We're ready to start
the recorded part of the lecture
now
so I welcome you
to the 3rd
in the 2015
Penn State Lectures on the
Frontiers of Science
today is February 7, 2015
My name is Barbara Kennedy
I am the chair of the organizing committee
for the Penn State Lectures on the Frontiers
of Science
Which Penn State
organizes and
supports as an annual free public
mini-course.
We've been doing this for the past
21 years.
And you all have been with us
for many of those years.
And we really appreciate your
participation in this lecture series.
This year we are grateful for additional financial support
from Penn State's Institute for Gravitation
and the Cosmos
We also are grateful to our speakers
who donate a considerable amount of their
time
to preparing their talks
which they give to us as a public service
our topic this year
which is the 100th anniversary of Einstein's
Greatest Discovery is New Science
from General Relativity
our speaker today
is Nergis Mavalvala
she is the Curtis and Kathleen Marble Professor of Astrophysics at the Massachusetts Institute
of Technology -- MIT
her research is helping to give birth to
gravitational wave astrophysics
an entirely new way of collecting
information from space.
That has the potential to provide a radically
different
view of our universe.
In recognition of her research achievements
Dr. Mavalava has been honored with
a number of prestigious awards
for example
the John de Laeter Medal of the Australian
Institute of Physics
and the MacArthur Foundation Fellowship
which is commonly know as the MacArthur Genius Award
The title of her lecture today is: The Warped Side of the Universe.
Let's give a warm Penn State welcome to Professor Nergis Mavalava
[ applause ]
So thank you
everyone for being here today
I'll start just by saying
thank you
to Barbara she's put together some
fantastic materials for you.
She's also made me sound
very accomplished.
So take that a little bit with a grain of
salt.
I also want to thank my colleagues in the
physics department
with whom I've had relationships with for
many years. 
It's great to be back
here. So let me
just tell you what I'm going to be
doing here today with you by pulling up my
slides
and getting them going.
Okay.
So the title
of my talk is Exploring the Warped Side of
the Universe. 
I want to say a few things about my title
slide right away
I put my name here simply because I just happen to be the messenger today
for the work of very very many people.
So I want to acknowledge my colleagues and our funding agency the National Science Foundation.
Right up front
because none of this would be possible without all of them
so the warped side of the universe
is a part..is those parts
of the universe
where we should be glad we are not. 
So I'll walk you through some of the
places that what they look like .... and our
efforts on how do we try to understand
these warped parts of the universe.
But really the hero of our story today of
my story to you, but of the series that we
are part of here is Einstein.
So lets so let me start with Einstein's legacy.
So my story today is really about a quest
to study the universe using a new messenger
and that new messenger is gravitational radiation.And this is one of the predictions of Einstein's
general theory of relativity. To detect these
we make detectors that are incredibly precise.
In fact they are the most sensitive measures of position of particles ever made. And as
a result of this precision even though the
detectors themselves are very macroscopic
in scale the quantum mechanics of microscopic systems becomes very important. The thing
that really kind of ties the story together
rather remarkably both these ideas: the idea
of gravitational radiation and the idea many
of the underpinnings of quantum mechanics
is something that Einstein actually struggled with. These were both ideas that he never
fully got comfortable with until later in
his career. And we'll see that a little bit
as the story unfolds. We're going to take
a walk through the very beginning of time.
The big bang. We're going to stop along the way at wrapped regions of space time spectacularly 
violent events can occur, and eventually we're going to make our way to these objects which
are detector, observatories, here on our planet. So that's our menu. Now I'm going to beginning
by telling you something about our own cosmic address as a way of setting up our journey,
if you will. Okay so we start right here in
Hub Robeson, and that's where we all are at
the moment. If we went along for just for
...our planet earth is about 8 seconds away
from our star, the sun, which is our solar
system. And this is our most local neighborhood.
If we go further out, we'll find that our
solar system lives about 2/3rds of the way
out in a spiral arm of our galaxy and it looks a little bit like this one by the way, this
is not actually a picture of our galaxy. We
don't really know how to photograph our own
galaxy from outside of it. But it sort of
looks like -- we expect that it looks like
a typical spiral galaxy. So here we are in
the Milky Way on one of the spiral arms now
if we continue our cosmic journey we would find that the Milky Way is part of a little
cluster of galaxies that are gravitationally
bound to each other so they kind of know about
each other through gravity called a local
group, and this local group, this small handful
of galaxies is part of a much larger bigger
galaxy cluster called the Virgo Supercluster.
So that's our address as now we are getting out to truly large scale -- the Virgo Supercluster
is something like 50 million light years away from us. As we continue our journey we would
find that galaxies in general live in bright
parts of our whole universe, and these bright
parts, these galaxy clusters are actually
connected to each other ...I'll assume that's
something someone else can do.... connected to each other by these filaments of dark matter.
This by the way is not a picture this is a
computer simulation of what we think makes
up the cosmic web of our universe and finally as we make our journey outwards -- we get
out to almost 14 billion light years away
we get to the edge of the visible universe.
The cosmic microwave background. And this is a picture of this glow that surrounds us
that rises from in fact from the early history
of our universe shortly after the big bang.
In this case is not so shortly. We're going
to see that this is there is more to the story
than just this. Um... Okay. So how have we
learned all these amazing things about our
Universe? And the answer actually is I could say it in one word but I'll say a little bit
more but that one word is light. We have learned all these things about our universe by pointing
telescopes into the cosmos. It can start with very simple things that we could do in our
own backyards as star gazers. And if you haven't tried this a great past time, uh, but then
you can have more sophisticated telescopes like the ones on the earth the Keck Observatory
in Hawaii, or the Magellan Telescope say on Las Campanas in Chile but then you also have
telescopes that are out in space. And here
are four of NASAs great telescopes in space,
the Spitzer telescope, the Hubble telescope,
the Fermi telescope, and Chandra. Why do we
need all of these different kinds instruments?
