#113 Sabine Hossenfelder - Superdeterminism: Why Are Physicists Scared of It?

0:00Prime delivery is fast. How fast are we talking? We're talking puzzle toys and lick pads delivered so fast you can get this puppy under control fast. P-pads, coley mat, pet camera, fast and fast. And those training T-R-E-A-T-S, faster than you can say sit fast. Fast free delivery. It's on Prime. Your book Existential Physics begins with a mental health warning. Why did you put that in there? because I have gotten a lot of emails in response to what I've written and said about the absence of free will. So I think that we don't have free will. And it made me realize that some people find it hard to cope with.

0:43And they ask me like, so what's the point of life if we don't have free will, to which I don't really have a good answer. So I wanted to put this out at the beginning. And personally, I found it very difficult. Like when I was a student, I studied physics. So you get to the point where you're like, okay, so that's how everything works. This is fundamentally, this is what we're all made of, right? Atoms, and they do this thing. and so where's the space for free will? We can talk about this in more detail, but it's taken me some time to wrap my head around it and get comfortable with it. So I wanted people to know what they are getting into, basically.

1:28Yeah, I suppose there's an expectation sometimes on physicists or indeed philosophers who come up with these crazy ideas like free will doesn't exist or there's no such thing as ethics or questions about God or whatnot. And then people come to them and say, oh, so what should we do in light of that information? And it's like, well, how should I know? I'm just here to diagnose a problem or tell you something I think is true. It's up to you to figure out how to deal with that. But do you recognize, I mean, in the areas you touch on as a physicist, you're talking about free will, you're talking about consciousness, you know, you talk about God sometimes.

2:03Do you recognize the desperation in comments like that? Like when someone says to you, I'm having an existential crisis, do you say, I'm sorry to hear it, but, you know, I don't relate to that? Or is that something that you also have sort of gone through but just managed over time to deal with? Well, yeah, I did go through it and I managed to deal with it. No, I definitely don't ignore such comments because I worry about people. And I try to help them because, I mean, I kind of managed to make peace with it and I try to convey that to people, but still I don't know, does it actually work? So that's why I worry.

2:46I understand why people might find it hard. Like, what's the purpose of anything? What do I do with my life? Why do anything? So I kind of feel like I'm a little bit the wrong person to talk about it, but I feel like I can't not do it, basically. Yeah. Well, what are the principal areas? You already mentioned free will, which I think people can understand why not believing in free will would cause an existential crisis. But some people might be surprised to think, I thought that Alex's guest today was a physicist, and yet we've opened here by alluding to these existential problems, which are usually in the realm of philosophy.

3:28So what other areas can a physicist be writing about and touching on that get people to send you emails like that? So one rather obvious question or topic that physicists like to talk about is the beginning of the universe or the origin of everything. as some people would put it. And generally, the question like, where is space for God? Anything beyond the fundamental laws of nature? There's also, and this has become much more widely discussed in the past two years with AI being everywhere. Is there anything special about consciousness? or I mean this is the way that people put it but I think what they really mean is there's something special about us right and I think some people find this really really important like there's something different about us that we can't build with a machine and I just think there isn't basically I think we're all machines in some sense just made out of other stuff.

4:48And there's no reason why a computer shouldn't be able to become conscious. And I do think that physics has something to say about it because, you know, fundamentally, we're all made of atoms. Yeah. Yeah. I mean, you have a whole chapter in your book. It's called something like, Are We All Just a Bunch of Atoms? or something like this, which discusses this idea of what, if anything makes human beings or sentient minds special and yeah i mean it does feel as though there's me and there's you know this this microphone that's sat in front of me as i like to point to as an example all the all of the time and well what's the difference between them okay the size shape and color but it also seems like there's something that there is like what it's like to be me in a way that there's not a what it's like to be the microphone and that seems to have something to do with the internal first person perspective feelings the fact that i can close my eyes and imagine things that the microphone doesn't have so i've spoken to philosophers about this over and over again you know where does this consciousness thing come from but from a from a physicist's perspective if we are just talking about atoms bumping together you can understand why people find it so difficult to imagine that if you throw atoms together in the right order you create a rock or a microphone or some water or if you put them together in the right order then you get first person conscious experience and imaginary rocks and imaginary numbers and all kinds of stuff like that that just seems totally incomprehensible for some people Yeah, so I want to start by saying that the German title of the book is Merzner Atome, which means more than just atoms.

