Brian Greene - "The Big Bang to the End of Time"

we will be cutting the question-and-answer session took 30 minutes that way there is still time for folks to be signed and whatnot but if you have a question you can simply raise your hand all those and I will be walking around with microphone and we will also periodically be interjecting with questions we have on our Twitter thank you for attending if space was created during the Big Bang how can it be infinite if space were created at the Big Bang how could it be infinite and it's a good question and it is a question that highlights the failure of some of the visualization that we often use to explain these it is weird the question ago just ever there goes right so so in all of my visuals and just about any visual you'll ever see that has to do with the Big Bang we picture the universe has this little tiny thing and then you're right to say how could a little tiny finite thing turn into an infinite thing if we believe that space is today infini we don't know that it is infinite but let's assume that it is to address your question and the answer that question is when we draw this little thing over here we're not talking about the entirety of the universe we're talking about the entirety of what today is the observable universe the part of the universe that we can see if we were to draw the entirety of the universe at time zero in the Big Bang Theory if space is infinite today then it would be infinite back then infinitely big with this swelling happening everywhere on this infinite expanse and you know that from the reason that you asked the question if it's infinite today then further back it might be half of infinity which is infinity and further back still it might be a tenth of infinity which is infinity and no matter how you slice it as you go further and further back the density across space would grow higher and higher but the extent of space would stay infinitely yes go ahead you create that's right so if space was created now again as you see I've shown you the state-of-the-art in what we mean scientifically by those ideas and in nowhere do I answer or does anybody answer the question well why is there something rather than nothing that's the deepest question of all and I don't have the answer to that and thankfully I'm not the only one who says that otherwise they should I'm in this talk but nobody on planet earth knows the answer to that question but if space was created at the Big Bang it was created infinitely big now for those who use that language or and think of those terms I have no idea if it's used you know if the universe was created by something that entity isn't limited to create something finite so you shouldn't be confused by that but scientifically that's completely unsatisfying and we ultimately want to come to some mathematical idea that will show us where everything I'm talking about here came from we can't do that yet but the hope is that one day we will thank you we have one question is it possible to detect one of these other universes is it possible what to detect is it possible to detect one of the other universes again a key chord because if there is absolutely fundamentally no way to ever detect one of these other universes then what would we be doing here then we are just talking a lot of poetic philosophical words that have no means of ever being verified no means of ever knowing whether the ideas are right or wrong so the answer is that in principle there are ways to detect these other universes and the picture actually suggests what that might be imagine you've got two universes out there each of them is expanding if they were spon sufficiently close to each other then the rate of expansion will be greater than the rate at which they're pushed apart by this repulsive gravity that's out there which means that the universe's can't collide with each other now calculations have been done as to what we would see if our universe had that kind of Thunder bender with another universe now if the collision is too dramatic we wouldn't be here to do the calculations but on a more glancing blow the implication would be a series of ripple like patterns in that microwave background radiation so I showed you these I don't know if you could have seen it maybe you did so we had these graphs up here with this tremendous agreement between observation and theory there are the possibility of even finer patterns in that microwave background radiation and if they fell in to the predicted pattern arising from universe collision that would be indirect evidence that the other universes are out there so in that sense the answers yes all right we have a question from our Twitter feed from Haneda loggy how many other universes exist that have the perfect amount of dark energy to exist well in most of the form that we use to talk about these other universes the totality of the other universes out there is actually infinite and that isn't again too surprising because the notion of time really applies time as we know it applies in our universe when we talk about the whole collection it's kind of a timeless realm even though we imagine that each one is being created like one after the other but even that language requires some notion of time that applies to the whole thing so if you take out the temporal quality and just look at the whole thing then it's as if you're looking over infinite time and therefore it isn't too surprising that there'd be infinitely many universes out there if the number of the fraction that have just the right amount of dark energy is even infinitesimal well an infinite Ezell fraction of an infinite number still yields an infinite number of universes so the answer is probably if these these are correct infinite now now there's there's interesting and curious implications of these ideas right so if you calculate the number of distinct particle configurations in a given volume of space it turns out that that's a finite number a finite number of distinct particle configurations which means if there are infinitely many universes out there there aren't enough distinct particle configurations to go around to make them all different which means sooner or later the particle configuration starts to repeat it's sort of like if I have a deck of cards there are a lot of orders of the cards if you keep shuffling them but there's a finite number of different orders