World Science U Live Q+A Session with Brian Greene

hey guys we're having some technical problems over here at world science festival world science u but i'm hoping that i'm streaming right now i could be talking to myself here in upstate new york but let me know in the chat if we're actually live that would be uh useful to hear and obviously i'd love to know where you guys are connecting from as we carry on with the live session you may note that there's been a a kind of a long break between the last session and today and you know a lot a lot has gone in the world a lot has gone on for me personally i think some of you know that you know my mom who came up in these sessions now and then and when we were first doing them she passed away on on june 6th so from the virus so we've been dealing with that and that was at least partly why we stopped these sessions for a while but i'm happy to start them up again if you guys are interested to continue the conversations that that we were having the other thing that motivated today's live session is a relaunch of world science u this is the educational platform of world science festival it's completely free and really cool you should go check it out and we launched it a long time ago with a handful of classes and courses and the relaunch if you go check it out you know there's about 40 or so faculty from around the world many of the most prominent scientists in the world nobel laureates people like barry barish who discover gravitational waves people like alan guth who discovered the inflationary theory people who have already established themselves as the next generation of leading scientists are part of this as well so definitely worth checking out world science u for these what we call master class experiences i will be interviewing as part of your daily equation a kind of combination of your daily equation and world science we'll be doing some live conversations with some of these great thinkers so you're used to these sessions where i just sort of sit here for some period of time and just talk and talk answer your questions and so forth we'll kind of break it up a little bit where you guys can ask questions not just of me but of some of these of these great figures that that you may know of that you may have read about their works you may be deeply influenced by the theories and discoveries that they have provided to us now my own particular course on world science use some of you may have already taken it focused on special relativity i still intend to have courses on quantum mechanics and general relativity and now that that site is up and functional i'm more motivated to consider doing that so i'm happy to uh to do that going forward but what i'd like to do today is in some sense interview myself so i'm going to kind of spend the first hour focusing both on your questions but also on those that are more tightly related to the special theory of relativity is that is what my world science u current course is all about so i think i'm going to jump in right now on some of those questions and some of them i've collected from various sources so i'm always excited to answer your live questions like m says is this john cusack uh no no it's just me but that just establishes of course that this really is live nothing better than answering an impromptu question to to establish that but i'm going to focus for a little bit on questions that focus on the special theory of relativity and one that i'm asked all the time is what's the best way what's the simplest way what's the most intuitive way to grasp the counter-intuitive notion that time slows down when you are watching a clock in motion so if you're watching a clock in motion that clock will take off time ever more slowly and the best answer to that is the oldest answer to that there is no newfangled approach that really blows out of the water any of the other attempts to explain this powerful idea of time and its rate of elapsing depending upon your state of motion than the light clock and the light clock is this very simple but powerful idea where you know when you think about clocks right i mean there are many many ways of of thinking about clocks they're basically devices that allow us to measure the duration between one event and another we do that by having a cyclical process so if the clock is an ordinary old-fashioned clock the cyclical process is a hand that just sweeps around the face of the dial that's one kind of cyclical process there are many such processes right a quartz crystal it vibrates in a particular cyclical manner you count the number of vibrations to determine how much time is elapsed but a light clock what is it it's a device that has two mirrors with a ball of light that bounces up and down between the mirrors and to calculate the amount of time that's gone by you simply kept the number of tick tocks of the bouncing photon between those mirrors and let me just give you a little visual of that if i can bring this up on a screen here yeah so you know if you see this clock and you see you got the two mirrors that are facing each other and the ball of light is bouncing up and down between them and each of those tick tock tick tocks that is a way of counting the duration of measuring the amount of time that has elapsed now once you take into mind into your brain fully the idea that that clock that you're seeing it's truly measuring time it's an unfamiliar clock you don't see people walking around on planet earth with a wristwatch that's a little box that has a photon bouncing up and down between two parallel mirrors but once you take that notion of time as really being time right if you're measuring how much time is a lot you simply count the tick tocks in that photon then there's an incredibly simple way of concluding that when a clock is in motion time slows down and to do that you simply show two of these clocks and you say put one oops i'm i'm blocking that thing over there i think so you put one on the other side of the laboratory let me get out of the way here and look at the photon in the moving clock it has to travel a longer trajectory a diagonal up and a diagonal down trajectory light always travels at the same speed so if the photon in the moving clock let me get out of the way here and play it again if the photon in the moving clock is traveling along a longer trajectory diagonal up diagonal down is much longer than the straight up and down of the stationary clock then look it will go tick tock more slowly than it would in the stationary clock and that example let me get out of the way here so you can see it that example right there is a beautiful illustration of how time slows down on a moving clock constancy of the speed of light and the longer duration of the tick tocks in the moving clock is to my mind the most powerful means of embracing viscerally this notion that time slows down on a moving clock and there you see the the essential new idea of special relativity that was einstein's insight that the speed of light is constant whether you're looking at the ball of light in the stationary clock or on the moving clock the speed at which light travels is the same 671 million miles per hour or whatever units you like to use 300 million meters per second and so if the light has to travel on a longer trajectory it's going to tick-tock less frequently time will slow down on a moving clock so if you have questions on that i consider this to be you should ask him now i consider this to be among the greatest achievements of the human mind that little illustration of the bouncing ball of light establishing that time slows down on a moving clock is one of the deepest insights of the human mind so if you have questions on that i'd love to entertain them but that's the the basic idea now others ask as i see some of you are asking well okay that's the effect on time is there an effect on space and there is an effect on space i don't know how easy it will be for me to show you that but i can show you the basic the basic idea and in fact let me just see if i can get this guy over here so yeah so this little illustration over here shows you that if you want the speed of light to be constant and if you learn that time is not constant then space can't be constant either because what is speed speed is nothing but how far you go divided by how long it takes you to get there and if the speed of light is fixed at 671 million miles per hour and if time is something that is malleable as we just saw time in motion slows down then space has to also have a reaction to motion because it has to react in just the right way to cancel out the slowing of time to keep the speed of light namely the ratio of space per time to keep that fixed so that's the basic idea where we learn immediately that space has to also be effective but let me show you now what that effect looks like so here's a taxi cab traveling along i'm gonna go where should i sit for these guys yeah i guess this is a good location as any of this sits let me show you this again this is a taxi cab that is speeding down a street in manhattan and look at that taxi cab it's squeezed along the direction of motion this is what you'd actually see if attacks if you could see things that are moving near the speed of light and if a new york city taxi cab could travel near the speed of light this is what you'd actually see space is crushed squeezed lorentz contracted along the direction of motion so those are the big effects of the special theory of relativity and they're they're deep right i mean you know they're absolutely deep you know and the reverse i should also say is true we in this little animation are on the sidewalk looking at the taxicab as it is streaming by right but you could also ask yourself what if you're in the taxi cab looking at the outer world from the perspective of an object that's moving near the speed of light i think i can show you that one too i think this will show yeah so here we are inside a taxicab here i am driving along near the speed of light facing the wrong direction normally you face forward right not to face like this but look outside so the world it's shrunken it's actually even curved in along the direction of motion that's because when we see things we see them because the light has to travel from the object to our eyeball and so light is traveling from different locations it will travel different distances and therefore