Antimatter and other deep mysteries – Public lecture by Dr. Gerald Gabrielse

hello welcome to fermilab to our lectures we  thank you very much for joining us tonight i'm   dave dykstra chair of the fermilab public lecture  committee so now i'd like to introduce tonight's   speaker dr gerald gabriels dr gabriels became a  professor at northwestern university a few years   and a few years ago and is the founding  director of its center for fundamental physics   prior to that for 30 years he was a professor at  harvard university he's a member of the national   academy of science and the american academy of the  arts and sciences he was a pioneer in the field of   low-energy anti-protein and anti-hydrogen physics  research and as a world leader in that field   he was awarded harvard's prize for the exemplary  teaching of undergraduates and their prize for   exceptional research along with major prizes  from the u.s american physical society from   germany and from italy i have a bit of a personal  connection with him myself since we both attended   the same chicago area college and and i've heard  him speak in other contexts on science and faith   but to welcome him now everybody please click or  touch on click on our touch your raise hand button   and uh we will get a count of that and go ahead  jerry well hello everybody um if you if you see   where i'm sitting uh i'm i i live in a state of  denial okay that's the building that i work in   and i've carefully removed all of the snow  from the lawn so that you would think that   or realize just what paradise northwestern  university is i hope to do this lecture i guess it   was last spring sometime in person but it wasn't  to be and so we'll do the best we can via zoom   it is a privilege to speak to you the topic  today is anti-matter and deep mysteries   and uh as was mentioned i'm the director  of the center for fundamental physics at   northwestern university i'm also on the faculty  there and i've been there for several years i   guess but my whole career i've been trying to  study the most fundamental physics that i can   and i'll show you a path which is a little  different than the fermi lab path which is also   important and which is a path that's followed by  by many more people than folks like me i'll talk   to you about tabletop physics but to start  out i want to introduce you to anti-matter   that's probably a bit more necessary than it  used to be because i think star trek is fading   from many people's memory memories and then after  introducing anti-matter i'll talk a little bit   about what the standard model of particle physics  is you can't really go to lectures at fermilab   without hearing about the standard model of  particle physics at least not scientific lectures   and i will try and explain why it's the great  triumph but also the great frustration of modern   physics and then i'll try and illustrate how  one can try and learn about this standard model   of particle physics and what's clearly wrong  with it you know probing for hints but using   a tabletop experiment and a tabletop experiment is  uh probably that shouldn't be hyphenated it's done   in different ways but a tabletop experiment is  something that's roughly the scale of a tabletop   rather than the scale of a very large building  that requires thousands of people to work on   okay and um to be a little crude about it okay and  my fermi lab friends will hate me for this but um   you know if i if you want to learn what's  inside of a chicken okay one way to do it   and this is very crude is you take two chickens  and you collide them and you see what flies out   now that's a an unbelievably awful way to do it  and the image probably is is scarring you even   as i continue okay instead what we try and do  is we try and measure instead of using energy   and just smashing things together in the way  that's been so fruitful at fermilab what we try   and do is measure with very very precisely but  with low energy much smaller scale experiments   we try and and see small little effects that  we can interpret and i'll illustrate that   and so the kinds of illustrations i'll give  are testing the most accurate predictions   of this standard model that's the fundamental  mathematical theory of physical reality testing   something that are called the symmetries of  the standard model and in particular comparing   matter and anti-matter is what i use to illustrate  and looking where the standard model and possible   improvements to the standard model that that have  been proposed to look look where those things uh   agree or disagree okay and uh okay so  let's start with what is anti-matter   now those of you who are a little older okay know  what anti-matter is because you heard or watched   star trek right so spock and kirk knew what uh  what anti-matter was that's well before kirk   got his cpap machine okay and there's the you know  the the the starships the the spaceship enterprise   was propelled by anti-matter and when klingons  were coming then uh you know uh anti-matter was   put into the containment pod and sometimes the  pod ruptured or threatened to do so and that   created various episodes um and uh dan  brown's book there's a best-selling book and   movie actually from from some years ago was  actually based on my research with anti-matter   okay and and i'll i'll discuss of that a little  bit as well now we actually do science not science   fiction and that's uh uh so we'll talk about what  the the science is behind the science behind this   what this the science is that's in front of the  science fiction so there's generations of trekie   there's all sorts of clever uh uh directions that  that show was taken but the science reality behind   behind the science fiction well what is matter  what is anti-matter let's do a comparison here   now we are made of matter okay matter for to be  over simplify a bit is anything that's made out   of electrons protons and neutrons now dark  matter may not be i'll say more about that   later but the matter that we know and love is  electrons protons and neutrons okay but the   electron is the very lightweight one there's  about two thousand of them per proton and a   proton and a neutron are about the same mass okay  so they all have a mass they all have a size well   the electron size is so small we haven't detected  it yet depending on how you define the size and so   we say it's it's smaller than 10 to the minus 18  meters which is not very large now those were the   matter particles and now the antimatter particles  uh you know uh what about those let's see let me   put my laser pointer on here so these are the  particles and now for the anti-miter particles   well there's one that corresponds to each of the  matter particles so the electron is matter there's   a positron which is anti-matter and the positron  uh you know has the opposite sign of charge   okay but it has the same sign at the same mass  okay so that's the uh that that's the difference   between the two okay just the the charge the  anti-proton is the anti-matter counter part of   the proton it has a negative charge rather than a  positive charge it has the same size and the same   mass so far as we know and then the neutron has  uh uh has the same mass as the anti-neutron and   it's also oppositely charged to the anti-neutron  but by a technicality they both have zero charge   so negative zero is zero so the rule still  still holds now only measurements will tell   how identical the particles really are okay so  in the end this is a kind of theory it's a model   and we always go in the science as we go to  reality to find out whether we're right or not now we can also make atoms out of matter that you  know and we can make them out of anti-matter so   in high school chemistry you studied the the  simplest atom and it was the hydrogen atom and the   hydrogen atom has a proton in the center and an  electron in orbit around the outside now of course   with quantum mechanics nothing's really in  orbit and there's no angular momentum and   this is fuzzed out and all this kind of stuff  i love quantum mechanics but we don't have time   to go into the details that would be a fun other  lecture but we won't do that tonight okay now an   atom has an antiproton with a positron in orbit  okay and and otherwise it's it's the same well   it's completely different because there's  different particles