Brian Greene and Gabriela González: World Science U Q+A Session

hey everyone welcome we're going to start up now welcome to this next live session of whatever you want to call it your daily equation was the original name many of you are familiar with that series that we started during the pandemic or world science u or a hybrid of the two whatever you want to call it of course we're meeting today at a different day and a different time than we are used to partly that's because look i mean the world is is carrying forward and the usual constraints of the academic life are coming to bear on my schedule and the schedule of all those that we would like to talk to during these sessions as well you may recall we were typically doing these fridays at 3 p.m but i now teach fridays from 2 to 5 p.m so that slot has gone away for that reason so we'll experiment a little bounce the time and day around and hopefully you just sort of keep aware of the schedule through either the world science festival website or the youtube page you should subscribe if you're not already a subscriber so you can be up to date on the sessions that we are going to have and today is a a particularly fun session you may recall there was some spectacular news back in 2015 that shook the world of physics both metaphorically and as we will discuss literally when the first detection of gravitational waves was achieved by the ligo collaboration and you will remember we'll talk about this in just a minute gravitational waves is an implication of einstein's general theory of relativity it was an implication that einstein himself kind of struggled with in trying to determine whether it was a bonafide prediction or whether it was something that ever would be detected i'd say the majority of physicists before the detection probably thought it was unlikely that we would achieve a detection within our lifetime but there were some scientists who were braver than all of us some scientists willing to put everything on the line for what could be one of the great discoveries of our age and those are the scientists who are the real heroes of the story that we'll be talking about here today and i'm thrilled that one of those heroes one of those great scientists from the ligo collaboration is joining us today who is going to take us through this wonderful dramatic story of scientific achievement so with that i'm pleased to bring in gabriella gonzalez from the ligo collaboration and gabby is a is chief spokesperson for the ligo collaboration if i have that correctly and she and i have spoken in various contexts about the discovery of gravitational waves throughout the last couple of years but i'd like to start with gaby if you don't mind before we get into the cutting edge research and and all that sort of stuff let me just quickly ask where are you joining us from at the moment hi well it's very nice to be here even if virtually i would like to be visiting beautiful new york city i am in baton rouge louisiana that's where i live i teach also monday wednesday friday at louisiana state university and and how has the um how is the pandemic i mean it's affected us all in in a in a wide variety of ways but are you guys able to get back to work uh how's teaching happen for instance well teaching is a completely new experience because it's the first time and i'm going to be teach i am teaching online uh i'm teaching a large introductory class and that is done online for the for safety uh and i like to teach in an interactive way and and that of course it takes it takes a lot of learning let's say that my students are learning and i am learning a lot too and what's the subject in the introductory class introductory physics or is it is it gravity or yeah it's electricity and magnetism which of course has a lot to do with interferometers and the detectors we use you know electricity and magnetism the introductory course to my mind is the first real step toward abstraction that that many students take i mean when you're talking about mechanics and you can think about balls flying through the air you can picture it you can do it but all of a sudden this weird thing called the electromagnetic field that you can't see or feel or touch in any direct way the way you can touch tables and objects it's it's a leap forward yeah yes it's a lot more abstract i mean we can see masses moving we can imagine planets we've been learning about planets from from school but to think about electric charges i mean apart from from electrostatics and things that make my hair frizzy that there is a lot of experience with electricity that's about it that's right it's so easy to take for granted that these concepts are somehow second nature when you deal with them every day as a professional but man when you first encounter the idea of electric charge and and electric fields uh it's hard it's very hard yeah so what's your own speaking of uh the beginning stages of becoming a physicist what's your own story where where were you born and and uh were you like a physics uh were you building like the proverbial radiology chemistry set that kind of a thing or is it a different one i was not i was not actually i'm i was born in argentina you can tell i wasn't born in the us from my accent i was born in a big city cordoba in argentina and i was very curious my mom says that and i remember that i i was i would ask about everything and i also liked math in school so in high school my parents because i liked all of this they looked for a school that had a that was specialized in chemistry so i have an associate chemistry degree or something like that from from high school and in learning chemistry and physics we took these classes from early on and 13 14 years old uh i love the explanations i love being able to explain everything and i thought physics was the science that could explain everything because it explained atoms some chemistries about atoms it explained motion of planets so physics was everything yeah so were you either kind of were you going around and uh pointing out to people hey you know you see that that that spinning wheel over there let me give you the formula for the the velocity in terms of the angular motion and things of that yeah i was a tutor and i worked as a teacher my classmates for free but also for many yeah but but presumably at some point you came to the realization that the explanations that physics could give could explain some things but there was still room they were still get in on it and to me that was a surprise because i went to college in fact it must be very different now because of these programs because of youtube and documentaries but in that in that time i mean i i started college in 83 that's that's a long while ago but in argentina when the internet didn't exist it was beginning to exist anyway i went to college to learn explanations that i thought were already in the books i just wanted to learn i didn't think about practicing science or practicing physics i just wanted to learn yeah and there i realized that of course we took classes and in classes every everything we learned in classes were things that were hundreds of years old but the teachers the professors were scientists were people who were investigating things that questions that didn't have answers and posting new questions it wasn't not only that answers didn't exist to every question not all the questions had been asked yet and i loved that and that's when i wanted to become a scientist myself too so did you start in did you do research as an undergraduate or indeed in argentina the college degree is a lot more specialized than here in the us so it's a five-year degree in which we only take physics and math classes really and i ended and it ends with a thesis uh i had a paper a couple of papers published with my with my undergrad and my college thesis and it wasn't the theory eisen theory of relativity that's that's the area i wanted to do researching and you and you did research in in relativity yes yes at that young age were you were able to actually get into some real physics problems i guess if you're only studying physics maybe you got advanced enough quickly yes yes actually we we did um the we had to have a thesis that was associated with a research group so i chose this group that was very active on ice and theory relativity it was actually looking for exact solutions to isis equations there are quite actually quite a few no not as many as relevant as as the numerical ones that we have but that's what i was doing i also like to say that in doing that research i provided wrong at that age what do you mean by that because um actually i met my husband doing this research my husband uh was studying his uh was doing his phd in a different university in the south of argentina but he uh he actually wanted to do his phd thesis also on the theory of relativity but that was not the research group where he was studying so he came to cordova to the university i was at to do his research for his phd and that's how we met thanks to einstein and isis said that he couldn't be blamed his theory couldn't be blank for people falling in love and we took it wrong i see that's very good that is very good he's had a lot of other things too my goodness we start to go down that direction that is great so so you you were looking at exact solutions of the einstein field equations that applied to cosmology presumably yes i'm sorry go ahead my thesis was called solitonic cosmologies i see and and so were you thinking that you would be a theorist is yes even at an early age that that was where i see and then and then so from from argentina you you came to the united states at some point uh when was that and where did you go but just right after finishing uh college my husband uh finished his ph.d and we came to the us to syria at this university he came with a postdoctoral fellowship i came to start my ph.d studies and it was in syracuse university actually started my phd thesis on on on theory on theoretical research of relativity looking for defining using new variables to define some conserved quantities sure and very mathematical relativity but then a professor joined syracuse university that was working with the project that was very mysterious called ligo that was going to measure space-time and space time so yeah so that that caught your attention no doubt oh yeah well i actually had to you know in in phd studies you have to take in most in most universities you have to take a graduate lab course right and in in syracuse we had to choose a research group to do a semester long project so i i chose his group because he was just a new professor doing some the experimental gravity i mean and i was doing gravity so it was a natural love to do he was just setting up the lab so i was helping him set up the optical tables and setting up this this is peter's also at syracuse university just retired this year and and i loved the idea of i had i had done very very few experiments before and experiments in which you knew the results so here not only uh learning that but you i was able to do things with my hands with measuring data but the answer was not known uh and and that that was part that was a building brick of something that it was going to be so big and it was it was amazing and i just fell in love again but this time with ligo yeah now it's so interesting because i had in mind when i was an undergraduate that the only thing that i ever wanted to do was manipulate mathematical equations so i engineered it and it was possible to do this in those days to never take a laboratory to never touch and it was the biggest mistake of my of my education to do that because as you're saying you know if you're in the world of abstract ideas and you never sort of reach out and get your fingers dirty there's a there's a separation disconnect exactly right way of saying it so much so that i have to tell you when i went to the san francisco exploratorium this is many years ago right and and i walked in because i was given some talk or something like that had like a few 20 minutes of walking around and there's this cloud chamber and i'd never actually looked at one i've read about them i knew about them i'd never and when i saw the particles streaming through this these are real particles coming i was mesmerized that was like it's renal the particles that we talk about in quantum field theory course they're actually out there and and to never have that experience in a deeper way we're actually doing the experiment is a big loss so all of you folks out there listening who are enamored with the mathematics enamored with the theory listen to gabby's experience not to my experience or at least learn from my mistake you've got to be willing to get out there and do the real work that allows you to connect the abstract to the the experimental so anyway so you did that you did that that that project there and and they were basically swept away i guess by the possibility of of pushing the frontier of understanding through the potential detection of gravitational waves so what what year was that though was that late i finished my phd in 95 95. yeah and and and and now i recall you know feeling the general consensus of the world of physics in the mid 90s and again tell me if you felt it differently but there's a general sense of there are these people who are out there trying to measure gravitational waves and man are they misguided what what are they doing because it's just so unlikely that they will ever realize that goal was was that a sense that was palpable for the researcher i'm i'm not so sure no i don't i wouldn't think so because like i said syracuse university had just hired this professor so so they wanted this and and the people in the in the group i was the group was led by abayastica uh that time in syracuse he was actually very supportive he was part of this effort to hire the person in what was a very very new field i think at that time the groups doing experimental gravity i mean related to gravitational waves where can tech mit with ligo colorado well of course the university of maryland with weber and but lsu lsu was doing had a bar also whoever is a good example right so some people i mean maybe you can tell us a little bit about him in the experiment because that is sort of the the initial black eye if you will of gravitational wave detection i i don't know if that's a description yes but you know uh even before meeting peter saltzon this was in my first year at syracuse university before peters also joined i went to a small it was a small meeting in pittsburgh another famous mathematical physicist in relativity that new man it was his birthday so we were uh celebrating that birthday and that meant it was a small meeting but it was amazing because it was it was the first time i really felt alone as a woman i mean there was one other woman there beverly berger who is also very important in the field uh but we were the only two women there so that was already strange but in the meeting um joe weber was there and keith thorne was there and joe webber was presenting a new result he had been claiming he had claimed that he had seen gravitational waves in the 70s and of course other people had tried to reproduce that and they couldn't so it was not believed but then in 1987 there had been this supernova and he claimed that he had seen gravitational waves in his bars and italian bars in coincidence um and people didn't believe it because well there were few other bars in actually there were almost no other birds there were other bars in around the world much more sensitive than his but they were not working because they were starting to coordinate iran in the future so anyway his bars were the only one working and he said that he had seen this but it was i mean calculations proved that it was impossible and he said that it was because his bars were more sensitive because of the way the atoms interrupted in the bar and there was a discussion and a very uh a very respectful but intense discussion between weber and and keeps on job evan and keeps on this and i said wow this was when i was still a theory is that yeah i was presenting there work on on something i was working on at syracuse and and and i said wow look this with experiments you don't always know the result and and they can be wrong you have to be sure and uh it was it was a big big experience but it also showed me that that you have to be very very careful with knowing what you claim and being assured of what you claim and being able to defend it in a meeting like these wars so without a bit of a background maybe we should actually have you say what gravitational waves are just that we're starting on the same page so yeah it was a time when almost nobody had heard of gravitational wave except for mathematical physicists but the way i like to imagine gravitational waves is is emotion a vibration of this jello that we live in which is space time and space time i like to draw it i'm not very good at drawing but you know if you have a three-dimensional grid uh where you use like like a grid paper but in three dimensions but all the distances are the same and you imagine clocks in all the corners that are all synchronized that's flat space time now imagine that space time with the clocks and the distances all oscillating that's a gravitational wave and it it is uh it is easy to imagine it in that way what's difficult to imagine and that's what einstein calculated just less than a year after publishing his theory of relativity with this space time is that masses are the ones that distort space-time so that makes space time curved so it was moving masses the ones that could produce gravitational waves right yeah so so so again just for the benefit of everyone around us you're making reference to the key idea of general relativity that masses warp or curve this fabric of space now you're saying if the masses are moving around space-time is going to be doing like this and 1916 einstein writes a paper on the possibility that these gravitational waves might be one of the implications of his general theory of relativity he made a little mistake as i recall good one but yes yeah 1918 he writes another paper correct some of those mistakes but einstein himself and again correct me if i'm wrong but einstein himself was on the fence for i mean and he had the right to be if in his 1916 paper he didn't say that gravitational waves were impossible to to detect but and it's german so different people translated differently