we'll reach our eyeball at different moments and therefore we're seeing a given object at different moments in time because the light had to leave earlier from a more distant location to reach our eye at the same moment that the light is traveling from a nearer location so that that's cool that's what a city block would look like if you're streaming along near the speed of light so you know it's kind of cool stuff and it's unintuitive stuff and that's how the world works according to albert einstein's special theory of relativity so let me take a couple questions and i see one here from aryan tewari if we move the light clock why doesn't the speed of light relative to us be greater than the speed of light yeah aryan you're asking the deep and important question at the heart of fundamental physics you would think ariane and everybody else that if you for instance turn on a flashlight while you're running forward you would think that your forward motion would kick up the speed of light to be a little bit larger than what it is when you turn on the flashlight from a stationary position i mean that's why in the game of cricket why does what's it called the dude who throws the ball in a game of cricket the bowler i don't know you guys i know some of you are from india so please correct my terminology but you know in baseball the pitcher doesn't run forward but in cricket the bowler does run forward why does the boulder run forward because the bowler knows that the bowler's motion forward will be transmitted to the ball that the bowler is throwing forward and it will go faster right you can make the ball go faster by not throwing it from a stationary position rather you throw it or you bowl it if that's the correct language from a running forward position it's so intuitive it's so basic it's how the world works in an everyday sensorial experience but that doesn't translate to light if you run forward while turning on a flashlight the speed of the light is exactly the same as it would be if you turn on the flashlight as at rest your forward motion unlike the case of cricket does not add any additional speed to that which is intrinsic to the light itself now ariana asks why is that answer i don't know i do not know why the speed of light is constant nobody really knows why the speed of light is gone let me take the word really out nobody knows why the speed of light is constant we do know that experiments and observation establish that the speed of light is constant and we do know that if you're albert einstein you can use that fact to deduce other qualities of the world that are completely unexpected like the slowing of time for a clock in motion like the squeezing of space for an object in motion but aryan could there be another reality another universe which the speed of light is not constant i i sure i don't think there's any logical necessity of the speed of light being constant and yet it is and all we meager human beings do is extract the consequences of this fact of the speed of life being constant and among those facts among those consequences i should say are the ones that i've shown you the slowing of time and the squeezing of space so so that's as far as you know that's how it all works and it could have been different but apparently it is not so coco coco asks if the time slows down for a moving clock shouldn't the rate at which the said clock goes decrease instead of increase as shown by the lorenz transformation it's really irritating for me i'm trying to understand the question coco coco let me just read it again if time slows down for a moving clock i'm good shouldn't the rate at which the that clock goes i guess moves decrease and say oh i see what you're saying yeah good good good i understand completely so here's the thing um coco coco imagine that instead of a clock in motion you're watching me in motion and i am say walking across and you say time for me is slowing down now what does that mean what that means is if you look at me carefully you will see me slow down you will see me in slow motion you will see my head turn slowly my eyes will blink slowly everything about me will be in slow motion so that's the sense coco coco in which the said clock will decrease that's the sense in which the object in motion will experience time slowing down my own speed let's say i'm on a skateboard or i'm in a car my speed won't slow down my speed is one of the givens of the physical situation our relative motion is what we are given and we are saying that you looking at me you are seeing my bodily form in aggregate moving at a certain speed near the speed of light that's a given but when you then look at my intrinsic motion within that vehicle that may be traveling near the speed of light you will indeed see me going slower you will indeed see time slowing down for me and in fact if i look back at you from my position in the car i will see you in slow motion your eyes will be blinking slowly your arms will be moving slowly so that's the sense in which the moving object appears to be in slow motion its own intrinsic speed from being in the vehicle is part of the given information of the physical situation that we're analyzing i hope that coca-cola that doesn't do it for you ask again but that's the uh that's the key idea orcas sorry again you know me i'm awful on learning how to pronounce names but o-r-c-v-s if s-dichia asks have you figured out why any of the constants are what they are and of course among those constants is the constant speed of light why do the constants have the values that they do well from one perspective when it comes to the speed of light there's nothing special about the number 300 million meters per second 186 000 miles per second 671 million miles per hour you see i'm doing this because you see that the numbers change depending on your units so it's merely you choose a unit for measuring distance you choose a unit for measuring time the second or the hour for distance it could be the meter or the kilometer or the mile or the inch whatever you choose your units and then the speed of light is some particular number in those units but that number is not special it totally depends on the units that you choose in fact if you choose your unit to be for distance to be the foot i know it's the archaic angular system but whatever and if you choose the duration of time to be measured in nanoseconds then the speed of light is very close to one foot per nanosecond one foot per nano so it's one speed of light is one in those units so there you see you can make it any number that you want the deep question though is if you look at ratios of these constants of nature ratios that have no units for instance the mass of the electron divided by the mass of the up quark that's a number that's unit independent whatever units you use for the mass of the electron and whatever units have used the same one for the mass of the up quark if you take the ratio of those two masses then the units drop out and you're left with a pure number and that pure number cries out for explanation and that orcas is really the question that you're asking and no we've not made any progress on understanding those dimensionless those unitless ratios we don't know why the electron mass to the various quark masses have the values that they do we don't know why you know the fine structure constant which as you know is a ratio of electric charge and planck's constant the speed of light we don't know why it has the value 1 over 137 at particular energy scales we don't know why and that's one of the deep questions that we hope one day to answer but as of today we don't look one answer i should say a far out answer is that maybe we live in a multiverse right maybe we live in a multiverse how does that help well remember what the multiverse is right i can even show you a little kind of picture of the multiverse i think right so right so there's the multiverse so each of those spheres represents a different universe and our universe would be one sphere in this grand collection of of different spheres different universes now why is that relevant to the question that was asked well imagine that in each of those universes the constants of nature may still be constant but they might have different values and that would mean that the values and the dimensionless ratios that's an environmental feature of the world it's not a fundamental feature of the world it depends on which of these bubbles you're in which of the spheres which of the universes in the multiverse you happen to inhabit and that's one possible answer and that answer would be there's no fundamental explanation of the fundamental constants of nature they vary from universe to universe and perhaps the values that they have in our universe are special because they allow for the chemical and biological and physical processes necessary for our form of life so maybe the answer is not some fundamental physics explanation but rather the concepts of nature have the values they do because when they have different values as they may in other universes highly speculative idea those universes aren't planets and people so the answer might be one of environmental influence as opposed to some sort of fundamental first principle explanation for why the constants have the values that they do and being told i'm out of focus on my webcam needs to refocus on me i don't know how to do that guys but uh now i can sort of try to do that you know i'm not a particularly good person when it comes to these kinds of things but let me shut off the autofocus turn on the focus i don't know that looks pretty good so let me know if that helps guys because it's kind of irritating to uh to view things that are blurry for the next period of time that we have together hopefully that helped but um let me know in the chat or wherever you can i'd appreciate that okay so carrying on with your questions kirag oh come on that was a good question and now i touched my scroll and it ran away from me i'm so sad that was a good multiverse question perfect question to go into um okay i'm told at least that i fixed the the focus problem so let me know if that happens again um so correct ask your question again it's somewhere in the in the in the feed and i lost it i think it was a multiverse question um akash shaylar asks is the universe expanding at different rates at different locations and it depends what you mean