The 2022 Clauser Nobel Lecture

so our next speaker is John klauser he was born in Pasadena California Us in 1942. he studied undergraduate physics at Caltech and Colombia University New York and received a PhD in physics from Columbia University in 1969 from 1969 to 1997 he worked at University of California Berkeley Lawrence Berkeley National Laboratory and Lawrence leave them all National Laboratory he's pressed presently research physicist at his own private lab in Walnut Creek California so please join me in welcoming John closer to the stage to tell us about the development that led to this year's price oops no wait a minute poof I'm not I'm not connected no that's we're not something is not right uh let me start over again then here okay okay uh what I did in all of this was the first experiments to actually uh test what uh John Bell had shown us was probably one of the most important uh discoveries I I would think of uh the recent decade or the recent Century if in fact the so these are so I will discuss the experiments and then a in order to understand the experiments Mike horn and I developed what's now called the theory of local realism which is in essence Einstein's whole program for uh doing physics and unfortunately it's wrong which is what the experiments show and finally I will end with the uh does this work yeah uh discussion of why I still am totally confused about what's going on with quantum mechanics okay let me start with question is what is quantum mechanic what is quantum entanglement okay uh quantum entanglement uh started out with Schrodinger Schrodinger produced not one but two important equations you started out with the first uh equation which was for single particles the particular hydrogen which has a single electron and he miraculously it described the structure the structure and the energy levels of hydrogen but more complicated was helium which had two electrons so he produces a a a second uh equation which now involves two electrons the two are very different equations the second one allows quantum entanglement which is a new equate uh Solutions emerged from from the second equation and the peculiarity is that the two electrons are now intimately uh correlated at the time nobody suggested doing any experiments to test this rather bizarre prediction however both Einstein and Schrodinger were very disturbed by this phenomenon and in fact uh Einstein badalski Rosen in 35 proposed the addition of additional variables through quantum mechanics to in order to explain what's going on Niels Bohr on the other hand said no they're not needed and and I discussed all of this very nicely so one of the question first questions I was asked when I was talking about this in the uh Swedish Embassy uh a couple of weeks ago was what is a bell inequality this is what we in fact uh tested there's not one but there's actually three important bill inequalities that I want to talk about the first of course was John Bell's 1964 inequality but uh uh and I'll described very nicely there's one problem with being of the theory in order to be useful a theory must make an experimental prediction and unfortunately uh John Bell's uh uh paper made no experimental predictions because it made demanded a perfect experiment and uh which which had certain uh certainty in the outcomes and as uh Ben Franklin pointed about the only thing certain in life are or in nature are death and taxes unfortunately this is not Texas so the uh uh with uh help from uh my associates uh Mike Horn uh admir shimone and Dick Holt who is here in the in the audience uh uh We've uh produced the uh closer horns for money Holt now commonly referred to as chsh inequality which was made the uh first real testable experimental prediction so and we proposed a detailed experiment to do that and we noticed various important loopholes uh one of which of course was mentioned that he tested but a very important loophole was that the data really couldn't violate the inequality on their own so we had to add some additional assumptions so the third inequality is now uh the was uh produced by Mike horn and I uh in 1974 and it is the first loophole free experimentally testable uh uh inequality okay let's start with the first one uh Atlanta's already noticed this I signed panelski Rosen had always and and others had always assumed that that quantum mechanics always made uh correct predictions the grand irony of this Bell's paper is that he showed that Einstein's original intent of that paper was exactly the opposite of what was true that the if they wanted to show that that the correct predictions led to uh the need for hidden variables and what bell showed was that if you put it hidden variables in then you can't get the uh predictions of quantum mechanics so again I said it was not really testable so uh chsh in 1969 we were inspired by this work and said wondered well this can we really relieve the get rid of Einstein's requirement for a perfect experiment and indeed we found yes we could and so we designed an experiment uh to actually test it we worked out all the details of what you uh you needed to do in order to test it uh and that was the first actual hard experimental prediction uh and it doesn't you require uh bills uh impossible to achieve its conditions so uh we now have two theories two different sets of predictions quantum mechanics and bills uh the CH inequalities prediction so being an experimentalist let's actually do an experiment and find out which one is true so in order to do this we had to add a minor supplementary conditions but they were we believe that they're of quite reasonable rather weak Okay the third inequality is the CH or the closer horn inequality that was developed in 1974 uh and it was to test uh what is now called local