but it it has the same   structure we believe now notice this atom the  hydrogen atom is held together because there's a   proton attracted to the electron they're opposite  signs of charge and opposite sides of charge   attract each other similarly for an antihydrogen  atom there's an opposite sign of charge a negative   nucleus and a positive electron and they attract  each other as well so that works that works also   now of course if we can make atoms we can  emit out of antimatter we can immediately   think why not make people out of antimatter  and if we can make people out of antimatter   why not make an anti-matter universe  so if we have matter particles we   can make matter molecules and atoms and matter  cells and matter people if we have antimatter   particles we can make antimatter atoms and  molecules antimatter cells and antimatter people   and the interesting thing is we currently do  not know any reason why people and of universe   could not be made out of anti-matter rather than  matter that's one that's what i'll refer to as   the the first the four mysteries that i'm going  to discuss uh deep mysteries as i called them   now would anti-matter and matter people oh i have  a typo here would matter and anti-matter people   differ okay so let's consider gabriel's made out  of matter okay there's me in an uncharacteristic   pose wearing a suit okay and you know we could ask  suppose we could take all of my particles all of   my protons electrons and neutrons and turn them  into anti-protons anti-electrons called positrons   and anti-neutrons what would happen okay would i  be smarter i'd be good would i be more handsome   would i be less massive all of those things would  be great would be great news okay unfortunately   the bad news is that modern physics predicts that  gabriels and the anti-matter gabriels would be   just the same it's very difficult in fact it would  be to tell to tell the difference between the two   now and so far as we know it's not only  people but the whole universe could have   been made out of anti-matter in fact it would  be nearly impossible to tell if we lived in   a universe made out of antimatter rather than  matter the only known differences would be so   tiny that very huge accelerators like at fermilab  or cern would be needed to tell the difference   so deep mystery number one why are people and the  universe made out of matter and not antimatter   and as advanced as we are in physics we do  not know the answer we are still now looking   for clues by comparing anti-matter and matter  for some possible differences that we've missed okay what happens when anti-matter and matter meet   this is key to the science fiction okay and that's  why there's so much fascination in science fiction   with antimatter and that word that's used is  annihilation which of course adds to the intrigue   on the particle uh on the particle scale here's  what happened if i have a matter particle called   an electron and it collides with an antimatter  particle called the positron okay we've gone   through those already and they hit each other  um they are attracted because they have opposite   signs of charge so they will they're quite  willing to hit each other both particles will   disappear entirely we say they annihilate and when  they annihilate energy is is is uh is released   and if for different annihilations the energy  is is uh released in in different forms but   here's one way to think about it if if this was  in a bucket okay and there was and this uh this   collision happened and the annihilation happened  what would happen afterwards is you would have a   hotter bucket okay there would be a little  bit of heat given off by this annihilation   okay a little bit of heat energy and it would  heat your bucket now the energy that's released   uh you all know uh the formula that applies to  it because almost everybody in our culture knows   e equals m c squared that's einstein's famous  uh formula now more people know the formula   than know what it means so i'm going to try  and explain what it means in this context   to do so let's ask the question what happens  when anti-matter and matter gabriel's meet   so here's the anti-gabriels and here's the  gabriels and they're about to shake hands okay   now you know this word annihilation is going to  happen uh up here somehow what's the story on that   well let's suppose i'm a hundred kilograms the  anti-gabriels is 100 kilograms and the gabriel's   is 100 kilograms because after all were identical  except for having matter changed to anti-matter   and since all the matter particles have the same  mass it's reasonable to assume that the two the   gabriels and the anti-gabriels will have the same  mass so in einstein's famous formula the e is the   energy that would be released okay and m will  be the mass that disappears which will be all   the mass assuming that all the protons find all  the anti-protons and alliance all the neutrons   find the anti-neutrons and we'll just assume that  for simplicity there may be a bit of an ignition   problem here but we won't go into that because  this is a conceptual discussion and the the energy   released and the mass that disappears is related  by the speed of light who would have expected that   okay that's why we needed einstein to tell us  this because that's quite quite a jump now if   we say how much energy is for 200 kilograms of  mass that's one over large uh you know male adult   okay how much energy is released well i wrote it  in different units here i hope i've calculated it   correctly but there's this many kilowatt hours we  pay our bill our electric bill in kilowatt hours   okay and a kilowatt hour well a typical  house will take about 20 kilowatt hours per   per day okay of power so you can see this would  give electricity for lots of houses okay or in   terms of the yearly output of 500 nuclear power  plants and you can see the scale because a nuclear   power plant you know gives electrical power to a  whole region of the country and or if you like to   have violent tendencies it's the energy from 4 200  mega tons of tnt now a modern missile can carry   about 20 megatons i'm told i'm not expert in  this okay but you know this is the you know   one person one matter and one anti-matter person  converting their inner their their mass to energy   would release an enormous enormous and  unthinkable amount of energy way way more   thousands of times more about a thousand times  more than a nuclear explosion per unit fuel mass okay now one could worry about having too much  anti-matter around more about that in a moment   so let's ask how much antimatter is there in  our universe well the answer is essentially none   okay there's a few positrons that emerge when  nuclei decay now nuclei these radioactive nuclei   are still remnants of the big bang they haven't  yet decayed because they have long lifetimes   okay these positrons are used in positron  imaging tomography they're very useful   and we use such positrons at at northwestern we  compare them with electrons as a way of studying   the symmetry between uh matter and antimatter  another way to do it is done both at fermilab   and at cern and i put a picture of cern because  it's further away and because i worked there   okay for 30 years i led a team at cern using  anti-protons but here's france over here and   here's switzerland with a medium-sized airport the  world's largest storage ring a big circular tunnel   that's 16.6 miles in circumference there and  and anti-protons and protons were at one time   put into there to collide with each other and and  make some nobel prizes okay but the anti-protons   were actually made in a smaller ring okay in in  in this part of the site but that's that's one way   to do it it takes a tremendous a lot of energy  and a lot of people to do this so relatively   speaking compared to the number of the protons in  the in the universe there's almost no antiprotons   also a very few antiparticles are produced  when ant when particles from space   smash into atoms in our atmosphere okay but  that's also a very rare event and there are some   positrons that have been detected annihilating  near the center of our galaxy so there's almost   no anti-matter in our universe and we either have  to get it from a radioactive source or we have to   smash protons together at tremendously high  energy actually this is this