Factually! with Adam Conover - Existential Physics with Sabine Hossenfelder

Episode Date: October 26, 2022

What does quantum physics have to tell us about the human experience? This week, Sabine Hossenfelder joins Adam to explain how quantum physics affects our notions of existence, time, and spirituality. Check out her book Existential Physics at http://factuallypod.com/books Learn more about your ad choices. Visit megaphone.fm/adchoices See Privacy Policy at https://art19.com/privacy and California Privacy Notice at https://art19.com/privacy#do-not-sell-my-info.

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So if all of that sounds good, if you want a big box of delicious snacks like this for yourself, use the code factually for $15 off your first order at Bokksu.com. That's code factually for $15 off your first order on Bokksu.com. I don't know the truth. I don't know the way. I don't know what to think. I don't know what to say. Yeah, but that's alright. Yeah, that's okay. I don't know anything. Hello and welcome to Factually. I'm Adam Conover. Thank you so much for joining me once again as I talk to an incredible expert about all the amazing things that they know that I don't know and that you might not know. Both of our minds are going to get blown together. We're going to have a great time doing it.

I don't know if it gets too repetitive when I say that at the beginning of every show, but I do kind of like it. You know, it's like a mantra. Let people know what the show's about and get on our way. Now, before we get going, I want to remind you that I am on tour right now. If you live in Philadelphia, Pennsylvania, or Raleigh, North Carolina,

come see me live. I'm at the Helium Comedy Club in Philly, the Good Nights in Raleigh. You can get tickets at adamconover.net slash tour dates. I got a brand new hour of stand-up. I do a meet and greet after every single show. Please come out. I always love to see you. And I especially love to see people who listen to the podcast. So many of you come up to me after the show, tell me how much the show means to you, and I can't thank you enough for doing it. Now, if you

can't see me live and you still want to support what I do, well, consider supporting me on Patreon at patreon.com slash adamconover. Five bucks a month gets you every episode of this podcast ad-free. You can join our community Discord. We even have a community book club where we get together and read recent nonfiction books together and discuss them over Zoom. It's a great time. Head to patreon.com slash adamconover. Now, this week on the show, we're talking about quantum physics. Quantum physics is often misunderstood, which is, you know, not surprising. It's, after all, the understanding of the physical world at its most basic level. And, you know, at that level, shit gets weird. It's complex and counterintuitive and bizarre. We have this

intuition that because it's so fundamental, it should help us understand our own lives in some way. But quantum physics is so difficult to properly comprehend that it's led to a lot of people misusing it or a lot of charlatans, frankly, lying about it in order to benefit themselves. It becomes a way to make anything seem science-y. You know, if you take a quick peek through the internet, you'll find people selling quantum spirituality, quantum wellness, even quantum astrology. And, you know, if you take a quick peek through the internet, you'll find people selling quantum spirituality, quantum wellness, even quantum astrology. And, you know, these things might be all well and good, but they have nothing to do with quantum physics itself. So here's what I'd like to know. What does someone who actually understands quantum physics and who can help us understand it think it has to say about the big questions of how we live?

Well, today's guest has the answer to those questions. Sabina Hassenfelder is a theoretical physicist at the Frankfurt Institute for Advanced Studies, and she has a fantastic YouTube channel with all sorts of very smart, very accurate science explainers, and her most recent book is Existential Physics, A Scientist's Guide to Life's Biggest Questions. Please welcome Sabina Hassenfelder. Sabina, thank you so much for coming on the show. Thank you. Good to talk to you. So you have a new book out. It's called Existential Physics, A Scientist's Guide to Life's Biggest Questions. How can we use physics to explain human questions? It's normally seen as a pretty impersonal field of science.

Yes, indeed. And this was one of the reasons I wanted to write the book, because I feel that a lot of people have kind of a bad start with physics in school. They get the impression that physics is basically about, you know, balls rolling down inclined planes and how do batteries work and that kind of stuff. And I wanted to say, well, physics is so much more than this. It tells you something about our existence because eventually everything in the universe

has to obey those laws of nature. And sure, I mean, physics doesn't really have to say a lot about life or sociology or psychology, but it tells you something about how all those particles have to behave that make up the brain. And we learn something from that. Yeah, and physics often seems to have this claim to be almost the most basic of all sciences, or at least the most basic that we have, although philosophers might disagree, I suppose. But at the same time, yes, I understand and I believe that my brain is made up of particles.

I'm a materialist in philosophical nomenclature that I believe that my mind is my body. My body is made of particles. But those things seem pretty remote from each other. That's like saying that, hey, I'm talking to you on Zoom right now, but my computer is nothing but electrons moving around. So if I understand electrons, I can understand what you're saying to me over Zoom. You know, they're at vastly different levels of explanation.

