Whenever I worked along with technicians, I had a feeling that there was a tension, sometimes subtle, and sometimes way more than subtle, in how we worked together.
The first time I noticed it was when an experienced tech and I were talking about inductors. Being a recent EE graduate, I gave him a little outline of the theoretical way I was taught to think about them. He listened patiently and then said something like: “Who cares about all that, I know what an inductor is and what it does — and by the way, what kind of fancy name is inductor — it’s a choke.” It got me remembering when I was in High School fiddling around with electronics. I “knew” what a choke was and didn’t bother to think about how it worked, I just knew what it was there for. He had a point — as long as you know what it does, why do you have to know the theory of it?
Fast forward a couple of decades: A tech and I went out to a customer to set up the equipment we had delivered. One of the meters on the panel was clearly not reading correctly. While I was standing there thinking about it, my technician friend was busy switching out some components. It didn’t work. Meanwhile, I had taken out my calculator and realized that all it needed was to add a certain size resistor. The technician insisted I had to be wrong, and I insisted he try it — I was right.
It wasn’t that I was smarter than him, it was that I approached the problem differently. I used the theory I had learned in school, and he went by his experience.
Through the years, sometimes it went well with the technicians and me and at other times, not so well. It worked when we respected each other’s strengths and would listen to each other creatively. I would come up with an idea from theory and they would raise an example from their experience that didn’t fit. We were an effective team if we took each other seriously and tried to figure out why there was a difference between us. Sometimes they were wrong, and sometimes I was, and in the best times, when we grappled with our differences, we discovered something that we had both overlooked.
The Physics of Everything
In my current job as an editor, I subscribe to news sources from university and government labs and came across this story and the delightful video below that got me thinking about my relationships with technicians — and more broadly, about the relationships between theory and practice.
The story is about a theoretical physicist, Kathryn Zurek, and an experimental physicist, Rana Adhikari, who plan on working together to understand the century-old puzzle of how gravity relates to the other forces in the universe, such as electromagnetism.
Zurek: “The work of a theorist is very nonlinear. It involves having ideas, tinkering with the ideas, trying to understand how they fit together, whether it's consistent with everything that we already know theoretically — then most of the time discarding the ones that don’t work. I spend months or years working it out.”
“At the end, if it hangs together theoretically, I come to an experimentalist like Rana and say, ‘I have this idea; I think you might be able to measure this.’ Maybe the first time, I say something like, ‘I think the effects of quantum gravity might be much bigger than we thought,’ and he says, ‘Oh, that's interesting, but that seems impossible.’
“Then I go back and spend another year or two thinking about it, get feedback from the theory community, and come back to Rana: ‘I did all these other calculations, and it's still there. It's not going away.’”
Adhikari: “When I hear about these new ideas, it's always exciting. But first, you try to come up with reasons why something can't be true. It starts to get more interesting when you determine there really is no evidence to contradict the new theory, so it could be true. Now the only way we could contradict it is by building the experiment.”
What’s interesting to me about this exchange is that Zurek came up with a theory she was certain of, but Adhikari, not so much. So instead of arguing, Zurek spent over a year re-thinking her work and consulting with other theorists and still came to the same conclusion. So, Adhikari’s pushing back helped Zurek bring even more clarity and certainty to her ideas. And that added certainty convinced Adhikari that it would be worth spending the next 10 years of his life trying to experimentally verify Zurek’s theory.
My Takeaway
When the technicians, with their practical point of view, and the engineers, with their theoretical point of view, listen to each other open-mindedly and with respect, they can reinforce each other and achieve a better outcome than either working alone.