All of them are looking at light from stars,
this is what we do we collect light from stars
and collections of stars: galaxies and so
on. Well it turns out that light has many
many more colors than just what our human
eyes can see and so all of these telescopes
are used to span those parts of the colors
of light that we wouldn't be able to see just
with our own eye. So these ones are on the
earth are mostly visible light, the things
we can see. But Spitzer is infrared light
that is redder than the red our eyes can see. Hubble is actually a visible telescope we've
all seen fantastic images from the Hubble
telescope and Chandra is an x-ray observatory
it sees highly energetic photons which originate from very different processes in the universe
then say visible light would. And then Fermi is a Gamma-ray observatory. So in terms of
energy of photos these are redder than we
can see, these are what we can see, these
are much much bluer than we can see, and then these are bluest that we know of. Okay? So
many many colors of light and why do we want all these colors of light? Well, it turns
out that our Universe is actually a very colorful
place. So here we have an explosion and this
is one of the most -- one of the very violent
events in our universe. What we see here is
a picture of an object called Cassiopeia A
, now remember you're gonna grade me with
your feedback forms. So I will also hand out
a quiz to you all in return, so keep in mind
all these little details I'm giving you. So
Cassiopeia A, what is it? Well it's something
called a super nova remnant. Its origins
were about 300 years ago, a star, like our
own sun exploded. Okay. Now why does the star
do that? Well our sun and many other stars
like our sun, the way that they live their
lives is that for much of their lives they're
burning hydrogen and helium. They are actually
doing -- having nuclear burning processes
and as this burning happens in the center
of the star light is given off. Now one of
the properties of light that we're gonna see
again in a little while is that this light
can absorb a force. Streaming out from the
center of rate star is the thing that keeps
the star from imploding on itself due to gravity
all the outer layers of the star has mass
and that mass is being attracted to the center
of the center of the star so the star through
gravity want to crush into itself the thing
that's holding it up is the light pressure
thats pushing it out. Now, as with all resources
eventually the star runs out of nuclear fuel
to burn. And when it does that it stops it
has fused everything to higher elements it
stops burning this light force that's pushing
out turns off and now the star it crunches
in on itself as the materials falls out there's
this big explosion and the star sheds off
it's layers and that in fact is what we're
seeing in all of these things. These are the
the ejected material that the star blew off.
Now what you see over here, that's also spectacular
that this picture is made up of three different
color using three of those different telescopes.
The very reddish colors here are actually
in fared they were done using Spitzer, the
yellowish colors here are Hubble's visible
that our visible band. And then finally the
greenish and blueish colors were images taken
by Chandra so these are x-ray observations.
So you can see that different colors tell
us about different processes. The bluest things
are at the edges these are the most energetic
parts of the explosion. They went out the
farthest. Now there is another reason that
you should be really glad that we could see
this object so many colors. And that is that
if you pay very close attention at the very
center you'll see a little turquoise dot.
This is a neutron star. This this was the
new starling that was born from death of that
star like our sun. Now lets talk about the
parent start that exploded when we look at
this object. Well we know that this star had
some something of the order of the mass of
our own sun. Or maybe a couple of times more
maybe three times more mass than our own sun.
And as a result what was left over after all
of this material was ejected was this little
neutron star. It's a really incredible beast.
This little neutron star because it has the
mass, roughly, of our sun, and it's size radius
is 10 kilometers. It packs all the mass of
our sun into the size of a small town. Okay?
So it's a really spectacularly dense object.
The gravity around this object is incredibly
strong. Just to put into scale, our sun size
is 700 thousand kilometers. Taking this huge
huge object and scrunching it down into this
10 kilometer object. Okay we're going to come
back to neutron stars now imagine that the
parent star instead of having been about the
size of the mass of our sun -- had been heavier.
If it had been a few times five or tens time
bigger the mass of our sun there's plenty
of stars like that in our universe as well.
In that case the outcome of this process when
the star explodes as a supernova the central
object would have been a black hole. K so
that's really the only difference between
these two -- the black hole or the neutron
star-- being formed is that the parent star
was heavier. Now how might we see this black
hole? Well, here is an image and this is actually
a schematic image made up of observations
again from the Chandra X-ray observatory of
what we think is a black hole GRO J1655-40
so what you see here is what we think here
is but what we really observe is we all have
heard about black holes and we call them black
holes cause the gravity in the vicinity of
the black hole is so so strong that even light
can't escape. So in principle you just have
a black hole sitting in empty space you see
nothing. But here we see something because
this particular black hole has a lot of gas
and dust swirling around it and it's own gravity
it's own strong gravitational field is causing
that gas and dust to swirl and dump on to
the black hole. And in that process this gas
heats up and this gas heats up so much because
of the strong gravity that it actually radiates
x-ray light. K so we've observed this light
in x-ray. We not only observed this light
these things which are called creation regions
but we have also found that this particular
surrounding gas flickers at 450hz, so much
faster than our eye could see but certainly
not too fast for X-ray telescopes. And this
flickering we believe is occurring because
this black hole is spinning on its on axis,
quite fast, 450Hz is a pretty fast speed for
something that's a few times the mass of our
sun. I mean I'll give you a scale if you get
a really fast high end blender it goes at
about 700hz so this is going about half the
speed of your blender blade but it's a Black
hole, it's something that has the mass of
our sun. So these are again, very spectacularly
warped regions of space-time. So one other
thing that you will notice, that as this material
falls onto the black hole the black holes
are known to be sloppy eaters now what this
means is that some of this material that falls
in on to the equator of the black hole finds
itself being ejected out at the poles. And
that then we see as these jets. So that material
is also glowing and giving off lots of light.