but he said given the constants in the theory and the constants are newton's constant and the speed of light when you calculate what magnitude these gravitational waves could have he didn't put numbers but he said they were negligible yeah yeah yeah they're good encryption so so so joe weber you mentioned these bars and i gathered these bars of these big chunks of metal that in principle for gravitational wave were to roll by would jiggle us it caused that metal to oscillate in some way weber joe webber was claiming that he'd measure those oscillations in that perhaps tense conversation at that meeting you're describing between weber and kip thorne the possibility that weber was confused or not interpreting whatever signal he was finding accurately was raised so so the issue was completely open at that point could we build a new kind of detector that might have the sensitivity to truly measure these ripples in the fabric of space and time um so that inspires what ultimately turns into ligo laser interferometer gravitational wave observatory what's the new idea for how you might detect these gravitational waves that ultimately yields ligo interference interference and this was an idea that that had been around in the 70s not just in the u.s but in the u.s and europe of using interferometers instead of the bars what happens is that the distances between the atoms change and that excites the resonance frequency of the burn and then if you motion if you measure the motion of the bar then you would detect gravitational waves but in interference the idea is using interference or interferometers to measure how distances change and this is something interference and lasers is something that is used in general to measure distances very precisely and distance and also motion changes in distance fluctuations in distance and interferometers are among the most precise instruments is what distances would you need to measure what changes is what you need to measure that's right and this is one thing i find amazing in in looking at the history of this like i said this history started in the 70s 80s when people began thinking about that and they had this magic number in mind that was uh 10 to the minus 21. uh that is that the amplitude of gravitational waves that's something we haven't said but it's important that the amplitude of gravitational waves even though they are changes in distance they don't have units of meters or centimeters or they don't have units of distance because the longer the distance you measure then the larger the fractional the change in distance so the fractional change is constant and that is the amplitude of the gravitational wave and that fractional change that was estimated that you needed to distinguish to measure to really measure be sensitive to astrophysical gravitational waves it was clear that you could not produce gravitational waves on earth that you could measure because those changes would be a parting 10 to the 40 or so so that's impossible but people thought to me if i had been hearing that it would have sounded almost as impossible that departing 10 to the 21 you could measure now to most people listening you know one part and 10 to the 21 one part and 10 to the 40. both sound pretty astoundingly difficult but but you actually have a little animation i guess of uh interferometer that yeah or the basic idea of how laser light and it's that's right and then it bounces on mirrors so the light comes back and then we measure the two beams coming from the two different arms interfering at the output that's why we call it interferometer and if the two distances are the same then the interference at the output is destructive there's no light coming out but if those distances change and that's what the gravitational wave would do it's a quadrupolar gravitational wave so it would make one distance shorter than the other one longer then the interference wouldn't be destructive anymore so if we put a photocell at the output of the interferometer and measure how much light there is and we see more light less light more light less light then we would be able to say there's something changing those distances one with respect to the other so when was the when was the first of these of these ligo detectors built well it depends on what you mean by lego detectors there were prototypes that were prototypes and those prototypes actually had a sensitivity that was uh of the la sorry let me refresh the ligo detectors are four kilometers long there are two of these one in louisiana and that's why i live in louisiana very close to one of those although i cannot go there now i wish i could um and then the other one in in the northwest in washington state they are four kilometers long a part in 10 to the 21 of four kilometers long is 410 to the minus 18 meters which is four parts in a thousand of a proton diameter it's no it's less than an atom it's less than a proton it's four parts in a thousand of a proton diameter so it's like measuring sub-nuclear distances there are lots of tricks we don't measure some nuclear particles we measure interference but that 10 to the minus 18 meters had been closely close to that had been achieved in some prototypes before ligo and that's why people thought it was it was possible you just have to make it longer because these prototypes were not shorter than last size or 40 meters now many many years went by without seeing signals say in the in the first official version of ligo that was that how many how many years did ligo one operate without success well this is also something that's also very interesting history and very admirable history of the well ray wise and keep thorn who were the ones proposing this but also the national science foundation because in the proposal sent to nsf for the funding of these two observatories in the late 80s it was approved funded in 1992 um they said that the there was the observatories needed to be four kilometers long uh and that that was going to the technology that was going to be uh installed in that was probably not going to be enough to get the sensitivity needed that a second phase was going to be needed so it was known from the beginning that we would have probably have to work on this for a long time but it was almost a question of when not weathered for us and we did um operate this initial version of initial ligo detectors between 2000 and 2010 only in 2005 was when we actually achieved the sensitivity that we wanted which was 10 to the minus 21 by the noise so we couldn't see a signal there not yet so we'll get to the the the first signal in in just a moment for those of you who are just joining let me just note that i'm have the pleasure of speaking with gabriella gonzalez from ligo we're talking about gravitational waves and now and then i will go to the questions of the folks who are watching let me just do one quick one if it's okay with you now gabby sam banner asks do gravitation waves affect only space or do they also affect time if they do affect time how do they affect time they do affect time just as much as they do affect space when we think about the distances oscillating those clocks that are also getting out of sync by a parting 10 to the 21. so that's also taken into account as you look for the various signals that that might come forward any other there are a bunch of other questions that i see that was the most relevant to gravitational waves i'm going to focus on those kinds of questions first and then after after we conclude our conversation i'll we'll deal with any questions that you want but now let's turn to the success right so this is now uh september of 2015. my understanding is that the ligo collaboration had done a lot of work to upgrade the sensitivity of the detector beyond ligo one to the levels that now in principle would be able to detect uh the typical gravitational wave that one might imagine being generated by some distant astrophysical phenomenon and then comes september 14th so what happens on september 14th of 2015 yeah well let me say that in 2015 2014 actually was when we first had light going back and forth in these detectors having them operational but not even close to the sensitivity we wanted we still don't have the sensitivity we want uh and in 20 and we had been planning from the beginning that if we were not going to wait until getting we were not going to be perfectionist around 2015 we were going we were planning to be three four times better than we had been before instead of ten times better that's what we wanted that's what we want um and then we would take data for a few months we were not expecting to see anything because this 10 to the -21 we had learned was actually a big big amplitude it was not going to be common and we were looking at signals we were counting on signals produced by binary neutral star systems because there are several of those binary neutral star systems known in our galaxy and we know they coalesce no coalescence had been seen but we knew that even given enough time millions or hundreds of millions of years they would call us so if we could see them further then we would see those but we didn't have the sensitivity that we we needed uh in 2015 for doing that but we had planned that we were going to take data and i am on record saying and who knows there might be black holes out there they would have to be close they would have to be big but who knows and rather than a neutron star dance a black hole dance would create a bigger a bigger signal which in principle ligo the advanced version would be able to attack but predictions were very very uncertain because if you have two black holes they don't produce light they might be dancing at tango like i like to say being from argentina but they don't produce light they produce gravitational waves but don't lie we know about black holes from x-rays because they sometimes are close to another star and then the particles that are that are traveling to the black hole from the other star they produce x-rays so we know we knew that we knew black holes existed right we didn't know we didn't think they were very big except the ones at the center of galaxies millions of mass solar masses but these black holes were usually 10 solar masses or less so those would have to be very close and but like you said on september 14 we were preparing for taking data we were not there yet because we wanted to have an automated system of alerts which was not ready yet we wanted to be able to simulate gravitational waves pushing the mirrors in the interferometer so that we could test our algorithms and we had not found yet the way to simulate gravitational waves the way we wanted so we had delayed the start of the run for a couple of weeks and it was in that period when we were getting ready that at night when the interferometers were operational but we were not doing tests we were taking data to practice the data the data algorithms and and one of those algorithms posted a webpage having a candidate that was amazing right so you were just at this point you're just setting up you know you're just sort of unpacking metaphorically the equipment and taking off the lab your outside coat to put on the lab coat metaphor it's just sort of the warm-up stage that's right and all of a sudden there's this big signal and the big signal was in both of the detectors it was in baltic thursday it was uh 5 am in livingston 3 am in in hanford it was very early in the morning so except for the operators on shift everybody else was sleeping well people in europe were not sleeping right so when you first saw this did you think uh glitch did you think sabotage you know what like the first thing we thought it was a simulation because we had been people had been practicing these simulations and we were all thinking why didn't they write it in the electronic logs because we have a public electronic log when we publish what we put all the things we are doing in the interferometer and but but simulation a simulation is like how does that work does someone actually program the machine to shake a little bit i mean yes actually we we produce a computer simulation of a gravitational wave or we take an approximation of a gravitational wave then we calculate what forces we we choose the direction in the sky and then we choose we we calculate what motion the mirrors would have to have different in each detector uh in livingston and hanford and then we push the mirrors to to prove uh to uh produce that motion simulating a gravitational wave yeah so you figured that you know we do we call these hardware injections because sometimes we do software injections we when we add a simulated signal to the calibrated data so in this case it's hardware because we do push the mirrors actually push the mirrors so you assume that somebody on the team had come up with an interesting simulation programmed it in and forgot to log it in the electronic logs and then so presumably you start to ask people hey did you put that simulation in that not only that but we also looked uh when when these simulations are done we have uh we have channels we don't only record the output of the interferometer in the photos and we also record how much force we put on the mirrors there are tons and tons and tons of channels that we that we store on disk to know what happens with interferometer and with environment magnetometer seismometers everything and and we could look in those channels and see that nobody had there was no push right were you at all worried that there might have been some prankster graduate student who might have you know programmed this in to get you all excited and not recorded any of it and then after an announcement is made you know it becomes clear that this was actually just a fake signal that was that question we didn't worry about that well we worried about that a lot but in the beginning i mean after i asked a few people and a few people i know well so i knew how to read the answers i knew that that now it wasn't and like i said we had evidence in we had no evidence in the channels that this had been an injection like the ones we planned yeah uh but also what what we were most worried about is that we didn't have enough data to know what the noise of the detector looked like because we have not taken any data yet right right so we really needed data to know what the noise was like and know whether this coincidence perfect as it looked was statistically significant i say i say and that was going to take a while i i'd assumed this is very interesting i'd assume that between september when the signal came in or the purported signal came in and february when you guys actually were confident enough to make the big announcement i assume that most of that period was interrogating people uh you know look at the signal in detail but actually you needed that period of time to measure the steady state noise of the detector itself to be able to subtract that out from the purported signal to see whether what was left was significant or not at that point that's right yeah we don't subtract the signal to see whether what we have noise it's we we do a statistical analysis you will see in the in that discovery paper that we had a histogram showing all the coincidences that we see between interferometers that we know are not astrophysical because we we cannot shield astrophysical signals like you would do in a lab experiment but uh what we do is we look for the time coincidences that when we shift the time in a detector we analyze the data the same way we analyze it for real but we say well the gps time in hanford it's going to be the gps plus three com 3.5 seconds by 10.2 seconds and then we know that any coincidence will not be astrophysicals because there's only 10 millisecond light travel time between the two detectors right right so the to show that these all came from the same source that same source is going to hit louisiana and washington state at slightly different moments and you're ensuring that it's compatible with your understanding of how fast that's right and that first signal had seven milliseconds uh different time difference first arrived in louisiana we always like to say here right right seven milliseconds later in hanford now you also are doing presumably supercomputer simulations at this moment because the signal has a very specific shape in fact you you have a picture of the signal from from september 14th don't you have a graphic yeah it doesn't have the simulation superimposed this is actually the signal from the photodiodes at hanford in orange and livingstone in blue and we have shifted it's shifted because the handful data is shifted by seven milliseconds notice that this is only a fraction of a second and notice the peak amplitude is 10 to the minus 21 exactly wow and and you can see this sine wave that increases in amplitude and frequency that's as the two black holes we from the frequency we could tell that these were black holes that were uh moving faster and faster together until they coalesce and they coalesce they form a bigger black hole that rings down and then you don't see anymore because the final black hole does not produce gravitational waves i see so the left hand side of that image are the black holes rapidly spinning again around each other then they smash into each other they coalesce that gives you the big right and then there is a little ring down two or three cycles and then it just goes away it noise you can see noise i mean of course we don't see a flat line and then a gravitational wave we always have noise in the detector and you see noise in the beginning and at the end now now to understand precisely who was dancing the tango that you described earlier that's where the super computer simulations come into the story i gather because you can take the theory of einstein's general theory take the equations and you can say okay let me imagine that there's a black hole of mass 10 solar masses and another of 13 put that into the simulation and get one particular signal or let me put one in the 22 solar masses and 18 and you can get another signal out of the mathematics so you already had presumably a whole library of wave shapes associated with all manner of astrophysical vision out there and so when you match that shape against that library what conclusion do you draw for who's dancing the tango out there that's how we can get the masses of the black holes we can infer something not very not very well but we can infer something about the spin of the black holes