so if you shuffle the cards enough top order of cards now four cards that isn't too dramatic but for particle configurations it is if you have the same configuration of particles out there somewhere well what would that mean well it mean that I mean I'm a collection of particles in a certain configuration as are you and you the earth the Sun the same configuration of particles you mean this reality would be repeated out there in fact it's even easier to get almost duplicates in that sense right that's like doing a shuffle of the cards and almost getting the same order that's even easier than getting exactly the same order a configuration of particles that's almost but not identical to ours might mean that you know I'm standing over there and you're standing over here or you know more dramatic changes to reality that may look familiar but things are just not quite the same in fact I when I first gave a talk on this since you asked the question I I remember there was one elderly woman in the front row and she said to me but if there could be other universes out there the particle configuration as close to ours but not identical does that mean there's a universe out there where Sarah Palin as president you know I again I'm not a political person I'm so I'm not going to enter that conversation luckily a guy in the back raised his head and said to the woman didn't you hear what the good professor said the particle configuration must be compatible with the laws of physics the the galaxies are expanding away from each other and yet our closest galaxy the Andromeda one is supposed to clad with us could you reconcile for that yes so so again the key idea in all of these cosmological discussions is that you are looking at the largest scale behavior of the universe so I can even give you a more dramatic version of the question that you just asked which is often asked of me which is look if space is expanding why aren't we expanding we've got a lot of space inside of us we're mostly empty space so why aren't we growing too with this cosmic expansion and the answer to that question is the same as the answer to your question we are held together by forces that are stronger on small scales compared to the outwards swelling of space the outward swelling of space is something that gains strength over larger and larger distances why larger distances means more space means more dark energy doing the pushing outward so over the largest of distances this kind of outward push will always win but over shorter scales there's historical contingency how the galaxies formed how they were moving when they were formed the forces that are acting between them and the constituents within them and those things can overwhelm the outward pushing but on the largest of scales they will always lose so from my limited research I came across the idea that Einstein not believe that space existed objectively like without matter he believed that it was the consequence of matter and gravitation the field associated with it does quantum physics or just bring strength here you actually speak to that you know we don't really know what the full answer to that question it's again one of those those deep ones it's a somewhat philosophical question because the issue is ultimately you know if you have space and somehow remove the Sun and the earth and the moon and every other constituents and every atom and every particle the question this has long been asked what remains is it the environment is it empty space or is it is it nothing I mean the analogy that that you can think about is you know if I have an alphabet I got 26 letters in the English alphabet I start throwing away W and X and a and B when I throw out the last letter what's left is it an empty alphabet most people would say no because the alphabet comes into existence with the letters that make it up similarly if I throw all this stuff out of space what's left is an empty space or just space kind of only have meaning when there's stuff inside of it now as you can see it's a hard idea to test experimentally right it's hard to empty out the universe but you can study that question to some extent mathematically and one of the results of general relativity interpreted in one way not everybody agrees even on what I'm about to say but one interpretation of general relativity which I do think agrees with Einstein's is that he's basically saying you can't ever totally empty out space because space always has the gravitational field even if there isn't any curvature that just means the gravity is of a very specific sort but mathematically speaking if you don't mind my segue into that language for a second the metric tensor would always be there so if that's the case gravity is sometimes always there no matter what you can't ever remove it and that sense Anton says space will always exist because it's always inhabited by basically gravity hi if mathematically we can't determine what happens at a time zero for the Big Bang why do we cling to an idea of a time zero as time that has is something that has a beginning instead of something that's infinite in both directions so not everybody does so I should say the question is you know if we don't know what happens at time zero maybe we shouldn't cling to that as a special moment and indeed there are many theories now that have been put forward where time zero isn't that special where there's a pre Big Bang era and there are pre Big Bang theories that imagine time goes down to minus infinity and their mathematical descriptions of what happens there there are other theories for instance the cyclic universe that was proposed by one of the guys over here Paul Steinhardt and collaborators which imagines that the universe repeats in time so that there can be times zeroes in any cycle but that isn't the end or the beginning it's just an interesting moment in a never oscillating universe so yes many people do speculate on other ideas where time zero isn't as special as it was back in these early ideas we don't know if those theories are correct but they certainly are studied for much the same reason that you suggest they should be true so I have a very rudimentary understanding of this stuff I'm not a scientist at all but I understand that in string theory apparently there has to be like 11 I think or 10 dimensions for it to make sense mathematically could you say a few words so we can sort of