Lex Fridman (1:20:27.120)
It might be oversimplifying things,
Lex Fridman (1:20:28.640)
but just observing the power of the evolutionary process,
Lex Fridman (1:20:32.560)
I tend to believe,
Lex Fridman (1:20:34.360)
and like you read different theories of how we went,
Lex Fridman (1:20:40.640)
how Homo sapiens evolved,
Brian Greene (1:20:43.200)
it seems like the evolutionary process
Lex Fridman (1:20:45.560)
naturally leads to Homo sapiens
Brian Greene (1:20:50.040)
or creatures like that or much better than that.
Lex Fridman (1:20:53.200)
So to me, there's several scary scenarios.
Brian Greene (1:20:57.320)
So, okay, the positive scenario
Lex Fridman (1:21:00.760)
is life itself is really difficult.
Lex Fridman (1:21:03.240)
So that origin of life is difficult.
Lex Fridman (1:21:05.840)
That's exciting for many reasons
Brian Greene (1:21:08.040)
because we might be able to prove that wrong easily
Lex Fridman (1:21:12.520)
in the near term by finding life elsewhere.
Brian Greene (1:21:14.760)
Sure.
Lex Fridman (1:21:15.920)
The scary thing to me is if life is easy
Lex Fridman (1:21:21.320)
and there's plenty of conscious intelligent civilizations
Lex Fridman (1:21:26.120)
out there and we have not obviously made contact,
Brian Greene (1:21:30.600)
which means with intelligence and consciousness
Lex Fridman (1:21:33.320)
comes responsibility and ultimately destruction.
Lex Fridman (1:21:39.920)
So with power comes great responsibility
Lex Fridman (1:21:42.840)
and then we end up destroying ourselves.
Brian Greene (1:21:44.760)
That's the scariest.
Lex Fridman (1:21:48.120)
The positive, I guess, version is that
Brian Greene (1:21:51.280)
maybe we're being watched,
Lex Fridman (1:21:54.280)
sort of like there's a transition
Brian Greene (1:21:57.200)
to where you don't wanna ruin the primitive villages
Lex Fridman (1:22:00.720)
out there and so there's a protective layer around us.
Brian Greene (1:22:04.600)
They're watching.
Lex Fridman (1:22:06.600)
So where do you in these possible explanations
Brian Greene (1:22:09.520)
to the Fermi paradox,
Lex Fridman (1:22:10.520)
why haven't we contacted aliens?
Lex Fridman (1:22:12.240)
Do you land on?
Lex Fridman (1:22:13.600)
Well, I think the most straightforward explanation
Brian Greene (1:22:17.720)
is that there aren't any.
Lex Fridman (1:22:20.320)
Now, there are many other explanations too.
Lex Fridman (1:22:23.160)
So you can't be dogmatic about things
Lex Fridman (1:22:25.560)
that are just sort of gut feel,
Lex Fridman (1:22:27.640)
but one of my favorite Twilight Zone episodes,
Lex Fridman (1:22:31.800)
I don't know if you ever saw this one
Brian Greene (1:22:33.280)
where this alien civilization finally comes
Lex Fridman (1:22:36.280)
to planet Earth and gives us this book
Brian Greene (1:22:39.280)
that they really want us to have and to hold
Lex Fridman (1:22:42.680)
and it's in this foreign language,
Brian Greene (1:22:44.760)
you don't understand it.
Lex Fridman (1:22:45.600)
The cryptographers, they desperately try to decipher it
Brian Greene (1:22:49.120)
as humans are gonna visit this other alien planet
Lex Fridman (1:22:52.480)
and they're all sending back postcards,
Lex Fridman (1:22:53.720)
how wonderful it is and so forth
Lex Fridman (1:22:55.240)
and they finally decipher the title.
Brian Greene (1:22:58.560)
It's To Serve Man and everyone's so thrilled,
Lex Fridman (1:23:01.480)
oh, they're here to serve us, it all makes sense
Lex Fridman (1:23:03.680)
and then just as one of the final cryptographers
Lex Fridman (1:23:06.240)
is going on to the alien ship,
Brian Greene (1:23:08.160)
his helper runs and says,
Lex Fridman (1:23:10.880)
I've deciphered the rest of the book.
Brian Greene (1:23:12.960)
To Serve Man, it's a cookbook.
Lex Fridman (1:23:14.920)
So yeah, is that a possibility?
Brian Greene (1:23:20.920)
Sure.
Lex Fridman (1:23:21.760)
And so could they be watching us
Lex Fridman (1:23:23.960)
and just sort of waiting for us to get
Lex Fridman (1:23:26.040)
to a mature enough level?
Brian Greene (1:23:29.680)
I don't know, it strikes me.
Lex Fridman (1:23:31.120)
Well, I think it'd be better to have this conversation
Brian Greene (1:23:33.440)
after the James Webb Telescope.
Lex Fridman (1:23:35.040)
I mean, I do think that if we look
Brian Greene (1:23:38.440)
at the atmospheres of many planets,
Lex Fridman (1:23:41.360)
I mean, there's now an estimate now
Brian Greene (1:23:42.520)
that there's on order of one planet per star on average.
Lex Fridman (1:23:48.000)
So we've long known that the galaxy,
Brian Greene (1:23:50.760)
hundreds of billions of stars,
Lex Fridman (1:23:52.800)
numbers of galaxies, hundreds of billions of galaxies.
Lex Fridman (1:23:54.800)
So we're talking about hundreds of billions
Lex Fridman (1:23:56.680)
of hundreds of billions of planets, oh my.
Lex Fridman (1:23:59.040)
And if we start to survey some of these planets
Lex Fridman (1:24:02.320)
and one after the other after the other,
Brian Greene (1:24:03.840)
we just sort of find no evidence
Lex Fridman (1:24:06.360)
for any of the biological markers.
Brian Greene (1:24:10.400)
It could be, of course,
Lex Fridman (1:24:11.320)
maybe life takes a radically different form.
Brian Greene (1:24:13.840)
It'd be hard to know that.
Lex Fridman (1:24:15.400)
But I think that would at least give us some insight
Brian Greene (1:24:18.280)
on the life question.
Lex Fridman (1:24:19.360)
But I just don't see how we get insight
Brian Greene (1:24:21.960)
on the civilization or consciousness question
Lex Fridman (1:24:25.120)
without the direct connection.
Lex Fridman (1:24:27.560)
And it strikes me that if consciousness is ubiquitous,
Lex Fridman (1:24:32.560)
let's say life is, I'm willing to grant that.
Brian Greene (1:24:35.080)
If consciousness is also ubiquitous,
Lex Fridman (1:24:37.280)
then I don't understand why they haven't been here
Brian Greene (1:24:41.680)
or why there hasn't been separation
Lex Fridman (1:24:43.520)
because presumably they should be much further ahead of us.
Lex Fridman (1:24:47.920)
How unlike would it be that we're like,
Lex Fridman (1:24:50.200)
of all consciousness in the universe,
Brian Greene (1:24:52.120)
we're the most advanced.
Lex Fridman (1:24:53.520)
That'd be such a special place for human beings
Brian Greene (1:24:56.960)
that it's hard for me to grant that as a likely possibility.
Lex Fridman (1:25:00.160)
Rather, I think we're kind of run of the mill.
Lex Fridman (1:25:02.680)
And there are many who are far more advanced than us.
Lex Fridman (1:25:06.000)
And I don't think that they would expend the energy
Brian Greene (1:25:09.080)
to hide themselves.
Lex Fridman (1:25:11.360)
I don't think they care enough.
Lex Fridman (1:25:12.800)
And so see, that's actually what I believe
Lex Fridman (1:25:15.880)
that there's a very large number of civilizations
Brian Greene (1:25:19.160)
that are far more advanced than us.
Lex Fridman (1:25:21.440)
But my sense is that humans are exceptionally limited
Brian Greene (1:25:25.200)
both in our direct sensory capabilities and our physics,
Lex Fridman (1:25:29.280)
our tools of sensing that just like with the string theory
Lex Fridman (1:25:33.240)
and the multiple dimensions, we're just not like,
Lex Fridman (1:25:36.520)
it's like, I honestly believe there could be stuff
Brian Greene (1:25:39.040)
in front of our nose that we're just not seeing
Lex Fridman (1:25:43.720)
because we're too dumb, too much hubris
Lex Fridman (1:25:48.720)
and I mean, there's a bunch of stuff
Lex Fridman (1:25:50.920)
and too ignorant to the fabric of reality,
Brian Greene (1:25:54.920)
all of those things.
Lex Fridman (1:25:56.280)
We're young in terms of intelligence.
Lex Fridman (1:25:59.840)
But I guess what I'd say is like, I'm on board
Lex Fridman (1:26:01.880)
with all of that as a real possibility,
Lex Fridman (1:26:04.120)
but then it does strike me that we are sufficiently
Lex Fridman (1:26:09.440)
able to observe the unit.
Brian Greene (1:26:11.760)
Look, we can look back to a fraction of the duration
Lex Fridman (1:26:16.760)
from here to the, just a fraction is left
Brian Greene (1:26:20.040)
that we are unable to see.
Lex Fridman (1:26:22.680)
So however young we are, we have been able
Brian Greene (1:26:27.320)
to sort of pierce the universe and it just strikes me
Lex Fridman (1:26:29.960)
that there would be some signature,
Lex Fridman (1:26:33.280)
but maybe that's coming.
Lex Fridman (1:26:35.240)
But look, having said that I do, look,
Brian Greene (1:26:38.080)
I certainly note the fact that it's rare
Lex Fridman (1:26:41.560)
that I stoop down while walking in Manhattan
Lex Fridman (1:26:46.120)
and sort of dig up some ants in the bushes
Lex Fridman (1:26:48.920)
on the side of the street and talk to the ants, right?
Brian Greene (1:26:51.520)
Because it's just not interesting to me.
Lex Fridman (1:26:52.960)
So if we're like the ants on the cosmological landscape,
Brian Greene (1:26:56.080)
then yeah, I can imagine that the super advanced aliens
Lex Fridman (1:26:58.760)
would be like, like whoever, you know,
Lex Fridman (1:27:01.960)
but I feel like we're sufficiently advanced
Lex Fridman (1:27:04.320)
that there should be some signal signature of that,
Lex Fridman (1:27:07.200)
but maybe it's coming.
Lex Fridman (1:27:08.320)
I think the deeper fundamental problem between us
Lex Fridman (1:27:10.680)
and the ants is that we don't have a common language.
Lex Fridman (1:27:12.760)
It's not the interest.
Brian Greene (1:27:14.600)
It's that we don't even have a common language.
Lex Fridman (1:27:17.280)
And so the alien civilizations don't even know how to,
Brian Greene (1:27:21.840)
like we humans have convinced ourselves we're special
Lex Fridman (1:27:24.720)
because we developed the language.
Lex Fridman (1:27:25.880)
And you talked about the importance of language
Lex Fridman (1:27:28.760)
to the intelligence, but it makes you wonder
Brian Greene (1:27:31.640)
like how very niche is that like club that we've,
Lex Fridman (1:27:36.360)
like tribe we've created of language
Lex Fridman (1:27:38.440)
and linguistic type of systems that are very specific
Lex Fridman (1:27:41.480)
to our particular kinds of brains
Lex Fridman (1:27:42.880)
and we share ideas together are all super excited
Lex Fridman (1:27:45.240)
that we can understand the universe
Brian Greene (1:27:46.520)
because we came up with some notation and math.
Lex Fridman (1:27:49.320)
I wonder if there's some totally other kinds of language
Brian Greene (1:27:52.440)
that communicates on a different timescale
Lex Fridman (1:27:54.440)
with different, very different mechanisms
Brian Greene (1:27:56.840)
in the space of information that just is not,
Lex Fridman (1:28:00.080)
it's everything, everything is lost in translation.
Brian Greene (1:28:03.200)
Yeah, and it could well be as a look.
Lex Fridman (1:28:05.120)
I mean, I think part of the reason I go
Brian Greene (1:28:07.800)
toward the possibility of the soul intelligence
Lex Fridman (1:28:12.840)
is there's a certain kind of romantic appeal
Brian Greene (1:28:16.400)
to looking out in the cosmos and it's just quiet
Lex Fridman (1:28:20.800)
and it's just eternal silence.