realism we wanted to we wondered when we were doing the experiments we wondered what is really being tested here is it just the addition of hidden variables or is it something more profound than that and we found that indeed it is far more profound it was a test of Einstein's whole platform for doing physics that we effectively were putting him out of business and so when we and in fact the theory when we develop it was effectively Dead on Arrival it was already refuted but nonetheless we tried to put it in as clear as possible set of terms as we could so and in the process we formatted a new inequality the CH inequality and it allows loophole free tests so uh now if with some even milder additional assumptions then the first experiments that uh that I had done uh 72 and 76 uh actually knocked it out so that it was already dead more recently and it's taken a long time because the technology did not exist at all to in order to test it in 1974. uh it has now been tested conclusively with so now without any loopholes at all one can say uh and I agree with the last early uh conclusion it's dead Jim so what are some of the experiments uh there are three important ones that that I did uh first was with Stu Friedman who was a graduate student at UC Berkeley in 19 uh we published a results in 1972 and this was the the first experiment to actually test the chsh inequality in the in parallel with us as Nicole I mentioned who is here was working with Frank Pipkin at Harvard and they got the opposite result oops one of us is is in trouble so they decided not to publish they were skeptical of their results but now I'm skeptical of my results so uh what do I do well I just decided Well I needed to uh repeat uh their version of the experiment which I did in 1976. and then there's just along the way one of our assumptions had uh and I was kind of searching for loopholes uh had required photons to act like particles but I discovered that there was no actual experimentals uh proof that that particles that photons did act like particles so I did an experiment 74 to prove that okay so here is the the first experiment a picture of it and that all at the uh right in it was a very young Stu Friedman uh in the middle is a the atomic beam apparatus sitting there pumping away oil leaking all over the floor pair of polarizers on each side which would which would rotate so and this one became a stu Friedman's PhD thesis at uh uh Cal Berkeley so what we did is we had a calcium Atomic beam and we excited it with this UV lab very weak extension we wished we'd had lasers which didn't exist at the time so uh we got 6.3 Sigma result I mean the five Sigma uh Criterion that is now common was invented by Louis Alvarez at Berkeley and he he uh was a a strong Taskmaster on any experimental results that came out of Berkeley so this was the the second experiment which I did I mentioned uh this was a repeat of the whole uh Pipkin experiment I use the same polarizers but I used their uh uh Source uh of mercury uh foreign the two photons and Dick Hort uh hold uh very generously taught me how to do it uh could not uh there's a it's not an easy and that is my Nobel artifact that I have donated is one of the the sources so it used Mercury uh with an electron beam exciting yeah the atoms and I got at least a four Sigma result there and we use this the same protocol in order to uh introduce the the assumptions so the other experiment that I mentioned had to deal with it did particles was there a real way experimentally demonstrated wave particle duality for photons photons started in 1917 when Einstein was trying to explain how do does a gas and a thermal uh applied spectrum of Life come to equilibrium thermal equilibrium with each other and he noticed that photons had to be behave by what he called directional energy bundles uh we now call them photons then Schrodinger noticed that what's the difference between asking the question well what's the difference between a particle and a wave well a a wave could be just as a classical pulse of light and that is commonly referred to as the old Schrodinger uh interpretation so how does one tell tell them apart suppose you have a source and you send light through a half silver mirror if it's a wave the wave will go both ways reduced intensity if it's a particle the particle will go one way or the other now if I have two detectors behind the uh the half silvered mirror if it's a wave they will both see this pulse and there will be finite a probability that both will register simultaneously if it's a particle only one of them so how does one uh do that uh so actually Schrodinger suggested this and yannisi and uh Budapest actually tried it but unfortunately they put in did an inconclusive experiment so I went back and started figured out how did one do it totally conclusively and uh so I did it actually where you're using the the same source that are used for the uh producing the for the Mercury uh bellotherm experiment uh who had photons going in both ways and two half silver mirrors and using some a work front by uh Glover's formulation what could show that's the The Coincidence rate between here and here there should be none of course if if it's a particle but but there should be an anomalous if it's a wave uh a coincidence rate the product of these two coincidence rates here and here uh must be greater than the the uh Pro uh the product of these coincidence rates and so here's the data and it's quite the opposite by about uh 20 Sigma so indeed particles to do act uh photons do act like particles so as I mentioned before Mike horn and I were trying to understand what it is that Bell's theorem experiments actually say so we developed What's called the theory of local realism originally we called it objective local