Transcript
00:00:01 [Music] good morning and thank you for joining us I'm Whitney claven a science writer and meet press officer at Caltech it's my pleasure to welcome you to conversations on the quantum world this series is hosted by the Celtic science exchange and gives us a chance to hear from scientists and Engineers who are working on The Cutting Edge of quantum
00:00:28 research I'm joined today by by theoretical physicist Katherine Zurich and experimental physicist ra adari the two have teamed up to do what some may deem impossible to design and run experiments to find signatures of quantum gravity what is quantum gravity it's one of the biggest questions in physics today and involves attempts to unify the microscopic world of quantum
00:00:54 physics with the macroscopic world of SpaceTime and gravity Katherine uses theoretical models to study dark matter and extreme compact objects such as neutron stars R is a member of the ligo team and builds ultraprecise instruments to better measure gravitational waves or ripples in Space and Time Katherine R thanks for being here thanks Whitney great to be here
00:01:18 yeah thanks for having us okay let's start off and Orient ourselves to the quantum World R can you start off and explain a little bit about what quantum physics is and and what it entails it sounds like magic but uh we're used to the regular world of big things and large objects and uh when we started to examine thing we and like hundred years ago when people started
00:01:43 examining things carefully they found you couldn't explain what goes on in nature without coming up with new laws to determine what happens to really small particles uh like atoms electrons positrons that kind of thing but that's the underlying kind of secret laws of how everything actually runs in the universe I some sometimes think about it like um
00:02:06 you know painting a pointless painting So when you look at it from a distance of course it just looks like uh you know ordinary uh painting but as you start to zoom into it on smaller and smaller scales you start to notice that there's more structure there and in fact rather than it being continuous you know objects uh you start to notice that it's actually made up of individ ual points
00:02:31 and as you zoom in further and further you can see the the individual points the the quanta uh that make up that painting and that's kind of like what we do in in particle physics what we're doing is zooming in on smaller and smaller structures smaller and smaller scales and as we do that kind of the continuous everyday world that we see out there we
00:02:54 start to notice that it's U actually made up of individual quanta uh and that there's a lot of uncertainty associated with those quanta and so what we're trying to do is to you know keep zooming in to understand more and more what the fundamental structures are in our universe okay all right well then before we explain quantum gravity let's tell people what is gravity and why do you
00:03:21 guys talk about SpaceTime and gravity like they're the same thing so I was just looking last night at the the image from wst uh which um shows uh if you know the audience members have looked at it uh shows these um images of galaxies that have been lensed and what that is is you have a mass that sitting between us and some
00:03:48 distant light source and that that mass uh actually bends the light and so one way you can think about that is that SpaceTime is just like a stretchy Fabric and you know if you put some heavy object onto the stretchy fabric what it does is to cause that stretchy fabric to to contour and so you can think about gravity in one way as uh the way that it
00:04:11 causes space time to curve and then you know matter or light now just follows the Contours of the space time so when we talk about gravity in space time we really use those words interchangeably for that reason okay all right so now both of are going to attempt to explain quantum gravity which is not the easiest thing to explain and we're going to start with
00:04:36 Katherine so Katherine what is quantum gravity so I used the analogy before of a pointless painting so um what we've been doing over the last 100 years really is zooming closer and closer in to um smaller and smaller structures um but and and we've learned a lot about the fundamental forces of nature by doing that you know uh electromagnetism uh the strong and the
00:05:03 weak forces which we all understand in the language of quantum mechanics the one piece that doesn't really big piece that doesn't fit into that puzzle is gravity gravity uh we only understand in that smooth language um and so that's actually not surprising based on what we know about gravity um we actually expect that we're going to have to keep zooming in to
00:05:29 smaller and smaller scales to be able to start to see the quantum effects of gravity and you know there are a lot of ways to understand that one is that if you just look at an individual atom like a hydrogen atom it doesn't care at all about gravity and yet quantum mechanics is present in that hydrogen atom so if we want to be able to start to see Quantum Quantum effects and gravity we
00:05:52 have to be able to zoom into even even smaller smaller scales okay ra do you want to add to that I I agree should say I I also I just wonder about every time we've had uh classical theories like speed temperature and all pressure and those kinds of things there are sort of Concepts from the 1600s or
00:06:19 1700s and uh as science has marched on we' figured out that there's a microscopic description for those kind of continuous macroscopic things and the good example is something like heat flow or temperature or those sort of things and those are their own properties back in the olden days like in the early 1800s when I was little uh and now those concepts are we know that those kind of
