Your Daily Equation | Live Q&A with Brian Greene

hey everyone welcome to this live session of your daily equation looking forward to spending about an hour with you fielding some of the questions comments or thoughts that you have and again I say anything you disagree with you should feel free to push back and I'll try to look at the comments to see if there's any responses to my responses so this really can be more of a conversation than you know one way you ask the questions and I try to give you the answers I am NOT the sage I know some things I do not know everything and I'd love to hear things in which you perhaps have a perspective that differs from my own all right I should also quickly say you know in these sessions and also in your daily equation we haven't you know I don't focus on the virus you we all know why we're here we all know what's going on in the world today but I do hope that you guys are doing alright and that your family your extended family your friends are I mean everybody is impacted in one way or another but I hope that the impact is something that is something that you have been able to deal with and maybe if your daily equation has helped a little bit with that well you know what could be more gratifying than that I should say quickly that on occasion when I miss the sessions it's you know it's not because I'm out usually you know playing baseball or doing something like that you know my mom is in the hospital she doesn't have the virus but it is so complicated anybody that has a loved one in the hospital right now you know how how difficult it is you can't visit you can't go in the patient your loved one feels completely isolated so I'm dealing with that as I'm trying to do some other things at the same time so apologies on occasion when I miss a session you know again I don't know how long we're gonna keep going on with your day of the equation but at least it's something that helps me clear my mind once a day as well all right let's move on then to the topics of the day and first question that I see here from Harappa Schad Ravikumar I think I may have actually pronounced that correctly maybe asks what happened to yesterday's video and actually that question is a good one it's related to what I just actually was mentioning a moment ago I was rushing so fast to get yesterday's video done that I made a little mistake toward the end of the video I don't know if you looked at it too carefully nothing obviously conceptually was wrong but one mathematical equation toward the end had one term that shouldn't have been there and it sort of made me feel like I needed to fix it so we took the video down I'm gonna fix it you know this weekend or something I know will repost it with that little change in there so that's what happened to yesterday's video very very good question you see that I'm totally straightforward with you all right so what other questions do we have on the more physics front let's see we have Brian our physical time so this is from Xin hang Chen says and this is I think one from Twitter and then I'll go back to the live YouTube in a moment our physical time measured with physical clocks is still absolute i invariant of reference systems and thus there is no relativistic space-time in nature therefore based on relativity all what the cosmology cosmology Oh Thea describes is wrong so I'm going to interpret that question in the following way which is you know if you have study relativity if you've gone through the early episodes of your daily equation where I was focusing more on relativity you know that one of the main lessons that Einstein taught us with relativity is that there is no preferred reference frame in the universe in the sense that if you and I are moving relative to each other at constant velocity no acceleration so we don't feel any feeding up speeding up I should say speeding up we don't feel and he's eating up and he's slowing down then we have the right to claim that we are at rest and it's the rest of the world that's rushing by us and any observer in a frame of reference that has that no acceleration quality associated with it can make that claim that they are the standard of rest against which all motion from their perspective is delineated now that then runs headlong into what seems to be tension with our cosmological theories and this is what's in hang is referring to our cosmological theories talk about things like the notion of the amount of time since the Big Bang we never say the amount of time since the Big Bang on this clock or that clock or that physical device that may be moving relative to other clocks when we speak cosmologically we say it is 13.8 billion years since the Big Bang period we describe it as if there is a universal time as if there is a universal frame of reference with respect to which that time is measured so what in the world is going on relativity taught us that there is no such universal frame of reference and the answer is that in the universe our universe there actually is a special frame of reference our universe appears to be homogeneous and isotropic which means that from an appropriate perspective if you look out in any direction the physical qualities you see are pretty much the same if you measure physical qualities in any large enough volume of space regardless of where that volume happens to be in the universe we believe that the physical properties that you measure will be the same that's what we mean by homogeneity and isotropy but that quality which is a very very special physical quality of our universe is something that only holds true in particular frames of reference and it's those frames of reference that we have in mind when we speak about the age of the universe or other cosmological properties so fundamentally there is no frame of reference that is singled out over all others but cosmologically because of the physical environment within which we live there is a special frame of reference it doesn't come into the laws of physics in any special you can choose any frame that you want to write down the laws of physics but if you want your observations to be as simple and clean and economical as possible there is a frame of reference that gives you that economy and that is any reference frame with respect to which we describe the cosmological features of the universe so yes very good very good question I appreciate that one read Johnson from the live chat asks what math classes should physics students take to become string theorists question number one that you need to ask yourself is do you want to be a string theorist and I don't mean that sort of tongue-in-cheek I mean you know I'm sort of identified as a string theorist I do other things it's not my be-all and end-all footprint and in science or in life but it's you need to ask yourself is the search for the unified theory is this particular search for unified theory is putting grabbing and come on tamiya does that fire you up and yeah if that fires you up then string theory may well be the right direction to go however you need to bear in mind it could be the case that you work on string gear for the next 20 30 40 years you advance the subject hopefully along with the other string theorists working around the world but you may still be in the position that I and other string theorists are in right now which is we don't know if this theory is right in the sense that we don't know if it describes our physical universe I mean you know we know when our mathematical equations are consistent we know when we haven't made a mistake but we don't know whether our mathematics is describing the world until we have observation and experiment that links the physical qualities of the world with the mathematical symbols that we develop on paper and so if that prospect frightens you or frustrates you then again I would think twice about imagining being a string theorist now putting all that to the side if you decide to be a string theorist the math that you need look you need all the basic stuff you cannot jump over the basic things mathematically you have to take differential equations you have to take all of the math necessary to do the calculations that for instance we've done in some of the earlier episodes multivariable calculus complex analysis is a pretty useful class to take as well and then as you keep on going you need differential geometry if you are going to focus more on say on the extra dimensional qualities of space you need algebraic geometry if you want to investigate those questions with the most powerful tools that mathematicians have developing the topology algebraic topology differential topology and you know what I would suggest is take as many of those courses as you can but ultimately you should learn the math that you need for the particular research problem at hand there's no better way to learn math then when you need it to actually solve a research problem as opposed to a homework set a problem set problem sets are artificial but if you're actually on a research project that needs a body of mathematics I gotta tell you I've been you know as a student you know when I was learning I don't know group representation theory I do remember this when I was learning group representation theory that's something else that you need I needed it for a research problem and I studied it with a kind of intensity that I never had when I was just studying a subject because it was a course I was taking so in the end of the day take as many courses in math as you can but ultimately your depth of understanding will really reach its potential when you need that math to solve research problems themselves okay the rarest one asks from the live chat why is gravity called a force if it needs mass is this not a reaction not a force well I'm gonna give two answers to this question the rarest the first one will deal direct with your question the second I'm gonna go in a direction inspired by your question so look what is what is the issue so forces are things that can exert influence but they also respond to influence you know if you have a magnet right the magnet is exerting the magnetic forces part of the electromagnetic force and my magnet in my left hand responds to the magnet in my right hand if I bring them close to each other that's still the magnetic force even though the magnet my left hand is responding to the magnet in my other hand so that's what forces do they exert influence they respond to the environment and that affects the influence that they subsequently exert there's another question though that comes to the fore when gravity is the force of interest which is Einstein teaches us and you know you all know this stuff at one level or another I'm gonna take on Einsteins ideas I think starting next week so you know we'll talk about gravity and then space-time curvature in connections and metrics and but with it you know all that sort of stuff but the bottom line lesson is that gravity is nothing but the curvature of space-time and so some people say you should no longer think about gravity as a force because objects are simply moving along the shortest possible trajectory in the curved space-time environment that other matter in the universe in the vicinity creates and so can we still think about gravity as a force in the old Newtonian perspective and my answer to that is you should feel free to use whatever perspective and whatever language gives you insight into a given problem you know if I have the challenge of plotting the course of a rocket ship to the moon I'm not using general relativity and warping and curbing the space-time I'm gonna use the simpler description that Isaac Newton gave us which is you know F equals G m1 m2 over R squared gravity as a force other problems if I'm looking at orbits in the vicinity of a black hole I'm going to use the general relativistic description and which I'll have geodesics in a curved space-time environment I'll then be using the geometrical as opposed to the force like language bottom line is use whatever language is relevant to the kind of problem that you have at hand and thinking about gravities of force even post Einstein is still a perfectly acceptable and reasonable thing to you manakish wrong John asks are you religious well you know not in a conventional sense we've taken ZUP here and there in these sessions but I'm happy to address it and maybe say something different or flesh out what I've said before I was born into a particular religion you know I'm culturally a member of that religious tradition I'm culturally Jewish I do not follow the religious rituals I do not adhere to the prescriptions of this particular religious perspective on the world however I've said before and many people react negatively when I say this but I speak freely here I hope you don't mind I do consider myself to be a spiritual person in the sense that I am deeply interested in how I and how others try to make sense within the confines of our own conscious awareness of why we're here and and but what we're meant to be doing with our time or if we can manufacture some reason for doing things with our time or if we can gain a deeper sense of what it means to be a human being on planet earth in the 21st century which is a very confusing very rich but very confusing anxiety-provoking exciting thrilling I mean it is something that all of us need to cope and deal with and and leverage and make use of in order that we feel that we have a full life and to me just understanding the external world which is my professional preoccupation you know physics what are we meant to do make predictions about how that stars going to move or make predictions for why the electron has the mass that it does or why it has the magnetic properties that it does all that's the external world then it's a beautiful focus for us to have within our sights to answer these questions of object of reality but that's not the full thing and again I know that some of you are familiar I have a book that came out a couple to go on it's called until the end of time and I blend in their explorations of the external world through the lens of a physicist trying to understand the origins of the universe and the origin of stars and planets and galaxies and life and consciousness but I also then turn the lens inward to try to understand why we humans do what we do is we try to cope with the world around us why we tell stories why we invent myths why we develop religions while we have creative expression so that book can give you a much fuller exploration of these ideas that I can do in this brief moment of time and I'll also note for those of you the one of you maybe who's on I'm actually gonna teach a summer course at Columbia University on that book on these very questions so if that is interesting to you for six weeks we'll get together you know four hours a week and talk about these things it won't be open to the general public but if you want to sign up for that course of Columbia I would love to have you in that class all right so that's my thoughts on that question let's keep on going Salman Suleiman asks hello from Edinburgh I hope I said that well I've had practice that you probably like oh god what a mispronunciation home of the Higgs can you please explain the Higgs boson for us yes I'd be happy to do that so so there was a big puzzle that Peter Higgs and others too were struggling with in 1960s which is how do fundamental particles like electrons the ones we talk about today or electrons and quarks and neutrinos where do they get their mass from and you