Making Sense - Sam Harris - #318 — Physics & Philosophy

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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00:00:38.840 well the big story of this week was the firing of tucker carlson from fox news i normally wouldn't

00:00:54.480 have much to say about this but this has been such an enormous story at least for those of us who

00:01:00.080 follow media and everyone has commented on it it seems but no one has made what i consider to be

00:01:10.080 the most important point about all this so i feel like i have something to add to this conversation

00:01:15.700 which is otherwise an extraordinarily boring one i don't know tucker i believe we've met

00:01:22.680 twice i think he interviewed me twice he was one of my first tv interviews i don't even know what

00:01:29.040 show that was back in the day i feel like it was a pbs show is that possible so i think he's

00:01:33.980 interviewed me twice but not for a very long time in any case almost no one has done more to stoke

00:01:42.320 the fires of trumpism and populist outrage than tucker carlson in recent years he's done hour after

00:01:52.200 hour of broadcasts on how the establishment is against you they are against you the you being

00:02:00.380 the millions of people in trump's base who have completely lost trust in institutions he has been

00:02:07.360 the journalistic foil to trump's demagoguery for years and for that reason alone it should be obvious

00:02:15.460 i would not be a fan of his but as a result of the dominion lawsuit against fox we now have

00:02:21.820 several text messages that carlson sent privately to his colleagues at fox right these were entered

00:02:28.500 into evidence for the upcoming trial which was only prevented by fox agreeing to pay three quarters

00:02:34.400 of a billion dollars in settlement to dominion for defamation in any case we now have a window

00:02:42.220 on to what carlson actually felt and presumably feels about donald trump in one text he says i hate

00:02:52.280 him passionately this was sent january 4th just two days prior to the attack on the capitol he went on

00:02:59.120 to say we're all pretending we've got a lot to show for it because admitting what a disaster it's been is

00:03:03.860 too tough to digest but come on there really isn't an upside to trump on the topic of trump skipping

00:03:10.800 biden's inauguration he texted hard to believe so destructive it's disgusting i'm trying to look

00:03:17.900 away just before the capitol riot carlson wrote we are very very close to being able to ignore trump

00:03:24.520 most nights i truly can't wait and right after the capitol was stormed he texted trump has two weeks

00:03:31.100 left once he's out he becomes incalculably less powerful even in the minds of his supporters

00:03:35.920 he's a demonic force a destroyer but he's not going to destroy us i've been thinking about this

00:03:43.080 every day for four years let me read that final line again he's a demonic force a destroyer i've been

00:03:51.500 thinking about this every day for four years okay so here you have someone who has done hundreds of

00:03:59.720 broadcasts supporting trumpism pandering to trumpism and distorting reality in all the ways you have to

00:04:07.680 distort it to disregard the danger that trump posed and here we see that all the while carlson believed

00:04:17.140 that trump was a demonic force a destroyer now here's the only point i want to make this should

00:04:25.620 matter it should be impossible for carlson to have an audience after it has been revealed that he's

00:04:33.460 capable of this level of dishonesty think about it in every other context think about the pharmaceutical

00:04:40.480 executive who knows that the drug he's marketing doesn't work or is dangerous but in public towns it is

00:04:48.940 both safe and effective revealing that about a pharmaceutical executive should be the end of that

00:04:55.360 executive's career is the very essence of fraud now i highly doubt that these texts were the reason why

00:05:02.800 carlson got fired from fox i guess that remains to be seen but if i had to bet i would bet that carlson

00:05:10.160 pays no price at all for his fraudulence in fact i expect him to build an enormous media business

00:05:17.680 once he finds his feet and that says something quite scary and depressing about our culture or at least a

00:05:26.760 large part of our culture but happily this tawndry business has absolutely nothing to do with today's

00:05:33.860 podcast today i'm speaking with tim maudlin tim is a professor of philosophy at nyu and the founder

00:05:40.900 and director of the john bell institute for the foundations of physics his interests primarily focus

00:05:46.400 on the foundations of physics as well as metaphysics and logic and his books include quantum non-locality

00:05:53.020 and relativity truth and paradox the metaphysics within physics and two volumes on the philosophy of physics

00:06:00.880 tim has also been a guggenheim fellow and he's taught at rutgers and harvard in addition to nyu

00:06:07.360 and i reached out to tim almost as an act of continuing education for myself in philosophy

00:06:13.600 his area of focus in the philosophy of physics and metaphysics has really not been my wheelhouse

00:06:20.180 philosophically and i had some questions i just wanted to put to him we talk about the nature of

00:06:25.100 scientific reductionism emergence the nature of time causation the nature of possibility natural law

00:06:34.440 david lewis's possible worlds rival interpretations of quantum mechanics we have a long wrestling match

00:06:41.320 over the topic of free will and touch a few other things here anyway tim performed a kind of

00:06:47.720 philosophical therapy for me on a few points and also i think we demonstrated that certain rival

00:06:55.560 intuitions on the topic of free will can't quite be resolved through argument i think i have come to

00:07:02.340 that conclusion after this conversation perhaps there's more to say on that topic but it just

00:07:07.720 seems to me that if you experience yourself in a certain way certain points just can't land whereas

00:07:14.680 if you have a different experience moment to moment certain points are not only obvious you can't see how

00:07:22.040 experience can be seen any other way anyway you can make of our exchange what you will

00:07:27.760 it was a lot of fun and now i bring you tim maudlin

00:07:31.280 i am here with tim maudlin tim thanks for joining me thanks for having me so um i'm thank you for

