Making Sense - Sam Harris - #18 — The Multiverse & You (& You & You & You...)

00:00:00.000 welcome to the making sense podcast this is sam harris just a note to say that if you're hearing

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00:00:32.500 therefore it's made possible entirely through the support of our subscribers so if you enjoy

00:00:36.540 what we're doing here please consider becoming one today i'll be speaking with max tegmark max is a

00:00:50.260 physicist at mit he's a cosmologist in particular he's published over 200 technical papers and he's

00:00:57.000 been featured in dozens of science documentaries and he's now an increasingly influential voice

00:01:01.300 on the topic of artificial intelligence because his future of life institute deals with this and

00:01:06.400 other potential existential threats max has written one book for the general reader a book that i found

00:01:11.980 incredibly valuable entitled our mathematical universe my quest for the ultimate nature of

00:01:16.960 reality and we'll be talking about some of that today i really enjoyed talking to max we talk about

00:01:22.520 the foundations of science and what distinguishes science from non-science we talk about the

00:01:27.680 mysterious utility of mathematics in the natural sciences we also talk for quite some time about

00:01:33.760 our current picture of the universe from a cosmological perspective which opens on to the fascinating

00:01:40.240 and totally counterintuitive concept of the multiverse which as you'll see entails the claim

00:01:48.440 that there may well be a functionally infinite number of people just like yourself leading nearly

00:01:54.780 identical lives and every other possible life at this moment elsewhere in the universe which is my

00:02:01.280 candidate for the the strangest idea that is still scientifically plausible and finally we talk about the

00:02:07.680 dangers of advances in artificial intelligence as we see them in any case there's a fascinating

00:02:13.180 conversation from my point of view max is a fascinating guy and i hope you enjoy it and i hope you'll buy

00:02:19.460 his book because it is well worth reading and now i give you max tegmark

00:02:24.240 how you doing max thanks for coming on the podcast thank you for having me it's great to be on it's really

00:02:35.020 a pleasure to talk to you i have a lot i want to talk to you about i'm reading your book our mathematical

00:02:40.260 universe which i highly recommend to our listeners and i'm going to talk about some of what i find most

00:02:47.940 interesting in that book but it's by no means exhausts the contents of the book there's no

00:02:52.260 conversation we're going to have here that's going to get into the level of detail that you present in

00:02:56.800 the book so it's i really consider your book a huge achievement you've managed to make an up-to-the-minute

00:03:02.140 picture of the state of physics and cosmology in particular truly accessible to a general reader and

00:03:09.780 that's that's certainly not something that all of your colleagues can claim to have achieved so

00:03:14.720 so congratulations on that oh thank you for your kind words it's important to remember also of course

00:03:19.200 that if in thinking about these things or reading my book one feels that one doesn't understand quite

00:03:25.400 everything about our cosmos you know nobody else does either so that's quite okay and in fact that's

00:03:30.760 really very much part of the charm of studying the cosmos that we still have these great mysteries

00:03:36.420 that we can ponder yeah and so i'm going to drive rather directly toward those mysteries and but

00:03:43.300 first i just want to give some context here you and i met in san juan puerto rico at a conference

00:03:50.320 you helped organize on the frontiers of artificial intelligence research and in particular focused on

00:03:56.760 the emerging safety concerns there i hope we're eventually going to get to that but that's that's

00:04:01.580 where we met and our obvious shared interest is on ai at the moment but i i do want to talk

00:04:07.800 first about just the pure physics and then we will get to uh the uh armies of lethal robots that may

00:04:14.680 await us that was great it seems pretty clear to me from our conversations also that we also have a

00:04:19.720 very strong shared interest in in uh looking at this reality out there and pondering what its true

00:04:26.820 nature really is let's start there kind of at the foundations of our knowledge and the foundations

00:04:32.820 of science because you know in science we are making our best effort to arrive at a unified

00:04:39.960 understanding of reality and i think there are many people in our culture many in humanities departments

00:04:45.720 who think that no such understanding is possible they think there's no view of the world that

00:04:51.640 encompasses subatomic particles and cocktail parties and and everything in between but i think that

00:04:58.860 from the point of view of science we have to believe that there is we may use different concepts at

00:05:05.080 different scales but there shouldn't be radical discontinuities between different scales in our

00:05:11.660 understanding of reality and i i'm assuming that's an intuition you share but let's just take that as a

00:05:17.540 starting point yeah when people when someone says that they think reality is just a social construct

00:05:24.240 or whatnot then other people get upset and say you know if you think gravity is a social construct i

00:05:30.380 encourage you to take a step out through my window here on the sixth floor and if you drill down into

00:05:35.400 what this conflict comes from it's just that they're using that r word reality in very different ways and