Brian Greene (1:28:22.520)
There's something that appeals to me
Lex Fridman (1:28:25.320)
at an emotional level that way.
Lex Fridman (1:28:27.840)
But yeah, I mean, nobody knows.
Lex Fridman (1:28:31.680)
And it's certainly conceivable
Brian Greene (1:28:35.480)
that there's just a radical mismatch
Lex Fridman (1:28:38.640)
between the kinds of things
Brian Greene (1:28:40.040)
that we are able to observe and sensitive to
Lex Fridman (1:28:42.840)
versus the kinds of structures that permeate the universe
Brian Greene (1:28:47.160)
in a manner that simply we're unable to detect.
Lex Fridman (1:28:50.400)
Well, if we are alone, that is exciting.
Lex Fridman (1:28:54.000)
And one of the ways it's exciting
Lex Fridman (1:28:56.560)
is that it's up to us to become,
Brian Greene (1:29:00.280)
to expand out into the universe,
Lex Fridman (1:29:02.760)
to permeate consciousness out into the universe.
Lex Fridman (1:29:07.760)
So that's where space exploration comes in.
Lex Fridman (1:29:09.960)
Let me ask you as somebody who's a screen theorist,
Brian Greene (1:29:12.440)
a physicist, do you think space exploration,
Lex Fridman (1:29:17.120)
a colonizing space is a physics or an engineering problem?
Lex Fridman (1:29:21.440)
What would you say?
Lex Fridman (1:29:22.280)
Yeah, I think it's fundamentally an engineering problem
Brian Greene (1:29:25.440)
if we're not trying to do things like build wormholes
Lex Fridman (1:29:30.440)
the way they did, say an interstellar
Brian Greene (1:29:32.960)
to get to a different place
Lex Fridman (1:29:34.160)
or trying to travel near the speed of light
Lex Fridman (1:29:36.880)
so that we would actually be able
Lex Fridman (1:29:38.360)
to traverse interstellar distances.
Brian Greene (1:29:40.120)
I mean, without that,
Lex Fridman (1:29:41.800)
our colonization will happen in a very, very slow rate.
Lex Fridman (1:29:47.920)
But one of the beauties of relativity
Lex Fridman (1:29:50.400)
is if you do travel near the speed of light,
Brian Greene (1:29:51.920)
you can actually go arbitrarily far in a human lifetime.
Lex Fridman (1:29:56.000)
People say, how's that possible?
Brian Greene (1:29:57.120)
You can't go billions of light years.
Lex Fridman (1:29:59.120)
Billions of light years, well, you can actually,
Brian Greene (1:30:01.720)
because as you can do the speed of light,
Lex Fridman (1:30:03.440)
the way in which space and time change
Brian Greene (1:30:06.080)
allows you to go in principle arbitrarily far.
Lex Fridman (1:30:08.640)
That's very exciting.
Lex Fridman (1:30:09.960)
But if we put that physics side of the issue
Lex Fridman (1:30:13.640)
and the manipulation of space and time to the side,
Brian Greene (1:30:15.960)
yeah, I think it's a deep engineering problem.
Lex Fridman (1:30:18.360)
How do you terraform other planets?
Brian Greene (1:30:21.680)
I mean, how do you go beyond our local neighborhood,
Lex Fridman (1:30:26.680)
say without using the ideas of relativity?
Lex Fridman (1:30:30.320)
So I think it's all quite exciting.
Lex Fridman (1:30:32.080)
And I think the idea is using solar sails
Brian Greene (1:30:34.920)
that people have developed
Lex Fridman (1:30:36.680)
and trying to take that first step to Mars,
Brian Greene (1:30:40.720)
I think that's a vital and valuable step to take.
Lex Fridman (1:30:43.960)
But yeah, I think these are
Brian Greene (1:30:44.800)
fundamentally engineering challenges.
Lex Fridman (1:30:46.320)
Or extending the human lifespan through biology research
Brian Greene (1:30:49.440)
or maybe reducing what it means to be a human being
Lex Fridman (1:30:54.440)
into information and uploading certain parts of it.
Brian Greene (1:30:57.720)
Maybe not all of the full resolution of a human life,
Lex Fridman (1:31:00.920)
but maybe the essential things like the DNA
Lex Fridman (1:31:03.920)
and be able to reconstruct that human being.
Lex Fridman (1:31:07.920)
But I have to ask about Mars.
Lex Fridman (1:31:12.600)
Do you find the dream of humans stepping on Mars,
Lex Fridman (1:31:17.520)
stepping foot first, but also colonizing Mars,
Lex Fridman (1:31:20.820)
one that's worth us fighting for?
Lex Fridman (1:31:25.020)
Yeah, usually so.
Brian Greene (1:31:25.980)
I mean, I think what we have long been
Lex Fridman (1:31:28.500)
not always in the best way is a species of explorers
Brian Greene (1:31:33.900)
in the literal sense of traveling
Lex Fridman (1:31:37.020)
from one part of the world to another,
Brian Greene (1:31:39.540)
or in the more metaphorical sense
Lex Fridman (1:31:41.340)
of trying to travel through our minds to the quantum realm
Brian Greene (1:31:45.100)
or back to the Big Bang or to the center of black holes.
Lex Fridman (1:31:47.740)
So I think that's fundamentally part of the human spirit.
Lex Fridman (1:31:51.460)
So I do think that's a vital part of our heritage
Lex Fridman (1:31:56.860)
brought forward into its next incarnation.
Brian Greene (1:32:01.020)
That's who we are.
Lex Fridman (1:32:03.740)
Do you think there'll be a day in the future
Brian Greene (1:32:06.860)
where a human being is born on Mars
Lex Fridman (1:32:11.300)
and has to learn about his or her human origins on Earth?
Brian Greene (1:32:16.300)
Like, they'll have to read in a book.
Lex Fridman (1:32:18.860)
Yeah, I don't think it'll be a book at that stage.
Brian Greene (1:32:20.420)
It'll probably just be uploaded into the head or something
Lex Fridman (1:32:22.900)
or imprinted into the DNA,
Lex Fridman (1:32:25.220)
and then they just sort of sense it.
Lex Fridman (1:32:26.900)
But yeah, I think there's, well, look,
Brian Greene (1:32:29.540)
the issue you raised before is the vital one.
Lex Fridman (1:32:32.340)
Is it the case that any sufficiently advanced civilization
Lex Fridman (1:32:36.020)
destroys itself?
Lex Fridman (1:32:37.420)
Is that sort of a commonplace quality?
Brian Greene (1:32:39.820)
I mean, that's the other potential answer
Lex Fridman (1:32:41.460)
to the Fermi paradox.
Lex Fridman (1:32:43.220)
Why aren't they here?
Lex Fridman (1:32:44.060)
Because by the time they got to the technological development
Brian Greene (1:32:47.020)
where they could travel here, they blew themselves up.
Lex Fridman (1:32:49.140)
They destroyed themselves.
Lex Fridman (1:32:50.300)
And that's an unfortunate,
Lex Fridman (1:32:53.060)
but not a hard to imagine possibility
Brian Greene (1:32:57.100)
based on things that have happened here on planet Earth.
Lex Fridman (1:33:01.020)
But putting that to the side,
Brian Greene (1:33:02.980)
I think that's the big obstacle,
Lex Fridman (1:33:05.460)
but putting that to the side,
Brian Greene (1:33:06.460)
we will resolve the engineering challenges.
Lex Fridman (1:33:09.140)
And I should probably modify my answer
Lex Fridman (1:33:12.940)
from before when you said, is it engineering or physics?
Lex Fridman (1:33:15.940)
It's really both, right?
Lex Fridman (1:33:17.460)
So we will surmount the engineering challenges
Lex Fridman (1:33:20.460)
and that will then make the physics challenges relevant.
Brian Greene (1:33:23.620)
It'll make it relevant to figure out
Lex Fridman (1:33:24.980)
how to travel near the speed of light.
Brian Greene (1:33:26.900)
It'll make it relevant to learn
Lex Fridman (1:33:27.980)
how to manipulate the shape of space time and so forth.
Lex Fridman (1:33:32.180)
So I think it's a multi stage process
Lex Fridman (1:33:35.660)
where it is engineering and ultimately physics.
Lex Fridman (1:33:38.100)
And if we stick around long enough,
Lex Fridman (1:33:40.380)
those are the kinds of challenges
Brian Greene (1:33:41.380)
I think that we're ultimately gonna surmount.
Lex Fridman (1:33:43.460)
And then the physics side is figuring out
Lex Fridman (1:33:45.340)
how to harness energy enough
Lex Fridman (1:33:46.700)
to travel outside the solar system,
Brian Greene (1:33:48.700)
which seems like a heck of a difficult journey.
Lex Fridman (1:33:51.140)
But even Mars itself,
Brian Greene (1:33:54.780)
I don't know, maybe because I was born in the Soviet Union
Lex Fridman (1:33:57.420)
and was born with the,
Brian Greene (1:34:02.140)
looking up at the stars and that dream
Lex Fridman (1:34:04.660)
of like the highest of human achievement
Brian Greene (1:34:06.740)
is the ability to fly out there,
Lex Fridman (1:34:08.900)
to join the stars.
Brian Greene (1:34:10.380)
I really liked the idea of going to Mars
Lex Fridman (1:34:13.220)
and not just stepping foot on Mars.
Lex Fridman (1:34:15.580)
And it wasn't until maybe misinformed,
Lex Fridman (1:34:21.060)
but for me personally,
Brian Greene (1:34:23.860)
it wasn't until Elon Musk started talking
Lex Fridman (1:34:26.420)
about the colonization of Mars,
Brian Greene (1:34:28.700)
did I realize like we humans can actually do that.
Lex Fridman (1:34:34.300)
And first of all, the importance of somebody saying
Brian Greene (1:34:38.100)
that we can do these seemingly impossible things
Lex Fridman (1:34:42.780)
is immeasurable because the fact that he placed that
Brian Greene (1:34:48.660)
into my mind and into the minds of millions of others,
Lex Fridman (1:34:52.140)
maybe hundreds of millions, maybe billions of others,
Brian Greene (1:34:54.860)
young kids today, I mean, that's gonna make it a reality.
Lex Fridman (1:34:58.660)
I, for some reason, am deeply excited,
Brian Greene (1:35:01.860)
even though my work isn't AI that echoes all of this.
Lex Fridman (1:35:06.260)
I'm excited by the idea that somebody would be born,
Brian Greene (1:35:09.500)
as we were saying, on Mars and sort of look up
Lex Fridman (1:35:14.180)
and be able to see with a telescope Earth
Lex Fridman (1:35:16.660)
and say, that's where I came from.
Lex Fridman (1:35:19.340)
I don't know, that idea scale to other planets,
Brian Greene (1:35:23.540)
to other solar systems, that's really exciting.
Lex Fridman (1:35:26.620)
And hugely exciting.
Brian Greene (1:35:28.020)
I think you're absolutely right.
Lex Fridman (1:35:29.300)
I mean, the vital thing is to dream, right?
Brian Greene (1:35:33.820)
I mean, and it sounds hackneyed,
Lex Fridman (1:35:36.380)
but it is so important for young kids,
Brian Greene (1:35:40.340)
for the next generation,
Lex Fridman (1:35:42.220)
to think about the things that are seemingly impossible.
Brian Greene (1:35:45.460)
I mean, that's what makes them possible.
Lex Fridman (1:35:47.140)
And this is one which is concrete enough.
Brian Greene (1:35:50.300)
I mean, this is something that's gonna happen soon
Lex Fridman (1:35:52.100)
in terms of actually going to Mars.
Lex Fridman (1:35:54.820)
And then the next step of establishing some presence,
Lex Fridman (1:36:00.340)
some semi permanent or permanent presence.
Brian Greene (1:36:02.620)
This is not something that's gonna wait
Lex Fridman (1:36:05.460)
to the 25th century.
Brian Greene (1:36:06.580)
I mean, this is something that's gonna happen
Lex Fridman (1:36:07.740)
relatively soon.
Brian Greene (1:36:09.140)
So, I mean, it could well be in your lifetime,
Lex Fridman (1:36:11.220)
unlikely mine, but possibly in your lifetime
Brian Greene (1:36:13.660)
that that kid will be born
Lex Fridman (1:36:15.460)
and have the experience that you described.