So how do you use, you know, understanding of physics to answer human problems? How do you bridge that gap? Well, I'm not using the foundational physics to answer human problems. If your problem is, say, I don't know, finding the key that you've misplaced or that kind of stuff. So, I mean, when you said that your computer

is just a bunch of atoms moving around or electrons and some kind of semiconductor or what have you, then the word just is doing a lot of heavy lifting. So, because, I mean, it's one thing to say, okay, we know what particles the thing is made of, and it's all in the sense of particle physics, and we know how to describe the interactions between those things. But a computer is more than just saying, well, it's a lot of particles. It's all in the particular configuration of those particles, and the same is true for your brain.

It's about the question, what can you do with it? And I would say that physics doesn't really have a terrible lot to say about the particular configuration of the atoms in your brain and what you can do with it. And I'm happy to leave this to neurobiologists or neurologists that don't ask me exactly what the difference is. I'm a physicist. But we can say something, for example, about the nature of time, which is something that we all perceive. And then there's the question, like, why do we perceive it one way and not the other way? Which, again, is a question that I would say isn't really in the realm of physics. But at least we can say something about what time fundamentally is or isn't,

and how we have learned it, just to give you an example. Or we can talk about questions like, what is everything made of? How do those fundamental particles behave? How did the universe begin? What are the limits of science? You know, are there limits to what we can possibly find out? And all of these are questions that find a place in the foundations of physics, which is why I think it's interesting. And it tells us something about our existence. Yeah. And when you get to the question of time, that is a fundamental physical property that

I am very concerned with. I do lie awake at night going, what is time? I'm about to turn 40 pretty soon, and I've started having the feeling of, like, hold on a second, it's, like, fucked up that I can't be young again, that I can't go, you know, like, I'm really starting to feel the, the passage of time, why is it one direction, what is it? So, so, uh, it's something that we're all very, very personally concerned with, even though it's, like, this fundamental, uh, factor of fundamental factor of physics. So let's talk about time. I mean, first of all, Sabina, what is time?

Sorry to ask you such a deep question right off the bat, but I am curious. Well, so physics doesn't really answer questions of this type. It's more that we have certain observations, and we have a good description of those observations. And to our best current description of the observations that we lump together as time is that time is a dimension. So this is how it works in Einstein's theories of special and general relativity. Time is a dimension, as opposed to being a universal parameter, which it used to be before Einstein.

So before Einstein, time was just this cosmic ticking clock that says, okay, now it passes one step to the next. And with Einstein, time became a label on a coordinate axis. And labels on coordinate axes are ambiguous. You can change them. You change to a different ruler or what have you, the same way you can do it in space. And it brings up the question, so then what does it mean?

What does time even mean? And it becomes very difficult to make sense of this. This is why people are worried about all those kind of paradoxes, like the twin paradox is one of the most famous ones that took some time to sort out, but we believe we understood it right now. So what happens is that time becomes this personal thing. So every one of us has their own ticking clock that depends on the exact way we move around in space-time. It's also called the proper time or the eigentime, if you like a German word. The eigentime in German.

Eigentime, yes. Eigent just means own. It's your own time. Yeah, and so this leads to some perplexing consequences. For example, in Einstein's theories, it becomes impossible to define one moment as now that we can all agree on. Any way you're trying to construct a moment of now, it depends on how you move. So every observer that moves at a different speed has their own notion of now. And, you know, who are you to say that one observer's now is any better than some other observer's now? So your now could be somebody else's past or it could be somebody else's future.

And the only logical conclusion you can draw from Einstein's theories is that all moments exist the same way as this present moment. This is what's called the block universe. Wow, okay, that was so much. All moments exist the same way as now, in that what every moment is now. This is almost a, I don't know if I want to say Buddhist or other, this is almost a religious thing that you've said, that everything, every moment is nothing but now. That's something that I've heard people say in a spiritual context. Am I making that connection correctly or is there something off about that? I've made exactly the same connection. And I say this in my book.

I think it's a fairly spiritual idea. And I think that a lot of physicists kind of hesitate to make this jump, you know, to talk about the spiritual underpinning. And it's something that I'm trying to get at in my book. I think this is a pretty big deal. At least for me personally, it's one of those things, you know, that we learn as students, like in the second year or something, a special relativity. And I think everybody's first reaction is like, wait, what? Like this can't possibly be correct. But you look at it and it's actually, you know, I mean, mathematically, it's not all that hard to see that it's not possible to define a moment that is now which works for everybody.