00:05:41.340 as a physicist the way i use the word reality is i i assume that there is something out there

00:05:48.240 independent of me as a human i assume that the andromeda galaxy would continue existing you know

00:05:53.500 even if i weren't here for example and then we take this very humble approach of saying okay there is

00:05:58.720 some stuff that exists out there our physical reality let's call it and let's look at it as closely

00:06:04.600 we can and try to figure out what properties it has if there's some confusion about something you know

00:06:10.340 that's our problem not reality's problem there's no doubt in my mind that our universe knows

00:06:16.320 perfectly well what it's doing and it's it functions in some way we physicists have so far failed to

00:06:22.080 figure out what that way is and we're in this schizophrenic situation where we can't even make quantum

00:06:28.000 mechanics talk to relativity theory properly but that's the way i see it simply a failure so far in our

00:06:35.080 own creativity and um i think it's not only would i guess that there is a reality out there

00:06:40.060 independent of us but i actually feel it's quite arrogant to say the opposite right because it

00:06:46.480 sort of presumes that we humans play should go center stage solipsists say that there is no reality

00:06:54.260 without themselves ostriches in the apocryphal story right make this assumption that things that they

00:07:01.040 don't see don't exist but even very respected scientists go down this uh slippery slope sometimes

00:07:07.480 neil's boer one of the founders of quantum mechanics famously said no reality without observation

00:07:13.480 which sort of puts humans center stage and denies that there can be things you should call reality

00:07:20.200 without us but i i think that's very arrogant and i i think we should we could use a good dose of

00:07:25.940 humility so my starting point is there is something out there and let's try to figure out how it works

00:07:31.860 right well so i will i think we'll get to uh boer and and to the his copenhagen interpretation of

00:07:37.780 quantum mechanics at some point at least on the fly because as you probably know it really is the

00:07:42.240 darling interpretation of new age philosophers and spiritualists and it's something that that i think

00:07:48.080 we have reason to be uh somewhat skeptical about but inconveniently for us this skepticism about the

00:07:54.220 possibility of understanding reality does sort of sneak in the back door for us somewhat paradoxically

00:08:00.520 by virtue of taking science seriously in particular evolutionary biology seriously and this is

00:08:07.060 something you and i were talking about when we last met where you know i think at one point in the

00:08:11.660 conversation i observed as as almost everyone has who thinks about evolution that one thing we can be

00:08:19.660 sure of is that that our cognitive capacities and our common sense and our intuitions about reality

00:08:25.680 have not evolved to equip us to understand reality at the smallest possible scale or at the largest or

00:08:33.640 things moving incredibly fast or things that are very old we we have intuitions that are tuned for

00:08:40.460 things at human scale things that are moving relatively slowly and we have to decide whether we can mate

00:08:47.240 with them or whether we can eat them or whether they're going to eat us and so you and i were talking

00:08:51.280 about this and and so i i know i said that it's no surprise therefore that the deliverances of science

00:08:58.380 in particular your areas of science are deeply counterintuitive and you that's right you did me

00:09:05.220 one better though you you said that not only is it not surprising it would be surprising and in fact

00:09:11.340 give you reason to mistrust your theories if they were aligned with common sense we should expect

00:09:17.760 the punch line at the end of the book of nature to be deeply counterintuitive in some sense and i just

00:09:23.620 want you to expand on that a little bit yeah that's exactly right i think that's a very clear prediction

00:09:28.020 of darwin's ideas if you take them seriously that whatever the ultimate nature of reality is it should

00:09:34.820 seem really weird and counterintuitive to us because you know developing a brain advanced enough to

00:09:41.080 understand new concepts is costly in evolution and it would we wouldn't have evolved it and spent a lot of

00:09:47.140 energy increasing our metabolism etc if it didn't help in any way if if some cave woman spent too much

00:09:53.780 time pondering what was out there beyond all the stars that she could see or subatomic particles

00:10:00.520 now she might not have noticed the tiger that snuck up behind her and gone clean right out of the gene

00:10:05.840 pool moreover this is not just a natural logical prediction but it's a testable prediction darwin lived

00:10:11.560 a long time ago right and we can look what has happened since then when we've used technology to

00:10:18.060 probe things beyond what we could experience with our senses you know so the prediction is that whenever

00:10:23.060 we with technology study physics that was inaccessible to our ancestors it should seem weird so let's look at

00:10:31.040 the fact sheet at the scorecard we studied what happened when things go much faster than our ancestors near the

00:10:36.900 speed of light time slowed down you know whoa so weird that einstein never even got the nobel prize

00:10:43.140 for it because my swedish commercially countryman on the nobel committee thought it was too weird right

00:10:46.920 you look at what happens when things are really really huge and you get black holes which were considered

