The Trouble With Quantum Physics, and Why It Matters

but thank you yeah first of all I just want to say thank you for having me here at kayuu it's a real pleasure to be here and talk with you for the department colloquium today without any further ado let's talk about the trouble with quantum physics and why it matters well actually first can everybody hear me okay okay good Oh wonderful my computer turned off yeah oops yes that's the trouble with quantum physics and why it matters it turns our computers off anyway quantum physics works I think we all know this it works phenomenally well it explains an enormous variety of phenomena to an incredible degree of accuracy you know it explains why I'm not passing through the floor right now it explains why the Sun shines and why I can see that the Sun shines you know it explains the nuclear hearts of the most distant space probes it helps us build all of the technology that's being used to present and record this talk right now it powers you know our medical imaging scanners and the lasers in the supermarket checkout scanner quantum physics certainly works but there's a problem quantum physics works but there's something funny about it it's certainly strange but the strangeness of quantum physics that's not a problem the world is a wild and woolly place there's plenty of room for strangeness the problem is that it's not totally clear how the theory lines up with the everyday world that we see around us and that's reflected in the mathematics of the theory itself so here's the Schrodinger equation right and we use that to describe how quantum states evolve when nobody's looking at them and you know those quantum states evolve smoothly they don't jump around there's just you know smooth undulation from one state to another this is why we call this a wave equation right waves wave but then there's the board rule right that's the lower equation and that's different it's uh it says that when we look at quantum states they jump they they pick an eigenstate of the basis that we're measuring them in and as you may have noticed these two equations they're not the same which leads us to the question when do we use one of these instead of the other now the usual answer to this question is will we use the Schrodinger equation when we're not making a measurement and then we use the born rule when we are which is true as far as it goes but what's a measurement is a measurement just when I look in which case why am I talking about quantum mechanics with all of you when it only applies to me is it just when humans look well you know we seem to think that quantum mechanics is probably true even before there were humans around you know we don't like to think that the wave function of the universe was waiting billions and billions of years for someone to come along like a Paramecium or maybe a better qualified observer like someone with a PhD that's not how we think the universe works so what's a measurement well that's not entirely clear and so this gets a special name the measurement problem you know when we're not looking before wavefunction collapse the wavefunction is you know spread out and then when we look we find a particle in a particular spot in the wavefunction instantly goes to zero everywhere else now it's tempting to say that this is about probability which is you know what we usually do when we talk about this but if it is about probability it can't be about probability in sort of a straightforward normal way what is it the probability of well the wavefunction we usually say it's the probability of finding a particle in a particular state fine that's fine but wave functions perform some tricks that we don't think of normal probabilities as being able to do so for example wave functions can interfere with themselves and diffract these are not things that we think of probabilities as being able to do so we can't just say it's probability there has to be something a little bit more going on there there has to be more to the story and there's also the problem of okay what's going on before we look when we look we find particle in a particular state what was going on before we looked well usually before we look objects' are in superposition of states what is a superposition what does it mean for something to be in a superposition why don't we ever see things in super positions and this leads us to the best-known problem associated with the measurement problem Schrodinger's cat right we've all seen this before you've got the slightly radioactive metal hooked up to the radiation detector and if the radiation detector measures some radiation coming off of the metal then it will smash the vial of cyanide and kill the cat that is sealed inside of the box now if you seal all this up inside the box and then you wait the right amount of time then quantum mechanics says that the radioactive metal will be in a superposition of both having emitted radiation and not having emitted radiation which means that that superposition will get entangled with the rest of what's in the box and you will end up with a box with its interior in a superposition of cat dead and vial smashed and cat alive and violent act now what happens when you open the box will you either see a dead cat or a living cat do you really think that if you open the box and see a living cat that the cat was not alive the moment before you open the box this is what or when Schrodinger asked when he first posed this puzzle in 1935 Schrodinger was not trying to he was not trying to show the strangeness of quantum mechanics as a beautiful feature of the theory he was trying to show that this was a problem it was a bug not a feature Schrodinger's cat said Schrodinger showed that there was a serious problem with her