00:06:45 emerge out of quantum mechanics so you take simple microscopic laws and you put things together and when you have really like billions and trillions of these things uh they have properties that you didn't maybe you didn't expect at first but you could calculate that they're there and those things uh act like these things pressure temperature thermodynamic things and I I have a
00:07:08 hunch that gravity comes in the same way and maybe other people do that there's some sort of underlying microscopic ground truth and gravity and SpaceTime and all that we see just come is sort of a what happens when you have a lot of these things whatever those things are I don't know what they and you had explained earlier that it's sort of like
00:07:29 gravity is like a build and quantum mechanics is like the bricks and that it's not that gravity is wrong it's just a different level of explaining something yeah I I think so so when you think about even like fluids you think about how things move in a swimming pool uh macroscopically we look at its body of water and there's waves on top of it but if you really want to know things
00:07:52 about like how sticky is the water how smooth does it feel you have to zoom in and find out what's in the water and is it made of water and oil and what other stuff is in there and those microscopic Quantum effects about how H2O sticks to this thing or that thing that actually when you put it all together it determines how squishy the water is whether it's olive oil or water or you
00:08:15 know tar or that kind of thing and that comes from the quantum mechanics of the particles but fish don't really care about that they just sort of swim around and they feel things like viscosity in temperature and they don't really need to know about quantum mechanics and planets are sort of like that they don't need to know about quantum mechanics they just feel the gravity and do what
00:08:32 they're supposed to do okay and then the other thing I hear a lot about is that part of the problem in merging these theories or making them compatible is that gravity is so weak it's the weakest force and that that always confuses me a little bit about why that matters so can you explain that a little bit sure either either one of
00:08:57 you so go ahead go ahead either way um well so it it comes back to what what I was saying before is is you know when we go into our lab or R goes into his lab and you know he's he's looking at uh you know individual uh you know the individual constituents of matter when you know there's no reason you can't come into the lab too
00:09:24 well yeah I should come visit your Labs uh um visited your chalkboard so yeah you visited my chalkboard but I haven't been in your labs yet so uh Absolutely I'll I'll take you up on that invitation um but you know when when we're exploring you know the individual constituents of matter like you know individual uh atoms I mentioned the hydrogen atom before we can study those
00:09:50 and completely ignore gravity and um you know another way of thinking about it is you know I'm sitting in this chair and um is you know some wimpy little chair and um yet it is counteracting the force of the entire Earth pulling me down towards the center of of mass uh and so that tells you that uh the ordinary electromagnetic forces are just much much much much stronger
00:10:21 than gravity and so gravity is by far the weakest force and so um I like to make analogies uh of to mountains when I talk about particles is like gravity is is the biggest mountain it's like Mount Everest and um and so it takes an enormous amount of energy to scale up Everest and to try to actually zoom in and uh find out about the most fundamental
00:10:51 constituents that uh make up the gravitational force and so um if we want to learn about you know quantum mechanics and gravity because gravity is so weak um we have to probe it on extremely short distance scales and just to give you a number you know kind of the size of of that we can probe um quantum mechanics is on the
00:11:17 order of 10 the minus 10 meters uh you know when we're looking at Atomic scales but uh quantum gravity at least when we do this naive estimate would actually appear at scale which are 10 Theus 35 M okay that's 25 orders of magnitude smaller and so that's the thing that's made probing quantum gravity so hard um and in fact why uh many people have said it's just impossible to look
00:11:48 for quantum gravity in the lab and that's what you know R and I are are trying to change is to think about ideas where quantum gravity would have still really small effects but uh bigger ones that we could potentially observe in the lab okay well before we describe your experiment um T I wanted to know a little bit more
00:12:12 about why we care about quantum gravity like what what is the reason to merge gravity and quantum mechanics why do we want to crack this problem I think I think Katherine's probably got like a more a smart answer but my answer is I just want to know what's going on I mean I could I can add a lot more sentences to it but I just feel like it's very strange everything
00:12:39 in the world is quantum and how could it possibly be that we have this thing space time or gravity and it's not Quantum it would be a mind-blowing thing that you know I could do things like make gravitational perations here with my hand and then somehow that gets communicated to Catherine across campus through Gra gravity but that is not somehow a Quantum information channel
00:13:04 that would be the first thing in the universe which is not like that and so I feel like it's got to be Quantum but uh and I want to know how that works it's just going to be some amazing new thing if we ever figure out how quantum gravity works and maybe we'll never use it for something practical but you know that is what they told Faraday about electromagnetism I I agree I mean we're