00:10:52.360 so weird again it took a long time until people really started to accept them and then you look at

00:10:58.640 what happens when you make things really small so small and our ancestors couldn't see them and you find

00:11:03.100 that elementary particles can be in several places at once extremely counterintuitive to the point that

00:11:08.800 people are still arguing about what it means exactly even though they all concede the particles really can

00:11:14.760 do this weird stuff and the list goes on whenever you take any parameter out of the range of what we

00:11:21.380 our ancestors experienced really weird things happen if you have very high energies for example like when

00:11:27.580 you smash two particles together near the speed of light that the large hadron collider at cern

00:11:32.720 you know if you collide a proton and an anti-proton together and out pops a higgs boson you know

00:11:39.200 that's about as intuitive as if you collide a volkswagen with an audi and out comes a cruise ship

00:11:44.380 and yet this is the way the world works so i think the the verdict is in whatever the nature of reality

00:11:51.960 actually is it's going to seem really weird to us and if we therefore dismiss physics theories just

00:12:00.440 because they seem counterintuitive we're almost certainly going to dismiss whatever the correct theory is

00:12:05.760 once someone actually tells us about it so i'm wondering though whether this slippery slope is in fact

00:12:13.140 more slippery than we're admitting here though because how do we resist the slide into total

00:12:20.720 epistemological skepticism so so for instance why trust our mathematical intuitions or the mathematical

00:12:27.800 concepts born of them or the picture of reality in physics that's arrived at through this kind of

00:12:35.260 bootstrapping of our intuitions into areas that are counterintuitive because i understand why we

00:12:41.020 should trust these things pragmatically if it seems to work we can build machines that work you know we

00:12:45.660 can fly on airplanes you know there's there's a difference between an airplane that flies and one that

00:12:49.760 doesn't but as a matter of epistemology why should we trust the picture of reality that math

00:12:56.140 allows us to bring into view if again we are just apes who have used the cognitive capacities that have

00:13:06.180 evolved without any constraints that they accord with reality at large and mathematics is clearly

00:13:14.920 insofar as we apprehend it discover it invent it an extension of those very humble capacities yeah it's a very

00:13:23.660 good question and and some people tell me sometimes that theories that physicists discuss at conferences

00:13:30.380 from black holes the parallel universes sound even crazier than a lot of myths from old time about

00:13:36.720 fire flame throwing dragons and and whatnot you know so shouldn't we dismiss the physics just as we

00:13:43.240 dismiss these myths to me there's a huge difference here in that these physics theories even though they

00:13:48.660 sound crazy as you yourself said here they actually make predictions that we can actually test and that

00:13:55.240 is really the crux of it so if you take the theory quantum mechanics seriously for example and assume

00:14:00.040 that particles can be in several places at once then you predict that you should be able to build this

00:14:05.000 thing called a transistor which you can combine in vast numbers and build this thing called a cell phone

00:14:10.200 you know and it actually works it's uh you know good luck it's a useful technology using the fire

00:14:18.340 drone hypothesis or whatever this is very linked i think to where we should draw the borderline between

00:14:24.200 science what's science and what's not science some people think that the line should go between that

00:14:30.580 which seems intuitive and not crazy and that which feels too crazy and i'm arguing against that because

00:14:36.880 black holes seemed very crazy at the time and now we found bunch loads of them in the sky to me

00:14:42.900 instead really that the line in the sand that divides science from what's not science is the way i think

00:14:47.860 about it is i what makes me a scientist is that i would much rather have questions i can't answer

00:14:53.860 than have answers i can't question one thing you're you're emphasizing here is that it's not

00:14:58.940 in the strangeness or seeming acceptability of the conclusion it's in the methodology

00:15:06.780 by which you arrived at that conclusion and falsifiability and and testable predictions

00:15:12.700 is part of that i don't think you would say that a popperian conception of science you know as a set of

00:15:19.600 falsifiable claims subsumes all of science because they're clearly scientifically coherent things we

00:15:25.640 could say about the nature of reality where we know there's an answer there we just know that

00:15:30.840 no one has the answer the very prosaic example i often use here is you know how many birds are in

00:15:36.720 flight over the surface of the earth at this moment well we don't know uh we know we're never going to

00:15:42.180 know because it's just changed before i can get to the end of the sentence but it's a totally coherent

00:15:47.660 question to ask and we know that it just has an integer answer you know leaving spooky quantum

00:15:54.020 mechanics or parallel universes aside if we're just talking about earth with and birds as objects

00:15:59.560 we can't get the data but we know in some basic sense that this reality that extends beyond our

00:16:05.680 perception guarantees that the data in principle exists i think you say at some point in your book

00:16:11.120 that a theory doesn't have to be testable across the board it just parts of it have to be testable

