Making Sense with Sam Harris - #120 — What Is and What Matters

Episode Date: March 19, 2018

Sam Harris speaks with Rebecca Goldstein and Max Tegmark about the foundations of human knowledge and morality. If the Making Sense podcast logo in your player is BLACK, you can SUBSCRIBE to gain access to all full-length episodes at samharris.org/subscribe.

Thank you. of the Making Sense podcast, you'll need to subscribe at samharris.org. There you'll find our private RSS feed to add to your favorite podcatcher, along with other subscriber-only content. We don't run ads on the podcast, and therefore it's made possible entirely through the support of our subscribers. So if you enjoy what we're doing here, please consider becoming one.

Okay, so not much housekeeping here, just a few words by way of context. This is the audio of the event I did in Boston a few months ago with Rebecca Goldstein and Max Tegmark. I introduced them both from the stage, so you'll be reminded of who they are in a moment. from the stage, so you'll be reminded of who they are in a moment. But we focus in this conversation on the foundations of human knowledge and morality as well. It's really a conversation about what is and what matters. And as is often the case with live events like this, there were some sound issues. The sound is definitely echoey and not perfect, but I think you'll acclimate. Hopefully, you'll find the conversation as interesting as I did. And so, now I give you Rebecca Goldstein and Max Tegmark. Thank you. Thank you very much.

Thank you. Thank you very much. Thank you. Thank you for coming out. I have some great guests tonight. I'm really looking forward to this conversation. My first guest is a philosopher and a novelist. She has written about the relationship between science and religion and science and values. And she's also just written wonderful books on some famous people, Plato and Spinoza and Kurt Gödel. And she's received many awards, including the MacArthur Fellowship and the National Humanities Medal from President Obama. Please welcome Rebecca Goldstein. And my second guest is a physicist at MIT. He's also a professor there.

He's authored more than 200 technical papers on topics ranging from cosmology to AI. And he's the president of the Future of Life Institute. And he's now one of my go-to guests on the podcast. I think this will be his third appearance, if I'm not mistaken. Please welcome Max Tegmark. Thank you so much for having me. Okay, so as I said, I've really been looking forward to this because these are two people who I can really just dive into the deep end of the pool with without much concern about whether or not I can swim. I say in the run-up to this, Rebecca sent me an email asking if I knew what I wanted to talk about, and I said something very vague. And then she sent me another email that had maybe a thousand words in it, and it was

just the most amazing roadmap to my intellectual life. It's what I want to spend the next 10 years thinking about. So I'm going to use that very much to guide this conversation. And Max hasn't seen any of this, so he should just be terrified. So I want to talk about what we think we know about reality and why we think we know it. And I want to talk about the parts of reality that matter and what makes them matter and whether we have to depart from scientific rigor in order to talk about anything mattering. And so this conversation will take us onto terrain that I love,

which is the relationship between facts and values. But to start, I want to talk briefly about the relationship between science and philosophy. And so, Rebecca, I'd like to start with you. There are many scientists who have said very disparaging things about philosophy. There's actually one who we both know, I'm having an event with in about 48 hours. He should probably remain nameless, but his name rhymes with Lawrence Krauss. But you repeatedly point out in your work that science is riddled with philosophy just from stem to stern, and that if you are not aware of your philosophical assumptions when doing science, you're very likely to be making illegitimate claims about how your science

maps onto reality. So start us off with a little bit on the relationship between science and philosophy, as you see it. Yeah, I sent you this roadmap, and now I'm trying to situate myself on it. I think that science is our great arbiter in trying to figure out the nature of reality, of what is. And I think that the synclinon of science, the amazing trick that it eventually worked out sometime in the 17th century was that it gets reality itself to collaborate with us because our intuitions are all off, right? And so our intuitions about space and time and individuation and teleology and causality, all of these very deep intuitive intuitions we have turn out to be off. I mean, the nature of reality itself turns out that reality out there exists exactly