grasp this idea of an 11 dimension universe or what what that means yes yes yeah it's a great story mathematician Thurston at Princeton who was teaching a class on higher dimensional space in mathematics class and he's lecturing about six dimensional spaces and he looks out in the class everybody looks a little bit confused and understand why they're confused and it kind of walks over to the side of the room and starts to think for a while ah I know why you're all confused it's so much easier to picture the stuff in 12 dimensions yeah but for for the ideas of string theory so yes I didn't talk much about strict theory in fact anything about string theory really but when you go to the other end of the spectrum we were talking about the big things for the duration here today we try to discuss the small things the molecules the atoms of subatomic particles a whole interesting collection of ideas emerge quantum mechanics being the first and then if you probe more deeply mathematically you are led as we have been to the possibility that the fundamental constituents of matter are little filaments little string like filaments that can vibrate in different patterns and the different vibrational patterns of these little filaments give rise to the different particle species in the world around us so in these ideas an electron wouldn't be a little dot the way we ordinarily describe it it would be a little loop vibrating in one pattern a cork wouldn't be a little dot it'd be a little filament vibrating in a different pattern now that's the basic idea of string theory and when you study the math behind that much as you noted we find that the math does not work if the universe only has three dimensions of space and one dimension of time now you might say well that's a pretty good clue that you should move on study something else and that may be the right answer but we also find that if you have an open mind and allow for their other do exist other dimensions beyond left-right back-forth and up-down in fact if you allow seven extra dimensions of space that we don't see then the math works now your question is what does that mean and it really means that in addition to being able to walk this way this way in this way if I was small enough I have other choices and I don't mean like a diagonal right I mean that's like going this way and this way simultaneously I'm talking about other directions other dimensions that you'd be able to move that we are not aware of because we're so big and clumsy according to these ideas and a good analogy just to keep in mind is you know imagine I have a garden hose is our canonical analogy man I have a garden hose right on its surface there are two dimensions left right and then this sort of circular dimension that goes around it so an ant on the garden hose can walk in in any of those two directions but look if I make that garden hose really skinny and you look at it from far away you don't see that curled up part of it you only see the length so you think that the garden hose only has left and right and you'd be wrong and you'd prove to yourself you're wrong if you had a powerful magnifying equipment and you realize whoa there's another curled up dimension that my eyes missed our thought is that may not just be finality that I have that space may have that quality so left-right back-forth up down there like the big part of the hose we see them but just like there's a curled up part of the hose that we don't see if it's small enough there may be curled up dimensions all around us some tiny that we don't see them but yet they're there that's the idea all right we have another Twitter question from Joseph gross how many years will it be until that dark universe you described happens the dark universe where everything disappears that will be in ten to the twelve years yes sorry I did that did that calculation two weeks ago ten to the 12 minus two weeks this question again why or comment again is about observable universe Big Bang happened about thirteen million years ago so since then currently our observable universe is about 40 billion light years when the inflation is going to be at the rate of speed of light we are going to see the darkness which will be end of our observable observable universe so is it fair to say or how would we interpret that at the time when the inflation started our observable universe was in finite let's see so I'll do my best I may not have caught the question precisely but in much the way that we discussed earlier that if space is simply big it has to always be infinitely big then if that is the correct model for space then even at the time of inflation space would have had this infinite extent now when you think about the extent of space you have to be a little bit careful so you mentioned that since the universe is about thirteen or fourteen billion years old that the extent of space should be about 13 to 14 billion light years that makes a lot of sense but it's not actually correct when you take into account the rate at which space expanded and it could have expanded and would have expanded faster than the speed of light in the earliest moments of the universe when you actually take that into account from one end of the observable universe and the other it's about 90 or 92 billion light years today not just 14 billion but again that's a finite number so if you're only concerned with finite versus infinite then that is sort of a switch it either is or is not and it will always be or will always be not you can't go from to the other let me just finish this answer with one other thing that may be relevant to what you're asking in all the pictures I showed you the universes were like these balls these spheres and you might say well are you've been committed to the universe being finite because the sphere certainly looks finite if you put arms around it writes its finite size and it's a remarkable fact that indeed from the outside the bird's eye view each of the universe is in this inflationary multiverse would be finite in size as the picture depicted but if you were to insert yourself into any of these universes then within them they appear infinitely big in spatial extent why is that it's the wonders of relativity space and time to the outside person are not space and time to the inside person and the way space and time relate to each other is such that infinite time from the outside