might say well it's kind of a strange question they sort of just have their mass but but the reason this question was so pivotal back then and still today frankly is that when we write down the mathematical equations that describe these particles those equations are highly symmetric which means that those equations don't change their mathematical form under particular rearrangements of the mathematical that make up the equations and in order for them to have that symmetry which turned out to be vital for the calculations that we do to make sense for those equations to have that symmetry that particles need to be massless and so there is this tension back in the 60s between the mathematical description which seemed to be doing a fantastic job at encapsulating the patterns evident in particle colliders and accelerators but those very same successful looking equations were suggesting that the particles the fundamental particles shouldn't have any mass at all they shouldn't in essence offer any resistance worried to push on them so Peter Higgs and others came along and came up with a solution and the solution is stunning it's a solution that people resisted but the solution is imagine that space itself is filled with an invisible substance called the Higgs field now but you can think of it as a cosmic molasses it's not a bad image to have my not perfect by any means but the idea is that particles fundamentally are massless but when they encounter the molasses the molasses exerts a drag force that if you're pushing on the particle you've got to overcome to get the particle to speed up and overcoming the Higgs molasses this cosmic force is the origin of the masses of particles so that's the new idea that Higgs came up with how do you test this idea well if you take two particles like two protons and you slam them together at high enough speed Berra mind that they are immersed in the cosmic molasses so when they collide they can shake the molasses and when they shake the molasses they can have a little speck of the molasses a little drop if you will kind of gets flicked off and that little drop of the cosmic molasses that little drop of the Higgs field is what we called the Higgs particle or the Higgs boson and that's the particle that was found at the Large Hadron Collider back in July 4th of I don't know 2012 or something and get the years mixed up by now confirming this idea that Peter Higgs and others as well put forward some 50 years earlier that's the idea of the Higgs particle okay so what do we have here oh I had a good question it ran away sir can we interpret the concept of so this is praia da sir can we interpret the concept of quantum entanglement to the emotional feelings that you have for your mom well IIIi it's a touching question and let me just take it out of the personal if you will there been many there have been many people who over the years have tried to usurp take over the ideas of quantum mechanics and use them to explain or even predict weird phenomenon on macroscopic scales like remote sensing you know these people who claim that they can see things that are happening far away or people that claim that there's some kind of extrasensory perception that links their mind with other minds and as far as I can tell all of that is utter nonsense as far as science seems to indicate there's no basis for remote sensing there's no basis for extrasensory perception at least as it's commonly described and quantum mechanics certainly is not the answer to that at all quantum entanglement is not the answer quantum entanglement is is a provocative but very delicate link between particles that allows them to correlate the behaviors over arbitrarily large distances we often describe it in terms of two particles because that's when the linkage if you will is strongest when we have three four or five particles you can still have entanglement but it gets so diluted among the large collection of particles that the weird properties of quantum entanglement do something here effects something over there they themselves get so diluted that they in essence disappear so when you're talking about something with this many particles like a human brain 10 to the 27 particles the notion of this whole collection being entangled with a whole nother collection is just beyond the bounds of an thing that makes sense with our understanding of physics or quantum mechanics so thanks for the question but I don't think it is the answer at all okay Kowalik ecology asks how does nature know to give every electron the same mass and its frame your Frank your questions framed somewhat anthropomorphic Li as if Nature has some kind of knowledge base and nature has some kind of particular ability to influence the world and nature sits there and says oh let Ron you've got five hundred eleven thousand electron volts as your mass that electrons say mass and so on we don't I mean I understand that language and you're probably just talking poetically of course that's not how the universe works the universe has these fundamental mathematical laws as far as we can tell or at least we develop these laws to describe with greatest precision as we can the properties of the external world and quantum field theory is our best understanding of the properties and the behaviors of particles and according to quantum field theory there is in essence an electron field throughout the universe and when that electron field gets a little bit excited with a certain kind of blip a certain kind of energetic excitation of that field that manifests as an electron particle and the mathematical equations that describe that have a parameter in them that parameter in essence is the mass of the electron we measure the electron get that number stick it into our mathematical equations but once it's in our mathematical equations it's one single number that will apply to any and all of these particular excitations of the electron field so it's not so much that Nature has to know to give each electron the same mass our understanding is if quantum field theory is the right description of the world that the excitations the the lowest possible excitation of this field is what we mean by an electron and the mass of that excitation is determined by one number in the mathematical formalism and that one number because it's not many numbers that one number is why there is a uniformity in the mass of every electron now not everybody is completely satisfied with that answer and I should say you know Richard Feynman had an idea I'm pretty sure Richard Feynman he had an idea a long time ago as to why every electron has the same mass imagine it goes like this he said what if the universe say early on had the shape like a doughnut not in terms of its spatial part but the temporal part imagine that sort of as an electron moves it can kind of circle around through time so here it is at one moment in time it circles around then it comes back to that moment in time but now there'll be two electrons there the original is still there and now the new one has joined it because it's done this circumnavigation around the expanse of time and imagine this electron goes over and over and over again around the temporal loop then you'll have many electrons but all of them are fundamentally the same electron just at different moments of time having circled around this circular temporal quality of the world so according this kind of crazy sounding idea the answer to your question as to why every electron has the same mass every electron has the same mass because every electron would be the same electron I don't really know if you can make full sense of this idea but certainly is a provocative way of addressing the question but the more traditional answer that I gave using quantum field theory is the one that I would really hope you take away from this discussion okay what do we have here so I have to have two answer a question from Ludwig von Beethoven one of the diehards of your daily equation so one of your equations questions is right here okay Ludwig von Beethoven asks to what extent is it valuable to try and study at a prestigious university abroad even if they basically teach you the same thing yeah I'd say it's obviously not a technical question but it certainly is a good question of life if you will because many of you who are watching this from other countries and want to be say a physicist you face that question do you go to school in your own country you go abroad you know to go to the United States you go to England you go to some of the other centres where certain kinds of science has been the center of attention for a number of decades and in the end of the day you can succeed regardless of where you go to school in the end the beauty of the field of physics is you're judged on your papers you are not judged on where you went you're not judged on who your advisor was you're judged on the quality of your research papers and regardless of where you're from you can write great papers now having said that there are some who would say what I just said was a little bit naive and it's slightly naivety in the following sense if you want to get a job teaching for instance in country X and I'm gonna take X to be the United States just because I'm here and I'm familiar with it if you want to get a job teaching in the United States it is useful to build up a network of people that know you in the United States and that can be achieved more easily for many people by being in the United States by being a student in the United States by being a postdoctoral fellow in the United States so from that perspective it can aid you in going forward but lid where you're completely right when it comes to learning the subject if you have good teachers regardless of where they are regardless of whether it's a prestigious place or not if you have a good teacher and you work hard of course you can make great strides and of course you can be successful so it's ultimately a personal choice but in the end of the day if you're just focusing upon can you learn the subject really well yeah you can learn the subject really well anywhere at all all right Caitlyn from North Carolina asks a good Bell's Theorem lecture Thank You Caitlin I appreciate that but I don't understand why the ratio is greater than five ninths definitely proves Einstein's hypothesis of locality I'd actually say I've disproved Einstein's hypothesis of locality so so here's how it goes Caitlin and for those of you who didn't watch the Bell's Theorem discussion of a few days ago check it out I think you'll enjoy it so as you know Caitlin Einstein was very disturbed by the spooky action at a distance he was disturbed by the seemingly non-local qualities of quantum mechanics do something here and it effects something over here that nonlocality was like to him reprehensible so he's trying to come up with his colleagues with an explanation that would not need this kind of non locality and so in an effort to get rid of nonlocality he imagined that the widely separated particles always have whatever property is revealed by measurement so it's not as though a measurement causes one to snap to attention and causes the other distant one to snap to attention that would be spooky he says if this is the result of your measurement then this particle was always up and this one was always down so he says quantum mechanics describes the world as if particles can be in a fuzzy mixture of here and there or up and down but that he says is a failure of quantum mechanics not some true feature of reality and many people said well that's an interesting idea Einstein but how would you ever prove it and the little example I gave him the in the discussion in that episode was you know where I to tell you that my hair is Inc except when you're looking how would you ever prove or disprove it because in order to access access the color of my hair you've got to look at me you've got observed me but I'm telling you when you observe me you change the outcome so it seems to be one of those statements that are untestable until 1964 john bell comes up with an experiment and as i described in the episode if you involve these more refined detectors have three settings and you imagine that these particles don't just have definite features along one axis but along three possible axes then what I did in the episode was I showed if the idea that the particles have definite features and there's no nonlocality because you don't need nonlocality if you have these definite features if they do have definite features John bells analysis shows there is an experimental prediction that that assumption makes and as I showed you the experimental prediction is that if you do a whole bunch of measurements of the particle spins among all sorts of random axes more than five nines of the time they should be pointing in opposite directions so again the logic is if Einstein is right and if there are these definite features and therefore there is no action at a distance no spookiness then the data had better show that they look like this or like this more than five ninths of the time the data does not show that the data shows that there like this and like this 50% of the time five nine six fifty five percent so the data rules out the prediction that comes from Einstein's vision that particles have definite features and you don't need this kind of nonlocality so when the data contradicted the prediction that emerges from einstein's idea you realize that there's something wrong with Einstein's idea Einstein's idea again is there isn't any non locality you only have definite features therefore what's wrong the assumption that there is no non locality therefore there is non locality what you do here affects something over there that's the argument I also gave some caveats as to potential loopholes I won't go through them here but Caitlin that's the answer to your question as to why the ratio being greater than five nines which is contradicting the experiments disproves the vision that Einstein was trying to put forward okay what do we have here all right pack D asks can you explain more how quantum phenomenon would apply to macroscopic objects like people and why that is not observable yeah again you know quantum mechanics does apply to macroscopic objects it applies to me it applies to you it applies to Swiss cheese it applies to everything because everything is made up of particles which themselves are governed by quantum mechanics so if you have little ingredients that are governed by quantum mechanics as you put more and more of them together you're still governed by quantum mechanics but what we also understand well and in one of the videos where I described how you go from quantum to classical mechanics in one of the earlier episodes I described this in a little mathematical detail but one thing that we understand quite well is when you have a lot of stuff a lot of particles a lot of mass it's not that quantum mechanics is no longer relevant it's that the most startling qualities of quantum mechanics get highly suppressed so what are these startling qualities of quantum mechanics they are if you're measuring the position of a particle at one moment you could find it here and next moment you could find it there and so for the next moment you might find it in principle near the moon that's weird right particles jumping around they don't seem to follow the nice kind of smooth Newtonian trajectories that professor Isaac taught us about back in the late 1600s particles can also tunnel through barriers I haven't