 Hello everybody and welcome to episode number 14 of Patterson in Pursuit. It seems like these interviews just keep getting better and better and more and more exciting. This interview I am the most excited about because in my own intellectual pursuit I have come across several areas of thought that people draw from when they try to make what I call Irrational conclusions. They try to say oh reality is logically contradictory we can't know anything about anything and the universe is a great blurry paradox or consciousness is at the center of the entire universe. These ideas I think are foundationally inaccurate, dangerous and are about as far away from rational clear-headed thinking as possible and quantum physics is arguably the area that gets the most citations from the irrationalists. An extraordinary amount of words have been written drawing from the supposed conclusions of quantum physics to show how irrational the world actually is but in my own research when I actually dove into the field I found a lot of these conclusions to be mistaken. I think people who draw from quantum physics to make radical conclusions don't actually understand what they're talking about. They make grave errors with very big implications. So what I did explicitly while in England was set up an interview at the University of Oxford with Professor of the Philosophy of Physics to try to get down and pin down the core concepts in quantum physics for everybody to understand. And this interview is with Dr. Simon Saunders who is indeed this professor I was looking for. Dr. Saunders is a professor of the philosophy of physics at Oxford University. He's written a ton of papers on the topic. He's written a few books and what I find of inestimable value is that Dr. Saunders focuses on concepts. Very often when you have elite intellectuals who are very who are nose deep in their own research they get mired up in a lot of jargon, a lot of mathematics, a lot of specifics that nobody outside their own field understands. And in this interview we only talk about mathematics really in the abstract. We just focus on the concepts which I think is necessary if you want to clearly understand whatever field you're talking about you have to be able to understand it clear enough where you can break down the basic concepts. That's not to say however that this is an easy interview or this is something that should be able to sit down and you know halfway ignore and still be able to follow along especially if you have no background in physics whatsoever. So what I've done to help make it a bit easier is for about the first 15 minutes or so I'm going to be chiming in to give additional clarity to the interview as it's taking place. So maybe five or so times I'm going to jump in and try to break things down to have that much more clarity. So before I start this interview I want to give a gigantic shout out to all of my Patreon supporters especially the ones who support my work the most. Thank you very much Mark Gauvet, Charlie Davis, Melvin Martinez, Sean Balada, John LeBlanc, the Georgia Freeman, Michael Sadlack, David Richardson, Samuel Robert and David Bomberger. Thank you all very much for supporting the creation of a rational worldview and everybody else that is supporting at smaller levels your support makes these interviews possible. Alright that's enough for me I hope you really enjoy my interview with Dr. Simon Saunders. So first of all thank you very much for talking with me today. It's a pleasure. I have asked a great deal of you because as you know in the world of philosophy in the general public quantum physics gets thrown about all the time people try to justify all kinds of remarkable propositions when they're talking about quantum physics. What I've asked is that we could slowly work through the basic concepts so when people are trying to evaluate the plausibility of some of these ideas they'll have kind of the conceptual toolbox that they need. So correct me if I'm wrong at any point in this that one of the peculiarities in the world of quantum physics kind of the first experiment or the foundational experiment is called the double slit experiment that's kind of where we see this remarkable phenomena that people make all kinds of incredible claims you can analyze quantum physics by analyzing the double slit experiment and what that is is we have three parts in our experiment we have a light source we have like a plate that we're going to be shining the light at and then we have a screen. Okay so this is the first time I want to jump in because when talking about quantum mechanics you must understand fully the setup of the double slit experiment really the double slit experiment is central that's really the whole everything really follows from the phenomena that you can observe with the double slit experiment so in this example when I'm talking with the professor we're talking about light because that's the actual setup that physicists used when they're performing the double slit experiment but conceptually you can also think of it another perhaps even more intuitive way instead of light let's talk about sand so imagine you have a setup of three parts on the top you have a hopper that's full of sand and the sand is slowly dripping down onto the second part of the experiment which is let's call it a card on the card there are two slits in the card that allow the sand to to pass through those slits below the card we have a screen where we can see the resulting pattern that happens once the sand goes from the hopper through the slits down onto the ground so sometimes we can plug one of the slits to record what happens as the sand passes through the one slit we can or we can have both the slits open and record the pattern that happens so conceptually that's what the double slit experiment is you have three parts you have the reservoir of particles that are being shot at a card or I call it a plate with two slits in it and then you have the screen behind it to record the pattern that results as those particles go through the slits and in that plate that we're shining the light at we have let's just say one slit now if we do that and we shine the light at the plate and see what happens you know if we're watching seeing what happens the pattern on the wall we're just going to have a blob of light on the wall regular light but when we open up a slit next to that first slit what we would intuitively think is you'd see two blobs of light or a different diffraction pattern what you see is what appears to be a wave interference where you have some bands of light are bright and then it goes dark and then it goes bright and it goes dark which is very peculiar because we I think we intuitively think correct if I'm wrong that in physics you have waves and you have particles and these things aren't really together they're kind of two mutually exclusive things but just in that in that experiment it seems like you have waveness and particleness at the same time is that fair so far yeah absolutely although you haven't indicated why we think we have particles present we have a light source I suppose it's of moderate intensity the sort of thing you'd get from a flashlight of course we see a blob but you have the two slits open we see what we call interference fringes but there's nothing strange about that all of that is wave theory of light what's strange is when you reduce the intensity of the light source yes to the point where we start to see not a very very very faint blob or very very very faint fringes but we see one speck at a time the the interference fringes are built up out of innumerable individual events each of which looks like a particle is impacted on the screen so let's let's say this even more clearly so if you reduce instead of just one stream of light let's say you do one little particle of light you've got to reduce the intensity enormously right what happens is you still have what appears to be the wave interference and the question is how's that possible because it's just one bit at a time right it's one particle at a time