Viewing the Beginning of Time from the Most Remote Places on Earth

Zeeshan Ahmed introduces the CMB, presents the sophisticated cameras we build to observe it, and describes the remote outposts of our planet where we deploy these cameras to take pictures of this faint radiation.



I would like to welcome everybody to our

public lecture series first of all I would like to thank all of you for coming here this is a great pleasure to

see the interest in those lectures and of course for us sorry you can't I think

that this is pretty good so we appreciate this we love doing science

and of course you are the ones who are funding it through taxes so obviously this is a great thing so welcome on this

particularly important day today as you know Nobel Prize was awarded today to people who are doing work in

astrophysics and cosmology the Nobel Prize was given to people who are working on gravitational waves and in

fact the detection of them was the was the reason for the prize so let me

introduce Zoosh of math today who is research scientist at Stanford and in

fact in particular he's working at SLAC zishe was another graduate student at university of southern california and

then went on to get his PhD at Caltech and came to work with us at stanford as

a postdoctoral fellow as time went on zishe was recognized as one of the leading people in his field and also

warded very prestigious panel sky fellowship which is the fellowship awarded only two of those every year for

people who are in the mid career who are continuing towards towards the owner trajectory towards being damn very much

leaders in the field and in fact was also recognized just very recently a few months ago that dishes research is very

much cutting-edge and he was given the department of energy's prestigious early career award most of his work is on

cosmic microwave background and various aspects of it on one hand these builds

and deploys instruments in very interesting remote places around the world but he's also one of the leading

people who are develops and understands the theory of they of the results of the observation so without much more ado

let's welcome zishe here

okay let's see is this can you hear me great thank you right for that generous

introduction so hi and welcome to slack today I'm excited to share with you a

very intriguing story so this is the story of the birth of the universe as seen through some of the most

sophisticated cameras we've ever built put into some of the strangest places on

earth to to get get images using these cameras

I guess figuring out how the universe started is one of the most profound questions we can ask it's certainly a

very compelling question for me I'm very personally interested in it and and I'm excited to work on it and so we'll be

we'll be talking about the birth of the universe from these strange places these

remote places today so my title slide I should I should point out what's going on over here so this is the bicep2

camera it is located at the South Pole so the geographic South Pole is about

one kilometer in that direction from the from the point that this picture has been taken and this picture has been

taken at sunset there's only one sunset per year at the South Pole there's one

sunrise in one sunset and this because of the tilt of the earth and most of Antarctica is either in the dark or in

light for six months of a year for six months of the year so this is that the

Sun is setting and it's about to be nighttime and winter at the South Pole

the the pattern you see up here we'll be talking about this later is the

polarization pattern of the oldest light in the universe that comes to us straight from the Big Bang and this is

the kind of stuff that cameras like this try to image and I'm I'll be talking more about this okay so the the the best

way to give an overview of my talk is is probably using this cartoon graphic over here that captures the story upfront for

everybody and then we can break it down and go through it so this is

on this horizontal axis over here is time and if that's a start of the

universe T equals zero or the starting time we're here today 13.8

billion years later okay we're here on earth this is this is a satellite this

in particular this graphic was made by the W map science team 2w map is the satellite and so that's that's our

satellite and so this satellites like this in cameras and Earth are observing our universe and if we keep going back

in time we we cross there the various phases of development of the universe

okay so any slice through here is a slice in time of how things looked in

the universe at that point in time so today we know the universe is accelerating and in fact the

acceleration is speeding up okay so that's that's that's actually another

talk all in itself the accelerated expansion of the universe the regular

expansion that happened over time is where and when galaxies and planets and

structure clusters of galaxies and so forth formed and if you go back far enough in time you eventually come to

the point about 400 million years after the start of the universe when stars were were first switching on right

before then it was dark there was nothing there or that was stuff there

wasn't glowing stars hadn't turned on yet and if you'd go back even further you get to a point 380,000 years after

the start of the universe and this is the glow of the Big Bang the afterglow

of the Big Bang and it's called a cosmic microwave background or CMB I'll use the word CMB quite a bit in this talk and so

this is this is the oldest light we can't see farther than this but we can see this point okay and then we have an

idea of what probably happened before then and the stuff that happens right

from from point zero up to this point but this is this is one of the most interesting areas of research in in CMB

today so we'll talk a talk a bit about that so that's the overview let's get started

so let me start with some basics you all probably know this but a reminder is

always good so so light is a traveling and and pulsating electromagnetic field okay so if I were to draw a cartoon this

is what it would look like a light ray travels in this direction and the electric field is pulsating up and down

like this and the direction of this electric field going up and down is called the polarization okay so here I'm

showing light polarized in this direction and here I'm showing light polarized in that direction so straight

like this or or like that okay so so this is important remember that we're

talking about electromagnetic fields there are waves and the direction of the field is a polarization

okay so unpolarized light or mostly light around us is a mixture of various

polarizations but if you put it through a polarizing filter like perhaps polarizing sunglasses polarized

sunglasses then you pick out one polarization okay and this is important

because there are things in the universe that preferentially pick out polarizations and this is why i'm

telling you this in general whenever light bounces off electrons there's some

kind of polarization effect going on okay so net polarization is what we care

about over here so if there's a preference of one polarization direction over others all right okay let's look a

bit more at waves so so this is the electromagnetic spectrum and many of you are probably familiar with it you can

have everything over here from radio waves to gamma rays is basically light

okay the distance between two consecutive

crests or troughs is called a weight wavelength okay and the number of waves that pass a

point at any given time per second is called the frequency so these are two related concepts wavelength and

frequency and really really short wavelengths are very energetic so gamma rays we've all we all have a sense we've

heard this are super energetic and and the wavelengths are about the size of atomic nuclei and you can go

this way to towards longer wavelengths and pass through x-rays ultraviolet visible infrared so forth keep going and

the sizes of things characteristic of that wavelength keeps on increasing okay so what I'm saying is as you get to

these lengths of kilometres radio waves are the size of buildings right and so

somewhere in the middle over here at these wavelengths or these frequencies is the visible spectrum this is what we

see with our eyes okay the next important point is that everything

everything emits light of some wavelength based on its temperature okay

so if you're the Sun and you're a few thousand degrees hot you fall here on

the spectrum and then you go back up and you see where you fall in the spectrum and what wavelength of light you're emitting so that's that's approximately

visible if you're a human being and you're about ninety eight Fahrenheit

is your is your temperature then you're somewhere over here and you're more in the infrared and that's what infrared

goggles work really well to find people in the dark and if you're really cold

you can be the temperature of the universe and you emit in the microwave

that's the general principle over here let me point out the scale over here this this might be a funny unit to you