00:07:44.040 doing this i i am uh very eager to talk to you about um the the interesting philosophical questions

00:07:50.700 thrown up by our understanding of physics but um in particular i have something that i'm curious about

00:07:58.500 that i will drop on you at some point as we take the tour here you being a philosopher who knows much

00:08:05.360 more about the current implication of physics than i do but before we jump in how would you describe your

00:08:11.100 intellectual background and the kinds of questions you focused on as a philosopher well i i when i was an

00:08:18.140 undergraduate i kept bouncing around between different things and i ended up getting a degree

00:08:23.520 that was a joint degree in philosophy and physics and then my phd was in history and philosophy of

00:08:28.720 science and in general philosophy and physics tend to go together pretty naturally probably most

00:08:35.840 philosophers of science who have expertise in a science have it in physics and i think that's

00:08:41.640 because the basic philosophical impulse is always to get to the bottom of things somehow and and there's

00:08:48.640 a certain sense it's not the only sense but there's a certain sense in which physics lies at the bottom

00:08:53.880 of the empirical sciences i don't want to say that sometimes physicists say that in a very denigrating

00:09:00.280 way i don't want to do that at all but there is a sense in which as you push down you kind of push

00:09:05.980 down from biology to to chemistry to physics so i think that basic search after foundations explains

00:09:16.560 both of my both of those interests maybe we can press into that question you just referenced which is

00:09:25.160 this the kind of the concept of reductionism and the occasionally overweening claims that that

00:09:32.040 physicists are apt to make about how everything reduces to physics and this connects to the the

00:09:38.700 concept of emergence and you know emergent phenomenon emergent properties uh you know the the mind is

00:09:46.020 generally thought of in science as an emergent phenomenon born of you know information processing

00:09:51.780 in biological brains such as our own uh as to whether or not that's going to happen in the computers

00:09:58.180 we're we're building and their software remains to be seen but um uh certainly we know intelligence

00:10:04.500 is an emergent phenomenon of information processing i guess we're we're the jury's still out on

00:10:09.040 consciousness and you know there being a qualitative character to mind but um how do you think about

00:10:16.380 reductionism and emergence in particular with respect to causal powers for instance a you know if we say

00:10:25.700 that something that is a higher level phenomenon is a you know an emergent phenomenon if it has causal

00:10:33.580 powers i mean so for instance you know we're we're using our minds we're using language we're perceiving

00:10:39.620 the world at this moment this is all considered to be emergent you know on the basis of to supervene on

00:10:47.020 the basis of um you know neurophysiology and its micro events but if it has causal powers if you know my

00:10:54.740 understanding of english grammar say or my intention to use a certain word in this sentence has causal

00:11:04.440 powers doesn't it only have causal powers at the level of its micro constituents which is to say at

00:11:11.580 the level you know at bottom at the level of physics um is it doesn't the reduction actually run

00:11:17.640 through even if we can't conceive of much less explain higher level phenomenon in terms of their

00:11:24.680 micro constituents which is to say we're never going to actually be able to think about things

00:11:30.380 like conversations or stock markets or cocktail parties or anything else in terms of subatomic

00:11:37.940 particles and and fields of you know electromagnetism but aren't the causal powers of those higher level

00:11:45.540 phenomena nevertheless reducible to their micro constituents okay so um there are a lot of words

00:11:54.160 you use that um are multiply ambiguous and so it's very easy to get lost in this thicket among those are

00:12:02.120 emergence supervenience explanation is going to be a big one here and causation and part of the problem is

00:12:11.760 even in the philosophical literature and and and in the physical literature people can mean literally

00:12:17.360 diametrically oppose things by emergence so there was a time when some of the so-called british

00:12:24.640 emergentists the hallmark of emergence was a phenomenon that could not be explained on the basis of

00:12:32.920 microphysics couldn't be accounted for and was fundamentally novel and only emerged at some time

00:12:41.740 or in some systems or something like that but my view is is that the the supervenience claim

00:12:49.540 as far as we know is true for what we call the ontology that is there's a certain sense in which

00:12:58.280 my computer just to take the example i'm about to give you my computer is nothing but a collection of

00:13:03.900 atoms put together in a certain configuration and everything it does we think in principle

00:13:10.280 could be accounted for by just studying how atoms interact and how electrons interact and then how

00:13:17.360 this whole very complicated gadget is put together but let me just give you an example i use a lot so

00:13:24.440 suppose i've got my computer it's on the table and there's a little display of spinning rainbow colors

00:13:31.100 going on coming off the screen photons coming off the screen and uh i call in a physicist kind of a

00:13:38.000 super physicist and i say can you make a prediction about about this display what's going to happen

00:13:44.720 and you imagine the physicist could kind of scan the thing all the way down to its microstructure

00:13:51.900 computer and do some calculations and say well that little spinny thing is going to go on

00:13:58.240 for the next four years and five hours and 47 seconds and then the screen is going to go blank

00:14:05.960 and i say okay thank you very much and and then i call in a computer scientist and i say you know what's

00:14:13.320 the deal with the screen and the computer science doesn't even look at the computer looks at a bunch of

00:14:17.900 papers that are sitting next to the computer that is the program i've just programmed the machine

00:14:22.900 and says look you got a loop here right step 10 says go to step 12 and step 12 says go to step 10

00:14:29.980 that little thing's going to spin forever because you're in a computational loop now in terms of the

00:14:38.160 actual prediction i take it the physicist will be right because in 10 years and so on the computer