absolutely okay so then there it gets even weirder if we were to ask the question when we shoot that one particle at a time at the two slits sensible question is to ask which slit is the particle going to go through the one on the right or the one on the left well when we try to measure that which one we put some detector there to see which slit it goes through the wave pattern disappears right now you can measure it'll go through the one on the right and the one on the left but you won't have the wave pattern right when you turn that measurement off right so you don't know which one it goes through boom the wave pattern reappears right exactly yeah so that's this is a fair restate absolutely okay so i want to state that again just so it's absolutely crystal clear when we fire the particle at the slit we don't know beforehand whether or not the particle is going to go through the slit on the right or the particle is going to go through the slit on the left so naturally a sensible question is to ask let's find out so what physicists do is they set up an apparatus which measures which slit the particle goes through however when they do that when they actively measure and find out which slit the particle goes through the interference pattern disappears on the screen behind them and similarly when they aren't measuring which slit the particle goes through the interference pattern it reemerges and this is precisely what has caused so much confusion is the peculiarity of this phenomenon so let's try to then break this apart and say what the heck is going on here because intuitively seems like there's some funny business there are different competing interpretations for explaining what that what that phenomena is how is this possible right one that would be the most intuitive just to anybody who's listening would be oh well what's happening is at least when we're talking about measuring or seeing which hole this the particle goes through whatever equipment that you're measuring that with that's got to interfere with the experiment some somehow because it's interfering with wave pattern right is that what is that yeah no that's a perfectly appropriate response to this straightforward fact determine which slit the particle goes through no interference pattern indeed and we think that the whatever the detection device is that's interacting with particles as they go through one or other of the slits or as they approach the two slits at any rate that that interaction it's a physical effect and it destroys the interference pattern so that is uncontroversial you would say that there's some kind of an okay right so the the standard theory in quantum physics for the last nearly a century now right has been the Copenhagen interpretation of quantum physics so right i mean i have some caveat about that but go ahead okay and from my understanding um that's a little bit less popular than it is now but it's still kind of the standard textbook theory that's taught uh well again i have a caveat okay so the caveat is this um Copenhagen was a coined termed by Werner Heisenberg in the post-second world war period uh to talk specifically about Bohr's interpretation of quantum mechanics Bohr was based in Copenhagen uh so if that's what the word means Copenhagen interpretation means Bohr's interpretation uh that interpretation was influential it was studied by physicists in the late 20s and 30s it's hardly ever been studied since really right and that was that so that's not the one that's being taught in terms of it's certainly not taught you won't find it in almost no textbook uh contemporary textbook published in the last 30 40 years well it may some no doubt will have Copenhagen somewhere occurring in the text but most of them the vast majority don't mention the Copenhagen interpretation but say do not mention Bohr's interpretation okay so what the Copenhagen interpretation can get to be get to mean these days is a kind of a minimal interpretation um which is in most textbooks and quantum mechanics and takes the form of the measurement postulates okay um so standard quantum mechanics comes with these measurement postulates uh physicists mostly just get on with the job shut up and calculate philosophers and people concerned with foundations of quantum mechanics are extremely troubled by the measurement postulates okay um and the reasons for that are interesting i could go into them if you wish uh yeah so let's talk a little bit about what do you mean by the the measurement what are the measurement postulates okay so what we have in quantum mechanics is um a uh a state space common to most other theories of physics a space indicating the possible states that a system can be in uh we have a dynamical evolution defined on that state space uh which goes by the name of the unitary evolution in quantum mechanics um because the relevant transformation uh has mathematical characteristics of a transformation called unitary um but it's very specific unitary transformation it involves all of the details of the dynamical interactions these details are what physicists work on uh in high energy particle physics for example we have the so-called standard model the standard model is all about the nature of that dynamical evolution of the state um and you can win Nobel prizes for coming up with new dynamical evolutions for the state there are lots and lots of empirical tests uh for determining whether a given dynamical evolution is correct so this is as we're the main the mainstay of uh physical research and foundations of let me not say foundations of quantum theory this is physical research in uh threshold physics let's call it that we're trying to get down to Planck scale physics in a sense this is physics is normal okay so that's a very tactical way of just saying that physicists like to very tightly control the environment and the setup of their experiments so when he's talking about state spaces and stuff just think of it as uh physicists are trying to precisely identify and control phenomena that happens in particular spaces and when he's talking about unitary evolution just think about record accurately recording the phenomena that's taking place in that space and the so-called standard model of physics has to do with macroscopic phenomena large scale phenomena so you know the bowling ball rolling down the lane that's something that the world of uh standard physics has sorted out to an incredible degree and as we get smaller and smaller and smaller scale so it's not macroscopic it goes microscopic and then you know super microscopic it appears as if the laws of physics are different so the beauty and the simplicity and the predictive power of standard physics when we're talking about the bowling ball is very precise however the smaller scale we go we go down to this quantum scale the micro microscopic skill the less precise and more difficult things are okay so go back to the measurement postulates we have the state space we have this unitary evolution which physicists are preoccupied with to get the details of that unitary evolution right but then we have the measurement postulates in addition to that and what the measurement postulates uh direct us to do is to interpret the state of the system in terms of a probability assignment and the probability assignment is to uh is about outcomes of measurement um depending on what sort of measurement is performed the uh the measurement postulate will tell you how to compute a probability for that outcome okay so this is a very central idea that comes up in quantum mechanics so we're gonna be talking about it throughout the interview but it has to do with the imprecision of our measurements when we're dealing with quantum scale phenomena so in contrast to the circumstance the macroscopic phenomena of the bowling ball going down the lane where we can have perfect precision so if you know all of the inputs and variables going into um the experiment let's say with rolling the bowling ball down the lane you're going to know a perfect precise outcome well in the world of quantum physics that's not