Lisa Randall - Are there Extra Dimensions?

Lisa we're now hearing about extra dimensions and physics some people have enough difficulty with four dimensions adding time to the three dimensions of space how can we begin to understand this concept of extra dimensions well first of all you might ask why we're even thinking about it and the reasons really really do have physics motivations there really are physics motivations for thinking about which we can come back to but how do we even start to think about what we mean by these extra dimensions well I think most people are familiar with three dimensions to be like left right forward backward up down but um one of the best ways to imagine how we should envision extra dimensions was actually done by Evan AI Bennett late 19th century and a book called flatland and what he said is if you lived in two dimensions you will have the same difficulties picturing and imagining to heard to mention that we have imagining a fourth spatial dimension or higher dimensions so what he said is suppose that there were creatures living on flatland say this tabletop and how would they see the world and I mean we know there's a third dimension but these Flatlanders wouldn't be aware of it so what would they see we'll suppose some objects like from the third dimension came through suppose a sphere came through a flatlander would never see the sphere in its entirety they can't see three dimensions this anyway we can't see more than three dimensions but what they would see is a series of disks that grew in size and then decreased in size as the sphere went through so they would get all the information about third dimension or about this three dimensional object even though they couldn't necessarily reconstruct it in their pictures to see that it was a three dimensional object so in the same way it could be that there are extra dimensions that we don't see directly so we can see the implications of those but there could be signs that we could put together to tell that those dimensions exist so what are the motivations from physics point of view why does physics seem to have a need for these extra dimensions well some people would say we do ever need some people would say we don't I don't want to overstate it but there's a there are several reasons why we think about extra dimensions one is a theory called string theory which is a theory of quantum gravity or purported theory of quantum gravity trying to put together general relativity and quantum mechanics and the point is that theory doesn't make sense if they're only three dimensions of space do you need extra dimensions so then the question that for a physicist is what are the implications of those extra dimensions and why haven't we seen them but there are other reasons too and one reason that I find very compelling is that there really are problems in particle physics that are very difficult to address in the context of just three spatial dimensions the standard model of particle physics which describes matters most basic internal elements and their interactions let's put together in the 1970s and there are some outstanding questions that's although the model works beautifully it makes beautiful predictions agrees with experiment to a high level of precision there are some fundamental elements of that theory that we don't understand yet and if people have been trying to solve it as I said since the 70s and haven't come up with a completely compelling solution and it seems that if there are extra dimensions of space it might be easier to find ways to address and also in the standard model of particle physics we have so many different parameters that have to be entered by hand that can't just fall out of the theorem of where the 26 or some large numbers but well there are a lot of parameters in the standard model namely masses of particles charges etc and there are ways of trying to address them in the context of three-dimensional space but again if I showed you one of these examples you would say that looks pretty complicated and so another possibility is that we can have extra mentions and try to address it there and we don't know the answers we don't know that those problems will be solved but it's a new forum and there's a lot of new ideas I should say that even if these ideas about extra mentions turn out not to be right it turns out that they've given rise to new ways of thinking about even three dimensions so there really are new ideas that have come back I think that's terrific that's the most important part of new ideas it's not necessarily they have to be right but they force us to to rethink our conception of everything else that we do although we do prefer that right of course let's talk about some of these extra dimensions what do they look like I know word is a compactification which means they're extremely small they're curled up but how can we understand that's one that's one way of but actually another possibility is that they're very curved or warped the way Einstein taught us can be true in the presence of energy and the implications of the extra measurements can be very different depending on whether they're hidden because they're very tiny or hidden because they're very warped so basically soon after the idea of F dimensions was introduced in the context of physics and so basically in the 1920s people started thinking about this idea that you could have very tiny dimensions and the idea is rather intuitive which is something that's really small you don't see it and that's basically what's going on perhaps with extra dimensions of the universe however as I said a moment ago it could be also that space time is really dramatically warped so that we only really experience one region of space and other regions of space have less influence on us and that could be another way that extra dimensions could end let's talk about gravity in the context of extra dimensions because gravity