00:14:44.160 screen is just going to burn out and that's not the business of the computer scientist to predict

00:14:50.520 i mean the computer scientist is dealing with the system using a different set of analytical

00:14:56.140 categories but i would claim that the computer scientist has actually given me much better

00:15:01.140 information or understanding than the physicist does right if the physicist has just ground out

00:15:07.380 a very long calculation on the basis of its physical structure it may give me good predictions but

00:15:13.640 it sort of gives me no real insight of the kind i wanted so to that extent these other categories

00:15:23.580 that we use to understand the world including biological categories computational categories economic

00:15:30.240 ones as you mentioned i mean the basics of economics presumably would not change if you change

00:15:36.340 fundamental physics as long as there were people or creatures that wanted to exchange goods

00:15:43.000 and that had more or less the same psychology that humans have that they're greedy uh and they're trying

00:15:49.940 to make money then all sorts of economic explanations for why things happen would be unchanged by even

00:15:59.380 radical changes in physics at the lower level so the the idea that all explanation or all scientific

00:16:08.260 scientific understanding reduces to physics i think that's just plainly wrong and in fact disciplines

00:16:14.540 other than physics are much broader because they would continue to have explanatory power even if the

00:16:19.760 physics were quite different but nonetheless my computer really is nothing more than a bunch of atoms put

00:16:26.160 together obeying the laws of physics right there's a in terms of what it is made of or what it really

00:16:30.940 is that's what it is and there's a sense in which the physical structure accounts for everything else that

00:16:38.020 it does i think what i hear you alluding to is what often goes by the name of functionalism

00:16:45.040 in the philosophy of mind i guess we could take it more generally than that which is and another way to

00:16:51.320 come at this is to distinguish the software and hardware layer of your computer or you know many other

00:17:00.060 things like minds and we could acknowledge that any physical instantiation of a certain function

00:17:09.900 that you know let's say a mind or a you know a stock market or anything else that physical

00:17:14.820 instantiation does in fact reduce to physics but it has a logical structure that can be implemented

00:17:23.440 in multiple instantiations even as you say in conditions where the the laws of physics are

00:17:29.420 different in important ways uh and certainly even within our world where you know the laws of

00:17:36.000 physics are the same we we know we can implement let's say in a you know a calculator on highly

00:17:42.880 you know non-analogous physical substrates and we can do arithmetic with the wetware in our heads

00:17:49.820 and we can do arithmetic in silico with a with on a computer and the same logic can be implemented

00:17:57.740 very differently but in each instantiation what happens next and the you know the the causal properties

00:18:05.160 of you know of each sequence of events is a matter of what the physics is doing but it can't be

00:18:13.560 understood at that level you can't look at a collection of atoms in a computer and a collection of atoms in

00:18:20.340 our heads and extract the rules of arithmetic from those two different systems even if each is

00:18:29.140 implementing the rules of arithmetic is that does that get it what you're saying something like that

00:18:33.720 or again to go back to your own example of the stock market you know you've got a broker sitting there and

00:18:38.900 he's either going to press the sell button or not and again theoretically a complete physical

00:18:45.560 specification of his brain should allow you to predict uh where his finger is going to go

00:18:51.140 but for all that you might say that gives me no insight of the kind i wanted right i wanted to know

00:18:57.400 what motivated him right what was he thinking what was he trying to achieve oh he's greedy right he thought

00:19:02.960 that the price was going to go down he thought he should buy it now or he'll lose money all of that

00:19:08.980 can be perfectly true right he can only do that because he has a brain and and he can only you know

00:19:15.680 he only has a brain his brain is made of atoms and it has a physical structure but there's just all sorts of

00:19:21.940 different levels of conceptual structure that one can bring to a given situation and those different levels

00:19:30.940 provide different sorts of insight into what's going on and in many cases the physical level even though it's not

00:19:38.580 there uh even though it's there isn't the right one to give you the kind of understanding that you want

00:19:44.640 to get i mean let's take another simple example pianos right there are no microscopic pianos they're kind

00:19:52.180 of can't be atomic level pianos because pianos are just complicated instruments that need lots of parts

00:19:57.980 put together in certain ways in that sense pianos only quote emerge at a higher level but are they

00:20:04.980 predictable well yeah in a sense i mean if you tell me how all the microstructure is put together i can

00:20:11.160 predict that that when you hit the key the hammer will hit the hit the string and it'll vibrate none

00:20:17.500 of that is a mystery physically so and that's because nothing new has emerged really ontologically i

00:20:25.460 mean there's a certain sense in which a piano is just a bunch of atoms that have been connected

00:20:30.600 together in a very particular sort of way so what would you put what would you class as an immersion

00:20:37.260 phenomenon that is perplexing and you know otherwise unforeseeable and not understandable at the level of

00:20:43.660 its micro constituents yeah i i think the only example i know of which is the hardest problem in

00:20:50.020 the world is consciousness right is subjective feelings pain you know to take an obvious example

00:20:55.920 there's nothing in physics there's nothing in the conceptual repertoire of physics which would

00:21:03.540 allow you to predict not just from small to large but no matter how big it is that any physical

00:21:11.060 behavior would have associated with it a feel or a subjective state that's why you know it's come to

00:21:17.740 be called the hard problem of consciousness i on the other hand contrast that you could predict all

00:21:24.140 kinds of behavior i mean just as i can predict the behavior of my computer we think if i knew enough

00:21:29.380 about the brain i might be able to predict the words that are going to come out of my mouth and your