understanding of the theory not that it was wrong just that it was incomplete there was something missing from the theory itself but Schrodinger's contemporaries by and large they didn't agree here's uh here's Niels Bohr here's Werner Heisenberg in the 1930s they just didn't agree with Schrodinger at all they denied exactly the point that he was making that you could talk about the cat being alive or dead before you open the box some of them said oh it's meaningless to talk about what happens before you open the box because before you open the box you can't see what's happening in principle and so that means it's meaningless to talk about it because it's in principle unobservable other people said no it's the act of opening the box that forces the cat to be dead or alive and other people said you know Irwin you're worrying about what the world is like physics isn't about what the world is like physics is just about issuing predictions about the outcomes of experiments that's all that physics does and this set of vaguely related and questionably coherent claims eventually came to be known as the Copenhagen interpretation of quantum physics the standard way that we talk about these things don't ask what's happening when you're not looking you can't talk about what's happening when you're not looking and eventually a slogan came to be associated with the Copenhagen interpretation shut up and calculate now there are some virtues to this right remember quantum physics works incredibly well right there are some reasons why we might want to shut up and calculate because it lets us get on with the work of actually calculating outcomes in quantum mechanics and that lets us do a lot of really really interesting science right but there are a few problems one problem is that if we really say that quantum physics has nothing to do with the world around us it's just like a black box an instrument where we turn the crank and it issues predictions then the explanatory power of quantum physics is pretty much zero because it's not related to the world it's just a black box it's just an instrument so it doesn't explain anything it just tells us how things will be second the fact that the theory works as well as it does would be a phenomenal miracle if it were completely unrelated to the stuff of the world if the theory just accidentally gives us phenomenally accurate predictions over and over and over again it stands to reason that there must be some connection between the mathematical structure of the theory and the stuff in the world and yet we don't know what that is another problem of course is that this isn't how we think about any of our other physical theories right we don't talk about Maxwell's laws this way we think that there are electric and magnetic fields and that they are things that are out in the world and Maxwell's laws tell us how those fields behave you know this is this is a strange way for us to be think about one of our best theories about the world and finally you know if you really insist on saying no measurement is essential to quantum mechanics there has to be a system that is the measuring device and a system that is not that is the the observed system then have fun doing cosmology where you want to talk about the entire universe all at once so that's not going to go too well for you now this is the part of the talk where I have to give a couple of warnings the first warning which is the warning I don't need to give any of you but I give when I give this talk to the public is that you know of course this is not the standard way that we talk about quantum mechanics I'm giving you a sort of minority or dissenting view but I'm still pretty confident in that dissenting view and part of it is that you know a lot of people have thought about quantum mechanics for many decades a lot of philosophers have done a lot of good work in the foundations of quantum physics a lot of physicists have done good work in the foundations of quantum physics and that makes me feel pretty confident in the view that I'm giving you which is compared to the views of some of those people fairly conservative part of the reason why I feel confident in this is also due to the work of many historians of physics who have really put the lie to some of the standard stories that we tell about the history of quantum physics itself and that leads me to the second warning which is the best psychology research says that if you want to debunk a myth you shouldn't start by repeating the myth I'm going to ignore that research I'm going to rehearse the myth that we all know about the history of quantum physics first and then I'm going to tell you what really happens so I'm going to signpost this as best I can so first here's what didn't happen here's the myth once upon a time there were a group of brilliant physicists in the first quarter of the 20th century who worked together to come up with one of the ultimate achievements of the human intellect quantum physics these physicists included Niels Bohr Verner Heisenberg Wolfgang Pauli whose back is to the camera because I couldn't find a picture of the three of them together where he had his face to the camera but but yeah those three many others Paul Dirac Max Born Max Planck and perhaps most famously of all Albert Einstein now Einstein had been a bomb-throwing revolutionary in his youth but by the time quantum physics came along he was elderly and not at the height of his powers anymore and he simply couldn't accept the randomness that appeared to be inherent in this new theory that he was partly responsible for he could not accept that the universe could be anything other than deterministic he said God does not play dice he knew that this theory had to be wrong deep in his bones and so