as it's represented to us in our subjective experience is off. And so this is an amazing thing that we've figured out what to do to get reality, to prod reality, so that it will answer us back when we're getting it wrong. So, oh, so you think simultaneity is absolute, do you? It seems intuitively obvious that two events are either simultaneous with each other or not, regardless of which reference frames they're measured in, moving relative to each other. Well, we'll just see about that. And somehow we prod reality to answer us back. And that seems to me, that's what science does. So any question that we can figure out so that somehow reality itself can kind of smack us around and tell us that we've

gotten it wrong, that's scientific. What philosophy, I think, is about is trying to maximize our coherence. We're very compartmentalized creatures. I think for reasons that science is beginning to tell us why, evolutionary psychology can tell us why we're such compartmentalized creatures. We live very happily with our contradictions. And it's philosophy's job to vitiate our happiness. And that's been the way of philosophy ever since Socrates was wandering around that agora in his dirty kite and annoying people, getting them, showing them the internal contradictions. The philosophy has to take all of the knowledge that science is giving us about what is, about the nature of reality, and test it against other of our intuitions and see which are compatible, which are incompatible,

what the options are. So a philosophy is always dependent on science. A good philosopher has to know, has to keep up the science. But it's a different kind of skill set that's called for. It's not figuring out how to describe reality and then tell us if it's right or wrong. And it's not merely a matter of being the birthplace of science because people, it's often said, and I think I've said it myself, that there was a time where all questions, virtually all questions of interest were philosophical. And then what's so-called natural philosophy birthed off these specific sciences. And I think in one of your papers, you talk about just people in philosophy signaling, you know, we need some more science over here, you know, come help us. Right.

And that's not what philosophy is doing. It happens in the course of asking these questions and trying to get our bearings in the world that sometimes philosophers very often will put forth proto-scientific questions. The science isn't there yet. The empirical means of prodding reality to getting reality to be our collaborator doesn't exist yet and often it's because the philosophers ask the question um that the science emerges it happened with physics it happened with biology it happened with linguistics um it's it's happening now and you know a lot of the fields that uh psychology and cognitive neuroscience is taking over before psychology. So that happens, but I think that that's not what philosophy is about. Philosophy

is not about prematurely ejaculating scientific questions, right? That's not what we're trying to do. It happens as a kind of accident, you know, in trying to maximize our coherence. All right, on that note, I'm going to ask Max what he thinks about philosophy. You're quite right. I've been in many physics conferences where some physicist has accused someone else of being too philosophical, as if that was supposed to be

a put-down. And I find it absolutely ridiculous. To me, philosophy is really a synonym of clear, logical thinking. And if you look at the PhD that I have and ask what does the PH stand for, I have news for those grumpy physics curmudgeons. It doesn't stand for physics. It's the doctor of philosophy. Why? Because, well, natural philosophy is the phrase we used to use

to describe what we now call science. It's the same thing. So within science itself, we often distinguish between theory and experiment. I guess in your words, Rebecca, you could say philosophy is the pure theory. We don't do the experiments. And we need that. Of course, all theory and no experiment, well, then you get string theory.

That might be too much of a good thing also. Generally, we've had the most healthy progress when we've had both, where you have those theorists to keep annoying the experimentalists, like pointing out inconsistencies and giving them new ideas for things to try, new ideas for them to try to shoot down. And at the same time, you have these experiments

to keep annoying the theorists by ruling out their theories. It's this interplay, which has always been at work whenever we've had really great progress, I would say. I think that's the biggest laugh I've ever heard with string theory is the punchline. Only in Boston did that happen. Let's just cut the enemies of philosophy a little slack here in that there's a difference in how we think about intellectual progress. So to say that there's been scientific progress is to say something that really would find no dissenters. The progress of science is all around us. Yeah.

How do you think about philosophical progress? What sort of philosophical progress have we made? Yeah. I'm sure you will say that we have made some and that it should be obvious to us, but we rarely talk as though we're making and have made great progress. Yeah, yeah. talk as though we're making and have made great progress. Yeah, yeah. I just, before I just, I just did want to say, you know, in my saying that science is, you know, our best means of answering the question of what is the nature of reality, for me to actually defend that view would take me outside of science. I would have to put forth a philosophical argument, which I'm very prepared to do.