And then at some point you just accept it and you get used to it and becomes like this normal thing. So every once in a while, I think it's worthwhile to remind yourself, even as a physicist, that that's actually how nature seems to work, mind-blowing as it sounds. Has that affected you at all personally? I mean, again, this book is about, you know, existential questions, or that's the connection that you make. And in terms of, you know, when you wake up in the morning and watch the sunrise, you know, does understanding this about the nature of time change at all your personal relationship to your life or to reality? I'm just curious. So sometimes it does, sometimes it doesn't. So I think when I'm kind of stressed out, let me put it this way, you know, if I'm having a hard time or something, I like to remind

myself of those big things and put things into perspective you know um we're just this tiny little spot in in the whole timeline of the universe um you think about those big questions cosmological questions also about the beginning of the universe why do we only get older and not younger does the universe think it puts your own life nicely back into perspective. Yeah, it does. I was just, it's really funny. I was just yesterday watching the finale of this very popular show over here in the States called Better Call Saul.

It was the series finale of the entire show. And about half the show was taken off, taken up with the characters talking about the possibility of creating a time machine, time travel, where they would travel to. It's this sort of abiding fixation of not just writers, but just individuals. It got me thinking about time travel and about the impossibility of going back to a place in your own life.

We have this deep relationship with the concept of time. That's why the concept of time travel is so, uh, you know, fixating to people because we, because of that, it just contains like a wistfulness and a melancholy and a, and a, you know, reference back to your own memory. Um, and, uh, I don't know. I have to say that the prospect that I exist in my own time and no one else shares it with me makes me feel even lonelier about time. Sorry about this. It wasn't my idea. Well, look, I want to ask you about free will and so much more in just a few moments, but we have to take a quick break. We'll be right back with more Sabina Hassenfelder. Okay, we're back with Sabina Hassenfelder.

We were just talking about time. Let's talk about free will. What does physics tell us about free will? Does it exist? Sorry, I feel like such a jerk. I'm just tossing the most massive philosophical questions at you. You're here to talk about physics. Answer however you would like to that. massive philosophical questions at you. You're here to talk about physics. Yeah, answer however you would like to that. Yeah, well, I got myself into this with writing the book, right? So I can't

blame you. Yeah, so the problem with talking about free will, and I've talked about this a lot, and most of the time it didn't go very well, to put it mildly. And I think the problem is that no two people really mean the same thing by free will. We all have some kind of experience that we associate with this term free will. But if you ask people to actually define what they mean by it, it's kind of vague. And of course, there are lots of philosophers who have come up with one definition or the other, but they also don't agree. So the way that I'm trying to get around it is that I first say, well, what do we know about the laws of nature that are relevant to the question? And the relevant term to think about here is determinism. So determinism basically says that everything which happens now has been determined by what happened in the past.

And then that earlier thing was determined by what happened even earlier and so on. In principle, all the way back to the beginning of the universe, if you want to go all that far. So in a completely deterministic universe, everything that happens was determined already at the beginning. Now, this is partly how the laws of nature work that we use today, but it became a little bit more difficult with quantum mechanics, because quantum mechanics, at least the way that we understand it right now, has a completely random element. And it's not random just because there are some things that we don't know, though there are things that we don't know, but it's really fundamentally random.

There are certain things that can't be predicted. So every once in a while there is some kind of a quantum jump, so to speak. Now, the thing with those quantum events is not only can you not predict them, they are also not influenced by anything. They are the way that quantum mechanics predicts their probability and that's it. So since they are not influenced by anything, they are in particular not influenced by your will, whatever you want this to be. So that's what we have. We have deterministic time evolution for everything, including all the particles in your brain with the occasional random quantum jump. And now, you know, I could just ask you, would you say that given that you know this, do you think you have free will? this, do you think you have free will?

I would say no. By the definition by which I understand free will, I would say no, in that I don't feel that there is any sort of other, like, metaphysical force emanating from my brain or my soul that is causing events to happen, causing my muscle

to move. I think we live in a universe, as you describe, and I think that those laws govern the motion of my body at root, you know? That's right. So I would agree with this. This is also my understanding of free will, and it's how I suspect most people would react if you stop them on the street and ask them about it. But as I said, there are philosophers and also a lot of physicists who like to dabble in those things, have come up with definitions for free will that are compatible with this determinism

plus the occasional quantum random event. And they normally talk about how much you can influence, for which it's okay if the evolution is deterministic or with some random quantum event. They talk about the autonomy by which you can make decisions as opposed to, say, a toaster. You push a button and it goes plick. So a toaster doesn't have free will.

Why? Because it just reacts to what you input. The same is not as obviously the case for the human brain. It does a lot on its own. It doesn't rely as much on external input. So, this is basically one definition that I've come across. Other people talk about more difficult explanations in terms of causal modeling. And this is all fine with me. So, you know, if you define free will suitably, it's compatible with what we know about the laws of nature.