Lex Fridman (1:36:18.260)
So yeah, it's spectacularly exciting.
Lex Fridman (1:36:21.620)
And I actually, I would love to go on Mars
Brian Greene (1:36:24.260)
on one of the early.
Lex Fridman (1:36:25.900)
You would? Yeah.
Brian Greene (1:36:26.740)
It would if it's one way.
Lex Fridman (1:36:28.180)
I'm happy to do it one way. Really?
Brian Greene (1:36:29.900)
Wow. Yeah.
Lex Fridman (1:36:30.740)
I'm single if there's ladies out there
Brian Greene (1:36:32.540)
that wanna start that family.
Lex Fridman (1:36:34.540)
Let's go out to Mars.
Brian Greene (1:36:36.540)
No, I think.
Lex Fridman (1:36:37.740)
See, I have to tell you something.
Brian Greene (1:36:38.580)
You spoke about terror, thinking about like black holes.
Lex Fridman (1:36:42.700)
If I actually think about going to Mars
Lex Fridman (1:36:45.420)
and being on Mars and put myself in there fully,
Lex Fridman (1:36:49.740)
that's terror inducing.
Brian Greene (1:36:51.780)
The idea of to be in this foreign world
Lex Fridman (1:36:54.940)
where you can't come back,
Brian Greene (1:36:56.740)
where you've made this choice that can't be reversed.
Lex Fridman (1:37:00.060)
Well, at some point it may be,
Lex Fridman (1:37:01.700)
but in that guise, that to me carries a deep sense of terror.
Lex Fridman (1:37:08.780)
I feel that sense of terror every time Kerouac,
Brian Greene (1:37:11.100)
Jack Kerouac talked about this on the road
Lex Fridman (1:37:13.860)
is when you leave a place, if you're honest about it,
Brian Greene (1:37:18.540)
like life is short.
Lex Fridman (1:37:20.740)
And when you leave a place, you move to a new place
Lex Fridman (1:37:23.140)
and you think of all the friends, maybe family
Lex Fridman (1:37:25.220)
you're leaving behind as you drive over the hill,
Brian Greene (1:37:28.060)
that really is goodbye.
Lex Fridman (1:37:31.460)
Like we sometimes don't think of it that way
Brian Greene (1:37:33.260)
when we're moving, but that really is goodbye to that life,
Lex Fridman (1:37:36.220)
to the person you were, to all the people.
Brian Greene (1:37:38.620)
Maybe if it's close friends, you'll see them maybe 10, 15
Lex Fridman (1:37:41.780)
more times in your life and that's it.
Lex Fridman (1:37:43.820)
And you're saying goodbye to all of that.
Lex Fridman (1:37:46.100)
And so in the same way, I see it as way more dramatic
Brian Greene (1:37:50.180)
when you're flying away from earth and it's like,
Lex Fridman (1:37:52.620)
it's goodbye to Dunkin Donuts and Starbucks.
Lex Fridman (1:37:56.180)
And it's goodbye to whatever, I don't know why I picked
Lex Fridman (1:37:59.420)
those, but some, all the things that are special to earth,
Brian Greene (1:38:03.820)
it's goodbye, but that's life.
Lex Fridman (1:38:06.900)
I suppose more, what excites me about that kind of journey
Brian Greene (1:38:11.700)
is it's a distinct contemplation of your mortality,
Lex Fridman (1:38:14.780)
acceptance of your mortality.
Brian Greene (1:38:16.660)
You're saying, just like when you take on any difficult
Lex Fridman (1:38:20.420)
journey, it's accepting that you're going to die one day
Lex Fridman (1:38:25.180)
and might as well do something truly exciting.
Lex Fridman (1:38:28.740)
Yes, I mean, I will, you know, I'm with you on that.
Brian Greene (1:38:31.580)
I'm a strong believer that deep underneath human motivation
Lex Fridman (1:38:36.780)
is this terror of our own mortality.
Brian Greene (1:38:41.020)
Yeah, there's this a wonderful book that had a great
Lex Fridman (1:38:43.180)
influence in me called The Denial of Death by Ernest Becker.
Lex Fridman (1:38:47.580)
And when you are aware of the ways in which our mortality
Lex Fridman (1:38:52.580)
influences our behaviors, it really does add a different
Brian Greene (1:38:57.020)
slant, a different kind of color to the interpretation
Lex Fridman (1:38:59.940)
of human behavior.
Brian Greene (1:39:01.620)
Yeah, it's funny that that book had a big influence
Lex Fridman (1:39:05.620)
in me as well.
Lex Fridman (1:39:06.460)
Oh, is that right?
Lex Fridman (1:39:07.300)
Wow.
Lex Fridman (1:39:08.140)
And the terror management theory and I, again,
Lex Fridman (1:39:12.140)
from an engineering perspective, I don't know how many
Brian Greene (1:39:14.620)
people that book influenced because I talk to people
Lex Fridman (1:39:19.100)
about the fear of death and it doesn't seem like
Brian Greene (1:39:21.220)
about the fear of death and it doesn't seem to be
Lex Fridman (1:39:24.140)
that fundamental to their experience.
Lex Fridman (1:39:26.580)
And I don't think on the surface it's fundamental
Lex Fridman (1:39:28.860)
to my experience, but it seems like an awfully,
Brian Greene (1:39:30.740)
in terms of we talk about models and strength theory
Lex Fridman (1:39:33.380)
and theories, in terms of theories of this macro experience
Brian Greene (1:39:37.380)
of human life, it seems like a heck of a good theory
Lex Fridman (1:39:40.940)
that the fear of death is at the kind of is the warm
Brian Greene (1:39:43.980)
at the core.
Lex Fridman (1:39:44.820)
Yeah, well, I mean, and the terror management theories
Brian Greene (1:39:47.420)
that you make reference to, I mean, this is a group
Lex Fridman (1:39:51.060)
of psychologists, social psychologists who devise
Brian Greene (1:39:54.380)
these very clever experiments, real world experiments
Lex Fridman (1:39:58.340)
with real people, where you can directly measure
Brian Greene (1:40:02.140)
the hidden influence of the recognition
Lex Fridman (1:40:05.580)
of our own mortality.
Brian Greene (1:40:07.460)
I mean, they've done these experiments where they have
Lex Fridman (1:40:09.220)
group of people A, group of people B,
Lex Fridman (1:40:11.540)
and the only difference between the two groups
Lex Fridman (1:40:12.900)
is that group B, they somehow reminded them
Brian Greene (1:40:16.180)
in some subtle way of their own mortality.
Lex Fridman (1:40:18.060)
Sometimes it's nothing more than interviewing them
Brian Greene (1:40:21.180)
with a funeral home across the street.
Lex Fridman (1:40:23.940)
And influence is there, but it's subtle,
Brian Greene (1:40:25.820)
you don't even think you'd take note of.
Lex Fridman (1:40:27.500)
And they can find measurable effects that differentiate
Brian Greene (1:40:32.260)
the two groups to a high degree of statistical significance
Lex Fridman (1:40:36.300)
and how they respond to certain challenges
Brian Greene (1:40:38.900)
or certain kinds of questions that shows a direct influence
Lex Fridman (1:40:42.820)
of the reminder of their own mortality.
Lex Fridman (1:40:45.980)
And I've read a number of these studies
Lex Fridman (1:40:48.620)
and they are really convincing.
Lex Fridman (1:40:51.660)
And so yeah, I would say that the reason why
Lex Fridman (1:40:54.060)
so many people would say that, yeah, fear of mortality,
Brian Greene (1:40:58.060)
it's not front and center in my worldview.
Lex Fridman (1:41:01.140)
Yeah, I don't really think about it much,
Brian Greene (1:41:02.380)
it doesn't really matter too much.
Lex Fridman (1:41:03.300)
The reason why they're able to say that
Brian Greene (1:41:05.100)
is because this thing called culture has emerged
Lex Fridman (1:41:08.540)
over the course of the last 10,000 years.
Lex Fridman (1:41:10.780)
And part of the role of culture is to give us a means
Lex Fridman (1:41:14.260)
of not thinking about our mortality all the time,
Brian Greene (1:41:17.060)
of not living in terror of the inevitable end,
Lex Fridman (1:41:20.020)
which faces us all.
Lex Fridman (1:41:21.780)
So it's completely understandable that that's the response
Lex Fridman (1:41:24.500)
because that's what culture is at least in part for.
Brian Greene (1:41:27.860)
Is it at least possible that the fear of death,
Lex Fridman (1:41:32.300)
the terror of your mortality is the creative force
Brian Greene (1:41:36.300)
that created all of the things around us
Lex Fridman (1:41:39.020)
at this human civilization?
Lex Fridman (1:41:41.540)
And I think about from an engineering perspective,
Lex Fridman (1:41:45.020)
this is where I lose all of my robotics colleagues
Brian Greene (1:41:49.220)
is I feel like if you want to create intelligence,
Lex Fridman (1:41:52.580)
you have to also engineer in some kind of echoes
Brian Greene (1:41:58.140)
of this kind of fear.
Lex Fridman (1:42:01.580)
Fear is such a complicated word,
Lex Fridman (1:42:03.420)
but it's kind of like a scarcity,
Lex Fridman (1:42:06.860)
a scarcity of time, a scarcity of resources
Brian Greene (1:42:10.540)
that creates a kind of anxiety,
Lex Fridman (1:42:12.500)
like deadlines get you to do stuff.
Lex Fridman (1:42:15.460)
And there's something almost fundamental to that
Lex Fridman (1:42:18.460)
in terms of human experience.
Brian Greene (1:42:21.460)
Yeah, well, that's an interesting thought.
Lex Fridman (1:42:22.660)
So you're basically in order to create a kind of structure
Brian Greene (1:42:30.940)
that mirrors what we call consciousness.
Lex Fridman (1:42:34.300)
You'd better have that structure confront the same kinds
Brian Greene (1:42:38.820)
of issues and terrors that we do.
Lex Fridman (1:42:41.980)
Consciousness and suffering only makes sense
Brian Greene (1:42:44.180)
in the context of death.
Lex Fridman (1:42:45.620)
If you want to, I feel like,
Brian Greene (1:42:48.100)
if you want to fit into human society,
Lex Fridman (1:42:50.740)
if you're a robot and if you want to fit into human society,
Brian Greene (1:42:54.420)
you better have the same kind of existential dread,
Lex Fridman (1:42:59.100)
the same kind of fear of mortality,
Brian Greene (1:43:00.740)
otherwise you're not gonna fit in.
Lex Fridman (1:43:02.340)
Right.
Brian Greene (1:43:03.180)
Right.
Lex Fridman (1:43:04.020)
That's good.
Brian Greene (1:43:06.180)
It might be wild, but it's at least,
Lex Fridman (1:43:09.580)
like we're talking about all the theories
Brian Greene (1:43:11.380)
that are at least worth consideration.
Lex Fridman (1:43:13.700)
I think that's a really powerful one.
Lex Fridman (1:43:15.780)
And definitely one has resonated with me
Lex Fridman (1:43:19.180)
and definitely seems to capture something
Brian Greene (1:43:25.700)
beautifully like real about the human condition.
Lex Fridman (1:43:31.340)
And I wonder, it's of course,
Brian Greene (1:43:34.180)
it sucks to think that we need death to appreciate life,
Lex Fridman (1:43:40.340)
but that's just maybe the way it is.
Brian Greene (1:43:43.180)
Well, it's interesting if this robotic
Lex Fridman (1:43:44.500)
or artificially intelligent system understands the world
Lex Fridman (1:43:49.420)
and understands the second law of thermodynamics
Lex Fridman (1:43:51.700)
and entropy, even an artificial intelligence will realize
Brian Greene (1:43:55.540)
that even if its parts are really robust,
Lex Fridman (1:43:59.220)
ultimately it will disintegrate.
Brian Greene (1:44:02.380)
Yeah.
Lex Fridman (1:44:03.220)
The timescales may be different,
Lex Fridman (1:44:05.180)
but in a way, when you think about it, it doesn't matter.
Lex Fridman (1:44:06.980)
Once you know that you are mortal
Brian Greene (1:44:09.220)
in the sense that you are not eternal,
Lex Fridman (1:44:11.580)
the timescale hardly matters
Brian Greene (1:44:13.740)
because it's either the whole thing or not.