the final mass which is not the sum of the masses these black holes had 129 solar masses the other one 36 and the sun had 62. and i know your audience is very literate so they will say that's wrong it's not wrong the rest was energy emitted in gravitational waves e equal equal and c squared formula so the lost mass from the from the union you're saying is transmuted transformed into this energy of the gravitational wave of the last the last bit of the gravitational waves yes you were talking about supercomputer simulations supercomputer simulations actually it was a big big um victory when they could simulate gravitational waves produced by black holes i remember that in the initial ligo era there were no yet results from black hole there were only head-on collisions but not this dance and we didn't we hadn't detected gravitational waves and there was a bit of a race that we're going to see them first or are you going to calculate them first they calculated them in i think it was in 2005 but yeah so there have been a lot of progress in that but they're still very very expensive so we don't have a library of super computer simulations what we do have is very good approximations formulas phenomenological formulas where we can put the masses and we test the validity of those formulas against supercomputer simulations and then we use these formulas to make these libraries so it's a big uh effort by numerical relativity people by analytical relativity people by experimental and so on because in the conversation that we had a while ago at the world science festival ray weiss was part of that conversation one of the striking things of that conversation was the fact that ligo went forward before it was certain that the supercomputer simulations could even be achieved because without them you'd get some signal but interpreting that signal would be virtually impossible without being able to calculate what the signal should look like based upon einstein's general theory of relativity so you know in my tradition we would call that incredible hutzpah to go forward with an experiment of this magnitude with so many people and so much money with the hope borne out but with the hope at that early time that the theory would catch up or as you say even win the race to uh to calculate these things was there a time when you were worried that maybe we won't be able to calculate these things and we'll have this machine and maybe they'll be sick and we'll scratch our heads saying that's an interesting looking signal but i don't know what it is well to be fair these simulations are essential to uh to see the validity of these formulas for signals that are so short but like i said before the the one signal the one population that we were sure existed out there even though it was more difficult to detect than black holes but we knew they were out there it was these binary neutral star systems and binary neutron star systems uh in this they take a longer dance uh in the detector and this part of this of the wave where you see the amplitude and the frequency increasing before the merger that is very well approximated by perturbative methods so that part was well known the problem is that for black holes that part shrinks to one or two cycles and then you then you're not sure for that you do need computers so so it all it all worked out the computers uh and the algorithms to run on those computers were developed um at what point between september of 2015 and february were you pretty sure that this was a collision between out there in space well uh i think we were sure that we had a great candidate when we took data we took data for about a month which is what we calculated we needed we were going to take data for four months and we kept taking data but we analyzed the data for about a month at 15 effectively 15 days of coincident data between the two detectors and in there we looked at the statistics and it was good i mean this was a very very significant candidate but from those preliminary calculations we didn't have simulations we didn't have the parameter estimation quite yet in fact we have not finished reviewing all the codes that we used to do these things so we have to do the two things in parallel but from those preliminary observations as i mentioned the masses of the black holes 29 and 36 solar passes were huge compared to the masses that were known so this one actually was very strange we really needed to be sure and like i said we hadn't finished reviewing the course which we had wanted to do before we started taking later you know everything runs late so that took us months and also at the same time we began looking for alternative explanations we had to rule everything out we had a team of people looking into possibly hacking and we realized from the outside world yeah yeah and we realized that we couldn't completely discard that possibility but it would have to be they wouldn't put signals in the the way we usually push the mirrors they would have had to uh to put some extra electronics and do extra simulations and do it simultaneously at the two observatories without everybody knowing uh you know we have cards to know where people are at what time so they would have to bypass everything so it would have to be have been at least four or five insiders very very insiders and we just didn't believe that was we don't believe that that's happened so you so what did it feel like when you finally had that confidence i mean you look back i mean it's einstein general relativity 1915 1916 he proposes that there might be these gravitational waves revises that in 1918 you know people start to build these devices through like the 50s and 60s but now the first moment of success right i mean that's like what what you dream about right i mean what was that feeling like well i have to say that uh i was at the time the spokesperson of the ligo scientific collaboration i'm not anymore actually these are two year positions i had three i said three terms until 2017 but i was delivered at the time so from the beginning i have to say that i lived in a state of panic well not panic but but but stressful energy it was boring boring boring everything and about things the right things to be happening the paper to be written and all the checks to be done and we were also very worried because if we had seen this gravitational wave before even trying why didn't we see another when we analyzed that amount of data some of us thought that we were going to see more than one but it was only an indication of a second one that could be real with one question later on we confirmed it with better analysis um but we didn't see another one so until we saw another one i have to say that we felt uncomfortable and in december we saw another one it was not as strong but it was longer so in significance it was also very significant we didn't have the analysis complete by the time we made the announcement but we were all breathing a bit easier because we knew that was it was not just a single example there was more of that so was there a point when the um the tension eased and you could just revel in you know it was two days after the announcement we made the announcement on thursday february 11 i remember yeah which by the way was the first time that was celebrate that the international day of women and girls in science was celebrated that is celebrated now every february 11 it was destinated like that by the u.n and but that was the first february 11 and there were two women among the five scientists on the podium all of this is a coincidence but then the next day friday there were lots of interviews i was talking at the conference the triple a yes conference the american american association for the advancement of science so it was the president of argentina called me obama tweeted it was i mean there was so much excitement that i was stealing this adrenaline field stage and then the next day i i actually woke up in the hotel still in washington and i i cried this is this was it this is it that's fantastic yeah no it's it's it's it's i mean physics is not often viewed as an emotional subject in the classroom but to a scientist like yourself who makes a discovery that will be remembered for you know eons to come yeah it's an emotional moment so your reaction is i think really indicative of why we do what we do it's for those of you but of course the announcement was was huge it was important but what we knew then is that this was the beginning yeah because we didn't have we knew we could improve the sensitivity we were already working on that we knew now that black holes binary black holes existed in more than one there was there have been more than one so we knew we were going to discover more and more things and we have been doing that so that's why we turned why don't we turn to that now last part of our conversation i mean what has happened uh since this discovery back in 20 years in 2016. well we let me say that we talked about the ligo collaboration making this discovery but actually it was two collaborations the ligo collaboration and the vigo collaboration the big collaboration is a european collaboration of scientists that has a detector in italy the virgo detector a three kilometer detector and we in the initial ligo era we had agreed to work together we had taken data together we had not discovered gravitational waves together uh but we were working in the analysis together so that first discovery paper was signed by both collaborations and in 2000 so we and the the earth detector was not operational uh yet but in 2016 in november 2016 we began taking data again with the ligo detectors and the vehicle detector was going to be ready in a few months actually ended up being ready in august of 2017 and we were going to take data until the end of august 2017. so it was only one month of the of that we took data together but in those months we detected seven coalescences of black holes seven more so with the other three were 10 we would have 10 mark already some of these with vivo 2 so we had good localization because we could triangulate and on august 17 all was running out of time in this observing run we saw finally a collision of neutron stars i see and those collision of neutron stars that collision because we were taking it together with vigo we could triangulate and moreover we could be sure it was neutral stars and not small black holes because there had been a detection of gamma rays coincident with our detection and that had been posted online an alert at the same time we had posted hours actually before we posted hours so we knew that there had been light coming electromagnetic waves coming from this event so we told astronomers we had lots of agreements with astronomers they looked there and they found first a red spot then a blue spot and then on blue and then red i forget and 10 days late later x-rays and and radio waves it was amazing that was one of the best objects started in astronomy and so by triangulate you're saying if on planet earth we've say got three locations that detect the gravitational waves from a single source by virtue of the time differences of the arrival of the signatures you can pinpoint where in the sky the signal that's right because with two detectors they are like microphones so you don't actually see the um you cannot tell where they come from from the time difference into detectors you can tell well it comes from a wing in the sky and by looking at the bit more data amplitudes and faces you can say well it comes from that banana piece we call the bananas in the sky but with three detectors then you have uh two pairs of those bananas so you have an intersection and that intersection is a little circle or a little wager not little for astronomers it's not a small region it's more than a full moon but but still it was enough for people to go and and look in there and they looked at galaxies and known galaxies and in one of those galaxies they discovered this bright spot that hadn't been there before fantastic but that was 2017. then we improved even more the detectors we took we began to take data again in 2019 last year in april first full day and then we were planning to take data with vidco from the beginning and we were planning to take data until the end of april we had to stop at the end of march because of the pandemic but we have been analyzing that data we actually had public alerts you could get an app i had two apps in my phone that sound and alert and those are public apps because the alerts were public so you could tag when they listen we had 56 alerts 56 candidates of gravitational waves 11 months almost 11 months you're saying that anybody can have this app and they can be alerted when when a new candidate for gravitational waves that's that's that's right that's right and so some of those alerts and subsequent confirmations have yielded some surprises uh yes yes actually like i said the candidates take a while into being confirmed so we actually have the alert we classified whether it's most likely binary black hole or a neutral star black hole and we have several candidates of that kind or a binary neutron star and and we have published now about four different candidates four different detections not candidates anymore that are confirmed as gravitational waves and we have published those on on their own uh we are going to publish a catalog but we published those on their own because they are all very interesting one is them some of the masses of the black holes are surprising right well the first detection had surprising masses but then in that catalog of ten uh black hole coil essences in one and o two that's how we call observation run so one and o two where the first two o three is this last one uh we had uh the maximum mass we had had of a black hole was uh was close to eighty 80 solar masses from the merger of two but indeed in the latest one we have confirmed that it had made it to the papers it was it appeared in lots of media had two big black holes 165 solar masses they added 80 some solar masses that formed 142 solar masses and these black holes this big are are in a region of masses of black holes that some astrophysical theorists say they cannot exist actually but they say that's what the new media says what they say is that they cannot be formed from an ex supernova explosion which is how we believe black holes are formed in supernova explosions that leave behind the neutral star or the black hole but if they do they have a maximum mass because masses that are bigger than that don't explode this way so there is a maximum mass for black holes to be formed this way and both of these black holes are larger than that mass especially the bigger one so the speculation is that these black holes or at least one of those was probably formed by the merger of two other black holes so it's sort of a sequence a cascade there may be some initial supernova gives you a black hole of a given mass and then these guys perhaps underground and then that performs another one but that means that there are a lot that these black holes are clustered because all that they have there are a lot more of these we don't know yet oftentimes people ask me they say well you're always talking about binary black holes what about the trinary are you are you do you ever i mean i guess in principle you've never seen anything like that presumably yet or well this could have been one we haven't seen it to see one what you would need to see is the coalescence of the office black hole and in the perturbations of the signal see the indications of the third black hole still there or the third mass but for that you would need a lot of definition on that waveform to see those small perturbations so so what is next and i i mean that really in in two in two ways one is what are the new detectors that are going to hopefully be built to increase the sensitivity in the manner you suggest but the other question and maybe just take them together separately as you see fit the the promise of gravitational waves has often been we're going to see some things that we expect like neutron star collisions or black hole mergers or which are spectacular but oftentimes those descriptions are concluded by saying and the most exciting thing is that we're going to see things that no one ever anticipated that's right so so where do you where do you stand on on that so first of all what's the new what's the new equipment new technology that you hope to be built in say the next 10 20 30 years well we still have improvements to make to the technology that we have in these facilities so we can still get a lot more of these facilities but if we really want that factor of 10 which is what we did from initial ligo to advanced ligo if we wanted the next factor of 10 which would give us all the black holes in the universe we could tell the story the history the cosmological history of black holes uh it would tell us it would give us most of the neutral stars the lord of neutral stars with the sensing the the precision we need to do nuclear physics nuclear physics out there in the universe imagine that to do that we we really need new facilities bigger facilities new technology and that technology is being developed cryogenics and new materials and new lasers but you really need facilities that are bigger 10 kilometers 40 kilometers there are different designs uh the international community is putting is working together on this because these would of course be very expensive too so they would have to be international collaborations no single country could do this and this would be space-based i mean lisa is the experiment that many people point toward is that that's right well i was telling you about our ground-based detectors to detect all of these compact smaller compact objects but if you want to see bigger black holes like the ones at the center of galaxies then you need to go to space and that's lisa it has it is actually not a project anymore it has decided it has a launch day 2034 so it's still a few years away you know running you say 2034 my first thought is to calculate what's the likelihood i'm gonna still be here but uh you know that that's how these that's how this progress is maybe do you have a picture do you have a picture of a prototype for lisa in your yes in the last slide uh it's a small picture but it also shows you the full spectrum i think yes yeah good i see it so on the on the right at the bottom right there's the ground-based interferometers we see collisions of