00:13:30 uh physicists and what we try to do is to understand nature at its most fundamental level um I think you know history is on our side in the sense that the drive has always been towards a deeper more unified understanding and you know up until quantum mechanics messed it all up you know a hundred years ago or so we had this beautiful unified picture of how all unified
00:13:56 understanding of how you know all the classical forces worked and then we had quantum mechanics and Quantum field theory that now explains all the forces of nature except gravity and yet we know that these things have to work together they have to fit together and so you know if you're a physicist you're always trying to solve the puzzle how do these things fit together you know how do they
00:14:22 work together how do I make a unified picture to understand all of the forces of nature together and you know there are very deep good reasons why you know we expect that uh there should be Quantum effects in gravity and we also have an understanding of why it is that they're so hard to see okay all right well then how do you propose to do this how are you going to
00:14:47 see signatures of quantum gravity when you've explained that you would have to maybe probed down to the plank scale of 10 to the -35 yeah so we're never going to see any effects at the scale of 10us 35 met um it's far beneath even what ligo which does these amazingly precise measurements uh can do um and so just to
00:15:16 step back for a second what are we looking for what we've been thinking about is um looking for ripples in the fabric of SpaceTime so I I a little bit earlier was talking about how you can think about gravity in SpaceTime as a stretchy sheet and uh classical gravity is like you put you know a mass down in it and it causes the sheet to bend but um quantum gravity in general we expect
00:15:40 that there's going to be ripples in that uh fabric um and in fact we already see this with the ordinary forces with electromagnetism that there are actually fluctuations in empty space empty space the vacuum is not so boring it's very interesting particles fluctuate inside in and out of existence in the vacuum and so what we want to look for is the fluctuations in space time due to the
00:16:06 quantum nature of gravity now if those effects just occurred at this plank scale this extremely small length scale we would just never be able to see them and so what I've been thinking about the last several years is whether there's a real possibility that those fluctuations in the fabric of SpaceTime are actually larger than you might naively expect and you know we can talk more about why
00:16:32 that might be um it has to do with the holographic principle is one one way you can think about it but um suffice it to say that we're looking for these fluctuations in the fabric of SpaceTime and sometimes think about it is you know you've got a very the fabric is like the this Pond very smooth Pond of water and then we're looking for you know drops on it and those little drops now create a
00:16:57 wave pattern on the water and looking for the interference you know when you look at a pond of water and you see those droplets uh um the wave pattern coming out they interfere with each other and so the way that they um interact or interfere with each other now you try to measure and um that's in fact what uh experiments looking for uh gravitational waves do like ligo which
00:17:27 which R um works on and um so we want to uh look for these Quantum fluctuations in SpaceTime in an instrument that works on the same principles Lego but is uh Specialized or kind of built for this this these vacuum fluctuations in SpaceTime okay then as the experimentalist r i mean can you tell us a little bit more about how you're actually going to do this um a lot of
00:17:58 cleverness and a lot of luck some funding and uh a lot of coffee and uh some good grad students I think that's that's the real secret but then uh beyond that level two I would say I like to think about the signal as um sort of like a hiss so ligo detects signals that are usually chirp likee like a bird chirping like a kind of thing and the quantum gravity signal is more likely
00:18:28 going to be something like and so Katherine gave a good visual description I'm giving sort of the audio equivalent um people you know people detected the cosmic microwave background a long time ago and that is also like a hiss but that comes from far out in space that sort of light is coming to us in the in the microwave and we detect it in its background hiss uh this is a
00:18:52 little bit different this is more like a his that is inherent to SpaceTime itself and it's analogous I guess to the electromagnetic fluctuations that Katherine was mentioning if you if you look in empty space the electric field is just you know it has fluctuations it has noise and if you could measure that uh that would tell you something about the electromagnetic field in space which
00:19:15 is which is cool and and people have done it uh what we'd like to do is measure something like that but it's what are the gravitational fluctuations in space uh when there's when there's no sources it's nothing coming from outer space or stars or anything like that um for the for ligo we were sort of forced to look for low frequency signals in the human audio band so you can always
00:19:36 whenever ligo detects a signal I can do the impression for you whoop and you know whatever these things that are very entertaining uh but the problem with that is that the rest of the earth is also down there making all kinds of noise and it's and it's tough to it's tough to live like that so I love this experiment because it has nothing to do it doesn't care about like what are the