the case you can know the inputs but you don't necessarily know the outputs so when physicists come up with a model to explain this they aren't dealing with perfect precision they're dealing with probability functions they aren't saying for example if you start the race here and you're moving with this certain velocity you'll end the race here they're saying if you start the race here then we have a relative probability function of where you're going to end up we can't be certain exactly where that is now that may or may not strike you as peculiar um what's peculiar and i think this is probably the core of the matter it's taken a long time to really refine this down to this but i think it is the core of the matter is that this postulate it depends on the kind of measurement we wish to make this is not got the character of a physical law it's one way of putting it is it's too high level what kind of experiment we're making involves intentionality it involves questions of the design of an experiment it seems to refer to actions taken by experimenters we know of no other physical theory in which facts of that sort are factored into the fundamental laws so in other words what you're saying is there's this essential connection between the setup of the experiment the experimenters and the results of the experiment right one would hope to make progress in getting rid of this measurement postulate referring to high level intentionality and so forth of what an experiment is supposed to do by just stating describing the measurement apparatus as a physical system just making that a part of the explicit dynamics to be dictated by this unitary evolution but when we do that what we get out the quantum state at the end of this dynamical interaction involving the measurement interaction what we get out the dynamical state that we get out uh has it seems no meaningful interpretation okay so what that means is when we're dealing with these extremely small scale phenomena the actual tools of measurement are essentially part of the experiment because the only way to record particular states of a system are to physically interact with that system the the physical interaction of measurement affects the whole experiment itself it's an essential part imagine that you're trying to take the temperature of a glass of water that you have in front of you well you could do that by placing a front thermometer in the water however just the simple act of placing the thermometer in the water is going to affect the water temperature itself there's no way to perfectly pristinely know what the temperature of that water is without interacting with it in such a way and usually when we're talking about macroscopic phenomena large-scale phenomena the impact of the measurement is negligible doesn't really make a difference however when you're talking about micro micro micro scale phenomena the actual measurement does make a difference and in fact appears to be a central part of the results that you get is this act of measurement and what he's saying is this goes very deep so it goes from the setup of the experiment to the tools of the experiment to the humans that are setting up the experiment to the intentions of the humans that are setting up the experiment you get this very unsatisfactory circular spiral in which just interjecting measurement into the equation the phenomena of measurement is going to essentially change the results the way to make it meaningful is again to apply the measurement postulates so we're back to square one in other words it just doesn't succeed you try to put the content of the measurement postulate into a physical characterization and experimental device run the dynamics you haven't you haven't got out a meaningful prediction to get a meaningful prediction out of this enlarged system now we've included the experimental apparatus we have yet again to apply the measurement postulates so the straightforward moves don't work and that really is the measurement postulate granted that the straightforward moves don't work what do you do about it okay right so let's try to take a like a metaphysical example of what we're talking about here to give it some concreteness let's talk about a famous example Schrodinger's cat where imagine that there's a cat in a box and inside of the box there's also let's say a flask that if the flask breaks then the cat will die if the flask doesn't break then the cat lives and what determines whether or not that flask breaks is some kind of quantum event that we can't necessarily predict beforehand whether it will or it won't happen but we have a probability function because well 50 percent of the time it will break 50 percent of the time it won't now in when you're talking about this interpretation of quantum physics what does it say about the state of the cat is the state of the cat both alive and dead is it neither is it only when you look at the box does then it take a state what is the position sure well taking the cat and the radioactive decay detector and so forth the whole contraption this is exactly a case of a macroscopic measurement device you might say this is what the measurement postulates involve now we've got the measurement device has this complex system involving a living cat do the dynamics the dynamical evolution will take you to a quantum state which as per what I was previously saying has no physical interpretation or not not in the first instance anyway what do we do well we can apply the measurement postulates when we apply the measurement postulates then we'll get outcome cat dead with some probability cat alive with some probability fine but we have had to apply the measurement postulates from the outside we can't for example regard the cat as itself in the position of a measure of an observer okay so the next central concept to understand has to do with terminology and this is where a lot of people get tripped up this is where you get a lot of really crazy ideas that coming from quantum physics it has to do with terminology about measurement and observation now in common parlance we think of terms like observation or measurement having to do something with awareness like human awareness of some phenomena well that isn't the case we talk a lot more about this later on in the interview but observation or measurement in regards to physics you have to think of it as physical interaction with a measurement device that is observation so for example with the cup of water the thermometer being placed in the water is the observation it is the measurement it has nothing to do with human awareness the cat as it were cannot apply the measurement postulates the measurement postulates seem to have to make a central reference in this case to something over and beyond the cat and the contraption that it's connected to so essentially what you're saying I think is that in this particular interpretation there's not an interpretation as yet this is just standard quantum mechanics well that's kind of what I the interpretation is that there is no interpretation right okay great right so yeah so the central idea in standard quantum mechanics is this that there is no meaningful unobserved state out there that we can really even talk about well when I said try to get rid of the measurement postulates by putting the physical apparatus into the physical description and just coupling it dynamically to the system under observation and just turn the handle evolve the dynamics we end up with something a quantum state that has no meaningful interpretation one way of describing that state is as the state in which the cat is in a superposition of being alive and dead okay so let's talk about that um and and generically can I say whenever you do a macroscopic experiment uh if you just rely on the unitary dynamics what you will get out is a superposition of all of the possible outcomes of the experiment so the cat is just a vivid way of illustrating that and how peculiar that is it's also peculiar and it's peculiar for a cat to be in a superposition of being alive or dead it's also peculiar