00:16:17.520 to give us some level of credence in its overall picture is that is that how you view it

00:16:22.160 i'm actually pretty sympathetic to popper in the idea of testability works fine for even these

00:16:27.900 crazy concepts like sounding concepts like parallel universes and and black holes as long as we

00:16:34.160 remember that what we test are theories specific mathematical theories that we can write down right

00:16:40.220 parallel universes are not a theory they're a prediction from certain theories the black hole isn't

00:16:45.520 a theory either it's a prediction from einstein's general relativity theory and once you have a theory in

00:16:51.360 physics it's testable as long as it predicts at least one thing that you can go check right because

00:16:57.000 then you can falsify it if you check that thing and it's wrong whereas it might also make just because

00:17:01.640 it happens to also make some other predictions for things you can never test you know that doesn't

00:17:05.640 make it non-scientific as long as there's still something you can test yeah black holes for example

00:17:10.560 the theory of general relativity predicts exactly what would happen to you if you fall into the monster

00:17:16.480 black hole in the middle of a galaxy that weighs four million times as much as the sun it predicts

00:17:21.140 exactly how you're going to when you're going to get spaghettified and how and so on except you can

00:17:26.880 never actually do that experiment and then write an article about it in physics review letters because

00:17:33.260 your insight diventerize and the information can't come out but nonetheless that's a testable theory

00:17:37.920 because general relativity also predicts loads of other things such as how your gps works which we can test

00:17:44.920 with great precision and when the theory passes a lot of tests for things that we can make and we

00:17:50.360 start to take the theory seriously then i feel we have to be honest and also take seriously the other

00:17:55.200 predictions for the right from the theory you know whether we like them or not we can't just cherry

00:17:58.920 pick and say hey you know i love uh what the general relativity theory does for gps and the bending of

00:18:06.720 light and the perihelion the weird orbit of mercury and stuff but i don't really like the black holes

00:18:12.880 so i'm going to opt out of that prediction that you cannot do the way that you just say i want coffee

00:18:18.480 and opt out of the caffeine and buy decaf in physics if you once you buy the theory you have to buy the

00:18:24.900 whole product and if you don't like any of the predictions well then you have to try to come up

00:18:29.900 with a different mathematical theory which doesn't have that prediction but still explains everything

00:18:35.140 else and that's often very hard people have tried for 100 years to do that with einstein's gravity

00:18:40.220 theory right to get rid of the black holes and they've so far pretty much failed and that's why

00:18:45.940 people have been kicking and streaming screaming dragged into believing in or at least taking very

00:18:51.540 seriously black holes and it's the same thing with with these various kinds of parallel universes also

00:18:56.220 that it's precisely because people have tried so hard to come up with alternative theories that

00:19:00.720 explain how to make computers and blah blah that don't have these weird predictions and failed that

00:19:08.240 you're starting to take it more seriously yeah well we're going to get to the parallel universes because

00:19:12.180 that's really where i think people's intuitions break down entirely but before we get there i want

00:19:17.520 to um i want to linger on this question of the primacy of mathematics and the strange utility of

00:19:25.640 mathematics at one point in your book you cite um the the off-sided paper by um wigner who i think he

00:19:31.660 wrote in um in the 60s about right in a paper entitled the unreasonable the unreasonable effectiveness

00:19:38.540 of mathematics and the natural sciences and this is something that many scientists have remarked on

00:19:44.860 this there seems to be a kind of mysterious property of these abstract structures and chains of reasoning

00:19:51.560 where mathematics seems uniquely useful for describing the physical world and making predictions about things

00:19:59.740 that you would never anticipate but for the fact that the mathematics is suggesting that something

00:20:05.580 uh should be so and that's right this has lured many scientists into essentially mysticism or the

00:20:12.700 very least philosophical platonism and you know sometimes even religion positing mathematical structure

00:20:18.300 that exists or or even you know pure mathematical concepts like numbers that exist in some almost

00:20:24.300 platonic state beyond the human mind and i'm wondering if you share some of that mathematical idealism and i

00:20:32.140 just wanted to get your reaction to a an idea that i believe i got from a cognitive scientist who lived in

00:20:39.260 i think he died in the 40s maybe the 50s kenneth craig who published a book in 1943 where he i think

00:20:46.460 just in passing he this anticipates wigner by about 20 years but in passing he tried to resolve this this

00:20:53.900 mystery about the utility of mathematics and he simply speculated that there was a there must be some

00:20:59.660 isomorphism between brain processes that represent the physical world and processes in the world that

00:21:07.420 are represented and that this might account for the utility of mathematical concepts i think he more

00:21:13.340 or less asked you know is it really so surprising that certain patterns of brain activity that are in

00:21:19.420 fact what mathematical concepts are at the level of the human brain can be mapped onto the world that