Lex Fridman (1:44:17.940)
Because on the scales of eternity,
Brian Greene (1:44:19.740)
any finite duration, however large is effectively zero
Lex Fridman (1:44:23.700)
on the scales of eternity.
Lex Fridman (1:44:25.580)
And so maybe it won't be so hard for an artificial system
Lex Fridman (1:44:28.820)
to feel that sense of mortality
Brian Greene (1:44:32.020)
because it will recognize the underlying physical laws
Lex Fridman (1:44:35.220)
and recognize its own finitude.
Lex Fridman (1:44:38.540)
And then it'll be us and robots drinking beers,
Lex Fridman (1:44:41.340)
looking up at the stars and just,
Brian Greene (1:44:48.500)
having a good laugh in awe of the whole thing.
Lex Fridman (1:44:51.100)
Yeah.
Brian Greene (1:44:53.140)
I think that's a pretty good way to end it,
Lex Fridman (1:44:55.500)
talking about the fear of death.
Brian Greene (1:44:57.340)
We started talking about the meaning of life
Lex Fridman (1:44:59.820)
and ended on the fear of death.
Brian Greene (1:45:01.060)
Brian, this is an incredible conversation.
Lex Fridman (1:45:03.140)
My pleasure, thank you.
Brian Greene (1:45:03.980)
I enjoyed it enormously.
Lex Fridman (1:45:04.820)
I really, really enjoyed it.
Brian Greene (1:45:05.660)
It's been a long time coming.
Lex Fridman (1:45:06.700)
I'm a huge fan of your work, a huge fan of your writing.
Brian Greene (1:45:09.700)
Thanks for talking to me, Brian.
Lex Fridman (1:45:10.700)
Thank you.
Brian Greene (1:45:12.060)
Thanks for listening to this conversation
Lex Fridman (1:45:13.580)
with Brian Greene.
Brian Greene (1:45:14.780)
To support this podcast,
Lex Fridman (1:45:16.100)
please check out our sponsors in the description.
Lex Fridman (1:45:18.900)
And now, let me leave you with some words from Bill Bryson.
Lex Fridman (1:45:22.940)
"'Physics is really nothing more
Brian Greene (1:45:25.500)
"'than a search for ultimate simplicity.
Lex Fridman (1:45:27.860)
"'But so far, all we have is a kind of elegant messiness.'"
Brian Greene (1:45:32.860)
Thank you for listening and hope to see you next time.
Lex Fridman (20:01.540)
I wonder if the mystery is an important component
Brian Greene (20:08.140)
of enjoying something.
Lex Fridman (20:10.120)
So once we know how this thing works,
Brian Greene (20:14.180)
maybe we will no longer enjoy this conversation.
Lex Fridman (20:19.220)
We'll seek other sources of enjoyment,
Lex Fridman (20:21.260)
but this is, again, from an engineering perspective,
Lex Fridman (20:25.340)
I wonder if the mystery is an important component.
Brian Greene (20:29.020)
Well, have you ever seen,
Lex Fridman (20:31.580)
there's this beautiful interview
Brian Greene (20:33.500)
that Richard Feynman did,
Lex Fridman (20:36.940)
great Nobel laureate physicist responsible
Brian Greene (20:39.620)
for a lot of our understanding of quantum mechanics,
Lex Fridman (20:42.060)
quantum field theory and so forth.
Lex Fridman (20:43.060)
And he was in a conversation with an interviewer
Lex Fridman (20:46.520)
where he noted that some people feel
Brian Greene (20:48.580)
like once the mystery is gone,
Lex Fridman (20:51.060)
once science explains something,
Brian Greene (20:55.900)
the beauty goes away, the wonder of it goes away.
Lex Fridman (20:58.300)
And he was emphasizing in his response to that,
Brian Greene (21:02.060)
he's like, no, that's not the right way of thinking about it.
Lex Fridman (21:05.060)
He says, look, when I look at a rose,
Brian Greene (21:07.700)
he says, yeah, I can still deeply enjoy the aroma,
Lex Fridman (21:11.540)
the color, the texture.
Brian Greene (21:13.940)
He says, but what I can do that you can't,
Lex Fridman (21:15.920)
if you're not a physicist,
Brian Greene (21:16.820)
I can look more deeply and understand
Lex Fridman (21:19.340)
where the red comes from, where the aroma comes from,
Brian Greene (21:21.520)
where the structure comes from.
Lex Fridman (21:22.740)
He says, that only augments my wonder.
Brian Greene (21:27.740)
It only augments my experience.
Lex Fridman (21:29.900)
It doesn't flatten it or take away from it.
Lex Fridman (21:32.580)
So I sort of take that as a bit of a motto in some sense
Lex Fridman (21:38.780)
that there is a wonder that comes from a kind of ignorance.
Lex Fridman (21:43.820)
And I don't mean that in a derogatory sense,
Lex Fridman (21:45.740)
but just from not knowing.
Lex Fridman (21:47.280)
So there is a wonder that comes from mystery.
Lex Fridman (21:49.700)
There's another kind of wonder that comes from knowing
Lex Fridman (21:53.500)
and deep knowing.
Lex Fridman (21:55.860)
And I think that kind of wonder has its own
Brian Greene (21:59.260)
special character that in some ways can be more gratifying.
Lex Fridman (22:04.640)
I hope he's right.
Brian Greene (22:06.080)
I hope you're right.
Lex Fridman (22:07.460)
But there's also, I remember he said something
Brian Greene (22:10.300)
about like science is an onion or something like that.
Lex Fridman (22:13.940)
You can peel back, you can keep peeling back.
Brian Greene (22:16.540)
I mean, there is also, when you understand something,
Lex Fridman (22:19.580)
there's always a sense that there's more mystery
Brian Greene (22:22.060)
to understand.
Lex Fridman (22:23.380)
Like you never get to the bottom of the mystery.
Lex Fridman (22:27.060)
But I think it's also different than,
Lex Fridman (22:28.780)
you know, I don't think you can analogize say
Lex Fridman (22:31.460)
to a magician, right?
Lex Fridman (22:33.620)
A magician does some trick.
Brian Greene (22:35.360)
You learn how it sounds like, oh my God,
Lex Fridman (22:37.780)
that's ridiculous when you find.
Lex Fridman (22:39.520)
But nature is perhaps the best magician
Lex Fridman (22:42.780)
if you wanna try to make the analogy there
Brian Greene (22:45.060)
because when you peel things back and you understand
Lex Fridman (22:48.860)
how it is that things have color and you have electrons,
Brian Greene (22:53.220)
dancing from one orbital to another,
Lex Fridman (22:56.420)
emitting photons at very particular wavelengths
Brian Greene (22:59.220)
that are described by these beautiful equations
Lex Fridman (23:01.900)
of quantum electrodynamics,
Brian Greene (23:03.460)
part of which that Feynman developed,
Lex Fridman (23:06.100)
it gives you a greater sense of awe
Brian Greene (23:09.460)
when the curtain is pulled back
Lex Fridman (23:11.700)
than what happens in other circumstances
Brian Greene (23:14.340)
where it does flatten it completely.
Lex Fridman (23:16.380)
Yeah, it's very possible then say in physics
Brian Greene (23:18.540)
that we arrive at a theory of everything
Lex Fridman (23:21.400)
that unifies the laws of physics
Lex Fridman (23:23.460)
and has a very strong understanding
Lex Fridman (23:25.000)
of the fabric of reality,
Brian Greene (23:26.540)
even like from the big bang to today,
Lex Fridman (23:30.380)
it's possible that that understanding
Brian Greene (23:33.000)
is only going to elevate our appreciation
Lex Fridman (23:36.520)
of this whole thing.
Brian Greene (23:37.360)
Yeah, I think it will.
Lex Fridman (23:38.260)
I think it will.
Brian Greene (23:39.100)
I mean, I think it has so far.
Lex Fridman (23:40.980)
But the other side of it which you emphasize
Lex Fridman (23:43.380)
is it's not like science somehow reaches an end, right?
Lex Fridman (23:48.380)
There are certain categories of questions
Brian Greene (23:50.700)
that do reach an end.
Lex Fridman (23:52.260)
I think we one day will close the book
Brian Greene (23:54.340)
on nature's ingredients and the fundamental laws.
Lex Fridman (23:57.500)
Now that we can't prove that,
Brian Greene (23:58.900)
maybe it goes on forever, smaller and smaller,
Lex Fridman (24:01.660)
maybe there are deeper and deeper laws,
Lex Fridman (24:03.140)
but I don't think so.
Lex Fridman (24:03.980)
I think that there's going to be a collection
Brian Greene (24:06.180)
of ingredients and a collection of basic laws.
Lex Fridman (24:08.620)
That chapter will close, but it's one chapter.
Brian Greene (24:12.940)
Now we take that knowledge and we try to understand
Lex Fridman (24:16.220)
how the world builds the structures that it does,
Brian Greene (24:19.740)
from planets to people to black holes
Lex Fridman (24:23.380)
to the possibility of other universes
Lex Fridman (24:25.640)
and every step of the way,
Lex Fridman (24:27.700)
the collection of questions
Brian Greene (24:29.580)
that we don't know the answer to only blossoms.
Lex Fridman (24:32.300)
And so there's a deep sense of gratification
Brian Greene (24:36.760)
from understanding certain qualities of the world.
Lex Fridman (24:39.020)
But I would say that if you take a ratio
Brian Greene (24:42.500)
of what we understand to the things that we know
Lex Fridman (24:45.780)
that we don't yet understand,
Brian Greene (24:47.680)
that ratio keeps getting smaller and smaller
Lex Fridman (24:50.020)
because the things that we know that we don't understand
Brian Greene (24:52.140)
grows larger and larger.
Lex Fridman (24:54.300)
Do you have a hope that we solve that theory
Lex Fridman (24:56.980)
of everything puzzle in the next few decades?
Lex Fridman (25:00.180)
So there's been a bunch of attempts from string theory
Brian Greene (25:03.820)
to all kinds of attempts at trying to solve quantum gravity
Lex Fridman (25:07.500)
or basically come up with a theory for quantum gravity.
Brian Greene (25:10.260)
There's a lot of complexities to this.
Lex Fridman (25:13.260)
One, for experimental validation,
Brian Greene (25:16.260)
you have to observe effects
Lex Fridman (25:17.820)
that are very difficult to measure.
Lex Fridman (25:20.420)
So you have to build,
Lex Fridman (25:21.340)
like that's like an engineering challenge.
Lex Fridman (25:23.660)
And then there's the theory challenge,
Lex Fridman (25:25.260)
which is like, it seems very difficult
Brian Greene (25:28.380)
to connect the laws of gravity to quantum mechanics.
Lex Fridman (25:31.820)
Do you have a hope or are we hopelessly stuck?
Brian Greene (25:35.500)
Well, I have to have to have a hope.
Lex Fridman (25:37.620)
I mean, it's in some sense,
Lex Fridman (25:39.640)
but I devote at least part of my professional life toward
Lex Fridman (25:43.660)
trying to make progress on.
Lex Fridman (25:45.020)
And I'm glad you used the phrase quantum gravity.
Lex Fridman (25:47.540)
I'm not a great fan of the theory of everything phrase
Brian Greene (25:50.300)
because it does make other scientists feel like
Lex Fridman (25:53.320)
if they're not working on this, what are they working on?
Brian Greene (25:55.620)
Man's like, there's not much left
Lex Fridman (25:57.500)
when you're talking about theory of everything.
Brian Greene (25:58.860)
Biology is just small details we'll figure out.
Lex Fridman (26:01.460)
Yeah, so it is really trying to put gravity
Lex Fridman (26:04.180)
and quantum mechanics together.
Lex Fridman (26:06.180)
And since I was a college kid,
Brian Greene (26:08.580)
I was deeply fascinated with gravity.
Lex Fridman (26:12.980)
And as I learned quantum mechanics,
Brian Greene (26:15.480)
the notion of physicists being stumped
Lex Fridman (26:19.000)
and trying to blend them together,
Lex Fridman (26:20.560)
how could one not get fired up
Lex Fridman (26:22.260)
about maybe contributing something to that journey?
Lex Fridman (26:25.940)
And so we've been on this,
Lex Fridman (26:27.660)
I've been on this for 30 years since I was a student.