seems to be the one part of reality that can communicate through extra dimensions because it's related to space-time itself I should say gravity is one part we know should be intimately connected to all of space-time there could be other particles there could be other forces that communicate through extra dimensions but gravity is one that we know has to be there and it has to be there because it has to be there for it basically Einstein taught us that has to be there in some sense because one thing is that gravity is connected to the geometry of space-time but another way of understanding it is that it gravity is something that interacts with energy if you have energetic objects it creates a gravitational field if something is moving through a gravitational field and has mass or energy it experiences gravity and it better be true that that's true anywhere if you have energy in any region of space whether tier or often in extra mention it still should experience gravity and the fact that it's an extra dimension we haven't seen it doesn't mean that the kind of gravity that we're experiencing well it may be different I mean the fact that it's a it's a dimension itself gravity must be similar in that dimension because since we know so little about it okay so what we know is the fundamental gravitational theory then how we experience gravity depends on the distribution of matter and energy which defines which gravitational field is in our environment so there are many different ways that gravity could be experienced in our world and that's one of the things that we explore for example if you're near a black hole you experience a very different fort sort of gravity than if you're in our environments here is that a good analogy to the gravity and extra dimensions to see what happens in in black holes so you have this enormous warping of space-time um there you have the in the black hole case you so have the warping of time for example and in extra mentions you could form space and time for example I mean you also get warping in some sense of space but it works differently in the context of a black hole but it is a good analogy in some ways is there any way that the extra dimensions and the gravity communication between them can can help us with what seems to be a very strange reality where the gravitational of power is so much weaker than for example electromagnetic force at 10 to the 40th it just seems a an odd thing in our world the two of the primary forces have this enormous difference in power that's right and I'm it's worse than just a mysterious question because if you take the principles we believe are true namely quantum mechanics and special relativity and put them together and try to predict how these forces should be related it would be much more natural for them to be of the same order it's only by an enormous fudge or what we call fine-tuning that we get away with having these forces have such different strengths so one of the ideas that my collaborator brahmand syndrome and i worked on is the idea that if space-time is really warped it could be that gravity is essentially really concentrated elsewhere so that we are getting a very weak version of gravity where we are um so gravity could be strong but strong elsewhere and we where we are we in fact is one way of thinking about is that particles would be lighter than you expect them to be in a theory without this warping and it's because particles are lighter that you experience gravity is weaker so this could be a very natural explanation for why we experience gravity as weak so in that model the the primary forces of physics would be much more similar it's just that the the power of gravity would be located another dimension but it has to do exactly you can solve for and you can see that Einstein's theory of general relativity tells you there is a particular type of warping that tells you how you experience gravity in different regions of space and and how that that that power and that warping would would transfer between one dimension and other the in terms well you can think of it as transferring point but really it's just that the field itself is distorted there really or if you like the space-time metric the way we measure things is a distorted with the things that could be heavy in one place you'd expect to be light in another is the way we're measuring things is so different because the gravity is telling us that how do you see the the continuing relevance to the development of physics of extra dimensions if you project forward you know the next several decades well we never predict or in several decades those things change too quickly but um a lot will depend on what the Large Hadron Collider the LHC finds that is to say there's a Collider it's gonna collide together protons enormously high-energy one of the questions is will it see evidence of extra dimensions if the idea I just told you about is right it should see some evidence that these extra dimensions exist it also will have to do with just our theoretical developments if it if it continues to give us new ways of looking at ideas that we've been thinking about for a long time or even new ideas and there's logical development until these extra dimensions or not and we don't know the answer to that but I think that certainly if we find experimental evidence then they're going to be part of the Canon if they don't I don't know how old receive

Channel: Closer To Truth

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Keywords: Lisa Randall, Closer To Truth, Harvard, PBS, physics, cosmology, theoretical, dimensional deconstruction, science, time, space, university, college, education, teaching, learning, learn, cosmos, laws, why, abstract objects, quantum physics, particle physics, string theory, quantum mechanics, relativity, knowledge, truth, STEM, women in STEM, school

Id: DJUnw8CHzsk

Length: 10min 30sec (630 seconds)

Published: Wed Nov 27 2019