for a measurement outcome to be in the superposition of one outcome and another outcome so let's explore that concept of the superposition because intuitively that seems like let's nonsense I mean you can't have a cat that's alive and dead at the same time and a lot of people this concept people have applied to justify the existence of logical contradictions they say things like oh we know classical logic doesn't apply to um to to the world because quantum physics shows that that you have a cat that alive and sound what is your response to right right well the idea that some revised logic is necessary to interpret quantum theory it was attractive it was first floated in the 60s by people like David Finkelstein taken up by Hilary Putnam it fitted with a view of the revolution brought by general relativity where geometry that was thought to be apriori uh and well understood we have a euclidean geometry this is fundamental to science fundamental to mathematics fundamental to our understanding of the world low and behold we've had to revise it in the light of general relativity and parallel logic apriori was thought to be apriori is involved in our dealings with the world as fundamental to science guess what we have to revise that to there was a a fairly attractive parallelism really between the two developments but the the long and the long and the short of it is when it comes to revising logic you can sort of do it but it doesn't help it doesn't actually resolve the conceptual problems so nowadays I think almost no one looks to a revision of logic as a solution to the measurement problem of quantum mechanics what we've been talking about is called that the measurement problem of quantum mechanics right right perhaps no one in the profession believes that because there's certainly lots of people outside the profession who uh who think that this does indeed show the problems the limitations the non-applicability really of classical logic yeah so let's try to take this if we can from Schrodinger's cat back to the double slit experiment so where does the concept of superposition um fit into uh the double slit experiment could you say something like the particle goes through the slit on the left and the right at the same time does that work let's be more accurate the particle is in a superposition right of passing through the left hand slit and the right hand so what does that mean right okay so we're back to the fundamental question of what does superpositions what do they mean yes okay so um uh there are essentially three ways of making sense of this okay okay let me go through the more intuitively the less challenging of them the less intuitively challenging so I think of all of of the three uh the straightforward idea is we need to add something more to the quantum formalism the quantum formalism with this dynamical evolution of the state is not the whole story what is also needed are further variables describing the actual particle motion the quantum state on its own is not enough I see and so such variables called hidden variables whether that's good terminology or not um let's not worry about it some people complain about the terminology they are additional variables and they describe the trajectories of actual particles and these are point particles okay so structuralist point particles are supposed to uh have definite trajectories these hidden or additional variables describe those trajectories such a particle either goes through the left hand slit or it goes through the right hand slit it never goes through both slits it eventually arrives at the screen um that explains how come we see the image at the screen built up one little pixel at a time one little point at a time uh and now the uh peculiarity of the two slit experiment is explained because there is in addition the quantum state and the quantum state propagates as a wave through both slits and that quantum state uh influences or guides as it's often called the the trajectory of the particle this point particle this guidance goes there's a mathematical equation corresponding to that called the guidance equation uh and uh actually there's no longer any problem with the two slit experiment according to this approach and this would be called something like the pilot wave theory right indeed the best developed indeed the only developed theory of this kind which adds these additional variables okay is called the pilot wave theory uh also called the de Broglie-Bohm theory after Louis de Broglie in the 20s who first proposed it and David Bowman the 50s who independently came up with it um and for reasons that aren't entirely straightforward is often also called Bohmian mechanics these are people who really have neglected de Broglie's contribution uh and so-called Bohmians um really became a significant movement in foundations of physics a significant school of thought uh really in the late 70s 80s partly under the influence of the work of John Bell um but certainly in the east coast there are various communities of so-called Bohmian people who promote this and that's different from Bohemian who promote this uh approach to quantum theory okay okay so that's that's one school and you might well think may I just interrupt you just here so to be clear as it relates to super position this pilot wave interpretation says it's it doesn't actually it's not actually a position that superposition there is a superposition but it's a superposition it's a superposition of the quantum state just think of a wave uh we have superpositions of waves superpositions of water waves uh you generate a water wave in your corner of the swimming pool I put a if I break my hand up and down in my corner of the swimming pool we can see those waves propagating towards one another and there's some interference among those waves we're very very familiar with this um we uh see the same phenomena in acoustics with sound waves yes interference we see it with radio waves we see it with light waves thinking of them as waves um there's no mystery with a waveform being a superposition um the mystery or the straight out apparent contradiction is when you talk about a particle position yeah yeah superposition right right right I see what you're saying I see what you're saying the pilot the particle always has a definite trajectory I see okay that's so that my mistake then in thinking about this was equating superposition with particle superposition and we're talking about wave superposition got it okay in this the pilot wave interpretation uh the thing is solved in that way okay so now um another approach the dynamical collapse approach it doesn't add new variables to the quantum equations of motion it changes those equations of motion and it changes them by building in really what is a fragment of the measurement postulate um uh that fragment is mathematically defined let me not try to articulate it in speech but so this modified dynamics it's uh as so long as as so long as the particle is roughly speaking not interacting with other particles so long as it's freely propagating through something like a a vacuum um it's what we have as a wave now that and that wave goes through both slits um and it produces interference effects with one another but that wave on interacting with the screen is subject to a dynamical process explicitly controlled by the equations which leads to the wave becoming localized one point on the screen rather than some other point in the screen so this is rather remarkable it's not easy to understand how the wave achieves this remarkable process of localization other than by going to the mathematics uh but the mathematics is well defined um that's what the quantum state does when driven by this modified dynamics and what is this called what is this theory a dynamical collapse theory okay and the best worked out version of it is uh the glw or glwp theory after garadi remini and vapor is this fairly new because i'm okay so this glwp theory uh uh first emerged glw first emerged in the late eighties i see uh and uh by the early nineties we had a fairly worked out and