Brian Greene: Quantum Gravity, The Big Bang, Aliens, Death, and Meaning

00:00:00.000 | The following is a conversation with Brian Greene,

00:00:02.840 | theoretical physicist at Columbia

00:00:04.900 | and author of many amazing books on physics,

00:00:08.120 | including his latest, "Until the End of Time,

00:00:11.480 | Mind, Matter, and Our Search for Meaning

00:00:14.440 | in an Evolving Universe."

00:00:16.880 | This is the Lex Friedman Podcast.

00:00:19.080 | To support it, please check out our sponsors

00:00:21.180 | in the description.

00:00:22.420 | And now, here's my conversation with Brian Greene.

00:00:26.240 | In your most recent book, "Until the End of Time,

00:00:29.960 | you quote Bertrand Russell from a debate he had

00:00:32.640 | about God in 1948.

00:00:34.920 | He says, quote, "So far as scientific evidence goes,

00:00:39.560 | the universe has crawled by slow stages

00:00:42.440 | to a somewhat pitiful result on this earth

00:00:45.720 | and is going to crawl by still more pitiful stages

00:00:48.920 | to a condition of universal death.

00:00:51.280 | If this is to be taken as evidence of purpose,

00:00:55.080 | I can only say that the purpose is one

00:00:57.780 | that does not appeal to me.

00:00:59.640 | I see no reason, therefore, to believe in any sort of God."

00:01:03.360 | That's quite a depressing statement.

00:01:07.080 | As you say, this is a bleak outlook on our universe

00:01:09.920 | and the emergence of human consciousness.

00:01:12.400 | So let me ask, what is the more hopeful perspective

00:01:15.920 | to take on this story?

00:01:17.220 | - Well, I think the more hopeful perspective

00:01:19.900 | is to more fully understand

00:01:23.440 | what was driving Bertrand Russell to this perspective.

00:01:28.360 | And then to see it within a broader context.

00:01:32.680 | And really that's in some sense

00:01:34.720 | what my book "Until the End of Time" is all about.

00:01:37.480 | But in brief, I would say that there's a lot of truth

00:01:41.720 | to what Bertrand Russell was saying there.

00:01:43.700 | When you look at the second law of thermodynamics,

00:01:45.700 | which is the underlying scientific idea

00:01:48.160 | that's driving this notion

00:01:50.040 | that everything's gonna wither, decay, fall apart.

00:01:53.500 | Yeah, that's true.

00:01:55.120 | Second law of thermodynamics establishes that disorder,

00:01:58.800 | entropy, in aggregate, is always on the rise.

00:02:02.640 | And that is indeed interpretable

00:02:05.960 | as disintegration and destruction

00:02:07.620 | over sufficiently long timescales.

00:02:09.560 | But my view is, when you recognize

00:02:12.480 | how special that makes us,

00:02:14.960 | that we are these exquisitely ordered configurations

00:02:18.560 | of particles that only will last for a blink of an eye

00:02:22.080 | in cosmological time-like terms,

00:02:25.400 | the fact that we're here and we can do what we do,

00:02:27.400 | to me, that's just really something

00:02:30.920 | that inspires gratitude and wonder

00:02:34.160 | and a sense of deep purpose

00:02:38.020 | by virtue of being these unique collections of entities

00:02:42.080 | that happen to rise up, look around,

00:02:44.640 | and try to figure out where we are

00:02:46.480 | and what the heck we should do with our time.

00:02:48.520 | So it's not that I would disagree with Bertrand Russell

00:02:51.740 | in terms of the basic physics and the basic unfolding,

00:02:56.740 | but I think it's really a matter of the slant

00:03:00.560 | that you take on what it means for us.

00:03:02.840 | - So maybe we'll skip around a bit,

00:03:06.680 | but let me ask the biggest possible question,

00:03:08.860 | then you said purpose.

00:03:10.260 | So what's the meaning of it all then?

00:03:12.520 | Is there a meaning to life that we can take from this,

00:03:18.160 | from this brief emergence of complexity

00:03:22.180 | that arises from simple things

00:03:24.260 | and then goes into a heat death

00:03:26.860 | that is once again returns to simple things

00:03:29.780 | as the march of the second law of thermodynamics goes on?

00:03:33.060 | - I think there is,

00:03:33.880 | but I don't think it's a universal answer.

00:03:36.640 | And so I think throughout the ages,

00:03:39.340 | there has been a kind of quest for some final way

00:03:44.340 | of articulating meaning and purpose,

00:03:47.660 | whether it's God, whether it's love,

00:03:50.540 | whether it's companionship.

00:03:51.660 | I mean, many people put forward different ways

00:03:53.700 | of taking this question on,

00:03:56.660 | and there is no one right answer

00:03:59.340 | when you recognize deeply that the universe doesn't care.

00:04:04.340 | There is nothing out there that is the final answer.

00:04:08.900 | It's not as though we need a more powerful telescope

00:04:11.900 | and somehow if we can look deeply into the universe,

00:04:14.940 | all will become clear.

00:04:17.300 | In fact, the deeper we've looked,

00:04:18.980 | both literally and metaphorically,

00:04:21.440 | into the universe and into the structure of reality,

00:04:24.860 | the more it's become clear

00:04:27.020 | that we are just a momentary byproduct of laws of physics

00:04:32.020 | that don't have any emotional content.

00:04:36.220 | They don't have any intrinsic sense of meaning or purpose.

00:04:39.660 | And when you recognize that,

00:04:41.340 | you realize that searching for the universal

00:04:43.860 | for this kind of a question is a fool's errand.

00:04:47.700 | Every individual has the capacity

00:04:50.260 | to make their own meaning, to set their own purpose.

00:04:53.700 | And that's not some platitude.

00:04:55.780 | That is what we are.

00:04:57.860 | Because there is no fundamental answer.

00:04:59.780 | It's what you make of it.

00:05:01.120 | And however much that may sound like a hallmark card,

00:05:04.200 | this really is the deep lesson of physics

00:05:08.740 | and science more generally over the past few hundred years.

00:05:11.420 | - But there's some level where you can objectively say

00:05:14.700 | that whatever we got going on here is kind of peculiar.

00:05:18.060 | It's kind of special in terms of complexity.

00:05:23.060 | And maybe you can even begin to measure it

00:05:26.580 | and like come up with metrics

00:05:28.900 | where whatever we got going on on Earth,

00:05:31.560 | these like interesting hierarchical complexities

00:05:35.620 | that form more and more sophisticated biological system,

00:05:39.340 | that seems kind of unique

00:05:40.800 | when you look at the entirety of the universe.

00:05:43.540 | The observable part that we can see with our tools.

00:05:48.540 | I mean, so I have to ask,

00:05:50.660 | as you describe in your book once again,

00:05:52.880 | Schrodinger wrote the book, "What is Life?"

00:05:56.220 | based on a few lectures he gave in 1944.

00:05:59.220 | So let me ask the fundamental question here.

00:06:02.740 | What is life?

00:06:04.580 | This particular thing we got going on here,

00:06:06.840 | this pocket of complexity

00:06:08.300 | that emerged from such simple things.

00:06:10.220 | - Yeah, it's a tough question.

00:06:11.660 | I asked that question even to Richard Dawkins once,

00:06:15.620 | and I already have my preconceived notion,

00:06:18.380 | which he pretty much confirmed,

00:06:20.060 | which is if one could give an answer to that question

00:06:24.940 | that allowed you to sort of draw a line in the sand

00:06:28.100 | between the not living and the living,

00:06:30.680 | then perhaps we would have the insight that we yearn for

00:06:34.020 | in trying to say what is so special about life.

00:06:36.460 | But the fact of the matter is it's a continuum.

00:06:39.260 | There's a continuum from the things

00:06:41.180 | that we would typically call non-living and animate

00:06:44.100 | to the things that we obviously call animate

00:06:46.660 | and full of the currents of life.

00:06:49.780 | Somewhere in there,

00:06:51.780 | it is a question of the complexity of the structure,

00:06:55.500 | the ability of the structure to take in raw material

00:07:00.320 | from the environment and process it through a metabolism

00:07:04.020 | that allows the structure to extract energy

00:07:07.260 | and to release entropy to the wider environment.

00:07:10.980 | Somewhere in those collections of biological processes

00:07:15.100 | is the necessity or the necessary ingredients

00:07:19.540 | and processes for life,

00:07:20.580 | but drawing that line in the sand

00:07:22.620 | is not something that we're able to do.

00:07:25.540 | But I would agree with you.

00:07:27.500 | It's deeply peculiar.

00:07:30.020 | It may, in fact, be unique, but it may not.

00:07:35.000 | It could be that the universe is such

00:07:38.260 | that under fairly typical conditions,

00:07:41.020 | a star that's a well-ordered source of low entropy energy,

00:07:46.020 | that's what the sun is,

00:07:49.120 | together with the planet being bathed

00:07:51.020 | by that low entropy energy,

00:07:52.700 | together with a surface that has enough

00:07:55.740 | of the raw constituents that we recognize

00:07:59.300 | are fairly commonplace result of supernova explosions

00:08:03.140 | where a star spews forth the result of the nuclear furnace

00:08:07.980 | that is the core of a star.

00:08:09.260 | It could be that all you need

00:08:11.700 | are those fairly commonplace conditions

00:08:15.040 | and maybe life naturally forms.

00:08:17.040 | Look, the James Webb Space Telescope

00:08:19.460 | is going up, hopefully, in December.

00:08:21.780 | And one of the goals of that mission

00:08:23.760 | is to look at atmospheres around distant planets

00:08:26.660 | and perhaps come to some sense of how special

00:08:30.460 | or not life, or at least life as we know it,

00:08:34.000 | is in the universe.

00:08:35.980 | - Which part of the story of life,

00:08:39.060 | let's stick to Earth for a second,

00:08:40.700 | do you think is the hardest?

00:08:42.760 | If you were like a betting man,

00:08:45.740 | which part is the hardest to make happen?

00:08:48.440 | Is it the origin of life?

00:08:50.180 | Again, we haven't drawn the line of where,

00:08:52.500 | as you say, the line between a rock and a rabbit.

00:08:57.820 | That part, is it complex organisms

00:09:01.180 | like multicellular organisms?

00:09:03.260 | Is it crawling out of the ocean

00:09:05.980 | where the fish somehow figured out how to crawl around?

00:09:09.380 | Is it then the us homo sapiens,

00:09:12.960 | as we like to think of ourselves, special and intelligent?

00:09:16.460 | Or is it somewhere in between, as you also talk about,

00:09:20.260 | again, very hard to know

00:09:23.500 | at which point does consciousness emerge?

00:09:28.500 | If you were to sort of took a survey

00:09:31.940 | and made bets about other Earth-like planets

00:09:35.220 | in the universe,

00:09:36.380 | where do you think they get stuck the most?

00:09:38.660 | - Well, I would certainly say,

00:09:39.500 | if we're gonna go all the way

00:09:40.380 | to conscious beings like ourselves,

00:09:42.420 | I would put it at the onset of consciousness,

00:09:45.180 | which again, I think is a continuum.

00:09:47.620 | I don't think it is something

00:09:49.120 | that you can draw the line in the sand,

00:09:51.660 | but there are obvious circumstances,

00:09:53.980 | there are obvious creatures such as ourselves,

00:09:56.020 | where we do recognize a certain kind

00:09:58.540 | of self-reflective conscious awareness.

00:10:01.820 | And if we think about what it would require

00:10:05.660 | for a system of living beings to acquire consciousness,

00:10:10.660 | I think that's probably the hardest part,

00:10:13.580 | because look, take Earth and recognize

00:10:16.740 | that it weren't for some singular event,

00:10:20.460 | 65 million years ago,

00:10:21.980 | where this large rock slams into planet Earth

00:10:25.340 | and wipes out the dinosaurs,

00:10:27.860 | maybe the dinosaurs would still rule the planet

00:10:31.380 | and they may well have not developed

00:10:35.580 | the kind of conscious awareness that we have.

00:10:38.900 | So for billions of years on this planet,

00:10:41.580 | there was life that didn't have

00:10:44.140 | the kind of conscious awareness that we have.

00:10:47.180 | And it was an accidental event in astrophysical history

00:10:52.180 | that allowed a mammalian species like us

00:10:56.140 | to ultimately be the end product.

00:10:58.260 | And so, yeah, I could imagine there's a lot of life

00:11:00.980 | out there, but perhaps none of it's wondering

00:11:04.780 | what's the meaning of life or trying to make sense of it,

00:11:08.620 | just going about its business of survival,

00:11:11.260 | which of course is the dominant activity

00:11:13.620 | that life on this planet has practiced.

00:11:15.620 | We are a rare exception to that.

00:11:17.900 | - And I really appreciate that you lean into

00:11:20.020 | some of these unanswerable questions with me today.

00:11:22.500 | But so you think about consciousness

00:11:25.420 | not as like a phase shift, the binary zero one.

00:11:28.420 | You think of it as a continuum,

00:11:31.580 | that humans somehow are maybe some

00:11:34.700 | of the most conscious beings on Earth.

00:11:37.020 | - I mean, people will dispute that.

00:11:40.820 | - Yes, I mean, well--

00:11:41.660 | - And it's a very hard argument to make.

00:11:43.660 | - People will dispute that.

00:11:44.900 | - Rocks probably will stay quiet on the matter.

00:11:47.220 | - Maybe not, right?

00:11:48.820 | For the moment, they're waiting for their opportunity.

00:11:51.620 | But I agree that, look, even when you and I

00:11:56.620 | look at each other, I am not fully convinced

00:12:01.660 | that you're a conscious being, right?

00:12:03.580 | I mean, I think that you are.

00:12:04.420 | - It's not to me.

00:12:05.340 | - I mean, your behavior is such that

00:12:07.340 | that's the best explanation for what's going on.

00:12:09.380 | But of course, we're all in the position

00:12:11.480 | of only having direct awareness of our own conscious being.

00:12:16.480 | And therefore, when it comes to other creatures in the world,

00:12:19.860 | we're in a similar state of ignorance

00:12:21.740 | regarding what's actually happening

00:12:23.280 | inside of their head, if they have a head.

00:12:26.560 | And so it's hard to know how singular we are.

00:12:30.360 | But I would say, based on the best available data

00:12:33.320 | and the best explanations that we can make,

00:12:34.960 | yeah, there is something special about us.

00:12:36.600 | I don't think that there are fish walking around

00:12:39.520 | and coming up with existentialism.

00:12:43.240 | I don't know that there are dogs walking around

00:12:46.840 | who've developed an understanding

00:12:48.280 | of the general theory of relativity.

00:12:49.640 | I mean, maybe we're wrong,

00:12:50.840 | but that seems the best explanation.

00:12:52.740 | - What do you think is more special,

00:12:55.720 | intelligence or consciousness?

00:12:57.960 | - I think consciousness.

00:12:59.320 | And I think that there's a deep connection

00:13:02.160 | between these ideas.

00:13:03.600 | They are distinct, but they're deeply connected.

00:13:06.000 | But look, I mean, to me and to, of course,

00:13:09.120 | many philosophers actually coined a name for this,

00:13:11.320 | the hard problem of consciousness,

00:13:12.920 | you know, David Chalmers and others.

00:13:15.480 | As a physicist, I look at the world

00:13:17.780 | and I see it's particles governed by physical law.

00:13:22.780 | We can name them.

00:13:24.440 | You know, we got electrons, we got quarks

00:13:27.800 | that come in various flavors and so forth.

00:13:29.920 | We have a list of ingredients that science has revealed.

00:13:33.480 | And we have a list of laws

00:13:34.840 | that seemingly govern those ingredients.