should say smash   protons and protons together at fermi labor cern  another typo okay sorry made the slides today   all right now a best-selling book was based  on our work um what we did is we went to   cern and we trapped uh um anti-protons in a small  container called the trap and i'll tell you about   such a trap in a few moments okay but this uh  apparently this author dan brown heard about this   and in his book and then in the movie thugs  stole the trapped anti-matter from the cern   lab where we did the research they buried  the trap anti-matter under the vatican   and then they threatened to let it annihilate let  it fall out of the trap annihilate with protons   and since they knew about the explosive power the  cardinals were really scared as they met to choose   a new pope okay so that that was the premise of  the book um there was one small missing detail   okay and the missing detail is if all the  anti-protons ever made in the history of   the world were annihilated at the same time  there's far fewer than there would have been   in the anti-matter gabriel's there wouldn't  have been enough energy to boil a pot of tea   so clearly that the cardinals should have  studied more science before they got all upset   and then made the movie but i always say that  what dan brown did for the roman catholic   church in the da vinci code he did for my  anti-matter research in angels and demons okay whenever anti-matter comes up people ask you  know what about anti-matter weapons then you know   could we blow up something that seems to be  a human thing to think about and the reason   is there's much more explosive power than nuclear  weapons with the same mass but i've already hinted   at some of the problems we simply do not know how  to make large amounts of anti-matter no one has   figured that out or even come close remember the  illustration that if we took all the anti-matter   ever made and annihilated it at the same time we  still wouldn't have enough okay to to heat a cup   of tea a pot of tea it takes a tremendous amount  of energy to to produce anti-matter it's almost   impossible to store it because you have to have  a container where the anti-matter doesn't hit the   walls more about that in a moment now that has  a disarmament opportunity of course because if   you did manage to make a weapon the person most  likely to be destroyed would be the weapons owner   so that's a that's a nice nice feature  but the rest make it kind of difficult   i'm often asked can you make an anti-matter energy  source well the answer is no again because storage   is essentially impossible okay and it takes much  more energy to produce the energy than is released   okay by many factors and and you know one thing to  remember is that when we uh produce fossil energy   from fossil fuel or from uranium in both cases you  know our our earth has prepared limited supplies   of these fuels and they're buried in our earth and  we dig them up and use them up once for all time   okay and that makes it possible for us to do it  if we had to take you know uh um organic matter   and turn it into fuel oil that would also be a  very time consuming and energy-intensive process   and i don't even know how we would make uranium  and we'd have to use accelerators again it   would be very inefficient take much more much  more energy than we could ever get from it so okay now let's change to the more to the the pure  science get back get to the standard model and the   deep mysteries so what is the standard model  of particle physics i'll try and give a brief   explanation then deep mysteries and antimatter  there are some deep mysteries that are directly   related to anti-matter and then i'll just mention  other deep mysteries just for general interest   okay now the standard model is the fundamental uh  it's the most fundamental mathematical description   of physical reality okay and i call it the  great triumph and the great frustration of   modern physics and i'll explain why first what is  the standard model well it's a postulated set of   standard particles okay there's quarks okay and  there's leptons okay and there's neutrinos and   then there's various glue particles some called  gluons some called photons these are also light   particles that we see and z bosons and w bosons  and then the higg boson which gives us a way to   to discuss uh a particles giving mass in kind of  a unified way all right so there's this collection   of particles and each of these particles also has  an antiparticle okay so it's a pretty large set   so it's it's much larger than just proton  neutron and electron that we started about   started with more about that in a moment so the  standard model is this collection of particles   it's a collection of interactions these  particles interact in different ways okay they   inter interact electromagnetically okay uh like  a charges repel each other and opposite charges   opposite charges attract they attract  gravitationally but that's very weak but   it's uh strong enough that it holds  us to earth which is a good thing   and they also interact inside of our nucleus in  a very strong way strong enough to overcome the   chart interaction of the charges so our nuclei  which are all positively charged don't blow apart   if you think about that all those positive  charges are crammed together that's a little uh   unstable but fortunately there's what we call the  strong force which overcomes that it holds our   nuclei together and then there's a weak force  okay that causes nuclei to decay so there's a   collection of particles and antiparticles  there's these four types of interactions   and there's something called symmetry and i won't  i don't really have time to talk about symmetries   so much though i would like to i'll give you  the names they usually have these initials   there's charge conjugation that's a symmetry  where you turn particles into antiparticles   there's parity which is reflecting uh um  some sort of physical experiment in a mirror   basically and then if you have parity symmetry the  experiment you see if you build an experiment that   looks just like the experiment in the mirror it  will have the mirror outcome and then there's   time reversal symmetry which catches people's  fancy i was once on npr and i there was a theorist   talking about clocks running backwards and all  this sort of thing that's not really what happens   uh time is a parameter in a lot of our physics  theories and it turns out the equations we develop   will describe a different set of circumstances  if you substitute for time you substitute the   negative of time and i don't really have time  to talk about that but these two combinations   of symmetries called cp and cpt applying all  three of these symmetries together are really the   symmetries that that turn matter into antimatter  in the most important way for fundamental physics   and then this whole standard model is stitched  together with a highly mathematical framework   which is called quantum field theory and out  of quantum field theory comes some invariances   again i won't talk about this but the i think the  idea to take away from this if you're not already   acquainted with this is there are particles  of antiparticles there are interactions   and there are ways that certain of these particles  relate to others those we call symmetries and then   there's a mathematical framework called quantum  field theory now i started the lecture with   electrons protons and neutrons and the electron is  in fact here on this standard particle chart but   the proton and the neutron are not okay so what's  going on here well here's the standard particles   and here's the electron the proton and the  neutron and their antiparticles and this   uh the sketch below represents the relationship  the proton is actually made of an up quark this is   one of the quarks another up cork and a down quark  okay and you put those three quarks together with   lots of glue well we call the glue that holds them  together gluons that's another kind of particle   so you put an up cork an up cork and down quark  and you stir in as many gluons as you need   and then you make a proton and and if  for an antiproton that's an anti up quark   so it's an anti quark an another anti anti-up  quark and an anti-down core and a similar sort   of thing happens with the neutrons so electrons  are fundamental particles protons or elementary   particles protons and neutrons are not really  elementary particles because they have other   stuff inside if the electron has other particles  inside we have so far failed to detect those now the great triumph of the standard model  let's start with that and then go to the   great frustration of the standard model in my lab  we've been able to measure the size of the magnet   in the electron so every little particle electron  particle acts like a magnet and here is the size   the details of this aren't so important what i'm  pointing to you is the number of digits that we   know this to okay there's lots of digits here  we know this to three parts and 10 to the 13.   