by universe here by universe you mean you know the multiverse which again i'm not saying that there is a multiverse but it's an interesting idea worthy of consideration then of course in the different universes space could expand at different rates in our universe as far as we know as far as you know the observations seem to strongly suggest that our universe is isotropic isotropic means that regardless of the direction that you're looking the physical features the physical properties on average are the same and that suggests that the rate of expansion in the different three dimensions that we know about those rates are the same and they're also the same in the sense of homogeneity namely regardless of where you are the expansion rate is the same so homogeneity and isotropy lead to the conclusion that the expansion of space is the same regardless of where you are located and what direction you are measuring but you know in a theory like string theory which has extra dimensions i wish i had some extra dimensions stuff that i could show you but i don't have anything in my little goodie bag over here at the moment but by the way should tell me if you enjoyed these these visuals you know i thought it'd be kind of fun to spice things up for this launch of world science you which is a highly highly visual platform for discussing all these ideas not just relativity but you know cosmology and consciousness and neuroscience symmetry again you should really check out world science you because uh it's a great opportunity to learn from from the great thinkers of the world but um in it's such a visual platform that i thought it'd be fun to introduce some visuals normally i'll just show you my real background right here that you see you know behind me right now it's sort of a a nice day out there today but i don't have any extra dimension stuff to show you maybe next time but you should tell me do you find the visuals fun in this context or do you find them irritating so kind of just let me know on that in the chat i'd be interested to know but the reason i bring up extra dimensions relevant to this question of the expansion of space it's certainly possible that in the very early universe all the dimensions assuming string theory is right so the three dimensions of space that we know about together with the extra dimensions of space that strengthen requires imagine that they were all very tiny early on and imagine much in line with the question that was asked the rate of expansion of those dimensions was different imagine that the three big dimensions that we know about you know left right back forth up down that these three big dimensions expanded far more quickly than the rate of expansion of the other dimensions of space and that's why we are all familiar with the three big dimensions of common experience because they grew large enough that we have direct access to them through our vision through our eyes and imagine that the other dimensions are just as real but they either didn't expand at all or they expanded so slowly that they're still so tiny that we don't have direct access to them through everyday experience through our eyes so that would be a nice application of the question to give an explanation for how it's possible in a theory that posits more than three dimensions of common experience how it's possible that we would only be aware of three of those dimensions a subset of those dimensions one possible answer is what the questioner asked the answer might be that the three dimensions you know that expanded much more quickly than the others and that's why they're much easier to see all right what else do we have in our question scroll here sun jal prasad asks from the world science festival webpage do you think that time travel to the past is possible and i don't know about time travel to the past i would say that the best answer as of today is that time travel to the past has not been ruled out it's a real possibility in the sense that the door has not been firmly shut and that means that creative individuals may find a way of walking through that tiny crack in understanding and one day establishing the time travel to the past as possible if you ask me though to go a little bit beyond what we absolutely know and to speculate my guess is that time travel to the past is not possible my guess is that time travel to the past will one day be ruled out fully firmly done but time travel to the future which you didn't ask about because i suspect you know the answer time travel to the future is possible it's exactly what i was saying early on when we talk about time slowing down for a clock that's in motion right you put that clock on a rocket ship it goes out it comes back less time will have a lapse on that round-trip journey than on your clock on planet earth so when that space traveler steps out of the portal in that rocket ship they will have aged less than you they will have aged less than all of earth has aged what does that mean that means they have jumped into the future to jump into the future simply to find yourself in a circumstance where the environment around you has aged much more than you have literally in the sense that the amount of time that's gone by one year for you but a million years for everybody else means that you have jumped into the future by roughly a million years or 999 999 years that's what it means and that is within the understanding of physics as we know it another interesting question along these lines giannis asks on the world science festival page so if you go to the past you go to your own past or in a parallel universe past and that's a that's a very important question to ask again number one i don't know if it's possible to go to the past number two i don't even know if there are other universes so speculation one and speculation too but be that as it may let's carry on and imagine what the possibilities might be and people have speculated that if you could travel to the past you would go to the past in a parallel universe not in your own simply because that's a way of getting around this famous grandfather or grandmother paradox remember what that paradox is if you can go to the past and perhaps prevent your grandparents from ever meeting then you would never be born right because your parents would never be born you know so if that's the case how are you ever there to effectuate the change that kept your parents or grandparents from meeting in the first place that's the paradox how do you solve that paradox well as giannis asks if when you travel to the past if you can you find yourself always in a parallel universe not the universe from which you originated then the question of your birth no longer poses a paradox you were born in universe number one you traveled to the past in universe two in universe two your grandparents never met your parents never met you were never born in universe two but that's not paradoxical any longer because you were born in universe one your origin is no longer cause for consternation if when you travel to the past you travel always to a parallel universe so that's why people talk about this idea and yeah you know it's it's not ruled out people have used ideas of special and general relativity to even suggest ways you might travel to the past but as yet i'd say it's highly highly highly speculative and again my gut feeling is that one day will be ruled out okay so let me just carry on with some of the questions in the live chat claudio barrosa asks how do you know if a body is stationary not moving in the universe and the answer is let me give two answers to that number one fundamentally speaking there is no answer in the sense of there's no absolute notion of rest so the only time that you can really ever talk about speed is when you're talking about the speed of one object relative to another so you can't say that an object is moving in the universe period end of story you can say object number one is moving relative to object number two you can the object number two is moving relative to object number three but if these objects in principle are moving at a fixed speed in a fixed direction and they always have been and they always will be then each of those objects can claim to be at rest can claim to be stationary and claim that the motion that's taking place is motion relative to their perspective to their frame of reference and that's something that every object moving at a fixed speed and fixed direction can validly claim now why do i say fix speed and fix direction because if it's not fixed speed in a fixed direction if there's acceleration or deceleration which can be speeding up or slowing down or going around a bend not in a fixed direction then that object can feel intrinsically that motion and that object therefore can claim to be in motion and cannot claim to be at rest to came to claim to be at rest you have got to satisfy certain conditions which roughly speaking can be summarized by saying that you don't feel any motion otherwise you are absolutely in motion but there's no notion of absolute rest now i said i was going to give two answers the second answer is well practically speaking what do we mean for instance about the age of the universe when we say that has a particular age 13.8 billion years right on whose clock and the answer to that is it's on those clocks for whom the observer moving with that clock would see the cosmic microwave background to be homogeneous and isotropic that it won't have a preferred orientation moving with respect to the cosmic microwave background radiation so in a certain sense cosmologically speaking there is a preferred frame of reference it's that one for which the background radiation has that particular property but putting cosmology to the side just thinking about an object moving through space no preferred frame of reference no absolute notion of being at rest okay let me go back to the the feed here charles moorer asks if time stopped and reversed direction how would we ever know wouldn't we unremember all those moments couldn't time always be moving back and forth and and the basic point that you make charles is an absolutely valid one the individual if the change in time speeding up or slowing down is a true property of the physical universe and if that individual's thoughts are nothing but a product of the physical processes within that physical universe then the individual never