spoken about that maybe I should maybe I should do a little thing on quantum tunneling yeah I think I may do that right so you know particles can encounter a barrier that the classical physics says the particle can't penetrate but when you do the experiment every so often the particle does penetrate the barrier weird but we never see people walking through barriers and reappearing on the other side not because it can't happen it can happen in principle but for a whole huge collection of particles each of which is unlikely to pass through a barrier for them all to pass through the barrier the odds are enormous Lee against that happening so if the odds are small for a single particle they become spectacularly small for a whole large collection of particles and that's why for macroscopic beings quantum mechanics still applies but you don't see the deeply weird features in the macro world because they're suppressed not that they're not they're not that that can happen is just that they happen far less frequently and by far less I mean spectacularly less often that is the issue okay what do we got here Goran Koehler says it's not live anymore yeah it's life I just answered your is it not live anymore so yes I'm completely here and live in the flesh as far as I know okay vesemir says would you say your new book falls more into the field of philosophy rather than physics and I understand the question vesemir my own view is that there's a somewhat artificial division between physics and philosophy between science and frankly other subjects in the world so yes according to those arbitrary artificial divisions what I discuss in until the end of time is sort of in the borderland between physics and philosophy but I don't really consider the way I deal with these issues in the book to benefit from thinking about the sideload nature of the academic world the academic world has generally found in university settings the questions that I take up in the book are honest powerful deep questions of physics entropy second law of thermodynamics the hour of time but I show how those questions in physics can give us insight into questions that we don't always talk about in physics like issues of free will or ease of consciousness or issues trying to make sense of the world beyond just making predictions for this or that quality to emerge from this or that experiment so yes I would say it does branch between physics and philosophy but I would encourage you not to look at that divide as something fundamental it's what we have erected in order to organize our understanding of the kinds of education that students can get in universities but that's not really a good way I think of feeling the kinds of insights and knowledge that we humans have developed thinking of it more holistically I frankly find much more interesting and useful okay so see cat from cat family says is it possible for you to go faster than the speed of light would you go back in time and um as far as we know it is not possible for a material object to speed up to and then exceed the speed of light roughly speaking as I described in the episode on relativistic mass as a body that has intrinsic heft rest mass if it is accelerated to faster and faster speed its relativistic mass gets more and more which means you have to exert it in ever it's powerful push to make it go faster still and as that body approaches the speed of light it's a relativistic mass source to infinity which means you need an infinite push to get that body to speed up to and to reach and then to exceed the speed of light and since there's no such thing as an infinite force material objects can't cross the speed of light barrier that does leave open the possibility though that there might be an entity that was born traveling faster than the speed of light always travels faster than the speed of light never travels less than the speed of light so that material object often called the tachyon would always be on the other side of the speed of light barrier and it would never cross just as we can cross 2 greater than the speed of light it would never cross 2 traveling less than the speed of light as a tachyon loses energy therefore it can't slow down right if it goes slower than the speed of light as a tack down loses energy it speeds up everything's kind of reversed on the other side now your question can had to do with what this would imply for the nature of time and yeah there's some weird temporal implications if I had a tachyon gun right and I fired it at you then according to some observers moving by us in the appropriate manner they would describe the sequence of events not as my pulling the trigger the tachyon traveling from the gun and hitting you they would say the tachyon hit you before I pulled the trigger the temporal order of what we would think of causal events can be come up ended if there are these particles that travel faster than the speed of light so most of us think that it's not possible to travel fast in the speed of light but it's just to say that no one has completely ruled out although most people do not believe in this possibility of these tachyons ok what else do we have here oh hi from Turkey so Baris gegen from Turkey if we consider Lorentz contraction now don't go away lunge contraction and time dilation is it possible to say a photon would experience the whole universe in an instant at a point and there's I would say poetically you can say that and what I mean by poetically well in your question you talked about photon experience and you do put quotes around experience because you and I and everyone else know well that photons don't experience things they don't have conscious awareness you might think that's secondary to the question but it's actually important to the question because when I say poetic I mean that in some sense a photon would experience all moments at once because our famous gamma factor 1 over the square root of 1 minus V squared over C squared that goes to infinity when V goes to C and V is C for a photon so there's this infinite time dilation factor infinite Lorentz contraction factors for things seem to be infinitely compressed and time to be infinitely slowed down but the problem is if you then want to interpret that as an experience that's where you run into trouble photons don't experience things and therefore the very notion of what it's like to be a photon is putting a conscious being in a frame of reference that a conscious being will never attain because conscious beings as far as you know require material structure a material structure cannot travel at the speed of light so yes is the answer to your question sort of but the quotes around the word experience that you wrote down they're actually quite essential to not over interpreting what this means take it with a grain of salt that a photon would experience all space at one moment in time ok so what else do we have here have 111 asked what do you think about controlled psychedelic experiences what today tell us about our mind its connectivity with the universe and so on well I don't know Aven off if you're really interested you could re you could listen to a podcast I did a couple months ago with Joe Rogan you know Joe Rogan kind of cool guy enjoyed that interview a lot I think it was number I can't remember the number but any find it Joe Rogan and I had a conversation and I spoke a little bit about psychedelic experiences there I don't want to spend a lot of time on and hear it beyond saying that the mind is complex and rich and refined organization of particulate matter which allows it to do spectacular things and among the things that are quite stunning about the mind is if you introduce just a few distinct chemicals from what the mind usually has coursing through its structure the experience the subjective experience can be radically different what does that teach us well some people say it doesn't teach us anything at all to me at least helps me gain an intuition for the fact that particles can think and particles can feel if they're arranged in the right way and if you shift the arrangement a little bit they think and they feel differently and to have an experience like that to me at least gives a more visceral understanding of how it is that the minds experiences are dictated by the particles that are moving through the brain change the particles a little bit and the experience changes dramatically and I'm not advocating anybody to undertake these kinds of experiences that can be dangerous but in answer to your question that is my own personal view and again feel free to look at the Joe Rogan podcast if you want to have a little further discussion of that Timm Harnick from belgium do you think math is invented or discovered actually addressed that a little bit in the very first episode of your daily equation which now seems like it was years ago but I guess it was just about a month ago or something like that so you can see a more complete discussion there but very briefly I've had both of those views throughout my life there are times when I thought math is out there and all we do is discover it I've had periods when I think that math is something that we human beings invent to encapsulate the patterns that we encounter in our excursions into the world around us if you were to ask me what's my perspective right now it's the latter I for a number of years seem to settle down on this view it's almost as though as I said I think in that episode when the mathematical research is going really well it sometimes does feel that all you're doing is chipping away the obscuring layers and the math is there for the taking and perhaps when the math isn't going as well you don't feel it way but this is not a view that's born out of going through sort of difficult mathematical times I really have come to the view that there are many languages that we human beings invent in order to be able to live more fully in the world and and live more effectively in the world of course we invent natural languages that allow us to communicate so we can coordinate our actions so that we can better survive not always but we also invent the language of mathematics that gives us a very precise way of articulating certain kinds of patterns in the world rising and setting of the Sun or the falling of objects or water as it's going down a stream and so my view for a while has been it's that it's simply the case that math is one more language very particular very precise language but just one more language that we humans invent in order to fully articulate the patterns that we encounter in the world around us okay how we doing on time Oh time flies I wonder if I should see if there's anything over on the other feed here I'll stick to the live one it's right in front of me Rob Vandenberg asks do Q&A sessions like this inspire you that they do I can't say that they actually literally inspired the next research project but engaging with you guys and and and and and thinkers and and folks who just want to know about the world to me is an exciting thing you know it's exciting that people want to know about things you can get the impression looking out at certain things that happen in the world and come to the conclusion that people don't want to think deeply people don't want to explore people don't trust science people are not interested in the insights that can come out of this kind of closed experiment observation and mathematical theorizing and to have a group of individuals that come together for these hour-long sessions and clearly have all sorts of interesting and exciting questions that they want to know the answer to yes it does inspire me in that way absolutely for sure okay so what do we have here so th asks as an infinitely expanding universe is energy density goes to zero does that mean it's total energy will decrease as T goes to infinity energy when it comes to the entire universe is a fairly subtle idea in fact the whole idea of energy conservation is one that you have to be very careful about depending upon the precise shape of the universe as you're noting if space was on infinitely far let's say it's flat and if there's a certain amount of energy density in each volume of space and the total energy would be infinite so what exactly does it mean even to have a conservation law associated with a number that's infinite so rather than talking about total energy which is somewhat hard to talk about generally in cosmology we tend to focus on a region of space and we ask ourselves is the case that the energy in that region changes only because there's some energy flowing out or some energy coming in and that kind of local notion of energy conservation is right there in Einstein's equations of the general theory of relativity the one thing I would say that's a little bit subtle is gravitational energy is a quantity that you recall from Newtonian physics is negative right the potential energy is minus GM over R right and that's negative in and it goes to 0 when masses are infinitely far away from each other but it has this negative value as you bring a mass in from infinity so in some sense gravity provides an infinite energy well that other things in the universe can mine in order to have positive energy at the expense of ever more negative gravitational energy and that we think may be the answer to how for instance during inflationary expansion which I've not discussed in these episodes but in an inflationary expansion the energy density actually stays the same as space expands density stays this bet is the same a space expand so there's more energy it seems where does that energy come from one explanation is that it comes from the negative energy that the gravitational field acquires and so it's sort of a trade-off negative gravitational energy against the positive energy filling space from the inflationary expansion van Ron asks when will your recent talk with Alan Alda be online um I believe that Alan is going to turn that into a podcast in his own podcast which I think it's called clear and vivid so if wherever you get podcasts wherever you get your podcast if you look up Alan all those clear and vivid I believe it should be coming out or you know it also do follow me on Twitter if you don't already at be green and I will definitely post that conversation with Alan when it becomes public it was it was a it was a it was a it was a really good conversation we have focus on some pretty thorny issues many of which that I discuss in my book until the end of time and I think I think you will absolutely enjoy that okay Archer says is a positive or dr. Greene to answer all questions at once especially mine well if it wasn't for the fact that the universe had something called time everything would be happening all at once but it does have time and we have a limited amount left so because of that I will not try to answer all questions at the same moment sanyukta asks can you explain Hawking radiation let me look at the clock yeah I can explain it so there there are many ways of explaining it in non mathematical terms none of them obviously are perfect and night razor asks about my my muddy water as I'm talking and so so here's the way to talk about Hawking radiation that I think is quite reasonable if you have a black hole right and in fact you know I have a black hole sort of in front of me right can bring this see this is my microphone right here so this is kind of like a black hole right here the surface of this here so right at the edge of a black hole you have the traditional property of quantum mechanics that