Kelvin that is counting temperature from absolute zero and up okay

so it Maps on fairly well to Celsius in that zero Kelvin is minus 273 Celsius

and then you just count upwards or so that temperatures about minus 460 Fahrenheit and when you get to really

high temperatures it's about the same right ten million Kelvin is about 10 million Celsius the difference is just

273 degrees so the point of it here is if you have a temperature for any object

then you know what wavelength it's approximately emitting in okay next

concept when objects that emit light move their wavelength can change okay so

we're interested in stars and galaxies and things out as we as we look out into

into our universe up in the sky and those objects are moving away from us

their wavelength gets stretched and they appear redder okay that's called a

redshift so if something's moving away from you and it's emitting some light the wavelength gets stretched its redder

redshift if it's coming towards you and emitting light and you look at that light the wavelength gets compressed and

it goes towards the blue side of the spectrum so let me go back over here so what's happening over here is if it's

getting shorter it's heading this way which is bluer and if it's getting longer it's heading heading this way to

the left it's getting redder so that's redshift an blue shift okay this is important because in the next

slide so in the 1920s Edwin Hubble noticed that galaxies in general seemed

to be receding from us and the way he figured this out is because their wavelengths were redder than they ought

to have been and he also noticed that they're redder the farther away they are so the farther away they are the redder

their wavelengths the faster they're moving away from us okay so after a few

years of observation by 1929 he concluded that the universe was expanding because objects were galaxies

were moving away from us the objects that were farther away were moving faster what would he guessed was that

the universe is sort of kind of like a balloon and it's expanding okay and so if this is the picture of the universe

today what he observed was as things were moving apart we'd probably the universe is going to expand and become

more like that in the future and in the past maybe it looked like that okay so perhaps it was really small at some

point in the past okay so keep that in mind let's talk about light for a second

and this is interesting it's worth a reminder that the speed of light is finite and it's 300,000 kilometers per

second so interestingly in our universe given how big it is that turns light

into a time machine what I mean by that is when I look at the Sun it's a hundred 50 million kilometers away we see it as

it is eight minutes old because it's taken eight minutes for that light to get here so this image of the Sun when it was

taken was already eight minutes old now in this beautiful picture of the the

Milky Way galaxy maybe some of you have seen this from from a desert or something where there's not too much light pollution the senator for galaxy

is about twenty five thousand light-years away so that means we're seeing it as it was twenty five thousand

years ago okay let's let's kick that up a notch so this is her neighboring

galaxy Andromeda and it's 2.5 million light years away so we're looking at it as it was 2.5 million years ago and

interestingly if they're andromeda over here human-like people over here or some

intelligent life looking back at us they're looking at the Milky Way as the Milky Way was 2.5 million years ago okay

we didn't even exist our species did not exist at that time when they were if

they're looking back at our galaxy today so again we can keep doing this this is

a cluster of galaxies call a bell 274 for its four billion light years away so the slightest four billion years old

same same thing when if they're looking at us they're seeing us as we were four billion years ago let's keep pushing

this Hubble ultra-deep field so this is one of the most sensitive optical images ever taken this was done by the Hubble

Space Telescope by pointing to a part of the sky that looked dark like there was nothing there and it's a very small part

of the sky it's actually smaller than the full moon in the sky so it's about a tenth of the size of the full moon of

the sky they added all these images together and they found 10,000 galaxies

okay so a seemingly blank space in a blank area of the sky or empty area of

the sky and there were 10,000 galaxies over there and the light from these these objects is 13 billion years old

okay so can we see all the way to the beginning so the III love this woodcut

because it really captures what we're trying to do over here look behind and look back in the past and see maybe

maybe we maybe we get to discover the workings of the universe okay so the peak we have then is as you keep looking back

in time so this is a cartoon of how light would appear to us based on where it's originating so this is 13.7 or 13.8

billion years which is the age of the universe and that is zero over there and the idea is if we keep looking farther

and farther we pass the Hubble Deep Field I didn't show a picture of the deep feel I showed you picture the deep field we're looking at the earliest galaxies

in the universe right when the universe was only about seven hundred four hundred seven or million years old if we

look past that can we look past that can we get to the point where stars hadn't even ignited yet can we look past the

dark ages and look at the very first radiation in the universe from the Big Bang itself so this is a video version

of exactly that that that graphic that I just showed you so we're zooming out from Earth and imagine you're you're now looking at

earth the farther and farther away you are from it and so you're sort of looking back in time at us so you're

zooming past objects the solar system were pretty pretty soon going to zoom

out of the our galaxy this is a video from from the W map team again so so

that's a cartoon representation of our galaxy and where we're going back farther and farther in time so we're

passing other galaxies now these are perhaps some of the earliest galaxies in

the universe these are the first stars switching on and then suddenly it's dark for a second that was the dark ages and

eventually the idea is we should we should reach the hot dense plasma of the

early universe pulsating this way and can we get an image of this that's that

that's the question over here and so it turns out that in 64 these guys

accidentally accidentally discovered this so in 64 Penzias and Wilson discovered the oldest light in the

universe using this contraption over here so it's a it's a it's a giant radio

radio horn and they were looking for reflections of microwave of balloons and

and satellites okay and they found they found a strange noise in their system so

the end of this horn is connected to an amplifier just like a stereo amplifier

but it's it's an amplifier it's it magnifies the radio signals and they

wanted they were looking at the signal and this was a very sensitive setup there their amplifier and sensor was

cooled by liquid helium ok at 4 Kelvin 4 degrees above absolute zero to reduce it's to reduce his noise and and and

they picked up this noise that was about

3 Kelvin in temperature ok and they couldn't get rid of it they they gotten

into the horn scrubbed it clean got rid of bird poo and still could not

get rid of this noise ok and so it turns out what they found was the glow of the

early universe just red shifted down and now in the microwave ok so I'm going to

show you in a second what what an image of this might have looked like so we don't have actual images for what we saw

but just to quickly orient into you the earth is a sphere I can flatten it out

and that's a flat projection ok and that's that's the equator as you would see it on a flat projection of our

spherical earth I can do the same thing with the sky so I can take the sphere of the sky flatten it out and this is the

Milky Way and what we've done is this is in galactic coordinates meaning that the Galactic plane has been put on the on

the equator for this for this for this map and so this is this is an optical

wavelength so you can see our galaxy and you can see stars and so forth this is what these guys saw basically ok it was

it was it was basically plane completely uniform with the exception of some of

the microwave glow of our own galaxy so this was about one millimeter wavelength

which corresponds to about 3 Kelvin and temperature and so this is a cosmic microwave background and what it is is

it's the glow of 3000 Kelvin plasma early in the universe but now extremely

red shifted okay and so this was emitted 380,000 years after the start of the universe

and over time as the universe has expanded that wavelength has gotten stretched and it has moved from from

infrared from visible and infrared a red-hot universe literally red-hot and

it is it is it is now in the microwave okay so this is the oldest light we can

see we can't see past this point the reason we can't see past this point I'm

gonna use this gaudy graphic over here to explain so we're showing the progression of time and the only thing

that's important over here on this plot in time is 380,000 years after start of the universe so this is this is the

point we can look back to okay so this is where the CMB the Cosmic Microwave Background starts and this is going

forward in time before this time the you know where universe was hotter than 3000