00:21:26.540 some kind of sameness of structure or homology there does that does that go any direction toward

00:21:33.740 resolving this mystery for you or do you think it exceeds that that's an interesting argument the

00:21:38.700 argument that our brain adapts to the world and therefore has a world model inside of the brain that's our

00:21:44.620 brain is just clearly part of the world and so there are processes in the world and there are

00:21:49.180 processes in the world that that have a by virtue of what brains are right have a sameness of fit and

00:21:55.980 kind of a mapping so i agree with the first part of the argument and disagree with the second part i i

00:22:00.700 agree that it's natural that there will be things in the brain that are very similar to what's happening

00:22:06.220 in the world precisely because the brain has evolved to have a good world model but i disagree that this

00:22:12.940 fully answers the whole question because the the claim that uh he made there that you that you

00:22:19.500 mentioned that brain processes of certain kinds is effectively what mathematics is that's something

00:22:25.020 that most math most mathematicians i know would violently disagree with that math has something to

00:22:30.540 do with brain processes at all they think of math rather as structures which have nothing to do with the brain

00:22:36.300 hold on let's just pull the brakes there though because i mean clearly your experience of doing math

00:22:42.220 your right your grasp of mathematical concepts or not the moment something makes sense or you you

00:22:47.980 persist in your confusion your memory of the multiplication table your ability to do basic

00:22:55.020 algebra and everything on right up all of that is in every instance of its being realized is being

00:23:02.220 realized as a state of your brain or you're not disputing that of course absolutely i'm just quibbling

00:23:07.180 about how you what the what mathematics is what's your definition of mathematics and i think it's

00:23:12.060 interesting to take a step back and ask what do mathematicians today generally define math as

00:23:18.780 because if you go ask people on the street you know like my mom for example they will often

00:23:25.420 view math as just a bag of tricks for manipulating numbers or maybe as a sadistic form of torture invented by

00:23:31.900 school teachers to ruin our self-confidence whereas mathematicians instead they talk about mathematical

00:23:38.940 structures and studying their properties i have a colleague here at mit for example who has spent 10

00:23:44.780 years of his life studying this mathematical structure called e8 never mind what it is exactly but

00:23:50.780 he has a poster of it he's made on the wall of his office david vogan and if i went and suggested to

00:23:57.900 him that that thing on his wall is just something he made up somehow that he invented he would be very

00:24:05.660 offended he feels he discovered it that it was out there and he discovered that it was out there

00:24:11.500 and and mapped out its properties in exactly the same way that we discovered the planet

00:24:16.860 neptune rather than invented the planet neptune right and then went out to study its properties similarly

00:24:23.340 if you look at something more familiar than e8 you'll just look at the the counting numbers one

00:24:27.660 two three four five etc you know the fact that two plus two is four and four plus two is six most

00:24:34.700 mathematicians would argue that the structure this mathematical structure that we call the numbers

00:24:40.860 is not the structure that we invented or invented properties of but rather that we discovered the properties

00:24:46.540 of in in different cultures this has been discovered multiple times independently in each culture people

00:24:53.820 invented rather than discovered a different language for describing it you know in english you say one

00:24:58.940 two three four five in swedish the language i grew up with you say but you can if you use the swedish

00:25:09.020 english dictionary and translate between the two you see that these are two equivalent descriptions of

00:25:13.580 exactly the same structure and similarly we invent symbols what symbol you use to write the number two

00:25:20.060 and three and it's actually different in the us versus in india today or in the roman empire right

00:25:26.540 but again once you have your dictionaries there you see that there's still only one structure that we

00:25:33.740 discover and then we invent languages yeah right to just drive this home with one better example

00:25:38.540 you know plato right he was really fascinated about these very regular geometric shapes that now bear

00:25:45.340 his name plutonic solids and he discovered that there were five of them the cube the octahedron the

00:25:52.860 tetrahedron the icosahedron and dodecahedron he he chose to invent the name dodecahedron and he

00:25:59.980 could have called it the schmodecahedron or something else right that was his prerogative to invent

00:26:05.020 name the language for describing them but he was not free to just invent a sixth platonic solid

00:26:11.180 yeah yeah because it doesn't exist so it's in that sense that that plato felt that those

00:26:16.060 exist out there and are discovered rather than invented well that makes sense yeah no i i certainly

00:26:22.060 agree with that and i i don't think you actually have to take a position on or you you don't have to

00:26:27.100 deny that that mathematics is a a landscape of possible discovery that exceeds our current

00:26:34.700 understanding and may in fact always exceed it so there's yes so you know what is the the highest

00:26:40.380 prime number above the current one we know well clearly there's an answer to that question if you

00:26:46.780 mean the lowest prime number above all the ones we know yes oh sorry yes the next prime number yeah