now that's a ridiculous precision you know almost  no measurements in physics are ever made at this   sort of precision okay this is the most precisely  measured property of an elementary particle now   more about that in a moment now the electron isn't  really a bar magnet there's no north and south   pole inside because there aren't any magnetic  charges that we've ever detected in reality   but it turns out if you have a little current  loop a little loop of charge turning in a circle   an electron has charge and maybe it's rotating  then you do get it does act like a little bit   of a magnet okay but the elect you really have  to use quantum mechanics to describe electrons   the uh that you know and and it's kind of strange  to make these pictures even though it makes it a   little bit more intuitively accessible because an  electron if it has no size it's a bit mysterious   how it could have a current loop right because if  the cur if it had no size the current loop would   have no radius so there would be no magnet okay  and also an electron doesn't rotate even though   it has spin but that you really have to take a  quantum mechanics course to begin to understand   well you don't really understand it i  would say you you learn to accept it   okay it's just the mystery of quantum mechanics  now we measure the size of the magnet the magnet   in the electron to a ridiculous precision  okay and the standard model's greatest triumph   is predicting what we measure to one part and  10 of the 12. that's a remarkably remarkably   accurate prediction okay i'll show you later how  that prediction is made but it's it's uh it's   it's again it's an exquisite precision it's a it's  the most precise prediction of the standard model   and it's the most precise confrontation ever  made of theory and measurement and of course   we made the measurement just to test the standard  model okay because we know the standard model uh   you know uh is is not right okay uh and and and  yet uh well more about that okay so now the other   triumph of the standard model predictions is  that it's consistent with all measurements   made to test the standard model so far okay  so that's that's a pretty good track record   because there's a sizable community of  people trying to test the standard model   now the great frustration is that the standard  model cannot predict basic features of our   universe i already mentioned deep mystery one  why is the universe made out of matter rather   than antimatter in science we always look for  explanations to these sort of things we don't   like the explanation so well because it is we  always try and find some way to explain it in   terms of something similar so far we haven't been  able to do that with the standard model so there   physicists tend to think that there's got to be a  reason that a matter universe is more likely than   one made out of anti-matter but it's something  that there must be something we don't understand   about differences between anti-matter and matter  deep mystery number two i will go over in the   next couple of slides how can a universe exist at  all following the big bang you know why did the   matter and anti-matter not annihilate okay and the  universe basically should not exist according to   the standard model as we currently understand  it and so let's take a closer look at that   a big bang is you know we we observe that  all the stars are rushing away from us and   we extrapolate back to a time when there was an  initial big bang everything was exceedingly hot   at that point uh and and space time was completely  warped and all those interesting things that we   don't really have time to go into right now  but after the big bang okay well in the big   bang according to the standard model essentially  equal amounts of matter and anti-matter would   be created during this hot time okay and so if  you have equal amounts of matter and antimatter   it doesn't annihilate right away because it's  moving so rapidly that the particles don't have   any interaction time but as the universe cools  the anti-matter and the matter would find each   other eventually they would collide and then they  would annihilate and if there's equal amounts of   matter and anti-matter over billions of years  as the universe cools we might expect that the   matter and anti-matter would all annihilate and  there's equal amount so there's nothing left   so those are pretty big questions how how did the  matter survive how did any matter survive at all   and how is it that we exist again  the conclusion is there must be   something we do not understand about the  difference between anti-matter and matter now i'll mention two other mysteries numbers three  and four these aren't specific to anti-matter but   you may have heard these and i think they're  worthy of mention we do not currently understand   most of what makes up the universe okay and  so most of the universe is made out of dark   matter which we know is there because of the way  galaxies move there has to be something there   if our theory of gravity is right okay and yet we  can't find it so far but a lot of us are looking   and the most of the energy in the universe is we  don't understand at all the universe is expanding   more rapidly so you can this is sort of depressing  that we have these really big mysteries yet in   physics or you can say it's exciting or  if you're an old or young person you can   say there's job security for physicists because  most of the universe we have yet to understand okay so what have we discussed so far we discussed  what is anti-matter what is the standard model how   can the standard model predict what we measure so  accurately and and not yet and yet not account for   basic features of the universe and so we've  concluded there must be something we do not   understand something significant in fact we do  not understand about the differences between   anti-matter and matter in the the following  minutes of my talk the last section i'm going   to talk about experiments that can be done to find  hints about what is missing okay so to find hints   of what is missing we need measurements and the  measurements i'll illustrate come in three forms   one is we want to test the standard model's  most precise predictions as accurately as we can   our electron magnetic moment measurement does that  already we can want to test the symmetry of the   standard model that relate matter and anti-matter  so directly compare them and we want to test where   the standard model and possible improvements to  the standard model make different predictions okay just a quick aside uh what difference will  it make if we solve the anti-matter mysteries   there's no evident practical use for these and  i'm always asked this when i give popular lectures   so i i'll just tackle it straight on okay and  and the implied question is does it make enough   difference that the uf's should provide finances  from taxes for such pure science with no evident   practical use and i'm going to give two answers  to that question one is the science answer if we   find a solution to these mysteries and if this  changes our fundamental description of reality   then big consequences typically result if we look  back in history for example before the discovery   of quantum mechanics scientists were quite  satisfied with what what is now the high school   physics description we call classical physics but  now we know about quantum mechanics and countless   quantum devices are common and have revolutionized  not only science but our whole culture   the societal answer is pure science provides  new possibilities for a technological society or   another typo society some of