00:13:37.320 | And nowhere in there is there even a hint

00:13:41.320 | that when you put those particles together in the right way,

00:13:45.720 | an inner world should turn on.

00:13:48.280 | And it's not only that there's no hint, it's insane.

00:13:52.080 | I mean, it's ridiculous.

00:13:53.720 | How could it be that a thoughtless,

00:13:56.680 | passionless, emotionless particle,

00:14:00.180 | when grouped together with compatriots,

00:14:03.200 | somehow can yield something so deeply foreign

00:14:07.280 | to the nature of the ingredients themselves?

00:14:09.380 | So answering that question,

00:14:12.900 | I think is among the deepest

00:14:14.920 | and most difficult questions that we face.

00:14:17.920 | - Do you think it is in fact a really hard problem?

00:14:22.920 | Or is it possible, I think you mentioned in your book

00:14:28.120 | that it's just like almost like a side effect.

00:14:30.080 | It's an emergent thing that's like,

00:14:32.000 | oh, it's nice.

00:14:33.200 | It's like a nice little feature.

00:14:34.920 | - Yeah, well, I mean, when people use the phrase

00:14:37.600 | hard problem, I mean,

00:14:38.760 | they mean in a somewhat technical sense

00:14:40.800 | that it's trying to explain something

00:14:44.760 | that seems fundamentally unavailable

00:14:47.640 | to third party objective analysis, right?

00:14:52.640 | I'm the only one that can get inside my head.

00:14:55.640 | And I can tell you a lot about what's happening

00:14:57.720 | inside my head right now is reflected in what I'm saying.

00:15:00.360 | And you can try to deduce things

00:15:02.160 | about what's going on inside my head,

00:15:03.520 | but you don't have access to it in the way that I do.

00:15:06.240 | And so it seems like a fundamentally different

00:15:08.080 | kind of problem from the ones that we have

00:15:11.360 | successfully dealt with over the course of centuries

00:15:13.760 | in science where we look at the motion of the moon,

00:15:15.880 | everybody can look, everybody can measure it.

00:15:18.280 | We look at the properties of hydrogen,

00:15:20.900 | when you shine lasers on,

00:15:22.640 | everybody can look at the data and understand it.

00:15:25.840 | And so it seems like a fundamentally different problem.

00:15:28.960 | And in that sense, it seems like it is hard

00:15:32.360 | relative to the others.

00:15:33.640 | But I do think ultimately that the explanation will be,

00:15:37.680 | as you recount, I think that 100 years from now,

00:15:41.160 | or maybe it's a thousand,

00:15:42.200 | it's hard to predict the timescale for developments,

00:15:45.520 | but I think we'll get to a place where we'll look back

00:15:48.440 | and kind of smile at those folks in the 20th century

00:15:53.320 | and before 21st century and before

00:15:55.360 | who thought consciousness was so incredibly mysterious

00:15:59.320 | when the reality of it is, eh,

00:16:01.400 | it's just a thing that happens when particles come together.

00:16:05.800 | And however mysterious that feels right now,

00:16:10.420 | I think, for instance,

00:16:11.260 | when we start to build conscious systems,

00:16:13.680 | things that you're more familiar with than I am,

00:16:16.000 | when we start to build these artificial systems

00:16:19.440 | and those systems report to us,

00:16:21.180 | I'm feeling sad, I'm feeling anxious.

00:16:24.320 | Yeah, there's a world going on inside here.

00:16:26.680 | I think the mystery of consciousness

00:16:28.640 | will just begin to evaporate.

00:16:30.880 | - Well, first of all, beautifully put,

00:16:33.480 | and I agree with you completely,

00:16:35.280 | just the way you said it, it'll begin to evaporate.

00:16:38.520 | I have built quite a few robots

00:16:41.280 | and have had them do emotional type things.

00:16:46.280 | And it's immediate that exactly what you're saying,

00:16:49.420 | this kind of mystery of consciousness starts to evaporate,

00:16:52.640 | that the kind of need to truly understand,

00:16:57.640 | to solve the hard problem of consciousness disappears,

00:17:00.400 | because, well, I don't really care

00:17:03.880 | if I understand or can solve

00:17:05.680 | the hard problem of consciousness.

00:17:07.360 | That thing sure as heck looks conscious.

00:17:09.560 | You know, I feel like that way when I interact with a dog.

00:17:12.880 | I don't need to solve the problem of consciousness

00:17:16.440 | to be able to interact and richly enjoy the experience

00:17:22.440 | with this other living being.

00:17:24.400 | Obviously, same thing with other humans.

00:17:26.440 | I don't need to fully understand it.

00:17:27.960 | And there's some aspect,

00:17:30.000 | maybe this is a little bit too engineering focused,

00:17:32.140 | but there's some aspect in which

00:17:33.920 | it feels like consciousness is just a nice trick

00:17:37.800 | to help us communicate with each other.

00:17:41.760 | It sounds ridiculous to say,

00:17:43.680 | but sort of the ability to experience the world

00:17:49.800 | is very useful in a subjective sense,

00:17:52.800 | is very useful to put yourself in that world

00:17:56.200 | and to be able to describe the experience to others.

00:17:59.360 | It could be just a social and the emerge.

00:18:01.840 | Obviously, animals, the sort of more primitive animals

00:18:04.500 | might experience consciousness in some more primitive way,

00:18:08.760 | but this kind of rich subjective experience

00:18:12.280 | that we think about as humans,

00:18:13.720 | I think it's probably deeply coupled

00:18:15.440 | like language and poetry.

00:18:17.840 | - Yeah, that resonates with my view as well.

00:18:20.720 | I mean, there's a scientist,

00:18:22.280 | maybe you've spoken to him,

00:18:23.400 | Michael Graziano from Princeton.

00:18:25.200 | Yeah, he's developed ideas of consciousness that,

00:18:29.640 | look, I don't think they solve the problem,

00:18:31.660 | but I think they do illuminate it in an interesting way

00:18:34.400 | where basically we are not aware

00:18:39.040 | of all the underlying physiochemical processes

00:18:43.120 | that make our brains and our inner worlds

00:18:45.960 | tick the way they do.

00:18:48.040 | And because of that dissociation between sensation

00:18:52.240 | and the physics of it and the chemistry of it

00:18:55.120 | and the biology of it,

00:18:56.600 | it feels like our minds and our inner worlds

00:18:59.600 | are just untethered,

00:19:00.960 | like floating somewhere in this gray matter

00:19:04.640 | inside of our heads.

00:19:06.500 | And the way I like to think of it is like,

00:19:08.600 | look, if you're in a dark room, right?

00:19:13.960 | And I had glow-in-the-dark paint on my fingers.

00:19:17.360 | So all you saw was my fingers dancing around.

00:19:20.360 | There'd be something mysterious.

00:19:22.000 | How could those fingers be doing that?

00:19:24.440 | And then you turn on the light,

00:19:25.280 | you realize, oh, there's this arm underlying it.

00:19:27.720 | And that's the deep physical connection explains it all.

00:19:30.800 | And I think that's what we're missing,

00:19:32.640 | the deep physical connection

00:19:34.340 | between what's happening up here

00:19:36.440 | and what is responsible for it

00:19:38.560 | in a physical, chemical, biological way.

00:19:41.440 | And so to me, that at least gives me some understanding

00:19:43.640 | of why consciousness feels so mysterious,

00:19:46.760 | because we are suppressing all of the underlying science

00:19:51.600 | that ultimately is responsible for it.

00:19:53.560 | And one day we will reveal that more fully.

00:19:55.960 | And I think that will help us tether this experience

00:19:59.280 | to something quite tangible in the world.

00:20:01.600 | - I wonder if the mystery

00:20:05.400 | is an important component of enjoying something.

00:20:10.160 | So once we know how this thing works,

00:20:14.200 | maybe we will no longer enjoy this conversation.

00:20:19.200 | We'll seek other sources of enjoyment.

00:20:21.280 | But this is, again, from an engineering perspective.

00:20:25.360 | I wonder if the mystery is an important component.

00:20:29.040 | - Well, have you ever seen,

00:20:31.560 | there's this beautiful interview that Richard Feynman did,

00:20:36.560 | great Nobel Laureate physicist

00:20:39.040 | responsible for a lot of our understanding

00:20:40.720 | of quantum mechanics, quantum field theory, and so forth.

00:20:43.080 | And he was in a conversation with an interviewer

00:20:46.520 | where he noted that some people feel like

00:20:48.760 | once the mystery is gone, once science explains something,

00:20:53.400 | the beauty goes away, the wonder of it goes away.

00:20:58.280 | And he was emphasizing in his response to that,

00:21:02.040 | he's like, "No, that's not the right way of thinking about it."

00:21:05.000 | He says, "Look, when I look at a rose,"

00:21:07.680 | he says, "Yeah, I can still deeply enjoy the aroma,

00:21:11.440 | "the color, the texture."

00:21:13.880 | He says, "But what I can do that you can't

00:21:15.820 | "if you're not a physicist, I can look more deeply

00:21:18.640 | "and understand where the red comes from,

00:21:20.260 | "where the aroma comes from,

00:21:21.420 | "where the structure comes from."

00:21:22.720 | He says, "That only augments my wonder.

00:21:27.720 | "It only augments my experience.

00:21:29.820 | "It doesn't flatten it or take away from it."

00:21:32.600 | So I sort of-- - I hope he's right.

00:21:34.440 | - Yeah, well, I sort of take that as a bit of a motto

00:21:37.920 | in some sense that there is a wonder

00:21:41.620 | that comes from a kind of ignorance.

00:21:43.840 | And I don't mean that in a derogatory sense,

00:21:45.720 | but just from not knowing.

00:21:47.280 | So there is a wonder that comes from mystery.

00:21:49.720 | There's another kind of wonder that comes from knowing

00:21:53.480 | and deep knowing.

00:21:55.840 | And I think that kind of wonder has its own special character

00:22:00.840 | that in some ways can be more gratifying.

00:22:04.140 | - I hope he's right.

00:22:06.060 | I hope you're right.

00:22:07.460 | But there's also, I remember he said something

00:22:10.300 | about like science is an onion or something like that.

00:22:13.940 | You can peel back, you keep peeling back.

00:22:16.540 | I mean, there is also, when you understand something,

00:22:19.600 | there's always a sense that there's more mystery

00:22:22.060 | to understand.

00:22:23.380 | Like you never get to the bottom of the mystery.

00:22:27.060 | - But I think it's also different than,

00:22:29.820 | I don't think you can analogize say to a magician, right?

00:22:33.660 | A magician does some trick, you learn how it sounds like,

00:22:36.260 | oh my God, that's ridiculous when you find.

00:22:39.580 | But nature is perhaps the best magician

00:22:42.820 | if you wanna try to make the analogy there

00:22:45.100 | because when you peel things back and you understand

00:22:48.900 | how it is that things have color and you have electrons

00:22:53.260 | dancing from one orbital to another,

00:22:56.460 | emitting photons at very particular wavelengths

00:22:59.260 | that are described by these beautiful equations

00:23:01.940 | of quantum electrodynamics,

00:23:03.500 | part of which that Feynman developed,

00:23:06.140 | it gives you a greater sense of awe

00:23:09.500 | when the curtain is pulled back

00:23:11.740 | than what happens in other circumstances

00:23:14.380 | where it does flatten it completely.

00:23:16.420 | - Yeah, it's very possible then, say in physics,

00:23:18.580 | that we arrive at a theory of everything

00:23:21.420 | that unifies the laws of physics

00:23:23.500 | and has a very strong understanding

00:23:25.020 | of the fabric of reality.

00:23:26.580 | Even like from the big bang to today,

00:23:30.420 | it's possible that that understanding

00:23:33.020 | is only going to elevate our appreciation

00:23:36.540 | of this whole thing.

00:23:37.380 | - Yeah, I think it will.

00:23:38.300 | I think it will.

00:23:39.140 | I mean, I think it has so far.

00:23:41.020 | But the other side of it which you emphasize

00:23:43.420 | is it's not like science somehow reaches an end, right?

00:23:48.420 | There are certain categories of questions

00:23:51.460 | that do reach an end.

00:23:53.060 | I think we one day will close the book

00:23:55.100 | on nature's ingredients and the fundamental laws.

00:23:58.140 | Now that, we can't prove that.

00:23:59.660 | Maybe it goes on forever, smaller and smaller.

00:24:02.380 | Maybe there are deeper and deeper laws.

00:24:03.860 | But I don't think so.

00:24:04.820 | I think that there's going to be a collection of ingredients

00:24:07.500 | and a collection of basic laws.

00:24:09.340 | That chapter will close.

00:24:11.300 | But it's one chapter.

00:24:13.660 | Now we take that knowledge and we try to understand

00:24:16.900 | how the world builds the structures that it does,

00:24:19.780 | from planets to people to black holes

00:24:23.420 | to the possibility of other universes.

00:24:25.660 | And every step of the way,

00:24:27.740 | the collection of questions that we don't know the answer to

00:24:30.900 | only blossoms.

00:24:32.340 | And so there's a deep sense of gratification

00:24:36.800 | from understanding certain qualities of the world.

00:24:39.060 | But I would say that if you take a ratio

00:24:42.540 | of what we understand to the things that we know

00:24:45.800 | that we don't yet understand,

00:24:47.720 | that ratio keeps getting smaller and smaller

00:24:50.060 | because the things that we know that we don't understand

00:24:52.180 | grows larger and larger.

00:24:53.380 | - Do you have a hope that we solve that

00:24:56.700 | theory of everything puzzle in the next few decades?

00:25:00.220 | So there's been a bunch of attempts from string theory

00:25:03.860 | to all kinds of attempts at trying to solve quantum gravity

00:25:07.540 | or basically come up with a theory for quantum gravity.

00:25:10.300 | There's a lot of complexities to this.

00:25:13.300 | One, for experimental validation,

00:25:16.300 | you have to observe effects

00:25:17.860 | that are very difficult to measure.

00:25:20.460 | So you have to build, that's like an engineering challenge.

00:25:23.700 | And then there's the theory challenge,

00:25:25.300 | which is like, it seems very difficult

00:25:28.420 | to connect the laws of gravity to quantum mechanics.

00:25:31.860 | Do you have a hope or are we hopelessly stuck?

00:25:35.520 | - Well, I have to have a hope.

00:25:37.660 | I mean, it's in some sense,

00:25:39.660 | but I devote at least part of my professional life

00:25:43.340 | toward trying to make progress on,

00:25:45.080 | I'm glad you used the phrase quantum gravity.

00:25:47.580 | I'm not a great fan of the theory of everything phrase

00:25:50.340 | because it does make other scientists feel like

00:25:53.340 | if they're not working on this, what are they working on?

00:25:55.660 | Man's like, you know, there's not much left

00:25:57.500 | when you're talking about theory of everything.

00:25:58.860 | - Biology is just small details.

00:26:00.260 | - Yeah, right, exactly.

00:26:01.500 | Yeah, so it is really trying to put gravity

00:26:04.220 | and quantum mechanics together.

00:26:06.180 | And since I was a college kid,

00:26:08.600 | I was deeply fascinated with gravity.

00:26:12.980 | And as I learned quantum mechanics,

00:26:15.500 | the notion of physicists being stumped

00:26:19.020 | and trying to blend them together,

00:26:20.580 | how could one not get fired up about

00:26:22.900 | maybe contributing something to that journey?

00:26:25.940 | And so we've been on this, you know,

00:26:27.660 | I've been on this for 30 years since I was a student.

00:26:29.820 | We have made progress.

00:26:31.820 | We do have ideas.