And we can see them as jets. So that's how
we kind of know about black holes. We mostly
know about black holes in our universe at
the moment at the present time because we
look for material around the black hole that
can glow. Now what would you do if you had
a black hole? Which we believe there are many
many of when there is nothing around it. Well
so far we don't know -- we don't know what
to do about that. We just can't really tell
if it's there because there's no glowing matter
or no object orbiting it that we can tell.
So if we have a black hole at the center of
our own galaxy we now know. It's actually
a very massive -- its a few million times
more massive then the mass of our sun. And
we know about it because when we look towards
the center of our galaxy we see stars zipping
about with orbits that can only be explained
if the central dark region had an enormous
amount of mass which corresponds to the black
hole. So my next question to you is how might
we directly measure something like a black hole.   
And here enters our new messenger. Gravity's messenger. understand a little bit about gravity. 
Now to understand gravity’s messenger the
first thing we need to do is to understand
a little bit about gravity. Now I will start
with our first hero of gravity. And that was
in the 16th century, Sir Issac Newton
and the had a really successful theory of
gravity he actually was the first to formulate
if you have two massive objects and you can
think of these with mass of M1 and M2 and
you put them some distance far apart that
this very quantitative way of saying, I can
tell you what the force is between the two
objects. I can tell you it's an attractive
force that depends on some constant which
we now know the mass of each object and it's
divided by the square of the distance between
the two objects and this is a successful theory
it could be it could explain apples falling
off of trees which by the way an apocalyptic
tale it could explain the motion of planets
and moons but Newton himself actually worried
about something and this something that he
worried about also occupied the hearts of
the ancients like Aristotle he worried about
this idea of action at a distance. he worried
about the question he has is how can this
object M1
real astronomical distances what is the means
by which they communicate that they should
be attracted to each other and feel this force.
and this kind of remained unsolved until the
next hero of gravity came along our hero today
that that was Einstein, Einstein as part of
his general theory of relativity said we just
got to stop thinking about this in a picture
of force gravity is the warpage of space time.
Gravity is geometry, he said. So let's understand
what he was really trying to tell us in a
somehow heuristic picture, imagine you have
an empty universe. A portion of the Universe
that's empty that does have any stars or planets
or anything it would look like a nice flat
sheet. Like the surface of a cushion. So if
you took that cushion surface and put a bowling
ball in the center, what happens? It curves.
If you took a little play marble and you but
it at the edge of the cushion what does it
do -- it falls into the bowling ball. It's
attracted. Gravitationally attracted to the
bowling ball. And that was actually Einstein's
picture -- he told us that space-time is something
that be warped by massive objects. and he
was also able to formulate that into a very
innocuous looking mathematical equation and
many of my colleagues here who work on the
solutions to this equations will tell you
it's a really horrendous beast. K? And so
solutions have been hard to get for too many
systems. But I'll come back to that, cause
of some recent breakthroughs. So Einstein's
picture is simply this Matter tells space-time
how to curve -- i have some region of space
time, i put something massive there it curves
and then that curvature tells matter how to
move. So my plain marble has no choice put
to crash into the bowling ball because of
the curvature of the cushion. It has no other
way to go.
If I give it some velocity at the edge of
the cushion it will just orbit. K? And so
that was the picture of Einstein. Now the
part that he then added to this picture was
happens if we take that bowling ball and we
bounce it up and down. K so if its just sitting
there it curves and there you go, but now
but if you bounce it up and down he then further
postulated that just if you drop a rock into
a pond or you put your finger into a tray
of water you'll see ripples. The surface of
the water will ripple and those ripples travel
out from where you're poking your finger.
In the very same way if you have matter that
accessorizing that the surface of space-time
will itself ripple. And those ripples will
travel outwards from where the object is bouncing.
And they will in fact, his theory that tell
us that those ripples will travel outwards
at the speed of light. And that then is the
gravitational wave, that was the piece of
his theory where he first turns space time
into and gravity into geometry then he adds
this part where the whole space-time itself
can ripple by accelerating at massive objects.
So the gravitational wave. So let's do a quick
little review of what gravitational waves
are. The basics are that they were indeed
a prediction of general relativity and and
in Einstein's picture they are really ripples
of the space-time itself. They're a property
of the gravitational waves that's really really
important for us because we're trying to detect
is that they stretch and squeeze the space
transverse to direction to propagation. So
imagine for a moment that the gravitational
wave from somewhere in the distant universe
is coming straight through me. Now I'm a little
piece of space time. Just as we all are. As
it goes through me what's it going to do it's
going to smoosh me in one direction and stretch
me in the other at the frequency of the wave
itself. So if I start off like this and the
gravitational wave goes by and something like
once per second I would be doing this .....
And in fact I am doing that but you'll see
in a little while at a level so small that
it would be undetectable so that's the gravitational
waves effect as it comes through it makes
space time distances longer and shorter. So
we'll use that to great advantage. So here's
a picture of what that would look if you have
this grid as the gravitational wave goes straight
through this grid it actually stretches and
shrinks the two directions of the grid.
Now how can put a scale or a strength to the
gravitational wave? Well it turns out that
the gravitational waves' amplitude we write
as this quantity "h" and I'll come back to
it a few times. So I'll just introduce it.
But it has scale in the real world that's
very important. In the real world it’s a
strain it’s like a tidal force it changes
some distance L by Delta L that depends on
the strength of the wave. So it's effect is
that it changes some space-time distance L
by the amount Delta L, and we're going to
come back to this, so basically if I'm an
object L I will change by an amount Delta
L that depends on the strength of the wave. Okay?