us do not worry much  about applications we do pure science nonetheless   pure scientists discover and invent things for  example atomic clocks led to the gps system   this was not envisioned at all when the atomic  clocks were invented scientists were trying to   have better timing for their experiments nuclear  magnetic resonance led to mri imaging one of   the inventors of nuclear magnetic residents told  the reporter there were no applications for this   it was esoteric okay he didn't envision that every  hospital would have as many mri imaging machines   as they could afford because you can look inside  of people without taking them apart transistor   was developed by scientists who were not trying  to make a computer and a cell phone that wasn't   what they were imagining at the time the laser  was invented to make a better light source not   imagining that cd players communications grocery  store checkout and so on all rely on lasers   the internet was invented essentially at cern okay  to handle a transfer of information i invented a   self-shielding solenoid okay because the subway  was too close to my experiments and it's now   in mri imaging machines because they can locate  these closer to elevators the point here is that   science discoveries and methods allow and fuel the  continuing development of a technological society okay now i want to give some examples of tabletop  measurements okay that seek answers to these deep   mysteries especially the ones having to do with  matter and antimatter and i'll use examples   from my research group because i have better  pictures and i know these well but there are   many other examples that could be done i'll give  one example of testing the standard model's most   precise prediction this one i've mentioned already  the magnet in a single electron but i'll show you   what the apparatus looks like and and say a  little bit more about it and then to test the   symmetries of the standard model that relate  matter and antimatter we compare the measured   electron and positron magnet so these two are  related they use basically the same apparatus   except in one case we put an electron in it one  electron that we hold for months at a time in fact   and then for this experiment we'll put in a  positron that will hold for months at a time   and then a third class of experiments  is to test where the standard model   and possible improvements disagree okay  and i'll use the acme measurement of the   shape of the electron charge it's  called an electric dipole moment   now my center for fundamental physics was set up  just to do these sorts of tabletop measurements   uh there's a if you search on the web you can  find an article about that um and i won't say   anything about that okay so let's let's do the  electron and positron magnetic moment measurements   these are the folks who are working with me  we're also lucky of late to have some fermi lab   uh of collaborators who are helping us divide uh  devise a future generation which will be better   but here's the standard model's  prediction very mathematical   you have to do 12 dimensional integrals you have  to do you know uh sort of like 12 13 000 of the   these integrals it's highly mathematical i won't  talk about it but that's what the standard model   theorists do when they make these predictions  and until very recently our measurement   um was agreeing with uh with the best uh standard  model prediction but the standard model prediction   uses something called the fine structure  constant as an input that has to be measured   and when that was measured about two years ago  then uh this discrepancy appeared and a lot of   theorists wrote papers about what may be causing  that very recently though another measurement of   the fine structure constant came out and the  prediction using that fine structure constant   puts it puts us over here so i would say things  are a little murky right now so for now that   the fact that it gets within parts and 10 to the  12th is the great triumph that i mentioned before   now how do you hold an anti-matter particle you  can't put a positron in a bottle right because the   positron will annihilate when it hits electrons in  the bottle so you need a bottle that has no walls   okay that's called the particle trap and  here's the physics you have to know if you   take a magnetic field you know directed along this  direction so if i had a horseshoe magnet i would   have the horse the horseshoe looking like this  okay and there's a magnetic field there and and   a particle a charge in a magnetic field goes in a  circle so here's a negative electron for example   going in a circle and since uh opposite charges  repel this negative electron is repelled from   the charges we put above and below and so it  stays stuck in between it's in a particle trap   and we actually hold particles for months and  months at a time just one at a time doing that   and then we we this is what an accelerator is  okay and it's just it's really big so the magnets   are expensive so they put a hole in the middle and  put little magnets all the way around but we don't   do that either what we do is we cool the particle  down so much that we see the quantum structure in   its cyclotron motion so this is becomes a homemade  atom when it's very cold and and and we see energy   levels just like in an atom the way you learned in  high school chemistry and you have to cool it down   in our case to a tenth of a degree above absolute  zero and i don't have time to explain that right   now but just just to give you the feel for what's  involved you get wave functions that are pictured   there in one state and the other and we put  photons in and make the state jump back and forth   okay but it's a homemade atom there's these energy  levels and we just measure the energy it takes the   light energy that we have to put in to make these  transitions it's a kind of spectroscopy and then   we use lots of quantum tricks that i don't have  time to talk about here's the scale of it we call   it table top physics but you need a pretty sturdy  table to put this on it so we put it on the floor   okay but this is the size of the device  that makes the strong magnetic field   the magnetic field is so strong that if you  drop a screwdriver inside the bore of this   it's there's a hollow bore inside that you can't  see if you drop a screwdriver inside you won't   have enough strength to uh pull it out it's at six  tesla okay here's a picture of the insides there's   lots of electrodes lots of machining the particle  sits way inside of the centimeter type cavity   okay so there's lots of engineering that has to go  into this we're now using superconducting quantum   interference devices to detect these motions  that's a promising new direction okay and so on so   i just wanted to give you a little bit of a feel  for what's involved in doing such an experiment   now let me switch gears well let me just  say we could put a positron or an electron   in this apparatus and use these methods  and by comparing the magnet of the positron   and the magnet of the electron we could test  the matter antimatter symmetry of the standard   model way more precisely than anyone else  can do with what's called the lepton particle   okay now another question is how spherical  is the electron charge now in order to do   this measurement we have to make an entirely  different experiment entirely different apparatus   we actually use molecules for reasons i'll i'll  say in just a moment but for those of you who   know the buzzwords we don't say how spherical is  the electron charge so that's really what we mean   we say we're measuring the electric dipole moment  of the electron does the electron have a little   bit of it's more of its charge on one end of it  than the other now that's a weird question because   if we believe the electron has no size how could  how can more charge be on one end than the other   but okay that's a classical question and  we have to answer it quantum mechanically   so i'm cheating a bit now there's all sorts of  predictions of what size electric dipole moment   what size of departure from sphericalness  we should see okay and and so these are   all the predictions so this is a case where  there are alternatives to the standard model   okay and the standard model says that there should  be an electric dipole moment that that electron   charge