The Runaway Universe

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

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

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

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

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

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

are timely that's for sure need a bigger

boom okay so any other open seats okay

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

of the newly started Caverly Institute of particle astrophysics and cosmology

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

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

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

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

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

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

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

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

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

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

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

we found yet another conundrum of extraordinary proportions we found that

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

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

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

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

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

welcome Roger Lansford well thank you

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

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

talk is discuss three propositions that

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

engineers and architects and their everyday work here is the computer

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

violates the assumptions of Euclid's

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

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

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

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

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

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

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

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

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

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

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

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

Archimedes how I mentioned parenthetically was the sun was a

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

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

second oldest profession now all of this may be cheating because

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

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

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

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

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

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

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

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

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

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

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

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

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

anticipated by another mathematician the

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

discuss how things move

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

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

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

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

other sort of very strange ideas now the

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

one second but it falling in falling

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

one and that distance is also doubled so

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

universe is accelerating so that's the

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

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

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

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

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

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

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

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

the acceleration a net for the force and

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

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

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

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

cluster of galaxies and this is what we have done

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

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

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

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

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

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

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

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

let me just move on clusters do not just

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

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

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

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

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

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

see is only about 16 of the total that

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

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

universe is not seen directly this is the dark

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

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

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

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

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

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

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

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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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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

story with its fundamental elements in

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

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

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

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

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

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

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

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

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

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

model we have here the neutrinos the

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

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

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

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

physicists the standard model comprises a list of fundamental particles and

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

years it is it is withstood a ferocious experimental onslaught experimentalist

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

stood up to a lot of criticism and

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

present generation of particle accelerators this total new set of

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

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

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

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

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

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

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

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

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

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

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

evidence for supersymmetry now slack

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

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

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

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

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

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

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

exploring this right there we go it's

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

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

regular atomic nucleus and create an

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

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

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

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

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

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

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

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

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

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

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

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

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

understand what it is let's go on to

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

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

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

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

insight was that gravity is not a force

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

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

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

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

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

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

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

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

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

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

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

have been measured to now better than a

hundred parts per million and so we have

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

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

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

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

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

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

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

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

might be important for cosmology

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

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

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

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

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

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

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

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

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

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

of everybody he worked all this stuff out by remarkable intellectual

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

tension so if you imagine a balloon

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

expanding you verse let me turn to my final the last

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

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

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

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

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

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

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

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

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

here is that if I imagine a balloon like

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

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

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

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

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

consequences has quantum effects associated with inflation and these

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

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

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

experiments to look for the ripples in the microwave background of

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

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

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

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

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

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

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

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

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

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

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

gravitational radiation often cosmological sources but produced by

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

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

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

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

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

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

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

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

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

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

technological sophistication of contemporary telescopes and the austere

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

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

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

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

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

universe that promises us expansion a

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

frost question okay walk away from that I always here

I'm that compared son I think you said to

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

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

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

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

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

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

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

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

confine it someone be 1,000,000

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

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

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

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

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

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

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

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

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

says sign will we tomorrow when they respond the dog

me that expression it's like island orbit

running with three separate attention to have inside question during

in our universe


you know

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

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

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

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

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