But I mean, there are other views about what science is all about, instrumentalism. I mean, that scientific theories never expand our ontology, our nature of reality of what is, but it's just, you know, it's a means of predicting future experiences. And it never, you know, so there's no reason to think

that these theoretical entities that are used in scientific theories really exist, that there are fields or quarks or, you know, black holes or anything. And, you know, and some very good scientists in the past and some philosophers as well, you know, put forth such arguments. So even to say what it is that science is doing, science, reality can't tell us, is it instrumentalism or is it realism, scientific realism? That, you know, depends on a philosophical argument trying to make coherent, you know, what we're getting, the input we're getting from science. So it's

just to, you know, to argue, I can understand how, I call them philosophy jurors, you know, some of our most celebrated or certainly high profile scientists who just really dismiss philosophy. You know, I understand what their argument is. Their argument is, what else is our intelligence good for other than figuring out what is? And it's science that does that. Therefore, you know, there are questions that we haven't answered yet about the nature of reality. But, you know but just give scientists enough time and research grants, and they'll get it. Well, there are other kinds of questions, including what is it that science is doing that is not itself a scientific question. So you can't even make the argument

without wandering into philosophy. But what was your real question? So I actually want to get there. So I want to talk about realism versus all of its enemies, like instrumentalism. But just briefly, it is often thought that we don't make philosophical progress because the same sorts of problems seem to come around, you know, we're still, and we're still reading Plato for like, why, if we made progress, why would it, why would anyone ever read Plato ever again? Yeah. So if you could just briefly address that before we move on to realism. It's a hard question. And one of the arguments that I try to make is first of all, when you read Plato and Aristotle, I mean, you're really

amazed at how good they were at spotting the questions, but how bad their answers were. I mean, a lot of these, you know, answers have been disposed of. And a lot of the other thing I think is that as we make philosophical progress, science has incorporated in a lot of the arguments about interpreting science that were really philosophical problems. The distinction between primary and secondary qualities that the 17th century philosophers made. The primary qualities are the ones that we captured in the language of mathematics, which was the language of physics. And they really exist out there. So position and motion and weight and anything that can be described and measured in purely mathematical language. And then you can subject them to mathematical equations and make progress. And everything else was deposited in the mind, you know, so the way things look and the way they taste and the way they smell,

that was all put into the mind. This was all a philosophical argument made in the 17th century that just sort of became incorporated into what we think of as a scientific point of view now. It's a philosophical interpretation, but it is philosophy, and the arguments were philosophy, and it is part of what we think of as a scientific world view now. I think that in general what happens, I think that there has been a lot of progress, and I think particularly in moral philosophy, progress. And I think particularly in moral philosophy, that these were moral, testing our inconsistencies, our moral inconsistencies, pointing them out, making arguments, and moving us forward so that it's inconceivable to us now when we look back at our slave-owning, wife-beating, heretic-burning, you burning, witch-stoning.

Immediate family. Right. It's like, how could they not have seen this? Well, they didn't see it. And it was philosophical arguments that got us to see it. So that now it just seems, you know, we don't see philosophical progress because we see with it. It becomes the very lens that we're looking at the world with. And so it becomes invisible to us. So yeah, it really is the water in which we swim

intellectually. And so I want to talk about realism, which can be defined in a few different ways. But when I think about it, whether you're talking about scientific realism or moral realism or even introspective realism, just trying to figure out what it's actually like to be you in each moment, it's the claim that there are truths whether you know them or not. It's possible to be right or wrong about the nature of reality, And it's possible to not know what you're missing. There's an appearance reality distinction where you're trying to get behind appearances. And science is arguably the most rigorous place where we try to get behind appearances, or it certainly has the most rigorous methodology. Max, how do you think about this appearance and reality distinction as a physicist and cosmologist? How do you think about this appearance and reality distinction as a physicist and cosmologist? How do I think about realism? Yeah, what do you think science is doing?