in an attempt to show that it was wrong he put together a series of thought experiments that that were meant to show that the uncertainty principle a core part of the theory itself had to be inconsistent that there were experimental ways around it so he kept proposing these thought experiments and then Bohr and company would knock them down and show that Einstein was wrong and this culminated in a particularly embarrassing episode in 1930 where Einstein tried to get around the energy time uncertainty relationship with a Rube Goldberg contraption with a a box hanging from a spring scale with a little door in it that would let out a particular photon of light at a particular time with a specified energy and a clock hanging off of the box and then Bohr showed that this ingenious scheme failed because Einstein had not taken his own theory of general relativity into account when coming up with this thought experiment and so slinking away in the deepest humiliation Einstein finally came up with one last thought experiment which he thought would really end this quantum charade called the einstein-podolsky-rosen thought experiment which he said showed that there was spooky action at a distance in quantum mechanics Bohr replied to this and said no there isn't and and or rather Bohr replied to this and said no there's not a problem here Einstein is wrong and quantum physics is fine and that's how it stayed for a long time until both men were dead it was thought to be a philosophical point of little interest until one day a brilliant physicist named John Bell came along and showed that no it was a matter of experiment you could show whether or not Einstein was right and Bell set out what you would have to do to do that the experiments were done and quantum mechanics was right Bohr was right Einstein was wrong and the world was finally safe for quantum mechanics and everybody lived happily ever after so first of all raise your hand if you've heard something that sounds a lot like that before yeah okay so how much of it is true well some one or two things about it are true but not a whole lot it is certainly true that there was a brilliant team of scientists who working both individually and collectively came up with what we now call quantum physics and the first three decades of the 20th century it is true that among them numbered Niels Bohr and Verner Heisenberg and Wolfgang Pauli it is also true that at the time that the first full theories of quantum mechanics were showing up in 1925 or 1926 I say look like this he was he was in his mid 40s he was not elderly he was not senile he was not having problems thinking clearly quite the opposite it's also true that Einstein had problems with quantum physics but it is not true that his primary problem with quantum physics was the randomness of the theory he didn't like that he wasn't thrilled but his letters and writings at the time make it very very clear that he had two primary concerns about the theory he was concerned about locality and he was concerned about realism he wanted to be sure that things were there whether or not we look at them and he wanted to know that things in one place can't instantly affect things in some other place he felt that these were two fundamental principles upon which all of science were based his concerns about randomness were secondary at best he made it very very clear that these were his problems and indeed these were the things that were at stake when Einstein came up with his series of thought experiments almost none of them were meant to go after any sort of uncertainty principles they were instead meant to demonstrate that quantum mechanics had a problem with locality and indeed that's what this thought experiment was meant to show this is a diagram based on a sketch made by Niels Bohr and it is incomplete Einstein's original thought experiment here included a mirror a light year away and it is unclear if there was a spring scale or a clock involved and this was actually a very early form of the EPR thought experiment it had to do with locality it had nothing to do with the energy time uncertainty relationship so Bohr completely misunderstood this and many other thought experiments and that actually gets worse for Bohr because even if Bohr was right about even if he had been right about what Einstein was trying to get at here which letters from Einstein and ehrenfest at the time make it very clear that this was nothing to do with the energy time uncertainty relationship but even if it was Bohr's reply and let me just lay this out for you Bohr's reply was Einstein your attack on the internal consistency of quantum mechanics is wrong because it violates general relativity a theory that we still don't know how to make work with quantum physics so his reply to the thought experiment that Einstein wasn't making was completely inadequate there is actually a way around this thought experiment that Bohr thought Einstein was making that works entirely within quantum mechanics before did not provide that so this should have been a massive humiliation for Niels Bohr but instead I'm Stein simply felt like okay he's still not getting it let me try again so here's I sign and Bohr talking at Aaron fesh house in the 1930s Einstein goes back and works with his colleagues Podolsky and Rosen and comes up with the EPR thought experiment which yes is about spooky action at a distance but specifically says look you have a forced choice here one of two things has to be true either the universe is non-local there's an instantaneous action at a distance or quantum physics is incomplete there are features of the universe that quantum physics does not fully represent this was what Einstein was trying to get at with the EPR paper it's very clear if you