00:26:51.740 yeah that number will be discovered rather than invented and to invent it would be to invent it

00:26:58.460 perfectly within the constraints of its being in fact the next prime number so it's not wrong to call

00:27:04.220 that a pure discovery more or less analogous as you said to finding neptune when you didn't know it

00:27:09.340 existed or going to the continent of africa you know it's africa is there whether you've been there or

00:27:13.980 not right so i yeah i agree with that but it still seems true to say that every instance of these

00:27:21.180 operations being performed every instance of mathematical insight every prime number being

00:27:27.020 thought about or located or having it every one of those moments has been a moment of a brain doing

00:27:33.420 its mathematical thing right so i'm just or a computer sometimes yes we have an increasing a large number

00:27:39.420 of proofs now done by machines right and discovery is also sometimes we're still talking about physical

00:27:45.660 systems that can play this game of discovery in this mathematical space that we are talking about

00:27:53.340 this fundamental mystery is that why should mathematics be so useful for describing the

00:28:00.060 physical world and for making predictions about blank spaces on the map and exactly again and i'm and i'm

00:28:07.260 kind of stumbling into this conversation because i'm not a mathematician i'm not a mathematical philosopher

00:28:12.860 and so i i'm sort of shooting from the hip here with you but i i just wanted to get a sense of

00:28:18.300 whether this could remove some of the mystery if in fact you have certain physical processes in brains

00:28:24.540 and computers and other intelligent systems wherever they are that can mirror this landscape of potential

00:28:32.540 discovery if that does sort of remove what otherwise seems a little spooky and platonic and represents a

00:28:40.220 challenge for mapping you know abstract idealized concepts onto a physical universe yeah that's a

00:28:47.500 great question and you know the answer you're going to get to that question will depend dramatically on who

00:28:52.540 you ask there are very very smart and respectable people who come down all across the very broad

00:29:00.700 spectrum of views on this and in my book i chose to not you know say this is how it is but rather to

00:29:07.580 explore the whole spectrum of opinions so some people will say if you ask them about this mystery there

00:29:12.700 is no mystery you know there is math is sometimes useful in nature sometimes it's not that's it there's

00:29:20.380 nothing mysterious about it go away and then if you go a little bit more towards the platonic side

00:29:28.860 you'll find a lot of people saying things like um well it seems like a lot of things in our universe

00:29:34.540 are very accurately approximated by math and that's great but they're still not

00:29:40.140 perfectly described by math and then there then you have some very very uh optimistic physicists

00:29:46.860 like einstein and a lot of string theorists who think that there actually is some math that we

00:29:52.140 haven't maybe discovered yet that doesn't just approximate our physical world but describes exactly

00:29:58.380 and it's the perfect description of it and then finally the the most extreme position on the other

00:30:04.540 side which i explore at length in in the book and that's the one that i'm personally guessing on it is

00:30:11.580 that not only is our world described by mathematics but it is mathematics in the sense that the two are

00:30:18.780 really the same so you talked about how in the physical world we discover new entities and then we invent

00:30:25.660 language to describe them similarly in mathematics we discover new entities like new prime numbers

00:30:32.380 the platonic solids and we invent names from maybe this mathematical reality and the physical reality

00:30:39.820 are actually one in the same and and the reason why when you first hear that and you know it sounds

00:30:45.180 completely looney tunes of course you know you look it it's equivalent to saying that the physical world

00:30:51.580 doesn't just have some mathematical properties but it has only mathematical properties and that

00:30:56.140 sounds really dumb when when you if you look at your wife or your child or whatever and you're like

00:31:01.340 this doesn't look like a bunch of numbers but to me as a physicist and when i look at them

00:31:08.060 of course when i met annika your wife for the first time of course she has all these properties

00:31:13.500 that don't strike me as mathematical don't tell me you were noticing my wife's mathematical properties

00:31:17.660 but at the same time as a physicist you know i couldn't help notice that your wife was made entirely

00:31:24.380 out of quarks and electrons and uh what property does an electron actually have well it has the

00:31:31.100 property minus one one half one and so on and we've made up nerdy names for these properties we

00:31:37.820 physicists such as electric charge spin and lepton number but the electron doesn't care what language we

00:31:44.460 invent to describe these numbers the properties are just these numbers just mathematical properties

00:31:49.340 and and for annika's quarks same deal and also the only properties they have are also numbers except

00:31:56.700 different numbers from the electrons so the only difference between a quark and an electron is what

00:32:00.540 numbers they have as their properties and if you take seriously that everything in both your wife and in

00:32:07.020 the world is made of these elementary particles that have only mathematical properties then you can ask

00:32:14.140 what about the space itself then that these particles are in you know what properties does space have