Brian Greene (26:29.820)
We have made progress.
Lex Fridman (26:31.800)
We do have ideas.
Brian Greene (26:32.860)
You mentioned string theory is one possible scenario.
Lex Fridman (26:36.240)
It's not stuck.
Brian Greene (26:37.520)
String theory is a vibrant field of research
Lex Fridman (26:40.900)
that is making incredible progress,
Lex Fridman (26:43.600)
but we've not made progress
Lex Fridman (26:45.980)
on this issue of experimental verification validation,
Brian Greene (26:49.460)
which is, you know, it is a vital part of the story.
Lex Fridman (26:53.940)
So I would have hoped that by now
Brian Greene (26:55.740)
we would have made contact with observation.
Lex Fridman (26:58.620)
If you would have interviewed me back in the 80s
Brian Greene (27:01.620)
when I was, you know, a wild bright eyed kid
Lex Fridman (27:04.940)
trying to make headway working 18 hours a day
Lex Fridman (27:07.140)
and this sort of stuff,
Lex Fridman (27:07.980)
I would have said, yeah, by 2021,
Brian Greene (27:10.380)
yeah, we're gonna know whether it's right or wrong.
Lex Fridman (27:12.160)
We'll have made contact.
Brian Greene (27:13.620)
I would have said, look,
Lex Fridman (27:14.460)
there may be certain mathematical puzzles
Brian Greene (27:16.020)
that we've yet to work out,
Lex Fridman (27:17.220)
but we'll know enough to make contact with experiment.
Brian Greene (27:19.900)
That has not happened.
Lex Fridman (27:21.580)
On the other hand,
Brian Greene (27:22.540)
if you would have interviewed me back then and asked me,
Lex Fridman (27:25.200)
will we be able to talk about detailed qualities
Brian Greene (27:29.140)
of black holes and understand them at the level of detail
Lex Fridman (27:34.140)
that we actually, I would have said,
Brian Greene (27:37.460)
no, I don't think that we're gonna be able to do that.
Lex Fridman (27:39.820)
Will we have an exact formulation of string theory
Lex Fridman (27:42.660)
in certain circumstances?
Lex Fridman (27:43.980)
No, I don't think we're gonna have that, and yet we do.
Lex Fridman (27:46.600)
So it's just to say,
Lex Fridman (27:47.440)
you don't know where the progress is going to happen,
Lex Fridman (27:51.020)
but yes, I do hold out hope
Lex Fridman (27:52.980)
that maybe before I move on to wherever,
Brian Greene (27:56.740)
I don't think there is an after,
Lex Fridman (27:58.100)
but I would love before I leave this earth
Brian Greene (28:01.780)
to know the answer, but science and the universe,
Lex Fridman (28:06.900)
it's not about pleasing any individual, it is what it is.
Lex Fridman (28:11.620)
And so we just press onward and we'll see where it goes.
Lex Fridman (28:15.000)
So in terms of string theory,
Brian Greene (28:17.100)
if I just look from an authoritative perspective currently
Lex Fridman (28:20.400)
at the theoretical physics community,
Brian Greene (28:22.480)
string theory as a theory has been very popular
Lex Fridman (28:26.500)
for a few decades, but has recently fallen out of favor,
Brian Greene (28:30.700)
or at least there's been like, you know,
Lex Fridman (28:32.940)
it became more popular to kind of ask the question,
Lex Fridman (28:36.980)
is string theory really the answer?
Lex Fridman (28:39.380)
Where do you fall on this?
Lex Fridman (28:40.900)
Like, how do you make sense of this puzzle?
Lex Fridman (28:43.220)
Why do you think it's fallen out of favor?
Brian Greene (28:45.480)
Yeah, so I would actually challenge the statement
Lex Fridman (28:47.900)
that it's fallen out of favor.
Brian Greene (28:50.300)
I would say that any field of research when it's new
Lex Fridman (28:55.180)
and it's the bright, shiny bicycle
Brian Greene (28:58.740)
that no one has yet seen on that block,
Lex Fridman (29:01.060)
yeah, it's gonna attract attention
Lex Fridman (29:03.060)
and the news outlets are gonna cover it
Lex Fridman (29:06.100)
and students are gonna flock to it, sure.
Lex Fridman (29:09.200)
But as a field matures, it does shed those qualities
Lex Fridman (29:14.260)
because it's no longer as novel as it was
Brian Greene (29:17.260)
when it was first introduced 30, 40 years ago,
Lex Fridman (29:20.340)
but you need to judge it by a different standard.
Brian Greene (29:22.660)
You need to judge it by is it making progress
Lex Fridman (29:26.220)
on foundational issues deepening our understanding
Brian Greene (29:29.380)
of the subject and by that measure,
Lex Fridman (29:31.620)
string theory is scoring very high.
Brian Greene (29:36.580)
Now, at the same time, you also need to judge
Lex Fridman (29:39.280)
whether it makes contact with experiment
Brian Greene (29:41.100)
as we discussed before too
Lex Fridman (29:42.900)
and in that measure, we're still challenged.
Lex Fridman (29:45.900)
So I would say that many string theorists,
Lex Fridman (29:49.220)
myself included, are very sober about the theory.
Brian Greene (29:54.220)
It has the tremendous progress that it had 30, 40 years ago
Lex Fridman (29:58.340)
that hasn't gone away, but we become better equipped
Brian Greene (30:02.780)
at assessing the long journey ahead
Lex Fridman (30:06.700)
and that was something that we weren't particularly good at
Brian Greene (30:09.580)
back, say, in the 80s.
Lex Fridman (30:10.860)
Look, when I was just starting out in the field,
Brian Greene (30:13.900)
there was a sense of physics is about to end.
Lex Fridman (30:18.100)
String theory is about to be the be all and end all
Brian Greene (30:21.940)
final unified theory and that will bring this chapter
Lex Fridman (30:26.580)
to a close.
Brian Greene (30:27.780)
Now, I have to say, I think it was more the younger
Lex Fridman (30:30.180)
physicists who were saying that.
Brian Greene (30:31.840)
Some of them were seasoned,
Lex Fridman (30:32.900)
even if they were pro string theory at the time.
Brian Greene (30:35.820)
I don't know if they were rolling their eyes,
Lex Fridman (30:37.700)
but they knew that it was gonna be a long, long journey.
Brian Greene (30:41.780)
I think people like John Schwartz,
Lex Fridman (30:43.860)
one of the founders of string theory,
Brian Greene (30:45.180)
Michael Green, no relation to me,
Lex Fridman (30:46.620)
founders of the theory, Edward Witten,
Brian Greene (30:49.660)
one of the main people driving the theory
Lex Fridman (30:52.100)
back then and today.
Brian Greene (30:53.900)
I think they knew that we were in for a long haul
Lex Fridman (30:58.900)
and that's the nature of science,
Brian Greene (31:01.780)
quick hits that resolve everything few and far between.
Lex Fridman (31:06.180)
And so if you were in for the quick solution
Brian Greene (31:12.220)
to the big questions of the world,
Lex Fridman (31:13.860)
then you would have been disappointed
Lex Fridman (31:15.100)
and I think there were people who were disappointed
Lex Fridman (31:16.820)
and moved on and work on other subjects.
Brian Greene (31:19.740)
If you're in in the way that Einstein was in
Lex Fridman (31:23.340)
for a lifetime of investigation to try to see
Lex Fridman (31:27.780)
what the answers to the deep questions would be,
Lex Fridman (31:30.660)
then I think string theory has been a rich source
Brian Greene (31:33.860)
of material that has kept so many people deeply engaged
Lex Fridman (31:39.100)
in moving the frontier forward.
Brian Greene (31:41.300)
There's a few qualities about string theory,
Lex Fridman (31:43.020)
which are weird.
Brian Greene (31:45.140)
I mean, a lot of physics is just weird and beautiful.
Lex Fridman (31:48.940)
So let me ask the question,
Lex Fridman (31:50.220)
what do you use most beautiful about string theory?
Lex Fridman (31:53.140)
Well, what attracted me to the theory at the outset
Brian Greene (31:57.900)
beyond it's putting gravity and quantum mechanics together,
Lex Fridman (32:00.980)
which I think is its true claim to fame,
Brian Greene (32:03.940)
at least on paper, it's able to do that.
Lex Fridman (32:06.740)
What attracted me to the theory was the fact
Brian Greene (32:08.260)
that it requires extra dimensions of space.
Lex Fridman (32:11.140)
And this was an idea that intrigued me in a very deep way,
Brian Greene (32:16.900)
even before I really understood what it meant.
Lex Fridman (32:20.620)
I somehow had, I mean, talk about sort of
Brian Greene (32:24.020)
the emotional part of consciousness and the cognitive part
Lex Fridman (32:27.180)
in some, perhaps you call it strange,
Brian Greene (32:29.460)
in some strange emotional way,
Lex Fridman (32:31.940)
I was enamored with Einstein's general relativity,
Brian Greene (32:35.420)
the idea of curved space and time
Lex Fridman (32:37.740)
before I really knew what it meant.
Brian Greene (32:39.420)
It just spoke to me, I don't know how else to say it.
Lex Fridman (32:43.300)
And then when I subsequently learned
Brian Greene (32:46.620)
that people had thought about more dimensions of space
Lex Fridman (32:49.620)
than we can see and how those extra dimensions
Brian Greene (32:52.380)
would be vital to a deep understanding
Lex Fridman (32:55.060)
of the things that we do see in this world,
Brian Greene (32:56.900)
four, five, six dimensions might explain
Lex Fridman (32:59.740)
why there are certain forces and particles
Lex Fridman (33:01.740)
and how they behave.
Lex Fridman (33:03.340)
To me, this was like amazing, utterly amazing.
Lex Fridman (33:06.300)
And then when I learned that string theory
Lex Fridman (33:09.060)
embraced all these ideas,
Brian Greene (33:10.700)
embraced the general theory of relativity,
Lex Fridman (33:12.500)
embraced quantum mechanics,
Brian Greene (33:13.620)
embraced the possibility of extra dimensions,
Lex Fridman (33:17.260)
then I was hooked.
Lex Fridman (33:19.140)
And so when I was a graduate student,
Lex Fridman (33:21.460)
we would just spend hours,
Brian Greene (33:23.780)
we, I mean, a couple of other graduate students and myself
Lex Fridman (33:26.260)
who had sort of worked really well together,
Brian Greene (33:29.300)
it was at Oxford in England,
Lex Fridman (33:30.940)
we would work these enormous numbers of hours a day
Brian Greene (33:33.900)
trying to understand the shapes of these extra dimensions,
Lex Fridman (33:36.340)
the geometry of them, what those geometrical shapes
Brian Greene (33:39.820)
for the extra dimensions would imply
Lex Fridman (33:41.460)
for things that we see in the world around us.
Lex Fridman (33:43.780)
And it was a heady, heady time.
Lex Fridman (33:46.660)
And that kind of excitement has sort of filtered through
Brian Greene (33:50.500)
over the decades.
Lex Fridman (33:51.420)
But I'd say that's really the part of the theory
Brian Greene (33:57.020)
that I think really hooked me most strongly.
Lex Fridman (34:00.260)
How are we supposed to think about those extra dimensions?
Brian Greene (34:02.860)
I was supposed to imagine actual physical reality
Lex Fridman (34:05.940)
or is this more in the space of mathematics
Brian Greene (34:08.620)
that allows you to sort of come up with tricks
Lex Fridman (34:11.620)
to describe the four dimensional reality
Lex Fridman (34:14.620)
that we more directly perceive?
Lex Fridman (34:17.420)
No one really knows the answer, of course,
Lex Fridman (34:19.700)
but if I take the most straightforward approach
Lex Fridman (34:22.700)
to string theory,
Brian Greene (34:23.540)
you really are imagining that these dimensions are there,
Lex Fridman (34:28.020)
they're real.
Brian Greene (34:28.860)
I mean, just as you would say
Lex Fridman (34:30.780)
that the three space dimensions around us,
Brian Greene (34:33.380)
left, right, back, forth, up, down,
Lex Fridman (34:35.700)
yeah, they're real, they're here.
Brian Greene (34:37.900)
We are immersed within those dimensions.