00:26:32.860 | You mentioned string theory is one possible scenario.

00:26:36.240 | It's not stuck.

00:26:37.540 | String theory is a vibrant field of research

00:26:40.900 | that is making incredible progress,

00:26:43.620 | but we've not made progress on this issue

00:26:47.320 | of experimental verification, validation,

00:26:49.460 | which is, you know, it is a vital part of the story.

00:26:53.940 | So I would have hoped that by now

00:26:55.740 | we would have made contact with observation.

00:26:58.620 | If you would have interviewed me back in the '80s

00:27:01.620 | when I was, you know, a wild, bright-eyed kid

00:27:04.940 | trying to make headway, working 18 hours a day

00:27:07.140 | and this sort of stuff, I would have said,

00:27:08.300 | yeah, by 2021, yeah, we're gonna know

00:27:11.100 | whether it's right or wrong.

00:27:12.100 | We'll have made contact.

00:27:13.600 | I would have said, look,

00:27:14.440 | there may be certain mathematical puzzles

00:27:15.980 | that we've yet to work out,

00:27:17.180 | but we'll know enough to make contact with experiment.

00:27:19.880 | That has not happened.

00:27:21.540 | On the other hand, if you would have interviewed me back then

00:27:24.220 | and asked me, will we be able to talk

00:27:26.840 | about detailed qualities of black holes

00:27:30.440 | and understand them at the level of detail

00:27:34.940 | that we actually, I would have said, no,

00:27:37.700 | I don't think that we're gonna be able to do that.

00:27:39.820 | Will we have an exact formulation of string theory

00:27:42.700 | in certain circumstances?

00:27:43.980 | No, I don't think we're gonna have that, and yet we do.

00:27:46.600 | So it's just to say you don't know

00:27:47.940 | where the progress is going to happen,

00:27:51.020 | but yes, I do hold out hope that maybe before I move on

00:27:56.020 | to wherever, I don't think there is an after,

00:27:58.100 | but I would love before I leave this earth

00:28:01.780 | to know the answer, but science and the universe,

00:28:06.780 | it's not about pleasing any individual.

00:28:10.420 | It is what it is, and so we just press onward

00:28:13.660 | and we'll see where it goes.

00:28:15.000 | - So in terms of string theory,

00:28:17.100 | if I just look from an outsider's perspective currently

00:28:20.420 | at the theoretical physics community,

00:28:22.480 | string theory as a theory has been very popular

00:28:26.500 | for a few decades, but it has recently fallen out of favor,

00:28:30.700 | or at least there's been like,

00:28:32.900 | it became more popular to kind of ask the question,

00:28:36.940 | is string theory really the answer?

00:28:39.340 | Where do you fall on this?

00:28:40.860 | Like, how do you make sense of this puzzle?

00:28:43.180 | Why do you think it's fallen out of favor?

00:28:45.440 | - Yeah, so I would actually challenge the statement

00:28:47.860 | that's fallen out of favor.

00:28:50.260 | I would say that any field of research,

00:28:54.220 | when it's new and it's the bright, shiny bicycle

00:28:58.700 | that no one has yet seen on that block,

00:29:01.020 | yeah, it's going to attract attention

00:29:03.020 | and the news outlets are going to cover it

00:29:06.060 | and students are going to flock to it, sure,

00:29:09.180 | but as a field matures, it does shed those qualities

00:29:14.180 | because it's no longer as novel as it was

00:29:17.260 | when it was first introduced 30, 40 years ago,

00:29:20.340 | but you need to judge it by a different standard.

00:29:22.660 | You need to judge it by,

00:29:24.300 | is it making progress on foundational issues,

00:29:28.180 | deepening our understanding of the subject?

00:29:30.180 | And by that measure, string theory is scoring very high.

00:29:36.580 | Now, at the same time, you also need to judge

00:29:39.260 | whether it makes contact with experiment

00:29:41.060 | as we discussed before too,

00:29:42.860 | and in that measure, we're still challenged.

00:29:45.860 | So I would say that many string theorists, myself included,

00:29:50.860 | are very sober about the theory.

00:29:55.020 | It has the tremendous progress that it had 30, 40 years ago,

00:29:59.020 | that hasn't gone away,

00:30:00.620 | but we've become better equipped

00:30:03.540 | at assessing the long journey ahead,

00:30:07.420 | and that was something that we weren't particularly good at

00:30:10.260 | back, say, in the '80s.

00:30:11.580 | Look, when I was just starting out in the field,

00:30:14.620 | there was a sense of physics is about to end.

00:30:18.820 | String theory is about to be the be-all and end-all,

00:30:22.700 | final unified theory,

00:30:24.260 | and that will bring this chapter to a close.

00:30:27.780 | Now, I have to say, I think it was more the younger

00:30:30.180 | physicists who were saying that.

00:30:31.840 | Some of them were seasoned,

00:30:32.900 | even if they were pro-string theory at the time.

00:30:35.820 | I don't know if they were rolling their eyes,

00:30:37.700 | but they knew that it was gonna be a long, long journey.

00:30:41.780 | I think people like John Schwartz,

00:30:43.860 | one of the founders of string theory,

00:30:45.180 | Michael Green, no relation to me, founders of the theory,

00:30:48.180 | Edward Witten, one of the main people driving the theory

00:30:52.100 | back then and today,

00:30:53.900 | I think they knew that we were in for a long haul,

00:30:58.900 | and that's the nature of science.

00:31:01.780 | Quick hits that resolve everything, few and far between.

00:31:06.180 | And so if you were in for the quick solution

00:31:11.180 | to the big questions of the world,

00:31:13.860 | then you would have been disappointed,

00:31:15.100 | and I think there were people who were disappointed

00:31:16.820 | and moved on and worked on other subjects.

00:31:19.740 | If you're in in the way that Einstein was in

00:31:23.340 | for a lifetime of investigation to try to see

00:31:26.900 | what the answers to the deep questions would be,

00:31:30.660 | then I think string theory has been a rich source

00:31:33.860 | of material that has kept so many people deeply engaged

00:31:38.860 | in moving the frontier forward.

00:31:41.300 | - There's a few qualities about string theory

00:31:43.020 | which are weird.

00:31:45.140 | I mean, a lot of physics is just weird and beautiful.

00:31:48.940 | So let me ask the question,

00:31:50.220 | what to you is most beautiful about string theory?

00:31:53.140 | - Well, what attracted me to the theory at the outset,

00:31:57.900 | beyond its putting gravity and quantum mechanics together,

00:32:01.020 | which I think is its true claim to fame,

00:32:03.980 | at least on paper it's able to do that.

00:32:06.780 | What attracted me to the theory was the fact

00:32:08.300 | that it requires extra dimensions of space.

00:32:11.180 | And this was an idea that intrigued me in a very deep way,

00:32:16.180 | even before I really understood what it meant.

00:32:20.620 | I somehow had, I mean, talk about sort of

00:32:24.060 | the emotional part of consciousness and the cognitive part,

00:32:27.180 | in some, perhaps you call it strange,

00:32:29.460 | in some strange emotional way,

00:32:31.940 | I was enamored with Einstein's general relativity,

00:32:35.420 | the idea of curved space and time,

00:32:37.740 | before I really knew what it meant, it just spoke to me.

00:32:41.180 | I don't know how else to say it.

00:32:43.260 | And then when I subsequently learned

00:32:46.620 | that people had thought about more dimensions of space

00:32:49.600 | than we can see and how those extra dimensions

00:32:52.380 | would be vital to a deep understanding

00:32:55.060 | of the things that we do see in this world,

00:32:56.940 | four, five, six dimensions might explain

00:32:59.780 | why there are certain forces and particles

00:33:01.740 | and how they behave, to me, this was like amazing,

00:33:05.460 | utterly amazing, and then when I learned

00:33:08.180 | that string theory embraced all these ideas,

00:33:10.700 | embraced the general theory of relativity,

00:33:12.500 | embraced quantum mechanics,

00:33:13.620 | embraced the possibility of extra dimensions,

00:33:16.320 | then I was hooked.

00:33:19.140 | And so when I was a graduate student,

00:33:21.460 | we would just spend hours,

00:33:23.780 | we, I mean a couple of other graduate students and myself

00:33:26.220 | who had sort of worked really well together,

00:33:29.260 | this was at Oxford in England,

00:33:30.900 | we would work these enormous numbers of hours a day

00:33:33.860 | trying to understand the shapes of these extra dimensions,

00:33:36.300 | the geometry of them, what those geometrical shapes

00:33:39.780 | for the extra dimensions would imply

00:33:41.420 | for things that we see in the world around us,

00:33:43.740 | and it was a heady, heady time,

00:33:46.660 | and that kind of excitement has sort of filtered through

00:33:50.460 | over the decades, but I'd say that's really

00:33:53.980 | the part of the theory that I think

00:33:57.540 | really hooked me most strongly.

00:33:59.360 | - How are we supposed to think about those extra dimensions?

00:34:02.820 | Are we supposed to imagine actual physical reality

00:34:05.900 | or is this more in the space of mathematics

00:34:08.580 | that allows you to sort of come up with tricks

00:34:11.580 | to describe the four-dimensional reality

00:34:14.580 | that we more directly perceive?

00:34:17.400 | - No one really knows the answer, of course,

00:34:19.660 | but if I take the most straightforward

00:34:22.140 | approach to string theory, you really are imagining

00:34:24.980 | that these dimensions are there, they're real.

00:34:28.780 | I mean, just as you would say that the three space dimensions

00:34:32.560 | around us, you know, left, right, back, forth, up, down,

00:34:35.660 | yeah, they're real, they're here,

00:34:37.900 | we are immersed within those dimensions.

00:34:40.340 | These other dimensions are as real as these

00:34:44.500 | with the one difference being their shape and their size

00:34:47.620 | differs from the shape and size of the dimensions

00:34:50.500 | that we have direct access to through human experience.

00:34:54.660 | And one approach imagines that these extra dimensions

00:34:57.700 | are tightly coiled up, curled up, crushed together,

00:35:02.240 | if you will, into a beautiful geometrical form

00:35:06.500 | that's all around us, but just too small for us to detect

00:35:11.220 | with our eyes, too small for us to detect

00:35:13.280 | even with the most powerful equipment that we have.

00:35:16.220 | Nevertheless, according to the mathematics,

00:35:18.940 | the size and the shape of those extra dimensions

00:35:21.580 | leaves an imprint in the world that we do have access to.

00:35:24.940 | So one of the ways that we have hoped yet to achieve

00:35:28.980 | to make contact with experimental physics

00:35:31.840 | is to see a signature of those extra dimensions

00:35:34.480 | in places like the Large Hadron Collider

00:35:36.620 | in Geneva, Switzerland.

00:35:38.240 | And it hasn't happened yet, doesn't mean it won't happen,

00:35:41.420 | but that would be a stunning moment

00:35:44.700 | in the history of the species

00:35:46.140 | if data that we acquired in these dimensions

00:35:50.140 | gives us kind of incontrovertible evidence

00:35:53.420 | that these dimensions are not the only dimensions.

00:35:55.860 | I mean, how mind-blowing would that be?

00:35:59.220 | - So with the Large Hadron Collider,

00:36:00.980 | it would be something in the movement of the particles

00:36:03.260 | or also the gravitational waves potentially be a place

00:36:07.720 | where you can detect signs of multiple dimensions,

00:36:10.160 | like with something called LIGO, but much more accurate?

00:36:12.340 | - In principle, all of these can work.

00:36:14.580 | So one of the experiments that we had high hopes for,

00:36:18.380 | but by high hopes, I'm actually exaggerating.

00:36:21.020 | One of the experiments that we imagined

00:36:24.340 | might in the best of all circumstances yield some insight.

00:36:27.540 | We weren't with bated breath waiting for the result.

00:36:30.100 | We knew it was a long shot.

00:36:31.580 | When you slam protons together at very high speed

00:36:34.660 | at the Large Hadron Collider,

00:36:35.940 | if there are these extra dimensions

00:36:37.540 | and if they have the right form,

00:36:39.620 | and that's a hypothesis that may not be correct,

00:36:43.140 | but when the protons collide, they can create debris,

00:36:46.460 | energetic debris that can in some sense leave our dimensions

00:36:50.900 | and insert itself into the other dimensions.

00:36:53.740 | And the way you'd recognize that is

00:36:56.340 | there'd be more energy before the collision

00:36:58.580 | than after the collision

00:36:59.820 | because the debris would have taken energy

00:37:02.420 | away from the place where our detectors can detect it.

00:37:06.500 | So that's one real concrete way

00:37:09.020 | that you could find evidence for extra dimensions.

00:37:11.980 | But yeah, since extra dimensions are of space

00:37:15.980 | and gravity is something that exists within,

00:37:19.340 | in fact is associated with the shape of space,

00:37:22.740 | gravitational waves in principle can provide a kind of,

00:37:27.380 | you know, cat scan of the extra dimensions

00:37:31.100 | if you had sufficient control over those processes.

00:37:35.300 | We don't yet, but perhaps one day we will.

00:37:38.620 | - Does it make you sad a little bit?

00:37:41.260 | There may be looking out into the future,

00:37:43.020 | you mentioned Ed Witten,

00:37:44.540 | that no Nobel prizes have been given yet

00:37:47.620 | related to string theory.

00:37:48.940 | Do you think they will be?

00:37:50.300 | Do you think you have to have experimental validation

00:37:53.620 | or can a Nobel prize be given?

00:37:55.540 | Which I don't think it's been given for quite a long time

00:37:58.700 | for a purely sort of theoretical contribution.

00:38:01.980 | - Yeah, it's certainly as a matter of historical precedent

00:38:06.180 | has been the case that those who win the prize

00:38:09.060 | have established, investigated, illuminated

00:38:14.060 | a demonstrably real quality of the world.

00:38:18.660 | So gravitational waves,

00:38:21.660 | the prize was awarded after they were detected.

00:38:24.140 | Not the mathematics of it, but the actual detection of it.

00:38:28.860 | You know, the Higgs particle.

00:38:30.740 | You know, it was an idea that came from the 1960s,

00:38:33.700 | Peter Higgs and others, in fact.

00:38:36.280 | And it wasn't until 2012 on July 4th

00:38:41.280 | when the announcement came that this particle

00:38:43.360 | had been detected at the Large Hadron Collider

00:38:45.720 | that people viewed it as eligible for the Nobel prize.

00:38:49.200 | The idea was there, the math was there,

00:38:50.760 | but you needed to confirm it.

00:38:52.840 | Indeed, the prize ultimately was awarded.

00:38:55.360 | So I'm not surprised.

00:38:57.000 | In fact, I would have been surprised

00:38:59.600 | if a Nobel prize had been awarded

00:39:02.200 | in the arena of string theory

00:39:04.400 | because it's far too speculative right now.

00:39:07.200 | It's far too hypothetical.

00:39:09.080 | In fact, I am sympathetic to the view

00:39:13.260 | that it really shouldn't be called string theory.

00:39:15.920 | It degrades the word theory

00:39:18.680 | because theory in science, of course,

00:39:20.920 | means the best available explanation

00:39:23.780 | for the things that we observe in the world,

00:39:25.960 | the things that we measure in experiments about the world.

00:39:30.840 | And string theory does not do that, at least not yet.

00:39:34.360 | So it really should be the string hypothesis, right?

00:39:37.680 | We're at an earlier stage of development

00:39:40.560 | and that's not the kind of thing

00:39:42.360 | that Nobel prizes should be awarded for.

00:39:45.640 | - What do you think about the critics out there?

00:39:47.920 | Peter White, he's from Columbia too, I think,

00:39:51.040 | Sabine Haffenstetter.