particles pop into and out of existence this is the quantum fulmination that happen in any region of space regardless of where that space might be something special happens when particles and antiparticles pop into existence near the edge of a black hole over here if they're far away from black hole particle/anti-particle pop into existence they find each other they annihilate you go from the vacuum to this protocol pair back to the vacuum near the edge of a black hole however when an anti particle and a particle appear sometimes one of those particles falls into the black hole that means the other does have a partner with which to annihilate what does it do it just streams away from the black hole so in essence at the edge of the black hole particle/anti-particle appear one can fall in the other races away now that can happen at every single point along the edge of the black hole and therefore you have particles streaming away from the event horizon of the black hole those particles streaming away constitute the radiation that Stephen Hawking was the first person to recognize back in 1974 and this is believed to be a very general feature that happens in any theory that blends quantum mechanics in the general theory of relativity so we think that quantum mechanics and general relativity are both part of the physical world and therefore we think that Hawking radiation is a quality of black holes all right time for a couple more what do we got here so campus cryptid I guess in response to that answer so we finally have our conversation going campus cryptid says what the universe creates particles from nothing what I hope that was right inflection Campus scripted and and yeah that's that's one of the weird qualities of quantum mechanics when you take into account the quantum mechanical uncertainty principle which tells you in the example that I did in one of these episodes that you can't nail down the position and the speed of a particle simultaneously well if you think about its speed is associated to energy and therefore it's telling you that energy can be uncertain and when you're a little bit more precise about this you learn that it's a trade-off between the amount of energy and the time which it takes you to measure that amount of energy it's a it's an E and T trade-off just like the usual position and momentum one is a P and X trade-off and so if the energy itself can be uncertain over short timescales the shorter the time scale the bigger the uncertainty in the energy and that means over very short timescales the energy can actually blossom up and that energy that just sort of appears even in empty space can manifest itself in the form of particles now those particles can't live long is the usual way that we say this all this can be made somewhat more precise so this loose language is obviously loose but when the particle and antiparticle pair appear they're living on borrowed energy if you will so they can't live on the barred energy for a very long period of time because they have the delta T Delta e uncertainty principle so pretty quickly the particle antiparticle find each other annihilate and they give back the energy borrowed in their own creation so those kind of processes but this excuse me those kind of processes are happening all the time they're happening right now right in front of my eyes it's just that the time skills are so short and the energies are such that they particles quickly annihilate that on average you don't see any of that happening at all you can measure these processes they have a measurable impact on certain particle properties that we can measure with great precision so we have no doubt that these kind of properties of the quantum vacuum are correct and when the quantum vacuum is near the edge of a black hole in answer to the previous question that inspired your response the weirdness is that one member of the particle pair can fall into the black hole leaving the partner to race off into outer space and that's the Hawking radiation all right well I think we're sort of done but let me see if I can I'll finish up with a dang Joss is question could to be multiple dimensions of time like there are four space and um you should have stopped a lies ahead man I'm starting to have trouble talking but um is it possible yes it is possible but I should emphasize that having many dimensions of space is something that we know how to cope with right we live in a world that has at least three dimensions of space left-right back-forth up-down so when the theory for instance like string theory comes along and requires more dimensions of space than that it's not really a big conceptual load is a big conceptual it's not an insanely big conceptual leap because we're already familiar with having a plurality of spatial dimensions three so to go to four is like just adding one more it's definitely a leap but it's not as big a leap as it would be to go from one dimension of space to to going from a singular to a plural that's a big leap for time we're familiar with one time dimension so go from one time dimension to two time dimensions that is a big leap how do you make sense of the second time dimension are there are there two notions of time that exists in in conjunction with or in parallel with each other you know is one aligned with psychological time is the other somehow a different temporal quality of the world so these are the notions they have to struggle with when you want to make a theory that involves multiple time dimensions but people have tried and there's been some degree of success friend of mine who have not seen in a very long time it's like bars wrote a number of papers you know maybe it's a decade or two ago exploring - time dimension theories and he as far as I recall was able to go pretty far and making sense of those theories I don't think that anybody takes them seriously there's no evidence for a second time dimension but it's at least interesting to see that you can make mathematical sense of a theory that has more than one dimension of time all right speaking of time well what the hell I'll just keep going a little bit that kind of gave me a little boost of energy so if there's something here that catches my eye before I sign off someone hit me with like you know the kind of question that I just could not possibly resist all right Aven oov asks me this question what do you think about the creation of consciousness in the paper of consciousness and microtubules of Roger Penrose and Hameroff Stuart Hameroff what do I think about that honest truth is I've not read the paper that care I have looked at the paper I've not read it extremely carefully and I say that you know I find it interesting that there are these processes that take place in the brain that there may be some suggestion that there's something to do between them and conscious awareness but the bottom line is there's nothing that I've ever seen in in the Penrose Hameroff ideas which addresses the really deep question of consciousness which is how is it possible any kind of physical process acting out on physical particles whether it's microtubules quantum entanglement any of those processes yield the sensation of inner awareness I mean I mean if you've never thought about this deeply after we finished today you should just sort of sit down and ponder this particles electrons quarks neutrinos protons neutrons electrons they don't have we don't think although some would disagree they seemingly don't have any kind of conscious self-awareness so how is it that by putting two of them together or three of them together or twenty of them together or ten to the twenty seven of them together how do you somehow yield this property that seems completely disjoint from the qualities of the particles themselves how is it that you and I have inner films inner voices inner lights that are on right now where in the world does that come from and nothing even if Penrose and Hameroff are correct in terms of the role of these processes and the microtubules I don't think that it addresses this question at all and from that point of view therefore you know it's interesting to think about but I don't think it gives us the insight that we are searching for so so Cuccia an answer to that says how about a higher level of biological experience and and yes look it is the case that there can be so-called emergent phenomena emergent properties right some people would say hey you know water has this quality called wetness but h2o molecules they don't seem to have this quality called wetness what would it mean for a single h2o molecule to be wet it's like just a thing you know to HSN a know in a particular shape there's no witness there so the folks taking this line of thought would say wetness is an emerging property when you have a lot of h2o molecule similarly conscious awareness is in a Mergent property when you have a lot of particles arranged in the right pattern and to some extent I have to say I believe that I still find it deeply puzzling I do however agree with the viewpoint that there's nothing more necessary to have conscious awareness beyond particles and physical laws so I am in that camp at the same time I still find it mysterious that we can have these inner sensations and I suspect at some point maybe the first artificially intelligent being that really has conscious self-awareness how would we know that I don't know but if there really is a being that has conscious self-awareness and convinces us that has emotions and feelings and it's just a box with chips wired up in the right way I think at that point the mystery of consciousness would slowly dissipate and we'd be like yeah consciousness yeah it's like wetness of water it's just the kind of thing that happens when particles are arranged in the right way all right someone just asked me if I was going to explain string theory someday and I'm happy to explain string theory you know it's a funny series this series your daily equation because I like the idea that we're talking a little bit of math in each of the episodes because I'm used to either doing my math in my research papers that go to esoteric journals or when I talk to a general audience I'm talking totally without mathematics you know the famous dictum of Stephen Hawking every equation and the book cuts down the readership I factor to write so so there's a sense that you don't put equations into the discussions you have with the general public so I like that this one is a little bit different at the same time it does sort of constrain the types of things that I speak about I mean if I was gonna try to explain strength here and actually include some of the mathematics you know it's it gets kind of involved pretty quickly so you know maybe I'll do a string theory episode and just at the very end throw at you a few of the equations the string theories that I keep in line with my own directive to have a little bit the math in these things but that's what makes it a little bit hard to jump right in to certain subjects where the mathematics becomes so so involved so quickly as M Nayeem s have you met Ashok Sen I have met Ashok Sen one of the great Indian physicist one of the great string theorists a brilliant individual and if you happen to know him do tell him I said hello and hope that he is doing well all right Zhang Jing Li says what is the significance or the status of string theory when there doesn't seem to be any experiment that can confirm or verify the ideas and yeah very quickly you're right Jung Yong Li sorry I'm trying yong yong li the big problem with strength there is exactly the one that you're talking about we've been working at the theory since the late 1960s we've made incredible strides strides that are well beyond what I would have thought we would have been able to achieve by the year 2020 if you ask me as a graduate student in the 1980s will we be able to have potentially non perturbative formulation of string theory I don't think so if it asked me you know will we gain insight into nature space and time the fundamental ingredients perhaps that make up space and time will we have anything to say about that question by 2020 I would say mmm I don't think so and yet we have gotten to those places the flip side though which is what the question is about if you ask me in the 1980s will we have experimental observations experimental data that we can link up to string theory bye dear 2020 I'd like yeah I think so yeah I would have said I think we'll find the supersymmetric particles that string theory requires it's called super string theory the super is supersymmetry we haven't found those particles I would have hoped that we define even evidence for extra dimensions the last couple decades a possibility that we find missing energy signatures at the Large Hadron Collider to give evidence for more than three dimensions of space but none of this has yet turned out to bear fruit so it's not that string theory somehow failed which is what some people say it's just that linking it up to experiment and observation has proven even more challenging than many of us thought decades ago so what's the current status the theory is alive and well and being developed by many people around the world the mathematical insights are significant the techniques that have emerged from string theory for dealing with a whole variety of different fields some in condensed matter theory some in issues of black hole physics I mean there's been a lot of fantastically deep developments but your question is right we do not have the observational evidence or the experimental data to show that this theory is a theory of our world one hopes that that will change but one also doesn't have a crystal ball to determine the timescales necessary for that to happen my one footnote to that question is you'd look at any other quantum mechanical theory of gravity loop quantum gravity dynamical triangulations whatever they face the same problem when you put gravity and quantum mechanics together you are exploring nature in extreme realms of very short distances and very high energy those realms are very difficult to access experimentally that's what the problem is it's not a string theory problem it is a problem of quantum gravity amanda asked as a science educator what do you think is the main technique that brings out the most interest curiosity and joy of learning from students well yeah it's a good it's a very good question and I guess I'd quickly say that I can answer in the negative first I know what does not bring out the interest curiosity and joy and that's the kind of education which is highly assessment focused when the kids are learning in order to avoid getting a bad grade on an exam when the way that you get a good grade on an exam is by just quickly memorizing a whole variety of qualities whether it's this or that formula or this or that part of the cell or this or that chemical reaction you spit it back on the exam you do well you leave it behind and on and on you go and science was just this thing that you had to get through and the sad truth is for many students but not all because there are some great science teachers around the world but for many students that they tell me is their experience so I am NOT soft on the details of science kids need to learn the details science can't just be some coletek subject but you need the poetry to go along with teaching the details you need kids to recognize that with these details they can learn about the origin of the universe and the nature of black holes and weird qualities of space