00:19:56 birds doing or traffic or anything like that because the hiss is really Broadband it's a goes to super high frequencies like out into radio frequencies and so that means what we're looking for is uh a really broadband like many frequencies kind of hiss and for that kind of detector what you want to do is is detect Broadband signals and so the design which is uh actually a
00:20:23 mainly the brainchild of Lee mcculler who's our new uh faculty member here in physics starting the fall uh he and I have been talking about this for for quite a while and so we came up with this idea I'm sort of he's sort of the brains of the outfit and I'm the what do you call it the older brains of the outfit uh but the idea is to make something that is a lot like ligo but
00:20:47 it's better on the quantum sensing side so ligo is sort of getting into the world of quantum engineering and we engineer the electromagnetic field so that it takes into account uh entang lement between photons and things like this but our new experiment which has to be more sensitive than ligo uh at measuring the uh displacements that one is more like um I would say it's like
00:21:13 Advanced Quantum engineering rather than simple this is no I'm not making fun of ligo here I I'm very proud of the quantum engineering there but this is sort of the the the next step which is to uh prepare Quantum states that are really unusual and you that to dig deep deep into what you can possibly measure on the earth so it's great for the main thing which is quantum gravity but I
00:21:36 think no one's ever attempted such a precise measurement of distance this will be if it works it'll be the most precise distance measurement ever done and is there something about a new center I hear of for this sort of precise measurement yes that's a good point uh so calch is building a new center for Quantum Precision measurement uh here on the on
00:22:02 the Celtic campus and it's you know you might ask why are we doing it here you know you could do it any place in the world we have a unique opportunity here we have Katherine here who knows about how this base time is supposed to work uh we have us who know about measuring small displacements and our goal is to go really into the big leagues in terms of quantum measurement uh and for that
00:22:26 we need uh people working on the theory of quantum information and measurement and also other people who do measurements like us so this new building uh in the basement will have the new Kip Thorn Laboratories where we'll be doing all of our uh stuff or Katherine will come visit us in the labs and on the upper floors we're going to have uh our great Quantum information
00:22:46 theoretical physicists like John presal and Lexi K um now can you explain a little bit more about what the experiment will look like because we know ligo or maybe some people know ligo is like really big and is I what is I forget what the distance is but it's huge and wouldn't fit in a lab but it sounds like this experiment will actually fit in this new
00:23:06 lab yeah that's right so uh the Lio has to be really uh long because it's looking for um strains in space which have a wavelength that's like hundreds of thousands of kilometers or something like that uh we're looking at very high frequency signals so it's not really necessary I mean we' still win by making it a bit bigger but um we I think we can do it all on the scale of several meters
00:23:31 so ligo is like a L-shaped Michaelson interferometer the laser comes in on one side the light goes two different directions uh and then it comes back and we measure how long uh it took the light to go this way and that way and we look at the difference and that tells us about the stretching of SpaceTime uh this experiment is like that it's exactly the same shape and
00:23:53 everything and from the outside it'll look like the same it's a bunch of metal tubes with lasers on the inside uh but the magic comes in at the output and which is sort of a counterintuitive thing but the quantum limits of these detectors have to do with uh what happens to the places where you're not in control of the electric field so we send in laser from one side but from the
00:24:15 other side we're not doing anything so all of this random fluctuations come in and bother us uh so we're going to put in uh Quantum magic you know TBD to to be determined what that is but we have a couple of schemes for uh make you know sort of reducing the noise that comes in from empty space okay all right well let's shift gears before the Q&A and talk a little
00:24:39 bit about your jobs so Katherine is a theoretical physicist and ra is an experimentalist so and you can see from their backgrounds a little bit about how their jobs are different R's involves rubber balls we know that but um can you so tell us a little bit maybe starting with Katherine about what your job entails and give us a picture of how you guys work
00:25:06 together so uh so the work of a theorist is um you know it's very nonlinear it involves ideas having ideas tinkering with the ideas and then uh most of the time discarding them trying to understand how they fit together whether it's consistent with everything that we already know theoretically uh and then um and then
00:25:33 trying to understand at least for me because I'm a theorist who's really interested in what we can measure what that implies for observation so uh oftentimes you know be tinkering like what you see on on the back Blackboard here this is you know not just one conversation this is multiple conversations over you know the course of weeks and you know we'll talk about
00:25:57 things or I'll sit down and think about something and uh work it out spend months or years working it out um and then uh have a proposal uh and at the end of it if it's something that hangs together theoretically which is again coming back to the mountain analogy I have this theoretical idea and and it goes through a series of consistency checks it hangs together and I write it