read that paper and even more clear if you read Einstein's later writings on the subject especially in his 1949 Festschrift Bohr's reply to EPR was um I'm gonna call it not clear Bohr himself actually later apologized for what he called the in Felicity of expression in his reply to EPR but he then didn't go on to explain what it is that he was trying to say in EPR or in his reply to EPR it is a very very strange document among other things that replied that Bohr gave for a long time the best place to get it was in a book edited by wheeler and Zurich called quantum theory and measurement that book came out in the early 80s and for about ten years two pages in Bohr's reply which was only four pages long were swapped and nobody noticed for ten years so that tells you something about the intelligibility of the writing of the great physicist Niels Bohr in any event many people were still convinced that Bohr had to be right nein Stein had to be wrong part of the reason was that you know Einstein wasn't proposing an alternative or a completion to quantum physics part of the reason was that Niels Bohr had tremendous you know group of people who had worked with him whereas Einstein sort of went through his professional life mostly alone but part of the reason was also due to a theorem from john von neumann that showed up in his famous quantum physics textbook of 1932 in that book von neumann presents a theorem that he says shows that the fundamentally statistical nature of the quantum state cannot be avoided there's no way to further complete the theory without just replacing the theory with an entirely new one and people took this at face value there were a few people that questioned it the first person to find that there was a serious problem with it was the mathematician and philosopher Greta Hermann who is a student of emmy noether she found a problem with von neumann's theorem in 1935 just a few years later but very few people listen to her in all likelihood at least part of that problem was or part of the reason that very few people listened to her was because she was a woman at a time when women were still generally not allowed to teach at universities but by and large people thought that von Neumann was right which you know he's John von Neumann it's it's pretty reasonable to assume that he's right he was usually right but in this case he was wrong and he was shown quite dramatically to be wrong by David Bohm in the 1950s now Bohm came up with an entirely new interpretation of the same theory of nonrelativistic quantum mechanics he found a way to add extra variables hidden variables to the such that particles have definite positions at all times under all circumstances while still being mathematically identical to regular nonrelativistic quantum mechanics in all of its experimental outcomes so for example the way he does this is essentially he says that every particle has associated with it a pilot wave and that wave guides the motion of the particle and so for example in the double slit experiment the particle goes through one slit but the wave goes through both interferes with itself and guides the particle to the correct position on the photographic plate leading to particle trajectories that look like this and give you an interference pattern that is built up one particle at a time now whether or not this is correct it certainly shows that von neumann's theorem had a serious problem but Bohm didn't do a very good job of identifying what that problem was in his paper and Greta Herman's work was still mostly unknown it took another physicist who was inspired by Bohm's work to figure out exactly what was wrong with von neumann's proof and that was John Bell John Bell hated the Copenhagen interpretation he said it was rotten he liked to reference Hamlet a lot when talking about the Copenhagen interpretation you know hence the rottenness right something rotten in the state of Denmark so Bell saw poems papers in 1952 and he said he'd seen the impossible done he immediately knew that von Neumann had to be wrong the problem is he'd only heard about von neumann's proof he hadn't read it yet he hadn't read it yet because von neumann's proof at that time was only available in German Bell didn't speak German by the time von neumann's book was published in English Bell was busy with other things but in 1964 Bell finally found the time to sit down and take a look at von neumann's theorem see exactly where the problem was and he published paper explaining where the problem was and that led him to another quest which is can you come up with a hidden variables theory of quantum mechanics that is local that doesn't have weird spooky action at a distance because Bohm's theory certainly does and that's where Bell came up with his famous theorem he said okay he PR said that it was a choice between locality and completeness but it's worse than that we have a choice between locality and correctness in other words either the universe either quantum physics is is is inaccurate in some experimental situations or the universe is non-local in other words Bell's Theorem states that quantum mechanics is incompatible with locality that's it that's what the theorem says now there's a little star there on incompatible why is there a little star there well there are ways out of it but they're very very very limited one of the only ways out of the conclusion that quantum mechanics is incompatible with locality was actually proposed though not as such a few years earlier than Bell's Theorem by this guy Hugh Everett he came up with the many-worlds interpretation of quantum physics and it turns out that if this interpretation is correct that gets you out of the non locality because one of the implicit assumptions that goes into Bell's