should not be quite spherical but notice  that my scale is broken okay and it jumps by   some five orders of magnitude here so it's  orders of magnitude smaller than we could hope   to measure using the methods that we've dreamed  up so far okay and our first measurement okay   uh you know uh brought us uh brought us this far  and our second measurement brought us brought us   this far and now we're making a third generation  where we haven't eliminated all these theoretical   possibilities or discovered the electric dipole  moment yet but we're still hopeful of doing so   here's another way to do it there's no possible  way to understand it unless you do going in   but what we do is for certain kinds of  particles called supersymmetric particles   we're able to set limits which are of much  higher energy than even the lhc concept okay   so even though these particles are done at  very low energies they can set what are are   considered in physics very high energy limits  but i don't have time to explain that now this   experiment is done by a team it was two of us at  harvard to start john doyle's group in my group at   harvard when i moved to northwestern  then we moved and then at uh my our   yale collaborator david demille recently moved  to the university of chicago the result is is   the the new generation the all-new apparatus  is being built up at northwestern it's moving   okay here's the history of measuring the  size of this departure from sphericity   the absolute numbers don't matter very much  here's one measurement it was consistent   with zero here's another measurement we made  someone else made a measurement in between   okay and so far we haven't yet to  detected any departure from sphericity   that means so far the standard model seems to be  correct uh not some of these proposed improvements   now in order to do this we have about 10 lasers  operating all the time one big laser makes some   molecules come out it's a process called ablation  those molecules move through a region here we   excite them with lasers we detect them with lasers  we apply electric fields we apply magnetic fields   we apply more lasers we steer them in  our new generation with an electrostatic   lens again the details aren't so important  and if you look at the the real apparatus   it uh you know we're straining that in the notion  of a tabletop a little bit because we have several   tabletops laser tables that are just covered with  uh cover covered with uh with lasers and optics   in the new measurement we're making a big shielded  box that's bigger than our previous one it's about   2.2 meters long several yards long and about a  meter and a half high okay and and that is uh that   that those parts are just ordered uh we don't have  engineers because we are just a tabletop physicist   and so unlike at fermi lab we're not privileged to  work with engineers so we do our own calculation   i i really enjoy this a picture  that one of my students gave me   of the mechanical vibrations of our new vacuum  chamber as you might expect this is slightly   exaggerated or maybe hugely exaggerated but the  picture i thought was hilarious the thought of our   delicate apparatus shaking around like that when  you vibrate it okay we're projecting for our new   measurement to maybe improve things by more  than an order of magnitude another factor of   30. the details of this are not so important  um i'm just again trying to give you the idea   okay let me conclude as i started what i've  tried to tell you about and give you a feel for   is what is anti-matter and how it's related  to some deep mysteries that are really nagging   mysteries that that that physicists strongly want  to solve okay i explained what anti-matter is the   anti-matter counterparts of of matter we  discussed the standard model of particle physics   the collection of particles and anti-particles  okay the interactions of these the symmetries   that they have matter to anti-matter for example  and the mathematics that holds it all together   and and the standard model is the great  triumph because it can predict things   predict predict physical quantities that we  measure to a remarkable remarkable precision   and it's the great frustration we know it  has to be wrong or have missing elements   because it can't explain some of the most  basic features of the universe like for example   why we have a universe at all why it didn't  all annihilate after the big bang and why   the universe is made out of matter rather  than anti-matter as experiments tell us   and then i tried to illustrate just to give you  the flavor of what the table top probes that   that we use to get hints as to what is  wrong or missing from the standard model   one class of such measurements is testing the  most accurate predictions of the standard model   there the the prototype example is the magnetism  of the electron which can be calculated by the   standard model much more accurately than  any other quantity and we can measure it   much more accurately than any other  property of an elementary particle   we can test the symmetries we can do that by  comparing the magnet in the electron which is made   of matter and the uh magnet in the uh um positron  the anti-electron which is made out of antimatter   and and so that will hopefully we find a  difference that would be great aside from   the obvious sign that's predicted by the standard  model but we'll see and then with the electron   electric dipole moment measurement what is the  electron spherical there we're looking where the   standard model and possible improvements disagree  and i didn't discuss it very much but we actually   use very different methods where we use molecules  because there's a huge electric field inside   again there are many details which i would  love to talk to you about the time is up   so in conclusion some of us are having great fun  doing this um if we're a bit lucky we'll get some   hints and maybe we'll uh contribute to changing  our picture of the universe and our hope always   is though there's no guarantee that we contribute  a bit to a revolution in our understanding of   physical physical reality and hence a lot of  unanticipated consequences and applications   so first question is how do you know that you  don't have two or more particles in the trap   at the same time and how do you just let  just one out well that's a good question   and uh i i like to joke that in order to even know  that our apparatus is turned on because it's so   precise we have to make a more precise measurement  than most physicists make in their whole career   okay so there's it takes a little time but but  in the end you can you can look for example   at how the electron responds to electromagnetic  forces that you apply to it suppose you take   a little voltage and put it on these  metal electrodes that are around the   trap okay and you drive it and you look at where  its response is biggest and if you look at the   width of that resonance curve you know there's a  it gets bigger when you're right on resonance just   like when you push your kid on the swing okay the  swing swings most when you're right in resonance   with the natural oscillation frequency of the skin  of the swing if you look at how wide that response   is it gets twice as wide for two particles and  three times as wide for three particles there   are other ways we can tell too but that's that's  one now how do we get rid of suppose we have two   or three and we don't want that well one way is  we just turn up the juice okay on the drive and   we drive it so that these electrons get perilously  close to the electrodes until one of them or more   hit the electrode and then we're uh you know and  then there's only one left now that's a little bit   nerve-racking when you do that you know when we  used to have an anti-proton in the trap at cern   and we couldn't get another anti-proton for  a couple of days and suppose we had three n   then there was a lot of pressure on the students  okay because you didn't want to dump three you   wanted to dump only two okay but you know after a  while you learn how to do it and most of the time   you could well in physics you often make your  own luck and and that's what we were able to do   did i answer the question i think  you did yeah that was very good   and what happens to a particle in the trap  that is chilled all the way to