00:26:26 up and I come to R and say I have this idea I think you might be able to measure this and you know maybe the first time I come and talk to R he says oh that's interesting are you sure maybe he doesn't say it exactly that way but of course to start you know the natural place when I'm uh you know I come with a proposal I think quantum gravity the effects might be much bigger
00:26:52 than you thought they were the natural uh response will be some possible yeah that's impossible that's crazy everybody knows it's at the plunk scale yeah exactly it's at the plunk scale you'll never see that I say um you know I I I think this is real so then I go back and I and I think about I spend a lot more time thinking about it maybe another year or two and I come back again and I
00:27:18 say look I did all these other calculations and it's still there it's not going away and so you know then you know ra might start to get more interested Ed and then you know we talk a little bit more and and you know of course I'm constantly in contact with the theory Community because of course this was not a mainstream idea and so you know I get feedback from the theory
00:27:42 Community why why didn't you try calculating that or what about this are you sure it's not a gauge artifact which means are you sure that this is actually an observable so then you go and you do some more calculations and then you know after talking with Ronnie says okay well I think there might be an interesting measurement we can do here and um you know that's when the the
00:28:02 brainstorming on the experiment uh side uh you know happens and then um in our case eventually uh you know through interaction with r and with Le mcculler um you know we came up with a concrete proposal so um you know ra can of course talk more about the details of how that happens but it's you know from my my end it's um really a lot of um I think sometimes people think that you just sit
00:28:33 down at you know some well- defined point and you just calculate from a to F and then you have the answer but it's much more Dynamic and creative and uh a lot of tinkering trying to understand um how things fit together it's a when when I hear about these new ideas it's always exciting um but then I I close my eyes and try to imagine what
00:28:59 does that mean about my life and one of these things I feel like oh it's not it's not I'm signing up for like a let's go play in the lab for a year or something it's more like here's the next decade you're gonna be working on this uh frustratingly difficult experiment down in the basement for a decade and do I really want to sign up to do that do I care about quantum
00:29:22 gravity enough to keep doing this until I'm old and gray and uh yeah I care about quantum gravity uh but yeah I think I think the way we work together is you know because it's such a Time investment I try to come up with reasons why it can't be true because it's it's much nicer to find out why the theory is bogus you know on day one rather than day 3,000 after you put in a
00:29:50 decade of work and but when it's not like that like it just looks as Katherine says like it's still there and you can't find a reason why it's not there and it starts to get more interesting because you find out well there really is no evidence to contradict this and so it could be true and the only way we could contradict It Is by actually building the experiment
00:30:08 and and seeing what comes out I think it's fine for there to be theoretical doubt and experimental doubt you know gravitational waves were like this gauge artifact that Katherine mentioned people thought gravitational waves were just sort of waves of the coordinate system or something and it was a it was a theory debate that went on you know and
00:30:29 Einstein was on the disbelieving side of it even and it went on for almost 40 years before it was really well settled that like this is a real observable thing and it's not just mathematical waves and so I think it's it's natural for us to be skeptical at the beginning because this is really a fantastic thing fantastic in a good sense hopefully we've learned a few
00:30:53 things and it doesn't take us decades to resolve this uh but you know I think there's a similar kind of debate in the sense that you know people are really questioning you know well are you sure this is observable or is this just some you know relic of the kinds of mathematical structures that you've written down and
00:31:14 of course think the skepticism and the debate is legitimate and healthy and it it also helps you you know develop the theory understand better what it is that we're writing down and how it's it's related to the thing that you observe in the [Music] experiment okay well it's 11:30 so I want to switch to Q&A unless you have
00:31:36 any last thoughts I just want to say it's uh it's it sound maybe sounded like drudgery when I said go down to the basement and work for a decade but I'd say it's more like a lot of it's a lot of fun I I always found that it's really challenging it's really hard um to measure tiny tiny things uh but it's really uh it's really satisfying when it
00:32:00 does and to be able to get there it's not it's not like a turn the crank kind of thing every day it's sort of a mystery of why is that thing moving so much and what's going on and it's a it's like a creative you know day-to-day thing we don't know what's going on we don't know what went wrong last night and what's happening what are we going to do
00:32:19 tomorrow and uh but it's it's fun it's fun to work with you know everybody's on a team and trying to solve the same mystery and so it's a it's a decade in the basement of fun I would say yeah I hear scientists love basements yeah there's there's a reason you go down there right it reduces the noise it's also yeah and and less people