And then they're emitted when large gobs of
mass accelerates. That's another requirement
that you need that bouncing bowling ball for
the wave part otherwise the cushion just kind
of distorts and sits there, right? Okay.
Now if you want to do astronomy with gravitational
waves we've had centuries of doing astronomy
with light, I mean in some ways you could
a medium because the accents used their bare
eyes to look at the sky and you construe many
thing about the objects there but even if
you saw that modern telescopes started 300
years ago we've had 3 centuries to perfect
that now what do we know about light? If you
want to make light if I've asked you to make
like, you know most of you would just get
up and go flick on a light switch. but if
you wanted to do it in a more fundamental
way than that you would take charge pull your
favorite electron out of your pocket and you
would accelerate it. You would bounce it
up and down and after the charge accelerates
it will give off light waves, and that's how
you make light. Now that analogy works pretty
well, not perfectly but pretty well with gradational
waves too, instead of getting charge to accelerate
you get mass to accelerate. So far so good.
Now it turns out that with light you can make
images -- you can make very pretty pictures
because the wave length of light is small.
Gravitational wavelengths are very very long
you know, and as a result it's hard to do
imaging so what we do instead with gravitational
waves is we make wave forms, and what do those
mean? that simply means we take we make plots
where we look at how the amplitude of the
wave changes with time. Now it turns out that
those of you who've worked with sound that's
pretty much how we represent sound as well.
Sound waves that have different properties
as a function of time is how we hear. So we'll
come back to that idea, now a very important
property of light that we all should sort
of sit up and know about is that light is
very friendly. Every time photos meet some
other particle they interact, they like to
scatter off of them they get absorbed they
disperse.
If you're an astronomer this is rather annoying.
Because you have light that originates from
some distant source by the time it comes to
you it can be quite altered by everything
yet met along the way. And we know of many
examples in astronomy most recently when the
dust in the universe has altered the single
of something we were looking for. So light
is a bit problematic that way. Gravitational
waves on the other hand are extremely aloof.
They come streaming to us from the source
and they don't interact with the things that
are in-between so they come through everything
so you can be very confidant as an observer
when you observe something with gravitational
waves you're actually observing the properties
of the source itself but not something along
the way that altered the wave. Now, if you're
someone who in the business of detecting these
no if you're an astronomer you're thrilled
oh my goodness we have a messenger that actually
tells the truth about the source. But if you're
in the businesses of building a detector to
detect these you are --- this is very upsetting.
Now why? Because for the same reason that
the gravitational wave doesn't interact with
matter out in the universe it also interacts
very weakly with our detector. So the business
of decking them becomes very hard. Now this
becomes a recurring theme for the rest of
my talk. It's hard it's hard it's hard but
we're making progress. Okay. Now it takes
one other thing to know about gravitational
waves is that because they are generated --radiated
by these very massive objects it's really
hard to get huge blobs of mass spinning or
accelerating very fast. So typically their
frequencies are quite slow they are 10kHz and
lower. And that's sort of the high end of
the human audio band. It's the band which
we hear and those frequencies and so that's
why sometimes people refer to observations
with gravitational waves as listening to the
sounds of the universe. as opposed to seeing
light from the universe.
Alright now what kinds of sources can radiate
well you need three ingredients you need -- two
ingredients rather, you need lots of mass
that's why we like neutron stars and black
holes remember those are those star that are
have the mass of our sun but they're only
kilometers in size. So they have really really
dense regions of gravity. And you need rapid
acceleration. Which means we need orbits,
explosions, collisions, and hence and now
I'm starting to get you to get used to the
idea that you don't really want to be near
either one of these things. There's lots of
mass the warpage from gravity was huge but
it's not just huge but it's quite violent
usually so the things that we hope to see
are the collations of these compact object
neutron stars and black holes supernovae,
there's lots of acceleration and mass but
there's a source here that holds the greatest
promise of all and I'll say it right now that
it's pretty hard the detectors -- we know
how to make at the present time aren't good
enough to for us to see this but in the history
of the universe shortly after the big bang
the universe was so hot and so dense so filled
with matter that the photons couldn't escape.
K, so remember they're friendly they need
something they like to hang out. Right? So
the analogy that's really nice is imagine
you and your partner go to a party and of
you is an introvert and one of you is an extrovert
so you decide you're going home, extrovert
it takes them hours to get out the door they
meet everyone they chat they finally get
out the door. Introvert just kind of put his
head down and walks right through. That's
the gravitational wave. So as a result if
when you look at light from the early universe
when you look at that cosmic microwave background
with the edge of the visible universe that
was when the photons were first able to escape
that was 400 thousand years after the big
bang. okay. But there's a history to the universe
that goes much further back in time that we
can not see with light but the gravitational
waves have been streaming out from that time
right after the big bang so if we could make
interments that are sensitive enough to see
them we would be looking father back in time
to the origins of our universe than light
would ever allow us to do. Okay.
So that's what for me one of the most beautiful
things about promise of this messenger.
Alright so I told you that gravitational waves
radiate from black holes. So here is a pair
of black holes you can see that, and this
is a movie and at the time it came out which
was a few years ago now in 2007, this was
the real it was one of the early solutions
to that horrendous equation of Einstein's, Einstein's equations. Now what you're going
to see in this movie is these yellow contours 
these are tidal forces just gravity pulling
between the two black hoes and as the movie
runs you'll see start to see red contours
which are the gravitational waves staring
to radiate. Now, Gravitational waves as in
most waves carry away energy alright, where
does this energy come from? well it comes
from the orbit. So you have two stars that
are orbiting each other to black holes or
two neutron stars that ware, as they orbit
and as they orbit they are emitting gravitational
waves because there's a lot of strong gravity
there, their orbits get smaller they get closer
to each other cause the energy is carried
away and as they get closer to each other
they get closer and faster and faster and
finally they collide. And that's the movie
I'm going to show you here. In this computer
simulation, k?