00:21:33.940 mouth and the vibrations of the air and so on but that any of that should be associated with a subjective

00:21:41.040 feel that i think we have no grip on whatsoever and i it's not just that we don't have a grip i don't

00:21:47.600 even know what a grip on it would look like yeah well you and i are in agreement there and you know

00:21:53.240 the hard problem of consciousness is something that's quite central to my interest but i'm going

00:21:57.040 to leave it to the side because i have so much else i want to talk to you about but just to revisit

00:22:02.540 this this issue of emergence for a second so come back to a property or a function like arithmetic

00:22:10.980 right the fact that it's substrate independent the fact that we could either there's a certain

00:22:17.000 concatenation concatenation of events can constitute arithmetic in our brains but it can also do that

00:22:24.860 in a computer made of atoms that don't at all resemble what's in our brains and presumably that you know

00:22:31.860 there we could do this in all kinds of systems that one would you know that currently wouldn't imagine

00:22:37.940 could be a proper computer it could could be made a proper computer in some sense and implement

00:22:43.080 arithmetic so therefore arithmetic itself can't really be reducible to any one of those things or

00:22:50.060 any string of those things or is there something about that that i'm confusing ontologically okay so

00:22:56.760 here here's now you've brought up opened yet another independent can of worms which is the status of

00:23:03.280 mathematics mathematical entities so this is not like stock trading and pianos we all agree that there

00:23:10.640 can't be stock markets without some physics or pianos without some physics they're fundamentally physical

00:23:16.780 things in that sense although i i guess i would i would hesitate with the the stock market in that

00:23:22.740 you know if stock markets are also substrate independent and open to a a functionalist definition

00:23:29.900 then doesn't that play the same kind of havoc with with uh reduction no no not really because um

00:23:37.780 if you give a functionalist definition of of the sort you're thinking of still that's in a way

00:23:45.480 substrate independent i mean take the definition of a turing machine okay it's given a kind of very

00:23:51.100 abstract it's got a certain number of internal states and their inputs and their memories and

00:23:55.520 then their rules for how things evolve nonetheless in order to have such a thing you need some

00:24:02.320 something physical right you need something it may be that many different substrates can realize it

00:24:08.440 but you need a physical substrate the question of the relation of mathematics or arithmetic

00:24:14.320 to physics seems to be quite different what we the normal thought is that arithmetic is just

00:24:22.300 completely independent of any physics that even if there were nothing physical it would still be the

00:24:27.420 case that one plus one equals two it would still be the case that they're an infinite number of

00:24:31.580 integers even if the physical world is finite and there aren't an infinite number of anything

00:24:36.900 physical still they're an infinite number of integers why because well you can't stop right

00:24:42.020 every time every time you get to an integer there's one a different one that's one bigger

00:24:46.440 so i mean my view about that is what's called platonism that is that the mathematical realm

00:24:52.840 is independent of the physical realm entirely in a way that stock markets aren't

00:24:59.580 well perhaps we'll touch on that again because i you know central to my concern today is to talk

00:25:06.080 about the existence of things that don't exist concretely and obviously mathematical objects

00:25:13.660 like numbers are part of that picture although different from what i want to focus on but before we get

00:25:19.300 there let's talk about time and why that is such a difficult notion scientifically i mean we have this

00:25:29.740 common sense experience of time which includes things like duration and change and sequence right it's bound

00:25:39.460 up with our capacity to remember what's happening and it's also bound up with our sense of that we

00:25:45.420 understand something about causation because you know causes precede their effects you know if my

00:25:51.640 thumb hurts now it's because i hit it with a hammer yesterday it's not because i'm going to hit it with a

00:25:56.000 hammer tomorrow and so that implies a certain structure which we we take into account in virtually

00:26:02.940 in every moment of our living how has physics put pressure on our common sense notion of time all right so

00:26:10.620 now i'm again i should just warn you that what i'm going to say you'll hear a lot of people object to

00:26:16.260 but nonetheless i'm going to say it because i think it's obviously true i don't think physics has put any

00:26:22.100 pressure on the idea that time is fundamentally directed that some things come before other things

00:26:29.860 that causes come before their effects there's a a very specific account of the structure of time or we

00:26:41.120 might call the temporal structure of the world that was given by newton that's kind of a very common

00:26:46.520 sensical one which involves the notion of simultaneity of thinking that uh if i snap my fingers here

00:26:53.680 okay at that very moment that's marked by that finger snap that moment as newton says exists

00:27:02.060 throughout the heavens right the very same moment exists in london and on the moon and you know at

00:27:07.480 the farthest stars newton said something like that and then you can think of time as the succession

00:27:13.960 of these global instance which is going forward right it has a direction in a way that space doesn't

00:27:21.120 have a direction and there's duration you can measure you know there's a fact about how much

00:27:25.160 time has passed and there's certainly a fact about what happens before what when we get to the theory of

00:27:30.420 relativity the special and general theories of relativity they deny that there's this global

00:27:36.380 simultaneity they deny that if i snap my fingers here there's any fact at all about exactly what was

00:27:43.680 going on on alpha centauri at that moment because there's nothing that counts as being at that very same

00:27:50.980 moment on alpha centauri so it's a it's a it's a shock in a way to the everyday conception on the

00:27:58.500 other hand the everyday conception not only believes that there's this kind of global instant but that

00:28:03.840 we're immediately aware of it i mean all of us are shocked the first time we're told when you look up at

00:28:09.820 the sky uh you know if you see a if you if you were to see a supernova uh your normal thought is gosh