Lex Fridman (34:40.340)
These other dimensions are as real as these
Brian Greene (34:44.500)
with the one difference being their shape and their size
Lex Fridman (34:47.620)
differs from the shape and size of the dimensions
Brian Greene (34:50.500)
that we have direct access to through human experience.
Lex Fridman (34:54.660)
And one approach imagines that these extra dimensions
Brian Greene (34:57.700)
are tightly coiled up, curled up,
Lex Fridman (35:01.060)
crushed together, if you will,
Brian Greene (35:03.380)
into a beautiful geometrical form
Lex Fridman (35:06.500)
that's all around us,
Lex Fridman (35:08.820)
but just too small for us to detect with our eyes,
Lex Fridman (35:11.940)
too small for us to detect
Brian Greene (35:13.300)
even with the most powerful equipment that we have.
Lex Fridman (35:16.220)
Nevertheless, according to the mathematics,
Brian Greene (35:18.940)
the size and the shape of those extra dimensions
Lex Fridman (35:21.580)
leaves an imprint in the world that we do have access to.
Lex Fridman (35:24.940)
So one of the ways that we have hoped yet to achieve
Lex Fridman (35:28.980)
to make contact with experimental physics
Brian Greene (35:31.820)
is to see a signature of those extra dimensions
Lex Fridman (35:34.460)
in places like the Large Hadron Collider
Brian Greene (35:36.580)
in Geneva, Switzerland.
Lex Fridman (35:38.220)
And it hasn't happened yet, doesn't mean it won't happen,
Lex Fridman (35:41.420)
but that would be a stunning moment
Lex Fridman (35:44.700)
in the history of the species
Brian Greene (35:46.140)
if data that we acquired in these dimensions
Lex Fridman (35:50.140)
gives us kind of incontrovertible evidence
Brian Greene (35:53.420)
that these dimensions are not the only dimensions.
Lex Fridman (35:55.860)
I mean, how mind blowing would that be?
Lex Fridman (35:59.220)
So with the Large Hadron Collider,
Lex Fridman (36:00.980)
it would be something in the movement of the particles
Brian Greene (36:03.260)
or also the gravitational waves potentially be a place
Lex Fridman (36:07.740)
where you can detect signs of multiple dimensions,
Brian Greene (36:10.180)
like with something like LIGO, but much more accurate.
Lex Fridman (36:12.340)
In principle, all of these can work.
Lex Fridman (36:14.580)
So one of the experiments that we had high hopes for,
Lex Fridman (36:18.340)
but by high hopes, I'm actually exaggerating.
Brian Greene (36:20.980)
One of the experiments that we imagined
Lex Fridman (36:24.340)
might in the best of all circumstances,
Brian Greene (36:26.580)
yield some insight.
Lex Fridman (36:27.540)
We weren't with bated breath waiting for the result.
Brian Greene (36:30.100)
We knew it was a long shot.
Lex Fridman (36:31.620)
When you slam protons together at very high speed
Brian Greene (36:34.660)
of the Large Hadron Collider,
Lex Fridman (36:35.980)
if there are these extra dimensions
Lex Fridman (36:37.580)
and if they have the right form,
Lex Fridman (36:39.660)
and that's a hypothesis that may not be correct,
Lex Fridman (36:43.180)
but when the protons collide,
Lex Fridman (36:44.940)
they can create debris, energetic debris
Brian Greene (36:48.060)
that can in some sense leave our dimensions
Lex Fridman (36:50.940)
and insert itself into the other dimensions.
Lex Fridman (36:53.780)
And the way you'd recognize that is,
Lex Fridman (36:56.380)
there'd be more energy before the collision
Lex Fridman (36:58.620)
and after the collision because the debris
Lex Fridman (37:00.940)
would have taken energy away from the place
Brian Greene (37:03.780)
where our detectors can detect it.
Lex Fridman (37:06.540)
So that's one real concrete way
Brian Greene (37:09.060)
that you could find evidence for extra dimensions.
Lex Fridman (37:12.020)
But yeah, since extra dimensions are of space
Lex Fridman (37:16.020)
and gravity is something that exists within,
Lex Fridman (37:19.380)
in fact is associated with the shape of space,
Brian Greene (37:22.780)
gravitational waves in principle
Lex Fridman (37:25.220)
can provide a kind of cat scan of the extra dimensions
Brian Greene (37:31.180)
if you had sufficient control over those processes.
Lex Fridman (37:35.340)
We don't yet, but perhaps one day we will.
Lex Fridman (37:38.660)
Does it make you sad a little bit?
Lex Fridman (37:41.420)
Maybe looking out into the future,
Brian Greene (37:43.020)
you mentioned Ed Witten that no Nobel prizes
Lex Fridman (37:46.140)
have been given yet related to string theory.
Lex Fridman (37:48.940)
Do you think they will be?
Lex Fridman (37:50.300)
Do you think you have to have experimental validation
Lex Fridman (37:53.620)
or can a Nobel prize be given?
Lex Fridman (37:55.500)
Which I don't think has been given for quite a long time
Brian Greene (37:58.620)
for purely sort of theoretical contribution.
Lex Fridman (38:01.940)
Yeah, it's certainly as a matter of historical precedent
Brian Greene (38:06.140)
has been the case that those who win the prize
Lex Fridman (38:09.020)
have established, investigated, illuminated
Brian Greene (38:14.180)
a demonstrably real quality of the world.
Lex Fridman (38:18.620)
So gravitational waves, the prize was awarded
Brian Greene (38:22.740)
after they were detected, not the mathematics of it,
Lex Fridman (38:26.580)
but the actual detection of it.
Brian Greene (38:28.980)
The Higgs particle, it was an idea that came
Lex Fridman (38:32.220)
from the 1960s, Peter Higgs and others in fact.
Lex Fridman (38:36.220)
And it wasn't until 2012 on July 4th
Lex Fridman (38:41.420)
when the announcement came that this particle
Brian Greene (38:43.300)
had been detected at the Large Hadron Collider
Lex Fridman (38:45.660)
that people viewed it as eligible for the Nobel prize.
Brian Greene (38:49.140)
The idea was there, the math was there,
Lex Fridman (38:50.700)
but you needed to confirm it.
Brian Greene (38:52.780)
Indeed, the prize ultimately was awarded.
Lex Fridman (38:55.260)
So I'm not surprised.
Brian Greene (38:56.940)
In fact, I would have been surprised
Lex Fridman (38:59.540)
if a Nobel prize had been awarded
Brian Greene (39:02.140)
in the arena of string theory
Lex Fridman (39:04.340)
because it's far too speculative right now.
Brian Greene (39:07.180)
It's far too hypothetical.
Lex Fridman (39:09.060)
In fact, I am sympathetic to the view
Brian Greene (39:13.220)
that it really shouldn't be called string theory.
Lex Fridman (39:15.900)
It degrades the word theory
Brian Greene (39:18.540)
because theory in science, of course,
Lex Fridman (39:20.900)
means the best available explanation
Brian Greene (39:23.740)
for the things that we observe in the world,
Lex Fridman (39:25.940)
the things that we measure in experiments about the world.
Lex Fridman (39:30.820)
And string theory does not do that, at least not yet.
Lex Fridman (39:34.320)
So it really should be the string hypothesis, right?
Brian Greene (39:37.620)
We're at an earlier stage of development
Lex Fridman (39:40.500)
and that's not the kind of thing
Brian Greene (39:42.320)
that Nobel prizes should be awarded for.
Lex Fridman (39:45.580)
What do you think about the critics out there, Peter White,
Brian Greene (39:48.700)
he's from Columbia too, I think Sabine Hafenstatter.
Lex Fridman (39:53.380)
Is that a healthy thing or should we sort of focus
Lex Fridman (39:56.340)
on sort of the optimism of these hypotheses?
Lex Fridman (39:59.540)
Yeah, it's actually a good way that you frame it
Brian Greene (40:03.060)
because I'm always somewhat repelled
Lex Fridman (40:09.060)
by views of the world that start from the negative.
Brian Greene (40:14.060)
Try to cut down an idea, try to say that's the wrong way
Lex Fridman (40:18.820)
of thinking about things and so on.
Brian Greene (40:21.540)
I'm much more drawn, maybe because I'm an optimist,
Lex Fridman (40:24.980)
I don't know, I'm much more drawn to those
Brian Greene (40:27.460)
who go out into the world with new ideas.
Lex Fridman (40:30.660)
And don't try to cut down one idea,
Lex Fridman (40:34.020)
but rather present another one that might be better.
Lex Fridman (40:38.020)
And so you make the first idea, maybe string theory irrelevant
Brian Greene (40:41.940)
because you've come up with the better approach
Lex Fridman (40:46.340)
to the world.
Lex Fridman (40:47.580)
So do I think it's healthy?
Lex Fridman (40:49.040)
Look, I think having a wide range of views
Lex Fridman (40:53.020)
and perspectives is generally a healthy thing.
Lex Fridman (40:56.600)
I think it's good to have arguments within a subject
Brian Greene (41:00.460)
in order that you stay fresh and you stay focused
Lex Fridman (41:04.060)
on the things that matter.
Lex Fridman (41:06.420)
But in the end of the day,
Lex Fridman (41:07.740)
I think it's a more vital contribution
Brian Greene (41:11.940)
to give us something new
Lex Fridman (41:13.260)
rather than to criticize something that's there.
Brian Greene (41:15.540)
Yeah, I'm totally with you.
Lex Fridman (41:17.020)
But it could be just the nature of being an optimist
Lex Fridman (41:19.780)
and also just a love of engineering.
Lex Fridman (41:24.220)
It helps nobody by criticizing the rocket
Brian Greene (41:29.300)
that somebody else built,
Lex Fridman (41:30.580)
just build a bigger, cheaper, better rocket.
Brian Greene (41:34.560)
Right, exactly.
Lex Fridman (41:36.580)
And that seems to be how human civilization
Brian Greene (41:38.980)
can progress effectively.
Lex Fridman (41:41.420)
We've mentioned the second law of thermodynamics.
Brian Greene (41:44.900)
I gotta ask you about time.
Lex Fridman (41:46.860)
Yeah.
Lex Fridman (41:47.700)
And do you think of time as emergent
Lex Fridman (41:51.380)
or fundamental to our universe?
Brian Greene (41:53.700)
I like to think of it as emergent.
Lex Fridman (41:56.080)
I don't have a solid reason for that perspective.
Brian Greene (42:00.940)
I have a lot of hints of reasons
Lex Fridman (42:02.720)
that some of which come out of string theory
Lex Fridman (42:04.340)
and quantum gravity that perhaps would be worth talking about.
Lex Fridman (42:09.140)
But what I would say is,
Brian Greene (42:11.980)
time is the most familiar quality of experience
Lex Fridman (42:17.020)
because there's nothing that takes place
Brian Greene (42:18.940)
that doesn't take place within an interval of time.
Lex Fridman (42:22.140)
And yet at the same time,
Brian Greene (42:24.500)
it is perhaps the most mysterious quality of the world.
Lex Fridman (42:28.420)
So it's a wonderful confluence
Brian Greene (42:31.020)
of the familiar and the deeply mysterious
Lex Fridman (42:33.500)
all in one little package.
Lex Fridman (42:35.980)
If you were to ask me, what is time?
Lex Fridman (42:38.580)
I don't really know.
Brian Greene (42:39.760)
I don't think anybody does.
Lex Fridman (42:41.000)
I can say what time gives us,
Brian Greene (42:45.220)
it allows us the language for talking about change.
Lex Fridman (42:48.740)
It allows us to envision the events of the universe
Brian Greene (42:52.580)
being spread out in this temporal timeline.
Lex Fridman (42:55.860)
And in that way, allows us to see the patterns
Brian Greene (42:59.080)
that unfold within time.
Lex Fridman (43:01.640)
I mean, time allows us the structure and the organization
Brian Greene (43:05.120)
to think about things in that kind of a progression.
Lex Fridman (43:08.920)
But what actually is it?
Brian Greene (43:11.420)
I don't really know.
Lex Fridman (43:12.740)
And that's so strange because we can measure it, right?
Brian Greene (43:16.380)
I mean, there are laboratories in the world
Lex Fridman (43:19.060)
that measure this thing called time
Brian Greene (43:21.100)
to spectacular precision.