6:37So the point is, we're more than just atoms. So it's not just about the things that we're made of. It's about the way that they're connected. It's about what they can do, which is exactly what you just said, right? So the human brain can do more than your microphone. It's just much more complex. And so that's the question, like, is this the only thing? Like, is this the only difference that the human brain has just many more connections, many more things going on, and it has many more emergent features, as philosophers like to put it, than your microphone? And I think the answer is yes, that's it.

7:23At the moment, the human brain is much more complex than anything else we can think of, but it may not remain that way. And so a related argument that I bring up in the book is this question like, do we actually need these atoms? Can we build consciousness from something else? so there's the question like do we actually need this particular biological substrate so to speak is it somehow essential and I think that physics tells us that the answer is no because we know that the exact details of what's going on beyond a certain scale at very short distances actually don't matter for exactly how information is being sent around in the brain.

8:21It's got something to do with the way that things are connected. And that makes me think there's no reason why we shouldn't be able to reproduce this with some other system, be it silicon or whatever they now work with. I always hear people talk of graphene, but it never seems to become reality. Yeah. So I totally think you can do it on some other system. That doesn't mean that we've actually managed to do it yet. Yeah, sure. I mean, I think for a lot of people, they sort of just have this confidence that one day we'll work out how that process would work. But if we could conceivably just put atoms together in the same way, there's that thought experiment of replacing every neuron in your brain with like a transistor or something, you know?

9:12And if you just replaced one single neuron with with a transistor or some kind of silicon would you notice a difference and the answer's like no i think everything would function the same and the brain would still act in the same way and well if you just kept doing that over and over again at what point would consciousness switch off it kind of seems like it wouldn't right but on the other hand there is this feeling that like i mean the question i always ask people is is quite like visually laden but a lot of people can't like visualize things in their head I don't know if you're one of these people who can close your eyes and imagine the color red, for example.

9:46Some people say that they can't, some people can, but at the very least you can probably imagine a triangle in your head if you think of it and it's got three sides and there are things that are true and there are false about it. And so is it your view that say this triangle that I'm picturing in my head right now just somehow is the same thing as some kind of atomic structure within my brain because I think the dualist will think no that triangle exists in the mind because it's it's got spatial extension it's got three sides for example your brain the the atoms in your brain doesn't have those properties so what's your view on that discussion like what is this triangle where does it exist how does it exist yeah I wouldn't call it an atomic structure because that makes it sound like uh it is some sort of material in your brain that you're assembling, but it's something that's going on in the circuits in your brain, is what I would say.

10:44Actually, I think we don't even have to speculate about this because people are now doing brain experiments, not my area, but where they can basically read out what images people are thinking of. And so, I mean, it's at the time, it's not great, but at some point, we're probably be able to do it. Yeah, I see. And so like by looking at the brain structure, we'll be able to sort of see what it is that they're picturing in their heads, something like that, which at least shows an intimate connection between those two things. But for me, I've always tripped up on this mystery of the line between like the mental activity associated with the experience and the experience itself.

11:29In philosophy, the experience itself as separate from the mental activity, there's a word for it. They call it qualia, right? And you've just put out a video about how science might have something to say on qualia. It's often thought that that's kind of where the science philosophy divide is with consciousness. Science deals with the brain, philosophy deals with qualia. But what is it that was, you know, interesting enough about the relationship between science and qualia that made you think you need to make a video about it recently. Yeah, so maybe let me say a more general thing. So I do these science news, I report on what other people do.

12:08So it's not that I did this research or something. And so what the video was about is that I see this trend of people working in neurobiology or neuro something, who write papers about how they've measured qualia, like it's a thing. And so the video was about this trend, basically, that this qualia is moving from the side of philosophy to the side of science, where they just go and measure it. At least they call it qualia. I guess there are philosophers who would disagree that this even is qualia. So, of course, if you define it as something that's unmeasurable, then we don't have to talk about it because you've defined it that way.

13:02So that makes it by definition unscientific. But I think if you're talking about this spirit of what was supposed to be, like this subjective experience, then you can measure it. you know, it's something that's going on in your brain circuits. Of course, that doesn't mean that somebody else can experience exactly the same. Because I would say we're the only way that somebody else can experience the same as some other person if they actually are that person. So that doesn't make any sense. Yeah, that's interesting what you just said about defining your terms. It's like, well, okay, scientists are beginning to study qualia, but philosophers look at that and go well the fact that you're studying it means it can't be qualia because you know qualia is something that can't be measured when you think of like redness or a triangle in your head or something do you think do you like understand the philosophers critique where they say that there is something about that individual experience of redness which is just inaccessible to the scientific method as in like do you think that it's appropriate to cool qualia that thing which is inaccessible to science or are you sort of more optimistic about the breadth of what science can do i i don't know what the part would be that's inaccessible to science so you you do have an experience we can measure that in principle you know maybe not in practice yet uh but in principle we could so i i don't see what else there is i'm sorry i'm a physicist all the way down.