solar mass black holes intermediate mass black holes may be and neutron stars with a space detector lisa it's a triangular detector we see here one satellite but it's actually three satellites with the light it doesn't go back and forth we have lasers one laser in each station that points to the other to the other station these would be two and a half million kilometers away and they would detect gravitational waves from not just these massive black holes at the center of galaxies but also white dwarfs in our galaxies that we know exist and produce gravitational waves in fact we could use some of those as calibrators right and then you want to go bigger you want to see super massive black holes and in fact there's so many of those that they would produce like a noisy background a stochastic background and those for those you have to go galactic not space but galactic and that is being done with what we call pulsar timing that uses the radio waves that we see from pulsars from neutral stars in our galaxy we know about them because we detect radius signals from these and and from looking at the correlations of these radio signals is like an interferometer the laser is the radio wave and and this is has been going on and my day is that the next instrument to detect gravitational waves is going to be that that technique really yeah i've been hearing about that yeah i've been hearing about that for a long long time it always sounded so incredibly exciting but you think that's on the cusp of uh yes wow and and oftentimes when talking about gravitational waves people make reference to primordial gravitational waves from the big bang itself not not detecting the waves of phenomena within the environment that we can sort of feel is there but even going right back to the beginning is that what's the likelihood of that kind of a success oh i think it's also likely to be seen in a different way for that you don't use interference this this early universe had gravitational waves uh like the cosmic microwave background and it is a background it's like a noisy because it's not waves of a single frequency or any particular frequencies these waves at all frequencies all mixed together and it is calculated it depends on the cosmological model so different inflation models have different predictions but the predictions they have certainly for for the lease of sensitivity for frequencies in the lisa band or in the ligo band it's we are just not going to see that it's going to be hidden by other sources astrophysical sources like both white dwarfs and lisa or or black holes in in ligo but you could see there is a prediction that those gravitational waves polarized that cosmic microwave background in a very particular manner and if you can measure the polarization of the microwave background which is being done at the at the moment but if you can measure it precisely enough and you can tell that the polarization is not caused by the dust in the way which has been the case so far then you can say this is a snapshot of gravitational waves imprinted in that cosmic microwave background and there has been i mean there was a an announcement of success that i guess uh yes apparently had to be uh re-uh reinterpreted perhaps as the yeah just like new to dust but those experiments are getting more and more sensitive all the time so that's also maybe some point let me just one question from uh the audience before we conclude here so uh shanti chandrasekhar asks do gravitational waves interfere with each other in principle yes but what we call interference is between two waves that have the same frequency like they are produced by a coherent source and we don't think that stars or black holes get in touch with each other to to produce to be coherent one with each other so that would not be the case however that would happen if we were to see length gravitational waves we could have an object far away like a coalescence a black hole binary system that produces gravitational waves and there could be something really big very very well aligned in the line of sight it would have to be incredibly well aligned with the line of sight and then that would distort the gravitational waves going through that are coming from the same source so they would be coherent with each other and then they would last when arriving to earth so in that case uh you could call that interference we call it lensing we haven't seen any evidence yet uh we cannot discard it completely but from the statistics that we have uh we these these lensing events are very very rare because you need that incredible alignment but that would be a case of interference right so so for yourself do you see sticking with gravitational waves uh for uh for the duration of your career or yeah so much more to do i i work mostly and my group works mostly on the instruments uh these days on diagnosing trying to clean up the data because the data is very glitchy the background that they produce especially for black holes is is big so we want to we want to be able to make to to diagnose where the noises come the glitches are coming from and and remove them from the data but i have also been involved and my and my group has been involved in the commissioning and the improvement of sensitivity of the detectors and there's so much to do we also are involved in in the discussions of future detectors which i i hope to i hope to see in my lifetime but i know they take decades uh to build so it's never late to start we are already working on that well you know you've already uh hit the pinnacle you know you know one of the discoveries that will be remembered as a as a high point of science in our era so uh anything else that you achieve of course is spectacular icing on the cake it's a sort of great position to be in so so you know obviously congratulations on you know the achievement well deserved and the continuing success of the collaboration and and finding unexpected things about the nature of the universe through the detection of gravitational waves uh thanks so much uh for spending the time here with us today the audience uh so appreciative of you know hearing directly from people like yourself who are on the on the front lines of pushing the boundary of understanding so gabriella gonzalez thanks so much for joining us and i look forward to future discoveries that will provide future material for conversations going forward so thank you very much for joining us thank you thank you for hosting this because i think that one of the advantages one of the few advantages of a pandemic like this is realizing ourselves that we can take advantage of this of this media to talk about science even though we cannot be together in the same room you know hugely so i mean in the program that that we did back in 2015 or 16 whatever 15 i guess it was you know on general relativity and the po it must have been the possibility of gravitational waves at that point yes i gave a lecture in world science university yeah exactly and and those you know i mean those are some of our you know millions of people have viewed you know some of the conversations that we've had there so it is a service that many people make use of so i think you're absolutely right there's a way in which we can make use of this medium to really uh get people excited about the power of science about the excitement of discovery and maybe combat some of the sentiment that we feel trickling down from arenas of government that at least uh some of us hope will shift on november 3rd but we'll leave that leave that conversation for a different day we'll stay in the realm of science here for now so again thanks for joining us and uh look forward to interacting with you at some point again in the future thank you all right folks so we're gonna now um move on to uh focusing on and some of the questions that are coming in on uh on youtube uh so let me just [Music] see what else we have here uh so uh priyanashu shukla hello sir brian what advice do you have for those who are aspiring to become physicists yeah i love that's a sort of a fun question to start look the advice is simple get inspired by the kind of conversation that we just had get inspired by seeing the kinds of discoveries that are still with us today right there can be a sense that the big questions of physics have been settled in an earlier era and there's not much left to do but there's a huge amount left to do you just heard from gabriella gonzalez about the spectacular insights in gravitational physics from gravitational waves their spectacular insights still awaiting us in the realms of quantum mechanics cosmology particle physics so my advice to the young aspiring physicist is to become excited about the possibility of contributing to those endeavors but at the same time focusing your studies on the very basics that you need and you will rely upon if you go into physics so the basics of classical mechanics of quantum mechanics of statistical mechanics of thermodynamics of the general theory of relativity of quantum field there i mean learn the basic subjects that you will encounter as an undergraduate and a graduate student learn that basic material inside out do not somehow feel you can skirt around that material and jump right to the frontier of understanding it just doesn't work that way so buckle down work hard do your problem sets and get inspired by these kinds of conversations that you can find all over the internet i mean i'm partial obviously to the material that we produce world science u world science festival excuse me but there's a lot of great stuff out there and in your off moments explore that kind of material but in your own moments that in the moments that are dedicated to your own education do not skimp on learning the basics that that to me is always the big lesson for for all of these ideas uh rob b asked dr green what do you think about the likelihood of time being a particle uh it's hard to exactly interpret that statement so i guess what i would say is i think there's a high likelihood the time and space as we describe them in the general theory of relativity as we describe them in the conversation with gabriella gonzalez that space is sort of like this fabric she used the metaphor of jello that the jello of space can vibrate it can shake that i think is a is a is a good metaphor but most of us believe that quantum mechanically space and time are not really fully articulated as a fabric or a jello that's a description that works on sufficiently large distance scales but if you get to very small distance scales it's likely that there is something like an atomic structure to space and an atomic structure to time by that i mean there's some kind of entity fundamental entity that might be called the most basic quanta of space or the most basic quanta of time just like a photon is the most basic quanta of the electromagnetic field so the gravitational field itself probably has a graviton and that graviton itself may give us a clue to what the most basic structure of space and time actually is and i think at that point we won't be talking about a fabric we won't be talking about a jello we will be talking about some fundamental quantum ingredient and you can think of it as a particle as you'd like whether that turns out to be the right language i don't know but i would say there is something else the fabric itself is made of something finer and that finer entity is what we're still searching for both theoretically and hopefully at some point in the future experimentally okay i'm just going to scroll through the questions that are coming in right now so if you asked a question earlier you might want to ask it again because the list of questions is just too long for me to uh scroll through all of them but let me see what else we uh we have here um so blue french horn dr green what is hawking's no boundary proposal of the big bang theory that's a great question a hard one to answer in words but let me just give you a feeling for the idea so normally we think about space and time as highly related but different we think about the capacity of motion through space to change your passage through time that's one of the big insights of special relativity we recognize that your location in space can affect your passage through time because if you're near one of those black holes that gabriella gonzalez and the ligo collaboration have now established are really out there if you're near the edge of a black hole einstein's theory shows us that time slows down so where you are in space here or here or here or here affects your passage through time so there's this deep association between space and time that's really been manifest since 1905. nevertheless we usually think about space and time as still having certain fundamental differences we can travel any which way in space but as far as we know we can only travel one way through time space doesn't have an orientation to it whether you sort of think about space this way or that way or that way there's no fundamental arrow there's no fundamental direction for space but there does appear to be a fundamental direction a fundamental arrow for time the arrow of time seems to point from the past toward the future right we ineluctably travel through time in one direction as far as we know whereas in space we can travel any which way there doesn't seem to be a fundamental direction which is just to say that space and time have deep associations they're linked but we do think about them as different the hurdle hawking idea is to imagine that in the early universe the distinctions between space and time go away that in the early universe time in some sense rotates into a fourth spatial direction and that's very interesting because if the space-time fabric let me use that metaphor really can be thought of as a four-dimensional spatial region well four-dimensional spatial regions they can naturally smooth off and they can naturally have a nice smooth end to them the image that we like to have in mind is if you think of a cigar a cigar has a cylindrical shape and then it has a kind of spherical end that's attached to the spherical part of the cigar so imagine that metaphor of the cigar could actually apply to space-time itself so imagine that as you go further further back in time you're going along like the cylindrical part of the cigar but as you head right back toward the beginning imagine the time this direction melds into space so that they're now all part of a spatial region that spatial region can pinch off like the end of a cigar and in that way there isn't really an end there isn't really an early mo earliest moment it just kind of smoothly draws to a conclusion if you will because of the overall shape of the space-time fabric and that's one way of thinking about the idea that there may not be an end a unique end to the space-time fabric instead it might kind of curve off and and end in that way so that's that's an idea that comes from hawking and hartle and these kinds of ideas we don't know if these ideas are right we don't know if they're wrong but they're interesting ideas for thinking about the earliest moments of the universe um physics club asked that 10 to the minus 21 change due to the waves can change then at atomic orbits uh well look you know if you have a gravitational wave that that rolls by a region of space in principle it is deforming the space-time fabric on all scales right i mean there's a wavelength associated with that wave but um any entity in principle is affected by that stretching and compressing of the spatial fabric however small so yes you could imagine that you one day if you had sufficient sensitivity could detect the kind of stretching and compressions on on any scale imaginable so the ones that we're talking about are are stretching in compressions that are on the order of a fraction of a proton diameter so compared to an atom that's that's quite small but uh yes in principle these kinds of stretching and compressions one day they may be commonplace that we can measure them on all scales which would uh be incredibly exciting andrew hanny asks in the poll and barn paradox so this is now moving from general relativity to special relativity which is fine for us to do will the pawl will the pole fall if the barn is replaced by a hole in the ground that is shorter than the pole from the poles view but longer than it from the whole view so this is andrew this is actually a well-known paradox i don't i don't remember i don't know why i can't remember the exact name of this particular paradox but you're right if you have an object that's say sliding along a surface and if that surface has a break in it where in principle an object could fall through the surface like you know imagine you have a excuse me have a skateboard that's going along say a very smooth straight track and imagine that there's an opening in the track where you could fall right through now you have a version of the story that you that you wondered about from the skateboards point of view it's the track that's moving and so the opening will be lorenz contract and it'll be very small so from the skateboarders perspective of course they're not going to fall through they are longer than the opening which has now been lorenz contracted from the person on the track looking at the skateboard the skateboard is incredibly compressed and therefore is much smaller than the opening and therefore from the perspective of somebody on the track this little tiny skateboard of course it's going to fall through the opening and now you have the paradox andrew that you ask about from one perspective the skateboard should not fall through the perspective of the skateboarder him or herself or themself from the perspective of the person on the track obviously the skateboard will fall through and the answer to your question like who's right and who's wrong this is one of those situations where the details really matter the details of for instance the exact speed and strength of the material out of which the skateboard is made because as you can imagine there's going to come a point perhaps from the perspective of those in the track frame of reference where the back of the skateboard is still on the solid surface and the front is not so does the material bend does the material angle downward these kinds of details actually matter when it comes to analyzing this situation so there's no uniform answer that we can give it depends on the details the precise details of how the object is rolling what it is