So let me see if i can get it to play. Alright,
so what you see is they are just orbiting each
other and then soon our view is going to zoom
outwards and we'll start to see the red contours
of the gravitational radiation and there you
start to see the red contours this is the
actual space-time distortions that I was describing,
the whole space-time is doing this incredible
jigging like a bowl of jello. Uh and then
as the two object collide they kind of merge
into one single object it sort of rings for
a little bit and then the source shuts off.
Okay?
Now if you could take this movie and include
it into sound because remember these things
happening at in frequencies that are very
close to our own human audio band you would
hear a sound that looks like ..I went too
far...okay
so they they are far apart getting closer
closer closer that's what it was, okay. So
that was the that was the death of this binary
system these two stars collide into teach
other they became one star we see this spectacular
flash of gravitational radiation if there
was other matter around if it was like neutron
stars instead of black holes you would also
see a flash of light. Okay but if it's just
black holes you would see nothing in light.
Okay here's a little bit of history that again
brings us back to our hero. So Einstein made
this prediction of gravitational radiation
in his original and seminal paper on general
relativity in 1916. In 1918 he actually got
the correct formulation so this is a nice
little lesson even a great man made mistakes.
So so the first formulation was quite right
he got it right just a couple of years later. And that was good. But he remained really
uncertain about this, not just about how it
measurable weak this radiation was but he
was also uncertain is it really necessary
do I really need this solution to my equations.
and in fact in 1937 he submitted a retraction
in a paper with a colleagues Rosen and then
he retracted the reaction after a discussion
with other colleagues who worked in the field.
And the controversy finally actually subsided
in the late 1950s with the work of Filmen
and others. But let me just say and this is
sort of a philosophical comment on theories
in general which is in the end experiments
and observations always have the final say.
Your theories is only as good as it can explain
what we see. How does nature really behave?
And it turns out that it was right again nature
does behave this way. And the way the evidence
came at last to us was by the discovery in
1974 of a binary neutron star system. So these
are two neutron stars just like the ones I've
been describing so far but in this particular
case one of those neutron stars was a pulsar.
Now what's a pulsar? It's a neutron star as
well but in this case it has such strong magnetic
fields, it's like our earth magnetic fields
that go around the - come out of the poles
this these objects have such strong magnetic
fields that instead of light shining in all
directions it shines in a pencil beam, in
a very pointed way. So our sun, any side of
the sun you look at it glows but this objects
are dark except in one sharp pencil beam and
they are spinning around their axis or orbiting
so it looks like a light house, what it is
every now and then and in this case every
8 or so minutes a light beam points into your
line of sight and you can count how many times
this light beam comes around and they counted
this not just from the discovery in 1974 but
look at this it goes from 1974 to 2005 and
they're still counting. So they are able to
count these light pulses. And what they noticed
was that the timing of the light pulses was
changing. Why would it change if two stars
are orbiting each other? because the orbit
is changing. They are getting closer to each
other. And so then they mapped this out over
many years and they found that indeed that's
what this axis of the plot is it's the change
in the orbital period. It's shows that the
orbit of these two stars is getting closer.
Okay? And in fact that was their data these
points and the black line is exact prediction
by Einstein's equations of general relativity
for this being this gravitational radiation.
This greatly impressed Sweden and in 1993
they also won the noble prize for this result.
So it's widely accepted that gravitational
radiation is there it behaves the way Einstein
told us it would. And this is the result that
has allowed us to feel so confident. Okay
now how strong would this radiation be coming
from say Hulse and Taylor binary system so
they were the discovers and the Nobel laureates
for that measurement so that particular one
will actually collide 100 million years from
now, which is good it's gonna live for a long
time. Uh when it gets close enough to collide
now here's a formula I put up here and I've
only put it up here for wow factor. Now what
do I mean by wow factor, I want you to see
something really incredible about this formula.
This is amplitude of the wave "h" in the demoniator
is the speed of light to the 4th power. The
speed of light is a pretty big number you
put it to the 4th power, that's an even bigger
number. You put it in a denominator it doesn't
feel good it makes a very small number so
"h" is a very small number because of the speed
of light to the 4th power. What else do we
have in the denominator? We have "r". "r" is
the distance between the observer and the
source and for this we should be really really glad
that "r" is a very big number, remember we don't want
to be around that terrible like disruptive
jello of gravitational radiation near the source so "r" is a very big number also in the denominator,
so as a result when you plug in the number
for the right masses and distances etc for
the Hulse Taylor binary which happens to be about 21 thousand light years away, we get
the amplitude of the gravitational wave to
be 10 to the minus 18. Okay it's a small number,
so you all notice that it's a number with
18 zeros after the decimal. But okay. Now
imagine that you took a system like this one
a binary system and instead of just limiting
yourself to this one system we know we could
look out farther into the sky say in our super
closer into Virgo, which is 50 million light
years away that "r" became a much bigger number
still and "h" is of order 10 to the minus 21.
K? Still it' just a number with lot of zeros
after the denominator, nothing to worry about yet. But now we're going to put a scale on it
again. Remember if we want to measure these
we have to measure a change in length and
a change in length is proportional to the
amplitude of the wave times the length itself.
So let me inject my self again into the story
I'm an object of length, one meter, if that
gravitational wave came through me my size
change my 10 to the minus 21 meters I millionth
the size of a proton that's a small number,
now I think you should sit up and say okay
these people are crazy okay. Because I've
put a real scale on it. Okay so we are now
a little bit sobered. I'm assuming.