Because as Rebecca said, you can spend a lot of time as a scientist reconciling yourself to being an instrumentalist, which is just, you know, the math works out, we can predict the results of experiments, but who knows what we're actually probing into. Who knows what it really looks like. One thing I've been quite surprised by over the years, actually, is how many scientists, even though you have an incredibly intelligent bunch of people, come to entirely opposing views on philosophical matters. And often when you probe a little bit deeper,

it's because they're quite naive about it and haven't even bothered understanding the various opposing points of views because they dismiss all of this as too philosophical. But then they have their own closet philosophy that they just don't call a philosophy. So basically haven't thought it through. And some scientists take this very instrumentalist point of view

that, hey, who cares about if there's an ultimate reality or not? We should just focus on building gadgets that work and so on. That's, I guess, really just a preference, a matter of interest. Some people like chocolate ice cream. Some people prefer strawberry. If someone doesn't care what exists. But I do. I find it absolutely fascinating. It's this deep curiosity to try to understand more about the cosmos we live in that made me want to be a scientist. Then there's a second school of dissent. Not the one to say, I don't care about what reality is, but that deny its existence at some level. You get people who deny what I call the external reality hypothesis, this hypothesis that there actually is an external reality independent of us humans. Of course, you get some extreme folks like solipsists will just say that

nothing outside their hand exists, but they're a small minority. Why do they bother to say it? But you also get the very famous people like Niels bohr one of the founding fathers of quantum mechanics who said no reality without observation about his quantum theory which when you think about it means that it's humans it's our observing that somehow makes things real. And this to me feels extremely arrogant, I have to say. No offense to you folks, or you folks, but I'm pretty sure that if all of us disappeared, the Andromeda galaxy would happily keep doing its thing. And it feels to me more like less of a thought through really scientific position or philosophical position and more like just the continuation of this human

hubris that set us back in so many other ways you know we used to be so obsessive about earth being the center of the solar system and then denying the idea that there could be other solar systems we even burned giordano bruno at the stake 400 years ago for saying that and then denying the idea that there could be other solar systems. We even burned Giordano Bruno at the stake 400 years ago for saying that. And then now resistance of the idea of maybe parallel universes, also this idea that somehow we're so special relative to animals or slaves or whatever. So now when we say, oh, we're so special that reality couldn't exist without us, I think it's silly, but it's a viewpoint I encounter quite a bit still in some scientists. So the interesting thing is, of course, if philosophical education was part of scientific education, they would find these kinds of viewpoints having been put forth.

I mean, Bishop Barclay, nothing, you know, S.A.S. Perkippy, nothing exists unless you perceive it. You know, he was putting forth these views and other people were criticizing them. And there's a whole long history where these things have been argued out and its weaknesses explored. And, you know, it just would be good. It would be so stupid of me as a, you know, as a non-biologist to think that I'm just going to charge in and say what's wrong with, you know, evolutionary biology or something without educating myself, there is a discipline in which all of these views have been argued out and hammered out and their strong points and their weak points evaluated.

And since physics and all science raises these philosophical questions, why not study the field? Exactly. But you see, this is precisely where this anti-philosophical snobbery comes in as a psychological defense mechanism. Because these scientists will say, well, I don't do philosophy. I think philosophy is stupid.

And then they will charge in and talk about all these philosophical questions, make up their own nonstandard terms for things that philosophers have discussed for hundreds of years and completely ignore everything that's been done. And effectively, what they're doing is bad, uninformed philosophy, right? Yes, exactly. And they justify it to themselves by saying that philosophy is somehow stupid. I don't think that philosophy can be avoided, not just by scientists, but by all humans. I mean, I in fact think, you know, one way or another, we're all trying to get our bearings in the world, figure out what is and what matters. And you can't avoid, you know, some kind of philosophy in doing that.