14:45You know, the famous Mary's Room thought experiment? There's the girl in the room. So for the audience, there's a girl in a room called Mary. And we can imagine that she's given access to all of the information that could exist about the color blue. That is not just like the Wikipedia page that we've got today, but like every bit of information we could ever have about the wavelengths, about the science of the eye, about the psychology of the brain. She reads up and is an expert on all

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15:43but she's never seen the color blue. But she knows everything that could be put into words about the color blue. And the question is, if she then, after learning all of that, walks outside and sees blue for the first time, does she learn anything new? And for a lot of people intuitively, the answer is yes. But if the physicist says that everything about the experience of blue can be described in in sort of scientific uh language would you therefore say that she doesn't learn anything new when she steps outside of that room or is there some sort of third answer that i'm missing well first of all i'm now super confused because i thought the color was red but i mean you never know maybe her blue is my red or the other yeah exactly yeah yeah yeah no of course she learns something new when she gets when she goes outside because you know suddenly she has uh you know photons of a certain wavelength hitting her eyes and and that sparks some reaction uh which she didn't have before so it's just a different thing um so so of course just you know having a physical sensory input isn't the same as learning everything about uh what the brain does in response to that input so those are just two different things i see so so i guess the question you could ask is like uh imagine she had all this information about uh what people experience uh when they see the color red or blue whatever and she also had a sort of brain stimulation machine uh by the help of which she could you know excite certain neurons in her brain if she knew exactly what to do, would she have the experience of seeing the color red?

17:31And my answer to this would be probably yes. Going by everything we know about how similar brains are. Now, you could always argue that, of course, strictly speaking, your red isn't exactly the same as my red because our brains are slightly different. But I would say, well, they're probably similar enough. that's really interesting i guess that would count as a third option which is that to to sort of truly know everything about blue without seeing blue you would also know exactly how to prod the brain in a right in the right way to bring about the experience of blue such that if she had the correct equipment to prod the brain in that way she could bring about that experience of blue and learn what that experience was like without actually seeing something blue like in the room is that what you mean yeah right that's interesting so you don't actually need the photon hitting your eye if you know what what it does in response in your brain basically i see that's that's cool that's cool and so the center of consciousness is the brain and consciousness is just like the product of complex arrangements of things or something like that like atoms arranged in a complex enough manner gives this centralized experience of consciousness because one of the other mysteries is like why if there are lots of moving parts all put together why there's like this one singular you know uh center for the consciousness you know yeah well so i think at this point it gets very difficult because we don't actually know exactly how consciousness works and everyone has their own theory about it uh and i i you know um i i think it's probably quite complicated.

19:22You need different specialized parts of the brain that do different things. And you think that that's ultimately going to be a scientific rather than a philosophical question, or do you think that that's a bit of a phony distinction? I think it's going to move from the philosophical realm into the scientific realm. And we're just we're witnessing this move right now basically. So at the moment I think if you look at those theories of consciousness they're all very very basic and I find them all quite unconvincing but I don't know give it a hundred years or who knows if AI comes and they'll solve the problem in about no time.

20:10There is also this I guess perception among some people that science and philosophy are at odds to the extent that a lot of physicists look at philosophy and sort of think that it's a watered down or ancient version of what the physicist is doing. I'm thinking of people like Lawrence Krauss, who've just said that philosophy is kind of nonsense. I think it assumes that there's like an empiricism to knowledge, that anything that can be meaningfully known is something that is open to the scientific method, is testable, that kind of stuff. given that you've written quite extensively on what people would call philosophical topics in existential physics what is your relationship to philosophy generally do you do you look at it that way or do you have a bit more time for it well i'd say there's good philosophy and there's bad philosophy um so you need to know what to look at but you know actually i think there's a second-order problem with the physicists that look down on philosophy, which is that a lot of philosophers think that all physicists look down on philosophy.

