Video

The Runaway Universe

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ah there's a

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good evening everybody we're going to try to get started there are a few

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isolated seats in the auditorium if there's a seat open next to you please

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put up your hand okay people at the back you can see where people have the hands up for those of you who can't find a

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seat in the auditorium I'm afraid to left to take a seat in the in the foyer we can't have people sitting in the

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aisles so I'm going to give people a few minutes to find a seat we still have

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people coming in the front gate so I don't want to keep up those of you who

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are timely that's for sure need a bigger

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boom okay so any other open seats okay

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so apologize to those who can't find a seat there are seats in the foyer and there is a screen so you will be able to

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both here and and see the transparencies so good evening can everybody hear me

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welcome to the Stanford Linear Accelerator Center a warm welcome to you

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all we're pleased to see you here very pleased that people have found our

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public lecture series to be so interesting we are filling this hole every time we have this lecture which is

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very heartwarming you're at slack slack is a department of energy science

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laboratory it is run by the Department of Energy by Stanford University who are

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the contractor so slack is part of Stanford University the research that is

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performed here is all in the open public domain we don't do anything that is classified to do everything in the

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public domain and researchers from around the world around 3,000 of them from 30 different nations propose and

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join experiments use the facilities at this laboratory to conduct their research research in three main areas

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one is using accelerators to study the structure of matter at very very small

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distances we use accelerators to create very intense beams of x-rays that we can

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study materials we can study biological systems we can study all manner of

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materials where x rays penetrate and then we have recently gotten into the

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business of particle astrophysics and cosmology which is the exciting subject you'll hear about this evening the

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physics of studying matter at the smaller and smaller scales takes us back to

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early at times and that is early in earlier times in our cosmos and so the

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study of the structure of matter and the study of our cosmos are intertwined ibly

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the same study and as we've gone to higher energies to smaller subjects we get to earlier in earlier times and

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these two fields simply have become an overlapping field and a very exciting time didn't introduce myself my name is

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Jonathan Dorf and I'm the director of this laboratory a very privileged this evening to have a distinguished speaker

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Roger blandford professor here at Stanford odor of the Chen chair director

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of the newly started Caverly Institute of particle astrophysics and cosmology

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roger is very distinguished member of the international community of scientists a theorists the prominent

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researcher a very influential leader in the world of particle astrophysics and

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cosmology we were very fortunate a year and a half ago to attract him away from

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Caltech bring him here to Stanford to head a new calves the institute of particle astrophysics and cosmology I

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think you'll have a great time this thing to Rogers lecture tonight the

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lecture comes in an extraordinary time in our history a time in which we are learning things about our cosmos that we

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didn't dream about maybe even five years ago you're all familiar with the

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luminous aspects of our cosmos the things you can see the stars the things

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you capture with your eye when you look up many of you probably know that we've

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known for some time that there's a large fraction of our universe it's dark it does not luminous we don't see it we

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sense it it's out there that's one of the mysteries we're chasing what is the dark matter in our universe but recently

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we found yet another conundrum of extraordinary proportions we found that

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our universe and as outer edges is expanding but it's accelerating in its

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expansion now what holds the universe together what gravity holds the universe together

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if the island nethers of the universe are expanding increasingly something is

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winning the tug of war against gravity we don't know what it is it's this

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conundrum and others that I've mentioned that Roger will focus on with his lecture tonight I'm very pleased to

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welcome Roger Lansford well thank you

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very much John and thank you very much to you and all your colleagues here at Stanford for your warm welcome to my

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colleagues and myself in the 15 months that we've been here in the Stanford community what I'd like to do in this

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talk is discuss three propositions that

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the universe is flat that is accelerating and that it's lightweight and what I'd like to do in this talk is

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to try and explain to you firstly what these words mean in this context how we

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know these statements to be true or think that they're true and then I'd

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like to go on to say why this might be so and what we must do next to

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understand more about the universe as we've discovered it to be over the last five years or so so let's just start off

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with the first proposition that the universe is flat many of you will have

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memories perhaps not too Pleasant of high school geometry you didn't know

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there's a three hour exam after this will take up their scripts of the other your exam papers at the end okay some of

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these names may be familiar to you you docsis and Apollonius two of the

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greatest greek geometers and then you cleared who although not one of the

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greatest geometers was one of the greatest teachers and textbook writers and they proved a many theorems and one

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of them which say in a language is slightly more modern language is that the sum of the

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angles inside a triangle like this on a piece of paper is two right angles 180 degrees as we'd say now now one of the

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things that you could did was to in writing his book was to recognize

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something slightly curious it's known as Euclid's fifth postulate the Greeks as

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you know were very keen on logic they were very keen on deriving results from

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assumptions and he recognized that there was something that he could not prove

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from elementary principles and was in fact a postulate an axiom hypothesis if

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you like and I stayed in the very sort of jock almost oculus sense rather than

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the precise mathematical language we might say that parallel lines meet at

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infinity and he recognized it was great credit that that was an assumption now

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if we adopt this we can generalize we can use all the geometry on a piece of

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paper that you cleared and his contemporaries derived and go into a

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third dimension the piece of paper is two dimensions we go off into a third dimension we call this three-dimensional

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Euclidean geometry and this is something that is used without thinking by

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engineers and architects and their everyday work here is the computer

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generated image of the Fred Kavli building which is now under construction just on the other side of the green

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outside and this is what we hope it will look like in about 15 months now the