and time I mean when you can have a parallel focus on the very things that make us professionals excited about a subject if you can get that across to kids then learning the details is something that has a purpose to it as opposed to the purpose being and getting a good grade on the assessment which I find tragic when it goes in that direction and I'm speaking from personal perspective I see this with my kids you know my kids just want for the most part to get through it and it's very sad to me and I do my best to inspire them on occasion I succeed and when that happens it's gratifying but for the most part their education is about assessment to say this students getting an A this students getting an A+ this ones getting and being I'm like oh my god are you kidding me that's not what education should be about and I don't have the answer I know that for education and we need to assess in order that the colleges need to know which students they want to take so they can assess them again and why do they assess them because in the job market we want to know which students should get the better I mean on and on it goes isn't there another there has to be another way and frankly for the health of the world there there better be another way okay so so I don't know I don't know people still hanging out I don't keep it going for a little bit if if you guys don't mind I'll keep answering a few questions all right all right all right what do we have Leslie Turner says professional people are boring uh yeah I'm not I'm not going to touch that one exactly some are I guess so [Music] Oh Amanda wrote back good conversation thank you I agree I'll try and implement another way on my own students as well Amanda that that would be great every step matters every person matters and as I said I don't know the answer kids have to take you know standardized tests they have to be able to have learned the material necessary so it's this tension between the way the world is set up and the way you can imagine the world could possibly be paddy Kumar is gravity fundamental or is it emergent is it an emergent force and I I don't know the answer but it is a profoundly interesting question prog deep in the last few years a number of scientists I mean this actually goes even further back back Ted Jacobson for Linda and so on have wondered about whether it might be the case that gravity is actually not one of the fundamental forces of the world gravity might emerge from properties of space and time when properly understood and that sense the charge of a fundamental theory would not be to explain gravity per se is to explain the deeper structure out of which gravity emerges that can sound really abstract let me just give you one little example which I think is useful to bear in mind you and I we all know what temperature means right we know what it means to be hot or to be cold but there's a deeper explanation at the level of particles something's hot when the molecules are moving really quickly right when I burn my mouth on my muddy Earl Grey tea water it's because the molecules are moving so quickly that bang into my tongue in my mouth and they sear it when it's cold the molecules are moving slowly so temperature is an emergent idea that emerges from this more fundamental description of the velocity of particles it might be the case that gravity is like that gravity might emerge from the more fundamental description of the ingredients of reality and therefore it is not a self fundamental idea rather it is simply a consequence of the particles behaving in the manner dictated by the deep equations that we are still trying to find so uh sour syrup asks do you think that we may be able to test quantum superposition principle someday and my answer to your Sarab is yes we do test it I mean if you go back to the episode that I had I forget which one it was but I did the double slit experiment maybe it was in the debris wavelength episode early on and in that example the traditional and famous double slit experiment of quantum mechanics you've got two openings and therefore your probability wave and the quantum description is going through both of those openings and it's superposing the wave from each opening is superposing with the wave from the other and that superposition is what dictates the interference pattern bright dark bright dark bright dark on the detector screen and we test that we do the experiment and we get that interference pattern we get the result of the superposition of the probability waves emerging from each opening so I would say yes is the answer for sure and indeed it has already happened and it happens in fact all the time ok what else do we have here muscle builder says how can it seem that the universe and reality is smooth and continuous if in reality it ticks with the Planck time and it's sort of pixelated on the Planck length and muscle builder I should tell you first it could be that space and time are smooth we don't know but you are right in saying that our deep descriptions are pointing toward the possibility that space and time are not smooth that space and time may themselves be quantized they may themselves be made up of ingredients that themselves do not look smooth and continuous but rather are chunked out on very small scale so your question is a good one how could the universe appear smooth and continuous if fundamentally it's not and and and and you know the answer to that question actually because right now you're looking at me on a screen if you were to look really closely at that screen you would see the little pixels but as you move away from the screen it all looks smooth and continuous at least if you have a good monitor like my monitor is a reasonably good one right here it looks perfectly smooth and continuous and yet I know that it's just made up of little pixels so it's just to say that on the scales that we have access to with today's technology tomorrow's technology - we can't probe the Planck length we can't probe the Planck time Planck length as I did in the Planck length episode that's about 10 to the minus 33 centimeters we can't probe even with the Large Hadron Collider smaller than whatever ten to the minus I don't know 18 centimeters 10 to minus 20 senators um like that it's many orders of magnitude to course to see if there is a pixelated nature to space similarly for time we can't probe down to 10 to the minus 43 10 to minus 44 seconds it's just too small our probing of the universe is so coarse by comparison that the world can look smooth both in space and time even though it may not actually be smooth at all so that's the way the world can fool us into thinking there are qualities out there when deep down those qualities are not part of the fundamental description of reality so what else do we have here Christopher asked what is the difference between M theory and string theory in some sense there is no difference string theory was the name that we gave to this purported unified theory developed between 1968 and 1995 let's say because it was clear from the mathematical description that the fundamental ingredient was a little filament of energy that could be with open ends or in a loop and it looked like a little piece of string so called its string theory something happened in 1995 that kind of blew all of our minds Edie Witten you've probably heard of him he is the Einstein of our age he's at the Institute for Advanced Study which is where Einstein himself was Ed Witten gave a lecture at University of Southern California that was completely unexpected and in that lecture we began to learn that string theory has other ingredients that are not string like that can be membrane like of various dimensions membrane starts with an M M for M theory that is one of the possible interpretations of the M&M theory and therefore we learn that string theory is really part of a larger theoretical edifice that includes these other entities not just vibrating filaments also vibrating flying carpets or vibrating globules and so forth and so M theory is in some sense the more refined description of string theory so they're all one and the same even though they emerged in some sense at different times and it for the names are somewhat different because of that all right so what else do we have here any other questions that people have yes it's rolling by we just try to stop it alie asks do you see any Universal time or would you like to define time tied to biological time sure and and I don't see any notion of universal time fundamentally written two laws of physics but as I mentioned earlier in the relevant frame of reference that allows our description of cosmology to be as simple as possible making use of the symmetry of the universe then there is a cosmic time it's the time that we quote when we talk about the universe being 13.8 billion years old but that's not fundamental that's just an environmental fact and so it's a quality of time in this environment that we call the universe but I wouldn't say that it's written in to the fundamental laws of physics itself all right another one from Sarab asks how did life evolve from nonliving matter answer I have no idea I have no idea you know that that is you know a deep question my guess and I believe it's the guess that most people would now put forward is that life is not like turning on a light bulb it's not as though you have no life you turn on the switch and you'll have life there's rather a continuum between what we would typically call inanimate nonliving matter to living matter and that continuum is along an axis if you will of ever greater biological organization or complexity of some sort so when you have molecules arranged in rather coarse configurations you can get things like cell membranes you can get some of the possibility of molecules being able to replicate themselves and so forth but you wouldn't call it a living system yet but as this collection of molecules is acted upon by natural selection natural selection works even before life emerges natural selection is just the capacity of particles that learn to replicate those that replicate faster more efficiently more stable e they're gonna draw in more of the raw material environment and thereby dominate the molecular demographics and as they mutate they can make even better molecules at reproducing and some of those molecules will find themselves inside a fatty lipid membrane and they find that they're able to carry the processes even better and over time the refinement that happens just gives us a continuum from nonliving molecules to what we would call living configurations of molecules that I think is the the best answer so I don't think they were ever going to come to a point where we say and there's the final ingredient that gives us life that's vitalism that's an idea that was put forward a long time ago that nobody really takes seriously any longer I think most people believe that particles and laws is all that you need in order for life to have a chance of emerging you do not need some other ingredient beyond that okay what time is it 428 Mable do two more minutes just call this a 90 minute session well you tell me when you want me to wrap it up you folks out there who are asking the questions because I'm happy to go a little bit longer today all right Daniel asks how do positrons move backward in time as proposed in a Fineman diagram and look this is a really is a really good question I mean Fryman had creative and unusual ways of interpreting physical law and one of the ones that really strikes the imagination is he said look you can think of an electron as a particle that travels in the ordinary direction of time going forward a positron an anti particle in the diagrams that he wrote down and in the equations that those diagrams represent he said you can think about that positron as if it's a particle traveling backward in time I consider that to be an interesting and useful mnemonic if you will for writing down Fineman diagrams I certainly don't think about positrons is travelling backward in time yeah I understand the mathematical equation I see it up there in the exponent you know either the minus IET versus e to the IET you know so so I totally get it and I totally get the diagrammatic representation of these things but I think I think in the end it makes the interpretation of the quantum mechanics seem more mysterious than it really is you can really think about particles is traveling forward in time even though phiman did give us this creative way of thinking about it i I don't find it particularly useful especially in these kinds of conversations because then you get into the issue of well if there's time travel in the microscopic lies in their time travel into the past in the macroscopic and I think all of that to red-herring just coming from a kind of misuse of the idea that phiman was putting forward okay so Corey O'Connell asks when physicists say our knowledge of physics break down at the singularity of a black hole what precisely breaks down thank you so much even there's a little picture there Thank You Cora tornado picture and and the answer is this quarry so we make use of Einstein's general theory of relativity in order to understand the nature of space and time in the vicinity of a black hole and I'm gonna talk about that mathematics I believe next week it comes from a refinement or really I should say an application of Einstein's equations by Karl Schwarzschild back in 1917 that's where the notion of a black hole emerges in Einstein's theory and here's what you find when you look at the equation so again I'll write this equation down next week you find that if you try to apply that equation right at the center of a black hole at the coordinate value R equals zero you find that the curvature of space-time blows up it goes to infinity in fact the curvature goes like 1 divided by R to the sixth power and as you know if you have one divided by zero you put that into a calculator it says era similarly if you put 1 divided by R to the 6 then you said R equal to 0 you get 1 divided by 0 to the 6 which is 1 divided by 0 you get era that's what we mean by a singularity the mathematics blows up in our face it goes to infinity it's something that we have difficulty making sense of so most of us interpret that singularity to mean that we need a more refined mathematical description of what happens in that region of space-time indeed Einstein's equations do not take into account quantum mechanics at all so the hope is that if what quantum mechanics and general relativity together then we won't have a singularity when we apply that combined mathematics near the center of a black hole and that's the hope it's been partly realized in other examples we're still not quite sure about what happens at the center of a black hole but that's what we mean by a singularity I should say just as an addendum to them sometimes people use the word singularity as this mysterious word I know Ray Kurzweil likes to use it that the singularity is near I think that was a point when computer power was meant to outstrip the power of the human brain and so forth but singularity to a physicist really means one and only one thing it means we don't know what the hell is going on when we see a singularity it means the math has broken down the math doesn't make any sense the equations are nonsensical like 1/0 at that point we say we need better mathematics so that's Cori the answer to what we mean by the singularity in a black hole okay okay anything left are we done Oh any any new results