But that doesn't stop us, but we still want
to detect these waves I've told you the science
we can do with it is just incredible so let's
push on.
And we do, so how we do make the measurement?
well we're going to use that property that
changes the space-time distance as it passes
through and then the principle of the measurement
is actually really really simple, imagine
I have a laser and I shine it at a mirror
that's some distance away and the light reflects
off the mirror and comes back to me and if
I have a really really good clock I measure
the light travel time. The speed of light
is known and so I can tell how far the distance
between the laser and the mirror was just
my measuring how long it took the light to
travel. Now if a gravitational wave came by
this distance would change a little bit and
the amount of time it took to travel would
change and I'll measure that. Okay sounds
easy the rub here is that the precision of
the clock I would need to do that does not
exist. By orders of magnitude, by millions
by factors of many millions, okay, so that's
a good idea but doesn't really work. What
we do instead is something that's just a little
slight variation of this which is we instead
we take our laser beam and we build an interferometer
now how does this work? The laser light meets
this mirror and this mirror is called a beam
splitter and it's job in life is to split
the beam the laser beam into two halves one
half gets reflected and goes to this mirror
the other is transmitted to the beam slip
litter and comes to this mirror reflects off
of these two mirrors back to he beam splitter
and we can measure the rate of interference
over here. Now, why is this better? It's better
than this simply doing I'm not looking for
an absolute time measurement all I'm doing
is all I want to know is the difference in
the light travel time between this direction
and this direction.
And so I don't need as much precision I'm
just asking for a relative measurement I'm
doing a comparison instead of saying i need
to know exactly how long it took and as a
result this becomes a workable method. So
now if you wanted to build a this gravitational
wave detector you have two things to do. And
only two really. Um you need to make mirrors
that are really really still remember the
scale is now set for you the motion that you
are trying to measure is 10 to the minus 21
meters a million times smaller than a proton.
Everything on our planet moves more than that
so we have to a lot of vibration isolation
we have to also control all the thermal fluctuations.
We do that. The second thing you have to do
is you can make this mirror and it's really
still and you can feel really proud of yourself
but it's kind of useless if you don't know
how to measure such small motions. How do
you measure something that is so so still?
We use the laser light itself. We use the
laser light to probe the position of the mirror
and the result the precision of our laser
beam will become important. Now I'll finish
my talk with that idea.
There's one other ... we can turn, which is
we don't have to limit ourselves to a 1 meter
long detector so we actually turn the knob
of making our detector longer and in fact
that sector of the laser in gravitational wave observation LIGO which is the US detectors
are actually 4 kilometers long. And you can
see here an aerial view of one of the observatories
where you have the laser sitting here and
four kilometers away are the two mirrors in
an L shape. Okay?
Now that, what that does for you is instead
of having to measure changes in distances
of millions of times smaller than a proton
you're actually up to 10 to minus 18 meters
that's a 1000 times smaller than a proton
and that's a piece of cake.
No no it's not it's not I wish it were. but
it bring it into the realm of possibility.
okay so where do this, we have done this over
the last decade and a half a number of observatories
have begun to be built an operated. The two
in the US are LIGO one in Washington state
just east of Seattle and one in Louisiana sort of half way in-between Baton Rouge and New
Orleans. These are each four kilometers long.
Remember, longer is better. So the longer you
can make it the better the easier your job.
The next longest is a 3 kilometer detector
VIRGO in Italy. uh then there is a smaller
.6 meter detector in Germany called GEO600
and under construction at the moment is a
3 kilometer detector in japan there is a plan
to put a 4 kilometer LIGO like detector in India and then there are some futuristic proposals
which are not yet funded at the level where
they'll be built. So that's the proliferation
of observatories that are all trying to measure
these gravitational waves if you were to take
a tour of the observatory you would see here
our LIGO Louisiana observatory you can see
there is the 4 kilometer long arms in an L
shape and the laser beam itself travels in
a stainless steel tube like this going for
4 kilometers and inside of that tube is ultrahigh
vacuum nothing to disturb the light travel
path. The tube itself is protected with a
concrete housing that sometimes proves to
be useful. And uh so this not Photoshopped
this is real now this at our Washington observatory
you can tell by the desert conditions and
this patrol car came flying over this dune
and just I think neglected to notice that
there was this four kilometer long barrier
in the dessert. Okay no one was hurt thankfully.
People or detector. If you go inside of the
buildings you see objects like these this
is these are vacuums chambers the scale on
them if i were to stand beside one of these
to top of my head reaches just below this
row of ports that are used to bringing laser
beams in and out. Why do we need such a big
house for a mirror? Well it turns out that
our mirrors are also big when laser beams travel
4 kilometers they diverting they are getting
bigger and bigger so our mirrors themselves
are something like 30 centimeters in diameter
so they are kind of this big and they weight
10 to 40 kilograms to they are big objects
and all of this space is needed for all of
the vibration isolation that needs to be done.
So if you looked inside one of these chambers
you would see things like this these are spring
and might remind you of shock absorbers in
your own car for example. This is an example
of a vibration isolation system one of over
a dozen used in these detectors. And then
the mirror itself looks like and object like
this like i say it's about this big in size
and it hangs uh from fibers so its free to
move. A zoom in of the mirror, there's the
laser, and then finally this is the control
room from which all of this is controlled.
So these are real this is happening this has
been happening for the last decade or more.