Lex Fridman (43:24.020)
But if you go up to the folks and say,
Lex Fridman (43:28.460)
what is it that you're actually measuring?
Lex Fridman (43:31.900)
I don't know that they can really articulate
Brian Greene (43:34.540)
the kind of answer that you would expect
Lex Fridman (43:37.180)
from those who are engineering a device
Brian Greene (43:39.360)
that can measure something called time
Lex Fridman (43:41.460)
to that level of precision.
Lex Fridman (43:43.100)
So it's a very curious combination.
Lex Fridman (43:46.860)
What do you make of the one way feeling of causality?
Brian Greene (43:51.260)
Like is causality a thing or is that too just a human story
Lex Fridman (43:56.260)
that we put on top of this emergent phenomenon of time?
Brian Greene (44:00.780)
I don't know.
Lex Fridman (44:02.220)
I can give you my guess and my intuition about it.
Brian Greene (44:05.940)
I do think that at the macroscopic level,
Lex Fridman (44:09.180)
if we're talking about sort of the human experience of time,
Brian Greene (44:11.280)
I do think at the macroscopic level,
Lex Fridman (44:13.320)
there is a fundamental notion of causality
Brian Greene (44:17.180)
that does emerge from a starting point
Lex Fridman (44:20.060)
that may not have causality built in.
Lex Fridman (44:21.760)
So I certainly would allow that at the deepest description
Lex Fridman (44:25.540)
of reality when we finally have that on the table,
Brian Greene (44:28.880)
we may not see causality directly at that fundamental level.
Lex Fridman (44:33.540)
But I do believe that we will understand
Lex Fridman (44:36.240)
how to go from that fundamental level
Lex Fridman (44:38.340)
to a world where at the macroscopic level,
Brian Greene (44:41.440)
there is this notion of A causes B.
Lex Fridman (44:44.460)
A notion that Einstein deeply embraced
Brian Greene (44:47.660)
in his special theory of relativity
Lex Fridman (44:49.140)
where he showed that time has qualities
Brian Greene (44:51.840)
that we wouldn't expect based on experience.
Lex Fridman (44:54.280)
You and I, if we move relative to each other,
Brian Greene (44:56.740)
our clocks tick off time at different rate.
Lex Fridman (44:59.780)
And our clocks is just a means of measuring
Brian Greene (45:02.540)
this thing called time.
Lex Fridman (45:03.520)
So this is really time that we're talking about.
Brian Greene (45:05.860)
Time for you and time for me are different
Lex Fridman (45:08.100)
if we're in relative motion.
Brian Greene (45:09.280)
He then shows in the general theory of relativity
Lex Fridman (45:11.500)
that if we're experiencing different gravity,
Brian Greene (45:15.040)
different gravitational fields
Lex Fridman (45:16.300)
or actually more precisely
Brian Greene (45:17.280)
different gravitational potentials,
Lex Fridman (45:19.180)
time will elapse for us at different rates.
Brian Greene (45:21.660)
These are things that are astoundingly strange
Lex Fridman (45:25.960)
that give rise to a scientific notion of time travel.
Brian Greene (45:29.700)
Okay, so this is how far Einstein took us
Lex Fridman (45:33.440)
in wiping away the old understanding of time
Lex Fridman (45:37.180)
and injecting a new understanding of its qualities.
Lex Fridman (45:40.420)
So there's so much about time that's counterintuitive,
Lex Fridman (45:44.420)
but I do not think that we're ever going
Lex Fridman (45:46.780)
to wipe away causality at the macroscopic level.
Brian Greene (45:50.300)
At the macroscopic, I mean, there's so many interesting
Lex Fridman (45:52.340)
things at the macroscopic level
Brian Greene (45:53.900)
that may only exist at the macroscopic level.
Lex Fridman (45:56.680)
Like we already talked about consciousness
Brian Greene (45:59.200)
that very well could be one of the things.
Lex Fridman (46:01.060)
You mentioned time travel.
Brian Greene (46:02.260)
So, I mean, according to Einstein and in general,
Lex Fridman (46:09.180)
what types of travel do you think
Lex Fridman (46:11.680)
our physical universe allows?
Lex Fridman (46:14.020)
Well, it certainly allows time travel to the future.
Lex Fridman (46:17.060)
And I'm not talking about the silly thing
Lex Fridman (46:18.660)
that you and I are now going into the future
Brian Greene (46:21.420)
second by second by second.
Lex Fridman (46:22.420)
I'm talking about really the diversion
Brian Greene (46:24.700)
that you see in Hollywood, at least in terms
Lex Fridman (46:27.460)
of its net effect, whereby an individual
Brian Greene (46:32.260)
can follow an Einsteinian strategy
Lex Fridman (46:36.460)
and propel themselves into the future
Brian Greene (46:40.660)
in some sense more quickly.
Lex Fridman (46:42.260)
So if I wanted to see what's happening on planet Earth
Brian Greene (46:46.020)
one million years from now, Einstein tells me
Lex Fridman (46:50.100)
how to get one million years from now.
Brian Greene (46:52.500)
Build a ship.
Lex Fridman (46:53.340)
I got to turn to guys who know how to build stuff.
Brian Greene (46:56.380)
I can't do it like you.
Lex Fridman (46:57.980)
Build a ship that can go out into the universe
Brian Greene (47:00.020)
near the speed of light, turn around and come back.
Lex Fridman (47:02.780)
Let's say it's a six month journey out
Lex Fridman (47:04.420)
and a six month journey back.
Lex Fridman (47:05.900)
And Einstein tells me how fast I need to travel,
Lex Fridman (47:09.420)
how close to the speed of light I need to go
Lex Fridman (47:11.180)
so that when I step out of my ship,
Brian Greene (47:13.740)
it will now be one million years into the future
Lex Fridman (47:16.980)
on planet Earth.
Lex Fridman (47:20.140)
And this is not a controversial statement, right?
Lex Fridman (47:23.300)
This is not something where there's differences
Brian Greene (47:25.940)
of opinion in the scientific community.
Lex Fridman (47:28.340)
Any scientist who knows anything
Brian Greene (47:30.900)
about what Einstein taught us agrees with what I just said.
Lex Fridman (47:35.100)
It's commonplace, it's bread and butter physics.
Lex Fridman (47:37.740)
And so that kind of travel to the future
Lex Fridman (47:40.660)
is absolutely allowed by the laws of physics.
Brian Greene (47:44.140)
There are engineering challenges,
Lex Fridman (47:45.820)
there are technological challenges.
Brian Greene (47:47.940)
They're close to the speed of light part, yeah.
Lex Fridman (47:49.460)
Yeah, and there are even biological challenges, right?
Brian Greene (47:52.780)
They're G forces that you're gonna experience.
Lex Fridman (47:55.180)
So there's all sorts of stuff embedded in this,
Lex Fridman (47:57.740)
but those I will call the details.
Lex Fridman (48:01.020)
And those details, notwithstanding,
Brian Greene (48:04.380)
the universe allows this kind of travel to the future.
Lex Fridman (48:07.820)
And if I could pause real quick,
Brian Greene (48:09.660)
you could also, at the macro level,
Lex Fridman (48:12.620)
with biology extend the human lifespan
Brian Greene (48:15.360)
to do a kind of travel forward in time.
Lex Fridman (48:19.300)
If you expand how long we live,
Brian Greene (48:22.540)
that's a way to, from a perspective of an observer,
Lex Fridman (48:25.300)
a conscious observer that is a human being,
Brian Greene (48:27.780)
you're essentially traveling forward in time
Lex Fridman (48:29.920)
by allowing yourself to live long enough to see the thing.
Lex Fridman (48:32.740)
So that's in the space of biology.
Lex Fridman (48:34.920)
What about traveling back in time?
Brian Greene (48:37.160)
Yeah, that is a natural next question,
Lex Fridman (48:41.980)
especially if you're going on one of these journeys.
Lex Fridman (48:45.540)
Is it a one way journey or can you come back?
Lex Fridman (48:48.860)
And the physics community doesn't speak
Brian Greene (48:52.480)
with a unified voice on this as yet,
Lex Fridman (48:55.220)
but I would say that the dominant perspective
Brian Greene (48:57.860)
is that you cannot get back.
Lex Fridman (49:00.260)
Now, having said that, there are proposals
Brian Greene (49:03.900)
that serious people have written papers on
Lex Fridman (49:07.300)
regarding hypothetical ways
Brian Greene (49:09.080)
in which you could travel to the past.
Lex Fridman (49:10.900)
And we've seen some of these.
Brian Greene (49:13.500)
Again, Hollywood loves to take the most sexy ideas
Lex Fridman (49:16.900)
of physics and build narratives around them.
Brian Greene (49:20.040)
This idea of a wormhole,
Lex Fridman (49:21.980)
like Jodie Foster in Contact went through a wormhole,
Brian Greene (49:25.480)
Deep Space Nine Star,
Lex Fridman (49:26.500)
I'm sure there are many other examples
Brian Greene (49:27.860)
for these ideas that I've probably never even seen.
Lex Fridman (49:30.480)
But with wormholes, there's at least a proposal
Brian Greene (49:34.460)
of how you could take a wormhole tunnel through space time,
Lex Fridman (49:38.200)
manipulate the openings of the wormhole
Brian Greene (49:40.520)
in such a way that the openings are no longer synchronous.
Lex Fridman (49:44.100)
They are out of sync relative to each other,
Brian Greene (49:46.300)
which would mean one's ahead and one's behind,
Lex Fridman (49:48.980)
which means if you go through one direction,
Brian Greene (49:50.500)
you travel to the future.
Lex Fridman (49:51.620)
If you go back, you travel to the past.
Brian Greene (49:54.380)
Now, we don't know if there are wormholes in the world.
Lex Fridman (49:57.740)
But they're possible according to Einstein, correct?
Brian Greene (49:59.820)
They are possible according to Einstein.
Lex Fridman (50:01.760)
But even Einstein was very quick to say,
Brian Greene (50:04.420)
just because my math allows for something,
Lex Fridman (50:07.260)
doesn't mean it's real.
Brian Greene (50:08.100)
I mean, he famously didn't even believe in black holes.
Lex Fridman (50:10.860)
Didn't believe in the Big Bang, right?
Lex Fridman (50:12.900)
And yet the black hole issue has really been settled now.
Lex Fridman (50:17.180)
We have radio telescopic photographs
Brian Greene (50:20.740)
of the black hole in M87.
Lex Fridman (50:22.820)
It was in newspapers around the world
Brian Greene (50:25.240)
just a couple of years ago.
Lex Fridman (50:26.360)
So it's just to say that just because it's in Einstein's math,
Brian Greene (50:31.180)
it doesn't mean it's real.
Lex Fridman (50:32.180)
But yes, it is the case that wormholes
Brian Greene (50:35.000)
are allowed by Einstein's equations.
Lex Fridman (50:36.680)
And in principle, you can imagine, you know,
Brian Greene (50:39.460)
putting electric charges on the openings of the wormhole,
Lex Fridman (50:42.300)
allowing you to tow them around
Brian Greene (50:44.380)
in a manner that could yield
Lex Fridman (50:45.560)
this temporal asymmetry between them.
Brian Greene (50:48.180)
Maybe you tow one of the mouths to the edge of a black hole.
Lex Fridman (50:51.780)
In principle, you can do this,
Brian Greene (50:53.380)
slowing down the passage of time near that black hole.
Lex Fridman (50:56.540)
And then when you bring it back,
Brian Greene (50:58.140)
it will be well out of sync with the other opening
Lex Fridman (51:02.060)
and therefore could be a significant temporal gap
Brian Greene (51:05.420)
between one and the other.
Lex Fridman (51:07.100)
But people who study this in more detail question,
Brian Greene (51:10.840)
could you ever keep a wormhole open,
Lex Fridman (51:13.060)
assuming it does exist?
Brian Greene (51:14.760)
Could you ever travel through a wormhole
Lex Fridman (51:17.420)
or would there be a requirement
Brian Greene (51:19.700)
to some kind of exotic matter to prop it open
Lex Fridman (51:22.940)
that perhaps doesn't exist?
Lex Fridman (51:24.420)
So there are many, many issues that people have raised.