absolute zero   well if it was chilled all the way to absolute  zero uh in those energy levels that i showed you   it would only occupy the lowest energy level right  there would be no motion but here's an interesting   thing about quantum mechanics even though we  don't cool nearly to absolute zero but only to   a tenth of a degree above absolute zero that's  pretty chilly okay but even at that temperature   the particle is going to stay in its lowest  state for more than 10 to the 30 some years   okay so for all practical purposes its cyclotron  motion this circular motion has completely stopped   already at the temperature that we do the  experiment and it stays in this ground state   until we put some electromagnetic  radiation some microwaves   just like from a microwave oven but higher  in frequency we put them into the trap   and persuade the particle to jump from its  ground state to its first excited state okay so um how do you measure  such small magnitudes accurately um well it's it's it's it's  challenging but fun okay i think one important thing to realize is that  you have to basically do it with ideas not just   fortitude and perseverance okay you can't make  order of magnitude improvements unless you have   better ideas so we use every quantum trick we can  think of or borrow beg borrow or steal as they say   okay and we invent some we just have a paper out  in physical review letters a couple of days ago   about a quantum detection back action  circumvention method for those of you who want   to really get into the details there but basically  what we try and do is we try and arrange our   experiment in such a way that we are sensitive to  only what we're really interested in and not and   you know and we measure try and measure that  directly rather than measuring a very small   effect on a very large quantity okay um yeah i  i don't know exactly how to explain that more   accurately so that probably will have to do yeah  it's just probably a pretty complicated answer   so um are there galaxies far away  maybe that are made out of antimatter   um well we kind of know about how big the  universe is and we can probe uh we can   you know get some uh see some effects of galaxies  that are quite far away right that seem to span   the the the size of our universe as we know  it and and so far we have failed to see any   significant signature say an annihilation signal  from other galaxies and and one would expect that   if there are galaxies made out of antimatter  galaxies are always colliding with each other   somewhere in the universe all of the time and we  would expect to have seen some evidence of that   but when people have looked for that even on  satellites to get more detection sensitivity   with less atmosphere they have failed to  detect any evidence of that whatsoever very unlikely so um how do you know that  you've created antihydrogen in that hydrogen   well that's that's that's actually pretty easy  okay what we do these days is we hold it in a trap   it's a kind of magnetic trap that i didn't have  time to talk about um uh and but what we do is we   hold it in the trap and then we say okay we've  held it for a while let's wait till there's no   background of any sort from the accelerator and  let's just dump it out of the trap by removing   the trapping fields okay and we'll let it hit the  wall and if we let it hit the wall then it makes   uh it makes some garbage particles i call them  called pions which comes screaming right out of   our apparatus we put up plastic simulator plates  okay and and we see the annihilation signal now   there's no way that a proton could ever make such  a signal so it's it's it's entirely unambiguous are there anti-photons uh well maybe the photon  is its own uh anti-photon so uh so some of these   things uh answers are yes but by a technicality  okay so yes all right uh are you using   any ai at northwestern as part of your tabletop  experience experiments uh oh hopefully not we have enough trouble getting enough real  intelligence let alone making artificial   intelligence uh no we we really don't okay now  it's not that we wouldn't you know if there was   some if there was some place where the a learning  mechanism would actually help and it would save us   some time and we could sleep while the computer  was what was you know running the algorithm that   would be great but most of our experiments are so  delicately balanced that you know again we have to   set up the apparatus following ideas that allow  us to directly detect something not just pick it   out of a you know a huge background uh and so so  far the answer is no but we would if there was a   good a good reason for it because it's a per  they're perfectly valid and useful techniques so this person asked for so  if you had an unlimited budget   i would you pursue further knowledge of dark  matters what they're interested in but maybe   i would broaden it to say what would you do  if you had you know i i guess i wouldn't want   an unlimited budget because i think an unlimited  budget makes creativity go right out the window so   an unlimited budget is not adequate budgets are  better than unlimited we are doing a dark matter   experiment right now in the center for fundamental  physics at northwestern all of the four   principles uh the four groups are collaborating on  this and what we're doing um is is we're looking   to see if a certain kind of dark matter comes  through whether or not uh well one effect of   this dark matter would to take an optical cavity  two mirrors and make the cavity change its size   as the dark matter came through and so we're  comparing uh we're well we're just setting up   the experiment but we want to look for a length a  length change of the cavity using laser techniques   and in order to i mean the problem of course is  we we need to compare um compare that change in   frequency to something and and the difficulty  is if you compare it to a clock you know there's   going to be the size change in the clock as well  so the dark matter will change the clock so you   got to come up with a different way to to tell  whether or not there's been a change so what we   want to do is is to suspend two mirrors and a  second cavity suspend them from very thin wires   very thin fibers okay so if the dark matter comes  through the inertia of that cavity okay it it it   will it won't respond right away okay and so by  comparing the length of that cavity with the rigid   cavity which can respond right away much quicker  anyway then we can see whether some dark matter   of a certain kind came through so the answer is  we would like to detect dark matter and in in in   our center there you know we're trying to detect  dark dark matter there's molecular spectroscopy   there's gravitational experiments there are  searches for gravitational waves we're interested   in all that kind of stuff what makes us a bit  unique though is we try and do it on table top   scales okay rather than on large facility scales  which means we don't need an unlimited budget okay so yeah if you have a very huge budget  then you have to get in all kinds of people   it makes it very complicated right  like yeah like an lhc for example   i mean the ferry lab people are experts at  managing a very large budget but there's a lot   of organizational charts and software to do that  and we're blissfully spared most of that so yeah   so uh how about this one someone is saying  could a sister universe have formed along   with ours such that the sister universe is  all anti-matter from our point of view um   i guess the answer is yes i don't usually spend a  lot of time thinking about that or talking about   multiverses because things which intrinsically  can't be detected seem to me off the radar screen   of at least this physicist okay so i i know  that that's a lively theoretical speculation   and it gets a lot of interest in all these  multi-verses as one theorist friend of mine who uh   once said and he had a nobel prize so it's  more respectable coming from him than from me   he said multiverses are a sign of weakness uh  if you have to re resort to a a multiverse you   you just fail to explain our own universe  but of course there are really good uh and   clever people who are are looking into  those ideas i'm just not one of them   so then a related question is does anti-matters  absence disprove the big bang theory   um well