What do we see. Okay we look for many different
things including some of the things we talked
about like neutron stars and black hole collisions
and pulsars. But with this first generation
of detectors there were no direct detections
we have not seen anything in our data that
we can say uh huh this was a gravitational wave
from this object. So I want to now tell you
a story about what you can do when you build
a detector that's really good and even if
it's not good enough to see what you are looking
for. And that story is one example of something
that I really like to tell especially young
people in the audience, uh okay. So this was
the search for GRB070201. GRB what is that?
That stands for Gamma Ray Burst. Now Gamma
ray bursts are rather peculiar and somewhat
mysterious objects in present times in astronomy.
What they are is you take patch of sky and
it's sort of nothing going on there it's dark,
and what people notice is that occasionally
in these dark patches of sky you have these
spectacular energetic bursts of light. And
it's very very energetic light it's gamma
rays. these are the most energetic photons
we know. So we have number of telescopes who's
job it is to look around it is to look around
in the sky and see these patches of sky light
up with these incredibly energetic light shows.
Now people don't know for certain classes
of gamma ray bursts what they are, but what
they are believed to be and you all will like
this now since you are part of you've been
following the story I hope what they are believed
to be are is the these are actually the final
flash of light when a pair of neutron stars
collides. After spends hundreds of millions
of year orbiting each other and then the very
last few seconds they speed up and collide
and in that collision you get this extremely
energetic burst of light. So when GRB070201
went off and this will be part of quiz, 07
for the year 2007 02 for the month of February
and 01 for the first day of February was
seen by all by these gamma ray and X-ray telescopes.
And they were able to actually constraint
it was consistent with being in the Andromeda galaxy which is our one of our nearest galaxies
neighbors so this is as good as it gets. A
really bright source really near by. LIGO
was on the air at the time so of course we
went to look. and we saw nothing. And what
that allowed us to say with a great deal of
confidence was that this gamma ray burst was
not cause by a pair of neutron stars colliding with each other. And so by seeing nothing
we were able to say something about the source. K? And in fact more data was taken and it
was found to be a giant flare. So that is
a story of how you can do science even in
the absence of positive singles you can make a good enough detector and that's key. But
we don't want to stop there. Clearly. We want to be able to go out and be able to listen
to more distant sounds in the universe. And so here for the first time I'm showing you
a real bench mark of the data we've been operating with so let me just say a little bit what
this plot looks like. So on the horizontal
axis here i have frequency so there is one
thing I want you to notice about that, the
frequency goes from 10Hz to 10kHz does
that sound familiar? It's the human audio
band. Okay. So on the vertical axis is just
Delta L what is the smallest L my detector
can measure what is that smallest placement
it can measure. And remember our target was
that it had to be something on the order of
10 to the minute 18 meters which is right
around here. Now these curves what they--
the way to understand them is that if there
is a gravitational wave at this frequency
that lives above the curve we would see it.
And the gravitational wave at any given
frequency has an amplitude such that it displaces
the mirrors by less than this curve it's hidden
by other noise sources that we can't help.
alright. So this was the first generation
of detectors that was built. I also want to
say something remarkable about these curves.
This red curve which was the target sensitivity of LIGO uh which we eventually built with the
blue curve in 2007 and the green curve in 2010
where we exceed that that red curve was written
down was calculated actually by the founder
of this idea of using of interferometers to detect
gravitational waves Rainer Weiss in 1972. So imagine
35 years later we built what he had the vision
to write down or calculate that could be done.
So again this is not an enterprise for the
impatient or the faint hearted. But the story
doesn't end here. We want to keep going and
keep building a better telescope and as a
result we are now building a telescope or
a detector that we hope will meet this target
sensitivity given by the black curve and so
the goal is for it factor of 10 better at
all frequencies. And remember in this in these
curves because this is a measure of Delta
L the lower we go the better. Pushing the
curves down makes our detectors more and more
sensitive. K? Now why do such a thing? Well
many of you will recognize this object and
this is what you would see if you pointed
a very crummy department store telescope at
what? Saturn. Okay. You can do a little bit
better if you spend a little bit more and
work a little harder but eventually and after
three centuries of perfecting telescopes you
would hope you could do that. Right? and that's
the game we're playing now. We're just trying
to get our detectors to be sensitive enough
that we can start to look at fainter sources.
So Advanced LIGO it's called, this new detector.
It's happening now. It's being built and commissioned,
we plan to do our first science data run uh
next year. And the progress on it is this
curve its the same frequency curve as Delta
L we're still working on it but it's about
a factor of 3 better at the moment then the
last one we had. The goal ultimately by 2020 is to get to that full factor of 10. Okay.
So I want to conclude my talk by coming to
this other thing that Einstein fused about
so much and that was the quantum limit. Why
does the quantum limit play a role in our
detector? and to understand that we go back
this curve right here, this is the advanced
LIGO curve, the one that we're working on
right now and the ultimate one would be another
factor of 3 below that and you notice that
our -- my legend here say this is quantum
noise. So what is this noise? Well it turns
out that this is the noise that comes from
the fact that light is made up of photons
and it's quantized. They are desecrate particles
they have to obey the laws of quantum mechanics.
And that is essentially limiting how well
we can make the measurement. So let's take
a look at why so here is a fundamental question
We use light to measure a position of a particle
and our particle happens to be this big 40
kilogram mirror but that's what we do we shine
light on it and say how far are you? Okay
where are you? And we do that simply by reflecting light of the mirror and measuring it. So now
comes the conundrum. We know that light carries momentum you'll notice already from earlier
in my talk that's how stars stay alive it's
the light pressure pushing out against the
gravity crunching it in. And this same momentum that's carried by light transfers to our particle
or our mirror. So here then comes the terrible rub the process of measuring where the mirror
is actually kicks the mirror every time I
shine light at the mirror my light is pushing
on the mirror and moving it. And this is a
well known conundrum in quantum mechanics
as well that...in quantum mechanics no matter
how good your apparatus you must have uncertainty.