00:39:52.540 | Is that a healthy thing or should we sort of focus

00:39:56.400 | on sort of the optimism of these hypotheses?

00:39:59.580 | - Yeah, it's actually a good way that you frame it

00:40:03.120 | because I'm always somewhat repelled

00:40:08.120 | by views of the world that start from the negative,

00:40:14.120 | try to cut down an idea,

00:40:17.920 | try to say that's the wrong way of thinking

00:40:20.920 | about things and so on.

00:40:22.400 | I'm much more drawn, maybe because I'm an optimist,

00:40:25.720 | I don't know, I'm much more drawn

00:40:27.760 | to those who go out into the world with new ideas.

00:40:31.640 | And don't try to cut down one idea,

00:40:34.900 | but rather present another one that might be better.

00:40:38.840 | And so you make the first idea, maybe strengthy, irrelevant,

00:40:42.760 | because you've come up with the better approach

00:40:46.360 | to the world.

00:40:47.580 | So do I think it's healthy?

00:40:49.040 | Look, I think having a wide range of views

00:40:53.040 | and perspectives is generally a healthy thing.

00:40:56.600 | I think it's good to have arguments within a subject

00:41:00.480 | in order that you stay fresh

00:41:02.720 | and you stay focused on the things that matter.

00:41:06.440 | But in the end of the day,

00:41:07.760 | I think it's a more vital contribution

00:41:11.960 | to give us something new

00:41:13.300 | rather than to criticize something that's there.

00:41:15.600 | - Yeah, I'm totally with you.

00:41:17.040 | But it could be just the nature of being an optimist

00:41:19.840 | and also just a love of engineering.

00:41:24.280 | It helps nobody by criticizing the rocket

00:41:29.360 | that somebody else built.

00:41:30.640 | Just build a bigger, cheaper, better rocket.

00:41:34.600 | - Right, exactly.

00:41:36.600 | - And that seems to be how human civilization

00:41:39.000 | can progress effectively.

00:41:40.460 | We've mentioned the second law of thermodynamics.

00:41:44.960 | I gotta ask you about time.

00:41:46.920 | - Yeah.

00:41:47.760 | - And do you think of time as emergent

00:41:51.400 | or fundamental to our universe?

00:41:53.760 | - I like to think of it as emergent.

00:41:56.120 | I don't have a solid reason for that perspective.

00:42:00.980 | I have a lot of hints of reasons,

00:42:02.760 | that some of which come out of string theory

00:42:04.400 | and quantum gravity

00:42:06.160 | that perhaps would be worth talking about.

00:42:09.180 | But what I would say is time is

00:42:13.960 | the most familiar quality of experience

00:42:17.080 | because there's nothing that takes place

00:42:18.960 | that doesn't take place within an interval of time.

00:42:22.200 | And yet at the same time,

00:42:24.560 | it is perhaps the most mysterious quality of the world.

00:42:28.440 | So it's a wonderful confluence of the familiar

00:42:32.000 | and the deeply mysterious all in one little package.

00:42:36.000 | If you were to ask me, what is time?

00:42:37.800 | I don't really know.

00:42:39.800 | I don't think anybody does.

00:42:41.040 | I can say what time gives us.

00:42:45.280 | It allows us the language for talking about change.

00:42:48.760 | It allows us to envision the events of the universe

00:42:52.620 | being spread out in this temporal timeline.

00:42:55.880 | And in that way,

00:42:57.220 | allows us to see the patterns that unfold within time.

00:43:01.680 | I mean, time allows us the structure

00:43:04.120 | and the organization to think about things

00:43:06.600 | in that kind of a progression.

00:43:08.920 | But what actually is it?

00:43:11.440 | I don't really know.

00:43:12.740 | And that's so strange because we can measure it, right?

00:43:16.400 | I mean, there are laboratories in the world

00:43:19.060 | that measure this thing called time

00:43:21.100 | to spectacular precision.

00:43:24.000 | But if you go up to the folks and say,

00:43:28.440 | what is it that you're actually measuring?

00:43:31.920 | I don't know that they can really articulate

00:43:34.580 | the kind of answer that you would expect

00:43:37.220 | from those who are engineering a device

00:43:39.400 | that can measure something called time

00:43:41.520 | to that level of precision.

00:43:43.120 | So it's a very curious combination.

00:43:47.000 | - What do you make of the one way feeling of causality?

00:43:51.260 | Like is causality a thing

00:43:54.380 | or is that too just a human story

00:43:57.580 | that we put on top of this emergent phenomenon of time?

00:44:00.780 | - I don't know.

00:44:02.220 | I can give you my guess and my intuition about it.

00:44:05.940 | I do think that at the macroscopic level,

00:44:09.180 | if we're talking about sort of the human experience of time,

00:44:11.280 | I do think at the macroscopic level,

00:44:13.320 | there is a fundamental notion of causality

00:44:17.180 | that does emerge from a starting point

00:44:20.060 | that may not have causality built in.

00:44:21.740 | So I certainly would allow that

00:44:23.100 | at the deepest description of reality,

00:44:26.280 | when we finally have that on the table,

00:44:28.900 | we may not see causality directly

00:44:31.700 | at that fundamental level.

00:44:33.540 | But I do believe that we will understand

00:44:36.260 | how to go from that fundamental level

00:44:38.340 | to a world where at the macroscopic level,

00:44:41.440 | there is this notion of A causes B,

00:44:44.460 | a notion that Einstein deeply embraced

00:44:47.660 | in his special theory of relativity,

00:44:49.140 | where he showed that time has qualities

00:44:51.840 | that we wouldn't expect based on experience.

00:44:54.280 | You and I, if we move relative to each other,

00:44:56.740 | our clocks tick off time at different rate.

00:44:59.780 | And our clocks is just a means

00:45:01.980 | of measuring this thing called time.

00:45:03.520 | So this is really time that we're talking about.

00:45:05.860 | Time for you and time for me are different

00:45:08.100 | if we're in relative motion.

00:45:09.280 | He then shows in the general theory of relativity

00:45:11.500 | that if we're experiencing different gravity,

00:45:15.060 | different gravitational fields

00:45:16.300 | or actually more precisely,

00:45:17.280 | different gravitational potentials,

00:45:19.180 | time will elapse for us at different rates.

00:45:21.660 | These are things that are astoundingly strange

00:45:25.980 | that give rise to a scientific notion of time travel.

00:45:29.700 | Okay, so this is how far Einstein took us

00:45:33.460 | in wiping away the old understanding of time

00:45:37.180 | and injecting a new understanding of its qualities.

00:45:40.420 | So there's so much about time that's counterintuitive,

00:45:44.420 | but I do not think that we're ever going

00:45:46.780 | to wipe away causality at the macroscopic level.

00:45:50.340 | - At the macroscopic, I mean,

00:45:51.260 | there's so many interesting things

00:45:52.620 | at the macroscopic level that may only exist

00:45:55.060 | at the macroscopic level.

00:45:56.660 | Like we already talked about consciousness

00:45:59.180 | that very well could be one of the things.

00:46:01.080 | You mentioned time travel.

00:46:02.260 | So I mean, according to Einstein,

00:46:07.020 | and in general, what types of travel

00:46:11.140 | do you think our physical universe allows?

00:46:14.020 | - Well, it certainly allows time travel to the future.

00:46:17.060 | And I'm not talking about the silly thing

00:46:18.660 | that you and I are now going into the future

00:46:21.420 | second by second by second.

00:46:22.420 | I'm talking about really the version

00:46:24.740 | that you see in Hollywood,

00:46:26.500 | at least in terms of its net effect,

00:46:29.140 | whereby an individual can follow an Einsteinian strategy

00:46:36.460 | and propel themselves into the future

00:46:40.660 | in some sense more quickly.

00:46:42.260 | So if I wanted to see what's happening

00:46:45.140 | on planet Earth one million years from now,

00:46:48.300 | Einstein tells me how to get one million years from now.

00:46:52.500 | Build a ship.

00:46:53.340 | I got to turn to guys who know how to build stuff.

00:46:56.380 | I can't do it like you.

00:46:57.980 | Build a ship that can go out into the universe

00:47:00.020 | near the speed of light, turn around and come back.

00:47:02.780 | Let's say it's a six month journey out,

00:47:04.420 | a six month journey back.

00:47:06.060 | And Einstein tells me how fast I need to travel,

00:47:09.420 | how close to the speed of light I need to go

00:47:11.180 | so that when I step out of my ship,

00:47:13.740 | it will now be one million years

00:47:15.980 | into the future on planet Earth.

00:47:20.140 | And this is not a controversial statement, right?

00:47:23.300 | This is not something where there's differences of opinion

00:47:26.940 | in the scientific community.

00:47:28.340 | Any scientist who knows anything

00:47:30.900 | about what Einstein taught us agrees with what I just said.

00:47:35.080 | It's commonplace, it's bread and butter physics.

00:47:37.660 | And so that kind of travel to the future

00:47:40.700 | is absolutely allowed by the laws of physics.

00:47:44.180 | There are engineering challenges,

00:47:45.860 | there are technological challenges.

00:47:47.980 | - Closer to the speed of light part, yeah.

00:47:49.500 | - Yeah, and there are even biological challenges, right?

00:47:52.780 | There are G-forces that you're gonna experience.

00:47:55.220 | So there's all sorts of stuff embedded in this.

00:47:57.780 | But those I will call the details.

00:48:01.020 | And those details, notwithstanding,

00:48:04.380 | the universe allows this kind of travel to the future.

00:48:07.820 | - And if I could pause real quick,

00:48:09.660 | you could also, at the macro level,

00:48:12.620 | with biology, extend the human lifespan

00:48:15.360 | to do a kind of travel forward in time.

00:48:19.260 | If you expand how long we live,

00:48:22.560 | that's a way to, from a perspective of an observer,

00:48:25.320 | a conscious observer that is a human being,

00:48:27.800 | you're essentially traveling forward in time

00:48:29.920 | by allowing yourself to live long enough to see the thing.

00:48:32.440 | - Yes.

00:48:33.280 | - So in the space of biology,

00:48:34.920 | what about traveling back in time?

00:48:37.160 | - Yeah, that is a natural next question,

00:48:41.960 | especially if you're going on one of these journeys.

00:48:45.560 | Is it a one-way journey?

00:48:46.800 | - Yeah.

00:48:47.620 | - Or can you come back?

00:48:48.840 | And the physics community doesn't speak

00:48:52.480 | with a unified voice on this as yet.

00:48:55.200 | But I would say that the dominant perspective

00:48:57.860 | is that you cannot get back.

00:49:00.240 | Now, having said that, there are proposals

00:49:03.880 | that serious people have written papers on

00:49:07.280 | regarding hypothetical ways

00:49:09.080 | in which you could travel to the past.

00:49:10.920 | And we've seen some of these.

00:49:13.500 | Again, Hollywood loves to take the most sexy ideas

00:49:16.920 | of physics and build narratives around them.

00:49:20.040 | This idea of a wormhole,

00:49:21.960 | like Jodie Foster in "Contact" went through a wormhole.

00:49:25.480 | Deep Space Nine star, I'm sure there are many other examples

00:49:27.860 | for these ideas that I've probably never even seen.

00:49:30.500 | But with wormholes, there's at least a proposal

00:49:34.480 | of how you could take a wormhole, tunnel through space-time,

00:49:38.240 | manipulate the openings of the wormhole

00:49:40.520 | in such a way that the openings are no longer synchronous.

00:49:44.120 | They are out of sync relative to each other,

00:49:46.320 | which would mean one's ahead and one's behind,

00:49:49.000 | which means if you go through one direction,

00:49:50.480 | you travel to the future.

00:49:51.640 | If you go back, you travel to the past.

00:49:54.360 | Now, we don't know if there are wormholes

00:49:57.760 | in the world. - But they're possible

00:49:58.600 | according to Einstein, correct?

00:49:59.840 | - They are possible according to Einstein,

00:50:01.760 | but even Einstein was very quick to say,

00:50:04.400 | just because my math allows for something,

00:50:07.240 | doesn't mean it's real.

00:50:08.080 | And he famously didn't even believe in black holes.

00:50:10.880 | Didn't believe in the Big Bang, right?

00:50:12.920 | And yet the black hole issue has really been settled now.

00:50:17.160 | We have radio telescopic photographs

00:50:20.740 | of the black hole in M87.

00:50:22.800 | It was in newspapers around the world

00:50:25.240 | just a couple of years ago.

00:50:26.360 | So it's just to say that just because

00:50:29.160 | it's in Einstein's math, it doesn't mean it's real.

00:50:32.160 | But yes, it is the case that wormholes

00:50:34.960 | are allowed by Einstein's equations.

00:50:36.640 | And in principle, you can imagine putting electric charges

00:50:40.880 | on the openings of the wormhole,

00:50:42.280 | allowing you to tow them around in a manner

00:50:44.840 | that could yield this temporal asymmetry between them.

00:50:48.120 | Maybe you tow one of the mouths to the edge of a black hole.

00:50:51.760 | In principle, you can do this,

00:50:53.340 | slowing down the passage of time near that black hole.

00:50:56.520 | And then when you bring it back,

00:50:58.100 | it will be well out of sync with the other opening.

00:51:02.020 | And therefore, it could be a significant temporal gap

00:51:05.360 | between one and the other.

00:51:07.060 | But people who study this in more detail question,

00:51:10.800 | could you ever keep a wormhole open,

00:51:13.020 | assuming it does exist?

00:51:14.720 | Could you ever travel through a wormhole?

00:51:17.380 | Or would there be a requirement

00:51:19.660 | of some kind of exotic matter to prop it open

00:51:22.900 | that perhaps doesn't exist?

00:51:24.380 | So there are many, many issues that people have raised.

00:51:28.020 | And I would say that the general sentiment

00:51:31.020 | is that it's unlikely that this kind of scenario

00:51:34.740 | is going to survive our deeper understanding of physics

00:51:37.940 | when we finally have it.

00:51:39.180 | But that doesn't mean that the door is closed.

00:51:41.300 | So maybe there's a small possibility

00:51:44.780 | that this could one day be resolved.

00:51:45.940 | - That's such an interesting way to put it.

00:51:48.460 | This kind of scenario will not survive

00:51:51.100 | our deeper understanding of physics.

00:51:53.540 | It's an interesting way to put it

00:51:54.860 | because it makes you wonder what kind of scenarios

00:51:59.740 | will be created by our deeper understanding of physics.

00:52:04.100 | Maybe, sorry to go crazy for a second,

00:52:08.380 | but if you have like the panpsychism idea

00:52:11.240 | that consciousness permeates all matter,

00:52:14.220 | maybe traveling in that, whatever laws of physics

00:52:18.020 | the consciousness operates under or something like that,

00:52:20.180 | in that view of the universe,

00:52:21.740 | if we somehow are able to understand that part,

00:52:24.180 | maybe traveling is super easy.

00:52:26.460 | - Yeah.

00:52:27.300 | - It does not follow the constraints

00:52:30.380 | of the speed of light, something like this.

00:52:32.740 | - Yeah, so look, I have a definite degree of sympathy

00:52:37.740 | with the possibility that consciousness might be

00:52:42.660 | more than what we described earlier

00:52:45.540 | as just the byproduct of mindless particles.

00:52:48.220 | - You just made the rock happy.

00:52:50.580 | - Exactly, so it isn't the approach

00:52:54.340 | that feels to me the most likely, but I see the logic.

00:52:59.340 | If you've got the puzzle,

00:53:01.700 | how do mindless particles build mind,

00:53:04.300 | one resolution might be the particles are not mindless.