00:28:16.200 that star just exploded and then someone says no no no no it exploded millions and millions of years

00:28:21.020 ago and the light has been traveling to us ever since what you're seeing isn't what's going on right

00:28:28.540 now and that's true even even for newton right for anybody so you you have this tendency to very

00:28:35.040 naively think that you're being presented right now with the world around you as it is right now

00:28:43.240 but any kind of just a little bit of thought about how the information got to you and you realize no

00:28:49.640 there must have been a time delay it took some time just as it would take time for a letter to

00:28:54.440 get to you right when you read a letter you don't think gosh this is going on right now you think

00:28:58.500 this happened a few days ago what's being reported yeah i would just add that the same you can say as

00:29:04.400 much neurologically i mean what's happening when you touch something with the tip of your finger

00:29:08.580 and you see your finger do that with your eye you know the transit time of through the visual system

00:29:14.920 and through the sensory motor system is different and there's got to be some time of integration at

00:29:20.040 the level of cortex that that's creating this unity of effect or you know the so-called right

00:29:25.840 solving the binding problem right so the present moment is a confection somewhat born of of working

00:29:33.580 memory and you know some period of integration that is not just truly punctate in the now conscious

00:29:40.740 absolutely i mean there's no question that time perception again the subjective feel of time

00:29:46.340 is a very complicated neurological construct and and there could be people you know there are sort of

00:29:54.600 temporal illusions you can make and trick people about events that are pretty close to each other

00:29:59.740 in time and get them to think that the time order is different than it was and we kind of understand

00:30:04.820 how that works that kind of complicated neural investigation is not where i spend my time and i

00:30:12.000 don't know i know a bit about it but not a lot on the other hand one does want to you know i think

00:30:16.440 say the perception of time is a bit different thing than time itself i mean we all think that after the

00:30:22.400 big bang there was nobody around perceiving anything but stuff happened and it happened in a certain order

00:30:27.700 and you know it took a certain amount of time for for stars to form and for galaxies to form and so on

00:30:33.460 so time itself physical time itself is independent of our perception of it and our perception may be very

00:30:40.700 very complicated in a way that time itself isn't okay so i just want to revisit this claim that the

00:30:47.400 notion of a present moment the notion of now is specious at the the widest scale right so if you

00:30:57.640 say that you know you snap your fingers now you know that now doesn't hold for anything outside

00:31:04.740 your reference frame so when you're talking about now in another galaxy you really can't you know

00:31:11.520 utter that sentence coherently right because and i guess just to spell this out a little more the

00:31:17.360 reason why is because based on relativity you know if you if you snap your fingers and then i snap my

00:31:22.520 fingers a second later you know so your snap preceded mine by a second in our reference frame well you

00:31:29.020 can based on on relativity you can imagine someone far enough away moving fast enough say in relation

00:31:38.700 to us where the sequence is truly reversed it's perceived that i snapped before you snapped well yeah

00:31:46.620 i mean no no i mean it for you and me if let me try and i'll try and get people to fire up their

00:31:54.460 imaginations and a bit which would help me try to explain this newton's picture which is kind of the

00:31:59.740 everyday picture is again that time comes in these global instance you can imagine the snap a snapshot of

00:32:06.800 the entire universe now another snapshot a second later another snapshot a second later and you sort of

00:32:12.880 stack up all those snapshots the way you would frames on a film and that gives you the entire history of the

00:32:18.720 universe okay and that idea the technical name for it is that there's a foliation of space-time so you

00:32:26.680 imagine space-time as being four-dimensional as having kind of three spatial dimensions and one time

00:32:32.460 dimension and then you imagine slicing it like a baloney into all of these layers that just one lies on top of

00:32:40.520 the other right so that was newton's picture nothing to do with anybody's reference frame or anything

00:32:45.060 this is just objectively the structure of time what happens when you go to relativity and it's you just

00:32:51.140 have to keep stuff about reference frames out of it it's nothing to do with reference frames or anything

00:32:55.160 like that it just doesn't have that foliated structure it has a very different one called a light

00:33:00.300 cone structure so for every event there's a past and future light cone and that's perfectly objective

00:33:07.100 that's just as objective as anything newton had it's just not a slicing and i'm sure people

00:33:12.760 interested in this have at least seen pictures of of light cones somewhere but you could kind of

00:33:18.740 imagine a double cone with the snapping of your fingers right at the apex with a cone going downward

00:33:24.340 and a cone going upward that are called the past and future light cones now those according to

00:33:30.380 relativity are as objective as anything they have nothing to do with anybody's reference frame or

00:33:34.980 anything and all of the things in my future light cone are objectively later than that finger snap

00:33:42.460 everything in its past light cone is objectively earlier than it and everything outside of those

00:33:49.480 two the whole region that's outside the cone these are events that are called at space-like separation

00:33:55.240 those have no definite temporal order with respect to the finger snap now if you and i tried to snap

00:34:02.920 our fingers at space-like separation we couldn't do it because we're too close and we would have to snap

00:34:08.800 with such precision that we could never ever do it so if you kind of imagine and again i'm sorry to

00:34:16.900 have people do this in their heads but if you have this picture of this double cone and then you keep

00:34:21.920 making the cone flatter and flatter kind of flatten it out you'll see that it more and more carefully

00:34:28.140 approximates a kind of plane and the those thin regions outside the cone those at space-like

00:34:35.680 separation you sort of never never run across them in everyday life but the further away you get the