Kelvin and so atoms weren't really atoms atoms were all ionized there were nuclei

so we show every here some hydrogen and helium nuclei which are basically protons and neutrons but they weren't

attached to electrons it was too hot for them to be attached so too many free-floating electrons out there and

when you have free-floating electrons these these yellow lines or these yellow waves show you light light keeps running

into the electrons can't really go straight very far so it's like a fog at that point it's opaque the light doesn't

get very far before it gets caught by another electron as the universe is cooling and the temperature drops below

3000 Kelvin which is that point 380,000 years up started the universe that's

when electrons can find the neutrons and protons and become neutral atoms for the

first time so now you have hydrogen and helium in their atomic form neutral and

light can travel straight and that light kept traveling straight and came to us

today so that's the general principle this is why you can't see beyond this point okay so let's get back to this in

here I've just removed the the stuff from the from the galaxies than the Galactic plane so this was what the

microwave background was in the midst okay then it took many many years a

couple of decades in fact to realize that there are actually small variations on this so this is an image from the

Coby satellite Kobe was cosmic background Explorer and this was a

satellite flown in the in the 90s and they realized for the first time that there are slight perturbations or slight

deviations from that three Kelvin and actually what they determined was that

the temperature was something like two point seven two five four eight and the deviation the variation was was after

that okay so the deviations are one part in a hundred thousand which means that this is precise to the first five places

of decimal and then the number changes so the color variation that I'm showing over here is is a part in in a hundred

thousand so very very tiny variations so there were more missions more satellite

missions there were a lot of ground-based cameras they continued refine in this picture so I've been showing you full sky maps eventually

we'll get to sectional maps made by ground-based cameras but over the next

twenty years we go from Kobe to W map the Wilkinson microwave anisotropy probe

and they refined that picture a little bit more the deviations in go away they were just found with more

signal-to-noise or the cameras were more sensitive and they they kept seeing that

the temperature was uniform and these these little spots were really changes in the sixth place of decimal okay

go another step this is the Planck satellite which imaged the CMB in the

late 2000s and so this is this is probably the the best resolution and

noise picture that we have of the full sky of CMB okay so let's take a break

for a second and look at how one actually takes sensitive pictures of the CMB light and so the answer is

unfortunately it's not as easy as with C CDs and with digital cameras it's a little bit more complicated so let's

let's work a little bit through the history of that so back in the day they use microwave

radiometers so this is just the Bell Labs horn antenna that that Penzias and

Wilson used so there's typically a horn okay and and an amplifier okay over here

it's it's a room and the amplifier has a room in there the room has two hamp Lavar in there but this was common to a

lot of the instruments back then even even in the COBE receiver receivers the

the camera unit in as of 1989 and and w map in 2001 so you had horns connected

to a low-noise amplifier so that's low noise amplifier in there low noise amplifier in there low noise amplifier

in there horn horn and a bunch of horns over here on both sides actually so yeah

it's hard to see the ones in the back but through the two through through the

90s so starting the 60s and through the 90s this was this was sort of the state of the art you'd you'd put horns pointed

the sky and connected to an amplifier the revolution was actually this idea of

a bolometer okay and that this idea was was actually is fairly old it comes from

the 40s and it's really interesting because at that time they imagined the bolometer as something that sees warmth

miles away will help fight disease warn of fire cash burglar spot heat leaks so

an idea probably ahead of its time but but the concept is basically if you have something that emits radiation and we

know everything does with a sufficiently sensitive sensor you would pick up that

radiation even even at normal temperatures over low temperatures and this was accomplished by putting the

sensor at very very cold temperatures okay so they have a can of liquid

hydrogen in here and liquid nitrogen so that's interesting but they would be able to do this kind of imaging so that

was the concept so let's let's break that down down a bit further so if you have incoming radiation or power and it

gets absorbed in something that is thermally isolated from a stable

temperature okay so there's an insulator separating the absorber from from from

from a stable temperature then you can stick a thermometer to that absorber and if power comes in it doesn't flow all

the way it doesn't flow it doesn't flow into the into your stable cold

temperature bath immediately if you've choked it a little bit okay this allows the temperature of the absorber to

change so the power increases over here the temperature goes up because all the heat has not immediately flowed into the

into the cold temperature bath so have a

great analogy for this that I thought I thought of the other day so what we're gonna talk about this now so my analogy

is imagine a kitchen faucet and the rate of that kitchen faucet and the water

coming out of it is your flow or your power and this kitchen sink is your absorber okay your garbage disposal if

it's blocked or it's choked a little bit is your is your insulator over here okay

obviously in in in our lives we don't want our garbage disposal to be to be choked but if you choke it a little bit

and you backup water over here then then then then you collect some water over

there and the amount of water over there is telling you what that incoming power was okay so that's the general concept

of a bolometer pedometers and the 90s look like this so this was made at Berkeley this is this contraption that's

one centimetre for scale it was a little sheet of sapphire so this is this

grating as a sapphire over here suspended by thin wires okay so that creates that thermal isolation and this

is your thermometer okay and so you'd have light fall on this thing and it would change the the temperature of this

very very sensitive thermometer and a typical bolometer camera as opposed to

one of those microwave radiometers would then have a few of these sensors and you would look at the sky okay so that's

that's in the early 90s then this beauty came along so this is

micromachined bolometer so that's that's a dime for comparison this was made at JPL so let me talk about that on the

next slide over here the idea is that they've used photo lithography to etch

silicon and create these thin legs that are that ice that isolation okay so this

is so heat gets picked up over here if light comes in over here onto this spot and so that light focusing by the way is

done by horns in this case and this is exactly the sensor that was used for plunk the planck satellite so like light

gets collected over here and then heat flows through over here and the temperature of this guy is changing as

that power is varying on the sky okay so as I'm looking at different pot spots in

the sky there's very very tiny differences in the temperature I just said it was about a part in 100,000 so

this thing is sensitive enough to pick up a part in a hundred thousand variations all right and so then a

typical camera consisted of about 10 to 50 of these sensors okay so let's get

back to dissecting these images a little bit more ok so I've shown you a bit about the camera technology at that time

then we made these images this is this is an image from from the Planck satellite now to make sense of this what