00:53:08.320 | The particles have some kind of proto-conscious quality.

00:53:10.960 | So there's something appealing

00:53:13.020 | about that straightforward solution to the puzzle.

00:53:16.220 | And if that's the case,

00:53:17.500 | if we do live in a pan-psychist world

00:53:20.180 | where there's a degree of consciousness

00:53:22.420 | residing in everything in the world around us,

00:53:24.700 | then yes, I do think some interesting possibilities

00:53:27.960 | might emerge where maybe there's a way of communing

00:53:31.740 | with physical reality in a deeper way than we have so far.

00:53:36.740 | I mean, we as human beings,

00:53:38.660 | a vital part of our existence

00:53:40.580 | is human to human communication, contact.

00:53:43.880 | We live in social groups,

00:53:45.300 | and that's what has allowed us to get to the place

00:53:48.040 | where we've gotten.

00:53:48.880 | Imagine that we have long missed

00:53:51.740 | that there's other consciousness out there

00:53:54.740 | and some kind of relationship or communion

00:53:57.540 | with that larger conscious possibility

00:54:00.020 | would take us to a different place.

00:54:01.420 | Now, do I buy into this yet?

00:54:03.880 | I don't, I don't see any evidence for it,

00:54:06.460 | but do I have an open mind

00:54:08.340 | and allow for the possibility in the future?

00:54:11.460 | Yeah, I do.

00:54:13.500 | - So if that's not the case

00:54:15.420 | and you have these simple particles

00:54:18.440 | that at the macro level emerges some interesting stuff

00:54:21.900 | like consciousness,

00:54:22.900 | another thing you write about in the

00:54:25.500 | "Until the End of Time" book

00:54:27.340 | is the thing that it seems to emerge at the macro level

00:54:30.900 | is the feeling like there's a free will,

00:54:35.020 | like we decide to do stuff.

00:54:36.540 | And you have a really interesting take here,

00:54:39.140 | which is no, there's not a free will.

00:54:43.340 | I'm just gonna speak for you

00:54:44.620 | and then you can correct me.

00:54:45.900 | No, there's not a free will,

00:54:48.060 | but there is an experience of freedom.

00:54:51.440 | - Yeah, yeah.

00:54:52.280 | - Which I really love.

00:54:56.100 | So where does the experience,

00:54:58.400 | where does freedom come from

00:54:59.780 | if we don't have any kind of physics-based free will?

00:55:02.700 | - Yeah, and so the idea follows naturally

00:55:06.820 | from all that we've been talking about.

00:55:08.480 | Let's make the assumption

00:55:10.500 | that all there is in the physical universe

00:55:13.220 | is stuff governed by laws.

00:55:15.380 | We may not have those laws,

00:55:16.500 | may not know what the fundamental stuff is yet,

00:55:19.500 | but everything we know in science points in the direction

00:55:23.700 | that it's physical stuff governed by universal laws.

00:55:27.860 | And that being the case or that being the assumption,

00:55:31.380 | then you come to a particular collection

00:55:33.880 | of those ingredients called the human being.

00:55:36.020 | And that human being has particles

00:55:38.120 | that are fully governed by physical law.

00:55:41.580 | And when you then recognize it,

00:55:43.060 | every thought that we have,

00:55:44.340 | every action that we undertake

00:55:46.460 | is just the motion of particles.

00:55:49.380 | When I'm thinking thoughts right now,

00:55:50.860 | of course, at this level of description,

00:55:53.820 | it is the motion of particles cascading

00:55:56.260 | down various neurons inside of my head and so on.

00:55:59.780 | And every single one of those motions,

00:56:02.780 | collectively and individually,

00:56:05.300 | is fully governed by these laws

00:56:08.500 | that we perhaps don't have yet,

00:56:09.860 | but we imagine one day we will.

00:56:12.060 | That leaves no opportunity for any kind of freedom

00:56:15.780 | to break free from the constraint of physical law.

00:56:19.580 | And that is the end of the story.

00:56:21.620 | So the traditional intuitive notion of free will,

00:56:24.460 | that we're the ultimate authors of our actions,

00:56:26.860 | that we were the buck stops,

00:56:28.300 | that there is no antecedent,

00:56:30.240 | that is the cause for our deciding to go left or right,

00:56:35.000 | choose vanilla or chocolate, live or die,

00:56:38.180 | that intuitive sensation does not have a basis

00:56:42.020 | in our understanding of the physical world.

00:56:43.740 | So that's the end of the free will of the traditional sort.

00:56:47.100 | But then your question is,

00:56:49.060 | what about this other kind of freedom I talk about?

00:56:51.900 | And the other kind of freedom,

00:56:53.860 | if you focus on it intently,

00:56:55.820 | I think is actually the true version of freedom

00:57:00.660 | that we feel.

00:57:02.140 | And that freedom is this.

00:57:04.260 | You look at inanimate objects in the world,

00:57:06.980 | rocks, bottles of water, whatever,

00:57:10.100 | they have a very limited behavioral repertoire.

00:57:13.300 | Why?

00:57:14.140 | Their internal organization is too coarse

00:57:17.060 | for them to do very much, right?

00:57:18.860 | You try to have a conversation with a glass of water,

00:57:22.000 | you send sound waves, it doesn't do much.

00:57:24.780 | It may vibrate a little bit,

00:57:26.120 | but the repertoire of responses are incredibly limited.

00:57:30.180 | The difference between us and a rock or a bottle of water

00:57:33.020 | is that our inner organization,

00:57:35.080 | by virtue of eons of evolution by natural selection,

00:57:38.380 | is so refined, so spectacularly ordered,

00:57:42.700 | that we have a huge repertoire of behaviors

00:57:46.420 | that are finely attuned to stimuli from the external world.

00:57:51.420 | You ask me a question, that's a stimulus,

00:57:53.300 | and all of a sudden,

00:57:54.420 | these particle processes go into action,

00:57:56.820 | and this is the result, this answer that I'm giving you.

00:58:00.040 | So the freedom that we have

00:58:02.100 | is not from the control of physical law.

00:58:05.560 | The freedom that we have is from the constrained behavior

00:58:08.220 | that has long since governed inanimate objects.

00:58:11.340 | We are liberated from the limited behavioral repertoire

00:58:14.660 | of rocks and bottles of water

00:58:17.180 | to have this broad spectrum of responses.

00:58:20.060 | Do we pick them?

00:58:20.900 | We do not.

00:58:21.800 | Do we freely choose them?

00:58:23.040 | We do not, but yet we have them,

00:58:26.060 | and we can marvel at those behaviors,

00:58:29.320 | and that's the freedom that we have.

00:58:31.480 | - The complexity and the breadth of that repertoire

00:58:34.300 | is where the freedom emerges.

00:58:36.720 | Is there something to be said about emergence?

00:58:40.240 | I don't know if you know or have looked at much

00:58:42.880 | about objects that I seem to love way more than anyone else,

00:58:47.280 | which is cellular top, like game of life type of stuff.

00:58:51.720 | From simple things emerges beautiful complexity,

00:58:56.720 | and so that's that repertoire.

00:58:58.980 | It's like it seems if you have enough stuff,

00:59:03.980 | just beautiful complexity emerges

00:59:06.300 | that sure as heck to our human eyes looks

00:59:09.600 | like there's consciousness there, there's free will,

00:59:12.040 | there's little objects moving about and making decisions.

00:59:15.640 | I mean, all of that.

00:59:16.820 | You could say it's anthropomorphization,

00:59:18.920 | but it sure as heck feels like

00:59:22.500 | there are organisms making decisions.

00:59:24.560 | What is that emergence thing?

00:59:27.660 | Is that within the realm of physics to understand?

00:59:31.220 | Is it within the realm of poetry?

00:59:35.020 | What is that, like complex systems, emergence?

00:59:38.640 | What is that?

00:59:39.620 | Will that ever be understood by science?

00:59:41.580 | - So here's the way that I think about it.

00:59:43.980 | So there are clearly qualities of the world

00:59:47.820 | that emerge on macroscopic scales.

00:59:51.000 | Our sense of beauty, wonder, consciousness,

00:59:53.740 | all these kinds of qualities.

00:59:55.900 | Do I feel that they ultimately are explainable

01:00:00.180 | from the laws of physics?

01:00:01.180 | I do.

01:00:02.540 | There is nothing that's not ultimately explainable

01:00:06.300 | with the laws of physics from this physicalist perspective,

01:00:09.460 | which is what I take.

01:00:10.880 | So you got the particles, you got the laws,

01:00:13.980 | and you have things that emerge

01:00:16.180 | from the choreographed motions of those particles.

01:00:20.780 | But is that the best language

01:00:23.060 | for talking about these emergent qualities?

01:00:26.100 | Usually not.

01:00:27.540 | If I was to take something even more mundane,

01:00:30.920 | like a baseball flying through the air,

01:00:33.180 | if I was to describe it in terms of the quarks

01:00:35.680 | and the electrons, I'd give you this mountain of data

01:00:39.020 | with 10 to the 28 particles and all of their coordinates

01:00:44.020 | and spaces as a function of time.

01:00:45.900 | I hand you this mountain of data, you're like,

01:00:47.380 | I don't know what this is.

01:00:49.180 | And then if you really were clever and you look at,

01:00:51.180 | oh, it's a baseball just described

01:00:54.020 | in the least economical way possible,

01:00:57.060 | it is much more useful and insightful

01:01:00.240 | to talk about the baseball flying through the air.

01:01:01.960 | Similarly, there are things at the macroscopic level

01:01:05.680 | like human experience and human emotion and human action

01:01:09.680 | and the sensation of free will that we undeniably all have,

01:01:14.680 | even if it itself doesn't have a basis

01:01:17.420 | in our understanding of the physical world.

01:01:19.460 | It's useful to talk about things

01:01:21.720 | in this very human language.

01:01:24.340 | And so, yes, it's vital to talk about things

01:01:26.700 | in the poetic language of human experience,

01:01:29.380 | but do not lose sight of the fact, and some people do,

01:01:31.820 | they say, oh, it's just an emergent phenomenon.

01:01:33.880 | Don't lose sight of the fact that emergent phenomena

01:01:36.100 | are emerging from this deeper understanding

01:01:39.820 | that comes from the reductionist account of physical law.

01:01:42.820 | And there's a lot of insight to come from that,

01:01:44.840 | such as the freedom that you thought that you had,

01:01:48.580 | the freedom of will that you thought you had.

01:01:50.340 | It doesn't have a basis in that reductionist account,

01:01:53.180 | so it's not real.

01:01:54.300 | - So speaking of the poetry of human experience,

01:01:59.060 | you mentioned the images of the black holes.

01:02:01.140 | How did it make you feel a few years ago

01:02:03.140 | when that first image came out?

01:02:04.820 | - Truly amazing.

01:02:06.280 | A sense of, well, I guess the feeling was both amazing

01:02:11.280 | and there was a little sense of,

01:02:13.800 | jealousy's not quite the right word,

01:02:17.340 | but a sense of longing.

01:02:19.540 | Yeah, I think that's a better word,

01:02:20.920 | because here's a subject that started with Einstein

01:02:25.460 | back in 1915, writes down the equations

01:02:28.520 | of the general theory of relativity,

01:02:30.620 | and then there are scores of individuals over the decades,

01:02:34.820 | starting with people like Karl Schwarzschild,

01:02:37.500 | who analyzed the equation,

01:02:38.860 | see the possibility of black holes.

01:02:40.340 | People develop these ideas.

01:02:41.620 | John Wheeler, all these greats of physics.

01:02:44.140 | It's still a hypothetical subject.

01:02:46.460 | It gets closer to reality through observations

01:02:48.900 | of the center of our galaxy,

01:02:50.460 | stars whipping around in a manner

01:02:52.360 | that could only really be explained

01:02:54.580 | by there being a black hole in the center of our galaxy,

01:02:56.900 | but it was still indirect.

01:02:58.740 | To actually have a direct image that you can look at,

01:03:03.540 | what a beautiful arc, narrative arc,

01:03:06.140 | from the theoretical to the absolutely established,

01:03:10.140 | and that's what we hope will happen with other areas,

01:03:13.600 | for instance, string theory, right?

01:03:15.100 | I mean, holy mathematical subject at the outset,

01:03:18.580 | and still pretty much a holy mathematical subject today.

01:03:22.540 | Yeah, do we long for that image

01:03:25.860 | where we can look at it and say, string, it's real.

01:03:29.500 | I mean, how thrilling, how thrilling

01:03:32.780 | to be part of that journey,

01:03:34.340 | to be part of that step that moves things

01:03:37.100 | from the abstract to the concrete.

01:03:39.000 | - Yeah, so like the image of the DNA,

01:03:42.820 | the early images of the DNA, for example,

01:03:45.860 | but there is something, especially,

01:03:47.540 | so the problem with strings is they're tiny,

01:03:50.940 | so it's harder to take a picture.

01:03:52.620 | In the following sense, when you think of a black hole,

01:03:56.900 | I mean, you have a swirl of, I guess,

01:03:58.900 | what is, I don't even know, it's dust, whatever, light.

01:04:02.380 | - Accreting onto the event horizon.

01:04:04.580 | - And then there's darkness in the center,

01:04:06.660 | and you just imagine, so that picture in particular,

01:04:10.140 | I guess, is of a gigantic black hole, so you just,

01:04:14.780 | I mean, it's terrifying.

01:04:16.180 | - Billions of times the mass of the sun.

01:04:17.580 | - Yeah, so it's both exciting and terrifying.

01:04:19.900 | I mean, I don't know where you fall on the spectrum.

01:04:22.060 | I think it's exciting at first,

01:04:24.900 | like the longer I think about it,

01:04:26.300 | every time I think about it,

01:04:27.460 | the more terrifying it becomes.

01:04:29.300 | So it always starts exciting,

01:04:31.300 | and then it goes to terrifying,

01:04:32.740 | and both are feelings, very human feelings

01:04:36.140 | that I appreciate.

01:04:38.380 | It's like terrified awe, somehow, is still beautiful.

01:04:42.740 | - That's a good way of saying it,

01:04:43.940 | and I think I kind of share that reaction,

01:04:45.940 | because there is a way in which,

01:04:48.220 | when you work on this subject, like all the time,

01:04:51.340 | I teach it, I teach about black holes,

01:04:53.540 | write the equations on the blackboard.

01:04:55.540 | The ideas reside in a very cognitive,

01:05:01.800 | I don't know, mathematical portion of the brain,

01:05:06.460 | or at least for me.

01:05:08.280 | And it's only when you sit down, and it's quiet,

01:05:11.900 | and you start to contemplate,

01:05:13.020 | wait, wait, wait, wait,

01:05:13.860 | this isn't just like a mathematical game.

01:05:16.180 | There are these monsters out there.

01:05:19.420 | Now, not in a sense of I fear for my life,

01:05:22.740 | but it's a sense of how extraordinary is this universe.

01:05:27.740 | And so it is breathtaking.

01:05:30.460 | - How powerful nature is.

01:05:31.940 | - Yeah, how stupendously powerful nature is.

01:05:37.300 | And so there is a deep sense of humility

01:05:42.120 | that I think this instills,

01:05:43.960 | if you really allow the ideas to sink in.

01:05:46.680 | - Well, I have to ask about

01:05:49.760 | the most stupendously powerful thing

01:05:52.720 | to have ever happened in our universe,

01:05:54.360 | which is the Big Bang.

01:05:55.560 | What's up with the Big Bang?

01:05:57.920 | So we can, I mean, with gravitational waves,

01:06:01.360 | the hope is, when you have more and more accurate

01:06:04.640 | measurements of the gravitational waves,

01:06:06.040 | you can crawl back further and further back in time

01:06:08.420 | towards the Big Bang.