00:34:41.480 bigger that region gets and so if you're if you're light years away then that region can get quite large

00:34:46.720 okay so there's this okay i mean you you seem to be endorsing more of a common sense notion of time than

00:34:54.680 certain physicists might i mean you alluded to that in uh offering a a footnote before you you began

00:35:03.300 i guess there's the two views here can be loosely described as you know presentism versus

00:35:10.400 eternalism in some sense where because the eternalism piece i've often thought of by reference

00:35:17.040 to the phrase a block universe which i don't know the do you know the origin of that phrase i i i don't

00:35:24.700 know who first started using it i do know that that is again a phrase that is objectively does us a

00:35:31.540 disservice and and i'll just say a word that i can say with certainty about it which is that uh hugh price

00:35:38.060 who wrote a book trying to argue against a fundamental direction of time and this is something

00:35:44.300 i believe that time has a direction time goes for we're all getting older right i mean physics didn't

00:35:49.220 tell us that isn't true um you know it would be a really amazing discovery i'm still i'm still waiting

00:35:55.040 actually getting older right um i'm waiting for the discovery that tells us that isn't true

00:35:59.240 right so i think there's nothing to that now what what hugh does in his book is he he gives us

00:36:05.280 explicitly there's a paragraph where he defines what he means by a block universe and the problem

00:36:09.660 is it has two pieces to it one piece is to say that the past present and future are all equally

00:36:16.980 real and i believe that i think they're just facts about what happened in the past facts about what's

00:36:21.860 going on now facts about what are going to happen in the future i i think the you know past people are

00:36:26.780 just as real as you know past pains and sufferings were just as real as the ones we endure and

00:36:31.720 the ones in the future will be just as real we're just as real or are just as real because

00:36:36.680 they will be just in the sense that they're to our future right i mean they haven't happened yet

00:36:41.580 but right they will happen in some you know case or asura things will happen in in some very

00:36:47.280 particular way and then he adds a second clause which is that and furthermore there's no fundamental

00:36:51.980 direction of time and i kind of endorse the first one and completely reject the second one so then you

00:36:58.240 say do i believe in a block universe well i'm not a presentist present i mean some presentists

00:37:03.160 hold to me the very peculiar view that all of reality is confined to what presently exists

00:37:10.680 and then if you say the sort of natural thing to say which is that well presently there are no living

00:37:15.720 dinosaurs you say yeah but still dinosaurs are not fictional right they're not fictional in the way

00:37:20.840 that you know sherlock holmes is fictional they're really you know dinosaurs are real and in in a

00:37:27.080 certain sense of real of course they existed earlier than we do they're in our past light cone

00:37:32.740 but they're not actual this actually brings me directly to the the topic i i do want to raise

00:37:38.000 good with you so um maybe well i'll just i'll start the slide into that but let me just prop up the

00:37:44.880 two views where we have begun to talk about here this you know presentism versus eternalism i mean

00:37:51.720 i think that presentism does to some degree i don't know all of its implications in science at the

00:37:58.100 moment but it my understanding of it does capture what i consider a common sense notion of time which

00:38:03.740 is that the past no longer exists you know whatever happened happened and its effects may be evident

00:38:11.280 in the present you know so we can see the ruins of the coliseum in rome or you can see the dirty

00:38:17.720 dishes you left from lunch but eternalism suggests and that's what's also going by the name of the block

00:38:25.380 universe suggests that in some very real sense the past time in which the coliseum was full of living

00:38:33.140 romans who were shrieking for the blood of gladiators is still real right and and as is your past self

00:38:40.760 still devouring lunch right like like it's not those moments have been experientially left behind

00:38:47.980 by you in some sense i mean you never were there in ancient rome and you are you are no longer having

00:38:54.780 lunch but or the you with with which you're currently identified as this sort of keyhole view of

00:39:00.820 of the cosmos through your you know your conscious mind in this moment but on this view of of a block

00:39:07.700 universe where you fully spatialized time and given it no real preferential direction the past is still

00:39:15.320 in some sense actual even though you can't actualize it and you know worse still for common sense the

00:39:23.660 future is also out there and i mean although there is a version of the block universe i think that's

00:39:29.280 called the growing block universe where the future isn't yet real but let's leave that aside for a

00:39:34.380 second i mean it's almost like you know the reality is a is a novel and you're on page 63 now and yet

00:39:41.560 page one and page 180 exist just as much as the page you're on and you know that that's the intuition

00:39:50.500 confounding sense in which time gets fully spatialized in a block and so it sounds like you're not signing up

00:39:57.680 for that picture no and again it's um i mean i just have to to kind of signpost some words you used

00:40:06.160 you used the word still right and still was doing a lot of work there you know it is is the gladiatorial

00:40:13.540 battle battles in the roman coliseum i mean you imagine a kid going to a museum and they see a picture

00:40:18.780 of these gladiators and they say is that real and there's obviously a sense in which you would

00:40:23.820 correctly if you've just been seeing pictures of unicorns and the loch ness monster you say oh no

00:40:28.980 that's real it really happened now of course it happened in the past if he says is it still real

00:40:36.320 then you might say oh by still you mean is it going on right now no no it's not going on right now it went

00:40:42.280 on in the past really did go on in the past and so if you have this picture with these you know if you

00:40:49.280 have this picture in this of this four-dimensional structure with these light cones kind of in your

00:40:54.720 mind and you say right now i'm at the cone point of one of these cones all of that is real the whole

00:41:00.940 thing is real the stuff in my past light cone i correctly say happened a while ago and isn't going