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architect Steve dangerman I don't think he wakes up every morning in a cold sweat wondering whoops is euclid's fifth

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postulate right when my buildings fall down I thought he was ever heard of u-kiss 50 are celebrities computer

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programs probably haven't either but he he know the less builds buildings I've

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seen them the square and so and I hope this one will be so but there

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is a possibility that we could say that Euclid's fifth posture that was wrong and then see where we would go in the

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Greeks who were very logical would very much approve of us exploring this possibility just to give you an inkling

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of what I'm all about just consider here a very simple sketch of the earth imagine this is a three-dimensional

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globe and I could have done it this way but you can imagine it on in two dimensions and imagine an excursion by

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car and boats on the surface of the earth no Aviators or minors involved in

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this experiment go from the North Pole to a point in the equator go along the

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equator and then return along a line of longitude back to the North Pole we regard those on the surface the

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two-dimensional surface of the earth are straight lines they're the shortest distances between points and if we adopt

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the angles in that triangle we find that they're not equal to two right angles the three right angles of 270 degrees

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this is a geometry that you might think is cheating but it is a geometry that

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violates the assumptions of Euclid's

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fifth postulate and the reason why is because the surface of the earth is

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curved and the man who in some sense understood all of this amongst the Greek

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geometers is Archimedes Archimedes who you may think of just as the you reach a

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streaker but I think I was one of the three great mathematicians of history a man who's

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independent thoughts and achievements think those that we know of and there

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are many that were probably lost place him as a mind in the in the modern in

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with the moderns and one of the things that he understood extremely well was

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the geometry is a set geometry of a sphere in fact to do this he was using

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differential and integral calculus nearly 2,000 years before it was

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reinvented by mutant live nets and others so the key point here is then is

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that we have a different type of geometry on the surface of a sphere where there's a whole lot of different

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theorems and so you'd have to go back to school and learn them all over again ok

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Archimedes how I mentioned parenthetically was the sun was a

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mathematician he was most proud to be a muffin he was also an engineer but he was i can say with pride the son of an

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astronomer which at least substantiates our claim that we belong to the world's

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second oldest profession now all of this may be cheating because

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it's just a sphere in three dimensions in flat Euclidean three-dimensional space but it isn't there's a really big

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idea here if we go back to our two dimensional geometry on a piece of paper

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we can imagine two ants crawling along their parallel lines and never meeting

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they won't get to infinity they'll get exhausted but they'll but they will never meet on their parallel lines if we

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went to the surface of a sphere here sewn appropriately enough tonight as a baseball then they will find positive

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curvature and they will meet it's different if we went onto the surface of

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a saddle we'd find negative curvature and they wouldn't meet in fact there are many lines that won't meet now the big

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idea is that you can construct logically and incontrovertibly two-dimensional

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surfaces but a curve like the ones I've sketched here that cannot exist in

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three-dimensional space they cannot sit in three-dimensional space and yet they exist and that was a remarkable

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discovery there were many people who made it in the 19th century and one of

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them for those of you are old enough to recall Tom Lehrer is Bubba jet ski and

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here I in fact would tell of a little get in this pack picture but actually Lobachevsky was almost certainly

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anticipated by another mathematician the

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second of the three great mountains of history will meet Karl Friedrich gas and

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what here he is on a on a banknote a German banknote no longer in use of course and and he actually not only

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realized that it was a possibility of non-euclidean geometry but he actually

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asked the question well is it really true that the space in which we live is flat and so the story is that he went

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out to the local mountains near brunswick the heart mountains and he went

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and surveyed them now in practice I almost certainly didn't do any of these things he's just sat in his office and

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somebody else went offered and surveyed them and he sat in his office in any act he was a very good mathematician so he

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could add up the angles in the inside of the this triangle and he found they got

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180 degrees so he proved that at least on the size scale of Germany and who care to who had any bigger than that the

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summers is it work there we go the sum of the angles was whoops so the sum of

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the angles was 180 degrees and so it looked like it was flat in fact you two had to have much more accurate surveying

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equipment that we can even muster today to show the small amounts of curvature that are in practice there any rate this

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was my sort of preamble to explain what it meant to something to be flat and it's a question that we can ask like

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Gauss Ted but as orbit jet ski himself actually suggested of the universe at

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large we can ask if triangles in our universe at large if the sum of the

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angles really adds up to 180 degrees all the other properties that go with being flat and you might think this is a

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pretty dumb question because that's a reasonable thing to assume and but for a

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long while of so strongly most cosmologists and physicist really did believe the universe was not flat but it

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was negatively curved but the experiment has recently been performed it's been

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performed by looking at the microwave background as I'm sure all of you know

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the microwave background is a relic radiation from the Big Bang that we look

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at from a time when the universe was a third of a million years old instead of

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the 14 billion years old that the universe is today and if we look at the

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microwave background a small patch of the sky looks like this and what we see

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are features of a certain preferred size you can see them here in this is about the same size as the full

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moon you can see outside tonight so you see these features and they constitute a

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measuring rod and we can calculate how big that measuring rod is and we can look at it with light rays that come

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from us come from it to us and the most recent and most accurate determinations

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have been done by a satellite called w map that's in orbit as we speak making

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measurements and we have here it's essentially forming a triangle and by

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adding up in a special way there's a lot more to it than this of course but this is the essence of what's going on by

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adding up the angles inside this triangle we can actually perform the test and see if the universe is flat and

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what we have discovered is to about two percent accuracy the universe is flat so