satisfactory such theory in the non relativistic regime okay and we'll get to that maybe a little bit right right let's get to that later okay so that's the second way of making sense of this phenomena and in this under the this dynamical collapse theory you don't need any measurement postures you just have the dynamical equation right okay so the third way of making sense of the theory is actually to leave the theory as it is don't introduce additional variables don't modify the dynamics just take the existing dynamics the standard dynamics the kind of dynamics that physicists routinely work on at threshold physics frontiers of physics take that dynamics apply it to complex systems um apply it to individual particles sure but equally apply it to the two slits apply it to the screen apply it to the shodding a cat apply it to whatever experimenters or observers there are in addition to shodding his cat in addition to the screen the two slits and the source in other words apply it ultimately to the universe as a whole okay now when you do that you get the extraordinary and apparently uninterpretable result that you've got a superposition of the cat alive and dead that you've got a superposition of the particle arriving at one point of the screen and at another point of the screen and guess what because now we put the observer into the picture as well you've got a superposition of observers seeing the cat alive okay and and observers seeing the cat dead right okay now because we're just allowing quantum mechanics to apply to the whole universe ultimately what you finally end up with is a superposition of two different universes the one in which the cat lives the other in which the cat dies i see right um and we okay so this is called the many worlds interpretation um also called the everett interpretation because the first person to come up with it was a physicist called Hugh Everett in the late fifties and of the three it's the only one that leaves quantum mechanics unchanged that's the fundamental point in its favor so with that one with the everett interpretation and the many worlds interpretation doesn't that imply then you have a very very very large amount of different universes absolutely that are constantly splitting off absolutely and and this is viewed as apriori unacceptable by many okay whether it's appropriate to have apriori judgments about fundamental physics is another question which i'm very happy to discuss but for many people this just rules it out as unacceptable okay so for those who are prepared to grant that the universe may be much much much stranger than we think it is the the fact that we have virtually an infinite number of parallel universes is not easy to get used to but put into the picture what cosmology teaches us because cosmology also by the likes of many is completely unreasonable and one might have apriori reasons to think that the universe can't possibly be as cosmologists tell us it is um cosmologists tell us that it is large um to a number which uh it defies imagination and it may indeed be infinite okay so physics is um not easy uh and i don't hear referred so much to the technical difficulties um i refer to the challenge that it presents to common sense right so let me ask you a question if this is a fair way to categorize the distinction between what i was calling Copenhagen which maybe i need a different term for and the many worlds right so when we're talking about superposition Copenhagen implies that in the same universe you have two what appear to be mutually exclusive states right whereas in the many worlds interpretation you have the two mutually exclusive states but they're not in the same universe right okay and is that the reason that for example i know you're you're a proponent you like the idea of the ever an interpretation is this why you find it i don't particularly like the idea of an interpretation um i think it's the best interpretation of standard quantum mechanics okay and and so what is your objection then just conceptually i mean i know what my objection is what is your objection to the idea that you could have a superposition of particles do you think that that is conceptually incoherent no no not at all no i think um the quantum states propagating at the level of microscopic systems uh where one has a superposition of states i don't find anything intellectually challenging even of particles well the the issue is how does such superpositions ever get to deliver discrete events that are well localized in space um and that has to be explained that has to be accounted for um and so it is on the many worlds interpretation but that at the microscopic level there are superpositions of processes um each one of which involves something well localized uh that seems fine to me um a superposition of two processes each of which is well localized is obviously not itself a well localized process but this is somehow spread out in space but the process is not the particle the thing that gets me there's no there's no particle in addition to the quantum state there is only the quantum state i see i see so that that is okay oh this is a perfect segment perfect segment because what i want to start talking about is a some more base concepts here one of them has to do with the nature of observation independent reality which is kind of this common sense notion sure and i think it i think what proponents of the Copenhagen interpretation and certainly the proponents of a lot of the wild interpretations of quantum physics say is that reality is something that is non-existent until it's been observed but what they mean by observation isn't interaction with other macroscopic systems they mean conscious observation right now is there any evidence that suggests it's its conscious observation that determines reality or another another way of putting it in the phraseology that a lot of people talk about is the collapse of the wave function like we were talking about earlier you have the measurement in uh when we're talking about the double slit experiment you have the measurement which when you actually measure which particle which slit the particle goes through the wave function collapses meaning we have no interference pattern and so they say observation collapses the wave function sure what do you yeah yeah right well no i don't think there's evidence for uh any involvement of consciousness but it's um understandable why people might be led to that point of view i mean the measurement problem is precisely the problem that if you just provide a physical description of a measurement device and put that into the formalism along with the system that is under that is being measured apply the unitary dynamics what you get out is this thing the superposition and now at the macroscopic level you get the superposition i can stick in an armchair i can stick in the walls of the laboratory i'll get a superposition uh when is there ever a problem with uh when does this when does the buck stop you know uh what breaks this endless superposition of outcome uh and for many the answer seems to be when a conscious observer actually looks now is there any evidence for that no there's no evidence for it it may be certain people anyway i'm prepared to tolerate a superposition of macroscopic outcomes i'm prepared to tolerate a superposition of a cat live and a cat dead what they bulk at is the idea of a superposition of a conscious observer uh being a superposition of two outcomes and i think what drives this is the view that ultimately what is the given in observation is what's given in sensory stimulus uh and what has to take place in order to break the superposition it's got to happen at least when it comes to what is my sensory stimulus or what is my conscious awareness now the obvious answer is to say um the the macroscopic superposition uh is broken long before it gets to my conscious awareness it's already broken at the level of the cat being alive the cat being dead it's already broken at the level of an experimental device recording one output rather than another so you know