00:41:07.140 on now the stuff in the future will happen and isn't going on now the idea of what's going on now

00:41:12.900 gets kind of a bit messed up in relativity because unlike there being just a single thing you have this

00:41:18.860 whole outside region that's actually quite large and doesn't correspond to your naive sense of the

00:41:24.880 present what really gets lost is the naive sense of the present quite honestly as stretching out

00:41:31.780 so but i think the other thing you said was well if i do all this and i completely spatialize time and

00:41:39.020 get rid of a direction but that's what i don't want to do i don't think time is that that's what many

00:41:44.600 people believe happens when you quote spatialize time you get rid of a directionality to it and i

00:41:52.660 think there's nothing in physics and never has been anything in physics that suggests that time doesn't

00:41:58.360 have a direction and certainly physicists always treat it as having a direction always often it's so

00:42:04.900 obvious because we know the way time normally goes when i put in a time coordinate the direction toward

00:42:11.800 the future is supposed to be where the numbers get bigger except when i'm sending off rockets then i

00:42:16.840 count down right then in the direction toward the future i go 10 9 8 but at all other times you kind

00:42:23.480 of if you just give me a time coordinate and don't tell me anything else the convention is that as the

00:42:29.400 time coordinate gets larger that's the forward direction of time so it's so obvious and so easy and

00:42:35.000 there's so little to to debate about it that you can kind of fly under the radar but it's there

00:42:39.860 well except if someone tells me there's no direction of time i just i literally have no

00:42:44.340 idea how to understand the world i'm living in but what about all the talk in physics around

00:42:49.380 the math actually having no implication of directionality that you know the equations are

00:42:54.940 reversible and and only and therefore entropy is the is sort of comes to the rescue of of intuition here

00:43:01.540 there again two things just happen the first thing is people say look there's no directionality in

00:43:08.360 equations then you say well actually it turns out there is because the cpt theorem and c and p are

00:43:13.160 right and there's a technical sense in which in quantum field theory which is the best theory we have

00:43:19.160 there is a directionality of time and nobody disputes that nobel prizes were given for the discovery of

00:43:26.520 parity violation and so there's no physical dispute that that there's a symmetry that's called cpt where the t is

00:43:35.080 time symmetry and there's a general argument that any good theory should should respect that symmetry

00:43:41.320 but the cp part violates it and so the only way to get the whole thing to work is to have t be violated

00:43:47.600 too you there can't be a time symmetry so they say look in the equations of physics you don't see this and

00:43:52.640 you say well actually in the equations of physics as we have it you do see it and then they say oh well

00:43:56.560 let's forget about that i mean it's a very strange situation and then they bring in stuff about

00:44:02.920 entropy now the thing about entropy is in everyday life of course there are many many time asymmetries

00:44:09.280 typically although not always if i show you two photographs taken a few years apart of somebody

00:44:15.540 you can put them in time order and figure which is a picture of them younger and which is a picture of

00:44:20.780 them older you might get it wrong you know if they had a lot of of cosmetic surgery you could mess that

00:44:26.780 up but you know there there are all kinds of pretty reliable temporal regularities and they demand an

00:44:35.740 explanation and the explanation for them is often goes through entropy that's true but what you what

00:44:42.880 are you trying to explain you're trying to explain why typically this happens before that and so you're

00:44:49.140 already assuming a time order and even stating what it is you're trying to explain you're trying to

00:44:54.540 explain why things typically happen in a certain time order and not in the reverse order and entropy

00:45:00.380 considerations are often important for understanding that they do help comprehend that but it that doesn't

00:45:07.260 at all suggest that time doesn't exist or time order doesn't exist you assume it exists just to state the

00:45:13.560 problem yeah well i will be the first to admit that they should hand a nobel prize out to whoever can

00:45:18.720 explain what's happening to my face in the mirror because uh that that shrieks for explanation but um

00:45:26.060 you alluded to the fact that many physicists or certain physicists wouldn't agree with you here i'm

00:45:32.480 i'm thinking of though i'm not super familiar with their work i'm thinking of people like julian

00:45:38.020 barbore or um carlo ravelli i mean what what's who who are you thinking of when you when you're

00:45:43.700 imagining having to debate someone on this topic well the the people you just i mean julian has an

00:45:49.880 extremely idiosyncratic view i don't think he he got interested in trying to get rid of space and time

00:45:57.100 spatio-temporal structure at a fundamental level altogether in favor of something called relationalism

00:46:03.980 or relationism and he pushed that program as hard as anybody has pushed it but that's not

00:46:09.840 mainstream physics right carlo's views i are are a little bit hard for me to understand but but the

00:46:16.400 idea that there's a deep problem that connects entropy to time itself as if i mean one might put

00:46:24.980 it this way some people seem to think that if entropy isn't going up or down then then time then

00:46:30.060 the direction of time will have disappeared that that you couldn't say that anything happened before

00:46:34.920 after anything else that's a pretty widespread view and one i think that just doesn't i don't think

00:46:42.340 there's any reason to believe that i don't think that there's a problem there the there is a problem

00:46:47.520 about explaining the manifest time symmetry asymmetries we see and that's a good problem a lot of this has to

00:46:55.860 do with what gets defined in terms of what and it's a very delicate situation to decide

00:47:03.100 what you think should be the defined object and what should be the defining object

00:47:08.240 so i i personally think for example to give the example i think you would agree

00:47:13.200 if we're worried about causation and causation can be a very puzzling subject