And it comes down to exactly what the definition is. I wonder, though, if that answer is suitable enough for people. I wonder, though, if that answer is suitable enough for people. If people will actually, you know, because what you're saying is that, well, in the absence of, you know, there's this, I think, older philosophical idea that, you know, the human mind existed in some sort of other material plane. You know, it's a different, well, there's physical stuff and then there's soul stuff. And the soul stuff, which is your experience of being conscious, can cause physical events to happen. And I think, you know, being good materialists, most of us wouldn't agree with that. But, you know, it still leaves, you know, makes us feel, OK, at the end of the day, we're atoms bouncing around.

And the laws that govern atoms bouncing around governs our actions. What you're talking about is a sort of more nuanced understanding of what free will might mean. Yeah, I'm different from a toaster. I'm a different sort of machine that is capable of much more complex behavior that is able to process information and then something happens to my brain 15 years ago and then it makes me do something today as a result of all these sort of mental processes

happening, et cetera, et cetera. And that explains how I am very interestingly different and valuable compared to a toaster. But I don't know if it does it still resolve that thing that people at root want to feel like they are not, you know, at at the mercy of forces that they don't control. You know, there's a there's a short story by the science fiction author named Ted Chiang. And it's called What's Expected of Us. I just looked it up. And it's a short story about a future in which people design like a box that through by some sort of discovery in physics is able to harness quantum mechanics such that the box is able to predict exactly when you're going to push the button that's on the box. A little red light flashes exactly a second before you push the box. And people try to beat it. They

try to say, oh no, it flashed. I'm not going to push the button. But they always end up pushing the button anyway. And if the light doesn't flash, they never push the button. And they can't really explain why. And it's basically direct proof to people that there is no, quote, free will in the old sense, right? That you are a collection of atoms. And the end of the short story is that people start committing suicide because they realize that, you know, that is what they are. I'm not sure I agree with that sort of catastrophic interpretation of what it would be like to have this proven to you. But it does sort of seem like there's a deeper unsettling quality to this knowledge.

I don't know. What do you think? Yeah, so it seems to me that this short story, which maybe I read it a long time ago, but I can't really remember, it's riffing off a proposal that was put forward by some philosopher a long time ago, which is a similar story. You give someone, basically this philosopher tries to prove that human behavior can't be predictable because if I gave you a prediction about what you're going to do, you would be able to do the opposite.

The issue with the argument is that it has absolutely nothing to do with free will. It's just that you have a system which is an open system and you input something, which is this prediction, and then the system reacts to it. So you can't predict the system without also modeling the entire system from the outside, including the prediction, which makes things much more complicated. But also, I mean, as you say, there is this deeper question about how would people react if they knew that their behavior is predictable. And I have to say that I kind of think I'm not in the business of only saying nice things, right?

I can't just, as a scientist, I can't only say the things that people would like to hear. And also, I mean, to be honest, I think people who have looked at the matter, like you are interested in physics, like you are, as your listeners are, they know this perfectly well, that there is this tension between what we know about the laws of nature and this naive interpretation of our free will.

So, you know, even if I would try to lie to them, they would probably know that I'm lying to them. So I think let's just be honest and talk about it. This is how it is. And so how do you make sense of this? Well, you know, one thing to keep in mind, this is something that I like to remind myself of, if you have a deterministic evolution, the way that we have it with the Hamiltonian in quantum mechanics, or even in general relativity, it's time reversible, leaving aside for a moment the quantum measurement, which we can talk about separately. And we often interpret this to mean that the present is determined by the past.

But the opposite is also true. The past is determined by the present, or to make it even weirder, the present is determined by the future, because those moments are all one-to-one maps to each other. So this, I think, is a pretty powerful argument to get you out of this. Oh my God, it's all been determined by the past. Well, it's also the other way around. The past is determined by the present. They're just all the same, which brings us back to this question about the block universe. I mean, I shouldn't say they're all the same. Of course, the configurations are different, right? If you look at the distribution of particles in the universe, but the information that's in it

remains the same. So this is one way to think about it. Another way that I like to think about it is that, yeah, so, you know, I'm just a complex computing machine, my brain is. It's good for some things, maybe not so good for other things. But I still have to make those decisions, right? That's what I'm here for, basically. So my brain is computing away, and I don't know what it's going to decide in the future. So I have to figure out what's going to happen. And so, I mean, of course, in reality, I live my life pretty much like every other person, because it's something that in normal decisions, you don't go through this whole elaborate metaphysical construct. But when I think about it, I think that that's the way I deal with it. You know, there is some kind of story in this universe and I have to live it out. I want to know what happens.