00:32:43 want to go down there so it's quiet you can think um okay well let's switch to the Q&A and um here's our first question comes from Kunal mully of Caltech um oh actually no that question changed hold on a second originally there was a question about quantum computers so let's go to that how will quantum computers help in the search for quantum
00:33:13 gravity um lot I think lots of ways so the the primary way I don't know about primary but the way the way I think about is uh one of the things we'd like to know about is what's really going around going on around the black hole Horizon and it would be great uh if you could build a Quantum simulator using regular stuff in the lab meaning like atoms
00:33:37 cubits that kind of stuff and if you could simulate something like a black hole Horizon on a quantum computer and a quantum computer might work to do that uh because we think the SpaceTime might have some underlying Quantum nature beyond that you could also think about using uh things like Quantum machine learning to look for the signal and separate that from the background
00:33:58 I think that's a that's I don't really know if that works but that seems promising so far okay all right um now here's a question where um let's see could you tell us a little more about the fluctuations you want to measure what are they fluctuations in yeah so there there fluctuations in
00:34:24 the in the fabric of SpaceTime so um so uh I think about it in analogy to gravitational waves of course gravitational waves that ligo measures come from these very distant astrophysical sources like you know black holes merging here these are actually little gravitational waves that are produced by the vacuum and um we're trying to measure
00:34:56 you know R described it as a hiss you know it's really a noise a characteristic noise uh that is associated with with the the quantum fluctuations in the in the fabric in the sheet of the of of fabric and um remarkably we can predict quite precisely um what kind of signal they should be able to
00:35:26 see uh in this instrument this interferometer that that R was talking about earlier okay all right well since we're in that realm let's try to explain the holographic principle so that this came up earlier and it's something people are asking about so can you try to explain what is the holographic principle it's not
00:35:53 easy Ron you want to take that one or should I uh I I'm okay with doing it because I I won't know it if I get it a little bit wrong uh so I the way I think about it is this is that uh the basic idea is that uh if you have a three-dimensional surface a threedimensional volume with a bunch of stuff going on like people and characters and whatever there's a
00:36:18 certain amount of information that describes can that can describe everything that's going on in this threedimensional world and you could also think about sticking it on a two-dimensional surface let's say that surrounds and in that case you would say essentially everything that's going on inside of this three-dimensional thing
00:36:34 can be described by some sort of cartoons on this two-dimensional surface and You Could reconstruct everything in the 3D World on the 2D world and so it's saying something like there's a correspondence between space time and three dimensions of space one of time and something else which is some other either higher lower whatever dimensional thing but it's a
00:36:56 it's sort of saying that you can rep you can think about things in both ways not just uh the usual way that we think about the universe yes the way that it applies to the measurement that we're interested in making is you know you take one of these interferometers you know it's an instrument that occupies a laboratory and so it it occupies some volume in
00:37:22 space and um the holographic principle says well even though you think theoretically that uh that each little part of the SpaceTime volume should have information in it actually the holographic principle says that that it doesn't that it's only the kind of surface area of that
00:37:47 volume that uh contains all that information so what is that mean for us it it actually means that in the process of projecting all that information out to the surface you actually kind of stretch out the effect so rather than seeing an effect at the plank scale the plank length which I was talking about earlier this 10 the minus 35 meters that's too tiny
00:38:12 to see what's happening is as you project it out into the surface you're kind of stretching out that information and so um what happens is not only that very very short distance scale enters but also the size of your measuring apparatus enters into the effect and that ends up making the size of the effect that we think we can see still really small but
00:38:41 observably large um and so with a very precise instrument like you know what what ra uh and and uh and Company wanted to build we we think we can see this um this this effect but really because the um bits the degrees of freedom the pixels of space time are um correlated with each other okay that's
00:39:15 better okay um now here's a different one um well different theories this is from Dean Ryder will different theories of quantum gravity such as String Theory or Loop quantum gravity be distinguishable in your experiment Al results so so would your results actually favor one Theory over another Well L quantum gravity is not a consistent Theory a fully consistent
00:39:39 theory of quantum gravity strength theory is really the only um fully consistent theory of quantum gravity and um everything that I've been working on is consistent with with uh with string theory as a matter of fact I I make use of tools that have been developed within the context of string theory but um as they uh are relevant for you know our for
00:40:08 what we can observe in an experiment I think they're much more generic you know this holographic principle is actually a very generic idea that uh technically has been worked out in some very concrete um theoretical framework so one that people talk about is the ads CFT correspondence which we're not going to get into in detail but it provides String Theory provides technical tools