scientists like to do is to break up this image by scale okay so there is

there's variations and remember these variations are a part in a hundred thousand so this is a very very sensitive measurement you can look at

big spots on the sky or you can look at tiny spots in the sky okay and what you

could do is you could look at all the all the sizes in between so if I were to divide up the sky into just two spots

what that would look like or if I were to divide to the sky into many many many spots what that would look like and so I

can take that image and figure out what the contribution of these various

components is so maybe it's a little bit of this plus a little bit of that maybe none of that but more of that so I can

do this okay so you can do this exercise and the skin this goes on for a few thousand spots you can do it as as much

as you want all right if I do that then I can make a graph like this and what's

going on in this graph is on the left end is big scales in the sky so fewer

spots so maybe there's like one two three spots in this image and on the right and I'm going through two more and

more spots so you can see the scale or the number of spots roughly over here and and then I'm turning up or turning

down the contrast on on that scale of spots so what this breakdown tells me is

that the contrast on the large scale is not that much but the contrast on this

particular scale is really really good is really high so the deviation from

that average okay the deviation from the average on this sized spot is quite a

bit higher than the deviation from the average of this or perhaps at that okay

so what does this tell us so this is really interesting immediately you can tell that there's some structure over here okay and this is this is this is

the most amazing part so this tells you what the most prominent spot is on this

spot sizes in the sky and this corresponds to the most prominent size of plasma fluctuation or plasma wobbling

in that early universe and that image that I showed you in that video that you saw earlier where you saw the plasma

pulsating okay so this is the fundamental note of our universe at the

time of the CMB and so for folks so for music enthusiasts this this corresponds

to let's say that the fundamental note of the universe if it were a musical instrument and then the rest of this is

harmonics so it turns out that if you study the the the fundamental note and

the harmonics you can reconstruct all kinds of things about the universe this tells you the geometry of the universe

the ratio of the heights of these Peaks tells you other stuff like how much stuff there is in the universe how much

matter how much dark matter and so forth and this is why studying this very early image of the universe tells you so much

about the universe and it's so important in cosmology ok so that that was that

was a cartoon representation this is actually the this is this is the real this is what our universe looks like this this tells you a lot of thing

about our universe this model is fit by data really well so all the pluses and

lines over here are data from these various instruments that's the plunk satellite and then the

rest of these are cameras on earth the plus tells you the amount of uncertainty

and you can see that the error bars the uncertainty from the plan satellite is

very very tight actually it almost disappears into the line over here okay all the way down to many many harmonics

and it starts blowing up over here because then the satellite dish is not big enough to get sufficient resolution

beyond that point that's where the the systems on earth help us out a bit more

but so we understand this really well we have the data it fits this curve really

really well okay so we understand the story of the universe as seen through the CMB

okay let's go back to one fundamental question though so we've we've kept saying there's a CMB so uniform it's so

uniform deviations are at one part in a hundred thousand why are the deviation so small okay why did the CMB not look

more like this okay why not more like this and millions of degrees variation okay

so there's no reason this shouldn't happen the the way we explain this is

inflation so this is now where we talk about what happens before the CMB and in

particular this point over here so what inflation does is shortly after the

start of the universe in a very very tiny split fraction of a second the

universe expands 10 to the 26 times that's one followed by 26 zeros okay in

a very very short amount of time 10 to the negative 32 0.31 zeros and then oh

one okay so very very voluminous expansion in a very short amount of time

and it what it does is it in it inflates a subatomic volume something very tiny

two very very large scales okay why does that how does that how does it help with a problem so if my universe were something

like this shortly after the Big Bang and then the universe expands maybe

somewhere in this orange patch very quickly then the whole thing becomes orange very simple idea in principle

okay if that sort of very rapid expansion happens and suddenly everything has become uniform inflation

stretches out space and removes all the unevenness except for the stuff that was

uneven at sub atomic or quantum skills okay and so that perhaps explains what

why you have these tiny variations so so so let me let me expand on that a bit more inflation expands subatomic

unevenness into lumpiness in that early hot plasma that video that we saw okay

so all of that lumpiness came from subatomic unevenness being magnified by

this idea of inflation okay so some spots end up being more dense some are

less dense and therefore some are more hot and some are less hot okay and and

so that that's how you end up with these spots and the most important thing is inflation is one of the only known

mechanisms we are is one of the only mechanism that we can think of that provides just the right amount of

lumpiness so that these dense parts eventually contract under gravity and

become our stars and galaxies and clusters of galaxies and all the structure we see in the universe so if

you don't have this then the unevenness is too big you don't get the right amount of stuff condensing and becoming

stars and galaxies and structures of galaxies inflation by magnifying the subatomic stuff gives you the right

scale the part the one part in a hundred thousand is what you need to start off the process of creating galaxies stars

galaxies and structures in the universe so that's why inflation is cool and it explains it's a good explanation for how

the universe started or what happened immediately after the Big Bang so now we've proposed this but can we look back

farther than the CMB and see inflation

turns out not directly because as I said the universe is opaque but there is a

way so here's another cartoon of the story of our universe and this time we

magnify the parts before the CMB so and the other one you saw the structure

formation and the dark ages and all that kind of stuff this is the modern universes where we are today and this is this is the moment of Big Bang it turns

out we don't need to worry about this for the purposes of our talk today but let me point out that this is the this is the Cosmic Microwave Background so

this so going forward this is the CMB light at 380,000 years and the idea is

that if inflation occurred and it magnified these subatomic the sub atomic unevenness into the lumpiness in the

plasma which over here the technical term is density waves but this just means unevenness in the plasma or lumpiness in the plasma if inflation did

that then the other thing inflation would have done is stretched and squeezed space-time itself and created

gravitational waves in it okay so we just heard and maybe many of you heard

today that the Nobel Prize for Physics this year was awarded for the discovery of gravitational waves that was

gravitational waves generated by colliding black holes okay work we're

saying over here that these gravitational waves are created by inflation they're not they're not

fundamentally different types I mean anytime you move matter around by shaking my fist over here I'm generating

gravitational waves it's just that they're really weak and LIGO detects them from cataclysmic events like

colliding black holes here the cataclysmic event that occurred was a very in the very early universe and it

created a lot of gravitational waves they're too weak to directly observe today so LIGO can pick them up what

we're counting on is the gravitational waves that are generated by inflation imprint themselves in the CMB itself

okay so we cannot see past it but if gravitational waves went through then

maybe the imprint of the CMB with polarization this is where polarization

becomes the implementation occurs in polarization of the light and we look

for a particular pattern called a b-mode pattern and I'll come to that in a second so remember this b-mode