01:06:09.600 | Do you have a hope that we'll be able to understand

01:06:13.460 | the early spark that created our universe?

01:06:18.100 | - Yeah.

01:06:18.940 | - You know, that and the deep interior of a black hole

01:06:23.300 | are, I think, the biggest mysteries that we hope

01:06:26.940 | the melding of quantum mechanics and gravity will reveal,

01:06:30.740 | will illuminate.

01:06:32.440 | And, you know, what question could be more captivating

01:06:36.980 | than why is there something rather than nothing, right?

01:06:39.940 | Why is there a universe at all?

01:06:43.260 | And will the theories that we're developing

01:06:46.340 | take us to an answer to that?

01:06:48.500 | I don't know.

01:06:49.740 | Even if we truly knew what the Big Bang is,

01:06:51.660 | and that's a big question in its own right,

01:06:53.500 | one would still be left with the question, well, okay.

01:06:56.660 | So you've explained the process by which

01:07:00.340 | a tiny nugget of a universe, a tiny nugget of space-time

01:07:05.340 | can undergo some kind of growth to yield the world around us

01:07:10.060 | but presumably in that explanation,

01:07:12.940 | you're gonna involve mathematics and some ingredients

01:07:16.380 | like quantum fields or matter or energy or something.

01:07:21.380 | Where did that stuff come from?

01:07:24.160 | You know, can we get to that level of explanation?

01:07:26.900 | I don't know, but it is remarkable

01:07:29.120 | that if you ask what happened a millionth of a second

01:07:34.120 | after the Big Bang,

01:07:36.020 | it's not really that controversial any longer, right?

01:07:40.240 | Even though there's a lot of argument in the field

01:07:42.760 | and it's very heated right now, I should say,

01:07:45.400 | regarding what is the right theory of the Big Bang?

01:07:49.920 | What is the right theory of early universe cosmology?

01:07:53.440 | Where I mean early, much earlier than a millionth of a second

01:07:56.040 | a lot of dissent, a lot of heated arguments about that--

01:08:01.040 | - No pun intended.

01:08:02.680 | - Yeah, right, exactly.

01:08:04.280 | But you go like a millionth of a second after that

01:08:08.180 | and we're on pretty firm ground.

01:08:10.080 | Isn't that amazing, right?

01:08:12.160 | To understand what happened from that point forward.

01:08:15.400 | But to go back is controversial.

01:08:18.220 | So there is this theory called inflationary cosmology

01:08:21.600 | which I would say has been the dominant paradigm

01:08:24.560 | since early 1980s.

01:08:27.120 | So what does that mean?

01:08:27.960 | Roughly 40 years now,

01:08:28.920 | it's been the dominant cosmological paradigm.

01:08:31.360 | And it makes use of a curious feature

01:08:33.760 | of Einstein's general theory of relativity,

01:08:36.000 | his theory of gravity,

01:08:37.260 | where Einstein shows us mathematically

01:08:39.800 | that gravity can not only be attractive,

01:08:41.840 | the kind of gravity that we're used to,

01:08:43.280 | things pulled together, but it can also be repulsive.

01:08:47.420 | And that fact is then leveraged by people like Alan Guth

01:08:53.200 | and Andre Linde and at the time Paul Steinhardt

01:08:56.240 | and Andreas Hallbrecht and others to say,

01:08:58.760 | okay, if we had a little nugget in the early universe

01:09:01.400 | which was filled with the stuff

01:09:03.520 | that yields this repulsive gravity,

01:09:05.520 | well, that would have blown everything apart.

01:09:07.360 | It would cause everything to swell.

01:09:09.240 | Beautiful explanation for what the bang in the Big Bang was.

01:09:13.040 | And then people mathematically analyze

01:09:15.720 | the consequences of this idea

01:09:17.760 | and they make predictions for tiny temperature differences

01:09:21.480 | across the night sky that in principle could be measured.

01:09:24.840 | You send up balloons, you send up satellites

01:09:27.120 | with very refined thermometers

01:09:29.920 | and they measure the temperature of the night sky

01:09:33.000 | and the statistical distribution

01:09:34.800 | of the temperature differences

01:09:36.040 | agrees with the mathematical predictions.

01:09:38.280 | I mean, you just sort of have to stand in awe

01:09:43.200 | of this insight.

01:09:44.560 | So you think, aha, the theory has been established.

01:09:48.320 | But scientists are an incredibly skeptical bunch

01:09:53.320 | and some scientists, including one of the people

01:09:56.640 | who helped develop the theory at the outset,

01:09:58.400 | Paul Steinhardt, comes along and says,

01:10:00.960 | well, yeah, this theory's done pretty well so far

01:10:04.120 | but there are aspects of this theory

01:10:06.480 | that are making me lose confidence.

01:10:08.180 | For instance, this theory seems to suggest

01:10:10.880 | that there might be other universes.

01:10:13.380 | Like how do you make sense of a theory

01:10:15.300 | that suggests there are other universes?

01:10:16.880 | Or there are others who come along and say,

01:10:18.920 | this theory seems to talk about length scales

01:10:23.240 | that are minuscule even by the so-called Planck length,

01:10:26.680 | the sort of shortest length that we can imagine

01:10:29.360 | making sense of in a theory of quantum gravity.

01:10:31.840 | How do you make sense of that?

01:10:33.440 | And so on and so forth.

01:10:34.280 | They develop a list of things that they consider

01:10:37.720 | to be chinks in the inflationary cosmological theory's armor

01:10:42.600 | and they develop other ideas which they claim

01:10:46.080 | yield the same predictions as inflationary cosmology

01:10:48.640 | for those temperature differences across space

01:10:50.440 | but don't suffer from these problems.

01:10:52.840 | And then the inflationary cosmology folks say,

01:10:55.120 | no, no, no, hang on.

01:10:56.760 | Your theory suffers from different problems.

01:10:59.920 | And so the arguments goes, it's a healthy debate.

01:11:02.600 | Talk about real debates in science.

01:11:05.120 | So when you ask what's up with the Big Bang,

01:11:07.800 | I don't know right now.

01:11:09.940 | If you would have asked me five years ago,

01:11:12.760 | maybe even less than that, three or four years ago,

01:11:15.160 | I would have said, look,

01:11:16.280 | inflationary cosmology has some issues

01:11:19.080 | but the package of explanations it provides is so potent

01:11:23.560 | and the issues that beset it are seemingly solvable to me

01:11:28.560 | that I would imagine it's going to in the end win out.

01:11:32.920 | I would still say that today

01:11:34.180 | but I wouldn't say it as loudly.

01:11:36.160 | I wouldn't say it as confidently.

01:11:38.800 | I think it's worth thinking about alternate ideas

01:11:42.140 | and it could be the case that the paradigm

01:11:44.300 | at some point shifts.

01:11:45.720 | - Does dark matter and dark energy fit into the shifting

01:11:50.520 | of the explanations for those?

01:11:52.560 | - Yeah, certainly.

01:11:53.400 | So dark energy has in the inflationary theory

01:11:58.400 | is kind of a big mystery.

01:12:00.260 | So dark energy is the observational realization

01:12:05.260 | in the last 20 years that not only is universe expanding,

01:12:09.480 | it's expanding ever more quickly.

01:12:11.560 | Something is still pushing things outward

01:12:15.120 | and the explanation is that there's like a residual version

01:12:18.360 | of the repulsive gravity from the early universe

01:12:20.600 | but it's such a strange number.

01:12:23.020 | When you write that amount of dark energy

01:12:25.660 | using the relevant units in a theory of quantum gravity,

01:12:29.120 | it's a decimal point followed by like 120 zeros

01:12:33.080 | and then a one.

01:12:34.680 | We're not used to those kinds of numbers in physics.

01:12:38.300 | We're used to a half, one, pi, E squared to two.

01:12:43.300 | Those are the kinds of fundamental numbers

01:12:46.740 | that emerge in our explanations of the world

01:12:49.880 | and we look at this bizarre number,

01:12:51.960 | decimal point, all these zeros and a one,

01:12:53.780 | we say something's wrong there.

01:12:56.200 | Like where would that number have come from?

01:12:59.640 | Now there are people who suggest resolution to it

01:13:01.800 | so it's not like we're totally in the dark on it

01:13:03.600 | but those people like Paul Steinhardt

01:13:06.680 | who have alternate cosmological theories,

01:13:09.080 | cyclic cosmologies as they call it,

01:13:11.120 | claim that they have a more natural explanation

01:13:14.440 | of the dark energy that it naturally feeds

01:13:17.160 | into a cyclical process that is their cosmological paradigm.

01:13:22.160 | So yeah, if the cosmology should change,

01:13:26.200 | it's conceivable our view of dark energy may change

01:13:29.800 | from deeply mysterious to deeply integrated

01:13:32.480 | into a different paradigm.

01:13:34.200 | That is possible.

01:13:35.520 | - I think it's Roger Penrose that think

01:13:37.400 | that information can bleed through

01:13:39.440 | from before the Big Bang to after the Big Bang.

01:13:41.920 | - Yeah.

01:13:42.760 | - Is the Big Bang like a full erasure of the hard drive

01:13:46.840 | or is there some information that could bleed through?

01:13:48.880 | - Yeah, I mean, so Roger is among the most creative thinkers

01:13:53.880 | of the last hundred years, rightly won the Nobel Prize

01:13:58.200 | for his insights into singularities in space time

01:14:02.000 | that we know to afflict our mathematical solutions

01:14:06.480 | of black holes and the Big Bang and so forth.

01:14:08.120 | And he has an enormously fertile imagination

01:14:13.120 | and I mean that in the most positive sense.

01:14:16.320 | And so he has put forward this idea,

01:14:19.640 | this conformal cyclic cosmology,

01:14:21.880 | I think is the official title

01:14:23.760 | although I could be getting that wrong.

01:14:26.320 | I can't say that I've studied it.

01:14:27.940 | I have seen lectures on it.

01:14:30.280 | I don't find it convincing as yet.

01:14:33.280 | It feels like it's being built to find a solution

01:14:38.280 | as opposed to sort of more naturally emerging.

01:14:42.200 | Maybe Roger would say otherwise

01:14:43.920 | and I don't mean to in any way cast aspersions on the work.

01:14:48.440 | It's vital and interesting

01:14:49.720 | and people are thinking about it.

01:14:51.400 | I don't consider it as close a competitor

01:14:55.400 | to say the inflationary theory as for instance,

01:14:58.100 | the stuff that Paul Steinhardt has put forward.

01:15:00.840 | But again, you've got to keep an open mind in this business

01:15:05.200 | when there's so much that we don't yet understand.

01:15:07.640 | - I mean, it is wild to think that information

01:15:09.600 | could survive something like that.

01:15:10.880 | Just like it is wild to imagine

01:15:13.320 | that information could escape a black hole for example.

01:15:16.560 | It just seems like by construction,

01:15:20.160 | these things are supposed to not bleed out anything.

01:15:24.160 | - But one of the challenges in all of these theories

01:15:25.840 | is when we talk about a singularity,

01:15:27.640 | has this real sexy term, the singularity.

01:15:30.220 | But a singularity is in more ordinary language,

01:15:33.580 | a physical system where the mathematics breaks down.

01:15:39.760 | It's nonsensical.

01:15:41.100 | It's like taking one divided by zero.

01:15:42.820 | You put that into a calculator and it says E, error.

01:15:45.700 | It does not make sense, doesn't compute.

01:15:48.220 | And so it's very hard to make definitive statements

01:15:53.220 | about things like the Big Bang or about black holes

01:15:56.660 | until we cure the mathematical singularities.

01:16:00.340 | And there are some who claim that in certain regimes,

01:16:03.540 | the singularities have been cured.

01:16:06.260 | I don't by any mean think that there's consensus

01:16:09.020 | on these ideas.

01:16:10.040 | So when one talks about information

01:16:12.320 | sort of bleeding through the Big Bang,

01:16:13.740 | you've really got to make sure

01:16:15.460 | that the equations have no singularity.

01:16:17.340 | You talk about cyclic cosmology,

01:16:18.740 | you've got to make sure

01:16:19.860 | that the equations don't have any singularities

01:16:21.660 | as you go from say one cycle to the next.

01:16:24.180 | Now, some of the proponents of these theories claim

01:16:26.140 | that they have resolved these issues.

01:16:28.060 | I don't think that there's a general sense

01:16:30.660 | that that is the case as yet,

01:16:32.260 | but it could be that, look, life is so short

01:16:35.340 | that I haven't had the time to deeply delve

01:16:37.700 | into all the mathematical intricacies

01:16:39.500 | of all the ideas that have been put forward.

01:16:41.260 | If I did that, I'd never do anything else.

01:16:43.240 | But that's what the issue is.

01:16:44.700 | - And of course, it's just math.

01:16:46.400 | There may be holes.

01:16:47.780 | There may be gaps in our understanding

01:16:52.940 | in the way we're modeling physical reality.

01:16:55.100 | - Well, that's the point.

01:16:55.940 | In fact, when you said I was about to jump in

01:16:57.500 | and say modeling, but you got there first

01:16:59.380 | and it's exactly the right point.

01:17:01.100 | We're talking about the universe here, right?

01:17:04.660 | And how do you talk about the universe

01:17:06.980 | with a straight face mathematically?

01:17:08.980 | And the way you do it is you simplify,

01:17:12.060 | you throw away those characteristics of the universe

01:17:14.660 | that you don't think are vital to a full understanding.

01:17:18.500 | And so we're gonna get to a point,

01:17:20.580 | people are starting to,

01:17:21.560 | where we've got to go beyond those simplifications.

01:17:24.780 | And so cosmology has for a long time

01:17:28.060 | modeled the universe in the most simplest terms,

01:17:30.460 | homogeneous, isotropic.

01:17:33.340 | It has just a few parameters that describe it,

01:17:35.940 | the average density of mass and energy and so forth.

01:17:38.580 | We have to go beyond those simplifications

01:17:40.380 | and that will require putting these things on computers.

01:17:43.420 | We're not gonna be able to do calculations there.

01:17:45.220 | So much as astrophysics has gone beyond many simplifications

01:17:49.660 | to now give really detailed simulations of star systems

01:17:53.300 | and galaxies and so forth,

01:17:54.940 | we're gonna have to do that with cosmology

01:17:56.900 | and people are starting to do that today.

01:17:59.140 | - Yeah, I've seen some interesting work on simulation.

01:18:02.940 | Most simulation cosmology, by the way, is just awesome.

01:18:05.780 | But just like simulation of the early formation

01:18:08.740 | of our solar system to understand how the Oort cloud

01:18:13.020 | and just, I don't know, the whole of it,

01:18:16.580 | how Earth came to be,

01:18:18.380 | like how Jupiter just the full--

01:18:21.180 | - Protects us.

01:18:22.020 | - Protects us and then there's like weird like moons

01:18:26.260 | and volcanoes and like modeling all of that,

01:18:30.620 | the formation of all of that is fascinating.

01:18:34.440 | Because that naturally is the question

01:18:37.100 | of how does life emerge on these kinds of rocks?

01:18:41.180 | How does a rock become a rabbit?

01:18:42.980 | But speaking of models,

01:18:47.420 | there's an equation called the Drake equation.

01:18:50.340 | We were talking about life.

01:18:52.700 | Have to ask at the highest level first,

01:18:56.380 | when you look out there,

01:18:58.060 | how many alien civilization do you think are out there?

01:19:01.220 | Well, zero, one or many?

01:19:04.660 | So if you say civilization,

01:19:08.200 | I would bring my number way down.