you know uh physics is an empirical  science and in physics we never say never um   but on the other hand i would say the odds  seem really unlikely because there is so much   evidence that a big bang happened i think that i'm  completely convinced at this point so i would be   absolutely floored if that weren't true and and  we scientists you know and we're we're always   provisional about things but that sort of empowers  some people in our society to say weird things   you know that there's no climate change or you  know dumb stuff like that okay and and i think   we have to be careful to say some of these things  the evidence is so overwhelming that you know we   really aren't provisional about it anymore and i  for me the big bang is in that category for sure okay um here's a question i don't i haven't heard of  this and if you have you heard of wheeler's one   electron universe idea um uh no i'll i'll  say no okay then i'll skip that question   if if anti-matter annihilates on contact with  matter how does that pet the positron electron   tomography scanning work well the basic idea is if  you eat something that has a radioactive nuclei in   it that will emit positrons say over the next uh  um several hours okay you can make such species   and you you ingest this and you ingest it if it's  attached to a molecule that goes to an important   place that that you want to look at say a brain  tumor for example okay then what's going to happen   is you're going to get positrons and electrons  emitted at the same time okay from from this uh   well sorry you're going to get positrons emitted  and when the positrons are emitted they make gamma   rays they decay into the gamma particles and they  go in in opposite directions okay and so if you   have detectors on either side you can extrapolate  back to where most of the positrons came from   and you can then with the right camera  system you can image you can image what the   uh you know where these uh these photons  these light particles are coming from   okay and that come come from the positron  annihilation that happens when a positron   hits an electron in the in in the material  that it annihilates it very useful technique here's another question about about your technique  is do your observations affect the outcome   you know does it does it affect you know just  observing it impact your system um well the answer   is yes um and um now one has to be very careful if  if you go say to our one electron or one positron   system and that's what the paper that just came  out in physical review letters is about if you   have a deep interest in this okay but there we  use a method called quantum non-demolition methods   called a quantum non-demolition method  and the basic idea is that when you first   measure a quantum state of our electron one of  these levels that i showed you uh well let's not   talk about the first measurement okay let's talk  about the second measurement if i measure it again   it it it'll be in the same state that i measured  after the first measurement and if i measure it a   third time it'll again be in the same state okay  so that measurement will not change the quantum   state so that's a valuable kind of measurement  because now i can do something on the side that   i think maybe will change these states like put  some photons in to make an excitation and and   you know if those photons don't make an excitation  i'll always measure the same state my measurement   itself won't change the state so we use tricks  like that a lot okay and so yes if you don't take   quantum mechanics seriously quantum mechanics in  general if you don't design your measurement right   the measurement itself will mess up some of the  things that you could be wanting to measure all   right so it's very important to keep your quantum  widths about you when you're doing these things if somebody's wondering if dark  energy could be created by the   annihilation of matter and anti-matter  maybe from even from microscopic black holes   i doubt it without it you don't really  know what a dark energy is coming from   yes we know so little about dark energy i mean  it's really incredible i would say i mean we're   a gazillion orders of magnitude away from  being able to estimate what it should be okay so you were talking about all  the symmetries so someone asked   is there a negative of time  is there like anti-time no there's not and clocks never run backwards  even though we talk about time reversal symmetry   okay and so i mean if i have an equation that  describes the motion of uh of a car let's   say okay and so i could take a high school  physics equation that describes the motion   you know something like a distance is  velocity times time right now i could change   the time variable in that equation to minus t now  it would say that distance is minus the velocity   of time that would not describe the car that i  was first describing it would describe another car   that was going the opposite direction okay and and  we say there's time reversal symmetry in that case   because both of those are possible motions of a  car but that's not to be confused that one car   is moving in both of those directions  at the same time or it suddenly changes   and goes the other direction so when when  theorists and you know talk about clocks   running backwards they're usually pulling your leg  a little bit okay uh though that's the way they   think about it in their imaginations okay but in  in reality it doesn't happen for us experimenters okay i'm just going to ask you two more questions  so um given that matter and anti-matter particles   exist are the force carriers the gluons  are the you know photons w and z bosons   are they applicable to both matter and  antimatter those those aren't reversed   yeah they're well what's reversed i let's just  say that matter and anti-matter particles are   held together by gluons okay and then you have  to sort of you know delve into the details more   okay so there aren't like anti-gluons uh yeah well  it's sort of like with the photon okay so yeah   yeah all right so the last question  is for the layperson what does what uh   what's the most exciting  recent discoveries in this area um what is the most exciting recent discovery well  i think you know for me it was sitting in the lab   when we last tried to measure the  whether the electron distribution was   was spherical or not okay and we we  did something we call blinding okay   we took the the measurements that we were doing  and we deliberately put an offset on it so that we   would analyze all of our data without knowing the  answer so we went through the whole process for   several years making this measurement and you know  building the apparatus for three years before that   okay made a couple years worth of measurements  and we sat there with a champagne and wine okay   some from France and some from California right  and we sat there and we unblinded the result and   there you know were we going to discover you know  that the electron wasn't spherical or it wasn't   um and either result was okay with me but it was  kind of exciting to unblind the result and and   see what what happened okay so i mean either we  would discover this new physics going on or we   would disprove a lot of theoretical models either  was fine by me and i found it was kind of exciting   what was the answer the answer was that we didn't  see a departure from sphericalness even though we   had measured well twice we did this we measured  ten times more accurately once and then we did it   again and despite the hundred-fold improvement we  did not see a departure from a spherical electron   charge okay and so so far the standard model  is right but hope springs eternal we hope that   another order of magnitude is going to perhaps  let us glimpse the the first difference all right   thank you so much for tonight it's been very  very interesting and people if want to they   can raise their hands again to to thank  you so thank you very much goodbye all you

Channel: Fermilab

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Keywords: Fermilab, Physics, Science, Arts and Lecture Series, lecture, particle physics, subatomic, technology, detector, particle detector, antimatter, antihydrogen, CERN, mystery, universe, big bang, Gerald Gabrielse

Id: sXEtgMSOmDA

Length: 77min 19sec (4639 seconds)

Published: Fri Mar 12 2021