polarization pattern in CMB imprinted by inflation is how you look for inflation

okay so so let's continue the story then okay now I through polarization into

this and now now I need to go take pictures of polarized CMB as well just-just-just temperature pictures is

not enough just intensity is not enough I need to look at polarized CMB so how do we do that so we we become clever

with with how to make bolometer x' and really you need some grids or something right I mean we talked about this idea

of polarisers or picking our polarization being related to a polarizing grid and so you could put two

grids like that together perpendicular this is this is a five millimeter

polarization sensitive bolometer in which you see both parts of the grid what they do is they fabricate this and

then they metalize only one axis for one polarization and they take another piece

and they metalize the other direction or the other polarization so then you stick

this behind a horn again and then you get another camera again the the temperature the bolometer part of it is

there's a sense of thermometer that's looking at temperature changes and and

so this was used in bicep 1 and also in plunk so the thing that I didn't tell

you earlier is plunk not only had spiderweb bolometer x' but the JPL guys

managed to get this onto the Planck mission as well so that's plunk that's the camera and there are a few horns in

here that do have polarization sensitive bolometer x' so now you can look a polarization of the CMB as well

the real amazing breakthrough came in came around 2008 when they figured out

how to do all of this stuff the printing of the polarizing grids and they combine

it with antennas so these are now antennas and they eliminated horns so

it's a one step process where they've made this grid of polarization sensitive

antennas and it all sits on one silicon wafer and you put a few of those together and

suddenly you have 500 sensors as opposed to the tens or 20s or 50s that you had earlier so now you have antenna couple

polarization sensitive bolometer x' the thermometers have become more sensitive too and suddenly you can go up to 500

sensors in a camera in fact that wasn't it this this technology is still in use today probably the most sensitive 95

gigahertz camera on the planet is this one over here that we built at slack this was slacks for CMB camera it has

2500 sensors it's called bicep 3 and we we deployed it in 2015 this is an image in 2016 and

so you see the squares again there 20 of those square tiles they're about three inches across and they have a few

hundred sensors each ok let me show you a few other cameras so I already told

you about the bicep series of cameras that's what they look like this is this is a telescope called class so these are

cameras that look straight in the sky without any radio dishes ok so there are a few of these then there are others

where the camera so these are a few different types of cameras for this is

called the Simon's array that's act or the Atacama cosmology telescope the 10 meters South Pole telescope this uses

actually little tiny lenses on top of each of the sensors these these use horns still

instead of using the antennas but here are these cameras are connected to a

radio dish and that radio dish looks at the sky ok so the camera for instance for this guy sits over here in here so

light comes in reflects goes to a secondary and then it goes into into the

camera ok so those are the cameras that take images of polarized light polarize CMB light so now we can say ok let's get

back to the question of what does it actually look like and what can we learn from it alright so now what I'm going to

do is take that CMB sky again so you guys have seen this image many times we've cut out a chunk of it a small

section of it in particular because I'm using bicep camera images and bicep images a small fraction of the sky so it

focuses all its observing power onto a couple of percent of sky instead of the whole sky and that's what polarization

looks like remember I said that it's basically the orientation of the electric field and so that image and you

see lines in here and the the length of the line tells you the strength and note that this is this says 1.7 microkelvin

so that's 1.7 millions of a degree so that is even more sensitive or it's a

lower number than the one in hundred thousand fluctuation we're talking about so cameras I've had to get this

sensitive to be able to pick out this polarization the way this image by the way gets built is because you have slots

like this as you saw in the camera so the images come out as pluses and crosses okay so so the pluses and

crosses combine to make that image but what is interesting for us to find inflation is not to break it into pluses

and crosses but instead to break it into this this mathematical combination of

what are called --mode x' and b modes okay Emo's are circular and radial

patterns and B modes are swirly patterns okay so that look for those patterns

basically so you can see some roundness over here some some radiative patterns over here and in a bicep2 image there's

there's hardly any any B mode signal okay so you have to magnify it quite a bit to find it and so if you zoom in and

go to what is that point point three microkelvin so point three millionths of

a Kelvin or degrees above absolute zero then you get something like that and now you see some of the swirly pattern okay

the key is that lots of stuff in the universe generates --mode polarization

so as that light is traveled from beginning the universe to us lots of

stuff has caused the e mode polarization there are very few things that cause b-mode polarization and inflation is one

of them okay but this doesn't mean we've seen inflation so this this particular p mode is actually caused by our own Milky Way

there's their stuff in our in our own galaxy that's radiating and it's radiating some B mode so we have to be

careful about this sort we're looking for inflation we have to look specifically for the B modes that

are generated by by inflation and not stuff that comes from from our galaxy

and the way we get to that is remember the scheme again you you take the image

you slice it up into its components by size and then you get something like that so this is for temperature and you

can do the same thing for --mode x' and B modes and this is what it looks like so again on the on the x axis I'm

talking about lark going from large scales to small scales okay and this is again deviation from average

this is what you've been seeing earlier and I showed you data on top of that earlier so that's CMB temperature but

the moment I start looking at polarization it drops quite a bit the signal is a lot weaker so email

polarization is only about 10% of this and and b-mode polarization is only 10%

of that so lots of email polarization still for our sensitive cameras the B

mode is rarer and it's caused by a few different things and we need to pick out the right thing so it's caused by just structure in the

universe okay we're gonna ignore that I'm not gonna go into much detail over there there's some stuff from the Milky

Way that we just imaged and on top of that we're looking for this slight hump over here and that's the inflation B

mode so if this shows up and we don't have the actual level of this so this curve could sit over here it could sit a

little bit lower but this is what we're after so if we make those images sort

them into this small big big to small scale and draw these plots if something

shows up over here that's the inflation signal we're looking for okay this is that same image with lots of

data on top of it and you know we don't have to worry about the details over here except to show that you've seen

you've seen that there's a bunch of data for temperature there's a bunch of data for for --mode and notice how the plus

signs are getting bigger and that's because the uncertainties are increasing because it requires that much more

sensitivity to get to these these smaller and smaller deviations from the

average okay so this is this is B mode and this is mode from structure and remember what I

said we would see a signal over here if we saw inflation so we need to get really sensitive in this area so cameras

that we build we want we want them to be really sensitive over here here's yet

another plot and I'm gonna show this only two point on one thing which is this is this is again Theory curves this

is what one model of inflation might look like and if it's suppressed a little bit then this is what another model of inflation might look like the

data is starting to hone in over here and a few years ago you might have heard the story of how bicep 2 potentially saw

a signal over here so bicep 2 2011 here

but it turns out that dust in the Milky Way accounts for most of it and so when you remove that dusty these points move

up a little bit and the this just says that it's an upper limit which means we

don't actually know what's going on over here just yet and and because it was

showing up in the right place that's why bicep 2 thought that maybe they'd seen a signal but it turns out with to dig deeper with a dig deeper and we have to