experiences time doing anything odd right i mean you're going back and forth and remembering un remembering that's a little bit more complex and it's a little bit more subtle but you can ask the same question using the special theory of relativity example that i was giving you before i mean look if someone is carrying this clock in motion right so the clock is in motion and time is slowing down from our stationary perspective on that moving clock you can see it it's ticking off time more slowly what about the individual that's moving with that moving clock well they experience time slowing down answer to that question is they won't experience time slowing down at all because when we talk about the light clock showing less elapsed time we're talking about time real time and because we're talking about real time it applies not just to the light clock that's slowing but it applies to biological processes chemical processes physical processes neurological processes so the individual carrying that light clock in motion the neurological processes responsible for their experience will slow down their thoughts will slow down and therefore as they look for instance at their clock they look at their environment it will appear to them that nothing has happened if they look back and by comparison look at our stationary clock they will say that our stationary clock has slowed down but their intrinsic experience the number of books that they could read in their lifetime will be the same regardless of whether they were with us sitting still or with that moving clock their life will elapse in slow motion and they won't feel it they won't know it because their thoughts are slowing down too because their thoughts are a physical process so in that sense the individual without reference to other external points of comparison the individual does not experience say the slowing or the speeding up of time so coco coco has come back with a follow-on question i like follow-on questions and coco says but sir why does a second manifest a bit more than a second on a moving clock wouldn't that imply that more time has passed for the moving being than in one second of the non-moving one yeah this is always a point of confusion and when we say that time has slowed down on the moving clock here's what we really mean what we really mean is for that moving clock to go tick tock okay and thereby register one on the counter on that moving clock tick tock we look at our stationary clock and say our stationary tacos tick tock and a little bit more so more than one second goes by on our stationary clock when one second has gone by on the moving clock that's the sense in which time is slowing down on the moving clock it takes more than one second for its clock to go tick-tock why because it's ticking off time more slowly that's the colloquial language you say it's ticking off time more slowly because going tick tock well our clock is going tick tock tick tock tick tock that's a sense in which less time elapses on the moving clock i hope that addresses the question coco coco but come back at me if i missed point or if you're not convinced by that explanation all right i'm scrolling through some of the live chat questions and chris arun asks what has that to do with age and i say chris that has everything to do with age age is nothing but a reflection of the physical processes that are taking place in your body and if those physical processes are taking place at a slower rate then you are aging more slowly so if i'm looking at you carrying that moving light clock just that we can have a very specific image in mind i look at the light clock in motion and it's going tick tock because the light's going on that double diagonal that longer trajectory at the same speed so i'm watching your moving light clock is going tick tock i conclude therefore that time is slowing down for you in motion and that time refers to true time it's time it's not some weird thing that a light clock measures it's what we mean by duration and therefore if time is slowing down then the molecular processes in your body are slowing down the neurological processes in your brain are slowing down the rate at which you are aging is slowing down and that's why this has everything to do with age i mean sometimes people they understand the light clock but they leave the example thinking that it's just some weird property of some weird contraption that happens to have two mirrors mounted in a parallel manner facing each other with a ball of light bouncing in between but it's not just some weird feature of some arbitrary gadget what we're actually tapping into is the rate at which time itself is elapsing and the light clock is merely a simple tool to measure the rate at which time is elapsing we could do with any watch grandfather clock rolex watch the clock on your iphone it doesn't matter the only reason i use the light clock is because the inner mechanism is so fantastically simple that with a little animation and a little thought we can conclude that the tick tock on the moving like clock is going slower it's the simplification of the inner mechanism that allows us to do that but although the journey would be more complicated we can do the same thing for any clock regardless of the mechanism it's just harder to come to the conclusion and i'm in favor of easier ways of getting to deep conclusions than hard ways to get at deep conclusions and that's why we use the light clock but don't be fooled into thinking that the conclusion is somehow only relevant to the light clock the conclusion is relevant to time itself you want an argument for that i'll give you an argument for that take your iphone give it to me yeah give it to me now okay i'm gonna take your iphone and i'm gonna strap it to the top of that light clock and i'm going to set that like clock in motion or assume that's always been in motion so i don't have to deal with acceleration but don't worry about those details if you are now walking along with your iphone and the light clock from your perspective you can claim that you are at rest and everything else is moving relative to you right fixed speed and fixed direction you can claim to be at rest and because you can claim to be at rest you of course are going to say that the tick tock of the light clock and the tick tock on your iphone are in sync we've set it up so they're in sync and because you can now draw that conclusion we who are watching you in motion say aha the phone the iphone clock and the light clock clock they are in sync and therefore if the light clock slows down the iphone must be slowing down too because they are in sync you've already established that by virtue of your ability to claim that you the light clock and the iphone are all at rest and everybody else is moving relative to you and how could any external motion affect the synchronization of your iphone and the light clock and therefore the slowing of time on the light clock is the slowing of time on the iphone is the slowing of time on each and every clock so again i mean clocks they come in you know all sorts of shapes all sorts of styles you know you know here's a kind of fun little animation showing the kinds of clocks that we have invented over the course of our species right from sundials to old-fashioned alarm clocks you know to quartz crystals to whatever my claim is the conclusion that we reached regarding the slowing of time in the light clock it applies to each and every one of the clocks that you are seeing and each and every one of the clocks that you can imagine as long as that clock is indeed ticking off in a regular manner as long as that clock is somehow advancing forward in a regular manner equal intervals between the numbers or the ticks or the blips whatever mechanism it uses all of that will be happening slower if that clock is in motion relative to us if we're looking at that clock in motion we will conclude the time is elapsing slower on that clock than on ours it is a completely general conclusion about the nature of time so chris that's uh chris arun maybe that was a more involved answer than you anticipated but i hope that convinces you that what we're talking about with the special theory of relativity has everything to do with age because it has everything to do with time all righty so i'm going to continue our session our your daily equation session but i wanted to kind of draw a little bit of a break between the world science u live session focusing upon the specialty of relativity and i really do encourage you guys to check out my course there at world science u which explains all these ideas and somebody asked if there's the math behind it and there is so there's two versions of the course the one at the moment that's up there is the non-mathematical version that explains the ideas in the kinds of language that we're using here today but those of you who like math and i know some of you do the math version of that will be reposted it's been up before but it's going to be reposted in a newly revamped and refined architecture for the experience so i think you'll enjoy that and over there's five courses there right now and over we're going to be releasing new classes about i think on the order of one per week for the next 30 or 40 weeks and the faculty is you know second to none some of the great thinkers in the world so you should go check it out world science you but i'm not going to segue a little bit to focus on yeah if you want to ask relativity questions more than happy to but i would now like to address any and all questions that you might have in mind so just throw them at me and i'm happy to uh to field as many as i can all right so um what do we have here uh the ubos asked dr bo's request to comment on if a potential imaging technique can be devised to select cancers over non-cancer cells and i would say dr bose thanks for your question it's not my field of expertise i can't really help you there i mean you all know that the way you know mris work is by using the ability to modify the spins of particles in a magnetic field and to thereby access the qualities of human tissue based upon the kinds of blood flow that they support and doctors and researchers have gotten very good at distinguishing different kinds of tissues by virtue of the different kinds of signals that they yield inside a magnetic resonant imaging device but beyond that unfortunately dr bose you're