Wow, that is fascinating. I mean, it also, what you're describing is much more interesting than the naive version of free will. It's a more interesting question if you say, okay, we live in a deterministic universe, and therefore my conscious experience is just sort of me as part of this system. particles in my brain, but I'm experiencing that happening. You know, I'm experiencing what it is like to be a collection of particles that are deterministically governed by the laws of nature. That's a really interesting place to be and to ask questions about. And you get a more interesting set of questions than you do if you just sort of stick with the naive interpretation of free will. Wow, there's so much there. I wanted to ask a little bit more. You brought up the block universe twice at sort of the end of an answer and said, oh, this is the idea of the block universe. Can you expand on what you mean by that a little bit? What is the block universe?

Yeah, so the block universe is basically the insight that the present moment isn't special in any particular way. So there is no now, but all moments are already there. They sit in this mathematical construct, which we call the block universe. So this is basically a view from out of time, so to speak, in which we make a particular trajectory or a story, as I just put it. So we are in the block universe living out our lives to the best we can.

But if you were able to look at it from the outside, you would see it all at once. It's all already there. So that's the block, which is the universe. It reminds me a little bit of, I used to do video editing for a living, and it reminds me a little bit of what you're describing. It makes me think of a video editing timeline where you sort of see all of the clips all arrayed together.

You see the timeline from beginning to end. You can scrub through it as you want. If you like, you can play it from beginning to end, but that doesn't change the fact that it's all sort of sitting there at once. Is that sort of part of the idea that in a much more radical way, because you're saying there's also no

like objective unit of time, everything has its own timescale, but that it's, just that image of like all of space and time is just sort of sitting there as it is and we're experiencing one tiny part of it is that am i getting some piece of what you're saying yeah i like the analogy it's actually pretty good up to um as you say that in in a video you have this discretization with the frame rate, which we believe we don't actually have in the real universe. Okay, okay.

Well, I brought up the question of consciousness a few minutes ago. Does physics have anything to say in your view about consciousness and the nature of it? Well, some physicists think it does. I think the answer is probably not much. So I have tried to not say too much about it, because I think it's all fairly vague. There are certainly some people who are trying to use mathematics to quantify consciousness. And I talked a little bit about this. I think the best known approach to this is what's called integrated information theory. That's basically the idea that you can take any kind of system, really, but specifically

the human brain and look at its connections and how much information is shoveled around from one side to the other. And you count how well connected it is and how well it integrates the information, hence the name. And it gives you a number which they call capital Phi. So it's the big Phi. And that's supposedly a measure for consciousness. So if you have a big Phi, you're very conscious.

If you have a small Phi, you know, like a carrot, maybe probably has a very small thigh. So that's the idea. I'm highly skeptical that this particular quantification tells you a lot about consciousness. Some people have claimed that it has a certain correlation with people who are undergoing amnesia. They have a very small thigh. And if they're awake, it's larger. So that's not a terrible lot of evidence, I would say. I generally find it extremely implausible that something as difficult and complex as consciousness can be measured with a single number.

I would agree. I find this a little bit far-fetched. But in any case, I think it's probably, you know, this is the particle physicist speaking here, but I think it's probably correct on some level that consciousness is a property which emerges in highly connected systems that process a lot of information and have certain structures,

but we don't currently know what exactly those structures are. I think sooner or later we'll probably know. Yeah. Man, it's really funny because when I was getting my bachelor's degree in philosophy, as I've said on this show many times before, not much of a degree, but the question that always transfixed me was like, you know, the nature of consciousness because consciousness is the one thing in the universe that seems to be made of other stuff or has seemed to be made of other stuff than material reality

to many philosophers and thinkers. I don't believe that it is, but it's still one of the most fundamental mysteries to me. I'd be very excited if we soon figured it out. What other existential questions do you seek to answer in the book using physics? Or do you seek to at least talk about and address?

Well, I guess one of the obvious questions that people always ask is, how did the universe begin? This is also something which is very close to my own research area. I don't actually work on the very, very, very early universe, but I do something with dark matter and modifications of gravity. And I've been a little bit bothered by how this research area has developed in the past, say, one to decades, which is that physicists put forward more and more theories about how the universe could have begun. The one that pretty much everyone is familiar with is the Big Bang. So the Big Bang is what we get if we take the present state of the universe and we take

Einstein's equations and we just roll them back in time. And since the universe is presently expanding, if we go back in time, then matter becomes more and more dense until eventually at a finite time, which is about 13.7 billion years, we reach a moment where the energy density must have been infinitely large. And this is what we call the Big Bang. Now, nobody thinks that this is actually what happened. Probably the sign, probably that we get the singularity is just a sign that the equations break down and they would have to be replaced by something better.