theories uh in our first paper on it and it's an extremely general theory that takes it to account all of the basic uh elements of Einstein's platform and uh in along the way we produced the CH inequality which is actually a hard experimental prediction with no loopholes we did not have any Assumption of causality which we had earlier in there was no Behavior requirement for a particle like Behavior uh and then there was some discussion among various other workers John Bell and admir shimoni added additional components so presumably uh it is better called Bill clauser Horn shimoni local realism it's very short-lived as I mentioned it was already Dead on Arrival but that wasn't good enough it had to really be shown to be dead with no loopholes to it by testing okay what does it assume localism is extremely Simple Theory Anton zeilinger and please quote me uh tell me if if I am misquoting you at one point he had a conference he said if Belle's inequality and local over realism had been discovered before quantum mechanics it is so reasonable it would have been taken as a law of nature or adapted as a law of nature uh unfortunately it's wrong so what does local realism assume it assumes that nature is made out of stuff um well what is stuff well we we may not even know what it is it is uh it is what I signed Podolski Rosen referred to as elements of reality it's what we call matter or uh uh What uh closer horn called objects John Bell referred to it as beebles it's there it's distributed throughout space now actually Einstein's whole program in general as if any in particular goes a lot further and he said they said says that well it has a finite mass energy density and it it is that density that determines the whole geometry of the universe we don't need that for local realism all we need is that it's there so it could it could evolve stochastically or it could evolve uh deterministically we don't care it's stuff is stuff you can put in a box you could uh throughout it and it's the stuff that's in the Box if you're doing an experiment the stuff determines the probabilities of the experiment that you actually do there we assume that there are Real Results the that happen when you do an experiment that is uh unlike uh Schrodinger actually he he thought the whole idea of the The Cat In The Box experiment was a total of absurdity we assume that the cat is either alive or dead and we just don't know which that a real result always occurs presumed that the properties of the stuff determine the results of an experiment you do the if you have a parameter setting on your apparatus and then you change the parameter setting presumably you will get a different result so what does it predict well suppose you have two very widely separated boxes each has stuff in it and you're doing experiments in these two uh wide separated boxes so you've hurt the Assumption the following Einstein's uh requirement for locality is that stuff in one box and the out of the parameter settings uh the result of the experiment in one box measuring that stuff cannot be influenced by the parameter setting Choice made in the distant box that's all you need to produce uh uh the uh the closer horn inequality okay so here's what are boxes well they're just closed surfaces they separate each closed surface separates has a an inside and an outside so here we have a pair of boxes okay these characters are uh well I made that drawing in 1976 uh before the characters had been named uh Alice and Bob well okay so this but she but she perhaps trans I don't know so what uh here we have Alice and Bob making measurements and they get a result yes no on each side so we have our boxes here are now shrinking at the speed of light and so there's drawn so that we're doing the experiments when there's space like separated so if I plotted versus X and time uh here are the boxes shrinking uh simultaneously and doing experiments so the assumption is that stuff back here in the common overlap region is what is the result of of the extremist if you read some of John Bell's stuff you have to be careful for some reason he had these reverse he had the arrow of time going to the left uh I'm sure he had a reason for it but I don't know what it was okay it's dead Jim I apologize to Star Trek who was for a long time it was very difficult to do this the technology just simply did not exist back in 74. but it has improved so it became very important to eliminate the loopholes in the earlier CH tests of the chsh inequality and uh to really do a loophole free experiment and finally most recently at a labs in Vienna and in Champaign Urbana uh Illinois uh it has been totally killed dead okay now I will use what my time remaining to make a a value statement if you will about why I have the fattest idea what's going on and I argue that in fact there's been an elephant in the room pardon the metaphor that has been hanging around ever since uh Schrodinger and epr remember the trottinger produced two very different equations he had one for hydrogen with only a single particle and he had another one for helium which had two particles nobody seemed concerned at the time about the fact that these two equations were formulated in very different spaces and they I are what I believe is improperly linked and I'll go on to that in a minute by what I call borns ambiguity born was the one who who said that they are equivalent and this this has been the elephant's been hiding in plain sight and I noticed that in fact the Einstein podolsky Rosen art debate a bore debate was never really settled various textbook authors believed one or the other of the authors and they're developed in the literature in the textbook industry two very different schools of thought and most people never seem to notice this but with