at a level of medical detail that is beyond my knowledge so i'll encourage you to ask that question to somebody who's in the medical field suman acharya asks is time and immersion property what is your thought and you know it's a hard hard question and i don't know nobody does their i guess my suspicion is that time is an emergent property my suspicion is that time is a very useful way to organize experience and that's why it naturally emerged in the course of our species and that's why we all have a deep intuition about time right now the intuition is not accurate when you're considering physical situations that are remote from human experience right so near the speed of light who would have thought that time slows down and yet as we've been discussing it does who would have thought that time slows down near the edge of a black hole we don't experience these things and therefore they lie outside the purview of our intuition so my guess is that the qualities of time that we hold dear and the ubiquity of time is an organizing principle i mean we can't even go half a sentence without talking about the past or the future or the present in some way shape or form we conjugate verbs based upon the tense so we can't get out of a temporal way of thinking about the world and i suspect that's because that way of thinking about the world had evolutionary advantages and we therefore evolved in a way to think about the world in temporal terms but are there other ways to think about the world and is it possible to imagine a non-temporal way of thinking about the world is it possible that time is emergent in this sense i think it's quite possible yes all right um let's see uh francis serafini says if to coco if you see him as blinking slower he then has to see who is blinking faster and that's an interesting interesting comment that is not completely true actually so you would have thought that in special relativity let's be concrete that if you see me blinking slower because i'm in motion and you're watching me and time for me from your perspective is slowing down you would think therefore that the symmetry of the situation might suggest that you see me slower i see you faster and that's not right so if i am moving away from you i can equally claim that you're moving away from me and then the symmetry of the situation is even more deep than you would have thought based upon a cursory analysis of the situation everything that you did to conclude that i am in slow motion whether it's through observation or mathematical calculation i can do regarding you and so you will see me blink slowly and i will see you blink slowly not faster and that is a curious quality of the situation now there's something else that i should bring up which is a little bit confusing but keep your head on straight if i am not moving away from you but rather i am moving toward you then the intrinsic effect of time slowing down because i'm a body in motion and you're watching me that is overwhelmed as it turns out by a separate but related effect the doppler effect where the light that's traveling from me to your eyeballs has to travel an ever less distance has to travel an ever shorter distance from my face say to your eyes as i'm approaching you and that shortened distance that the light travels makes it appear that i'm speeding up right because as i'm blinking the light from when my eye is open and the light from when my eye closes the light from my closes doesn't have to travel as far therefore it in some sense gets to you more quickly than it otherwise would if i were stationary so as i'm traveling toward you you will see my eyes blink more quickly and i will see your eyes bring blink more quickly now you might think that that would suggest that time is speeding up but it's not if we carefully unravel our observations of the eye blinking more quickly we will realize the time intrinsically is slowing down but this doppler effect of the light having to travel a shorter distance makes it appear as though my eyes are blinking more quickly so and it's again completely symmetric i see you blinking more quickly you see me blinking more quickly in the reverse not the reverse but if i'm moving away you'll see my eyes blink more slowly i will see your eyes blink more slowly perfect symmetry you might say well okay then how does this answer the twin paradox it does in a very beautiful and simple way maybe i'll leave it to one of the views to uh to give that answer in fact maybe i'll bring in some visuals next time to show that bottom line is just for you who are interested and this actually is covered in one of the modules in the special relativity course to the person in motion half of the journey if they had a powerful telescope look back on planet earth half of the journey they'll see my eyes blinking slowly and half namely on the return they'll see my eyes blinking more quickly for the person on earth namely me looking at the space travel let's say it's you i will see your eyes blinking slowly for a much longer fraction of the journey than one half why when you turn around and come back i don't see that you've turned around yet because the light from your turn around has to travel all the way back to my eyeballs for me to see it so it takes a long time for me to recognize that you've turned around which means it takes a long time for me to see your eyes blinking quickly so for the majority of your round trip journey i see your eyes blinking slowly and just for a little bit at the end i see your eyes blinking more quickly which means overall i will have seen you more in slow motion than in fast motion you will have aged as i watch you less than you will have seen me age for half of my time half of the journey i'm slow and half i'm quick it's theirs where the asymmetry comes in the person who's actually in motion has to turn around and come back and when they turn around they immediately know that they've turned around they felt the motion and they immediately are encountering light signals that are subject to this blue shift the subject of this lorentz this doppler effect that's the difference that's where the asymmetry comes into the story if that's confusing to you don't be upset it's a complex idea i spell it out visually on world science you so again not to plug it too much but worth checking that out okay ellen asks is math brain a myth can an adult still learn and it's half a myth and half not a myth ellen i would say so it's not that the adult brain can't somehow learn things that the younger brain can it's just harder i found for the adult brain to do so and certain tasks you know neuroscientists have studied the plasticity of the brain and the brain is more able to take in novel behaviors and novel concepts when it's in its most formative stages and therefore you know we see it you want to learn piano do it as a kid i tell this to my kids all the time and they roll their eyes which hurts me to my core because you all know you've met so many people maybe you yourself have fretted over the fact that you gave up piano you say why did i do that because now when you try to go back it's so much more difficult so much more difficult because your brain doesn't have the plasticity that it once did and therefore it's harder for it to learn new tricks so there's something to be said about that for mathematics i mean math prodigies have the ability to absorb math at an astounding rate and i don't know a single example of a math prodigy whose prodigious talents emerged in adulthood i mean maybe there are examples i'd be interested to hear about it but i don't know of an example and it kind of makes sense to me because the brain is more set in its structural form after whatever i don't know what the age is called 20 or 20 plus years and it makes it harder for that brain to do the kinds of things that a younger brain does with ease so ellen yes you can learn math at an older age it's just more difficult one amelica asks if two objects in space move away from each other and we don't know which one is actually moving who is time going to slow for and i love the question one amelka because it highlights it i don't i don't mean this in a mean sense but it highlights a real confusion that many people have not just you look at the language that you're using one amelca you see if two objects in space are moving away from each other and we don't know which one is actually moving you have in mind that there's a notion of absolute motion and absolute rest and there isn't there is no notion of which is actually moving again i'm assuming fixed speed fixed direction you know they're moving away from each other like this there is no absolute answer to the question of who is actually moving they're moving relative to each other and what that means is if one of those objects looks at the other this observer will say that that observer's clock is taking off time slowly if that observer looks back at the first object that observer will say that the other observer has a clock that's taking up time more slowly and that's it there's no absolute notion of time there is no absolute notion of time slowing down that has in mind there's some grand cosmic clock in the newtonian sense that's the real clock that really measures time and we are comparing to it but there is no such cosmic universal time there is no such cosmic clock it is time from one person's perspective relative to time from another's perspective and that's it there's no notion of absolute rest there's no notion of absolute constant velocity there's no notion of absolute time it's always one relative to another okay let me uh see what else we have here um zero oscar asks why do you use newtonian gravity and einsteinian gravitation as interchangeable terms oh i hope i don't i hope i don't when i'm talking about newtonian gravity i'm talking about the kind of gravity described by f equals g m one m two over r squared it's gravity that exerts and influence instantaneous across any distance and it's the version of gravity that was put down in the late 1600s when i talk about einsteinian gravity i'm talking about gravity that follows a different equation r mu nu minus a half g me new arc was 8 pi g over c to the fourth t mu nu einstein's field equations and it's a version of gravity that differs from the newtonian one in situations that involve large speeds large velocities and exceedingly large gravitational fields like