I think that it's part of being human. Yeah, and unfortunately, there are impressive reasons to be skeptical that we're good at doing any of that. Yeah, and unfortunately, there are impressive reasons to be skeptical that we're good at doing any of that. Yeah, yeah. clear that there are two inconvenient facts here. One, reality wasn't designed with us in mind. It wasn't designed so as to be perfectly interpretable by us. And that's provided we're not living in a simulation that was run by the Mormons who actually conquer the world at some point. I'm waiting to find that out, that Mormonism is in fact true in this simulation and everything I've been saying is going to consign me to hell. But there's also the fact that we have not evolved our cognitive toolkit, our intuitional toolkit, and we'll talk about the primacy of intuition

in a moment, it hasn't been tuned up by evolution to track reality as it is. It's just, that's just not the sort of apes we are. I think that's very astute what you're saying there, Sam, because the, one of the reasons that has caused a lot of curmudgeonly scientists again and again,

dismiss philosophers and often dismiss even other scientists, like we're a little too radical for their taste. you know, Einstein, say, was precisely by saying, oh, these ideas are too weird. And when they couldn't refute them with experiment, they would refute them by saying, that's not science. And but what that really meant, saying that it was too weird, if you reinterpret that sentence in the context of evolutionary psychology really meant that you know you know obviously as you said we evolved our brains to have intuition for the things that were useful for our ancestors right like how to hurl rocks at people and not get hit by the parabolic motions and stuff we had no intuition whatsoever for anything that wasn't useful to them, like things moving much faster

than us near the speed of light or things much smaller than us like quantum particles. So what evolution actually predicts for science is that whenever we use tech to see things that our ancestors had no access to, it should seem weird. It should challenge our very notion of what the boundaries of science are. It should probably force us even to redefine from time to time what we mean by science. So one could say, in that sense, that people who are being dismissive like this of things just because they say they're too weird

or this is not science or too philosophical are really denying the fact that they're evolved apes and and they're they're taking this evolved evolution and their notion of what's intuitive and what's weird we're conflating that with some kind of truth well so this is actually a point that we we hit in a previous podcast but i think it's worth reiterating, is that you would be suspicious of any final description of reality that was commonsensical, right? Because we know our common sense isn't fitted to timeframes in billions of years or to the Planck scale or to anything else that is at the frontier of your discipline. Exactly. The common sense,

we should assume from evolution that it should simply be a useful approximation for that very limited domain of reality that we had access to without microscopes or telescopes or particle colliders or any modern tech. Yeah. So that's, of course, I mean, of course, science has come too far. We could never go back to something that's commonsensical. I mean, relativity theory, general relativity theory, quantum mechanics, it's already blown our minds, right? And so we know that reality

does not correspond. Some of our deepest intuitions about space and time and causality, they've already been, they're gone. And so there's no going back. Except for those people who believe that all of this was created by a person just like us who doesn't like homosexuality for some reason.

Yeah. And I guess that's, I mean, you said that there are two great obstacles to our understanding the nature of reality, what is and what matters i mean to me those are the two big questions um and uh you know and one is that yes obviously unless um unless this world was created by some designer who made sure that our cognitive abilities are up to the task. Not much evidence for that. Yeah, this world, the laws of nature, they were not designed with our cognitive faculties and capacities in mind. And so it's amazing to me when people talk about all that we don't know, I'm not amazed by that. I'm amazed that we know anything given that we are these evolved apes. And the other thing that keeps us, and here it's a little more about moral knowledge, that keeps us from understanding nature of certain aspects of reality,

including moral reality, is, you know, our own self-involvement, our own way of privileging ourself and those we love and our kin, our tribe, all of that. And that also is a tremendous obstacle in terms of, we've made very slow moral progress. We've made it, but there's a real, and there, it's not getting reality to answer us back. It's more looking at the various things we believe and seeing the internal inconsistencies. So we've got science to this great thing of just, you know, we need reality to answer us back. Because reality wasn't created with our capacities in mind. So we've developed these scientific tools. And I say philosophy is these other different set of tools, thought experiments and forcing people to put all their premises out on the

table, digging them out, going further and further. What are the presumptions of your belief? And the end game of that is to, the end of that game is to expose our inconsistencies, our internal incoherencies. And we don't like that. That's our saving grace, really. We find all sorts of ways of denying that we are internally inconsistent because it's usually working to our advantage to deny these inconsistencies. usually working to our advantage to deny these inconsistencies. But if you really keep hammering at it and you push people's faces into it, eventually they give it up. And I think that's