the Advent of local realism and quantum entanglement then it became clear that one could actually contrast and identify these two schools of thought okay School number one either is essentially a form of local realism so one of the textbooks that promote uh uh uh the School number one it is what I call the laboratory space formulation of quantum mechanics okay it was taught you're all I kind of cut off the uh the list at about 1980 begin at first was born born's textbook two very important uh textbooks uh familiar Dickie and whitkey and mersbacher were very popular uh all follow this uh like for example inborn case the waves are propagating in the lab and he shows pictures of waves moving around all of these books show waves in the it was propagating through a two-slit experiment in lab space Feynman uh this is his review article 1948 even puts it into the title this is a space-time uh operation French French and Taylor uh using MIT and of course the Original Classic shift okay what is School number one Quantum Mechanics for single particle systems is formulated in lab space or real space the XYZ of this room and Heather is a point every point in this lab space has a vector to it and Schrodinger's wave function is a function of its position uh in the room or in the lab and more importantly the probability density PSI star PSI is a function of his position in the room it is the evolution of of these waves is governed by Schrodinger's equation in lab space and it depicts waves of probability you've probably heard any number of people describe quantum mechanics says waves the probability moreover there's also it's defined by born a conserved uh probability current which flows like a fluid through through the lab and he famously used that uh of current to describe flux conservation frieden Rutherford scattering unfortunately it only works the slab school of thought number one only works for single particle systems it cannot describe two particle systems or and it cannot describe entanglement so what's goal number two also had a large group of textbooks which very specifically said we are in configuration space okay probably one of the most important ones but beta and saw Peter with the authoritative work on hydrogen and helium Jordan and Drell relative is a quantum mechanics caught in and shortly uh calculate Spectra of atoms land down on lift shits great quantum mechanics to expect it was translated by John Bell actually and messiah's famous book uh except he he claims he's in in configuration space but actually he cheats a bit and probably most importantly fall was Von Neumann's textbook okay what is the configuration space School of quantum mechanics it is a very very different from what I just described the wave function depends on A System's degrees of freedom this Kim's there could be many of them uh there could be k degrees of some large number k and so we have a wave function and these are all this is straight out of Von Neumann's uh both so if you have say two particles in helium then now the argument space of the wave function is very different it has an x y z of particle one XYZ of particle two wait our lab does not have six dimensions something has dramatically changed importantly the position in the lab is not one of the arguments that means that its value is the same everywhere is base unlike the lab space formulation that there were it's different every point in space so Schrodinger's equation now is very different it's divided describing the evolution of particles in this configuration space it's an abstract mathematical space it is not at all this the space uh that Star Trek was exploring the a few important and it's absolutely required if you want to discuss more than one particle systems borns conserved currents cannot be drawn in a configuration space Green's theorem does not apply more importantly the there is no prohibition for propagation of signals faster than life in configuration space it's a purely arbitrary space totally as fact it's what the imaginations call a vector space not at all so it was been asserted and I as far as I could trace back this was originally to to Bourne's uh dog that uh these two cases are are the same they are not clearly the two uh wave functions are very different they are not equivalent one depends on the position of space one does not there are no Associated probability waves for configuration space so for my last slide I will describe why I find this all totally confusing you gotta have configuration space in order to describe more than one particle systems but there's no reason uh that the special case of signal particle systems should be any different so you need a so and we notice really that the lab space formulation is uh really a form of local realism it's dead Jim so now all of these great models conceptual models of probability waves propagating in space are also dead the flow of currents probability currents are dead I don't know how to visualize propagation in configuration space there are a lot of people here who know a lot more quantum mechanics than I do and maybe one of them will help me understand what does it mean to have a way of propagating and configuration space I don't know uh thinking Wiki and Bruce bucker were on my side they both said gave up and said oh gee this is all our our great models i.ei earlier uh sections of the book we really should throw throw away so I have one final challenge to my theorist friends if I still have any remember we said that that general relativity uh is a form of local realism so and it is a general relativity that for example gives us black holes so but that's all formulated in under a local realism Theory so my challenge is to the theorists is it possible to have two entangled black hole spins thank you