those of a black hole so if i've given you the impression that i'm conflating newtonian gravity and einsteinian gravity i apologize for that i'd like to know further where you thought i was conflating them because at least in my mind maybe not in my language i keep them quite separate quite distinct okay gcell asks is it possible that the speed of light in the far future is faster and and yes there are people who have discussed what are known as vsls variable speed of light theories and they've exacted a degree of controversy from the community but the notion that the speed of light at one moment and the speed of light at another moment might be different values seems to me a logically possible way that the world could behave speed of light you measure it on whatever you know july 23rd 2020 you measure the speed of light on july 24 2020 and you take the ratio of those numbers and it seems logically possible that that ratio would not be equal to one and some have wondered if the speed of light was very different in the early universe whether it might help address certain cosmological puzzles that we have fretted over i don't think these theories have really gathered a great deal of support in the physics community largely because there's no evidence for the speed of light changing over time but as a logical possibility yeah i think it is an absolute logical possibility um a l a asks professor are dimensionless physical constants rational or irrational and i see no reason why these ratios can't be irrational you know when we measure a physical quantity using a real device you know we measure it to a certain degree of accuracy and therefore we measure it as a real number to a finite number of decimal places which means of course we measure a rational number and therefore when we take the ratio of two measured constants of nature it's irrational over a rational so it would be i hope i said that clearly it's a rational divided by another rational and therefore that quotient is also an a rational number not an rational number but those are just measurements i don't see any fundamental reason why the constants of nature might not be like pi or e and therefore irrational so in answer to your question i don't see any reason why they can't be irrational but maybe if you have an argument otherwise i certainly would be game to hear it all right um charles maurer if we looked at a black hole shouldn't we see everything that has ever fallen into it around the event horizon aren't we seeing those objects time approach zero and the answer that is yes so from the perspective of somebody outside of a black hole watching an object heading toward a black hole you're absolutely right that much is in the light clock in motion although the argument is more involved but similar to that you would find that time on a clock of an object heading toward the event horizon of a black hole would tick off ever more slowly and as that object got right to the horizon the rate at which his clock would tick would approach zero you're absolutely right so from our perspective watching it it's as if the object not just goes in slow motion as it's approaching the enterprise actually freezes now why don't we see that well [Music] the light that the object gives off has oscillations that go ever more slowly which means a wavelength that grows ever longer which means that it's redshifted in fact as it approaches the edge of a black hole the light that we receive from that object is infinitely red shifted which means that it becomes increasingly difficult to actually see that object so in some sense all the objects that fall into a black hole from our perspective are there on the horizon but they're so redshifted that we can't ever see them now again that's a very different story from the perspective of the object itself from its perspective it's just going along and it crosses the event to rise and it falls in and gets crushed at the singularity according to the classical general theory of relativity so again it's two very different perspectives they're mutually compatible but the stories that we tell are are quite different from one another and that's the lesson of relativity we have to admit distinct narratives describing reality they can't be mutually contradictory narratives but they can be different narratives and here's an example where the narratives are quite different they're not contradictory as i've described it people have tried to find contradictions and interesting insights have emerged from the studies and that's a whole different story but there are different narratives describing reality based on the perspective that you take okay carry on um so gokul oh i had a i'm sorry monjeb's tv when two particles are collided some of their energy is lost where does it go could it go to another dimension if yes then is it possible that some energy may come from another dimension to our dimension and in brief the answer is yes to all those questions in fact one of the ways that we'd hope to gain experimental evidence for the existence of other dimensions is through proton proton collisions at the large hadron collider the hope monjeb's tv is exactly the question that you've articulated the hope was that proton against proton slam together very high speed and some of the debris from the collision according to the math of string theory might be ejected out of our three-dimensional spacing get crammed into another dimension of space how would we notice that well you measure the energy just before the collision you measure the energy remaining after the collision and if some of that energy has disappeared into another dimension you'll have more energy before the conclusion collision than after it missing energy signature now we looked for those and we have yet to find any missing energy signatures what does that mean number one it could be string theory is wrong it could be that there aren't extra dimensions simple explanation it could also be however that there are extra dimensions it's just that they're so tightly curled up that the energy that you need to get into them to seep into them is larger than the energy of the large hazard on collider and that's why we haven't seen any missing energy signatures or you know it could be that well there are a host of other possibilities but let me leave it at those two and there by pivot to the second half of your question which is if in principle energy could go into the extra dimensions if the large hadron collider was bigger if the extra dimensions were larger could it be that energy could come the other direction in principle yeah in principle yes in principle you could have energy seeping in energy that we aren't cognizant of in our three big dimensions could show up and uh that's a possibility now don't go crazy on this idea this doesn't mean all of a sudden that the ideas that you see in science fiction where somebody you know snaps a finger and they disappear you say oh that's scientific because what happens is their energy went into another dimension no it's not as though these possibilities can be realized in familiar physical situations we're talking about extreme physical situations but in those extreme situations yes energy can pop in from another dimension okay let's see um so kirag baltha shirag balfa asks are other universes also having the same speed of light since the speed of light is constant and and i don't know the answer to that question number one as i mentioned before the speed of light in principle can vary in our universe there are there are theories that have been written down these variable speed of light theories that i've mentioned and so you know even in a situation that's not as exotic as you know the one that you talk about so you know here's another way of thinking about the multiverse so imagine that there's a big bang that yields you know the grand expanse of everything and within that grand expanse imagine that little pockets open up where the energy transforms into particles and each of those dark regions would be a universe now that's a very exotic idea and if the speed of light can vary in our universe then you can certainly imagine it varying across the multiverse but a a related question that that perhaps is more insightful is to ask what about the dimensionless ratios like the mass of this particle to that particle to that vary across the multiverse and the answer that is is surely yes and our theories allow for that kind of thing to happen and as i mentioned before that maybe gives us an explanation for why those dimensionless ratios have the values that they do it's a different kind of answer it's an environmental answer it's not an answer where we say the mass of this particle to that particle had to be this value because of pure logic or the only logically consistent theory of the universe demands that that ratio have this particular value that'd be a very convincing and satisfying explanation but we don't have any evidence that our theories have the power to yield that kind of explanation so the reverse explanation championed by people like lenny suskind is that those dimensionless ratios vary from universe to universe across the multiverse and the value that those ratios have in our universe is simply the value as i mentioned before that allows for the physical properties and chemical processes and biological development that yields human beings and life as we know it and the answer therefore for why the ratios have the values they do is much more situational we are here and observe those values because those values are such that the physical and biological and chemical processes necessary for our form of life can take place so that would be a distinct way of thinking about the explanation for the dimensionless constants of nature um josh antencio asks when you die will you promise to let us know if there is an afterlife and um josh you've got my word if it's possible for me to let you know that there is no you know what josh i'm going to take that back think there must be something powerful about not knowing the answer to that question and i would not want to somehow eliminate the mystery of life after death from all human discourse so i'm going to leave that as a mystery you're going to have to get the promise from somebody else um vishvesh patel asks what mechanism at the quantum level gives light its speed what gives the photon the push from zero