a different kind of reason. It's not science, a different kind of reasoning activity. And it also helps us to make progress. It's humbling to consider just how ill-prepared we are for our modern circumstance by evolution. When you think of something as simple and as obviously evolved and as fundamental to our survival as pain. So we've obviously evolved to feel pain, but we have not evolved to sense pain in a way that is especially useful in a modern context. For instance, you can feel excruciating pain or be at least seriously inconvenienced by having an eyelash in your eye, right, which means nothing. But your body can be riddled with cancer and you feel no pain at all because we have not evolved in a condition with oncologists and hospitals. But it would be very useful to feel pain associated with

cancer. And so it was detected early. There's almost certainly intellectual equivalence to that sort of disability where it would be so much nicer to be able to do something intuitively or effortlessly that is in some way crucial to the whole enterprise. You're at the frontier of thinking about AI. And so we're now talking about the prospect of building minds better than our own at doing some of these things. Do you spend any time worrying that there are certain questions that can be posed that are interesting? But take string theory as an example. Is string theory just an intellectual dead end that has absorbed the careers of a full generation of physicists?

I don't want to make you any enemies here, but if not string theory, do you worry that there is something very much like that, where we are just playing with tools that are too blunt or not shaped appropriately for that corner of the universe. Well, let me say two things. First about string theory, and then more broadly about what we can and can't do with our evolved minds. For string theory, even though I was joking about

it earlier, and even though Sheldon on the Big Bang Theory has now broken up with string theory, hope I'm not spoiling it for anyone who hasn't seen that episode yet. The fact of the matter is that most physicists today who say they're working on string theory are actually working on much more broad questions of just fundamental theoretical

physics, and string has just been kind of the thing they call themselves, to sort of have a little community and get jobs, but it's more like this what was the theory it's a string and i think there's a lot of promising avenues in there for sure that doesn't mean every physicist should work on it obviously but it's good to take swings for the fences sometimes on the broader question about um what we can and can't do with our evolved mind i think as an antidote,

we had a lot of negativity here where we were lamenting, oh, evolution has limited us so much like this. We can't get intuition for this and we're no good. Wouldn't it be great if we could have better pain sensors for this? And so the flip side of that is,

I think there's a lot we can be very grateful for also that works remarkably well. And as you said, that's in a way worked way better than expectation. It is a kind of a miracle that it works as well as it does. It is. Look at the chimps, and the chimps are not doing much of anything.

It is. And first of all, if you think about what we actually evolved for, our bodies haven't evolved that much in the past thousand years, but yet we're living lifestyle. Now we're sitting, we're in a big giant wooden stone box with weird artificial suns here and, and strange stuff on our bodies.

And everything is about, we spend large fractions of our lives staring at different angles. And, uh, might have a angles. Hold on one second. I just want to remedy this problem because civilization is not working as well as advertised. Maybe it's the Mormon simulators. This will be the first time.

Okay. So, but on the optimistic side, first of all, it's remarkable how adaptable we are. And second, I do think it's actually really remarkable how much better we've been able to do with science than one might have thought. We are actually the masters of underestimation, as I think the summary of what

we've learned from science in the past many thousands of years. First, we've, of course, underestimated dramatically the size of reality and everything we thought existed was just a small part of a much grander structure, right? A planet, a solar system, a galaxy, galaxy cluster, universe, maybe more. But more fundamentally, we've also underestimated our own potential as humans to figure out our world i think you were in plato and aristotle were so on we're trying to understand a little bit of physics they almost everything was mysterious and there were just a few things they thought they could find some formulas and regularities for like motion and then it turned out that was also completely wrong what aristotle. And it took 1,500 years until

Galileo fixed it. And yet today, we can turn it around and note that actually, you know, whereas Galileo, he could have a grape and a hazelnut and tell you how they would move if you threw them, right? But he couldn't tell you why the grape was green and the hazelnut was brown and why the grape was soft and the hazelnut was brown and why the grape was soft and the hazelnut was hard. Now we can answer all of those questions with electromagnetism, with quantum mechanics, and we have managed to bring into the domain of science almost all aspects of the physical world now, except for consciousness and intelligence.