the the idea that consciousness comes into the picture is better phrased as we'd better make sense or get rid of macroscopic superpositions before we get to a conscious observer being involved so what people um people give examples like this they say uh we'll go back to Schrodinger's cat example so um the cat is in a state a macroscopic state of alive and dead and then when we look then pops into one or the other well it's a better pop into one or the other up to the point where we look what the point where we look is as it were the last resort if you can't find a way to block it before when we look then it must be the very act of looking that does it which is precisely what why they say so I want to make that very clear because for me in terms of like coming from a position of I'm very sympathetic to common sense the idea tell me if this is a correct analogy so let's say that I was flipping a coin and 50 percent of the time I get heads 50 percent of the time I get tails and I can't know beforehand because I have some inherent limitation I can't know whether or not it's going to be heads or tails but I have a probability function I say 50 percent 50 percent it would be as if it appears what I'm saying is when I flip the coin the coin is in a state of heads and tails but when I look boom it pops into one state is that a fair analogy right now that does not that seems to me if it's not a right outrageous to say that seems absurd right yeah well I think um seeming absurd isn't a great counter argument method really in debating these things sure it may well seem absurd um but that's a fair way that is a fair it's a fair characterization of what kind of the flipped coin is in a superposition of being spin up spin down whatever the word superposition means somehow maybe and not interpretable in ordinary terms but when I look when I open my eyes and I look then I must see either the coin head or the coin tail that must happen and the I mean you spoke of what is the evidence and of course the evidence of our eyes tells us that macroscopic things are never in strange superpositions we don't even know what it would be like to to be witnessing a strange superposition would it be like double vision or something you know would it be that everything is sort of made out of jelly or I don't know what you know so you speak of evidence well certainly we have evidence that at the level of things we can see we always see macroscopic objects um well localized in the way that classical physics and common sense tells us things are well localized with well-defined properties right but I think the right way to understand this appeal to consciousness is that we've got to resolve the difficulty by the time we get to consciousness yes maybe at consciousness but I think a more yeah that's a very good level headed um answer is no we we deal with it already at the level of macroscopic systems they don't have to be conscious it's irrelevant whether or not they are conscious um and that's what happens and all three of the solutions that I've just quickly summarized in the pilot wave theory you never get peculiar superpositions of things built up out of particles because these particles are not themselves in superpositions it's just the quantum state that is we never see the quantum state we just see the particles in the dynamical collapse theory um the quantum state uh becomes well localized when you've got interactions with other particles you might ask well what what are the particles doing here in relation to the state um that's quite a subtle question but anyway bottom line the fundamental thing is the quantum state and the quantum state becomes well localized when you get to anything that could count as a macroscopic system okay and then back to many wells you get these macroscopic superpositions all right but all macroscopic objects are caught up in each term of the superposition so that if you only look at ultimately you get a superposition of different universes but each universe so described macroscopic bodies are well localized and so forth in none of these three approaches do you ever need to make any reference to consciousness excellent and so i'm gonna get one more example and then a point and another question so it would be fair to say returning to the coin flip analogy what many the many worlds interpretation says is that um when you flip the coin or when you look I should say it's not the case that there was ever a actual superposition in the same universe you have one universe in which its heads and you have another universe in which it's right okay right so then the that's there's the point is it fair to say that um the great deal of words that have been written about the collapse of the wave function as it relates to consciousness are most likely unjustified when some of the conclusions come from people because they take this and they say this is the spiritual nature of consciousness that consciousness is this divine thing which in a very real way creates reality you don't buy that no and I don't think there's any evidence coming from god and mechanics to that effect okay so then I have a few more questions for you a few more concepts to get through so let's talk about a central concept or a central formula in quantum mechanics and that's bell's theorems can you just kind of conceptually explain what is what is bell's theorems what does it try to do sure um so uh what bell's theorem is um is a very simple model uh as to what sorts of correlations can be produced by especially distant systems um and there's a locality assumption uh one or two other apparently very innocuous assumptions um which then lead one to conclude that uh the the various correlations that can be produced are constrained by an inequality okay we don't have to go into the mathematical details right so quantum mechanics you can actually do these experiments producing correlations and these specially remote systems and you find they violate this inequality so um the straightforward implication seems to be that the locality assumption uh together with the I mean let's not question the one or two innocuous assumptions let's look at the locality assumption okay that locality assumption is violated in quantum mechanics so that is what is taken to be the import of the bell uh inequality or violation of the bell's inequality the quantum mechanics is non-local in some fundamental respect so what does that mean so the locality principle that appears to be violated by quantum mechanics appears to be something like this that um by performing a measurement in some remote place that the outcome of that experiment in that remote place cannot affect um what goes on locally nearby right right if those two places are sufficiently remote from one another we're talking about they're sufficiently close to the same time uh such that it would need faster than light influence um uh that is what we mean by locality um but this locality assumption seems to be violated actually it's explicitly violated in the pilot wave theory right um it's pretty explicitly violated in dynamical collapse theory uh the situation with many worlds theory is not so clear okay um there's fairly compelling arguments to say that actually no there's no violation of of non of locality according to the many worlds interpretation okay is it is it fair could I could I phrase it this way that what bell's theorem bell's inequality is supposed to show is that there is no local hidden variable show so if it's the case that there is a hidden variable it must be the case that is a non-local right right yeah I mean initially bell's result was tied to hidden variable theories it was um investigated by bell in the context of hidden variable theory he was interested in the question of well what he saw was that the pilot wave theory was non-local he was interested in the question would any hidden variable theory that reproduces the results of quantum mechanics be non-local and the answer appeared to be yes now isn't that evidence for something like pilot wave theory it seems like that would be the intuitive