Lex Fridman (51:28.060)
And I would say that the general sentiment
Brian Greene (51:31.060)
is that it's unlikely that this kind of scenario
Lex Fridman (51:34.780)
is going to survive our deeper understanding of physics
Brian Greene (51:37.980)
when we finally have it.
Lex Fridman (51:39.220)
But that doesn't mean that the door is closed.
Lex Fridman (51:41.340)
So maybe there's a small possibility
Lex Fridman (51:44.800)
that this could one day be real.
Brian Greene (51:45.640)
That's such an interesting way to put it.
Lex Fridman (51:47.780)
It will not, this kind of scenario
Brian Greene (51:49.820)
will not survive deep understanding of physics.
Lex Fridman (51:53.500)
It's an interesting way to put it
Brian Greene (51:54.860)
because it makes you wonder what kind of scenarios
Lex Fridman (51:59.700)
will be created by our deeper understanding of physics.
Brian Greene (52:04.080)
Maybe, sorry to go crazy for a second,
Lex Fridman (52:08.340)
but if you have like the pan psychism idea
Brian Greene (52:11.220)
that consciousness permeates all matter,
Lex Fridman (52:14.200)
maybe traveling in that, whatever laws of physics,
Brian Greene (52:17.980)
the consciousness operates under something like that.
Lex Fridman (52:20.140)
In that view of the university,
Brian Greene (52:21.740)
if we somehow are able to understand that part,
Lex Fridman (52:24.140)
maybe traveling is super easy.
Brian Greene (52:26.420)
Yeah, it does not follow the constraints
Lex Fridman (52:30.340)
of the speed of light, something like this.
Brian Greene (52:32.700)
Yeah, so look, I have a definite degree of sympathy
Lex Fridman (52:38.380)
with the possibility that consciousness might be more
Brian Greene (52:42.980)
than what we described earlier
Lex Fridman (52:45.500)
as just the byproduct of mindless particles.
Brian Greene (52:48.180)
You just made the rock happy.
Lex Fridman (52:50.500)
Exactly, so it isn't the approach
Brian Greene (52:54.340)
that feels to me the most likely, but I see the logic.
Lex Fridman (52:59.580)
If you've got the puzzle,
Lex Fridman (53:01.680)
how to mindless particles build mind,
Lex Fridman (53:04.280)
one resolution might be the particles are not mindless.
Brian Greene (53:08.320)
The particles have some kind of proto conscious quality.
Lex Fridman (53:10.960)
So there's something appealing
Brian Greene (53:13.020)
about that straightforward solution to the puzzle.
Lex Fridman (53:16.180)
And if that's the case, if we do live in a pan psychist world
Brian Greene (53:20.140)
where there is a degree of consciousness residing
Lex Fridman (53:22.980)
in everything in the world around us, then yes,
Brian Greene (53:25.220)
I do think some interesting possibilities might emerge
Lex Fridman (53:28.820)
where maybe there's a way of communing
Brian Greene (53:31.720)
with physical reality in a deeper way than we have so far.
Lex Fridman (53:36.940)
I mean, we as human beings,
Brian Greene (53:38.660)
a vital part of our existence
Lex Fridman (53:40.580)
is human to human communication, contact.
Brian Greene (53:43.860)
We live in social groups and that's what it's allowed us
Lex Fridman (53:46.540)
to get to the place where we've gotten.
Brian Greene (53:48.820)
Imagine that we have long missed
Lex Fridman (53:51.700)
that there's other consciousness out there
Lex Fridman (53:54.700)
and some kind of relationship or communion
Lex Fridman (53:57.520)
with that larger conscious possibility
Brian Greene (53:59.980)
would take us to a different place.
Lex Fridman (54:01.380)
Now, do I buy into this yet?
Brian Greene (54:03.860)
I don't, I don't see any evidence for it,
Lex Fridman (54:06.420)
but do I have an open mind and allow for the possibility
Lex Fridman (54:10.460)
in the future?
Lex Fridman (54:11.420)
Yeah, I do.
Lex Fridman (54:13.460)
So if that's not the case
Lex Fridman (54:15.380)
and you have these simple particles
Brian Greene (54:18.420)
that at the macro level emerges some interesting stuff
Lex Fridman (54:21.880)
like consciousness, another thing you write about
Brian Greene (54:24.900)
in the Until the End of Time book
Lex Fridman (54:27.280)
is the thing that it seems to emerge at the macro level
Brian Greene (54:30.860)
is the feeling like there's a free will,
Lex Fridman (54:34.960)
like we decide to do stuff.
Lex Fridman (54:36.380)
And you have a really interesting take here,
Lex Fridman (54:39.100)
which is, no, there's not a free will.
Brian Greene (54:43.500)
I'm just gonna speak for you and then you can correct me.
Lex Fridman (54:45.900)
No, there's not a free will,
Lex Fridman (54:48.080)
but there is an experience of freedom.
Lex Fridman (54:51.420)
Yeah.
Brian Greene (54:54.260)
Which I really love.
Lex Fridman (54:56.100)
So where does the experience,
Brian Greene (54:58.400)
where does freedom come from
Lex Fridman (54:59.780)
if we don't have any kind of physics based free will?
Brian Greene (55:02.700)
Yeah, and so the idea follows naturally
Lex Fridman (55:06.820)
from all that we've been talking about.
Brian Greene (55:08.480)
Let's make the assumption that all there is
Lex Fridman (55:11.860)
in the physical universe is stuff governed by laws.
Brian Greene (55:15.380)
We may not have those laws,
Lex Fridman (55:16.520)
may not know what the fundamental stuff is yet,
Lex Fridman (55:19.500)
but everything we know in science points in the direction
Lex Fridman (55:23.700)
that it's physical stuff governed by universal laws.
Lex Fridman (55:27.860)
And that being the case, or that being the assumption,
Lex Fridman (55:31.380)
then you come to a particular collection
Brian Greene (55:33.880)
of those ingredients called a human being.
Lex Fridman (55:35.900)
And that human being has particles
Brian Greene (55:38.120)
that are fully governed by physical law.
Lex Fridman (55:41.620)
And when you then recognize it,
Brian Greene (55:43.100)
every thought that we have,
Lex Fridman (55:44.380)
every action that we undertake
Brian Greene (55:46.500)
is just the motion of particles.
Lex Fridman (55:49.400)
When I'm thinking thoughts right now,
Brian Greene (55:50.900)
of course, at this level of description,
Lex Fridman (55:53.840)
it is the motion of particles cascading
Brian Greene (55:56.320)
down various neurons inside of my head and so on.
Lex Fridman (55:59.820)
And every single one of those motions,
Brian Greene (56:02.780)
collectively and individually,
Lex Fridman (56:05.340)
is fully governed by these laws
Brian Greene (56:08.540)
that we perhaps don't have yet,
Lex Fridman (56:09.900)
but we imagine one day we will.
Brian Greene (56:12.060)
That leaves no opportunity for any kind of freedom
Lex Fridman (56:15.780)
to break free from the constraint of physical law.
Lex Fridman (56:19.580)
And that is the end of the story.
Lex Fridman (56:21.660)
So the traditional intuitive notion of free will,
Brian Greene (56:24.480)
that we're the ultimate authors of our actions,
Lex Fridman (56:26.880)
that we were the buck stops,
Brian Greene (56:28.300)
that there is no antecedent,
Lex Fridman (56:30.260)
that is the cause for our decided to go left or right,
Brian Greene (56:35.000)
choose vanilla or chocolate, live or die,
Lex Fridman (56:38.180)
that intuitive sensation does not have a basis
Brian Greene (56:42.060)
in our understanding of the physical world.
Lex Fridman (56:43.780)
So that's the end of the free will of the traditional sort.
Lex Fridman (56:47.140)
But then your question is,
Lex Fridman (56:49.100)
what about this other kind of freedom I talk about?
Lex Fridman (56:52.020)
And the other kind of freedom,
Lex Fridman (56:53.900)
if you focus on it intently,
Brian Greene (56:55.860)
I think is actually the true version of freedom
Lex Fridman (57:00.700)
that we feel.
Lex Fridman (57:02.180)
And that freedom is this.
Lex Fridman (57:04.300)
You look at inanimate objects in the world,
Brian Greene (57:07.020)
rocks, bottles of water, whatever,
Lex Fridman (57:10.140)
they have a very limited behavioral repertoire.
Lex Fridman (57:13.340)
Why?
Lex Fridman (57:14.180)
Their internal organization is too coarse
Lex Fridman (57:17.100)
for them to do very much, right?
Lex Fridman (57:18.880)
You try to have a conversation with a glass of water,
Brian Greene (57:22.040)
you send sound waves, it doesn't do much.
Lex Fridman (57:24.800)
It may vibrate a little bit,
Lex Fridman (57:26.140)
but the repertoire of responses are incredibly limited.
Lex Fridman (57:30.200)
The difference between us and a rock or a bottle of water
Brian Greene (57:33.060)
is that our inner organization,
Lex Fridman (57:35.100)
by virtue of eons of evolution by natural selection,
Brian Greene (57:38.420)
is so refined, so spectacularly ordered,
Lex Fridman (57:42.720)
that we have a huge repertoire of behaviors
Brian Greene (57:46.460)
that are finely attuned to stimuli from the external world.
Lex Fridman (57:51.460)
You ask me a question, that's a stimulus,
Lex Fridman (57:53.320)
and all of a sudden,
Lex Fridman (57:54.460)
these particle processes go into action,
Lex Fridman (57:56.860)
and this is the result, this answer that I'm giving you.
Lex Fridman (58:00.080)
So the freedom that we have is not from
Brian Greene (58:03.760)
the control of physical law.
Lex Fridman (58:05.580)
The freedom that we have is from the constrained behavior
Brian Greene (58:08.260)
that has long since governed inanimate objects.
Lex Fridman (58:11.380)
We are liberated from the limited behavioral repertoire
Brian Greene (58:14.700)
of rocks and bottles of water
Lex Fridman (58:17.220)
to have this broad spectrum of responses.
Lex Fridman (58:20.100)
Do we pick them?
Lex Fridman (58:20.940)
We do not.
Lex Fridman (58:21.840)
Do we freely choose them?
Lex Fridman (58:23.060)
We do not, but yet we have them,
Lex Fridman (58:26.060)
and we can marvel at those behaviors,
Lex Fridman (58:29.340)
and that's the freedom that we have.
Brian Greene (58:31.460)
The complexity and the breadth of that repertoire
Lex Fridman (58:34.300)
is where the freedom emerges.
Lex Fridman (58:36.700)
Is there something to be said about emergence?
Lex Fridman (58:40.260)
I don't know if you know,
Brian Greene (58:42.060)
I've looked at much about objects
Lex Fridman (58:43.700)
that I seem to love way more than anyone else,
Brian Greene (58:47.280)
which is Sally or Tom,
Lex Fridman (58:49.420)
like game of life type of stuff.
Brian Greene (58:51.700)
From simple things emerges beautiful complexities,
Lex Fridman (58:56.740)
and so that's that repertoire.
Brian Greene (58:58.980)
It's like, it seems if you have enough stuff,
Lex Fridman (59:04.060)
just beautiful complexity emerges
Brian Greene (59:06.300)
that sure as heck to our human eyes looks
Lex Fridman (59:09.620)
like there's consciousness there, there's free will,
Brian Greene (59:12.060)
there's little objects moving about and making decisions.
Lex Fridman (59:15.640)
I mean, all of that,
Brian Greene (59:16.820)
you can say it's anthropomorphization,
Lex Fridman (59:18.920)
but it sure as heck feels
Brian Greene (59:21.820)
like they're organisms making decisions.
Lex Fridman (59:25.580)
What is that emergence thing?
Lex Fridman (59:27.660)
Is that within the realm of physics to understand?
Lex Fridman (59:31.220)
Is it within the realm of poetry?
Lex Fridman (59:36.100)
What is that, like complex systems, emergence?
Lex Fridman (59:39.620)
Will that ever be understood by science?
Lex Fridman (59:41.580)
So here's the way that I think about it.
Lex Fridman (59:43.980)
So there are clearly qualities of the world
Brian Greene (59:47.820)
that emerge on macroscopic scales,
Lex Fridman (59:50.980)
our sense of beauty, wonder, consciousness,
Brian Greene (59:53.740)
all of these kinds of qualities.
Lex Fridman (59:55.900)
Do I feel that they ultimately are explainable
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