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it's a little bit of an irony here if we

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go back to the days of Columbus and his much fame sailor about sailors they

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thought the the world was flat and they were going to sail over the edge of it and he turned out to be curved by

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contrast us astronomers thought the universe was curved and it turned out to be flat so you shouldn't treat trust

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anybody I might also mention like many other measurements that I could make

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this is a real fear of experimental tour de force these fluctuations that you see

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here are a few parts per million it's almost completely smooth they're tiny fluctuations and you need very sensitive

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telescopes least 8 40 years to get to this point but it's been a remarkable accomplishment to make these measurements so we said the universe is

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flat now let's turn to the second proposition that it's accelerating I must go back again to the beginning and

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discuss how things move

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well this is again a problem that that in feed the Greeks Aristotle who

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although he is known to ethicists and philosophers and so on as one of the great servants of antiquity is no to

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physicist for having got almost everything wrong and one of the things that he said was that thing's arrows and

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stones and so on kept on going because they were pushed in the air so rushed behind it kept on pushing it lots of

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other sort of very strange ideas now the

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person who is credited with a hit he essentially ruled the roost for eighteen

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hundred years or so so the person who sort of credited with having set us on

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the right track although earlier people in fact had got the right idea to with Galileo but Galileo and his young man

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was a follower of Aristotle a scholastic as they were called here he is again on

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an Italian bang no you see there's money in physics so then but I don't use it anymore it's no good to you do Amelia

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half okay now what he said was if he dropped something on the floor like that

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that's not her that's what happened to you sometime okay I'm drop this on the floor like that I'm going to eat this

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and then he said that in his scholastic phase that the speed with which that

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Apple of the stone or whatever it was would fall increased in proportion to

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the distance now he deduced this law by pure fort it's a quite clever argument

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not a very clever argument and he's just plain wrong but nonetheless he did this by pure thought he was a theorist like

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me you see now but to our Galileo's eternal credit he didn't stop there he

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realized that he had the opportunity as indeed others before him had to perform a measurement he realized that he could

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drop a cannonball or some other volley from the Leaning Tower of Pisa now I

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suspect that like many of these other tales this never actually happened he was just trying to explain to people what he had in mind or

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maybe somebody else did it but he performed the equipment we do know he performed the equivalent experiments and

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what he found was and I'm probably over simplifying slightly here is that in falling one floor the Cannonball takes

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one second but it falling in falling

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four floors it takes two seconds and if you think about it for a moment what

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this is saying is that the speed increases in proportion to the time if we double the time we double the speed

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not double the distance and double the speed and so this is Galileo the scientist this is what he said and this

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was in fact one of regarded as one of the sort of turning points in the development of Science in the urine

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essence because it showed how you could really get the important correct and useful answer by performing the

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experiment rather than just by thinking about it so just to reinforce this point

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if we look at the experiment and look at Aristotle Theory there really is a

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difference if we make them synchronized say at the bottom of the first of the

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first rule from the top then you can see at one second two sec what excuse me

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let's go back again one second after one second and after two seconds where first

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floor and then the fourth floor in in truth in experiment but in Aristotle's argument where the speed increased in

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proportion to the distance we fall from there to there in one second from the hair all the way down to the bottom it turns out in two seconds and he was able

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to distinguish that so that's very important and that's paper all part of the expanding purse of the scientific

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process now now let's try and apply some of these ideas to the universe the

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universe as you know is expanding a discovery who was made or quantified at

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least by Edwin Hubble shown here smoking his pipe and he essentially said that if we look at

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nearby galaxies and measure their speeds and measure their distances then the

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speed goes as the distance this is known as Hubble's law how do astronomers in

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practice measure speed a measure distance you can't sort of go out there with a stopwatch or something like that at least I don't think you can watch

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late-night TV you may get different ideas but there you go so what one of

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the there are many ways that astronomers use to measure distances one of the ones

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that's proving somewhat surprisingly to be the most effective is to look at supernova explosions and basically

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distant galaxies have explosions of old stars which make them shine bright

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almost as bright as a galaxy for a month or so and then fade and by measuring the

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brightness of that supernova explosion there you see it and now you see it they

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you'll see fading again by measuring the brightness of that supernova explosion

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then you know what the luminosity is you measure how much energy comes into a telescope now that gives you a measure

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of the distance if you imagine somebody with a flashlight and they stand 10 foot away from you the flashlight looks very

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bright if they stand 20 foot away from you it's four times fainter and it's that effect that the astronomers are

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using to measure the distance how do astronomers measure speed or what they

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do then if they use an effect called the Doppler effect to explain this I should remind you that

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light is as you see visually is decomposed into colors here a good

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example is the rainbow from red to violet and this is the spectrum now that

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of course is is ultimately a solar spectrum and if you look at the solar spectrum with a very sensitive instrument you will see as you see from

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many cosmic objects that in fact it isn't a continuous gradation of color from the red to the violet but you can

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see a lot of very special lines in there very special wavelengths the correspond

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to the wavelengths of light that are emitted by certain atoms like hydrogen and the wavelength of the light is

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lengthened if the source of the light recedes from us this is known as the red

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shift and the whole effect is called the Doppler effect and it may be familiar to

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those of you who've been chased by police on the freeway or whatever and then you police car comes up behind you

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and you hear a high-pitch as is approaching towards you and then it's not you there chasing they go straight

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past and then you hear a low pitch as it goes past you that's the sound version of this astronomers use the light