01:19:11.420 | It could be zero.

01:19:13.860 | If you talk about life,

01:19:17.660 | I think it could be many.

01:19:20.500 | As we were saying before,

01:19:21.780 | I think the move from life to consciousness,

01:19:25.820 | the kinds of beings that would build

01:19:27.460 | what we would recognize as a civilization,

01:19:30.700 | that may be extraordinarily rare.

01:19:34.220 | I hope it's not.

01:19:35.300 | As a kid, I loved Star Trek.

01:19:38.060 | I just loved the idea that we would be part

01:19:40.580 | of some universal community where,

01:19:43.660 | look, experience on planet Earth

01:19:46.020 | suggests it doesn't always go so well

01:19:48.120 | when groups who are separated try to come together

01:19:50.900 | and live in some larger collective.

01:19:53.780 | But again, as an optimist,

01:19:55.940 | how amazing would it be to converse

01:19:57.900 | with an alien civilization

01:19:59.140 | and learn what they've figured out

01:20:01.420 | about physics and cosmology and compare notes

01:20:05.320 | and learn from each other in some wonderful way.

01:20:09.300 | I love that idea.

01:20:10.500 | But if you ask me the likelihood of it,

01:20:13.780 | I would err on saying it may be so improbable

01:20:18.560 | that the conditions conspire to allow life

01:20:21.700 | to move to this place of consciousness

01:20:24.680 | that it might be rare.

01:20:27.120 | - It might be oversimplifying things,

01:20:28.640 | but just observing the power of the evolutionary process,

01:20:32.560 | I tend to believe,

01:20:34.360 | and you read different theories of how we went,

01:20:38.980 | how Homo sapiens evolved.

01:20:43.220 | It seems like the evolutionary process naturally leads

01:20:46.440 | to Homo sapiens or creatures like that,

01:20:51.440 | or much better than that.

01:20:53.200 | So to me, there's several scary scenarios.

01:20:57.320 | So, okay, the positive scenario

01:21:00.760 | is life itself is really difficult.

01:21:03.240 | So that origin of life is difficult.

01:21:05.860 | That's exciting for many reasons

01:21:08.040 | because we might be able to prove that wrong easily

01:21:12.520 | in the near term by finding life elsewhere.

01:21:14.760 | - Sure.

01:21:15.940 | - The scary thing to me is if life is easy

01:21:20.940 | and there's plenty of conscious,

01:21:23.840 | intelligent civilizations out there,

01:21:26.780 | and we have not obviously made contact,

01:21:30.620 | which means with intelligence and consciousness

01:21:33.340 | comes responsibility and ultimately destruction.

01:21:39.940 | So with power comes great responsibility.

01:21:42.780 | And then we end up destroying ourselves.

01:21:44.780 | That's the scariest.

01:21:48.140 | The positive, I guess, version is that

01:21:50.220 | maybe we're being watched,

01:21:53.080 | sort of like there's a transition

01:21:57.220 | to where you don't want to ruin

01:21:58.820 | the primitive villages out there.

01:22:01.400 | And so there's a protective layer around us.

01:22:04.180 | - Yeah.

01:22:05.020 | - They're watching.

01:22:06.620 | So where do you, in these possible explanations,

01:22:09.540 | the Fermi paradox, why haven't we contacted aliens?

01:22:12.260 | - Yeah.

01:22:13.100 | - Do you land on?

01:22:13.920 | - Well, I think the most straightforward explanation

01:22:17.740 | is that there aren't any.

01:22:19.380 | Now, there are many other explanations too.

01:22:23.180 | So you can't be dogmatic about things

01:22:25.620 | that are just sort of gut feel.

01:22:27.700 | But one of my favorite Twilight Zone episodes,

01:22:31.860 | I don't know if you ever saw this one,

01:22:33.340 | where this alien civilization

01:22:35.380 | finally comes to planet Earth

01:22:37.700 | and gives us this book that they really want us to have

01:22:41.820 | and to hold.

01:22:42.700 | And it's in this foreign language, you don't understand it.

01:22:45.620 | The cryptographers, they desperately try to decipher it

01:22:49.140 | as humans are going to visit this other alien planet.

01:22:52.500 | And they're all sending back postcards,

01:22:53.740 | how wonderful it is and so forth.

01:22:55.260 | And they finally decipher the title.

01:22:58.580 | It's to serve man.

01:23:00.340 | And everyone's so thrilled.

01:23:01.500 | Oh, they're here to serve us.

01:23:02.620 | It all makes sense.

01:23:03.740 | And then just as one of the final cryptographers

01:23:06.260 | is going on to the alien ship,

01:23:08.220 | his helper runs and says,

01:23:10.820 | "I've deciphered the rest of the book to serve man.

01:23:13.940 | "It's a cookbook."

01:23:15.020 | You know, so.

01:23:15.860 | (laughing)

01:23:17.140 | You know, so yeah.

01:23:18.380 | Is that a possibility?

01:23:20.980 | Sure, you know.

01:23:22.180 | And so could they be watching us

01:23:24.020 | and just sort of waiting for us

01:23:25.180 | to get to a mature enough level?

01:23:29.700 | I don't know, it strikes me.

01:23:31.140 | Well, you know, I think it'd be better

01:23:32.380 | to have this conversation after the James Webb telescope.

01:23:35.100 | I mean, I do think that if we look

01:23:38.460 | at the atmospheres of many planets,

01:23:41.380 | I mean, there's now an estimate now

01:23:42.540 | that there's on order of one planet per star on average.

01:23:47.540 | So we've long known that, you know,

01:23:50.020 | the galaxy, hundreds of billions of stars,

01:23:52.820 | numbers of galaxies, hundreds of billions of galaxies.

01:23:54.820 | So we're talking about hundreds of billions

01:23:56.700 | of hundreds of billions of planets.

01:23:57.980 | Oh my, you know.

01:23:59.060 | And if we start to survey some of these planets

01:24:02.340 | and one after the other after the other,

01:24:03.860 | we just sort of find no evidence

01:24:06.420 | for any of the biological markers.

01:24:10.460 | It could be, of course,

01:24:11.340 | maybe life takes a radically different form.

01:24:13.900 | It'd be hard to know that.

01:24:15.440 | But I think, you know, that would at least give us

01:24:17.660 | some insight on the life question.

01:24:19.420 | But I just don't see how we get insight

01:24:22.000 | on the civilization or consciousness question

01:24:25.140 | without, you know, the direct connection.

01:24:27.620 | And it strikes me that if consciousness is ubiquitous,

01:24:32.620 | let's say life is, I'm willing to grant that.

01:24:35.100 | If consciousness is also ubiquitous,

01:24:37.300 | then I don't understand why they haven't been here

01:24:41.700 | or why there hasn't been sub-conception

01:24:43.540 | 'cause presumably they should be much further ahead of us.

01:24:47.940 | How unlikely would it be that we're like,

01:24:50.240 | of all consciousness in the universe,

01:24:52.140 | we're the most advanced.

01:24:53.540 | That'd be such a special place for human beings

01:24:57.020 | that it's hard for me to grant that as a likely possibility.

01:25:00.180 | Rather, I think we're kind of run of the mill.

01:25:02.740 | And there are many who are far more advanced than us.

01:25:06.060 | And I don't think that they would expend the energy

01:25:09.120 | to hide themselves.

01:25:11.380 | So I don't think they care enough.

01:25:12.820 | - And so, see, that's actually what I believe,

01:25:15.920 | that there's a very large number of civilizations

01:25:19.200 | that are far more advanced than us.

01:25:21.460 | But my sense is that humans are exceptionally limited,

01:25:25.240 | both in our direct sensory capabilities and our physics,

01:25:29.300 | our tools of sensing,

01:25:31.860 | that just like with the string theory

01:25:33.260 | and the multiple dimensions, we're just not,

01:25:35.620 | I honestly believe there could be stuff

01:25:39.100 | in front of our nose that we're just not seeing

01:25:42.820 | 'cause we're too dumb, too much hubris.

01:25:48.740 | And I mean, there's a bunch of stuff,

01:25:50.940 | and too ignorant to the fabric of reality,

01:25:54.940 | all of those things.

01:25:56.340 | We're young in terms of intelligence.

01:25:59.900 | - But I guess what I say is,

01:26:01.060 | I'm on board with all of that as a real possibility.

01:26:04.140 | But then it does strike me

01:26:06.740 | that we are sufficiently able to observe the,

01:26:11.740 | look, we can look back to a fraction of the duration

01:26:16.780 | from here to, just a fraction is left

01:26:20.060 | that we are unable to see.

01:26:22.720 | So however young we are,

01:26:26.400 | we have been able to sort of pierce the universe.

01:26:29.160 | And it just strikes me that there would be some signature,

01:26:33.320 | but maybe that's coming.

01:26:35.240 | But look, having said that, I do,

01:26:37.880 | look, I certainly note the fact that it's rare

01:26:41.600 | that I stoop down while walking in Manhattan

01:26:46.140 | and sort of dig up some ants in the bushes

01:26:48.940 | on the side of the street and talk to the ants, right?

01:26:51.560 | Because it's just not interesting to me.

01:26:52.960 | So if we're like the ants on the cosmological landscape,

01:26:56.080 | then yeah, I can imagine that the super advanced aliens

01:26:58.760 | would be like, like whoever, you know.

01:27:01.960 | But I feel like we're sufficiently advanced

01:27:04.320 | that there should be some signal signature of that,

01:27:07.200 | but maybe it's coming.

01:27:08.320 | - I think the deeper fundamental problem

01:27:10.120 | between us and the ants

01:27:11.240 | is that we don't have a common language.

01:27:12.720 | It's not the interest.

01:27:14.600 | It's that we don't even have a common language.

01:27:17.280 | And so the alien civilizations

01:27:20.480 | don't even know how to communicate.

01:27:21.840 | Like we humans have convinced ourself we're special

01:27:24.720 | because we developed a language.

01:27:25.920 | You talked about the importance of language

01:27:28.760 | to the intelligence, but it makes you wonder

01:27:31.640 | like how very niche is that club that we've tried,

01:27:36.640 | we've created of language and linguistic type of systems

01:27:40.280 | that are very specific to our particular kinds of brains.

01:27:42.900 | And we share ideas together.

01:27:44.320 | We're all super excited that we can understand

01:27:46.000 | the universe 'cause we came up with some notation and math.

01:27:49.340 | I wonder if there's some totally other kinds of language

01:27:52.440 | that communicates on a different timescale

01:27:54.480 | with very different mechanisms in the space of information

01:27:58.160 | that just is not, everything is lost in translation.

01:28:03.160 | - Yeah, and it could well be.

01:28:04.760 | So look, I mean, I think part of the reason

01:28:07.320 | I go toward the possibility of the soul intelligence

01:28:12.320 | is there's a certain kind of romantic appeal

01:28:16.400 | to looking out in the cosmos and it's just quiet

01:28:20.820 | and it's just eternal silence.

01:28:22.520 | There's something that appeals to me

01:28:25.320 | at an emotional level that way.

01:28:27.860 | But yeah, I mean, nobody knows.

01:28:31.680 | And it's certainly conceivable

01:28:35.500 | that there's just a radical mismatch

01:28:38.660 | between the kinds of things

01:28:40.060 | that we are able to observe and sensitive to

01:28:42.860 | versus the kinds of structures that permeate the universe

01:28:47.200 | in a manner that simply we're unable to detect.

01:28:50.400 | - Well, if we are alone, that is exciting.

01:28:54.000 | And one of the ways it's exciting

01:28:56.560 | is that it's up to us to expand out into the universe,

01:29:01.560 | to permeate consciousness out into the universe.

01:29:07.760 | So that's where space exploration comes in.

01:29:09.960 | Let me ask you, as somebody who's a screen theorist,

01:29:12.440 | a physicist, do you think space exploration,

01:29:17.120 | colonizing space is a physics or an engineering problem?

01:29:21.440 | What would you say?

01:29:22.280 | - Yeah, I think it's fundamentally an engineering problem

01:29:25.440 | if we're not trying to do things like build wormholes

01:29:30.440 | the way they did, say, an interstellar

01:29:34.000 | to get to a different place

01:29:35.240 | or trying to travel near the speed of light

01:29:37.920 | so that we would actually be able

01:29:39.420 | to traverse interstellar distances.

01:29:41.140 | I mean, without that, our colonization will happen

01:29:44.680 | in a very, very slow rate, right?

01:29:48.160 | But one of the beauties of relativity

01:29:51.400 | is if you do travel near the speed of light,

01:29:52.880 | you can actually go arbitrarily far in a human lifetime.

01:29:57.040 | People say, how's that possible?

01:29:58.120 | You can't go billions of light years.

01:30:00.160 | Well, you can actually,

01:30:01.720 | because as you can do the speed of light,

01:30:03.440 | the way in which space and time change

01:30:06.080 | allows you to go, in principle, arbitrarily far.

01:30:08.640 | That's very exciting.

01:30:09.940 | But if we put that physics side of the issue

01:30:13.640 | and the manipulation of space and time to the side,

01:30:15.960 | yeah, I think it's a deep engineering problem.

01:30:18.200 | You know, how do you terraform other planets?

01:30:21.660 | I mean, how do you go beyond our local neighborhood,

01:30:26.660 | say, without using the ideas of relativity?

01:30:30.360 | So I think it's all quite exciting.

01:30:32.080 | And I think the idea is using solar sails

01:30:34.920 | that people have developed

01:30:36.680 | and trying to take that first step to Mars.

01:30:40.780 | I think that's a vital and valuable step to take.

01:30:44.020 | But yeah, I think these are fundamentally

01:30:45.380 | engineering challenges.

01:30:46.380 | - Or extending the human lifespan through biology research

01:30:49.500 | or maybe reducing what it means to be a human being

01:30:54.500 | into information and uploading certain parts of it.

01:30:57.740 | Maybe not all the full resolution of a human life,

01:31:00.940 | but maybe the essential things like the DNA

01:31:03.940 | and be able to reconstruct that human being.

01:31:07.140 | But, you know, I have to ask about Mars.

01:31:11.500 | You know, do you find the dream of humans stepping on Mars,

01:31:16.500 | stepping foot first, but also colonizing Mars,

01:31:20.800 | one that's worth us fighting for?

01:31:25.000 | - Yeah, hugely so.

01:31:25.960 | I mean, I think what we have long been

01:31:28.480 | not always in the best way is a species of explorers

01:31:33.920 | in the literal sense of traveling

01:31:37.040 | from one part of the world to another,

01:31:39.560 | or in the more metaphorical sense

01:31:41.360 | of trying to travel through our minds to the quantum realm

01:31:45.140 | or back to the Big Bang or to the center of black holes.

01:31:47.780 | So I think that's fundamentally part of the human spirit.

01:31:51.460 | So I do think that's a vital part of our heritage

01:31:56.460 | brought forward into its next incarnation.

01:32:01.020 | That's who we are.

01:32:03.760 | - Do you think there'll be a day in the future

01:32:06.840 | where a human being is born on Mars

01:32:11.280 | and has to learn about his or her human origins on Earth?

01:32:16.280 | Like they'll have to read in a book?

01:32:19.360 | - Yeah, I don't think it'll be a book at that stage.

01:32:21.960 | It'll probably just be uploaded into the head or something,

01:32:24.460 | or imprinted into the DNA,

01:32:26.720 | and then they just sort of sense it.

01:32:28.400 | But yeah, I think there's, well, look,

01:32:31.040 | the issue you raised before is the vital one.

01:32:33.840 | Is it the case that any sufficiently advanced civilization

01:32:37.540 | destroys itself?