sort through all this mess over here we've to sort through dust within our own Milky Way be able to separate all

these contributions to to be modes and to do that we need more powerful and

multicolor cameras it turns out the trick to distinguish these things is color so I can't look in just one

frequency I need to look in multiple frequencies so basically all I've told you right now is black and white

technology and we need to get to this color technology we have in the field now but we need bigger cameras multi

color cameras to find this inflation b-mode ok so in the last little bit of

the talk let me finally take you to through the places that people go to to

take pictures of CMB so there's obviously space most of the images that

I've shown in this talk are our maps that have come from satellites in space so it's been very successful there's

been co BW map plunk this is a video from the Planck science team and they're

not beaming out light by the way this is just showing you that this is how they scan the sky okay so this is their scan pattern and

so it rotates it maps out the whole sky the sphere of the sky and as soon as

that is done you'll you'll see how the the sphere then gets flattened out into

the sort of image that I was that I've been showing you okay so that's that's that's where that comes from so you get full sky images the problem

of course it takes a while to put together space mission lots of money

can't make it too big because you haven't fit in a satellite and typically it's older camera technology it takes

about 10-15 years to put together a satellite mission okay but it's still an

excellent way and then this is this if we were to see any hints of inflation from Earth we would put together a

satellite mission to go after it another way is somewhere in between which is

which is ballooning so that's a boomerang balloon this is a spider camera and so you could image the CMB

from the edge of space so put a camera on a balloon get it just high enough to

to clear the atmosphere get to the edge of space this is an actual GoPro image up from this camera GoPro strapped to

this took that and there's a full video that goes with it actually all right well you can do with this as you can you

can't map the full sky you map some fraction of sky about 10% of the sky you can fly newer cameras because you grab a

new camera put it on there fly it for a month and it comes back down but typically the the lifetime of these

balloons is about a month okay and then same over here weight constraints so the

ground program has taken off and is very successful and if you want to do this in the ground you go to a high dry desert

okay and that's basically to minimize seeing through water vapor in the

atmosphere remember we're looking for microwave water absorbs microwave that's

how your microwave oven works so we want to minimize the amount of atmosphere

we're seeing through so that we can avoid water water vapor so high dry

deserts when the most popular sites for running CMV cameras is in the Atacama

Desert in Chile so this is one particular site this is cero toko this entire setup is called

assignment Observatory and there are a few different telescopes over here and this site is great because one it's

extremely dry so over here you're seeing it in the wet season but otherwise it's it's a very very little water vapor and

it's high altitude oh and I think so this is sorry this is closer to 17,000 feet so very high altitude so minimizing

the amount of atmosphere you're looking in looking through and extremely dry so so that's water vapor so this is a fun

drone shot video of of this site so that's the that's the act telescope and

so by the way I haven't I haven't yet been to this site though I'm now participating in the project for which I

hopefully will get to go over here so getting here is it's pretty interesting so you fly from here to Santiago then

you fly from Santiago to Kalama from Kalama you drive to San Pedro and so

that that drive is about an hour and then there's another couple of hours so and and San Pedro is at about 8,000 feet

and then the rest of the day it's rest of the way up to 17,000 feet you drive on a daily basis so you go in the

morning come back in the evening okay and you go over a highway that connects

to Bolivia but right before entering Bolivia you're turning left that's what I've been told and and you

go up this this dirt road and and you get to this this wonderful site this thing is called a ground shield by the

way this structure around the telescope and that's so that you don't have a direct line of sight to the mountains

around you okay so this thing this thing is on saratoga it's a very tall mountain but you don't you don't want to directly

see mountains as you're looking up you don't want any rays of light coming off of mountains and entering your setup so

then you have something like that okay so so that's this wonderful sight and that's that's a simons array so these

are smaller telescopes but also CMB polarization imaging telescopes then the

other great site for CMB observations from Earth is is the South Pole

so that's at ten thousand feet lower altitude but Antarctica is the driest desert in the planet so desert knots and

dry okay so so we want to go to the driest places it doesn't matter if

they're sand there or not so let's see if you hear extremely dry this is even

better water vapor conditions then then Atacama high altitude so minimizing the

atmosphere and the other advantage of course is there's one really long night so you can keep observing continuously

okay all right so now I'm gonna walk you through through the biceps story so this

is a story of this gang of people from all these institutions over here including Stanford and slack and and and

our cameras in particular this is the this is a cat camera and this is how it observed so this is a video that that's

been sped up and you lock onto one spot in the sky and continuously keep scanning across it this is not like a

digital camera where you where you take an image and you're done you continuously take keep making images and

keep adding them on top of each other for years okay so basically cameras like this

continuously scan they take breaks for calibration so that was a calibration right over there and then they'll

continue doing their thing that just keeps scanning the same patch of sky so we've picked out that couple percent

patch of sky that I showed you earlier and and it just says that and as data

comes in this is what it looks like so let me quickly orient you so what's going on over here so a few maps are

going to show up over here and this this graph over here tells you as a function

of time so this is going from 2012 to 2016 as various cameras which on and

their sensitivity starts getting better and better as they're observing you will see the map quality get better and this

is this is a this is not a EB map --mode B mode map this is a this is a plus map so you'll see the plus pattern develop

over here so that camera is kicking in its first noise but very slowly you're seeing pluses starting to develop over

there okay so that's polarize we use a grayscale map over here and I know I've used many different color

scales in this in this talk but our our team uses black and white this is

another camera switching on at a different color or a different frequency so this is this is our multi color program now and this is a third one

switching on and and first noisy but as time goes on the the pluses all start

showing up okay let's go to the South

Pole this is how you go there so we start in Christchurch in New Zealand so flight commercial to there and then you

take one of these el c-130s or or a c-17 and you fly to Antarctica you first go

to McMurdo Station which is at the edge of the continent and there's there's a few landing strips over there one of

them is actually out here to the right a little bit and this is sea ice it melts in the summer so that's amazing they can

land a plane early enough in the summer but then that that that entire runway just disappears it just melts away

that's God's Hut so this is what Robert Scott used as one of his storage

locations starting his Antarctic expedition in in 1911 so that's a

preserve site now you take another flight from there again on an LC 130 and fly over most of Antarctica to get to

the South Pole so this is going over the Transantarctic mountains and then eventually you get to the South Pole

it's flat out there there's there's nothing there's quite literally nothing there so and it's hard to tell in this

picture it's kind of disorienting but that's the horizon and this is all all ice and it's two miles of ice it's two

miles high so that entire altitude is ice actually sitting on top of bedrock

so that's the geographic South Pole is somewhere over there this is the station this is all the spread of the station