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version because Sam doesn't do too well in intergalactic space so they use the light version and the lite version gives

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you a shift in the how we do that one now there we go from the shore went for

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the long wavelengths it gives you a shift in what we have here this is the comparison spectrum at the telescope and

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here's one particular spectral line it's a line of hydrogen associated with hydrogen atoms and then it shifted

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towards the red by this amount here this is a measure of the spectrums of that amount there by measuring that you can

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tell her what tell how far away for a child with receding space or the

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recession speed of the source and this is a very famous spectrum it's the first one that was used to find the very first quasar so that's how astronomers measure

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speed the Doppler shift so let's just show you what the expanding you

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verse in the very amateurish simulation might look like we have that focus on

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that white galaxy in the middle and we can see the other galaxies moving away from it like that so as we saw the

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universe expand we actually saw the distance between this white galaxy in

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that blue galaxy more or less double as you can see here so the start to the end

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the distance doubled then there's a yellow galaxy you can just see there you can see down there it's a rather faint

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one and that distance is also doubled so

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what happened is the yellow galaxy is at all times twice as far away as the blue galaxy and the blue galaxy doubles its

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distance the yellow galti doubles its distance in the same time and so therefore the speed of the yellow galaxy

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is twice the speed of the blue galaxy that was the law that Hubble discovered

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and it's if you like the first approximation it turns out to be true the details Hubble actually got wrong

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but that's another story but we know that in an outline it all is correct now

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what we have done since then is use these supernovae they're fluxes and

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their and their velocities and their speeds to not look not just at the speed

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but to look at corrections to this law and the very remarkable thing was discovered what was discovered is

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perhaps shown here if we look at say let me just go on if we look at ten billion

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years we find the separation between our old white galaxies and the blue galaxies

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and there's the galaxy there we just take a look at the white and the blue in 10 billion years that's the separation

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between the galaxies I'm sort of reconstructing is if we have some sort of celestial perch from which we could

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peer down on all of us okay but we can reap by measurements we can reconstruct this after 12 billion years it's

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increased and so that separation has increased a bit and after 14 billion

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years which is more or less where we are now not quite but almost then it's increased

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a bit more and what we find is the increase in the separation from 10 to 12

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billion years is less than the increase in 12 to 14 billion years the speed is increasing that's what we mean when we

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say that something is accelerating the speed increases and what we have found

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is quite contrary to our expectation or for most of us our expectation that the

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universe is accelerating so that's the

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second of our propositions let's go on to the third the universe is lightweight what do I mean by that now I come to the

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third of my great mathematicians Isaac Newton no less and he invaded the law of gravity and what he observed was the

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gravity causes apples like this and the moon to accelerate and it's the same law

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the works on apples falling off the tree in wolves Thor and the moon going around the earth they're both accelerating and

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gravity is doing its work on both of them now this is encapsulated in

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Newton's law in words it basically says that force causes acceleration but

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probably says that in Latin if you go back to the brink appear but this is it in English if you wanted right a

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shorthand as an equation you'd say the famous equation F equals MA and notice the Prem stands for the Marseilles for

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the acceleration a net for the force and

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what's important for my story is with that mass there by looking at the

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planetary motion this measures the mass of the Sun so by measuring the acceleration of the planets as they

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change this their velocity as they go around the Sun you measure the mass of the Sun now we can astronomer can go off

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and carry out an analogous experiment not using planet but using a distant

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cluster of galaxies and this is what we have done

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this is basically an accumulation of about a thousand galaxies they're the

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yellow ones there and we can measure their speeds and their distances using techniques like I just described and if

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we do this we applied Newton's law just the same as you did to the planets and we find that the mass within this is

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basically about six hundred trillion Suns worth of mass we measure the mass this way I just want to say

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parenthetically I want to draw your attention to this beautiful image from the Hubble Space Telescope I want you to

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see all these gravitational lens arc see because I'll return to them later just observe them here these long elongated

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features that background galaxies whose images have been highly distorted I'll

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return to this later by gravitational lensing will see this a bit later okay

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let me just move on clusters do not just

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contain galaxies and stars within those galaxies they also contain a lot of hot

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gas and we know about this and we can see it and we can measure it by measuring the x-rays that it creates the

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hot gas creates x-rays and we're using x-ray telescopes like the Chandra x-ray

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telescope we can study it in considerable detail and we found something rather surprising that the

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mass of this gas which is actually most of the mass in the cluster of galaxies but we can also include the galaxies to

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if we have they say the galaxies and the mass together then it's about a hundred trillion Suns so the mass that we can

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see is only about 16 of the total that

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Newton's laws told us should be there and this phenomena is also true of the

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individual galaxies themselves so the conclusion is the 56 of the mass of the

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universe is not seen directly this is the dark

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matter that Jonathan mentioned so what I've done is say the universe is flat

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accelerating and lightweight and I've done this in a rather deliberate way I presented you with the evidence and I

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haven't actually tried to put any interpretation on it I've just presented you with the evidence and I just like us

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to absorb that now and as I come from Southern California on its natural at

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this time to have a commercial break or a message from our sponsors this is sort

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of a higher quality operation and the commercial break is that the will in

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fact be more unless you're all driven away by the quality of this lecture

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there will be further lectures in this series to be enjoyed or suffered this one we brilliant lecture I know because

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the lecture is very good on magnetism and x-rays from the compass of modern

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technology by you q mr. who is here in the SS RL and you can find out more