proof is that there are only single measurement outcomes of any particular variable when you do a measurement but if every time you do a measurement you get all possible outcomes the theorem breaks yeah this is this is just a quick demonstration of how Everett's interpretation works the basic idea is the entanglement that I was talking about between the radiation source and the other components in the Schrodinger's cat box that doesn't stop when you open the box when you open the box you get entangled with the superposition and then everything else does too and so suddenly there are two of you and the reason you don't feel like there are two of you is each one of you can only be in causal contact with one copy of the universe you are separated from the other copies through decoherence I'm not saying that this is correct I'm not a partisan of any particular interpretation I'm just saying this is an option so there are other viable options on the table we don't have to just say shut up and calculate there are other solutions there are many more than just the two options I've proposed here in fact both pilot-wave theory and ever-ready in many worlds theories those are more like families of interpretations than singular interpretations themselves and in this field of quantum foundations there are also many open problems that still remain for the many worlds theory there are problems related to how we get probability out of the theory if if you never have wavefunction collapse then where does borns rule come from because borns rule is certainly correct for pilot-wave type theories the question is okay this works for nonrelativistic quantum mechanics how do we get a relativistic extension how do we get a quantum field theory out of this and do some particle physics but all of this may leave you with a different and much more difficult question than any of those who cares quantum physics works quantum field theory works all of it works it works incredibly well so why does any of this matter why does it matter if there's a measurement problem why should we care about this well that's a really good question and I'm gonna need to give someone much smarter than I am the opportunity to answer that question [Music] [Music] [Music] [Music] [Music] which would be something which is infuriated [Music] [Music] [Music] another thing and that is the philosophy or the ideas around the theory there are there is space or something like that I did change enormously when there are changes in the tiny tiny difference the difference in the entire account of the theory with which you're started was enormous reason is these are so simple so perfect they produced definite results in order to get something [Music] [Music] [Music] yes I know it's good in the sense you maybe if you only get these you're not prejudiced in yourself you'll get better on the other end they could possibly help get against buddy Marcus that those people would insist however that the only thing that's important is that the theory agreed with experiment I would like to make an imaginary discussion between a - tada - spoon the Mayans were able to talk tonight quite receive a precision the predictions for example eclipse [Music] [Music] time they appeared so people say someone comes up with an idea that suppose the world and you stay tuned [Music] [Music] so Feynman was certainly wrong when he he was certainly wrong about some things including including his apparently implicit assumption that only men can do physics but but he was certainly right about the importance of the ideas behind our theories they help us not just with our current work but with coming up with the next theory that will go beyond the theories that we currently have because in addition to I think everyone in the room agreeing that quantum physics works I also hope that everyone in the room can agree that quantum physics is not the last word there will be another theory that goes beyond it whether we find it tomorrow or a hundred years from now or five hundred years from now there will be another theory but these ideas also matter beyond the world of physics in the world of science remember for for thousands of years at least in Europe the standard picture of the universe had the Sun at the center and the earth going around it and when Copernicus and others came along and uncentered the earth from the center of the universe that made possible a great shift in the way that people thought once they were exposed to that idea if he had not done that is hard to imagine that Charles Darwin could do what he did with unsent ring humans from you know the field of biology and and the animals and plants and life in the world and if Copernicus and company and Darwin and Russell and company had not done what they did it is very sorry Darwin and Wallace and company had not done what they did it is very hard to imagine that Stanley Kubrick would have been able to do what he did so these ideas do not just matter for physics or for science the picture of the world that comes along with our science matters for the wider world beyond the scientific enterprise now there's a lot more to say about all of this which is why I wrote a book about all of this it would be wonderful if you would buy the book but if you don't want to buy the book they probably have it at the library and if they don't you could ask the library to get it but in any event these are the sorts of questions that I go after in my book and the sorts of issues that I talk about I hope that you found it interesting before I finish I just want to thank the Alfred P sloan Foundation who gave me a very generous grant to help work on this book and the sukkah and Osage peoples whose land we occupy here in Lawrence with that any questions thank you