made of and so forth so so it is a resolvable question if the details are specified but without the details you're left somewhat up in the air but bear in mind it is not a paradox there is an answer but the answer depends on the details so it's a very good question but not one that can be answered in generality without specifying those details arjun kr says how does the speed of gravity become equal to the speed of light that's interesting we didn't i guess we did in the conversation with gabriella gonzalez we did make use of the fact that the speed of gravity is equal to the speed of light which means that these ripples in the space-time fabric they travel from the source to the receiver at the speed of light now now why how do we make use of that we made use of that recall that gabby was saying how the time delay in when the signals were received in washington and in louisiana that was an important piece of the story establishing that these gravitational detections were real because if there's a fixed source in space then the distance to louisiana and the distance to washington state are slightly different and therefore if the wave is traveling at the speed of light you can calculate the kind of time difference that you expect between detection at each of these two locations and the answer that they got agreed with the actual measured difference which was a nice piece of corroborating evidence that this was indeed a gravitational wave from a single source in in outer space but the question that's being asked is why is it that the speed of light equals the speed of gravity and that's something that's manifest in einstein's general theory of relativity you see directly that ripples in the fabric of space you can calculate how fast they travel and it's a fairly straightforward almost one-line calculation in some sense if you think about it correctly that there's almost only there's only one speed in the general theory of relativity and that is the speed of light c appears in the general theory because the general theory embraces the special theories of special case and the special theory we know that the speed of light is a natural number that comes into that story so it's quite natural that the speed of gravity is the speed of light and the general theory of relativity makes that precise okay a question here that i just saw about the size of space uh here it is ignacio jar gui i hope i'm pronouncing that correctly how can the universe be infinite if it had a finite beginning yeah it's a it's a it's a very good question because if you think about the universe the universe is extent in space as being finite at the time of the big bang then if the big bang happened say 13.8 billion years ago and if the expansion of space is finite then a finite stretch of space at the beginning would get larger over time but over a finite time interval 13.8 billion years that finite distance in space that finite extent of the universe would only be finite today so how in the world can we possibly say that the extent of space might be infinite if indeed it was finite at the big bang and the answer is we can't if the extent of space is infinite today then it would have been infinite at the time of the big bang and that is an idea that perhaps we don't emphasize as much as we should but i suspect that the dominant view among professional cosmologists has been maybe it's shifting over time i haven't done a study a statistical survey so i'm just basing this on my sense of people's view from conversations over many years but i think the dominant view is that space is infinite and what's being pointed out by ignacio in this very good question is that if it's infinite today then if you go halfway back toward the big bang halfway back in time then the universe will be smaller but whatever fraction it is a half a tenth a millionth if it's infinite today then a half a tenth or a millionth of infinity is still infinite so the universe would be infinite halfway back toward the big bang and if you go three quarters of the way back to the big bang it'll be some fraction of the infinite infinite size today which will still be infinite in size and as you wind the clock ever further back in time you have a universe that's ever smaller in the sense that objects in the universe will get ever closer together but the entire expanse of space will continue to be infinite so the image that we often have of a very tiny speck at the big bang expanding into the universe that we are familiar with is a little bit misleading that picture is true for all the finite distances that we say are aware of that we can observe and can measure but if you're talking about the expanse of reality the spatial expanse of the universe in its totality then at the big bang that would have been infinite infinitely big it would have been infinitely dense and perhaps empty hot depending on which cosmological theory you subscribed to but it would be infinitely long in the actual expanse of space itself so it is a somewhat different image for the big bang than what we often have in mind but if it is infinite today it will be infinite all the way back okay what else do we have here um at pratim rostoki asks hello professor brian what is the flop transition was a flop transition well that's a a question that's uh close to my heart flop transitions uh i was part of the discovery of that now it's a long time ago it's just a young man with dark hair and more hair this was 1992 at the institute for advanced study in princeton i think it was 1992. yeah and i was spending a semester there and was working with some of my good friends david morrison paul aspinwall also ronan plesser was part of the conversations that in pert important and and uh important stages of that discovery and um we asked ourselves whether the fabric of space well we all we know from einstein it can stretch it can twist it can compress it can warp it can curve we asked ourselves if you included quantum effects in the way that the general theory of relativity does not but string theory at least allows you to begin to include these uh post general relativity effects maybe that's the best way of saying it we asked ourselves whether space could rip whether this fabric you know excuse me this fabric itself could puncture and tear and of course we were studying it mathematically as i described in the first hour in the conversation with gabriella gonzalez i don't do anything experimental unfortunately the closest i get to experimental physics is like measuring for a shoe rack that i'm going to build this week in our house up here and that's as close as i get i'm going to measure the alcove and i'm going to use a saw to cut it cut the wood that's about as close as i get but so we were doing a theoretical investigation about whether the fabric of space could puncture or tear and we were doing this using the mathematics of string theory and within that mathematics we found the possibility mathematically that a certain operation that mathematicians know about they call it the flop transition where you take a region of space and within that region of space you collapse down a spherical portion and you collapse it all the way down to a point and then you blow it up is the technical language but it sort of sounds metaphorical you kind of blow air back into that sphere but you inflate it in a different direction in a different way than the direction and the progression that you used when you were shrinking it down so you take a sphere you shrink it down and then you re-expand it and by doing the re-expansion in a different way you actually puncture the fabric and then you repair it but when you repair it the shape that you wind up with is fundamentally different topologically different we call it from the shape that you started with and we asked ourselves could that mathematical flop transition i don't know why it's called a flop maybe because the sphere comes down and then you flop it over when you when you re-expand it maybe that's the origin of that terminology i don't actually know the full origin but that operation is called the flop transition and we asked ourselves whether that might be realized by the physics of string theory and what we found after some some pretty substantial pretty heavy calculations some by hand some by computer we found that string theory does allow for the flop transition to take place which means you could imagine an actual sequence of events described by string theory in which a spherical portion of space itself now not just an abstract geometrical entity but a spherical region of space itself would shrink down puncture and then re-inflate in a flopped direction fundamentally changing the shape of space fundamentally changing the topology of space and so we were able to establish that those operations actually happen at the same time at the institute for advanced study we would we would meet every four o'clock there's a very genteel tea time this is einstein's old stomping ground the institute for vance studies so there's this wonderful tradition that everybody from all of the schools at the institute for advanced study from natural sciences you know from social sciences from history all get together in this big open area which i suspect is no longer happening now that i obviously think about the uh the environment that we're in right now but we'd all meet and talk and ed whitton one of the the greatest physicists of our age who of course is in some sense einstein's successor at the institute for advanced study we would tell him about our work so dave morrison myself paul aspinwall who were all at the institute at that time we tell edward whitney about our work and he got really interested in this possibility of the flop transition and he found his own way into the subject very different from from ours but his own way into the subject and we came to the same conclusion at the same time that these uh topology changing transitions could actually occur within string theory and so we we coordinated the publication of our papers so that each of us would feel that we had gotten the uh the priority for the discovery that we all deserved that we weren't gonna one-up anybody and it was a very uh very uh a very kind of satisfying gratifying really beautiful period of time for me to be part of a discovery of of significance but one that was being done in a very cordial and very information sharing a very open manner so that's kind of how you uh hope these things would would actually work so that's what the flop transition was all about uh mukherjee asked sir is consciousness a property of particles or is it something else and upal i hope again i'm pronouncing your name correctly i apologize uh the answer to your question is i don't know nobody does so it's one of the big big unanswered questions of not just modern science but of of modernity right modernity right i mean this is one of the big questions that we ask ourselves is the light that's on is the movie that's playing inside of our head is the voice that we hear chattering away between our ears is that conscious experience of sight and sound and smell and taste and internal abstract reflection is that due to the motion of particles inside of our brain and nothing else or is there something else and now certainly the motion of particles does affect our conscious awareness right anybody who's had some kind of uh issue with their brain or anybody who has injected foreign substances into their brains knows that those new particle motions affect the conscious experience that you have that's unassailable right that's that's manifestly the case but the question is is it just the particles or is there something else what might the something else be well some people say there's a consciousness field out there like the electromagnetic field or like the gravitational field that we're talking about in the first hour with gabriella gonzalez and that our brain somehow tap into that external consciousness field is it possible yeah it's possible i don't see any evidence for it but i don't dismiss it out of hand as being nonsense i don't think it's true but i have an open mind could it instead be that there is no consciousness field per se it's just the particles inside of our head but maybe almost as uppal suggested maybe the property of consciousness is somehow embedded into the particles themselves particles somehow are imprinted with have embedded within them the properties of of mass of spin of electric charge could there be another kind of quality a consciousness charge that's also embedded within particles and when many of these particles come together their individual consciousness charges can coalesce to yield consciousness as we experience it is that possible yeah definitely possible again i consider it a far out idea a beautiful spectacular idea but one that i don't see any evidence for which doesn't mean it's not true and so my my view is somewhat more conservative or depending on your perspective some people call it more outlandish but my conservative view is that all you need is the known particles with the known qualities and all you need is those particles to come together into the right organized pattern and to carry out the right organized motions you know various electromagnetic charged particles moving along various quantum mechanical trajectories i think that's all you need to yield consciousness as we know it so i am a great fan of these more exotic proposals i would be tickled silly if one day we learned that there is a consciousness field i would dance for joy if one day we could prove that electrons have another quality called proto-consciousness that's the precursor to consciousness as we experience it if any of that were ever to happen oh my god invoking now even another explanation i mean holy cow or whatever excited word you use for things that are wondrous that would be fantastic to learn that consciousness is inside of particles or out there in a field i don't think it's going to happen i think that we're going to come to the conclusion incrementally i don't think it's going to be a big breakthrough one day but step by step we will see that every quality of consciousness including the inner experience of it that's the big controversy but i even think that the inner experience of conscious awareness we will one day be able to explain using the language of physics particles and laws or whatever language supersedes particles laws and fields in the future so that that's where i come down on that story but uh it's a it's a big and important open question that um we just have to uh wait and see where where it all comes out so kev's creations on the youtube chat says god would be the best explanation for consciousness and you may be surprised kev's creations or everybody else who's uh with us at the moment i i i kind of agree with that in a way i don't know about best per se but it would be a spectacular explanation if god is the explanation for consciousness i don't resist that idea again i don't see any evidence for it i don't see any evidence for god doesn't mean that god is not real as i've discussed in these forums earlier i view religion as a vital quality in the human progression and i view it as a very beautiful way of trying to make sense of our place in the grand cosmic schema i don't see god as an explanation for things like the electrons magnetic moment or einstein's field equations that we spoke about in the last hour that isn't i think where the invocation of god provides us any particular insight but any place where it can provide us insight i welcome that insight and if one day it gives us insight into consciousness wow great amazing again i don't think that's where things will go but if they do go in that direction it's not something that i find distasteful it's not something that i find giving up if you can really establish and that's the big question how do you establish that the inclusion of god in our musings and in our descriptions of consciousness adds real illumination deeply satisfying and gratifying and even predictive illumination great that would be that would be fantastic again i don't think that's where it's going but i allow for that possibility rob b asks is there a distance limit for cause and effect can a butterfly on another planet have an effect on earth no there's no distance limit that we know of we recognize that there is a limit on the speed of propagation of an influence i do something here i clap my hands it took some fraction of a second for the oscillating air molecules to bounce into my microphone which then took some time to send an electric signal along the cables that are plugged into my computer which then travel and yield a cascade of other influences that travel through other wires and other means of communication through the internet ultimately reaching your speaker on your computer which then vibrates in a manner that reflects what i just did and then that vibration travels through the air and causes your eardrum to vibrate so that cascade of influence travels from me up here in upstate new york to wherever you are around the world and there's a time delay for that to happen but there's no distance limit it's just a speed limit and that speed limit is the speed of light so no signal can communicate information from one location to another at a speed greater than the speed of light but no there's no distance limitation so yeah if there is another planet that has a butterfly on it the you know proverbial disturbance on planet earth from a butterfly flapping its wings in early times and that causing a domino effect little tiny domino effects that can influence how the world is subsequently that can happen from an influence on a distant planet even right now you know if i snap my fingers or let me even just say i rapidly move my arms i am creating a gravitational disturbance gravitational disturbance and that disturbance is tiny but it ripples out there in space and there's no distance limit in fact you know the disturbance that gabriella gonzalez spoke about in the first hour we didn't talk about it i guess but the two black holes that collided giving rise to the signal on september 14th at five o'clock in the morning those two black holes were more than a billion light years away a billion light years right a light year i don't know what units you like to use but it's something like you know six trillion miles if you like miles but kilometers will hardly be different so call it whatever four trillion kilometers or bigger