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about this I nevitt ibly on the web and you can also sign up for a tour of slack so please come along to that lecture 2

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i'm going to be here it'll be a great lecture ok so let's go on with the

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second half of my lecture I presented you with the facts now I'm going to try

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and put some interpretation on it and I've given you enough cautions about theorists that you can take what i have

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to say with whatever pinches of salt or any other substance you may find helpful under these circumstances i'll also sort

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of say if you is any doubt left in your mind that i know what i'm talking about how we might explore these issues

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further okay so i gotta do some reverse order let's deal with the proposition

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that the universe is lightweight and we'll talk about the light and the dark

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basically what I've said is the galaxies that we see here and these things are

36:21

actually one of the this is the faintest image taken by Hubble Space Telescope which you're actually seeing on the

36:27

screen here so she'll be treated with some reverence this ok so these galaxies here famous galaxies that we have been

36:34

able to see actually what you're looking up there is the light this is the light

36:39

from the stars in those galaxies but in fact what we what we know is that an

36:48

individual galaxies say with ten billion suns is surrounded by a halo a much

36:55

larger region containing this dark matter the ways about five times as much

37:01

so in every time you see one of those galaxies you've got to imagine that invisible halo of dark matter around it

37:07

that is the dark matter and in some sense the stars are sort of in significant afterthought in the real

37:16

dynamics of the dark matter which is really ruling the roost under these circumstances this is true of all of

37:24

these galaxies and it's true in fact of the universe at large in fact dark

37:29

matter is everywhere this idea is not new there are many precedents for it in

37:37

the history of ideas and one of the most famous is manicheism in the third century a Persian mystic or money

37:45

proposed a philosophy a fusion of Christianity and Persian ideas it was

37:51

both a theology in the cosmology he saw the universe as a mixture of light and

37:58

dark stuff and these represented to him good and evil man EK ism is an elaborate

38:05

story with its fundamental elements in

38:10

it our light wind fire water and breath a little bit like what Aristotle said but a little bit different and all of

38:17

this good stuff the light wind water fire and breath and all of that is trapped by all the bad dark stuff

38:25

and the light stuff has to escape to form an inert heaven on earth and then

38:33

sometime later in this story in this cosmology in the original sense of the word life emerges still contaminated

38:41

with the dark stuff which is bad there is really not a bad metaphor for what's

38:47

going on here now manicheism died out in the 13th century although some claim

38:54

that is having a revival of the present time but we now think about this problem

39:01

in a much more scientific way as a manicheism if you look actually create a lot

39:08

of beautiful art if you look at our new elements now our other words they would

39:16

be fundamental particles and the story that we tell now is called the standard

39:21

model we have here the neutrinos the

39:27

quarks and the particles that are meant to help them interact with one another

39:32

and slack I might say parenthetically had a big role in devising this standard

39:39

model here's dick taylor and his part but richter and his marty pearl and hit

39:46

and of course there's much more of this that has its origin from local

39:51

physicists the standard model comprises a list of fundamental particles and

39:57

their properties and together with the rules for their engagement and for 30

40:02

years it is it is withstood a ferocious experimental onslaught experimentalist

40:09

have tried to knock holes in it try to bash it and change it and they frankly not been terribly successful it's really

40:15

stood up to a lot of criticism and

40:20

experimental tests and all these measurements have been made all these numbers are known to large numbers of

40:26

significant figures it really is a remarkable intellectual and technological achievement and one that I

40:32

don't think has been ever fully appreciated in the world at large

40:38

however it's incomplete there are many ways in which there are questions that

40:43

are not answered by it and it is quite possible that there are many more particles that not included within these

40:50

are in the standard model now I'd like to draw your attention to the two

40:55

classes that are here that are known as fermions and bosons they're actually

41:01

named after people believe it or not but these are fermions and bosons and for present purposes all you need to know is

41:08

that bosons are very gregarious and friendly sort of people you'd like to

41:13

meet and fermions are the opposite they're totally antisocial and really quite unpleasant but if you go beyond

41:25

the standard bottle there are many people who think including myself that there is a second family of

41:32

supersymmetric particles out there in which is some sort of gender bending

41:37

symmetry transformation the quarks and the electrons become the bosons and the photons become the fermions and so we

41:45

have to give the different names like squawks and select ron's of the dates as many ways for having jokes in this

41:51

business and so it could be that out there not seen and not created by the

41:57

present generation of particle accelerators this total new set of

42:02

particles and perhaps one of these most favorite something like a fo t know is

42:08

the dark mother now if we carried this idea further as theorists and use what

42:14

evidence we have from astronomy and from physics to try and guess where to look we deduce that the mass is about the

42:21

same as that of 100 protons the average spacing will be about in intergalactic

42:27

space about three meters between these particles in this room it'll be about five centimeters Chuck ok speed a

42:35

thousand times the speed of sound roughly or 1,000 the speed of light if

42:41

you prefer it so what are we doing about it well the

42:50

first thing is what the Swiss are doing about it and the Swiss are of course the hosts of a large international

42:56

collaboration that is building the large hadron collider and hadrons means protons and here you have beams of

43:04

protons which are sent around is enormous speed and collided into each other and one of the big hopes of these

43:11

experiments which will start in 2007 is that they will in cover the first direct

43:17

evidence for supersymmetry now slack

43:22

doesn't do protons but they do do electrons and their partners positrons

43:27

and slacks role in this is to get involved in the linear collider which

43:33

will be the next big accelerator that will actually explore supersymmetry if

43:41

it can be found at the Large Hadron Collider as many of us believe that it will and so this is what the soup the