Probably a theory that takes into account the quantum properties of space, but we don't have this theory. So this is the theory that's called quantum gravity, which we're still looking for. So this is somewhat unsatisfactory for physicists. So I think the honest answer to the question is how did the universe begin is we don't know. But what you can do is that if you go back in time, you change the equations. So you slide them over into slightly different equations, or I mean, you could just chop them off and add another equation. And this is something which you can certainly do mathematically. And what happens, of course, if you go back in time, you change the equations that you don't get the Big Bang,

you get something else. That could be, for example, a bounce. So this is quite popular. So you have an earlier universe that collapses and then it bounces and it grows again into a new universe. So in a Big Bounce scenario, you would have an earlier universe. Those bounces, in some theories, they can repeat over and over again. Then you get a cyclic universe. But it could also have been something else. We could have come out of a black hole.

It could have been a higher dimensional black hole. It could have been five dimensional. It could have been some kind of state that didn't have any time. That was just only space without time. So this is called a no boundary proposal. It was put forward by Jim Hartler and Stephen Hawking. And there are lots of other ideas. It could have been a gas made of strings, or it could have been a collision of high-dimensional membranes or something with the fifth force, and so on and so forth. So there are

loads of them. And I think that they're basically creation myths written in the language of mathematics. And none of them is actually supported by any kind of evidence. They can all be made to fit with the current observations. And if there will ever come any observations that don't fit with them, you can just fiddle with the theory until they fit. So this is why I'm a little bit unhappy about it. I'm not saying that they are wrong. I'm just saying that we don't have any evidence that speaks for them. So if you want, you can believe them. You know, if you want to believe that there was an earlier universe and I was just

bounced from that, that's fine. You can believe it. But it's not that actually science speaks for it. Wow. So, okay, hold on. So first of all, I want to make sure I'm understanding everything correctly. First of all, you said the story of the Big Bang, which is what everybody knows, you said nobody believes that actually happened. That's not actually a widespread belief among physicists. And that's because when you get to that, that very, very early singularity point, the equations that we currently have break down. Is that correct? Yes and no. So I think your confusion comes about because some people use the word Big Bang to actually to refer to much later moments. But the original meaning of the word Big Bang was actually this singularity.

And as I said, no one really thinks that this singularity actually happened. Now you can say, well, maybe I just use the word Big Bang to refer to whatever came after the singularity that we can agree on. Some people even use the word Big Bang to something that came much, much later. So it's a little bit ambiguous. But yeah, so in the original meaning of the word, it refers to the singularity, and we don't actually think that this happened.

So the expansion, that is everything, that did happen, but you're talking about the singularity itself, is that's where our understanding of that moment and what came before is there's nothing there. And scientists have been, in your view, just filling it in with their own creation. Hey, here's what I think might have happened. And the math checks out fine, but there's no particular reason to believe in any of it. Yeah, but of course, that's not the way that they say it, right?

But everyone has some kind of reason for why their particular theory is the best one of all the theories. Yeah, but the problem is, as you say, it's basically you just fumble the math together in place and then you weave some kind of story around it. And technically there are infinitely many stories you can weave around it because you can change the equations any way you like. And I just think it's bad science. Is this a state of affairs that you would expect to change as we make more fundamental discoveries

in physics? Is the Large Hadron Collider going to find anything that is going to help us? I'm joking, but that is going to help us solve this problem? Or do you feel that this is sort of a veil over deep history that we're never going to be able to get past because of how the math works? Yeah, basically, it's one of the ways that physics in particular, but science in general is fundamentally limited. But I should probably say it's quite conceivably the case that our theories for cosmology will get a little bit better. So I'm not saying we have totally reached the end. And if we're very, very lucky, then the Large Hadron Collider will actually discover some kind of new particle and we'll figure out what dark matter or dark energy is. I don't think it's going to happen, but it could happen.

And also, we now have the Webb telescope, which is collecting data from the very, very young galaxies, so much further back in time than we have ever been able to look. And this is telling us already, as we speak, about how structures form in the early universe, which will almost certainly help us improve the current theories. But the time that I'm talking about is much, much earlier still. And I think eventually we'll just run into a limit. And then you can make up whatever story you like, and you can just pick one of them and say,

okay, this looks better to me than this one, so I'll just stick with that. But it's kind of like, you know, different stories about the origin of the universe that you find in different parts of religion. Yeah, I want to ask you more about religion and science because it's come up a couple of times. We have to take one more quick break.