And continuing just on the optimistic gratitude side of this, this understanding has been wonderful, not just for satisfying our philosophical curiosity, but it's precisely this deeper understanding, which has, of course, given us the technology, which has transformed our lives. That's why our life expectancy isn't 35 anymore, right? And so even though, yeah, it kind of sucks that I'm so dumb

and that evolution... That's the tag-mark quote I want on Twitter. It kind of sucks that I'm so dumb. You know, actually, things were not mysterious to Aristotle. That was the problem. I mean, he had a complete worldview that seemed to answer everything. But it was just all wrong. It was a completely wrong methodology of explanation because teleology was at its center.

I mean, the incredible thing that happened in the 17th century with Galileo, and then even more with Newton, is that this marriage of mathematics with empirical observation and prediction, this is an extraordinary thing. It's not at all intuitively obvious that you take this, you know, what philosophers call a priori mathematics. It's a priori. It's not at all dependent on experience, right? It's completely deductive. And you marry it to observations, and you get this powerful methodology for exploring reality. And for Aristotle, you know, the quantitative was just one of the 10 categories of description, which were not very, very important. It was all teleology.

What processes have an end? And we understand a process, a physical process, all processes, by understanding what is supposed to be accomplished through it. So it was a, you know, it was a way of explaining, but it just didn't work. And so, you know, it was, so really, you know, science, we haven't been at work in science, I would say, for thousands of years. I'd say we've been at work since the 17th century. So it's even more amazing how much progress we've made.

Yeah, and if I may just add a little bit to what what you said there i think this is also a tribute to modern philosophy where the key word i think is humility the idea that to get things right we first have to be open to the idea that we might be wrong and actually question everything and particularly question our own prejudices. And that's what was really missing in Aristotle's time. And once we got used to this idea that not only were we often wrong and it was a good idea to question it, but often when we questioned ourselves,

that's precisely when we were able to get great new breakthroughs, which helped. That's ushered in the modern revolution, the Renaissance science and all the tech yeah no it's great i mean you're right there's a kind of collective humility i think in both science and in philosophy which very fortunately doesn't require that the actual practitioners be humble scientists are known for their humility We can be thankful for that. Yeah. But there's a kind of collective humility. Yeah.

So I often think, to me, the very definition of me being a scientist is that I would rather have questions I can't answer than answers I can't question. That's good. Yeah. So I want to talk about the concept of possibility. Much of what we talk about in our personal lives and in science and in philosophy takes as an assumption that there is a world of possibility. To talk about counterfactuals, things that might have been different make sense, to talk about certain things that could have happened but in fact didn't happen. What gives us license to say that we might have done this event yesterday as opposed to today?

And is this necessarily a scientifically or philosophically meaningful statement? necessarily a scientifically or philosophically meaningful statement. I guess there are two views in philosophy and science that seem on their surface to be almost the same. They have different origins. So I wanted you to describe what's called modal realism in philosophy. And I wanted to connect that up with this picture of the many worlds interpretation of QM and then just talk a little bit about what it means to think in terms of possibility. Because my default setting now is that it may not make any sense at all to talk about possibility. That what is actual is in fact all there is and ever is and ever will be. all there is and ever is and ever will be. And that possibility is just a fiction that we have spun in our conversation about what is in fact unfolding or seems to be unfolding. Yeah.

Bring us to modal realism. Yeah. Actually, Max would be better about modal realism because I think he believes in it, and I don't. Do you use that word for it? Well, you're more of a card-carrying philosopher than I am. We should defend And I don't. Do you use that word for it? Well, you're more of a card-carrying philosopher than I am. We should defend... I could explain what it means, but yeah. But if you loosely speaking take it to mean that everything that could exist does exist,

I find that an interesting idea, but it's a little bit too wishy-washy to be really scientifically testable. And the various theories of physics that give you some kind of multiverse, whether it be distant regions of space that light hasn't reached us from yet, which are predicted by, you know, some versions of inflation that gave us a big bang or the ones of quantum mechanics or something else, those are more restrictive in a way. It's not like everything I could think about after I had too much wine exists,

but rather if you have some particular equations, physics have this solution, if they have another solution too, maybe that exists. That's the kind of alternative realities that these theories tend to give. But the shocking thing is that those alternative realities are still, in those cases, very many. And this bothers a lot of people. So, for example, my colleague Alan Guth here at MIT, when he and others came up with this inflation theory, which is the most popular mainstream theory of science right now

for what caused our Big Bang, what it basically says is, yeah, you took something smaller than an atom and it kept doubling its size over and over and over again until it was vastly larger than all the space that we can see, that we call our universe. And it also predicts that all this other space is also kind of uniformly filled with stuff initially.