to c instantaneously the photon when born wouldn't have speed instinctively and i'm answer those questions in reverse i would say the photon does have the speed c instinctively i would say that there is no notion of a photon speeding up from zero to c photons as disturbances in the electromagnetic field those disturbances always end forever travel at the speed of light so there's no notion of an electromagnetic disturbance of the sort that isn't traveling at the speed of light but then you say you know how to explain this at the quantum level look we have quantum electrodynamics within quantum electrodynamics we have a quanta a minimum excitation a minimum quantum excitation of the electromagnetic field that we call a photon and within quantum electrodynamics you see directly that the speed of this disturbance will be equal to the speed of light and the speed of light being the number that emerges say from maxwell's equations by considering the permeability and the permittivity of free space and that ratio gives you the speed of light and indeed it's a ratio that comes right out of quantum electrodynamics so i don't know if that's a satisfying answer but that's one rigorous way that we can think about photons as disturbances as quanta that have a very specific speed what happens to light after we switch off a bulb as energy can't be created nor destroyed and the answer to that is when we turn off a light bulb we are no longer exciting the electromagnetic field and therefore we are no longer emitting photons from the bulb so as long as the the bulb is on as long as current is flowing through we're able to excite the electromagnetic field and the result is a torrent of photons that are emitted by that process turn off the bulb and you turn off the process you turn off the emission of new photons that's all there is to it um neutrino says no there is no god sorry you may be right neutrino so we sometimes talk about those issues here i'm not going to talk about it right now um but you may be right um let's see if there's something on the wsu page oh yeah a bunch of questions there [Music] sam wilcox on the world science u page asks if past present and future all exist simultaneously parenthetically which i still have not understood exactly doesn't mean we have no free will our future is fixed and uh in answer to the free will question yeah you do not have free will i would say that your future is fixed though in the sense that you're a collection of particles governed by quantum mechanical laws and the quantum mechanical laws only describe the probability of one or other future for your collection of particles so if that's what you mean by your future is fixed namely the probabilities of this or that eventuality are fixed yeah the probabilities are fixed but the eventuality what actually happens is not fixed so even though you don't have free will even though you're fully governed by the mathematical laws that describe how your particles behave and interact even though you don't have free will i would say that your future in the conventional intuitive sense of what will actually happen is not fixed so it's kind of an in-between place you don't have any choice you don't have any control you don't have any willful ability to determine what will happen even though what will happen is not determined as yet because the physics only determines the probabilities of getting one or another outcome now you'll notice that i didn't rely upon the first part of your question the first part of your question was if past present and future all exist simultaneously then does it mean that i don't have free will my argument that you don't have free will is more general than the one that you're anticipating but the one you're anticipating is compatible with this idea because if the future exists now that's a classical sense in which it exists special relativity is a classical theory so in the sense of special relativity that the future exists because my future might be your past and therefore your past has already happened and therefore in some sense my future has already happened because it coincides with your past that we are in relative emotion so yeah i mean the so-called block universe picture that this yields does have a future that is set in stone so but i would say in a classical world if you're willing to go be classical which is what this is i would say you're done with free will from the get-go because in the classical world you give me the state of the world now and i'll tell you the state of the world later and therefore your will has nothing to do with the state of the world later your will is part of the unfolding it's part of the sequence of events that gets us from here to there or perhaps i should say from now to then but it is not as though you freely exert your will allowing you to contravene the mechanistic development from today till then so in a classical world it's done there's simply no free will in a quantum world some people argue there's a little bit of room i don't think there's any room at all because if your will can't determine the outcome of the quantum events then you don't have free will but it is the case that there is greater flexibility regarding what happens because the quantum laws only predict the probabilities so good and subtle question all right how are we doing here 4 30. boy i don't have the stamina that's i do have to build up give these long sessions some of you may know by the way and i'd be interested to know in the chat you know some of you know i did an hour before this live session on reddit you know this rpan reddit public access network you know my book publisher some of you know i had a book come out in february until the end of time they've been encouraging me to do some of these reddit sessions you know answer questions about the book and other things so i did that from two o'clock eastern time to three o'clock eastern time and then our session is on the heels of that session every other week i may do that i'm not completely sure how long i'll do that but uh so this is now two and a half hours for me so i'm going to try to go a grand total of three hours which would take us to five o'clock which would be a good hour less than the record that i've done in the past but um i'm feeling um somewhat more exhausted although i'm going to pump up the energy for the last half hour here easy spark if you're tired we understand thank you easy sparky but i'm going to give it my all for the last half hour so don't think that i'm going to somehow shirk my responsibility here um but let me find some good questions that i haven't um already addressed robinson infant says are you here in new york it's 4 35 p.m new york time yes i'm here humans yes robinson i'm i'm not in new york city but i'm outside of new york city you have kind of a as you can see it's kind of a a nice space up here in the catskill mountains a little gentle breeze behind me which is uh kind of fun but uh dang joe's i remember that name from when we were doing these sessions earlier and i touched my scroll and i lost your question dang jose but i remember it from a half a second ago reading it quickly i believe dangerous was asking how does relativity work if you take into account that the speed of light in say water is slower than the speed of light in a vacuum and and that's a well-known fact that the speed of light in a vacuum is different than the speed of light in a medium be that water or glass or anything else and this has no impact on any of the occlusion on any on any of the conclusions take a drink of water on that one any of the conclusions that we've been talking about it's a well-known fact that as light meanders through a medium that's populated with atoms the transmission of the light through that medium is slower than it is through a medium that isn't populated by the collection of atoms so when i talk about the speed of light being constant and i talk about the speed of light being whatever 300 millimeters per second i'm talking about the speed of light through a vacuum so bear in mind that that's what i mean when i make that statement and the fact that the speed of light differs as speed traverses various media is well understood and it fits perfectly within our relativistic description of things so it doesn't in any way impact our conclusions it just enriches the physical situations that we are able to describe cosmic slice asks on one of our platforms did you borrow tracy's glasses again and cosmic slice you have a keen sense of the obvious indeed i have i do have another pair that i had around here someplace but i couldn't find them so in the last minute desire to be able to see what's going on i have stolen tracy my wife's glasses again so thank you for pointing that out cosmic slice um keurig i love the chemistry between you and dr neil degrasse tyson well thank you i've always enjoyed being on neil's shows uh he's a very energetic and very smart individual and always has great questions and always makes it an enjoyable journey that with that we just go i think the last thing i did was with him and chuck nice i think i did yeah in in neil's office just before the uh just before the lockdown and the virus hit maybe the last thing that i did actually before the the virus hit and uh yeah we had a nice little session which was actually talking about my book oh good gives me a nice segue back in so we were talking about until the end of time and we were taking audience questions on the book and there were some great questions so so if you if you like neil and you like the things that i talk about go check out that segment on star talk star talk cosmic queries things called star talk cosmic queries if i'm not mistaken um okay um andre zamfir hi professor could you explain in a simple manner why m theory requires 11 dimensions andre unfortunately i cannot i don't know how to do it i don't often say that sometimes i say we don't know the answer that's different that's where research hasn't progressed to answer questions like what was before the big bang or the ratios of the fundamental constants and so forth questions which i think we one day will answer but when it comes to andre's question i don't have a simple intuitive explanation for why m theory or string theory in this more robust setting requires 11 space space-time dimensions i can describe it mathematically and roughly speaking the mathematics is