that's the ski way in which planes land here's where the CNB telescopes are and

you might have heard of a neutrino Observatory called Ice Cube and it's out there as well once you land you're here

this is the Amundsen Scott Scott South Poles this is the actual South Pole and you

can you can pull this off without a facemask if it's minus 15 as opposed to

you know minus minus 40 so cargo and people all come this way

with on these planes so everything that's been built to the South Pole has sat in the belly of one of these one of

these planes and these planes land on skis so these are special L c-130s they have skis to be able to land on ice

here's our team or part of our team in 2015 this might have been a member just

having joined for for that part of the season that's the South Pole Station

it's an excellent NSF run National Science Foundation run facility inside

the station it's nice and warm 68 Fahrenheit we have control we have a control center for the telescopes we've

conference rooms a dining hall dorm rooms so you can stay there and of

course outside a kilometer away from the station is where all the science

activity occurs so and in this building over here is where the bicycle bicep experiment lives this is this is a new

ground shield being put on for bicep so that structure that prevents other light from getting in this is what's working

on the bicep 3 camera so those are the actual sensors and this is this is this is this is a camera here's a here's a

cut through the camera and it's like what you would imagine a camera to be so there are sensors so this is a cartoon

of the sensors and that for tile version this is a this is the bigger version and then there are 2 lenses and they focus

the light coming in ok so jet so like a regular camera you put together this is

this is this bigger and as fewer pixels ok this is how you get the telescope up

into its observing condition it's a human power lift and Roger or Bryant

well I challenged Roger Bryant to two playing with a yo-yo while doing this lift so that's that ok and this is this

is the finished product so the the title image was bicep 2 then that's been replaced with bicep 3 so

it's a bigger camera and this is reactions to the first light of bicep 3

the so I picked this off Google photos actually if it sees a bunch of similar pictures it turns it into a jiff so I

thought that would be entertaining but this is us basically seeing the first light being captured and the first image

is coming in a quick shout out to the people who stay behind after we install

those cameras so these are our winner overs so these are the folks who stay there overnight it's only one night

right for six months some of them grow long beers by the end

of the buy they by the end of the winter but they stay over the winter and and and run our operations over there okay

I'm already a bit over but let me quickly tell you what's coming up in the next decade bigger more sensitive

cameras of course so our bolometer technologies continuing to advance we are now able to put

multicolor capability into the same antenna and sensor so that's really nice

and we've been able to make the replicate a lot of sensors on bigger and bigger chunks of silicon ok this has

work done by our colleagues at Argonne National Lab and this is the this is all designed to basically go into cameras

that have 10,000 or more sensors in them and this particular thing has already been been fielded it's it's an SPT which

is our neighbor by by bicep this is stuff we're doing over here and at at

NIST so these are again same scale antennas and we're trying to pack 2,000

multicolored sensors into these 15 centimeter silicon wafers that we can

then tile and edge-to-edge and build a big camera ok and so the idea of a here

or two is that this is this is the technology these kinds of sensors will go into future bigger cameras and we're

doing that because we don't want to stop with a small fraction the sky we want a survey as much of the sky as possible

from Earth and we want to match our surveys with some of the other

prominence that are going on some of you might have heard of LSST or des these are other

optical surveys and the structure that they see we want to be able to match to the structure that we see in the CMB so

this is looking at much more recent stuff and matching it to stuff thirteen billion years ago so this is this is this would be a great step for everybody

this is again of this is a different projection this is a this is a celestial projection so that that is the Galactic

plane but this tells you very nicely the amount of sky that you can observe from different locations so everything south

of here is stuff that you see from the South Pole this is stuff that you can see from from Chile and we can probably

get to 40 70 percent of the sky if we put something like five hundred thousand sensors on the sky so that's what we

want to do next that project you might hear up in the next few years it's called CMBS 4 you'll notice of course

there's a chunk missing over here and and of course we want that - because we're greedy so a couple of other sites

that were interested in now so there is summit station in Greenland that's in the northern hemisphere so maybe you can get to part of the sky there and and in

the Himalayas there's a site in in Tibet that some folks are interested in and so

with those two additional sites perhaps we can we can survey the entire sky from the ground ok so I'm gonna stop there by

just saying the CMB has given us a wonderful glimpse into the very early

universe it's light that's coming from 380,000 years of the start of the universe but there is there's quite a

bit more to learn from it our camera is getting more and more sophisticated and

over the next decade we're hoping that we'll be able to understand event so the very very start of the universe so in

particular we want to image the effects of inflation and understand what happens

this short fraction of a time after the Big Bang so let me stop there thanks


at this point we're going to open the floor for questions but before we start I have to tell you that we have a very

nice sophisticated system which actually uses the microphones that are placed in front of you if you're recognized by me

please at that point push the button in front of the microphone and you can speak to the microphone but when you're

done you should turn it off so somebody else can use it so maybe you can serve with the gentleman here who is the sound

first okay so this is working one term I've heard regarding the early universe

is reaiiy ionisation can you comment on where that fits in to what you've talked

about tonight right so okay I got to

show you that image - in a second but here let me go back to one of these

okay so there's a Dark Ages which is when all the stuff in the universe is

neutral so it's a neutral hydrogen neutral helium and and that happens

because the universe is become cool enough now that the electrons and and and nuclei don't live separate

separately anymore they become neutral atoms when the first star switch on is believed that they they start reaiiy

annive all that medium all that hydrogen and helium so that's that's somewhere around

here that we ionization kicks in then then the medium becomes ionized for the

rest of time yeah so can we see light from the real ionization period right so there is

actually CMB signals we could see from the realization period there are

actually many different ways of getting to Rihanna's ation one of them is that neutral hydrogen has a spectral emission

at 21 centimeter so the wavelength is 21 centimeters and so that 21 centimeter

ought to start disappearing as Rihanna's rihanna's ation occurs and so one hope

is that you could actually see realized bubbles popping up if you image the sky

in 21 centimeter with CMB at the very largest scales CMB light a scattering

off of these electrons that are now you know coming about

so realization is not uniform it's bubbles here and there and it takes time

yeah and so it starts with smaller bubbles that's that that's what we believe right now and and that those

bubbles get bigger and bigger until they all combine and it becomes all realized thank you the fact that you scan the

same point over and over again suggested is static why isn't it constantly changing why isn't the image constantly

changing of thee oh great that's a great question why isn't the image constantly changing so so so two parts to that

the actual CMB is not changing because the the the the point at which that

light gets released it captures the state of the plasma right there and then

so the plasma was pulsating at the time and when that light gets released off it you've taken a snapshot of it so that

particular image is not changing that instant in time is not changing so that that picture that that picture that

we're trying to make is not actually changing what is changing is the atmosphere right above us and so that's