i said i said that backwards right to be greater than than 6 trillion but whatever it's trillions of kilometers in a single light year you're talking about more than a billion light years and that influence which happened more than a billion years ago when those two black holes collided more than a billion years ago more than a billion light years away that ripple in the fabric of space just continued to travel outward until on september 14th at five o'clock in the morning it reached us in louisiana and in washington state and caused the two ligo detectors to shake so there you have it a beautiful example of there being no distant no distance limit on how far away something can be and have uh some influence on us here now i just noticed somewhere in capital letters in the chat somebody in capital letters wrote you are wrong but they didn't tell me what i was wrong about [Music] and i can't actually even find it any longer so if whoever thinks that i'm i'm wrong with such vigor and vehemence i'm i'm open to being told where i'm wrong but you got to give me more than just you are wrong not much i uh not much that i can do with that at all okay what else do we have here that we could have some fun with i'm gonna go to the other twitter feed let me see if there any things coming in from there that catch my eye i don't seem to have the twitter feed at all okay so if you're asking questions on on twitter unfortunately they're not coming through to me so apologies let me just go back to the uh to the youtube thread here um um so if gravity and light have the same speed this is another question for margin i like these this line some do the unusual thing to give origin maybe it's not the same person though i think the last name may be different if gravity and light have the same speed can we say that light and gravity are made of something which have a common property and i i don't know i don't think so right when we talk about light as the electromagnetic field we're talking about it in a quantum language we introduce a notion of photons and we're talking about gravity we talk about the fabric of space-time we talk about ripples in the fabric of space-time and there if we inject quantum mechanics we are talking about gravitons and fundamentally we really do think about light and gravity photons and gravitons it's just being different i mean there may be a unified theory maybe it's string theory in which they are brought together into a single rubric maybe vibrating strings is the right language to talk about there but fundamentally just because photons and gravitons travel at the same speed we would not say they're made of the same stuff but then you could say like why the same speed i started tried to give some insight into that earlier but but maybe a way of saying it would be the speed of light and the speed of gravity are indicative they are reflecting a more fundamental quality of reality that transcends light and it transcends gravity and the feature that i'm talking about sorry about that phone ringing and i forgot to shut it off you know out of i'm out of practice hey if someone's listening for this at the main house can you pick up the phone so i don't have to have that irritating ring happen great thank you so much picked it up so the point i was making is that the more fundamental quality that the speed of light and the speed of gravity tap into is causality causality is the more fundamental quality of reality that each of these things reflect and what does causality mean we know what it means it means that a an event and b another event a can only affect b if there's enough time for a signal from event a to reach event b before event b actually happens right again you know just now i caused your ears to hear my finger snapping and that means that the event of you hearing my finger snapping and my finger snapping they have to stand in a very particular relationship which means there has to be enough time between my finger snapping and your ear hearing my finger snapping there must be enough time for the signal to travel from here to wherever you are now on earth that's not much of a constraint light can go around the earth seven times in a single second so signals travel really quickly on the scales that we are talking about but fundamentally that's what the speed of light is it is something that is deeply reflective of causality that event a can affect event b only if they stand in a very particular causal relationship and that then gives us a different way of thinking about the speed of light the speed of gravity speed of light and speed of gravity are both in some sense reflecting or ensuring or protecting causality and causality transcends light it transcends gravity it transcends the signal by which an influence is transmitted from here to there so the universe basically says that causality demands that there is a limit to how fast signals can propagate and light reaches that limit and gravity reaches that limit and that limit in conventional units is 671 million miles an hour or whatever units you like 300 million meters per second and light reaches that limit in its speed and gravity reaches that causal limit and its beat and that's why fundamentally light and gravity have the same speed they are maxing out the speed if you will of causality so they're reflecting the causal nature of events in the world and therefore their speeds are the same not because they are deeply related although they may be their speeds are related because they are both reflecting causality the nature of causality in the world okay um martin topinka what is the easiest explanation for why gravitational waves start with a quadrupole radiation as opposed to the monopole or the dipole in the language that we physicists would use and um you know uh i don't know that i have a really good intuitive explanation for that so what martin is pointing out is if you have a a completely spherical motion of matter that is spherically symmetric then even though you've got matter moving it won't generate a gravitational wave you need a more messy motion that doesn't respect that spherical symmetry in order for gravitational radiation now this emerges right from einstein's theory you know one way of saying it i don't know if this is going to help at all but in general relativity the degree of freedom that's really fundamental is the distance between two locations because after all what does a gravitational wave do it changes that distance now how do you measure distance what's the mathematical gadget that you use well it's something called the metric the metric tensor you know about this metric from the pythagorean theorem right if i have two points on the cartesian plane that are separated by delta x and delta y how do you get the distance from one point to another how do you get the distance of that hypotenuse well it's delta x squared plus delta y squared that gives you delta z squared or delta c squared if it's usually delta a squared delta b squared delta c squared so so you see that there's a way of measuring distances that makes use of the squares of the separations more generally it's a quadratic form it's an entity that has in a delta x delta y even cross terms like delta x delta y can show up in the most general version of this quadratic form and because it's a quadratic form that it involves squares in the pythagorean theorem that means that the metric tensor has two indices not one index we usually write it as g mu nu times delta x mu delta x nu in the more general way of framing things if you let me speak math speak for a moment and the fact that the metric tensor has two indices not one is what takes us to the quadrupole as opposed to say the dipole or even the monopole and that mathematically is where it comes out in einstein's general theory of relativity i i know that's not particularly intuitive i gotta think of a better intuitive explanation but mathematically that's the answer to your question all right what else do we have here what time is it oh it's uh it's 104. we've been going about two hours um let me just uh answer a few more questions and then we'll uh try to uh try to wrap that up eric w says i like brian's hair today well thank you eric my wife tracy actually snipped off a few of the ends of my hair the other day my first haircut in six months so if you like how it looks then we have tracy day to thank for that okay back to physics spin foams asked sir what is quantum romanian geometry in the mathematical context of strength well a lot of technical questions at the moment let me just take a sip of my my mud water here uh coconut tea with soy oat milk today so we all know or at least we've heard if you don't know in detail that what einstein did in classical general relativity is borrow the whole mathematical structure of romanian geometry developed by bernard riemann 1800s who worked under gauss who also made use of the ideas of other mathematicians like lobochevsky and others and so there is this body of classical geometry by which i mean the ordinary geometry that you learn about in school but augmented to include curved surfaces right so standard euclidean geometry that we all study at least in america we typically study in the 9th or 10th grade it really focuses upon shapes that are drawn on a flat surface or 3d shapes but again embedded in a flat euclidean environment einstein and his physical incorporation of these ideas into the general theory of relativity generalizes this to make use of the romanian geometry of curved surfaces and curved shapes if you now include quantum effects you're in the realm of quantum romanian geometry or quantum gravity so the answer to your question really is that quantum gravity can be thought of as the mathematical structure that injects quantum mechanics into the classical geometrical structure of general relativity which is romanian geometry so what is quantum gravity in some sense it's quantum romanian geometry now string theory is one approach to quantum romanian geometry and in answer to an earlier question about flop transitions flop transitions i've already noted one weird quality of quantum romanian geometry that is not manifest that does not exist really in classical romanian geometry which is that there's a smooth operation that allows you to tear the fabric of space that was that flop transition that i that i mentioned earlier where you take one shape of space squeeze down a sphere puncture the space then re-inflate that sphere in kind of an orthogonal or flopped direction and that new smooth geometry that emerges from that process has a fundamentally different shape fundamentally different topology that would not happen in classical romanian geometry there'd be a singularity in the process but in quantum romanian geometry there's no singularity it's a smooth physical process but look string theory is just one approach to quantum gravity and therefore it's just one approach to quantum remaining geometry there are other approaches and we don't know which is right and so we'll have to wait for future insights to tell us which of any of those is right but that is what quantum remaining geometry is and that gives you some sense of the string theoretic approach to this kind of geometry a local titans asked do gravitons in gravity act just the same as photons and electromagnetism the anger is totally not local titans i mean we often analogize between say the photon is to the electromagnetic field as the graviton is to the gravitational field so that's a nice a nice analogy that gives you a sense of what a graviton is but the detailed mathematical description about how a graviton behaves how it interacts how it moves the kinds of processes that it can be involved with that mathematics is completely different from the mathematics that governs similar questions for the photon for the photon it's maxwell's equations or more precisely the quantum mechanical version of maxwell's equations which is known as quantum electrodynamics for the graviton it's quantum gravity and again there are approaches still tentative for what quantum gravity is and string theory is one of those possibilities but within string theory the quantum mechanical property of gravitons they're very different from the quantum mechanical property of photons for instance their spin is different the photon has quantum mechanical spin of one in the appropriate units that we use the quantum mechanical spin of a graviton is spin two double and that relates right back to my earlier remark about the metric being a quadratic form it has two indices these the analogous degree of freedom for the photon is the electromagnetic potential or the u1 gauge connection if you want to use technical language often written down as a mu that is one index that one index is indicative of the photon having spin one whereas the two indices g mu nu on the metric tensor are indicative of the photon having spin two so the answer is no their properties are absolutely not the same um mr space is space distance measured in zoom in if yes what is the start and end point zoom in i mean i i got that has nothing to do with how we're communicating zoom or youtube i i tauren i don't understand the question mr space maybe you can reframe it sorry i don't know what to say in that um what else we have here time walker is there any upper or lower limit to the wavelength or frequency of light if you're dealing with classical electromagnetic theory and you're ignoring gravity then the answer is no you can have a wavelength of any size that you like the math is agnostic to the particular wavelength or the particular frequency if you're doing quantum mechanics and you're including gravity in your story as well then the situation is somewhat different because we know that the energy of a photon is directly proportional to its frequency e equals h nu nu is the frequency and if the energy of a photon exceeds a certain value like that of the uh the planck mass then you have to start worrying about does that photon turn into a black hole because its energy is so large and its its wavelength so short that it exceeds the bounds allowed for an object to resist gravitational collapse so the formation of black holes comes into the story and makes it a far more complicated situation than in the case of classical electromagnetic theory in the absence of gravity for which the answer to your question would be yes taken to these other effects the answer would be no um do you think a theory must be true if it seems elegant karam absolutely not absolutely not so the ultimate arbiter of what's right what's wrong is observation it's experiment there's no substitute for that so you know my first book was called the elegant universe and within that book i try to make the case that string theory is a very elegant theory that it is a very elegant way of combining the general theory of relativity and quantum mechanics but nowhere in that book and nowhere in the many many conversations since that book was published back in 1999 have i ever made the argument that because the theory is elegant it is true i never say that i say because it's elegant it inspires us because it's elegant it may give us additional motivation to consider it and to examine it i mean if you come to me with a very inelegant very clumsy very clue-g version of a theory i'll look at it and i'm repelled by the mathematics and i don't want to study it it may be true but i don't feel compelled to study it because my aesthetic sensibility is violated by the ugly theory that you've presented me with yes i will say that but i would never say that the beauty of a theory is the ultimate arbiter of whether it's right or wrong and that's why i'm the first to say that i don't know if string theory is right i'm the first to say that i'm highly skeptical about string theory i'm impressed by the beauty i'm impressed by the elegance of the mathematical formulation i'm impressed by the achievements that string theory has already made in understanding things like black holes in the nature of space-time and things of that sort but all that is circumstantial the only thing that would truly convince me of the veracity of string theory is some kind of observation or experiment that we simply could not explain in any other way or better still if it was a prediction that came out of the analysis of the mathematics of string theory and then we go and look for it and we confirm it that's the dream that's the goal we're not there yet we are not there yet with string theory but to answer the question beauty elegance will never be enough never be enough sounds like a lyric from the greatest showman it'll never be enough for me never never somebody out there sing it for us i'm not gonna embarrass myself my daughter was here i'd ask her to sing it okay what else do we have here geraldine morrow asked dr green does quantum mechanics allow free will and i would say sure it allows free will because there are aspects of quantum mechanics that we don't yet fully understand the quantum measurement problem is still an unresolved issue as far as i am concerned and yeah so it's possible that one day when we fill in these final details of quantum mechanics somewhere within those details we will see ah-ha there is free will and the quantum mechanical equations properly and completely formulated do i think that's going to happen i do not my suspicion and that's all that it is my suspicion is that the final details of quantum mechanics when fully understood will not change the current view that i hold and many others too about free will which is that it's not real in the traditional formulation again the argument is simply that you and i are made of collections of particles those particles are governed by laws of physics whatever those laws may be quantum mechanical certainly as far as we can tell but provisional in our current understanding and because you are made of particles and your brain is made of particles and because every decision you make and every thought you have and every sensation that you acquire amounts to your particle configuration shifting from one configuration to another and those configuration shifts are fully governed as far as we can tell by mathematical law there's no opportunity for a you to intercede and somehow change the course of the law progression of the particle configuration taking place in your brain what would it mean for you to have free will you'd have to be able to get in on the action intercede and somehow violate the physical laws