43:47

linear collider will do here in about 2050 and many people here are working

43:53

very hard on trying to design what again will be another of these great marvels

43:59

the largest particle accelerator of its generation there are other ways of

44:08

exploring this right there we go it's

44:13

possible to look for these particles directly I've given the impression that they're quite inert they are pretty

44:20

enough but not totally inert and very occasionally one of them will hit a

44:25

regular atomic nucleus and create an

44:30

event which can be seen in the detector you have to do this experiment to look for this on the ground my colleague

44:37

glass Cabrera here is leader of a team that is doing this deep down in mines

44:43

he's the one with the hard hat on miss him and and he's looking we haven't

44:49

found any yet for dark matter particles colliding with normal matter but there's a little bit of optimism that if they

44:55

just dig deeper as they used to say in the movies then he will find one there's a good

45:01

chance that you will that they will actually there's a fair chance that they will find something and so the maybe

45:06

they maybe even the people at the particle accelerator bit of a race on

45:13

another way that involves slack and Stanford is to use the gamma-ray large

45:19

area Space Telescope this is a telescope that should be launched in 2007 and it

45:27

will have look at gamma rays from many different sources and one of the chances that it has is a finding indirectly the

45:35

dark matter through the gamma rays that it might create when it collides with

45:41

itself and it can crow actually create photons this again is a bit of a rare event but gas may be able to see it so

45:53

those are the ways that we're trying to look for the dark matter particles and

45:58

understand what it is let's go on to

46:04

talk about why is the universe accelerating and here along last is the

46:11

figure you've all been waiting for Albert Einstein again he's on his this

46:17

time an israeli banknote there now Einstein is famous for many things

46:23

including especially the general theory of relativity and in words his great

46:30

insight was that gravity is not a force

46:36

as Newton described it but is actually a curvature not a space so much but a

46:44

space and time and we call that space-time it's four dimensional or three dimensionals place plus time we

46:50

call it space time and just like the surface of a sphere is a two-dimensional

46:56

curved surface there can be four dimensional curve space-time and what he proved or postulated at that time was

47:05

that there was an equivalence between the curvature of space-time

47:11

I'm the amount of matter in it or energy they're equivalent that we're around and that's codified in this famous equation

47:19

here G equals 8 PI T in suitable units I'm not going to tell you what G is but

47:24

it's a measure of the space-time curvature of the gravity if you like H you might be worried about but pi is

47:31

about three in a bit and T is a measure of the amount of mass and energy that

47:36

you've got ok so that's just the way we would think about in terms of equations

47:41

now Einstein produced this theory which has been tested and its consequences

47:47

have been measured to now better than a

47:52

hundred parts per million and so we have

47:57

pretty good confidence that it's um this theory is correct at least in the wheat field limit but there's no guarantee

48:04

that is true on the scale of cosmology and so one of the things that is truly

48:13

remarkable about Einstein was that he recognized by pure thought by symmetry

48:20

if you like by applying a sort of symmetry type argument that the and the

48:26

cosmological scale this equation shouldn't be just like that we could add

48:31

an extra bit to it and it was the genius of Einstein to realize and to retain

48:38

this possibility he called it lambda this term it's known as lambda the Greek

48:43

letter lambda or the cosmological constant and he recognized on quite general grounds that might be there it

48:50

might be important for cosmology

49:00

nowadays we will call this stuff that there's represented this is if you like

49:06

the amount of matter that we've got we call that the dark energy that would be

49:12

a sort of colloquial term for it now now if we go on and say well what did they do Einstein tried to create a cosmology

49:20

he hadn't met hablar at that point he didn't know the universe was expanding and the naturally enough the cosmology

49:27

that he created was a static one it had this lambda term here that was pushing

49:34

out and gravity pulling in there was just matter there but everything was at rest his Dutch contemporary Willem de

49:42

sitter in 1917 elucidated what this lambda was all about by making a cosmology in which there was no matter

49:49

it was a purely artificial thing but there was motion he was an astronomer

49:56

she said uh this is a meteorologist this is a Russian meteorologist this is a

50:02

real rag bag of people here Friedman matter in motion completely independent

50:08

of everybody he worked all this stuff out by remarkable intellectual

50:13

achievement with almost no stimulus from anybody outside and he created models of

50:19

the expanding universe that allowed for the universe to be expanding long before Hubble that had matter in the motion

50:26

there and then finally it was a Belgian priest called George Lamech and he

50:33

included matter and the cosmological constant as well and the motion and sort

50:38

of sort of generalized independent of freedmen nobody knew about Freeman at this time these ideas and this is it

50:44

free lometa actually correcting one assumption that he made which we no longer make that really got the the

50:51

essence of what's going on correct so what is this dark energy this mysterious

50:57

dark energy I've tried to explain the dark matter is the short answer is we don't know but there is a simple version

51:06

of it the one that Einstein used that at least will help us to think about

51:11

problem and everything we know about it so far is consistent with the simple Einsteinian view rather than a more

51:19

general view which may still be possible so I just take the simple Einstein view

51:24

and then basically this dark energy is always in everywhere the same so as the universe expands it remains the same so

51:31

what that means is that if the universe is expanding we've created all this

51:37

bigger space the dark engine medicine we've got to create more energy so we've got to replace the energy as it expands