Kevin asks from LIGO since 2015 oh yes Kevin maybe they haven't made the headlines as much but Kevin you're noting that in 2015 we received the first gravitational wave signal two colliding black holes that was a spectacular moment confirming an idea that emerges from Einstein's theory that had been kicking around for a hundred years and we finally captured one of these ripples in the fabric of space-time but since then there been many other gravitational waves that LIGO has detected collisions between neutron stars is a notable example that has given us new insight into how certain kinds of elements are synthesized and I don't know I think it could be well over 50 events now have been detected by the LIGO gravitational wave Observatory so yes it's alive and well and making progress so it's a very exciting field of physics research Sun yolk to ask do you think that the Big Bang was an accident it's hard for me to interpret what that means whose accident would it be could it be that you know some advanced civilization was playing around with their universe creating equipment and accidentally produced this universe I guess but now we sort of venture into the land of silliness right it's hard for us to make sense of what that would really mean I don't ascribe any overarching intelligence to the cosmos doesn't mean that there can't be we discussed that earlier but I don't find any need for it therefore the whole notion of what an accident would be in the absence of a guiding intelligence it leaves me with a sense of I don't know what I'm talking about so I hope that gives you some sense to why I have not much to say on that at all Andreas has 53 exclamation points wow I had no idea referring to the LIGO detection yeah and that's why you come to these live Q&A s andreas to be wowed no I think many of you are familiar with that but I'm happy to fill you in on what's been happening in the last few months or last two years sooo Bargh TV ask wait don't run away let me scroll you back what do you think could be the next big discovery in science well look I'm extremely excited about the gravitational wave observations that we just mentioned I'm extremely excited about work that's happening in other fields there's so much wonderful research on the brain and consciousness and memory and you know if I was starting out again as a young man with with with dark dark black hair I think I would be tempted to go into the area of neuroscience or even computational neuroscience you know really trying to model the processes in the brain using our detailed insights into machine the machine learning I think artificial intelligence in general artificial intelligence I think it's just such an exciting kind of endeavor that's going on so so all that's great if you ask me in my own field what I think the next big discovery will be or what will spark the next big revolution I think it is when we finally gain insight into the true nature of space-time you know is space-time emergent we spoke about emergent gravity earlier space-time and it's curvature that's what gravity is so we're talking about emergent space-time as well if we could really understand the molecules or the atoms of space and time then yeah I think that could easily spark the next revolution our Pitt asks is the universe infinite answer I don't know nobody does one possibility is that space does go on forever and that's all there is to it bear in mind that if space is infinite today it would have been infinite near the Big Bang as you want the cosmic film further and further back in time infinity if you got 1/2 infinity winding halfway back it's not exactly linear in that way for all but you got the idea half of infinity is still infinity 1/4 of infinity is still infinity so when we talk about the Big Bang as being this little tiny speck in an infinite universe that's kind of the wrong image the Big Bang would have happened on an infinite expanse everything that we know in our observable universe which is a finite distance from us would have emerged from a little speck on that infinite expanse but the totality of reality would not have been this little tiny dot that we always picture with the Big Bang the totality of reality in the infinite version would have been infinitely big even at the Big Bang itself do we know that that's the extent of space we don't it could be finite in which case the little speck image would be a fine image because if something's finite and you wanted to film back it gets smaller and smaller and when finite things get smaller they truly get smaller infinite things when they get smaller don't so that's the difference between the two um what else [Music] inflation I saw an inflation question could inflation this is mr. s but inflation could be at separate spaces at an infinite space that's exactly right mr. s so so you could imagine that there are infinitely many big bangs even our Big Bang could be one of that grand collection and it is the eruption of this region of space but there could be eruptions that happened a different and far flung locations within this wider cosmological landscape so yes it could be that the picture of the grandest view of the cosmos is completely different from the one that we entertain when we think about our single universe that could be a small part of an astoundingly much larger reality if the Big Bang that we know to yield at our universe yield at universe upon universe upon universe far out on the cosmic expanse okay let's see si monster asks hey professor a simple question what are you working on at the moment are you working on a theory or are you busy with the world science festival well look I do split my time between research and bringing projects of various sorts out to the public on the on the physics front you know I've been working for a while I'm trying to understand these ideas of a multiverse if we can identify a notion of probability on the multiverse to say which universes will be likely or not if we can develop a notion of stability on the multiverse to figure out what universes would hang around for a long time and those universes that would quickly disintegrate that led me into some work having to do with mining quantum entanglement from the vacuum which is something I worked on with one of my students in recent times and I also have an interest on trying to explain the dark energy with quantum mechanical processes perhaps with the Casimir Energy so I have a variety of research projects of that sort but you're right the world science festival was meant to go live in New York at the end of May obviously we're not going to do that but we are developing programs that number one we are distributing now this actually is sort of one of them but you know more straightforward and more familiar world science festival offer where we have a variety scientists and conversation about cutting-edge ideas we are going to start releasing those new programs sometime probably in June and throughout the summer so that is another thing that I'm involved with but if you're asking I'll tell you a few other cool things that I'm doing I have this piece that I did with the composer Philip Glass about a boy going to the edge of a black hole it's a symphonic piece it's a stage with an orchestra and a film and an arat it's called Icarus at the edge of time I'm working on a sequel to that right now so that's kind of fun I'm also working on a live stage show on quantum mechanics we have a live stage show you may know on the general theory of relativity called light falls it was on PBS last May you're not supposed to be able to see it unless you pay for it but you go to you search for it online and someone has a bootleg copy up and take a look love to hear your comments so that's a version of the kind of presentation I'm talking about but we're building a new one on quantum mechanics so kind of a range of things both in the physics research and in the science for the public the blending of science and art and as I mentioned before I'm also teaching a course this summer on my book at Columbia NE Columbia students or you don't even have to be a Columbia student I do think that make you pay though but if you want to interact with me on some of the big ideas of the origin of the universe and life and mind and galaxies and what it will be like in the far future will be meeting twice a week Tuesdays and Thursdays from 6 p.m. to 9 p.m. Eastern Standard Time as part of this course called origins and meaning at Columbia and you guys want to go check that out love to have you in that class anyway that's gives you some flavor of the things that I'm working on in the moment as seif asks does the fabric of space-time really exist or isn't an idea that Einstein used to visualize gravity and if it does exist what's it made of can it bending can space-time tear and look that's a deep question as Heath I believe that Einstein thought that space-time was a real thing people debate this and philosophers have written you know thousands of pages on the reality or not of space-time in the same I'm Stein Ian sense here's where I come down on it space-time is enough of a something to define what we mean by accelerated motion you see if the universe was completely empty no matter nothing in there but space-time itself according to the equations of general relativity if you were to take two rocks say and have a rope between them and spin them around according to the equations of general relativity those rocks would pull taut as you would think they would based on your experience in the everyday world but if there's nothing else in the universe what are these rocks spinning with respect to in fact can you even define a notion of spinning if there aren't any benchmarks physical benchmarks for motion and according to the general theory of relativity you can talk about the acceleration that these rocks are experiencing what are they accelerating with respect to space-time itself so space-time itself seems to be enough of us something to allow us to define accelerated motion now given that can space-time tear and you're talking to somebody for whom the tearing of space-time is especially close to his heart you know one of the insights that I was fortunate to be involved with is to show that within string theory the fabric of space can rip in fact we did this in two stages our our first insight was that space-time could rip in very mild waves that are called flop transitions that's a technical mathematical term however weird and colloquial it sounds we then subsequently show that far more drastic rips in the fabric of space so called khana fold points or conical transitions were also allowed by string theory so it's pretty much accepted that if string theory is correct that there is a no of the tearing of the fabric of space and again it's hard to imagine what woman mean by the tearing of the fabric of space if the fabric of space were not actually a real thing so an answer to a question I would say yes it is enough of a real thing to talk about acceleration to talk about ripping okay what else we got here um any other questions or should I well you know for I'm gonna go for a few more minutes and then wrap it up okay so felis super it says if you have two entangled particles far apart and you observe one of them then can you still observe interference pattern in a double slit experiment on the other particle and and it's hard for me to answer that question in full generality but let me let me say it this way so when you talk about the double slit experiment the part of that experiment that really matters to this question is the ability of the superposed waves from the two different possibilities to blend and mel to interfere and yield the bright dark bright dark pattern so the critical thing here is can we retain that level of quantum weirdness even after a measurement and the answer to that is largely no when we measure a particle the impact of that interaction is to get rid of all of the weird quantum possibilities force them to ante up is the language that I'd like to use and decide on a single definite outcome and when you have single definite outcomes you're suppressing your basic getting rid of the quantum weirdness so in entanglement you measure this particle and it causes this one to snap out of the haze you're now in one of the single definite States you have eliminated all of the quantum weirdness associated with superposition the possibility that a particle could be a multiple states at the same time and in that sense you have gone away from the possibility of being able to expose superposition exposed quantum weirdness by virtue of your interaction by virtue of that measurement so the quick answer would be no pink lady asks oh and pink lady apples those in fact those are my favorite apples pink lady good did Einstein ever believe in a multiverse or a fourth dimension well four multiverse I don't think so you know like I don't really know precisely the history of the multiverse certainly the quantum mechanical multiverse was introduced by Hugh Everett in 1957 Einstein died in 1955 so he probably didn't think about that at all for the fourth dimension that was an idea that emerged from Einstein's teacher Hermann Minkowski who may you may recall was the teacher who thought I'm Stein wasn't going to achieve very much in his life he said that Einstein was a lazy dog and yet Einstein showed Hermann Minkowski to be wrong but anyway so in her Mankowski learned about Einsteins insights into special relativity he was the one who introduced this idea of time as a fourth dimension Einstein resisted this idea at first I think he felt it was too formal too mathematical ultimately though he realized the power of thinking about space and time in a uniform language and that uniform language is indeed the language of the fourth dimension that Minkowski introduced so yes Einstein definitely did believe in time as a fourth dimension uh what else do we have here somebody asked why'd lecture 24 is not visible I answered that earlier so you can look back at the beginning the very very beginning of this live session [Music] let's see Cambridge Cambridge breeze Brian what is your opinion on Steven Wolfram's claim about his unified theory I don't know I think I addressed this a little bit in the last live session but very briefly look Steve is a brilliant person huge impact on the world of science and mathematics with Mathematica anything that he says is worth thinking about worth looking into I haven't had time yet to do so I do intend to try to get a better understanding of what he has in mind my gut feeling is it's not the unify it's not the answer to everything simply because almost every proposal is every put forward is not the answer so throwing it into that bin leads me to have skepticism when new ideas are proposing big revolutions in our thinking but when it comes to Steve Wolfram maybe it is a big revolution so all just to say I need to look into it further before I can pass any sensible judgment on it whatsoever and he's actually broadcasting the discussions that they're having and trying to push this program for it I believe it's made publicly available so if you want to listen in to people trying to develop Wolfram's idea you can do that and that's kind of very different very cool very exciting so you look it up online and and maybe you guys can report back next time on if I haven't had a chance to look at it by then if if there's anything that you got excited about listening to that all right all right what is your favorite sci-fi movie of all time