adding noise and by by taking multiple images over and over again and adding

them on top of each other we're suppressing the variation in the atmosphere that averages out we say that

it a verge is out by repetitive addition of the images on top of each other and would you left with is that static image

back there sorry I don't understand it all why it isn't changing you said they

caught it in a moment in time but the moment in time is a little bit later is a different moment in time this is

coming at you continuously right yeah that's right so so there's another part of it here which is the farthest out we

can see is this point this the this light and the far as the universe continues expanding it turns out that

that will always be the farthest point we'll be able to see and so we'll see it cool off so it's changing in that the

temperature is dropping over time and that frequency is slowly red shifting so yes it is changing but on the time scale

in which we were taking the pictures the change is really really slow we always see always see one point in time yeah

we're saying we're seeing we're seeing one point in time for all practical purposes a thousand years from now maybe

they may changes slightly yeah so that's right so it is it is changing very very slowly for all practical purposes it's

static how do you differentiate between B modes

from the Milky Way and B notes from the CMB that's that's a great question so it

turns out let's see if I can just pull up something that's helpful here

let me replay this video again so this will be helpful so it turns out I guess

I have to say there we go okay this particular color is sensitive

to both CMB and stuff in the Milky Way this color is more sensitive to CMB and

this color is more sensitive to dust in the galaxy so the Milky Way so the different colors

are differently sensitive their sensitivity to the different components

were interested in is slightly different so you can add and subtract images in

the right combination and tease out the parts that are only CMB versus the parts

that are only stuff from our galaxy that's the general principle and you can

do this with not just three images but with eight different colors or 15 different colors we believe that from

from from Earth with the cameras that we can build over the next decade we can probably do this with eight colors with

a satellite would probably go up to sixteen twenty colors if we wanted to really get very high resolution if we

needed to

hello I just wanted to say I thought it was really fascinating that you're using cameras to photograph this and then when

you were looking at the universe and talking about the polarization that that's almost like a sensor on a camera

giving you that data it was just really interesting parallel thank you thanks for that coming yeah looking at your

your cartoon history of the universe it looks like there was a big deceleration

after the inflation period is is that true or is that just the way you had to

draw the cartoon right so let's let's go back to the cartoon so the so the

question is is this a deceleration of it here right yeah so that is that is

inflation switching off so inflation

inflation starts and it happens very very rapidly in a very short amount of

time of course if it doesn't stop then we don't have a universe and maybe there

are some universes out there where inflation occurred and never stopped fortunately we're in one where it did

stop and then it just continues coasting until dark energy kicks in and the

expansion picks up again so you're saying that that's not actually a

deceleration that a cessation of acceleration yes

is there a cosmic neutrino background there is absolutely a cosmic neutrino background so there's a cosmic neutrino

background there's probably a cosmic gravitational wave background all these things from the very very early universe

that that have survived into modern times there's probably some kind of

background but it is also but that but there are many things that the temperature of the universe is not not

high enough to to sustain those things or sustain those processes so anything that survived that early era has a

cosmic background there's a cosmic neutrino background were I should say

probably on the verge of picking that up too with some of the more advanced neutrino instruments maybe did we start

with this go ahead you have to push the button on here so you are saying that

the polarization is caused by gravitational waves so how exactly do

gravitational waves polarize the light right so so that's a that's a subtle

thing that I decided not to go into in this particular talk and unfortunately I don't think of a supporting graphic so

maybe if you're interested I can I can show you something offline from one of my other talks but the general principle is just like you create so so hot and

cold spots and temperature are created by these density variations in the plasma right and that's actual stuff

being either more dense or less dense the idea is that some some part of this

can also be caused by the way gravitational waves act on stuff and how

they twist space and time and as photons

or light is scattering off electrons that are caught in those dense less dense areas they get polarized regular

plasma unevenness creates only e-boat

polarization and gravitational waves the way they can twist and distort space-time they can

create both a mode and B mode and the actual mechanics of how that B mode gets

created I might have a picture I can show you offline but and also folks you

should feel free to look this up but the the general principle is that gravitational waves can create effects which can cause both

a mode and b-mode polarization or make

both of it so go ahead how many orders of magnitude more sensitive would the

laser interferometer have to be to directly detect the gravitational waves

that's an excellent question so there are a couple of pieces over there one is

just sheer sensitivity and the other is what frequency range they're sensitive

to so on earth they can probably not achieve the raw sensitivity or probably

the frequency range that they have to go into space you might have heard of this concept called Lisa which is putting

these gravitational wave interferometers out in space you know in a in a

satellite triangle formation or something or so if you can do that then

there are a couple of other problems still all the other gravitational wave

signals that are going off from colliding black holes colliding neutron stars and all these kinds of things it

turns out I believe this is correct and so and and you should feel free to look this up but I think you actually have to

end up subtracting every single known source and then what you're left with

might be the the cosmic gravitational wave background question whether or not

yes on the day that the CMV signal was

generated throughout the universe what was the approximate diameter of the universe and was the distribution of

matter homogeneous and then what does that say about our physical location in the universe right

so that that's an excellent question so the universe on the day the CMB was

generated was a thousand times smaller in one dimension so a billion times

smaller and volume than it is today and the the size today of the observable

universe again we don't know how big the universe is we can just say what what stuff might have contacted light will

ever contact light that's about 45 billion light years so that's the size today on one side make that a thousand

times smaller that's the size of the universe and on the day the CMB starts propagating okay so that would be more

or less five four five billion light years and how long ago did this happen

this was okay so yeah it sounds like we miss the event yeah so yeah so there

there there are few subtleties over here this is this is where inflation becomes important so inflation does this thing

so that you don't have to extend this all the way back there so if you didn't

have inflation then the universe doesn't become big enough in size for us to be able to observe this so uniformly and

such across such a big universe that's the general principle because if yeah

III I know what you're saying basically you'd have to extend back quite a bit longer than the age of the universe

would have to be a lot longer for the scales and the size to make sense this is where inflation saves you that's

another reason you need inflation so we're not near the edge of the universe first yeah so we're in the middle in

general the universe appears homogeneous and isotropic in all directions that we look in yeah and so for all practical

purposes we're at the center of our our observable universe and at the edge of that those guys are

at the center of their observable universe for us to allow the camera

people to go home to pack up here but we will still spend some time outside of

the room maybe for a few more minutes if you have any pressing questions we'll be very happy to answer those so let's

thank fish again and just before you depart I wanted to mention that we were

planning we're in planning stages of establishing sort of ongoing astrophysics and cosmology public talks

and the first one of those would be I believe 15 of November but certainly Ward's the same place we found the

information about the slide public lectures and will once again thank you

very much for coming [Music]

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