that ordinarily hold sway and i don't see any opportunity for you to do that i don't see any opportunity for you to get in on the action in that way i don't see any opportunity for you to exert free will in the usual sense of transcending outside influence in this case the outside influence being the fundamental laws of physics but again as i'm said at the outset if the laws are such that they do allow for that in a way that we don't currently understand because the laws are provisional sure possible but again just to put that in context if you were to ask me is it possible that the moon is made of blue cheese or mozzarella cheese or swiss cheese i say yeah it's possible you know maybe underneath the surface it's swiss cheese i don't think so but you know we've not dug it down 10 miles and show that we haven't encountered swiss cheese or you know we know the density of the moon so i have to be swiss cheese of the right density and all that sort of jazz but you get the point there are many things that could be true that i would nod my head and say yeah it could be true but it's pretty far-fetched and i consider the moon being swiss cheese to be one of them and i consider quantum mechanics giving rise to free will to be another one of those unlikely but possible ways in which things will advance ayanna enache is it possible that the human brain may may be a quantum computer well in a sense it is i think the brain does undertake computations and i do think that those computations are fully governed by quantum physics so there is a manifest way in which the brain already is a quantum computer but i know what you mean you're talking about the kinds of computers that were now on the road and route to building in the laboratory could those more correctly capture the kinds of processes in the brain sure it's possible it could be that the metaphor for brain processes will change over time from the classical computational metaphor that we use often the brains like a computer maybe as we understand quantum computation and as we build quantum computers maybe that metaphor will change and we'll say oh yeah the brain is much more like a quantum computer could well could well be going forward i just don't know all right let's see uh sanjay powwar says wait for a minute i am writing okay i'm waiting sanjay waiting waiting i don't see anything yet from you so i'm going to move on to somebody else saad raza tell us how to learn math there's really only one way to learn math and that's by practice you know you can watch videos and get the basic idea but in any math course i've ever taken it wasn't until i began to do calculations with the math that i understood what's going on in fact i had a very interesting experience as a graduate student many years ago i was taking an advanced mathematics class at harvard with a great math teacher cannot remember his name i do remember he came to class with two big dogs a bit unusual but but a great math teacher and we were learning things about algebraic geometry we're learning things about abstract things about various kinds of spaces and you know vector bundles and principle bundles and all this stuff and i remember i was using that math i was learning it to sort of reaffirm what i already knew from my physics research and string theory so anyway i'm taking this class and i'm i'm like lining up the things that he's teaching us with the kinds of calculations that i was already doing in string theory so one day after class i go to this professor with i guess i was a graduate graduate i go to this professor with one of my calculations and i just wanted to ask him some questions about the calculation and he turned to me and said he said look i think you know these calculations better than i do he said look i'm teaching these ideas in abstract he said but i rarely if ever do any calculations with this mathematics so there was a weird way in which i knew the math better in some way than he did because i was actually using it to get numbers to calculate things whereas he was just way up in the clouds teaching it in a fully abstract way so it was an enlightening moment for me when i realized that doing calculations finding examples of the abstract mathematical concepts is absolutely essential at any level that you're learning to have the the deepest understanding of what's going on so saad raza that's my advice for how to go about learning mathematics um akshat shukla is math the language to write the universe uh certainly there are people who thought that i mean you know plato famously over the entrance to one of the places where students would gather he said something like you know if you don't speak the language of math or geometry there's no place for you here because that's like where the deepest truths were galileo thought that the language of math was written in the language of geometry so many people have said that math is a language for writing the universe i i don't know i don't know that that's true i've lived my life as if it is true because i've lived my life spending a long time learning the the language of mathematics and applying that language to try to understand things about the world better and math unassailably undoubtedly is a powerful tool for making things about the world clearer but i've said this before is it possible that one day we'll have a conversation with alien life forms and those life forms will say to us no it's not math they'll say to us hey we tried that for the first 10 000 years of our civilization and yeah we came upon something analogous to your general relativity we came upon something analogous to your quantum field theory or they may say we came up on this other thing that you guys never figured out never discovered but it might all be mathematical but then they'll say at some point we realized that math was a dead end we realized that math could take you part way along the road to reality but only part way and we realize that this other approach non-mathematical in its basic structure is really how you grasp reality i don't know i've said before i don't know what that other approach would be in fact i can't even imagine what it would be and not somehow secretly be mathematics disguised in a different vocabulary a different formulation but if math is just sort of pattern recognition encapsulated in a predictive way it's hard to imagine what description of the universe doesn't fit that rubric and therefore wouldn't be math and disguise but i don't know i certainly do allow for the possibility that um that math is not to be on end-all that it's just a stepping stone to a deeper understanding i don't know if you guys have any ideas what might supersede mathematics in describing reality be interested to hear whatever possibilities come to mind but akshat shukla i don't know that math is the language to write the universe could be also could not be um sam o'neill says could it be possible that we need a new math like newton invented calculus to understand the universe and sam certainly that's the case and earlier i don't know if you were with us somebody asked about quantum ramanian geometry which is a new mathematical structure that did not come out of mathematical research it came out of physics research so those physicists like me who spend time thinking about quantum gravity have been led to develop a new mathematical structure that incorporates quantum mechanics into the old gravitational mathematics which was romanian geometry developed in the 1800s so that classical romanian geometry from the 1800s updated with the insights from physics quantum mechanics in particular yields exactly what sam is suggesting a new math that new math is quantum remaining in geometry that has things like i described before topology changing transitions and other qualities as well so in fact there was a there was a class held at the institute for advanced study which i brought up earlier when talking about flop transitions reinstein was for for many decades there was a class held i don't know 10 years ago maybe longer time flies and it was a class for the world's greatest mathematicians to learn about the new math emerging from string theory and other cutting edge approaches to physics so it was kind of the striking thing where you had a tutorial for some of the greatest mathematicians in the world so that they could learn about the new mathematical ideas emerging from physics so yeah sam this happens it happens all the time and it happens in a very uh interesting and productive ways [Music] safiq raza sir you really look like old century great scientists like newton and galileo do i i don't know if that's a compliment or an insult or just an observation i'll just i'll take it as a compliment although the pictures of newton with the long frilly curly blonde hair i don't know maybe i guess i got all these curls happening at the moment but actually i'll tell you something my student pontus alquest great student of mine one of the best students i've had now works for google i believe or alphabet or whatever it's called he sent me an email yesterday i would try to find it but there's a psychology project i don't know if you've ever looked at this where for every researcher in math maybe physics too you can figure out from the genealogy project who their advisor was and who the advisor of their advisor was and you can like follow this trail it's like a family tree but not for birth relations not for genetic relations but rather for who is your advisor advise advisorial relationship if i can use that language so he told me and if i i can't remember how many but he he found out from the math genealogy project that i and hence he since he's my student that i am the great great great great great great great great great great great great great great great i think it was 15. great grand advisee of isaac newton that's funny right so you got isaac newton and he has some advisor who has another person that's their advisor and you follow it all down the family tree and you get presumably to graham ross at oxford who is my graduate advisor great advisor in particle physics i was doing my dissertation in the early days of string theory graham ross with my advisor and then then comes me so that that that family tree from adviser to student goes all the way back to isaac newton and pontus my student gets one more grand in that story because he's one step further down the train so yeah so maybe maybe somehow the influence of isaac newton however diluted follows through that that family tree that's uh that's what you hope all right anyway what do we have here um taj thomas asked brian we now have scientific evidence of consciousness existing outside of the body you're going the wrong way wrong wrong way um i'd love to see that evidence charge thomas i've looked at times as carefully as the literature allowed to see the claims that consciousness exists outside the body i've never seen anything convincing so if you have something convincing i would love to see it because look as i said i'm not dogmatic about these things if there truly is evidence that consciousness is beyond the physical i'd love to see it but every supposed piece of evidence of that sort every purported piece of evidence that people point toward to establish that consciousness supersedes the physical is beyond the physical every piece that i've looked at either was not convincing or wasn't doing the work that the interpretation suggested that it was doing it may have suggested something interesting about consciousness [Music] but i've never seen anything that's proven established that consciousness exists beyond the body so i'd love to see it i i don't know i don't know what that would be like uh moniel corania how does thermodynamics explain the universe that's a big question mo neil and that's one of the rare times that i'm actually going to refer to a book i'm going to ask you to look at until the end of time get it from your local library not trying to make any sales here i think that's all gross when people do that you know how people have these interviews and they say well you know in my book you know until the end of time you know or you know it's funny you should ask that question because in my book until the end of time i hate it when people do that it makes my skin crawl so i'm not doing that but what i am doing is say look at the book until the end of time in a library or get a bootload copy online they exist and that book is all about entropy helps explain the origin development the evolution of the universe and how speaking of which the word evolution is a counterpart to entropy that allows us to understand how interesting structures can emerge in an environment heading toward ever-greater disorder as demanded by the second law of thermodynamics so that's my best statement that's my best answer on the role of thermodynamics in explaining the universe so check that out read it if you have questions come back when we have another one of these meetings and i would be more than happy to address any questions that come up guy richard says yes you are lol i guess you are promoting your book i guess i am but i'm seriously saying get it from a library or search online for an illegal bootleg pdf copy i don't care about where you get it it's just it's the best answer i can provide okay what else do we have um uh rbs do you think time travel to the past is possible by using a machine yeah referring to the papers of ronald mallett yeah so as i've said many times before i don't think time travel to the past is is likely to ever happen and um the reason for that is manifold there's a deep tension between time travel to the past and our understanding about physics and causality it doesn't mean it's impossible for time travel to the past to happen it's just very difficult to see how it fits in with our understanding of things that's not an argument obviously but um and there are proposed ways and there are people who have thought deeply about this kip thorne joe polczynski delay joel pochinski great physicist uh and and uh the papers that you refer to they're interesting definitely interesting papers but i would say most people believe that when we understand physics to a greater level of precision than we do today we understand some things quite well but we understand to a greater degree of precision we're going to find that time travel to the past is ruled out again no argument that fully closes the door on try and travel to the past so it may happen but uh i just uh i just don't think uh i just don't think it's possible so guy richardson comes back and says i love you man well thank you i appreciate that i appreciate that somebody else wrote you look as tired as hell i know where that is do i i don't actually feel that tired i have been talking now for two hours and 40 minutes so i may not have the same zip that i might ordinarily and i will be wrapping this up there satya satya how ladder you look tired as well thank you satya i'm always appreciative of when people say how tired i look you know it's always a wonderful moment in a public setting so thank you thank you so much for uh for bringing that to everybody's attention but actually i feel okay so i'm gonna answer a few more few more questions um karam salangi is the idea of living in a simulation unfalsifiable i i do think it's unfalsifiable for the simple reason that if the simulator can always go into the record of your memories and rewind that record and undo them if they for instance came to an argument that established that the simulation was real or not but have to be real if that can if that memory and thought process can always be erased within the simulation i don't see any obstacle to that then that's a version of the simulation hypothesis in which any individual within that simulation who figures out that they are in a simulation the moment they figure that out that memory will be wiped away if so facto it seems that that simulation that version of the simulation hypothesis is unfalsifiable uh hassan ali do you think the neurolink will succeed uh you know i think we're in the infancy of understanding the mind i think we are at the very beginning of sorting out the physical physiological the physiochemical the physical and biological qualities that allow the mind to exist that any attempt at this early stage to really tap into that in a manner as suggested by things like the neural link i think it's extremely unlikely to work now but let's take time scales out of the question and just talk about will these kinds of things work ever and if we survive if we don't annihilate ourselves then yeah i think that's the kind of mind machine interface that's the kind of mind reality interface that i do think will be in our future now that can be good or can be bad depending on how such technology is used i'm an optimist and i like to think that things will be used in a good way so i find it deeply exciting that our ability to reach inside the mind will have such sophistication in the future in fact i imagine that it would be so sophisticated that many of the issues that now befuddle us about the nature of mind i believe that they will go away once you're able to reach inside the mind and erase the boundary between the outer world and the inner world perhaps once the outer world and the inner world become become so deeply connected that the move from one to other is smooth and continuous the idea of the inner world being radically distinct from the outer world will go away and just as we deeply understand the outer world in the language of physics and particles and laws and rules i believe that that will be the same kind of description that we will give for the inner world and at that point the mysteries of consciousness the mysteries of inner awareness that's when i think that they will evaporate when the border between outer world and inner world is breached you know it's like it's like you know you've got the the the northern wall in game of thrones and it's breached and the worlds now become interconnected that's the kind of interconnection i imagine will one day happen okay um any i am asks any insights in what makes space and time the constituents and you know we're going to have a conversation in the not too distant future about the work in relating quantum entanglement to the space-time fabric and i say that's the most advanced language that we have that the threads stitching space-time may themselves be the threads of quantum entanglement if that doesn't mean anything to you don't worry