00:32:19.260 well it has the property three for starters you know the number of dimensions which again is just a

00:32:25.580 number einstein discovered it also has some more properties called curvature and topology but they're

00:32:30.700 mathematical too and if if both space itself and all the stuff in space have only mathematical properties

00:32:38.700 then it starts to sound a little bit less ridiculous idea that maybe everything is completely mathematical

00:32:45.340 and we're actually part of this enormous mathematical object i don't want to spend too much more time here

00:32:50.780 because there's a many other things i want to get into and in your book but this is just a fascinating

00:32:56.140 area for me and again unfortunately one that i feel especially unequipped to um really have strong opinions

00:33:04.060 on but so in listening to what you said there how is it different from saying that you know every

00:33:11.980 description of reality we arrive at everything you can say about quarks or space or anything it's not

00:33:23.340 as you just said just a matter of math and values we could also say it's a matter of in this case

00:33:30.140 english sentences or sentences spoken in human language could we be saying something as in the

00:33:36.780 end trite as saying that the question of why mathematics is so good at representing reality

00:33:43.980 is a little like saying why is language so good for speaking in or so good for capturing our beliefs

00:33:52.620 is there a kind of a disanalogy there that can save us the language we invent to describe mathematics

00:33:59.100 the symbols for the numbers and for plus and multiplication and and so on is of course the

00:34:04.700 language too so languages generally are useful yes but there's a big difference the human language is

00:34:10.700 notoriously vague and that's why the radio and the planet neptune and the higgs boson were not

00:34:17.580 discovered by people just sitting around blah blah blah in english but with the judicious use of

00:34:23.660 the language of mathematics and all of these three objects were discovered because someone sat down

00:34:28.700 on the pencil and paper and did a bunch of math and made a prediction if you look over there at that

00:34:33.100 time you'll find neptune there a new planet if you build this gadget you know you'll be able to send

00:34:37.740 radio waves and if you build this large hadron collider you'll find a new particle there's real power in

00:34:43.260 there and i think that before we leave this math topic i just want to end on an emotional note that

00:34:49.420 some people don't like this idea because they think it sounds counterintuitive we already laid that to

00:34:55.580 rest in the beginning of our conversation uh other people don't like it because they feel it sort of

00:35:00.220 insults their ego they don't want to be thinking they don't want to think of themselves as a mathematical

00:35:05.660 entity or whatnot but i actually think this is a very optimistic idea if it's true because if it's wrong

00:35:12.300 this idea that nature is completely mathematical that means that this fantastic quest of physics

00:35:18.380 which has exploited the discovery of mathematical patterns to invent new technologies right that means

00:35:24.620 that quest is going to end eventually that physics is doomed one day we'll hit this roadblock when

00:35:30.300 we've run out found all the mathematical patterns that were defined we won't ever get any more clues

00:35:36.220 from nature and technology and then we can't go any further with our understanding or technology whereas

00:35:43.340 if it's all math then there is no such roadblock right and there the ability for life in the future to

00:35:50.380 progress is really only limited by our own imagination and to me that's the optimistic view

00:35:56.460 is there any connection between this claim that it's all math at bottom with the claim that it's all

00:36:02.860 information i'm now getting echoes of john wheeler who talked about it from bit this concept that at some

00:36:10.060 level the universe is a computation is that is there a connection between these two discussions or are they

00:36:18.780 distinct yeah there probably is there probably is i mean i had john wheeler is one of my great heroes i

00:36:23.980 had the great fortune to get to spend a lot of time with him when i was a postdoc in princeton and he

00:36:28.940 really inspired me greatly and my hunch is that we will one day in the future come to understand more

00:36:35.420 deeply what information really is and its role in physics and also come to understand more deeply the

00:36:42.380 role of computation and quantum computation in the universe and well that will one day come to realize

00:36:48.780 maybe that mathematics computation and information are just three different ways of looking at the

00:36:54.060 same the same thing we're not there yet but that that would be my guess are we there on the topic of

00:37:00.060 entropy is there's a relationship between entropy in terms of energy and entropy in terms of information

00:37:05.100 is there a unified concept there the or is there just a kind of an analogy bridging those two discussions

00:37:11.020 um there are things that's fairly well fairly well understood even though there's still some

00:37:14.860 controversies that are brewing but they're this is a very active topic of research in fact you

00:37:20.860 mentioned that you and i met at a conference that i was involved in organizing the previous conference

00:37:25.820 i organized you'll be pleased to know was called the physics of information where we brought together

00:37:31.020 physicists computer science people neuroscientists and others and philosophers and had a huge amount of

00:37:37.180 fun discussing exactly these these questions so i think i think um there's a lot more to come in for

00:37:43.180 to me the these ideas i the most far out and um speculative ideas i i explore in the book about the