We know that in this neck of the woods, that stuff, those atoms and so on, gradually coalesced into form among other places, the Milky Way galaxy, our solar system, and Sam Harris, respect Rebecca Goldstein and me and you, and here we are, you know. But we know that the probability that this would happen in some random place isn't zero because it happened here. And inflation typically predicts you actually have an infinite amount of other places with stuff. So if you roll the dice infinitely many times, of course, it's going to happen again. It's going to happen again. And the shocking prediction is then that if you go far enough away,

you're going to get to another place where this identical conversation is taking place. The first one you come to, the person wearing the red sweater is going to be named Max Schmegmark, and he's going to be speaking some incomprehensible different language, whatever. But if you go far enough, you'll even find someone who speaks English and has the same memories. Very disturbing notions. But you can't dismiss it just by saying it sounds too weird, right? The way you dismiss it would be to falsify this physics theory, Alan Guth's equations. And there are people building experiments right now to try to falsify it or test it better and that's how we're ultimately going to sort it out not by having prejudice about it yeah yeah yeah so the the philosopher who was um argued very strongly for modal realism was david lewis

yeah um and uh did Did you know him? Yeah, no, when I was a graduate student at Princeton, he was actually on my dissertation committee. I won't pry any further. Maybe I will pry. Yeah, he's a very sweet man. He's a very sweet man. I never met him, but he was supposed to be very smart.

He was a formidable philosopher and a very sweet man. I actually have a very strong mental image right now. He had a train set in his basement, and he would only take people he liked very much down there. And I did go down there once. You were a train set material. And it was. That sounds kind of sketchy when a professor says,

hey, do you want to come down to my basement? That sounds kind of sketchy when a professor says, hey, do you want to come down to my basement? Anyway, yeah, you really stole the thunder from this David Lewis story, I have to say. We can edit that out. We'll edit the thunder back in. But anyway, when he was running the train set, he put on this little engineering cap, and it was just the cutest thing I ever saw.

But yes, he took very, very seriously. Well, he had a way. You asked, is it meaningful to talk about, you know, had I not gone to college, then I would not now be a philosopher or something. You know, what are the truth conditions of that? I mean, how do you figure that out? And the way he did it was by reifying possible worlds and saying, you know, that there are a whole bunch of possible worlds and they really exist. And you go to the nearest possible world in which I didn't go to college and you check it out. You know, we can check it out. But what would make it true is if that antecedent, you know, were true, would I not be a philosopher?

Right. Or, you know, if I didn't go to college and I wasn't a philosopher, then I'd be a millionaire now or something. And you go to the nearest possible world. So he really took possible worlds very, very seriously in order to formulate what he took to be the truth conditions for counterfactuals. He got there for none of the probability reasons that that max just no it was about it was you know counterfactuals make sense right we understand them you know if i you know if you hadn't called me right then i you know would have missed the most important phone call of my life or something you know we say these things all the time and they seem meaningful. What are the truth conditions? And he thought that the only way to do it was to say that all these various possible worlds in some sense really exist. And, you know, so when I didn't get hit by

that truck this morning, which was a very near miss, there is a counterpart in a very close possible world of me who did get hit, who did get killed. So... It is funny that it is strangely convergent with the many worlds interpretation.

It is. It is. And I reflected a lot about that because I was almost hit by a truck going biking to school one day. If you'd like to continue listening to this conversation, you'll need to subscribe at SamHarris.org. Once you do, you'll get access to all full-length episodes

of the Making Sense podcast, along with other subscriber-only content, including bonus episodes and AMAs and the conversations I've been having on the Waking Up app. The Making Sense podcast is ad-free and relies entirely on listener support. And you can subscribe now at SamHarris.org.