We'll be right back with more Sabina Hassenfelder. Okay, we're back with Sabina Hassenfelder. So right before break, religion came up again. There is something that you hear a lot from folks who are anti-science. They will say, oh, scientists are just, they have their own religion too, and they're just making it up in science as religion. Scientists generally push back on that statement and point out the very, very big methodological differences between science and religion and those types of knowing,

what belief means in vastly different meanings of that word in science and religion. You've brought it up a few times, and I'm curious what you think about that. Like, is there some element of religious thinking among, you know, some physicists to some degree or not? Yes, though they wouldn't call it religion. And I'm not entirely sure it's a good word, which I prefer to talk about spiritual ideas, but it's very, very similar to religious beliefs

that you find in some of the big organized religions. But it's, of course, true that science has a particular methodology which you don't use in religion. So in this sense, the knowledge discovery process is entirely different. But I'm very focused on the foundations of physics and by their location, so to speak, in the tower of knowledge, it's where you cross over into philosophy. And there are some physicists who are not mindful of when they leave the boundaries

of science, so to speak. And then they fill in a lack of knowledge with their belief, oftentimes without actually noticing. So this is, for example, what happens with these theories for the early universe. It's also why we have those theories of multiverses that you've undoubtedly heard of, like why do some physicists believe that unobservable universes exist? It doesn't properly sound like science. And to come back to the complaints from religious people,

I think partly what's happening is that they read some of this stuff, because, I mean, it's like in the foundations of physics, this is kind of really a niche topic, I have to say. Like, there are not all that many people working on multiverse theories, but they have a disproportionately huge impact on the popular science press. Yeah, we've had about five movies about multiverses come out this year alone. So, yeah, it's pretty popular. Yeah, and I can understand that because it's really thought stimulating, right? It's just fun to talk about.

Like, well, what could happen if you could travel to a parallel world? You know, maybe there are copies of me and so on and so forth. I understand why people are talking about it. But, of course, you know, the people say rightfully, if that counts as science, then I don't trust science. I don't think it's science. It's more like a kind of religion. And that's actually correct. But then they take the step and say, therefore, I throw out all of science.

This is the problem. And so this is also why I think it's really important that scientists are clear about when they move beyond science into speculation. It's not that I'm against people working on the multiverse or talking about the multiverse. I mean, you know, if that's how they want to lead their life, that's fine with me. But I have a problem when they make big claims that science actually supports this. But I do think that, look, scientists are humans walking around like anybody else. They have these existential questions. They understand science very, they understand the limits of the physics very deeply. But then they might get to a point where they're like, well, I just need to answer a fundamental philosophical or religious question about the nature of existence myself. extend it a little bit. I remember I interviewed a year ago Carlo Rovelli on this show, and he had a few statements that he went that far with it. He's like, well, here's how, this is what this makes me think about free will or consciousness. And I believe that he made that distinction and

said, I'm not talking about science anymore, but my belief here is informed by the science. And I think that is a really interesting area to explore if we are honest about the fact that, okay, we're leaving the boundaries of science a little bit. if we are honest about the fact that, okay, we're leaving the boundaries of science a little bit. Now we're talking about philosophy and spirituality, but we can do it while deeply informed by the science. That can be a really great discussion and exploration. Yeah, I would agree with that. Do you have one other sort of existential question you can share with us from the book that you explore within it?

I have to remember what we already talked about how about how will the universe end that's on my question list is that yeah well that's but that's a very brief one to answer i think in this case too the answer is we don't know though for a slightly different reason so when we try to answer the question how will the universe end uh we again take the present state of the universe, and then we take the equations that we have, and we extrapolate them into the future, sometimes over trillions of years. And the problem with this is that if there's any teeny tiny contribution to those laws that we currently use, something that is so small, we had no chance to

ever measure it, or maybe some kind of process that is so incredibly rare, we just have never seen it. That could make a big difference in the future. And so what's happening is basically that your error bars are just blowing up all over the place. And in the end, you just can't say anything. up all over the place and in the end you just can't say anything um so i mean it's again it's i mean if people want to talk about it as some kind of um mind exercise uh maybe um that's all fine with me you can for example ask like what's going to happen with galaxies what's going to happen with stars depends on how fast the universe is expanding um If it's expanding more slowly, then more of the stuff will clump and will succeed in forming black holes and so on.

So those are kinds of questions that you can reasonably address, but I don't think one should take it too seriously. Okay. When it comes to the end of the universe, don't take it too seriously. It's not that big a deal. When you said, you alluded to whether the universe is fine-tuned for life,

that's an idea that I've heard that the conditions needed for life are so rare and seem so impossible that is there – I've heard this idea that there's a multiverse, there's an infinite succession of universes. And the reason that we live in one where life is possible is because this is the only one that we live in. And so we just happen. I'm going to explain this very poorly that, you know, in this in this sort of infinite succession of universes. Of course, we have appeared in the one that has conditions that are right for life and that therefore the universe that we live in is somehow tuned for life. Is that an idea that you like or that you dislike? Well, I don't think it's scientifically fruitful.