51:44

that's a rather funny thing because if you imagine letting the air out of a bicycle tire that energy wilt outer air

51:50

will all cool off and it'll push against the surrounding gas and so on if you think a moment about it the only thing

51:56

you can do is not have pressure like you have air in a bicycle tire but you have

52:02

tension so if you imagine a balloon

52:08

there's tension in two dimensions there on the surface of the balloon if you imagine a rubberband like this this

52:15

tension there in one dimension what we have in this dark energy is tension in

52:20

three dimensions alright so there's tension are not pressure in this dark

52:28

energy that's a remarkable thing and there's an even more remarkable thing that happens is if you think through

52:34

this through is the combination this tension in three dimensions and the energy the dark energy itself leads to a

52:43

reversal of Newton's law instead of having an attraction we get a repulsion

52:50

the famous string theorist and popularizer of science Brian Greene described this situation the way that

52:56

only in New York accord he said we live in a pushy universe and eventually if we

53:05

let this habit sway the speed will go as the distance eventually so galilea the

53:13

Scholastic may have known something after all what is this dark energy well

53:18

we don't know I've emitted that but there are of course a thousand theories out there the most simple and prim

53:24

visit is an energy associated with the vacuum this is a perfectly reasonable idea what is not reasonable is the

53:30

amount of energy associated with it it could be a new field bit like the magnetic field but different it could be

53:38

something like that sometimes in despair physicists and astronomers will call it

53:45

quintessence they were hark back to our good friend Aristotle who of course

53:51

invented quintessence he had earth fire air and water where his natural elements for the stuff like you and I and then to

53:58

explain what was going on the heavens which he got all wrong he had this mysterious ethereal stuff which was

54:05

called quintessence now I think really probably the joke is on us because we

54:14

may be just as wrongheaded as Aristotle was in our attempts to understand what's going on so maybe quintessence isn't

54:20

there bad a bad thing to to call it so what are we going to do about this well

54:27

locally we're very excited about a large telescope project called LSST it's an

54:32

eight meter telescope and it will observe at a given time 50 moons worth

54:38

of the sky and it'll take a picture about every 10 seconds with 3 billion pixels you won't get that from Kay Bart

54:47

okay and its main purpose is to look at gravitational lenses it will have lots

54:54

of other things that will do and by either studying these gravitational lenses it will be able to measure the

55:02

properties of the dark matter and the dark energy from an astronomical perspective there's a second project

55:08

called snap which is collaboration lead led by our neighbors of the Lawrence

55:13

Berkeley Laboratory and we're very excited about this one too it will be a complementary telescope that this time

55:20

will be in space it will be 2.5 meters it will produce Hubble quality images go

55:26

into the infrared and its main purpose and it will have many others as well but

55:32

its main purpose what we look at those supernova I told you about so we can understand better the kinematics of the

55:37

expanding you verse let me turn to my final the last

55:42

proposition the one with which I started why is the universe flat

55:48

well there was in fact a theory it was the theory called inflation it was

55:55

dreamt up by Alan Guth who at that time was a postdoctoral fellow here at slac

56:02

and has been developed bubblies mysidia says anybody by my current colleague a

56:09

professor here at Stanford and raelynn day and basically they propose something

56:16

really rather similar to dark energy but operating in the very earliest times of the universe they said there was a

56:22

fundamental field there was just like dark energy called a very rapid acceleration in which the speed went

56:28

proportion to the distance and the consequences of this inflation our kites

56:37

are quite simple firstly there is a flat space the reason why and to show you

56:42

here is that if I imagine a balloon like

56:48

that and then I just look at the surface a small region on the surface of this bloom say between my thumb and

56:55

forefinger you can see a lot of curvature there but then if i expand it

57:03

you will see this much less curvature between my thumb and forefinger now I keep on expanding it many times over

57:09

over and over and over again it must end up very very very very flat well I

57:19

better not let it do that because the Big Bang is supposed to be before not after they is raised um okay has other

57:26

consequences has quantum effects associated with inflation and these

57:32

cores tiny fluctuations those the fluctuations out of which the galaxies grew and you and I developed so we have

57:39

a personal interest in this and those fluctuations create this microwave background stip lingual ripples and they

57:46

will also create some gravitational radiation some ripples in space-time itself and here we can perform lots more

57:57

experiments to look for the ripples in the microwave background of

58:02

special sort that are polarized and would be a hallmark of the gravitational

58:10

radiation from the earliest time in the universe perhaps in the epoch of inflation and my colleague here say it

58:16

Sarah church is soon to go to the South Pole with her telescope and we'll look

58:24

at these fluctuations and look for the polarization in them polarization like you see with polarized sun polarized sun

58:31

closer izing sunglasses Polaroid sunglasses and she's looking for a very special pattern which may be this

58:39

experiment of some successor experiments will see which will be a telltale signature of the time to inflation we

58:46

don't know what we're going to find but it's a very exciting prospect gazed upon

58:52

the other way to do this and this is a much longer shot is to see this these

58:58

ripples in space-time from the earliest stage of the universe directly this will be very hard but it's something that

59:05

people at least are dreaming about at the moment a step along the way is a project that my colleagues in Applied

59:11

Physics baba Liggett by buyer and his colleagues have been working on for some time to measure this gravitational rage

59:18

gravitational radiation often cosmological sources but produced by

59:23

orbiting black holes and similar types of object so this is a pretty sort of

59:31

exciting time to be around and contemplating the this activity so what

59:38

I've tried to show you in this talk is the universe is flat accelerating and lightweight my time is almost up and I