conclusion well if it's the case we don't even hold on to locality then why would we posit that there's this pilot wave phenomena going on well that would seem to for many it was that was taken as evidence against hidden variable theory it was it was mostly understood um from the the late 60s on that bell's theorem was all about hidden variable theories uh and what it said is a hidden variable theory um that reproduces results of quantum mechanics must be non-local that was taken by many most to mean it's unacceptable in other words hidden variable theories are unacceptable I see I see so what I'm saying is now right that's very interesting what I'm saying is quite the opposite so that's almost like uh that's supposed to disprove the idea of hidden variables but if we just change the assumption of locality then it seems like in fact that's not the case that you could have non-local hidden variable theories sure sure of which pilot wave is an example right right so I mean okay I think this is perhaps what you're getting at um you might have thought uh pilot wave theory okay that's great but unfortunately got no locality in it let's find a better hidden variable theory that is local uh bell's theorem tells us or violation of bell's inequality tells us we can't construct such a theory therefore let's just make do with pilot wave theory well kind of the way that I'm coming at it is um I'm not a big fan of the many worlds interpretation or the Copenhagen interpretation and because I'm not a physicist I don't I have yet to see the dire implications of giving up locality now I realize generally that relativity is based on this idea of locality can we talk just a little bit about that idea why locality is such a central concept to why it would be a huge deal if it's the case that non-locality is right so it depends very much on the kind of non-locality okay one kind of non-locality that involved faster than light signaling would directly violate special relativity and general relativity uh so if we had evidence of that um we'd have radical falsification of one of the two or three fundamental theories of modern physics right so that's a certain sort of non-locality this the kind of non-locality that would involve faster than light signaling okay okay now the sort of the violation of locality that goes on with bell's inequality violation of bell's inequality does not imply faster than light signaling oh so the the kind of non-locality that a hidden variable theorist would say we have to accept is uh when it comes to actual experiments that you can perform not in contradiction to either special or general relativity interesting because it's not the sort of non-locality that you can use to signal with so to me just again intuitively that seems like further uh reason to believe that pilot that the pilot wave theory is the one which doesn't have any unintuitive conclusions doesn't necessarily violate principles of special relativity um so why like in your mind for example why do you why do you why not embrace yeah why not absolutely answer because uh there's two answers two I mean they can be taken together or they can be taken singly uh so one problem is we don't have a relativistic pilot wave theory or not one that describes any non-trivial relativistic phenomenon so the most trivial most trivial but the most simple of relativistic phenomena in quantum theory is say particle creation or annihilation uh we don't have a pilot wave theory um that can describe particle creation or annihilation you can try to concoct a sort of hybrid of pilot wave theory with dynamical collapse theory people have produced some toy models um but those toy models don't connect with actual physics um and the prospects seem poor uh what you can try to do and what pilot wave theorists have tried to do is um take uh typically work with field configurations rather than with particles um so the fundamental reality is built up from fields uh and you can have a sort of the hidden variable theories in terms of this dynamically evolving field um there isn't really a particle interpretation alongside of it um and I mean perhaps the bottom line is to also to say the um the dynamical evolution of these fields is not relativistically invariant now is that in terms of it can't be or is it just that work hasn't been produced yet well it seems that it can't be I see it really seems that you need a privileged reference frame uh in order to describe any um evolution in terms of classical fields using pilot wave theory ideas uh there's in other words there really does seem to be a fundamental discord between relativity and pilot wave theory ideas that's one sort of reason not to embrace pilot wave theory another reason not to embrace it um is because pilot wave theory has the quantum state it has the uniterally evolving quantum state that uniterally evolving state involves also macroscopic structures um that uniterally evolving quantum state has all of the structure that the many worlds theory says it has you can read out from that macroscopically evolving quantum state um all of the details of all of the worlds with all of the observers in each of the worlds seeing the various outcomes that they have you can decipher to discern in that uniterally evolving quantum state all of the structure that there is in the many worlds interpretation now a pilot wave theorist has got to say okay but I'm somehow discounting all of that I'm not going to take any of that seriously but it doesn't imply that those different states have an actual existence like the many worlds interpretation the quantum state the act is an actual quantum state isn't actually uniterally evolving quantum state just as it is in many worlds okay they've got everything that many worlds theory has but they are adding in particle trajectories in the non relativistic case I see now how is it that you add in additional stuff and you get out less stuff yeah it's kind of an interesting I see puzzle there okay so that's a second kind of objection to pilot wave theory and the third kind of objection to pilot wave theory is it's just proved it's never been fruit fruitful and uh it puts in by hand a picture of reality you've got to discount a big major part of it namely the many worlds because that's in there too but it's putting in by hand a picture of reality that is just more you know sort of intuitively acceptable right which I intuitively like right but this is a methodology in physics and by hand is a great way of putting it right it's a bad methodology you know you might as well put in by hand a little rule that says you know these incredibly weak electromagnetic excitations electromagnetic signals that we're getting from the sky that they're incredibly minute and tiny and we should basically ignore them in our picture of the universe that really the universe is because it's pretty or otherwise yeah that's right it's just nicer to think that the bright lights in the sky are just bright lights let's not go into it you know all of the details of the electromagnetic because it's all electromagnetic pretty well we have some cosmic rays results but otherwise everything we know about the universe comes through electromagnetic signals I mean there is something that's philosophically interesting about many worlds that I think ought to be noticed especially if you're particularly more interested coming at this from say epistemology the many worlds interpretation carries with it an analysis of probability which is better than anything we've ever seen before okay in any physical theory in any toy model so if you're interested in why is it that there's some objective stuff out there in the world that dictates what we ought to believe in the ways of subjective degrees of belief that credence should conform to the Everettian quantum theory or many worlds theory explains why it tells us why we should conform our rational expectations to certain physical quantities out there in the world interesting right and no other theory does that and it tells us what objective probability is in the world and again