perspective translates into infinite space on the inside perspective so those universes even though they looked finite or infinite to anybody who is inhabiting them all right ok we'll be taking this question and then one more question okay so in this bubble bath of multiverses do you think that we're still following the quote-unquote rules that we're dealing with in this universe and do you think that there could be two simultaneous multiverses overlapping whether that's a time and space or outside of time and space and then what are we bathing in I guess well you're making my head hurt so yes the answer the first question is yes so anything that we're talking about here we are imagining that there is a set of mathematical rules that is generating all of the ideas the conclusions and the conjectures they're all coming from the mathematical rules and therefore the mathematics applies to the whole thing so everything that I've said fits into that context could I envision that there's like some kind of parallel parallel universe you know a multiverse that is separate from this multiverse can I imagine it yeah I got an imagination I I can imagine it you know I can also imagine that the moon is made of cheese right and the reason why I don't focus on the moon being made of cheese is because there's nothing that I see in the equations that leads me to even have a remote possibility or speculation that the moon is made of cheese so I'm like it's possible I'm just not that interested in that idea similarly when it comes to this other multiverse idea it sounds cool and you know be a good movie or something but when it comes to science I see nothing in anything that we're doing that suggested and that's why however interesting or cool it might sound it doesn't draw me to it in any way if the math that we developed should lead to that then yes we would think about that we think about it intently and that was part a and B what was Part C what are we bathing in Oh what are we bathing in I mean I like bath salts you know you know my wife likes the low certeyn it's expensive you know now what are we bathing it if you're talking about the steamy stuff that was surrounding all of the universes then that is the very same dark energy that I was describing earlier on and I'm glad you asked the question because I didn't say it but it's worth mentioning right now so we often think about the Big Bang and my visuals again reinforce this idea as something expanding outward from a small size if the multiverse picture is actually true the right way of thinking about is a little bit different the right way of thinking about it is you've got this big cosmic expanse filled with this dark energy think of it like big Turkish DiMeo filled with steam it's all rapidly expanding because of the repulsive gravity various locations in that environment the dark energy decays which opens up a little hole in this big bat and if that little hole that opens up that is universe upon universe upon universe each hole is its own universe so it's not so much as something expanding and exploding outward within this environment it's more regions that are dropping out of the rapid swelling because the dark energy Debaters into case into particles that make up stuff like you and me so that's kind of the difference the bath is the norm the universe's are the little things that happen when the steam decays thank you we'll be taking one final question but stick around if you have more questions there will be a book signing immediately afterwards you can purchase a book if you would like and have him sign it and ask your question then and feel free to keep tweeting questions out with that hashtag green at Rhodes and if you would like to answer some of them through the social media you can with the discovery of the Higgs Posehn a few years ago has that led any to to any further confirmation or disapproval of multiverse theory or for supersymmetry or any of the other theories that are out there yeah so the quick enters is not not really but the can overstate how profound that moment was in the history of this kind of science so when you think about the the Higgs idea it started in 1964 Peter Higgs walking around the outskirts of Glasgow and has this idea and writes it down for how particles will gain mass and it has to do with a bath of energy filling space who sounds familiar right and particles going through this and they're experiencing kind of friction like force as they try to push through this bath and that's where their mass comes from writes it up into a paper send it to the journal drooler rejects it he rewrites it changed a little ascended to another journal it gets published nobody takes it seriously nobody thinks it's right he goes on a kind of a crusade lecturing on it in various places around the world and little by little as people study the mass they're like wow this makes a lot of sense this might actually possibly be right 1970s 19 1985 I'm a graduate student and I'm learning about this Higgs idea in my quantum field theory class and the professor is teaching the idea with such certainty that as I was mentioning earlier today in our gathering for many months after that class I didn't know it was just a theory I thought it was true that's how certain it was in people's mind by the mid-1980s and then people are convinced by the possibility that this might be ripe to build the machine the Large Hadron Collider ten billion dollars are spent they smash stuff together they're able to jiggle this field in just the way right to flick off a little speck a Higgs boson Higgs particle and the idea is confirmed that progression 1964 to 2012 you go from a mathematical idea that nobody believed everybody thinks is crazy gets rejected in a journal to being proven true by experiment and that's the name of the game so when we see that happen that's exactly the pattern that we hope that we imagine that we are following developing mathematical ideas it's sound crazy that seem like they can't possibly be true until sometime later on observation shows that they are so from that perspective it's a profound moment in the history of these ideas thank you very much

Channel: Rhodes College

Views: 25,127

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Keywords: Rhodes College, Communities in Conversation, Brian Greene

Id: AhSEKej3kHA

Length: 30min 17sec (1817 seconds)

Published: Wed Apr 01 2015