we're going to come back to it in a nice conversation in the next few weeks so look out for that world science festival discussion with uh leaders in this charge mark vomronsdoc lenny suskind others as well where we'll start with the very basic ideas of quantum entanglement move through some of the ideas of wormholes and then come to the union of these ideas as suggested by recent work in string theory so so that's my best answer and i'm deferring it somewhat because we'll have a full programmatic coming forward but that's about the best thing that we can say the most detailed thing that we can say about the constituents the possible constituents of space and time hamanchu asks why are the extra dimensions curled up and small is there any way to visualize them intuitively um there are ways to invisalize them into they don't have to be incredibly small in fact i don't even know if now we'll test the uh the the the swiftness of our world science festival team i don't know if josh can actually find the video where we penetrate into the fabric of space and we see the extra dimensions as tiny and curled up shapes the the analogy we often use starts with a garden hose and ants walking upon it i don't know if we can find that kind of visual if we do i'll show that to you but but the answer to question is the extra dimensions don't have to be small they could be big we often describe them as small that's one way of making them invisible they're just so small that we don't see them but uh they could be big and it's just that light can't penetrate through them and they're invisible because we don't have access to them because the forces by which we access the outer world don't penetrate into those extra dimensions that is a possibility too so if we're able to find that that kind of fun video um uh just run it at any moment and i'll uh and i'll just uh break into a description of it because it's kind of fun to have a an actual visualization of these curled up extra dimensions within the ordinary environment that we all exist within but uh it's hard to give a visualization without visuals so if that happens to uh come up as i'm talking i will break in and uh and explain it to you it's kind of fun to see um but i'm going to move on for now josh paul what are my thoughts about boltzmann brains boston brains this possibility that the far future random particle motions out there in space might sort of come together and just random particles reproduce a brain floating out there in the void and it's a beautiful and strange idea because let's say my brain right now if my brain is just a particular configuration of particles an arrangement of electrons and protons and neutrons and so forth if i was somehow able to have that particle configuration reproduced out there in space that brain would think it's me because if you don't agree that there is anything beyond consciousness which i that's my suspicion if you do agree that particles and laws is all that there is once you reproduce the particle arrangement you're done you've reproduced the conscious experience so a boltzmann brain is a possibility of a brain randomly coalescing from random particle emotions out there in space could it happen yes it's possible most of us view boltzmann brains as a kind of diagnostic tool where if our theories allow them to form or at least form too easily then we don't trust our theories because look if my brain could form out there in the void then my brain would have all the memories that i currently hold in this brain but that brain couldn't really trust those memories because those memories weren't of things that actually happened that brain is a memory of general relativity learning in school but that brain never had that experience that's just a figment of that brain's memory imprinted by the particular arrangement of particles out there in the void which is just to say that you become skeptical of everything if the possibility that you are a boltzmann brain is brought into the story so again like many of my colleagues i view baltimore brains as a diagnostic tool where we say if our theory allows for them too easily to form then we don't trust our own theory then that's often how people look at these things i i don't really sit around and worry that i actually am a boltzmann brain that isn't the attitude that i take in response to the possibility okay patrice young says i am here i'm glad you are patrice i'm not sure if i'm supposed to conclude anything by your presence if i am to include more details but welcome patrice um rutra kunha asks what's your strategy to learn really complicated ideas when you're stuck that's a good question not often asked that what is my strategy well my strategy often is to come up with examples so if i'm stuck i'm usually stuck because the idea is too abstract and it's too far from the things that i think about or it's like a mathematical equation i'm simply stuck on how to make the next step and in each of those cases examples really help i mean with the with the calculation oftentimes if i'm trying to do an abstract calculation i try to do 10 examples of the calculation first not try to prove the theorem which is universal i just look at example after example after example and i try to see a pattern in the calculations and with that pattern i then go to the abstract one that stumped me and i say oh wait a second from those four examples now i believe i understand the right move to make here and i try to make that move in determining the next step that might get me unstuck and similarly for purely abstract ideas oftentimes what i'll do is i'll say this is really abstract i don't quite get it let me see if i can find an example of this abstract idea and then i find another example and i'm like okay now it's coming into focus now i understand what i'm doing because rather than focus solely on the abstract i've got these concrete examples that i that i can study so that's probably the best way that i can summarize my own process when i got stuck on things um a few more questions i'm gonna have to go actually because i just saw a truck roll up here because um we're actually building a small little space near here where i'll be able to do these live sessions a little bit more easily than the manner that we're doing them here and and film various programs that we'd like to release on the world science festival website so the construction workers are here yay they're going to break ground today that's exciting um james mitchell what's my favorite music well that's off the beaten track but why not my favorite music oh well uh classical music i'd say i find the most moving brahms is my probably my favorite composer you know beethoven not anything weird or unexpected but you know there's some popular music show music film music that i think is wonderful too so i'm kind of all over the place but with the big focus on you know brahms symphony 3 beethoven symphony 9 brahms piano concerto rhapsody and g minor those are kind of the things that oh you know what there's actually a program i did um on uh on i guess it must have been bbc radio where uh it was all about your favorite music so if you search under that i can't remember the exact name of the show but it's a nice it was a nice uh survey of well of different individuals the music that they find um most meaningful so there's a whole 60-minute program that you can find if that really interests you um okay what else have we got here in the last few minutes um um let's see uh let me see if i can find uh so muhammad swali what is our latest understanding about singularities and that's a big open-ended question singularities come in different flavors what is a singularity it's a it's a situation when we're doing a calculation when the calculation breaks down how does it break down we get something like one divided by zero we're like oh my god what does that infinite expression mean or you know something where um there's just an undefined mathematical term that pops into uh our calculations the one divided by zero is probably the best example of all that sort of thing happens and when we find those in our physics calculations we usually interpret it as meaning that our physical theories have broken down there aren't any one divided by zero calculations that are actually relevant to the real world the real world doesn't have those kinds of infinities crop up so generally we try to modify our physical theories so that singularities don't emerge don't arise and we've been successful we've been successful certainly so there are certain kinds of singularities that we have found the math to cure the flop transition that was mentioned uh earlier like an hour and a half ago that was an example where sphere collapses down to zero size and that zero size is the zero volume and when you talk about density mass divided by volume a zero volume is a bad thing it's got divided by zero in the bottom so mathematically you understand how that could arise but physically you're like no no that can't describe the real world and indeed string theory cured that particular singularity the singularity that would come from a flop transition there are other singularities though that we've yet to resolve and we hope that one day we will we believe that quantum mechanics sort of fuzzes out little tiny sizes so if you do have a a puncture divided by zero volume that quantum mechanics will kind of fuzz that out into something non-zero so that that's the general way in which we envision quantum effects curing singularities but as yet we do not have a universal answer where we can say all singularities are now cured here's the solution that's not the way it works that's not the way that things have transpired at least not yet um rachet asked is string theory why we could feel emotions due to music and vibrations around i don't think so i mean i get the the the the reasoning there you know if strings if we're made of strings and strings have resonant vibrations and then there's actual vibrations in the outer world could there be some kind of sympathetic resonance between the vibrations of music and the vibrations of strings that make us up and that inspires emotion and the answer to that is no as far as i can tell the scales are just radically different so when i talk about the strings of string theory i'm talking about something that's probably you know 10 to the minus 30 10 to the minus 35 meters across the physical processes that give rise to emotion rely upon the physics down there but take place on scales that are orders and orders of magnitude larger so who knows maybe one day we'll understand brain processes well enough to line up emotion with physics i think we can in principle do that one day but do i anticipate that that alignment of emotion and physics will be as crude as you know vibrations of strings and vibrations of music no i don't think i mean cruz the wrong word i don't mean to say it that way will it be as direct that's a better way of saying no i do not think it will be it'll be much much more indirect because the scales have to bubble up from 10 to minus 35 meters to 10 to the minus 30 to 10 to the minus 20 then to minus 10 till finally it gets up to the kinds of physiochemical physiobiological processes that happen inside the brain at a direct manner yielding inner experience of course if strings are strings and they're in the brain then those processes are happening but i don't think there'll be a direct link between that string vibrating and you feeling excited when that high g happened in the aria and the puccini you know it's just i i i don't think that kind of a direct link will ever ever be found all right let's go on for another couple minutes sort of sometimes like the cross a three hour limit just uh just to prove to myself that i can do it [Music] do your thoughts have vibrations angel uv s dmv asks uh yeah sort of i mean thoughts are the product of brain processes brain processes ultimately emerge from the processes of the particles making up the brain and quantum mechanically the particles making up the brain do have quantum mechanical vibrations there's a schrodinger equation that describes the wave function of these particles and that wave undulates in a manner dictated by schrodinger's equation so in some in some abstract way it is the case that you know thoughts are vibrations but again as my friend ken weinberg always asks me to emphasize like ken weinberg actually designed the building that this truck just came in to start building so all everything's coming together here this is the finale of our session here and it's all coming together can always feels like i mislead people if i don't in the next breath emphasize that a chunk of swiss cheese also has vibrations because the particles that make up it are governed by the schrodinger equation of quantum mechanics and that wave of schrodinger vibrates inside the swiss cheese too so it's not like thoughts inside the brain in my description are having a vibrational quality that is somehow different from the vibrational quality of the particles inside the block of swiss cheese so so when we say that quantum mechanics is relevant to the brain and consciousness we're thinking about it in a manner that's not special to the brain that applies equally well to inanimate objects like a chunk of swiss cheese will we one day be able to say something more refined that really does link up the experience of consciousness with some direct quantum mechanical quality of the world that i don't know for that we don't have any evidence we don't have any reason to believe it yet but we don't have any reason not to believe it either so remains to be seen all right we got a minute and 50 seconds left oh oh wait a second we have the visual what a way to end this is a visual extra dimension so look at this guys that is space on large scales you don't see anything but the dimensions on the screen but according to these ideas if you go small enough you can have extra curled up dimensions look at them these little curled up tiny circles that you miss and if you have a little microscopic ant walking around the ant would have access to these extra dimensions even though we big lumbering beings would be unaware of their existence and again an idea like string theory doesn't say that the extra dimensions are curled up into little circles per se string theory actually suggests that the extra dimensions are curled up into more exotic shapes these little so-called columbial shapes named after two mathematicians kalabi and yao and yao was also one of my supervisors it turns out and so these ideas are correct this is a shape that might constitute the extra curled up dimensions of string theory so as you pull back the big dimensions that we experience that's the grid you can only show two on a flat screen and the extra curled up dimensions these beautiful shapes these beautiful kalabi yao shapes so when i was talking about these flop transitions i was actually talking about flop transitions inside those curled up purple shapes you take a clavial shape for the extra dimensions you squeeze down a sphere inside of it it punctures that shape you then flop it over and inflate it in a different direction and that repairs the singularity in a physically smooth manner but changes the topology the fundamental shape of that clavial shape so there we go wow i think we have to give a little round of applause for the world science festival team for grabbing hold of that visual in real time and i think that's a pretty good place for us to end that intuitive explanation for the extra dimensions of space that comes out of the mathematics of string theory but again until these ideas are observationally confirmed or experimentally confirmed they're just speculative ideas but let me now to end reflect back on the first hour of our session the idea of gravitational waves was just as speculative as the idea of extra dimensions when the idea of gravitational waves first emerged mathematically in 1916 in a paper of albert einstein and yet today we had a conversation with a member of the ligo team here in the 21st century recounting that on september 14th of 2015 the idea speculative though it may be of gravitational waves was confirmed through an observation was not an easy experiment wasn't an easy observation but that pattern from abstract mathematical idea to confirmed observation is the kind of rhythm that inspires us theorists that keeps us theorists going that keeps us theorists imagining that one day we too might have an experiment or an observation that confirms ideas of extra dimensions confirmed ideas of string theory maybe one of you the young members of the internet audience now listening to this maybe you way you will be inspired one day to build the device that shows us the reality of extra dimensions the reality of strength how how exciting would that be but again as i mentioned in my advice to young aspiring physicists be inspired by that possibility be inspired by the possibility of discovering a quality of the world that we've thought about for a long time but nobody has yet detected be inspired by that possibility but spend your time learning the basics inside out it's the only road to success learn the basics inside out all right so thank you all for um for sticking with us for this three hour session i think we'll be back probably not next tuesday but maybe the tuesday after but i'm not going to commit to a time because the times are bouncing around a little bit but you know subscribe there's some sign of subscribe button somewhere that you can see please join us as part of the world science festival and world science you community and uh i look forward to having this ongoing dialogue this ongoing conversation and the uh continue in the not too distant future until then stay safe and looking forward to seeing you then you

Channel: World Science Festival

Views: 62,048

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Keywords: Gabriela Gonzalez, gravitational waves, LIGO, Astronomy, gravitational wave arrives to Earth, LIGO detectors, general relativity, ripples in spacetime, black hole collisions, black hole, massive astronomical event, Brian Greene, Special Relativity, Albert Einstein, Free online course, Special Relativity course, What is Special Relativity?, physics, best physics course, space and time, Relativity of Simultaneity, Clocks in Motion, World Science U, WSU, World, Science, 2020

Id: fnk4dMW7AzY

Length: 181min 38sec (10898 seconds)

Published: Tue Sep 08 2020