yeah yeah so well so there's a few I certainly agree that our mind boggling is not a legitimate problem that we can you know or charge that we can level at the many-worlds interpretation that's not a problem at all there are a lot of people who say things like Oh a multiverse can't be right it's too much there's too many things Occam's razor I think that's very silly there is however a pretty reasonable category of objections to the many-worlds interpretation which before I go into that I should say I think that the many-worlds interpretation is one of the strongest currently existing contenders for a good interpretation of quantum physics so with that I have a lot of sympathy with you but there is still this question of probability because in the many-worlds interpretation there is no wavefunction collapse the show your equation is just sort of exactly true at all times or you know it's relativistic extensions like the the Dirac equation and the klein-gordon equation so those equations are just exactly true at all times which leads to the question okay so if if we have a deterministic theory where does probability enter into it because it's certainly true that the predictions that quantum mechanics issues are of a probabilistic nature one proposed solution to this is to say okay well in the many-worlds interpretation there are many copies of us so we don't know where in that multiverse we are and so the probability comes about as a result of self locating uncertainty we have to find ourselves in this infinite multiverse so the two problems there are first of all okay how do you put a probability measure on an infinite multiverse which is a problem that we also run into in inflationary cosmology but the other problem is is that really a legitimate move can you really say okay that's where the probability comes from and that's a philosophical issue that you know there are plenty of good philosophers and physicists who think that they have solved this problem and they may well be right but there are also other people who've said no there's still work that you need to do there so for example one possible objection to the self locating uncertainty thing and I want to make it clear I'm not endorsing this objection I'm just saying that it's an objection that someone is raised is okay but when you say I am one of these copies and after a split occurs I still persist in just being one of these copies you are saying that there is something that is not obeying the Schrodinger equation that is you know providing your continuous singular experience down one path of the branching and that sounds an awful lot like any material soul and I don't believe in a material souls and so I find it hard to believe that self locating uncertainty is the place where probability comes from in the many-worlds interpretation now I'm not endorsing that objection I am just saying that that is an objection that people have which at least seems like something that someone should respond to and and people have so this is an ongoing debate in the literature I will certainly say that I think as I said one of the strongest contenders many-worlds I there are days when I when I'm sort of asking myself why do I not believe in many worlds and then there are other days where I think no that probability thing's a real problem one of these others looks better yeah well so that's a good question um I think that ultimately we should shoot for testability and it's certainly true that there are solutions to the measurement problem that are testable at least with current technology or you know pretty easily envisioned future technologies so for example there are theories that involve apps like actual modifications to the Schrodinger equation let's say okay Schrodinger equation applies most of the time but there's also a little stochastic term that we're going to add so that every so often wave functions basically get multiplied by a narrow Gaussian in position space and and the frequency with which this occurs depends on the number of particles in the system in question so you'll never see it if you're only looking at a handful of particles but it'll happen basically all the time for anything that has an Avogadro's number of particles in it so that is the kind of thing that leads to experimentally different outcomes and people have started testing it and putting bounds on the parameters in such collapse theories but for something like say the pilot wave interpretation versus the many-worlds interpretation well if I were feeling particularly uncharitable to the pilot wave interpretation I'd say there isn't a relativistic generalization so the entirety of particle physics can't be explained but assuming that that problem can be solved and there are people working on that those two theories are completely identical for now it may be that when we come up with a theory in the future we find that it favors one or the other interpretation or some other interpretation and that it is accessible to experiment so yes it would be nice if we can distinguish between these things experimentally the hope is that at some point in the future we will be able to and there are people working on that right now for example for all we know when someone does come up with a relativistic extension of pilot wave theory it may lead to genuinely new predictions we just don't know yet so thank you comment what do you think about the device which is almost universal in the quantum mechanics literature actually lying about theory and falsifying the content of physics nor to make the discussion more than 13 and in order to dumb it down so let's go home and go to school and legend actually substituting false premises they're known by all experts are all four they studied Atticus and