maybe that's a good good nice light question to finish up with although I have to tell you part of me wonders how long would you go with this session would we would we all just sort of peter out or would be like be able to go like 10 um so so what is my favorite sci-fi movie of all time well I loved the original Planet of the Apes you know Charlton Heston on the sand you know looking at the half sunken Statue of Liberty wow that's spectacular I love contact you know I thought it just had a really good feel for the wonders of space and and and the wonders of time and had a had a strong emotional component to it I know that there other sci-fi movies that I really loved and I know that I'm they're gonna all come flooding to me maybe you guys can tell me your favorite movie in the chat right here and as they scroll by perhaps I can be remembered would be reminded of the ones that really mattered to me but those are the ones that that come to mind so Dan Cooper says 10 hours sounds good all right one person is uh happy to do that contact bomb deals like that film Oh 2001 thank you Eric W yeah 2001 a great film but I have to tell you and you're gonna perhaps consider me a Philistine for saying this I tried to watch it a couple years ago with my kids but maybe because my kids were there that was part of it but it was so incredibly slow in the beginning maybe we've all become accustomed to things having to move fast and and the velocity of the story that it was really hard to hold my kids attention and I have to say I began to wander a little bit too in the very beginning of 2001 yeah interstellar good film you know you know and and close to my heart - because interstellar there's a beautiful scene in which characters go near the edge of a black hole they spend time there time slows down near the edge of a black hole so they come back and everybody else is aged a lot and as it turns out that's actually the operative element in a story that I wrote back in 2008 and it was this one Icarus at the edge of time that I mentioned before about the boy going to a black hole so that is the operative element in that particular story so yeah I think it's really cool when Einstein's general theory of relativity is brought into a narrative setting absolutely other uh Monty Python yeah so meaning of life part one love it yeah can run low the run you know I like Run Lola Run somehow it didn't really stick with me as well there it is but rang thank you the matrix how could I leave out the matrix now the matrix speaks to all these issues about what consciousness is the degree to which you can trust your conscious experiences to what degree reality could be completely different from what you think it is based on your everyday experiences so in fact in the course that I'm teaching we wants the matrix because even if you've seen it before it just brings right to the fore these important philosophical issues about what science can ultimately tell us about the true nature of reality because science is ultimately processed through the human brain so everything that we know about the world is colored by our ability to think through and to experience reality and therefore there is this intermediary between us and the true nature of the world and the matrix shows you how that intermediary can yield a deeply misleading view on what reality actually is oh yes a bi choco thank you inception I loved inception I think inception is again you know it's one of these films that plays with perception plays with understanding you know and and look how can you fault a film that uses a spinning top and perhaps the the procession of the top to be used to distinguish between worlds that are real and worlds that are not yes so so some really great examples you guys give as the scroll is going by here Paola asks would you do a series on explaining the science and movies I'd love it if you would do and yeah you know my friend Neil Tyson likes to take that particular arena on and he does it with a wonderful degree of entertainment value and so on occasion you know I do weigh in on the science in movies and I think you know there could be a good series in there in fact you know we've been chit-chatting with some television producers and that is one of the ideas that we've been kicking around just a little bit the most important thing to bear in mind though is I think you know when you watch a film or at least let me speak person when I watch a film I like to just let it wash over me I love it when if there is science I don't need to think about the signs I need to evaluate it I just like to be transported into a different world when a film fails for me with their science in it we're either it's like so blatantly ridiculous that I just dismiss it or if the film breaks its own inner rules I don't mind bending the rules of physics but don't bend them at will bend them let me know the kind of rules that are gonna govern the world that you're studying and don't change it at the last minute because I hate that because that just feels laziness on the part of the writer or the director of the producer so but yes I think that would be a fun yes d hhhh ace has a beautiful mind yes I loved a beautiful mind you know how how wonderful to have an inner glimpse of the kinds of experiences that a brain can have if it's not working in the manner that's more familiar to us it goes back to our question earlier on psychedelics in consciousness here's a case where it's not psychedelics per se it's a brain whose functioning is somewhat different from the functioning of most of our brains and that allowed that brain to have experiences that are are spectacularly unfamiliar and I thought that film did a wonderful job of giving us a sensation of what it was like to be inside that mind and what it was like to be inside a mind that is at one and the same time troubled but also deeply insightful so yeah I think that's a that is absolutely a beautiful a beautiful example okay is the speed of light Mohammed asks the limit in the multiverse and how do I answer that question um so so I would say that the answer is yes in the following sense did multiverse theories that are really worth thinking about are the multiverses in which the distinct universes emerged from some underlying mathematical law I mean anybody can say hey what if there are other universes and maybe those universes are filled with Swiss cheese whatever anybody can do that that's not interesting what's interesting is when you have a mathematical theory that is motivated by understanding things in the world around you and that mathematical theory then predicts the possibility of other universes and in the mathematical theories that we study of that sort the speed of light is an intrinsic quality of the mathematics a general theory of relativity special theory of relativity all in there so in that sense the qualities of light and its speed is not something that you change willy-nilly from universe to universe it's something that's dictated by the underlying mathematics now having said that environmental differences in different universes can affect the kinds of speeds or kinds of qualities that inhabitants in those worlds would measure so even in eso so yes so there is a flexibility in that the environments can look quite different the force of gravity can have radically different strains the qualities of electromagnetism can differ and so for the electromagnet ultimately to do with light so in that sense there is a flexibility from universe to universe but I don't want you to think that there is a things that are just changed at will it emerges from some underlying fixed mathematical structure that can yield universes that have different environmental details those environmental details can affect the things that we measure alright guys what do you what do you think quickly tell me you want to ask a few more or do you want to take a break until til next time like if they love it will answer this question as you're answering them so ash aunt asks if quantum mechanics makes the universe non-deterministic then how are you going to figure out the grand unified theory and I love that question because it's one that I get a lot and it allows me to emphasize what quantum mechanics is not quantum mechanics is not a theory that somehow imbues the universe with some kind of deep in determinism the equations of quantum mechanics which we studied in one of the episodes in Schrodinger's equation those equations are deterministic the math of quantum mechanics is just as deterministic as the math of classical mechanics the only difference is whereas the math of classical mechanics predicts definite outcomes for observation and experiment the deterministic math of quantum mechanics only predicts the probabilities of getting one or another outcome but predicts those probabilities with deterministic mathematics so quantum mechanics is deeply deterministic but what it determines our possibilities as opposed to definite outcomes and therefore it's not like quantum mechanics makes everything uncertain or prevents you from making progress not at all in fact quantum mechanics yields the most precise predictions that we have ever had we can make calculations with quantum mechanics and do experiments and find that they match to the tenth decimal place after the decimal point you call that kind of undetermined ISM or some kind of uncertainty uh uh that's pretty damn certain and that's really what quantum mechanics gives you so you really need to avoid hearing the words Heisenberg uncertainty or quantum indeterminacy and employing them in a way that they are not meant to be used and I hope that that clarifies that very important point all right Danny long as why did the universe immediately clap I think Donnie long means why didn't the universe immediate collapse into a black hole following inflation and and this is an interesting question because if a black hole is when you have a lot of matter in a region of space and that region of space is affected and in some sense collapse in on itself well you know near the Big Bang wasn't there a lot of matter why didn't the whole universe collapse in on itself two answers that number one the black hole solution of Einstein's general relativity assumes that the matter you're talking about is within a pre-existing spatial environment when we talk about the Big Bang there is no pre-existing spatial environment the Big Bang creates the spatial environment and therefore our intuition from black holes in ordinary space needs to be updated when we are trying to think about matter in a context like the Big Bang second we believe that the early universe was very homogeneous highly similar indistinct locations and so it didn't to create the centers the gravitational centers around which matter would fall in to create black holes so as inflation is happening it propels everything outward it propels space and time themselves to stretch and in the aftermath of that you have this nice largely homogeneous realm in which things are moving outward and so the homogeneity which requires you not to have these gravitational centers which will suck in the matter surrounding as well as the outward swelling itself counters the tendency for things to fall together in to come P objects' like black holes there was an interesting one I just saw and it just went by anon as was your opinion about the Rigveda I I can't give you an opinion on that for that you need to ask my brother maybe you've got me confused with him he is an expert on these particular texts and he actually just taught a course on the Rig Veda I believe at Hofstra University in New York online so look him up ask him tell him I sent you all right someone just asked if I could say a few words about the many-worlds interpretation of quantum mechanics I don't know where that question went but yeah look I just mentioned that the math of quantum mechanics is deterministic but that it determines probabilities so if the math determines that the probability of an electron to be here is 30% and here to be 50% here to be 20% the natural question is when you undertake a measurement why do you only find it at one place or another what happens to the other possibilities that emerge from the mathematics of quantum mechanics and in many worlds interpretation from Hugh Everett says well what here's what happens if there are three possible locations for the location of the electron and you measure its position you find it here the court in Hugh Everett there are actually versions of you that find it here and here as well those possibilities do not go away but rather they take place in a completely separate reality a reality that in some sense the math of quantum mechanics separates off from the reality which you found the Allah Tron here so each of these possible outcomes is realized in its own separate world and that's why it's called the many-worlds interpretation of quantum mechanics so it's a highly controversial subject my friend Sean Carroll recently wrote a book he is a dedicated mini-world er if you will I am not as dedicated to this approach I think there are mathematical details that still need to be ironed out before we can take this idea seriously but yeah you know it is one viable approach to trying to make sense of the reality which the quantum mathematics is leading us to not everybody does so eric w says shout out to the eels and that's right so cue everett sun i forgot his first name Oh Doran maybe Erika can tell me but Hugh Everett son formed a group called the eels and in fact participated in a very interesting film that I can't remember the name of the film got him becoming forgetful in my old age here and and there's a very interesting film in which cue Everett's son was reflecting on his father and his father's role at least in part on developing this many-worlds approach to quantum mechanics let's see what else we have here uh Naveen asks about my opinion on white holes and white holes are basically time reversed versions of black holes so since the laws of physics are time reversal invariant if they allow black holes to form you to assume that white holes were not everything's falling in but everything's spewing out would be allowed to many people think that there are principles that forbid the creation of white holes I am of the opinion that white hos likely do not exist but I should say that there are people who think about these ideas and have different opinions and have thought about it more than I have so I can't really give you a the answer on white holes but no I do not think I do not think that white holes are real someone asks and it went by Oh William Selby asked what are your thoughts on loop quantum gravity and the William my view is that I'm glad that there are people developing alternative approaches to blending quantum mechanics and general relativity is a very important subject you know we we we have been struggling to realize the dream of a unified theory that would put together the laws of the big and laws of the small into one coherent mathematical framework and to put all your eggs into one theoretical basket namely that of string theory would not be a good strategy for the species right so I'm glad that there are other approaches to quantum gravity that are being developed I think that string theory has the better chance of being the right theory for many reasons the mathematical structure of the theory feels more convincing to me the way it deals with quantum mechanics feels more convincing to me and and a variety of other technical details