21:18So I get a lot of hate from philosophers because I'm supposedly dismissive of philosophy. And I'm like, no, no, I'm just dismissive of what I think is bad philosophy, like panpsychism, if you want to talk about this at some point. But no, I actually think that most physicists, and I totally disagree with Lawrence Krauss on this. Don't take philosophy seriously enough, especially when it comes to the foundations of physics. Think of stuff like quantum mechanics. You need to know where does the science and where does the philosophy start? And I think physicists are really, really bad at figuring out where they cross over into philosophy.

22:05And this is where a lot of things go wrong. And I wrote about some of these issues already in my first book, like when they make mathematical assumptions that are actually metaphysical and they don't see the difference. So they think it's a requirement. It needs to be. It's mathematical, right? When it's actually something else that they postulate the laws of nature must be like. and so I think that this is a huge problem which is why I got interested in that and then as you probably know philosophy is kind of the rabbit hole once you start looking into it I'm really interested in what you said about I guess like philosophical assumptions that people unknowingly embed into their scientific worldview so famously Albert Einstein sees that his equations point to a finite universe or something like this.

23:21And so he adds in his cosmological constant to his equation so that the universe could be eternal. Because of course, philosophically, he knew that the universe had to be eternal, just like Aristotle thought and everyone in between. And so he adds in this constant and later takes it out again and calls it his greatest blunder right and that blunder that einstein if einstein can do it we can all do it made was a result of essentially a philosophical assumption that well the universe has to be eternal because otherwise it sort of wouldn't make sense we now don't think that's the case at least this universe is probably not eternal but that philosophical assumption changed what einstein ended up you know finalizing his equation as if i'm if i'm not mistaken And I suppose that's something that can sort of crop up everywhere.

24:11One of the really big assumptions, philosophically, that seems to send people into an absolute frenzy when it comes to all areas of science is the existence of free will. You've already mentioned it, but there's a particular area of application here. Now, I'm hoping you can help me understand this. I did a video recently called the existential crisis iceberg where I went through all the different levels of Of ideas that might give you an existential crisis and somewhere near the bottom Was this thing called super determinism Now super determinism is something like Determinism, but as applied to the quantum realm everything is ultimately fundamentally determined And if i'm not mistaken a lot of physicists reject this they say super determinism is nonsense and at least a lot of them do that because they have to assume that free will exists or something like that.

25:02Can you help me understand what's going on there? That's a very interesting question. I think this has a long historical backstory. So if you don't mind, I'll try to briefly summarize it. So we already talked about Einstein. Einstein, for all I know, didn't have any strong feelings on this free will thing, but Niels Bohr did. Niels Bohr, interestingly enough, he wanted quantum mechanics to be indeterministic because he thought that makes room for free will, which I think is a position that most philosophers now reject. But for him, that's actually what he wrote, if I remember this correctly, in some letters to Einstein.

25:54So for Bohr, who's often credited with being kind of the father of the Copenhagen interpretation, this was really important. So now Einstein had misgivings about quantum mechanics that didn't have anything to do with free will, but it was the measurement process so the collapse of the wave function is faster than light and of course Einstein didn't like this this is what he called spooky action at the distance so he tried very hard, he had a long argument with Bohr to try to pin it down like something is wrong and he ultimately failed at it but he had this idea that there is an underlying probably deterministic reality in which particles all have definite properties.

26:47So there's nothing of that sort going on that you can't measure two things at the same time or that particle goes in two places. He didn't like that sort of stuff. He thought a particle is a particle, a particle goes one place, and that's the end of the story. We just don't know where the particle is going. So Einstein died, And then came John Bell, who tried to finally pin down the difference between the Einstein view and the Copenhagen interpretation. And this is where Bell's theorem comes from. So he said, let's assume that Einstein was right. And there is this underlying reality, which is deterministic, and it has no spooky action.

27:37It's local. there's nothing like a collapse going on then what are the predictions that they sort of theory generically would make and how does it compare to quantum mechanics and so now here's the thing in his proof he made an assumption which is now called often the free will assumption and you need this assumption that the experimenter has free will to derive this inequality, which basically says that the Einstein type, local theories, local deterministic theories obey an inequality which we know experimentally is violated. So if you make this assumption, if you make the free will assumption, then the Einstein idea is ruled out.

28:30If you throw out this assumption, you get what's called super determinism. And then you can reproduce our observations with a local deterministic theory of the type that Einstein might have had and might or might not. Unfortunately, we don't know what he would have thought about this. So this is the reason why free will became tied up with with this super determinism thing. Now, the issue is, though, that if you look at exactly what do they mean with free will, it doesn't have anything to do with what philosophers normally, or even, you know, stand up people on the street. Let's not even talk about philosophers mean by free will.