00:40:32 that allow me to make precise calculations to understand how these effects can arise in these kind of well-controlled theoretical environments it's kind of like a theoretical sandbox in some ways that helps us understand what are the general rules what are the traffic laws for quantum gravity what is it that I think has to be true and then um based on what
00:40:58 I know of the structure of these theories and then I can understand how that applies to um a measurement that we would are looking to make in the lab okay all right let's go on to another one um here's just a very basic science one from anastasios lopis how's the uncertainty principle factor into your experimental design oh
00:41:27 good I like this question better so less less confusing for me uh it's it's a good question so in the in the community in the in the 70 there was a debate about whether or not the uncertainty principle uh affects us because of uh like the mirrors of our system are uncertain we don't know where the mirrors are or something um and it's true that's that's a real effect um but
00:41:53 the mirrors that we're planning to use are like the size of my hand and the uncertainty of your hand Quantum mechanically is not as much as the uncertainty of our measurement and so if you say I have a thing which is like a kilogram or something like that uh the positional uncertainty of that is is pretty tiny it's probably you know I don't want to say a number but anyway 10
00:42:17 the minus 25 meters or something like that pretty tiny and our measurement is aiming for something more in the range of 10 minus 20 M and that arises because of the uncertainty in the electromagnetic field that we were talking about before if I try to measure the electric field here uh at a frequency like the frequency of green light or something like that there's
00:42:39 some uncertainty in what is the magnitude of the electric field and that's a Quantum effect that the electromagnetic field in its lowest energy state that of empty space fluctuates up and down all the time and that interferes with our measurement that's really our limits or our limit so far yeah the the theoretical effect that
00:43:01 we're trying to measure is really a Quantum uncertainty of SpaceTime itself so um so you know coming back to the fact that you know we're trying to make a measurement of some volume of SpaceTime with this instrument one way you can think about it is that uh quantum gravity actually just kind of fuzzes out the positions of everything and what
00:43:26 we're trying to do is actually makeing a measurement of that of that fuzziness which has a particular you know size and a particular frequency or actually a range of frequencies associated with it so um we're really uh making a measurement of the uncertainty in SpaceTime itself okay all right let's do two more questions before we stop um or maybe
00:43:56 just one I'm getting the signal we should just do one okay well I think we might have time for two I I see some questions about entanglement so wondering if you can try to answer it fairly briefly talk about this idea that people talk about that space and time is emerging out of entanglement or some other Quantum property I know that's hard to explain
00:44:20 quickly okay yeah so uh so actually one of the uh theoretical tools that's used in these calculations that I do is what's known as the entanglement entropy and it just uh one way of thinking about it is that when I'm measuring again coming back to the fact that I'm measuring a volume of space that means there's part of the
00:44:43 space that's in in causal contact it means it communicates with each other and there's part of the space that's not and um one way you can think about what we're measuring is that you can quantify now the quantum entanglement between the pixels that I'm measuring in my volume and the pixels outside and uh one way of quantifying that is what's known as this
00:45:07 entanglement entropy and what we're looking for is actually fluctuations in that entanglement entropy that manifest themselves as fluctuations in in the SpaceTime okay R do you have anything to add to that yeah I think you know generally entanglement means something like you can't consider these systems separately
00:45:38 and so when we say something like entangled photons we mean something like maybe the photons were born from the same process and they came out waving opposite like this so when you talk about it you consider the photon pair as sort of one object because it's just different it's like it's kind of one system it's the best way to describe it and
00:45:58 and and for SpaceTime if it turned out to be true uh that it was emergent you know and whatever people mean different things by that but that would be one of those things where we'd say like the individual Quantum SpaceTime whatever that is they're all just related to each other strongly in the same way that photons or electrons or things are talking to each other and then in the
00:46:19 same way that matter emerges out of atoms we'd have SpaceTime emerging and all these things if if that's true okay well I hope it's true because that would be cool and um why don't we end on that note we're at 11:46 so uh thank you so much Katherine and ra for being here and thanks to everyone for joining us if you're interested in learning more
00:46:46 about the bizarre world of quantum physics and want to at least attempt to understand things like superposition and entanglement at a deeper level check out the Caltech science exchange the site provides clear explanations of not just quantum physics but other topics in science and technology like climate change and covid-19 find it at science exchange. caltech.edu
00:47:08 thanks thanks wne