00:37:50.060 role of math are not to be viewed as sort of the final answer to end all research but rather simply as

00:37:57.660 a great way to generate new cool practical applications of things it's a roadmap to finding new problems and you

00:38:04.540 hinted on on at some of them here i think i think uh there's a lot of fascinating relationships between

00:38:11.660 information computation and math and the world that we haven't discovered yet and they probably have a

00:38:17.740 lot to do with the conscious of how consciousness works as well as my guess and i think we have a lot

00:38:22.780 of cool uh science to look forward to consciousness is really the the center of my interest but we may

00:38:28.300 not get there because i now want to get into the multiverse which is probably the strangest concept in

00:38:34.140 science now it's something that i thought i understood before picking up your book and

00:38:39.580 then i discovered there were there were three more flavors of multiverse than i realized existed

00:38:45.420 i want to talk about the multiverse but first let's just start with the universe because this is a a term

00:38:49.900 that around which there is some confusion let's just get our bearings what do we mean or what should

00:38:53.980 we mean by the term universe and i want to start with your your level one multiverse so if it's possible

00:39:00.940 give us a uh a brief understand brief uh description of the concept of inflation inflation

00:39:07.660 that that gets us there sure so what what is our universe first of all before we start talking about

00:39:13.260 others many people as sort of tacitly assume that universe is a synonym for the for everything

00:39:19.420 that exists and if so by definition there can't be anything more and talk apparently universes would

00:39:24.540 just be silly right but that is in fact not what people generally in cosmology mean when they say

00:39:29.900 universe and they say our universe they mean the spherical region of space from which light has had

00:39:37.180 time to reach us so far during the 13.8 billion years since our big bang so that's in other words

00:39:42.780 everything we could possibly see even with unlimited funding for telescopes right and so if that's our

00:39:50.380 universe we can reasonably ask well is there more space beyond that you know from which light has not

00:39:55.420 yet reached us but might reach us tomorrow or or in a billion years and if there is if there are if

00:40:01.820 space goes on far beyond this if it's infinite or just vastly larger than the space we can see

00:40:07.420 then all these other regions which are as big as our universe if they also have galaxies and planets

00:40:12.780 in them and so on it would be kind of arrogant to not call them universes as well because the people

00:40:17.820 who live there will call that their universe and um inflation is very linked to this because it's

00:40:25.580 the best theory we have for what created our big bang and made our space the way it is so vast and so

00:40:32.620 expanding and it actually predicts generically that space is not just really big but vast and in most

00:40:40.620 cases actually infinite which would mean if that's true if inflation actually happened that what we call

00:40:45.900 our universe is really just a small part of of a much bigger space so in other words space then is

00:40:52.460 much bigger than the part of space that we call our universe and this is something actually i don't

00:40:57.900 think is particularly weird once one gets the terminology straight because it's just history all

00:41:03.660 over again right we we humans have been the masters of underestimation we've had this overinflated ego

00:41:10.380 where we want to put ourselves in the center and assume that everything that we know about is everything

00:41:15.340 that exists and we've been proven wrong again and again and again discovering that everything we

00:41:19.820 thought existed is just a small part of a much grander structure a planet solar system a galaxy a

00:41:27.740 galaxy cluster our universe and maybe also a hierarchy now of parallel universes it would just continue

00:41:35.820 the same trend and um for somebody to just object on some sort of philosophical grounds that things can't

00:41:44.620 exist if they're outside our universe if we can't see them that just seems very arrogant much like an

00:41:50.700 ostrich with its head in the sand right saying if i can't see it it can't exist right but things things

00:41:55.420 begin to get very weird given that this fact that inflation which as you said is is the best current

00:42:01.820 picture of of how things got started given that inflation predicts a universe of infinite extent

00:42:09.740 infinite space infinite matter and therefore you have a universe in which everything that is possible

00:42:17.260 is in fact actual everything happens everything happens in fact an infinite number of times which is

00:42:22.780 to say that you and i have this podcast an infinite number of times and an infinite number of different

00:42:29.500 ways you know in one in one version you know in some universe or some part of now we're still

00:42:35.260 talking about the level one multiverse here so we're so we're just talking about you know if you

00:42:39.740 if you could travel far enough fast enough away you'd arrive on some planet disconcertingly like earth

00:42:46.940 where you and i are having a virtually identical podcast but for a single change in term or you know i

00:42:53.500 just decide to shave off my eyebrows in the middle of this conversation exactly and or i switch

00:42:59.500 talking french this is well stop me there is is that in fact what you think a majority of

00:43:08.220 cosmologists believe so this is a great question first it's a great illustration of

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Making Sense - Sam Harris - September 23, 2015

#18 — The Multiverse & You (& You & You & You...)

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