29:18It's an assumption that's, you know, more technically, it's known as measurement independence. It's got something to do with the correlation between the thing that you want to measure and the measurement settings. You can choose measurement settings with a computer. It doesn't necessarily have anything to do with free will. But yeah, so this is where it came from. And I think part of the reason this happened is that Bell himself, in his original proof of the theorem, seemed to have not noticed that he even made this assumption. So this was later pointed out to him by, among other things, John Clauser, one of the guys who won the Nobel Prize in 2022, that there was this extra assumption, which Bell then justified by alluding to free will.

30:15I see. So you can kind of think, he must have thought like, damn, right? So suddenly there's this hole in his theorem. So he had to come up with a reason for why we need this assumption. And that was free will. That was free will, yeah. Interesting. So let me see if I've got this right, right? So we've got this weird quantum stuff that goes on. People can imagine like the double slit experiment where there's like a wave pattern, but if you observe it... With the Venmo debit card, you can Venmo everything. Your favourite band's merch? You can Venmo this. Or their next show? You can Venmo that. Visit venmo.me slash debit to learn more.

30:55The Venmo MasterCard is issued by the Bancorp Bank and a pursuant to license by MasterCard International Incorporated. Card may be used everywhere MasterCard is accepted. Venmo purchase restrictions apply. And it's a particle, all a little bit strange. And so there's this Copenhagen interpretation which says that the electron is actually a sort of cloud of probability, a wave function, which is a sort of prediction of probabilities of all the places it can go. And when you observe it, what happens is that wave function collapses, so to speak, and the particle is in a particular place. And that happens when you observe it.

31:24Before you observe it, there's this big wave of probability. The problem is that if you've got this wave of probability that goes from my left hand to my right hand, and then I observe it, and it collapses, and the particle's on my right hand, there needs to be this information over at my left hand that the particle isn't there. But because it happens instantaneously, this information seems to travel from my right hand to my left hand in an instant, which means faster than the speed of light. So Einstein says that can't happen. Therefore, this idea that the electron is just a cloud of probability is wrong.

31:59There must be some kind of foundational nature. It must have of foundational property we just don't know what that is yet and so after this bell wants to retain the idea that information can't travel faster than the speed of light that everything is local in other words it has to if it's at my right hand it stays at my right hand it can't just zip across space instantly and in order to retain this locality he comes up with this bell's theorem but that theorem assumes something it assumes something about the way that the the scientist interacts with the experiment which is an assumption but he doesn't realize is an assumption and only later when that assumption is pointed out to him he says okay well if we didn't assume that then free will wouldn't exist and that was the reason he gave for agreeing with this assumption.

32:56But we could just deny that assumption and everything still works. Something like that? Yeah, almost. I made two notes about things that I'm slightly unhappy with. One is you said something about the way that information travels. So there isn't actually any information being exchanged. This is actually the big headache because if there was information being exchanged faster than the speed of light, then we could measure it. So the entire problem with the collapse of the wave function is that it's completely unobservable. So there's nothing observable actually going faster than the speed of light.

33:37I mean, it would actually be cool if that was the case, right? We could send information faster than the speed of light, but that isn't so. So this is the one thing. The other thing is that mathematically, this assumption to Bell's theorem doesn't really have anything to do with free will. That's just an interpretation. So what it really is like mathematically, it's a type of correlation between things. and you can try to connect it to the choice that the experimenter has in deciding what to measure. You can actually, since you mentioned the double slit experiment, you can actually see in the double slit experiment why that helps.

34:32Because one of the weird things about the double slit experiment is, so you have these two slits and then you get a wave pattern that comes from the interference of the two parts of the wave function that go through each slit. So the weird thing about this is that the one particle even if it's only one particle it kind of needs to go through both slits to interfere with itself because if it goes through only one slit it can't interfere with itself. So now what you can do is you can put a measurement device into one of the slits. And what happens then is what you said, is that the interference pattern goes away.

35:16Because now the particle kind of, it knows I'm being measured. So it goes only one step. So either it goes in the detector, then the detector goes pling, or it doesn't, then it goes through the other slit, but you don't get the interference pattern. So now, I think you can see from this example that if the particle, what the particle does, does it split up or does it only go one way, is correlated with what you measure. Do you measure at the slit or do you measure on the screen? Then you can explain what's going on. because if these two things are correlated, then you have a deterministic variable that tells you, does it go through both slits or does it go through only one?