It has very little to do with what I like, but I have to correct you on one point because you were talking about this succession of universes. Normally in the standard multiverse, it's not a succession. They don't happen in any particular time order. They're just all there, which makes it a little bit less confusing when you're talking about the idea that all of those constants, all of the combinations of constants are somehow there in this big multiverse. We just happen to live in one which is hospitable to life because otherwise we wouldn't be here to ask the question, like, why are the constants of nature what they are?

So I'm not particularly enamored with this supposed explanation, because if you look at what it actually does for you in terms of predicting observations. It does absolutely nothing. You know, just by saying, well, there's a multiverse and all possible combinations of constant exists. That doesn't do anything for you. If you want to make a prediction for what happens to the galaxies in our own universe, you still have to actually enter the values of the constants of nature that we actually observe. So from a purely scientific point of view, it does nothing for you.

So I would say, again, it's not a scientific theory. There are lots of words have been written about, you know, countless books about this idea that if we were to slightly change one or the other constants of nature, then life would no longer be possible. The problem with all those arguments is that they eventually rely on a statement about probability. It comes down to saying, and it would have been so improbable that we would have gotten just this particular combination, improbable that we would have gotten just this particular combination. Therefore, God must have made it, or therefore we live in a multiverse and all the other possible combinations also exist. So I'm lumping here together God and the multiverse, because I think from a logical

point of view, they come from the same place. Both of those arguments have been made to explain something that, in my opinion, doesn't need an explanation, which is why do we have constants of nature that have particular values? Well, maybe that's just because. That's the theory. Maybe there just isn't any explanation. I don't even know what could possibly answer this question. Now, you can go beyond the scientific question in which you would ask, well, what's the theory that I can write down that actually allows me to explain our observations and seek explanations beyond that? And then I would say, sure, you can believe that God made it.

It's not that this is wrong. It's just that it's not supported by science. Or you can believe that there's an infinitely large multiverse with infinitely many other universes with all constants of nature. That's fine. You can believe it if you want to, but it's not actually supported by science. Let's end here. I think this will be an interesting question to end on. Talking again about philosophy and religion. These are fields that, in the ideas that they share with the public, they generally come with this idea that they're going to be comforting to understand the wisdom that philosophy and religion have, or that they're going to help us live a better life in some way,

that answering these existential questions can bring people relief or can perhaps help them adjust their behaviors in some positive way. I'm curious if connecting physics to existential questions, if you think that's true at all of the answers that physics provides. Have you received any comfort in your own life from understanding these truths about time or consciousness of the universe, or do you expect that for other people having heard them? I'm curious. So before I answer the question, I would like to say that I think religion is much better at actually answering questions than philosophy. Philosophy, at least in the way that I look at it, it's better at classifying the possible answers. And then you can go and pick one, basically.

You can decide, am I a realist? Am I a structural realist? Am I an instrumentalist? Or, I don't know, a solipsist or whatever. You can just pick your philosophy and then you can go for it. And I do think that a lot of people find it comforting that you bring some order into this mess that are your thoughts. Now, when it comes to physics, I certainly hope that it'll bring some comfort to people.

I mean, it's not, I don't have any particularly great revelations there. Everything that I talk about is basically what we have learned in physics in the past 100 years. Maybe mixed some of the more modern stuff about quantum gravity. So it's not that I can say big things like we're all going to be reborn at the end of the universe or something like this. I'm really sorry. But at least for me, thinking those things through

has changed my perspective on life and the passage of time and also what to make of the eventual demise of our planet. You know, we know that the sun is going to blow up at some point and it's going to eat up our planet. And I mean, it's like eight billion years or something, but eventually it's going to happen. And I take some comfort in the fact that for all we currently know, the information that is contained in all the matter on our planet and also in everything that's happening on our planet can't be destroyed. Wow, Sabine, that is so fascinating. I can't thank you enough for joining us on the show. It's been wonderful having you. The name of the book, again, is Existential Physics, A Scientist's Guide to Life's Biggest Questions. You can get it at our special bookshop, factuallypod.com slash books. Sabina Hassenfelder, thank you so much for being on the show.

Wonderful to talk to you. Well, thank you once again to Sabina Hassenfelder for coming on the show. I hope you enjoyed that conversation as much as I did. If you want to pick up her book, head to factuallypod.com slash books. That's factuallypod.com slash books. I want to thank our producer, Sam Roudman, our engineer, Kyle McGraw, and everybody who supports this show at the $15 a month level on Patreon. That's Adrian, Akira White, Alexey Batalov, Allison Lipparato, Alan Liska, Ann Slagle, Antonio LB,

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