that maybe I'll spell out and one of these your daily equation episodes and maybe I should do one on loop quantum gravity like I said in one of the earlier episodes so many equations so little time I don't know what I'll get to but um you know so my thought about loop quantum gravity it could be the right theory I'm glad people are developing it maybe we'll find connections between it and string theory before all the dust is settled so so I'm a proponent of the varieties of approaches that we take to solve deep challenges and Luke on gravity is an absolutely viable approach and I'm glad that people are working on it I don't think however that it's the right approach where I'd be working on that myself okay man what do we it still is still rolling along here okay okay what else how does it Priok has it feel to be vegan I don't know I feel I think I've been weak ever since it turned vegan 25 years ago so I'm not sure I don't know how to answer that question Debra dr. Brian from Mohammed how was it sufficient for just one difference between matter and antimatter to create everything that's referring to a little video that we had a quick year daily equation where I noted that if you had a billion in one particles of anti it's called a matter billion one particles of matter for every billion particles an antimatter then when the matter name to matter find each other and collide one particle of matter would be left over the question is how is that enough well it's an enough to create all the stuff in the universe which is not just one particle well when you look at the cosmological evolution of matter from just after the Big Bang until today you can calculate how much stuff would be say in our observable universe and the amount of stuff that you need in order to have the stars and galaxies ultimately form is such that you only need about one part to billion of all of the matter particles that could have been created so I wasn't trying to say there's only one particle left because the universe has much more than 1 billion in one particle is a matter and much more than 1 billion particles of antimatter but I'm saying if that level of imbalance persists throughout all of space and applies to all of the gargantuan numbers of particles of matter and antimatter that are across all the observable universe then the amount of matter left over when the matter and antimatter collide and annihilate would be enough to yield the stars and galaxies what else all right already asked would you rather time travel to the past or to the future if you could only take a one-way journey are already my view and that is quite straightforward I would absolutely prefer to travel to the future which is a good thing because time travel to the future is within the laws of physics and time travel to the past is likely not but why would I rather travel to the future when I get to the future I can read about the past I can see videos about the past I can whatever put on neural implants that will allow me to learn about what happened in the past the future is the big mystery the future is the one that we seem not to be able to learn about in detail by sitting here at this present moment and therefore the future holds much more of an allure to me than the past having said that as a human being I'm not going to the future if I can't take the people that make life worth living I'm not going if my wife says no I'm not going if my kids say no maybe there are a few others I throw into that group so I don't mean to exclude anybody but yeah in terms of the distinction between past and future to me it is the future that holds the the greatest attraction not the past can I explain a bias about the delayed choice quantum eraser and I can I'm actually going to refer you I don't do this often but I'm going to refer you to my book fabric of the cosmos chapter 7 I'm sure you can get a bootleg PDF version online I'm not asking you to buy it and there I go through great detail on the question that you address so I'm going to leave it at that because it would take me pretty far afield to even set up how that expired Nomad ask is there a Heisenberg principle for thought processes and look this is similar to a question from before does the uncertainty principle apply to thought processes yes it does does it apply to blue tea and Swiss cheese it does because all those things are made up of particles is there something special about the Heisenberg uncertainty principle as applied to human thought as applied to Swiss cheese or blue cheese I don't think so now could I be wrong about that could quantum mechanics be more tightly connected with conscious processes people have suggested that serious people have suggested that Eugene Wigner one of the great minds of the last centuries suggest to that at least for one period of time I don't feel that way I don't think mind is special in the sense of having any other qualities beyond particles and physical law governing those particles and that's exactly how I would describe cheese what is special about the mind is that the particles are highly arranged having emerged from eons and eons of evolutionary processes that's what's special about the mind not that it deals with quantum mechanics in some different way but rather that it's highly organized the pattern of the particles is just exquisite compared to the pattern of particles that make up a chunk of cheese so in that sense yes Heisenberg's uncertainty principle matters but no it doesn't play any special role and that really is the key thing to keep in mind okay so Gabor asked as bomi mechanics of any problems in replicating entanglement and it does not and in fact bohmian mechanics is in some sense an antidote to the weirdness of entanglement as described in the more conventional quantum mechanical approach the Copenhagen approach say Copenhagen approaching tankmen totally weird because particles really are in a mixture of say up and down at the same time so how in the world could measuring a particle over here cause this particle to snap out of the up-and-down that's the spookiness that's the craziness bohmian mechanics comes in and says there's a very simple explanation this particle when you measured it and found up it was always up this particle when you measured it and found it down it was always down nothing snapped out of a fuzzy haze because there is no fuzzy haze in bohmian mechanics and bohmian mechanics that probabilistic nature emerges from a different source it emerges from your inability to understand the true qualities of a particle but the particle itself does have the qualities that measurement reveals measurement doesn't cause those properties to emerge measurement simply reveals the pre-existing properties that the particles have so from that point of view there is absolutely nothing strange about entanglement in bohmian mechanics all right so what did we do should we wrap this up here paradox as on you can find that in one of the earlier episodes I want to answer one good question and then be done for today I keep saying that I think I said that two hours ago what form of matter Akash asked what form of matter does a black hole consist of and look in the traditional description Akash shal r of a black hole matter falls in to a black hole that gets infinitely squeezed what does that really mean infinitely squeezed at the center and there isn't really much happening between say the center and the event horizon of a black hole that's say been hanging around for a long time so in that sense a black hole kind of consists of this singularity which as I said earlier means we don't know what's going on at the center empty space event horizon which itself is empty space but it does have a very important implication that anything that folds over the edge can't come out that's the traditional classical description quantum mechanically this story is more involved people envision that maybe the edge of a black hole is a firewall a place of increasingly high temperature anything that falls and gets incinerated at the edge maybe there isn't even an inside beyond the firewall my friend Sameer Mathur maybe you guys know him as I think there are I think there are a few folks from India that are following our discussion here Sameer Mathur is at Ohio State of brilliant Indian physicist I shared an office with him back in the 1980s and he came up with an idea that black holes may actually really be in some sense made of strings veteran that are entangled with each other and what he likes to call a fuzz ball and so a black hole might actually be a fuzz ball which mean the black holes not that different from a star a star you know you got this structure that burns on the outside a fuzz ball could be a structure that burns on the outside to it just as an extreme version of that so we don't really fully know the quantum mechanical answered to the question of the deep constituents of a black hole so BOM dia says I'm in Columbus Ohio fantastic you should go look up Sameer tell him I said hi Oh Traci day asks what are we having for dinner Traci day is my wife who has entered the conversation with a very very deep question which I suggest I suggest she means I should probably wrap this up so Traci day wife I think will have tofu black bean sauce but I'm going to answer one more question that just really wait wait wait could this be it no it's not wait I like this one so John Faulkner asks about entanglement I'd love to answer that but I've done so much on entanglement John that I'm going to do the rude thing and refer you to my your daily equation episode on entanglement which you can easily find what else what else what else give me that one question I'm looking for come on there must be one year good someone now talking to my wife Tracy that's nice I appreciate that so I'm going to end with with my friend Ludwig von Beethoven you know a great supporter of the series who asks how is the proposal the time might be just an illusion compatible with the theory of relativity and and you're right a little bit von Beethoven there are people who say at that time is an illusion and I will to answer so so so there is a long history of work that's been done I'm trying to argue that the right way in the right way to formulate physics and even the right way to formulate the general theory of relativity it's all about relationships as opposed to there being this drumbeat of time even if that drumbeat is different for us depending upon our motion and the gravity we experience that the real fundamental right way to formulate relativity would not have time in those basic equations the time itself would simply emerge from those basic equations and there's some evidence for that in string theory too so I'm not suggesting that this is the right way of doing physics or the wrong way of doing because I'm merely noting that there's a long history of people developing that idea and and the reason I raise that is because you can have time emerge all of these approaches so such that it has the qualities that we experience in everyday life and it has the experience that Einstein revealed through special and the general theory of relativity it could be the time is a quality that is only relevant on say certain length scales or certain duration scales or in certain environments and then fundamentally there is no time written into the deeper laws that we've yet to fully discover that wouldn't mean that time is an illusion that would mean that time is emergent and and so I think that that's the way that most of us think about this possibility of there not being any notion of time in the true fundamental equations at that level I guess time would be a loser II because in those basic equations you wouldn't see any conception of time but certainly time as we experience it is real we all experience it time as Einstein articulated in relativity would be real too it just wouldn't be as fundamental so there's a difference between something being illusory and a mistake and shouldn't be spoken of and something being a loser e in the sense that it's not fundamental that it's emergent so I think emergent would be the better language for discussing that notion of time all right so I think that's more or less it for today you should join us on Monday for the next episode of your daily equation again some of you asked where episode 24 is and we'll get it out maybe this weekend or maybe on Monday as I noted early on the session I made a small mistake a small mathematical mistake in an episode I want to fix it so we're just going to fix that and we'll get it out to you nothing conceptual is just a technical thing I wrote an extra derivative I'm in one equation so yeah I'm being perhaps a little bit too persnickety to ensure that that is done right but I'm going to do that right and then on Monday or Tuesday will pass into Einsteins ideas of general relativity we did special relativity and we'll talk about curvature and gravity space-time curvature and maybe we'll do some things on black holes that would be quite natural I'll turn to cosmology I want to give you an understanding of the Big Bang and inflationary cosmology and who knows where we're gonna go from there if at all maybe that would be a natural winding down time for this series but you know if you keep watching and keep talking and keep asking I'm gonna still be here so who knows maybe we'll keep on going a little bit further into the summer than I initially anticipated you know life issues can sometimes get in the way of that but I'm willing to keep an open mind and listen to what you guys would enjoy doing alright again if you don't follow me on Twitter please do in fact sometimes when I'm not doing an episode of your daily equation I wish I could just send out a tweet and reach you guys because I kind of feel bad so if if more of you would follow me it would be an easier way for me to be in touch with you guys world science festival you should subscribe I think there is a subscribe button somewhere in this down there and a lot of great content that's already on the world science host website final announcement before I go world science you the educational arm of the world science festival we are relaunching really soon with a lot of really interesting online courses that are all free I have a full special relativity course they're both with math and without math we have courses that go from cosmology all the way to issues of consciousness so all for free you should definitely check that out it'll be available I think I think very soon I think April no or in May already so maybe maybe it's in the next week or two so keep your eyes out for that alright guys thank you I've enjoyed this session with you and looking forward to picking it up live next Friday but we'll have our usual doses of your daily equation coming up this week all right until then this is brian greene signing off

Channel: World Science Festival

Views: 82,134

Rating: 4.8453608 out of 5

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: 0rlpIokH0cc

Length: 147min 16sec (8836 seconds)

Published: Fri May 08 2020

Reddit Comments

[u/Heads_up_eyes_open]

Basics of known science and the forces they exert.

Worth a watch to see how they might fit into your own interpretation of ufology.

[u/Dave9170]

As much as I'd like to sit through another 3hr podcast. Brian Greene, while a smart man in his particular field, doesn't offer any deep insights into UFOs or alien visitation. In fact his ideas are quite outdated. Here's a short 8 minute segment from Rogans show: https://youtu.be/BRo3YXCvgPI