no other theory does it pilot wave theory doesn't do it dynamical collapse theory doesn't do it they sort of build in probabilistic structure in the dynamics in the case of collapse theory but what you'd have to say is to question what is probability you'd say well it's just built into laws you want to say what is it about a given physical situation that makes the probability 0.6 rather than 0.2 what is it about that physical situation and the answer will be it's just built into the laws in pilot wave theory something similar in many worlds theory you say oh what makes it 0.6 rather than 0.4 is because the amplitudes for branches the modular squares of which are 0.6 and 0.4 these amplitudes for branches are out there in the world so last question I want to ask you is we're pointing at a fundamental tension between quantum mechanics and regular macroscopic mechanics is there any way right now that these two things can be put together in a coherent way because what I have heard is that when you're looking at microscopic phenomena it appears as if you know the laws of physics are different than when you're looking at macroscopic phenomena but but by the time you get to macroscopic phenomena we don't really have to worry about all the weird quantum phenomena and even if those two principles like even if there's two actually different laws of physics that we're talking about and they're mutually exclusive we shouldn't worry about it because everything resolves itself yeah so it just doesn't work that way I mean the reason it doesn't work is that we don't have a classical physics for tables and chairs we really don't classical physics was never able to explain stability of macroscopic structures it was never able to explain um how you can have a grain of dust even which has a stable shape um try yeah imply quantum classical physics you know point particle interactions whatever potential functions you like it's unstable um it's quantum mechanics uniquely that explains and predicts stability of structures bound states um it explains why atoms are stable it explains why collections of atoms can stably be coupled together to one another so as to have a stable shape and structure and form and that's what's needed to build up and use actually any branch of the special sciences you know metallurgy crystallography hydrodynamics you name it all of those branches of physics um require stable structures actually they're provided always by quantum theory so you can't do without quantum theory there is no autonomous classical theory of of matter so would you say it's fair to say if to the extent that there's any tension between the two quantum mechanics is more fundamental and therefore oh sure any theory needs to be adjusted it's what lays on top of what it's fundamental yeah absolutely and and what's um and this wasn't obvious back in the 20s and 30s when Bohr was laying down his uh interpretation what Bohr thought is that classical physics is the more fundamental um and quantum mechanics is just a calculus that explains why we have small departures from the classical uh small dimensions okay so what changed that picture is um partly what I've already spoken about classical physics actually doesn't account for stability of matter at all um but partly that quantum mechanics increasingly was able to recover quasi classical approximately classical physics in so far as issues of um I mean it puts in the stability and then it shows how those stable structures evolve over time in approximately classical ways okay you might think look this is a bit weird classical theory doesn't give stability but it does there is a way of being classical but there isn't a way a classical way of being stable that's about right there is a way of being classical newtonian mechanics we all studied at school a little bit there's a way of being classical but what it is that behaves in that approximately classical way can't be accounted for in classical principles quantum mechanics can account for what it is that not only for what it is that obeys those approximately classical equations but that that thing obeys those approximately classical we can deduce that extract that from quantum physics itself the way of doing that though is exactly the way that yields the many worlds interpretation it's not a route that makes much sense either from dynamical collapse or from pilot wave theory you know pilot wave theory the methods used to get out stable structures evolving in approximately classical ways seem to be a whole a whole sort of dimension of physics that in principle shouldn't be there at all because what pilot wave theory is telling you is you've got these classical trajectories well the trajectories may not look particularly classical but they're trajectories you sort of you build in what seems to be required for classical classicality right there in the macroscopic level and then you ask so how come we see at the macroscopic level anything classical and the in a way the pilot wave theory wants to say well look it's just more of this stuff so you know where's the there is no complicated story it's just more and more trajectories but actually what you've got to do is you've got to show how the more and more trajectories actually start to behave as stable bits of matter obeying approximately classical equations and the only way to do that it's not through the guidance equation the way to do it is the same way that it works in many worlds theory so this is another you understand you get lots of hints that pilot wave theory doesn't actually deliver or as far as it delivers it's giving you a very simple intuition for things like the Toothless experiment but not much more I think that's an excellent known to end on I really appreciate this conversation okay well thank you so that was my interview with Dr Simon Saunders of Oxford University I hope that you found it helpful obviously the topic is gigantic there's lots and lots to say there's lots and lots that has been said much of which in my evaluation is nonsensical and what it stems from a lack of understanding the basics so if you're new to the realm of quantum mechanics I hope that this interview can serve as a springboard to learn more information about the competing theories in the world of quantum physics and the different experiments that are taking place because it's really obviously a fascinating and cutting edge area of inquiry I've also done a little bit of writing on the topic specifically combating the explicit irrationalism that comes from people drawing from quantum mechanics to try to justify conclusions like we can't know anything about the world because reality is logically contradictory and the universe is just a great big blurry paradox that only resolves itself into one way or another by our minds which are at the center of everything I combat these ideas very sharply directly and perhaps derogatorily in a piece that's called quantum physics and the abuse of reason which is one of the most popular articles that I've written if you just google that title it'll come up but I'm very glad that I got Dr. Saunders to sit down and work through these things with me I also learned a lot myself so this interview took quite a while to put together as you can imagine and if you valued it if I've created value for you then please go to patreon.com slash Steve Patterson and show your support if you want more interviews and content that's produced like this you can become a patron of my work which means that you pledge a dollar when I release new material like this I am trying my best to create as clear and rational a worldview as possible all right so I have lots more to say on the topic I'm sure I'll do more interviews and more detailed breakdowns of these ideas and in fact coming up I'm going to do a whole breakdown episode where I'm going to spend a lot of time on this interview to give you more of my own personal beliefs and more further clarification of the ideas that we've been talking about so thanks for listening everybody I really hope you found this useful and have a great day