59:51

try to explain these cset through simple propositions to you I tried to show you

59:57

why we now believe them to be true and to present some of the most popular

1:00:03

at least theoretically Asians of what is going on I've also tried to outline some of the very exciting projects many of

1:00:10

which were involved in here at Stanford but we hope will test these theories

1:00:15

it's a wonderful story that I think I've been able to tell you well i have i've been able to communicate it to you I

1:00:21

have to say I feel highly privileged to be around and working at a point in space-time where so much is being

1:00:29

discovered now preparing this lecture I be impressed but for all the

1:00:36

technological sophistication of contemporary telescopes and the austere

1:00:42

beauty of modern theoretical physics most of the ideas that I have described

1:00:47

to you have deep roots in our culture the geometry can be traced back to the

1:00:52

Greeks the kinematics and the dynamics to their innocence and our invocation of

1:00:58

dark matter and dark energy would hardly surprised and then break and chain of philosophers priests mystic stretching

1:01:05

back to the dawn of recorded thought I think that are as we contemplate a

1:01:13

universe that promises us expansion a

1:01:20

sort of cosmic alienation and eventual decay the fact that earlier generations

1:01:27

have found the expiration of these ideas both exciting and fulfilling is a

1:01:33

thought that I personally find comforting I hope you do too thank you very much indeed

1:01:59

those are young people with black hats outside to available to answer questions

1:02:05

for people as you have some refreshments and weather may be on how you do that I

1:02:13

thought the idea was actually to do this at our website we just won a series of

1:02:23

questions yet show slide earlier on the gravitational lenses and you mentioned

1:02:28

some curve next we will talk about later like this better no prob which is not

1:02:35

right the relativity talk so we're good I'm glad you asked that question and

1:02:41

this is why I love this stuff ok here is the hope is that on a deep field seen by

1:02:48

the Hubble Space Telescope I gave the film if you put a gravitational lens in front of it which is a sort of galaxies

1:02:54

like that you can help it like a great then you can see I think those are in

1:02:59

the front and you've come a look at this later you can see he creates distorted in particular tangential elongations of

1:03:07

these background images we can do this way you want to do this at home and then

1:03:13

you can take a away laughs like that and just stick it down sometime script I

1:03:18

first and just look at it and you'll see exactly the same event I need to drain the wine glass

1:03:27

these this is the effect and basically what's happening is the force of gravity

1:03:32

pulls on those photons into light and deflects their ways just in an analogous way the one this Plexiglas experience in

1:03:42

fact is the how gravitational field effectively has a refractive index of those humans each other's and so the

1:03:48

same sort of orchids to be used to design telescopes let residents are applying foundation lenses we use this

1:03:57

now ultimate superiors at all is that all the measurement is a total measurement existence is it is at all

1:04:04

for measurement of mass because the amount they need depends on the amount of that so it turns out that which i

1:04:10

showed you that cluster of galaxies through several ways of measuring the mass we can counter the amount of mass

1:04:15

associated with emitting x-rays on the stars we can also gather up the Novalis

1:04:22

associated with moving galaxies and then we encounter the mast estimated by the brass sectional lenses the story is all

1:04:28

consistent path there's basically five times as much dark matter there as there is luminous panel so thank you very much

1:04:36

frost question okay walk away from that I always here

1:04:43

I'm that compared son I think you said to

1:04:49

the sudden rheumatism there is a luminous that make the earth dark

1:04:55

who's fashioned booing at discuss thank you basically when you

1:05:02

the stomach the start of you and I mostly the protons and the electrons in the neutrons the atom of the wizard

1:05:09

familiar when I think the Sun suddenly in the Sun in the earth in the planets

1:05:15

in the gas in the from the in the atmosphere in movies interplanetary

1:05:20

media that if the start we know about the main our will be luminous but the

1:05:26

first former we may require to luminosity because most of it is in the form of either orgasm star so we may

1:05:33

require fit those be done back glowing of these conditions but around us I mean we want it to be going around us to

1:05:40

confine it someone be 1,000,000

1:05:46

degree of God but the so we we talk about the slides let me practice to an

1:05:53

astronomer it is like most of it the baby is a food pocket in the service

1:05:58

of you so in fact that's why we can exist in getting to be going on right now nor the rest of it now the older

1:06:04

stuff is totally we think we're not sure okay with our theory is this is only

1:06:10

given set of particles that are related to the world that you and I are made up but they get in front of their

1:06:16

interaction is only really strongly by geography if you have any weed interactions like any one another very

1:06:23

occasionally but mostly is just by gravity and this is this sort of nether world with many day and outside of star

1:06:29

wars whatever you want and then and not the contrast fair need this theory is right to be a very clear distinction in

1:06:36

particle physics it could be wrong from my parents had a laboratory in which he

1:06:42

says sign will we tomorrow when they respond the dog

1:06:52

me that expression it's like island orbit

1:06:57

running with three separate attention to have inside question during

1:07:09

in our universe

1:07:18

Oh

1:07:24

babe you know

1:07:30

there's one big thing somewhere in relation to that big bang equally like

1:07:35

the world could be like that remove we destroyed it as far away from sir this is a resident

1:07:44

I won't be accessible to is a tiny bit of a mood as far as we're concerned so

1:07:50

fast terrible service vendors the two-dimensional service under center with a tweaking six

1:08:07

you

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