00:47:17.300 i think it's part of the definition of a cause is that when you have a cause and effect

00:47:22.180 pair the cause precedes the effect right so i'm going to assume i have a good notion of time precedence

00:47:29.100 of time order of earlier and later and use that in defining causes there are people who want to flip

00:47:37.100 that around and say no no no i don't understand what before and after mean but i have some independent

00:47:41.660 grip of causation and i'm going to somehow wheel in causation to define time order well and it seems

00:47:47.940 to me this is just putting the cart before the horse i mean this is putting the thing to be defined

00:47:53.120 in the wrong spot trying to define the later thing in term you know the the earlier thing into the

00:47:58.060 later thing it's just doesn't make any sense to me well i think we do have at least we think we have

00:48:04.300 an independent grasp of the the concept of causation because we can talk about the possibility and

00:48:12.020 in general the the non-existence of things like teleology right that the causes could stand as some

00:48:19.300 kind of attractor in the future you know pulling events toward them as opposed to pushing from

00:48:24.480 behind so the fact that we can have a conversation about that suggests that causation is is separable

00:48:29.640 from from the temporal order you just sketched right but i i guess my feeling is that that part of the

00:48:36.220 great triumph of the scientific revolution was to eliminate that kind of teleology that oh i understand

00:48:43.980 understand why things are doing what they're doing now in terms of them being pulled by something in

00:48:50.180 the future now of course often you understand why things are going on the way they are now in the

00:48:55.380 sense that someone is aiming at something in the future right i mean you look at the builder building

00:48:59.440 the house and uh you understand what he's doing in terms of having plans in his head and wanting to

00:49:04.920 accomplish something and you know taking steps to accomplish it that's a kind of teleology and

00:49:10.000 teleological explanation but the the theory of evolution successfully eliminated the kind of

00:49:18.500 teleology you're mentioning yeah from biology and i think did a good job of it and said you know uh

00:49:24.820 evolution and evolutionary pressures and selection pressures all explain why there's this appearance of

00:49:32.460 design in nature even though there isn't a designer even though it's not aiming at anything

00:49:40.000 and i and i take that to be a great triumph of of science uh if someone says gosh the reason that

00:49:47.860 such and such is going on today is that something that's going to happen in a hundred years is pulling

00:49:52.340 it forward i think that's contrary to physics it's contrary to biology it's contrary to chemistry it's kind

00:49:57.840 of contrary to everything so i think we've gotten rid of that i hope we have okay so let's um land on

00:50:04.980 my uh topic of you know where i'm genuinely uncertain which really is the genesis of my interest in this

00:50:10.920 conversation and it relates to the concept of possibility as it exists in physics but also as

00:50:18.600 it exists in i guess metaphysics and in philosophy and i guess my my question is what if there is only

00:50:26.200 the actual is there some scientific reason or logical reason to rule out the possibility i realize

00:50:34.360 that's circular that possibility itself is just an illusion right and that because so so the current

00:50:41.700 sense of possibility i think we all have is that it itself is kind of mysterious because on some in some

00:50:48.500 sense it is the assertion that reality includes things that don't exist you know that there's more than the

00:50:55.960 actual right there's the actual there are the things that actually happen but then there are the

00:51:00.240 things that haven't happened yet but might happen they're the things that could have happened had we done

00:51:07.960 something differently but they didn't happen because we didn't do something differently and and and all of

00:51:13.000 that space seems to exert an influence on what is actual in a way that is kind of inscrutable so i guess

00:51:22.440 the because i mean because so it seems that if something comes into being at time t1 say right and

00:51:30.960 becomes actual at t1 it does seem somehow necessary to say that its possibility was real at time t0 and so

00:51:41.240 the question is in what does that possibility consist and perhaps now i'm realizing that we could start

00:51:47.460 talking about david lewis's modal realism here which it might be worth addressing however however

00:51:53.100 briefly but my underlying concern is whether the actual and the possible are in fact identical sets

00:52:01.340 and that anything that is possible really is in fact actual and all we're adding to this picture is

00:52:08.420 an idea we could we live with this persistent idea that other things might have happened or might yet

00:52:15.960 happen you know you could have married a different person you could have worn a different outfit

00:52:19.720 but in reality there is always only the person you married and the outfit you wore and the rest is

00:52:27.820 something you're thinking yeah i i i understand what you're what you're saying let me go back there's a

00:52:34.100 kind of wonderful discussion of these basic questions by nelson goodman in his book in his set of lectures

00:52:41.580 fact fiction and forecast and he talks about everyone has a philosophical conscience and that

00:52:47.160 conscience is a set of things you think are pretty much okay to believe in and then there are things

00:52:54.080 that are not obviously okay to believe in it doesn't mean you immediately rule them out but you you would

00:53:00.060 require some work to explain them right and he says people have different consciences for him among the

00:53:07.160 things that he can't accept without further explanation are unrealized possibles which is

00:53:12.860 exactly the thing you've been talking about angels he says neutrinos he says i it's not that he won't

00:53:19.460 accept neutrinos but he needs some explanation he doesn't quite understand what they're supposed to be

00:53:23.540 uh two out of three ain't bad you know you know he has a whole list and and he just says look this is

00:53:29.560 my conscience if you have a different conscience you're gonna think i'm you know you might think

00:53:33.320 i'm i'm allowing too much you might think i'm allowing too little and part of what you were

00:53:37.920 saying was look what about un unactualized possibles right we all agree that everything

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Making Sense - Sam Harris - May 01, 2023

#318 — Physics & Philosophy

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