very straightforward you look at certain equations but in the theory and you imagine that the universe has any number of space-time dimensions and you see that the equations only make sense if you have 11 space-time dimensions so it's an internal mathematical consistency argument that drives you to this conclusion but i agree that's not particularly satisfying and when i wrote my first book the elegant universe i tried to answer that question and i felt that i couldn't and i was upfront about that in the elegant universe and i've been upfront about it ever since i can show you some nice visuals and maybe i'll do it next time i don't have any queued up so it's hard for me to grab them quickly but i'll show you some visuals of extra dimension in fact i have a video out there right now i don't know how i could show it to you probably can't but i do have a video on on hyperspace i'm building four dimensional spaces and five dimensional spaces you can find it on youtube i think it's on the world science festival youtube page i don't i don't have the link maybe uh maybe someone can send me that link in in in one of these pages and i can then post it in the chat that'd be kind of i've never done that before yeah in fact sometimes people say that i'm i'm not me and and i'll just tell you i am me here i am writing in the chat all right so there you go so i just uh i think there may be a time delay between what i say within the chat but there you go so that truly is me and if if one of our folks would give us the link to this video this youtube video which i show how to go from a point to a line to a square to a cube to a hyper cube you know tesseract to a penter act and and higher dimensional versions of those shapes but i i can't explain to you why it is that in an intuitive way beyond using that mathematical explanation for why it is that we need extra dimensions in in string and m theory uh eddie hernandez can you come and give a lecture at cal tech sometime in 2021 yeah i'd love to i you know eddie like everybody else i don't know what the heck the world's going to be like in the near term or even the time scale that you're talking about you know it's it's it's it's leaders who don't understand science or who willfully ignore science or who put politics above science have gotten us into a tragic situation especially in this country right i mean other countries some are having trouble too but many other countries they looked at the situation and they dealt with it they listened to the scientists and the medical professionals and they dealt with it but what did we do in this country some officials did that here we are in new york state cuomo did a good job listen to the medical professionals listen to the science and you see the curve boom nice and down other states georgia florida texas didn't listen to the science didn't listen to the medical professionals open too soon and look at what's happening and look a country is a country there are no borders in any real sense we are literally in this together in the sense that illness in one part of the country necessarily will infiltrate other parts of the country so i don't know i don't know eddie california too right resurgent there too but at least i think the reaction there will be more rational so yes if the world is better i'd be happy to accept your invitation to come to caltech in 2021 but i just don't know i just don't know um all right a few more questions before we wrap this up i'm anderson you're the best house thank you m anderson it gives me more energy to keep on going but i'm not like the guy at the political top here i don't need flattery but i don't mind it but i don't need it that's the difference who doesn't like to hear nice things about themselves but it is pathological when you absolutely need it and can't live without it and will do anything lie cheat steal break the law in order that you can get it you know what i'm talking about right you know it's sort of like voldemort i will not mention his name and by the way i did follow your advice i've watched all harry potter films with my son except film number two he wouldn't show me number two for some reason he didn't like that i've now seen all the harry potter love it was great so thank you for encouraging me to do that but uh yeah like like voldemort i will not mention the name of the person to whom my small diatribe is referring okay back to physics um maria mario cognac i'm going into high school soon and i'm hoping to go into a field revolving around space do you have any advice for volunteering classes and so forth and i would say maria number one the number one priority is to do your work in school study the basics hard study the basics of physics and chemistry and biology and and what other other sciences your high school might offer learn the material inside out don't shirk that chore which is vital in favor of volunteering and doing research projects and things of that sort but if you find that you can master all the material that you need to master and you still have additional time and energy on your hands by all means contact professors at a nearby university contact graduate students in nearby university let them know that you're interested to work on a project with them look i did this when i was quite young when i was in junior high school i had finished everything that my local public schools is 44 on 76th street in manhattan i exhausted everything that they had to offer in mathematics so a teacher gave me a letter and i recently found this letter right i was telling you guys that my mom passed away so i went back into her apartment and i've been cleaning out her things and one of the letters i found was a letter that my seventh grade teacher wrote for me gave to me and said go up to columbia university and knock on doors and the letter basically said can you use this kid in some research project or some class or something because he's hungry to learn and i handed this to various people and i handed it to one graduate student in mathematics and he read it and he said yeah i'd be happy to teach you we didn't have any money it wasn't for any financial gain and he met with me for multiple days over the course of weeks during the summer every saturday i would take the bus up to la salle street 125th street in manhattan walk over to claremont avenue and this this graduate student neil bellen said it was so generous i mean i think back on it i'm like it's so astounding every saturday he'd get up early to teach this kid for a couple hours number theory and geometry and and various other things of that sort and allowed me to sort into regions of the mathematical universe that in any other [Music] context i would have never encountered and it had a profound impact on me in fact a statement that he made to me statement that neil balanced he made to me is the very first sentence in in my book until the end of time and so you should do that maybe your teacher can write you a letter or maybe there's a nearby university where you can knock on people's doors and if you can find the right person i was fantastically fortunate but if you can find the right person it can be life transforming so maria i would encourage you to do your work but follow the passion that your questions suggest that you have and find somebody to nurture your talent and enthusiasm okay let's see uh mr castle dk asked why is the top quark so much larger than other quarks and larger i think you mean by mass and you're right it is spectacularly larger much heavier much more massive and nobody has an answer we do not know why the particles the fundamental particles of nature have the masses that they do and they span many orders of magnitude right i mean the electron you know you know roughly one two thousandth the mass of the proton and then the top cork you know you know roughly what is 170 odd times the mass of a proton right huge range many factors of 10 but nobody nobody has any explanation for why those fundamental particles have the masses that they do that's one of the goals maybe unified theory would be able to do that i don't know you know that would be that would be really cool really spectacular but no one has been able to do that yet now look having said that we do understand how it is that quarks come together and yield the mass of a proton using quantum chromodynamics and lattice gauge theory researchers some of them are good friends of mine have been able to calculate the mass of these combinations of particles we don't know the masses we don't have an explanation for the masses of the fundamental constituents but when we group them together we have been able to use our understanding of physics to predict the mass of the conglomerate like a proton so there is insight to the masses of some entities but we do not have insight into the fundamental particles themselves at least not as yet so that's uh that's where things stand on that carbon heart triple zero i have great respect for you dr green i hope i can meet you in person one day thank you carbon heart if our paths were to cross someday remind me of this message and this conversation and i'd be uh more than happy to talk physics and the universe with you kenny biddle if the big bang happened in 0.3 seconds 98 of the known universe trillions of light years in every direction so what about the speed of light limit kenny i guess i get what you're after you're after how could the universe have grown so big in such a tiny fraction of a second if nothing can go faster than the speed of light and kenny the the issue there is to really understand deeply what the dictum that nothing can go fast in the speed of light what does it mean what it really means is that no entity no object can pass through space and speed

Channel: World Science Festival

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Keywords: brian greene, Live stream, #livestreaming, #livestream, #live, #streaming, Albert Einstein, daily math lesson, Your Daily Equation, brian greene interview, brian greene until the end of time, professor brian greene, astrophysicist brian greene, professor brian greene interview, physicist brian greene, brian greene book, professor brian greene until the end of time, brian greene physics, brian greene joe rogan, brian greene string theory, number theory, daily series, math series

Id: ntZO0lZiV-4

Length: 105min 25sec (6325 seconds)

Published: Fri Jul 24 2020