01:32:38.920 | Is that sort of a commonplace quality?

01:32:41.360 | I mean, that's the other potential answer

01:32:42.960 | to the Fermi paradox.

01:32:44.640 | Why aren't they here?

01:32:45.680 | Because by the time they got to the technological development

01:32:48.680 | where they could travel here, they blew themselves up.

01:32:50.760 | They destroyed themselves.

01:32:52.000 | And that's an unfortunate,

01:32:54.600 | but not a hard to imagine possibility

01:32:58.680 | based on things that have happened here on planet Earth.

01:33:02.600 | But putting that to the side, I think it,

01:33:05.840 | you know, that's the big obstacle,

01:33:07.100 | but putting it to the side,

01:33:08.120 | we will resolve the engineering challenges.

01:33:10.720 | And, you know, I should probably modify my answer

01:33:14.340 | from before when you said, is it engineering or physics?

01:33:17.020 | It's really both, right?

01:33:18.480 | So we will surmount the engineering challenges,

01:33:21.520 | and that will then make the physics challenges relevant.

01:33:24.760 | It'll make it relevant to figure out

01:33:26.180 | how to travel near the speed of light.

01:33:28.040 | It'll make it relevant to learn how to manipulate

01:33:30.480 | the shape of space-time and so forth.

01:33:33.320 | So I think it's a multi-stage process

01:33:36.860 | where it is engineering and ultimately physics.

01:33:39.320 | And if we stick around long enough,

01:33:41.560 | those are the kinds of challenges

01:33:42.720 | I think that we're ultimately gonna surmount.

01:33:44.720 | - And on the physics side,

01:33:45.780 | it's figuring out how to harness energy enough

01:33:47.880 | to travel outside the solar system,

01:33:49.920 | which seems like a heck of a difficult journey.

01:33:52.340 | But even Mars itself, I don't know,

01:33:56.140 | maybe because I was born in the Soviet Union

01:33:58.600 | and was born with the, you know,

01:34:03.480 | looking up at the stars and that dream

01:34:05.840 | of like the highest of human achievement

01:34:07.880 | is the ability to fly out there,

01:34:09.480 | to, you know, to join the stars.

01:34:12.040 | I really like the idea of going to Mars

01:34:14.840 | and not just stepping foot on Mars.

01:34:17.200 | It wasn't until, maybe I'm misinformed,

01:34:22.440 | but for me personally, it wasn't until Elon Musk

01:34:27.060 | started talking about the colonization of Mars

01:34:29.940 | did I realize like we humans can actually do that.

01:34:34.940 | And first of all, the importance of somebody saying

01:34:39.380 | that we can do these seemingly impossible things

01:34:42.820 | is immeasurable because, you know,

01:34:46.620 | the fact that he placed that into my mind

01:34:50.140 | and into the minds of millions of others,

01:34:52.180 | maybe hundreds of millions, maybe billions of others,

01:34:54.860 | young kids today, I mean, that's gonna make it a reality.

01:34:58.660 | I, for some reason, am deeply excited,

01:35:00.900 | even though my work is in AI, that echoes all of this.

01:35:06.260 | I'm excited by the idea that somebody would be born,

01:35:09.500 | as we were saying, on Mars and sort of look up

01:35:14.180 | and be able to see with a telescope Earth

01:35:16.660 | and say, "That's where I came from."

01:35:19.360 | I don't know, that idea scale to other planets,

01:35:23.540 | to other solar systems, that's really exciting.

01:35:26.580 | - And hugely exciting.

01:35:28.020 | I think you're absolutely right.

01:35:29.300 | I mean, the vital thing is to dream, right?

01:35:33.820 | I mean, and it sounds hackneyed,

01:35:36.380 | but it is so important for young kids

01:35:40.340 | for the next generation to think about the things

01:35:43.620 | that are seemingly impossible.

01:35:45.460 | I mean, that's what makes them possible.

01:35:47.140 | And this is one which is concrete enough.

01:35:50.280 | I mean, this is something that's gonna happen soon

01:35:52.120 | in terms of actually going to Mars.

01:35:54.840 | And then the next step of establishing some presence,

01:35:59.840 | some semi-permanent or permanent presence,

01:36:02.600 | this is not something that's gonna wait

01:36:05.480 | to the 25th century.

01:36:06.560 | I mean, this is something that's gonna happen

01:36:07.720 | relatively soon.

01:36:09.140 | So, I mean, it could well be in your lifetime,

01:36:11.200 | unlikely mine, but possibly in your lifetime,

01:36:13.640 | that that kid will be born and have the experience

01:36:17.120 | that you described.

01:36:18.280 | So, yeah, it's spectacularly exciting.

01:36:20.760 | - And I actually, I would love to go on Mars

01:36:24.240 | on one of the early-

01:36:25.880 | - You would? - Yeah.

01:36:26.720 | - What if it's one way?

01:36:28.160 | - I'm happy doing one way.

01:36:29.120 | - Really? Wow.

01:36:30.480 | - And I'm single if there's ladies out there

01:36:32.480 | that wanna start that family.

01:36:34.520 | Let's go out to Mars.

01:36:36.520 | No, I think-

01:36:37.360 | - See, I have to tell you something.

01:36:38.480 | You spoke about terror, thinking about like black holes.

01:36:42.680 | If I actually think about going to Mars

01:36:45.400 | and being on Mars and put myself in there fully,

01:36:49.720 | that's terror-inducing.

01:36:51.760 | The idea of to be in this foreign world

01:36:54.920 | where you can't come back,

01:36:56.700 | where you've made this choice that can't be reversed,

01:37:00.000 | or at some point, it may be, but in that guise,

01:37:03.600 | that to me carries a deep sense of terror.

01:37:07.160 | - You know, I feel that sense of terror every time.

01:37:10.600 | Kerouac, Jack Kerouac talked about this on the road,

01:37:13.840 | is when you leave a place, if you're honest about it,

01:37:17.400 | like life is short.

01:37:19.800 | And when you leave a place, you move to a new place,

01:37:23.080 | and you think of all the friends, maybe family,

01:37:25.180 | you're leaving behind as you drive over the hill,

01:37:28.020 | that really is goodbye.

01:37:31.480 | Like we sometimes don't think of it that way

01:37:33.300 | when we're moving, but that really is goodbye to that life,

01:37:36.280 | to the person you were, to all the people.

01:37:38.660 | Maybe if it's close friends,

01:37:40.280 | you'll see them maybe 10, 15 more times in your life,

01:37:42.840 | and that's it.

01:37:43.840 | And you're saying goodbye to all of that.

01:37:46.120 | And so in the same way, I see it as way more dramatic

01:37:50.200 | when you're flying away from Earth,

01:37:52.120 | and it's like, it's goodbye to Dunkin' Donuts and Starbucks,

01:37:56.200 | and it's goodbye to whatever,

01:37:58.680 | I don't know why I picked those,

01:37:59.660 | but all the things that are special to Earth, it's goodbye.

01:38:04.660 | But that's life.

01:38:06.920 | I suppose more what excites me about that kind of journey

01:38:11.680 | is it's a distinct contemplation of your mortality,

01:38:14.800 | acceptance of your mortality.

01:38:16.680 | You're saying just like when you take on

01:38:19.620 | any difficult journey, it's accepting

01:38:22.840 | that you're going to die one day,

01:38:25.200 | and might as well do something truly exciting.

01:38:28.760 | - Yes, I mean, I'm with you on that.

01:38:31.560 | I'm a strong believer that deep underneath

01:38:35.640 | human motivation is this terror of our own mortality.

01:38:41.280 | There's this wonderful book that had a great influence

01:38:43.600 | on me called "The Denial of Death" by Ernest Becker.

01:38:47.560 | And when you are aware of the ways

01:38:52.320 | in which our mortality influences our behaviors,

01:38:56.320 | it really does add a different slant,

01:38:59.720 | a different kind of color

01:39:01.000 | to the interpretation of human behavior.

01:39:03.640 | - Yeah, it's funny, that book had a big influence

01:39:07.600 | on me as well.

01:39:08.440 | - Oh, is that right?

01:39:10.440 | - And terror management theory.

01:39:12.000 | And I, again, from an engineering perspective,

01:39:15.880 | I don't know how many people that book influenced,

01:39:18.380 | because I talked to people about the fear of death,

01:39:22.040 | and it doesn't seem to be that fundamental

01:39:24.960 | to their experience.

01:39:26.560 | And I don't think on the surface

01:39:28.200 | it's fundamental to my experience,

01:39:29.560 | but it seems like an awfully,

01:39:30.720 | in terms of we're talking about models

01:39:32.160 | and strength theory and theories,

01:39:34.480 | in terms of theories of this macro experience

01:39:37.360 | of human life, it seems like a heck of a good theory

01:39:40.920 | that the fear of death is the warm at the core.

01:39:44.760 | - Yeah, well, I mean, and the terror management theory

01:39:47.320 | is that you make reference to.

01:39:48.460 | I mean, this is a group of psychologists,

01:39:52.580 | social psychologists who devised

01:39:54.440 | these very clever experiments,

01:39:57.400 | real-world experiments with real people,

01:39:59.760 | where you can directly measure the hidden influence

01:40:04.120 | of the recognition of our own mortality.

01:40:07.520 | I mean, they've done these experiments

01:40:08.640 | where they have group of people A, group of people B,

01:40:11.640 | and the only difference between the two groups

01:40:13.000 | is that group B, they somehow reminded them

01:40:16.240 | in some subtle way of their own mortality.

01:40:18.140 | Sometimes it's nothing more than interviewing them

01:40:21.260 | with a funeral home across the street.

01:40:23.780 | You know, an influence is there, but it's subtle.

01:40:25.880 | You don't even think you'd take note of.

01:40:27.560 | And they can find measurable effects

01:40:31.280 | that differentiate the two groups to a high degree

01:40:34.760 | of statistical significance in how they respond

01:40:37.780 | to certain challenges or certain kinds of questions

01:40:40.840 | that shows a direct influence of the reminder

01:40:44.840 | of their own mortality.

01:40:46.040 | And I've read a number of these studies,

01:40:48.700 | and they are really convincing.

01:40:51.720 | And so, yeah, I would say that the reason why

01:40:54.140 | so many people would say that, yeah,

01:40:57.360 | fear of mortality's not front and center in my worldview,

01:41:01.200 | yeah, I don't really think about it much,

01:41:02.440 | doesn't really matter to me much.

01:41:03.360 | The reason why they're able to say that

01:41:05.160 | is because this thing called culture has emerged

01:41:08.600 | over the course of the last 10,000 years.

01:41:10.840 | And part of the role of culture is to give us a means

01:41:14.360 | of not thinking about our mortality all the time,

01:41:17.120 | of not living in terror of the inevitable end

01:41:20.080 | which faces us all.

01:41:21.840 | So it's completely understandable that that's the response

01:41:24.600 | because that's what culture is at least in part for.

01:41:27.960 | - Is it at least possible that the fear of death,

01:41:32.360 | the terror of your mortality is the creative force

01:41:36.360 | that created all of the things around us

01:41:39.080 | at this human civilization?

01:41:41.600 | And I think about from an engineering perspective,

01:41:44.880 | this is where I lose all of my robotics colleagues

01:41:49.280 | is I feel like if you want to create intelligence,

01:41:52.600 | you have to also engineer in some kind of echo

01:41:58.160 | of this kind of fear.

01:41:59.760 | And fear is such a complicated word,

01:42:03.440 | but kind of like a scarcity, a scarcity of time,

01:42:08.440 | a scarcity of resources that creates a kind of anxiety,

01:42:12.520 | like deadlines get you to do stuff.

01:42:15.480 | And there's something almost fundamental to that

01:42:18.480 | in terms of human experience.

01:42:21.480 | - Yeah, well, that's an interesting thought.

01:42:22.720 | So you're basically in order to create a kind of structure

01:42:27.720 | that mirrors what we call consciousness,

01:42:34.360 | you'd better have that structure confront

01:42:37.800 | the same kinds of issues and terrors that we do.

01:42:42.040 | - Consciousness and suffering only makes sense

01:42:44.240 | in the context of death.

01:42:45.680 | If you want to, I feel like if you want to fit

01:42:48.920 | into human society, if you're a robot

01:42:52.400 | and if you want to fit into human society,

01:42:54.520 | you better have the same kind of existential dread,

01:42:59.160 | the same kind of fear of mortality,

01:43:00.800 | otherwise you're not gonna fit in.

01:43:02.200 | - Right.

01:43:03.040 | (both laughing)

01:43:06.240 | - It might be wild, but it's at least like we're talking

01:43:10.360 | about all the theories that are at least worth consideration.

01:43:13.760 | I think that's a really powerful one.

01:43:15.800 | And definitely one has resonated with me

01:43:19.240 | and definitely seems to capture something beautifully,

01:43:24.240 | like real about the human condition.

01:43:31.320 | And I wonder, it's of course sucks to think

01:43:35.120 | that we need death to appreciate life,

01:43:38.220 | but that just may be the way it is.

01:43:43.160 | - Well, it's interesting if this robotic

01:43:44.480 | or artificially intelligent system understands the world

01:43:49.480 | and understands the second law of thermodynamics

01:43:51.720 | and entropy, even an artificial intelligence

01:43:54.760 | will realize that even if its parts are really robust,

01:43:59.280 | ultimately it will disintegrate.

01:44:02.720 | I mean, so the timescales may be different,

01:44:05.240 | but in a way when you think about it, it doesn't matter.

01:44:07.040 | Once you know that you are mortal in the sense

01:44:09.800 | that you are not eternal, the timescale hardly matters

01:44:13.760 | because it's either the whole thing or not.

01:44:17.960 | Because on the scales of eternity,

01:44:19.760 | any finite duration, however large is effectively zero

01:44:23.720 | on the scales of eternity.

01:44:25.600 | And so maybe it won't be so hard for an artificial system

01:44:28.840 | to feel that sense of mortality

01:44:32.040 | because it will recognize the underlying physical laws

01:44:35.240 | and recognize its own finitude.

01:44:38.720 | - And then it'll be us and robots drinking beers,

01:44:41.360 | looking up at the stars and just, you know,

01:44:46.360 | having a good laugh in awe of the whole thing.

01:44:51.120 | - Yeah.

01:44:51.960 | - I think that's a pretty good way to end it,

01:44:55.520 | talking about the fear of death.

01:44:57.360 | We started talking about the meaning of life

01:44:59.840 | and ended on the fear of death.

01:45:01.100 | Brian, this was an incredible conversation.

01:45:02.720 | - My pleasure, thank you, I enjoyed it enormously.

01:45:04.400 | - I really, really enjoyed it.

01:45:05.240 | It's been a long time coming.

01:45:06.760 | I'm a huge fan of your work, a huge fan of your writing.

01:45:09.760 | Thanks for talking to me, Brian.

01:45:10.760 | - Thank you.

01:45:12.080 | - Thanks for listening to this conversation

01:45:13.560 | with Brian Green.

01:45:14.780 | To support this podcast,

01:45:16.120 | please check out our sponsors in the description.

01:45:18.880 | And now let me leave you with some words from Bill Bryson.

01:45:23.000 | Physics is really nothing more

01:45:25.580 | than a search for ultimate simplicity,

01:45:27.940 | but so far all we have is a kind of elegant messiness.

01:45:32.940 | Thank you for listening and hope to see you next time.

01:45:35.840 | (upbeat music)

01:45:38.420 | (upbeat music)

01:45:41.000 | [BLANK_AUDIO]

Brian Greene: Quantum Gravity, The Big Bang, Aliens, Death, and Meaning | Lex Fridman Podcast #232

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