all concerned know those false premises are completely hogwash and yet the people who are left out of it don't know I'll use Bell's own your own this example imposes a binary choice either you either your view of reality is this absolutely stupid naive form of probability that he poses or you have to deny the existence of realism and middle ground tonight I took the course of quantum mechanics I'm not going to buy and the absolutely stupid primitive idea of particles distributions that you pose for me seems to be what Einstein was trying to say and and so when Einstein it's incomplete you say if you believe that happening started to discuss it incorrectly yep in presentation of my question for you is what do you think of that technique of lying to people so that the message is more interesting and they can swallow it easier and postponing an evil develop mean I definitely think that there are some inexcusably bad garbling and misunderstandings and Union just flat-out wrong presentations of Bell's Theorem in almost any quantum mechanics textbook I care to think of and I do think I think the only place where I disagree with you is and I'm not sure if this is more charitable or less charitable I don't think that these people are lying because lying involves intention I think these people genuinely don't understand Bell's Theorem I think that for cultural reasons and this is something I talked about in the book at great length and is something that Bell talked about himself quite a bit the full consequences of Bell's Theorem have been fairly difficult for a lot of physicists to swallow you know Bell himself said repeatedly I don't think that there's any way out I think that you know this means that you have to give up on locality if the experiments turn out the way that they have the one hope he held out for some sort of exception was the many-worlds interpretation and even on that he was wobbly he didn't say it was a choice between you know locality or realism or locality or hidden variables he knew better than that and yet I can't think of a single textbook that's not true I can think of a single textbook that represents this correctly and that textbook is not an introductory textbook in quantum mechanics it's an introductory textbook to quantum foundations so huh oh by norson came out I think two years ago anyway yeah so there this is this is very hard to understand you know why this happened it's possible that it's deliberate I don't think it is similarly you know i-i've always been puzzled by the emphasis that some physics textbooks place on some other things like complementarity the idea that oh you have these two contradictory pictures and they will give you incomplete you you you you have to use them together to get a complete picture of what's no no there's nothing contradictory between a particle and a wave you can have both that's what Bohm said whether or not Bohm was right is immaterial because it shows that they're not contradictory you can do both it's not a problem and if the many-worlds interpretation is right you can also explain everything with waves and no particles or fields and no particles as the case may be so I find this very puzzling and and unfortunate but I'm also I'm fundamentally an optimist about this I think you know we are getting to a better place on this than we were a generation or two ago and although the textbooks haven't really reflected it yet you know these days I can give a talk like this and not get you know driven out of town right which I think would not have been true a while back yeah I think that it depends on the level of the quantum mechanics course I think of that if it's an introductory course I think it's important to bring this up at the beginning of the course and then check in with it every so often throughout the course but to spend most of the time saying look here's the math and here's how you solve a because I think you really need to understand how to solve Schrodinger's equation and see the consequences before you can get a full appreciation for why these questions are so weird because if someone said to me hey I have this black box theory that says that there's a law of nature which is intermittently suspended and replaced with a different one when I look at things I would say okay so you're nuts and why should I believe you but if you make me go through solving the hydrogen atom first then maybe I'll believe you so I'm not saying that you know that's how we should do things but but I do think that this is something that we should foreground very early on because there are I also think that there are a lot of students who go into these courses and ask questions like what's happening when we're not looking get unsatisfactory answers and assume oh I must be too stupid to understand what's going on here and that discouragement will sort of ride with them and either it will drive them out of the field or will drive them into some sort of denial about what's going on in the theory so I think it's important to foreground it I don't think it needs a lot of time in early courses especially in in you know in a world where most courses don't talk about this at all it'd be a disservice to students to give them a wildly different course that leaves them with you know the inability to do things that you know other students at the same level at different universities can do but I think as you get to higher level courses you can spend more time talking about this yeah any more questions and anybody anybody who's not faculty [Laughter] okay well thank you and I'll be around afterward [Applause]

Channel: KU Physics & Astronomy Colloquium Series

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Length: 52min 54sec (3174 seconds)

Published: Wed May 22 2019