You can not know things with infinite precision
and then that is then limiting how well we
can measure the position of our mirrors. Okay?
And that's really the thing that Einstein
struggled with. So the quantum uncertainty in
the photons the fact that quantum mechanics
dictates that we can't know exactly how many
photons we have in our beam is causing our
mirrors to move around. And then our brings
up the question of how do we how can we do
this? How can we measure the position of the
mirror if the measurement itself disturbs
the position of the mirror. And that is conundrum
of quantum mechanics. So what does this have
to do with our detector here?
LIGO, well it has to do every bit with it.
This limit, this black curve that I've shown
you is the limit that we have because of this
quantization of light it is precisely because
we are limited to this and don't go lower
than that. There are techniques and clever
scientists are working on techniques to better
than that. but that at the moment sets the
limit the fact that we use light gives us
this curve. We use lots of photos, we can
measure with great precision. But then those
photons kick the light as well. Okay so I
am going to finish with a truly remarkable
observation so Advanced LIGO is going to have
30 kilogram mirrors and they are going to
be so well shield from external forces the
vibration isolation and the thermal control
is so so good that in fact the motion of these mirrors will be dictated by the laws of quantum
mechanics. and people are really amazed by this and should be because when you have an
object that is about my size it's 2/3 of my
mass its 40 kilograms and it won't governed
by the usual classical laws that we see it
will be governed by the laws of quantum mechanics.
So this is an incredible thing and something that I think that Einstein would have been
tickled by. Okay when we capture this illusive
wave we will have great test of general relativity
the astrophysics promise really spectacular
we should be directly be able to observe big
bang and black holes but of course there are
objects that are way beyond our current imagination
that could show up. And then of course as
a nice side effect it -- these detectors are
so precises that we should also be able to
do quantum mechanics in these very human scale
objects. The cast of characters in this business
is large. Many many institutions and even
many more individuals uh we're here at Penn
State so I'll point out there are an shave
been for many years a important player in
this and the whole the US part of this whole
enterprise is funded by our National Science Foundation and in fact the International Science
Foundations from our international partners
of course also contribute. So I'll leave you
with this one last thought every time we pointed
our telescopes in new frequencies into the
sky we learned new things about the universe,
things that we had not predicted not expected.
and so in this coming decade as we turn on
our more sensitive gravitational wave detectors
we will start to fill in the questions of
what does the gravitational wave sky look
like and I hope I've convinced you that we
will not only be adding another wave length
or better eyes but for the first time we're
gonna be adding ears to listen to universe
as well. So thank you.
[ applause ]
Barbara Kennedy:  Who has questions? Time for your questions
we need some help collecting them because...some
have already been passed up. Okay. We'll get
started.
Nergis Mavalvala:   Sure.
Barbara Kennedy: If there was a large amount mass moving at
the speed of light would it not result in
a gravitaional wave because the speed of light
is constant?
Nergis Mavalvala: Uh Yes. So the speed of light indeed is one
of the constants. If you had a large enough
mass moving at the speed of light it would
actually disrupt itself completely very quickly.
So it's not a very stable source. Okay?
Barbara Kennedy: What causes this spike in quantum noise at
500kHz?
Very observant!That's actually a mechanical resonance
of our mirrors. Our mirrors are just like everything
else they have modes of oscillation and that one mode of oscillation happens to be one that
would show up on our in our data. There are
many others that I didn't put in that curve
so it was a bit of a misrepresentation that
line is there but there would be a few others
as well.
Barbara Kennedy: With the recent BICEP 2 unsupported conclusions
what happens now with that work?
Nergis Mavalvala: Okay so that's a great question. So let me
just make sure everybody's on the same page.
Uh BICEP2 was an experiment where there
was released a very spectacular result in
April 2014 where they claimed they had observed
gravitational radiation from the early universe.
These are primordial gravitational waves but
how they were observed they were observed
by the way imprint that gravitational waves
imprints themselves on the cosmos microwave
background so these cosmos microwaves background
photos are streaming out towards us and they
are coming from all directions and we believe
that the originated by 400 thousand years after
the big bang. Now gravitational waves were
already populating the universe at that time
too and it turns out that because of the way
that gravitational waves were around as well
we expect that the proliferation of the light
the direction in which the light oscillation
should be ever so slightly polarized. If you
just take light that's un-polarized it's oscillation
going all directions randomly at the same
time. But if you then let that light interact
with some materials or gravitational waves
you get a slight polarization. which means
it has a slight preference to oscillate say
in this direction as it propagates. Not just
every direction. SO they measured the polarization
of this cosmic microwave background and they
found a result that supported that the light
was indeed polarized and it was polarized
in sort of consistent with the expectations
that it was due to primordial gravitational
waves. So it was a big and very celebrated
result. Now it turns out there is one effect
that could confuse this result and that is
that the cosmic microwave light that's coming
at us could also be polarized by dust. Remember
light loves to chat with everyone so there's
dust in the universe as it's coming towards
us and dust in our own galaxy in particular.
and that dust can also cause polarization
of the light. and the BICEP 2 team very hard
to account for the dust this was a known affect
that can happen but it turns out another experiment
now Plank was able to also do some measurements
where they took into account the dust and
it looks like the BICEP 2 result is not going
to hold up. In other words it was not primordial
gravitational waves that caused the polarization
of the cosmic photons, microwave photons but
it was likely the dust. So yes, where do we
go next I think this is a very solvable problem
uh one can actually get a good measure of
the dust if you measure at many different
frequencies so we just have to get a research
program into place it's not cheap so I'm making
it sound easier and lighter than it is, you
get a research program into place where if
you can measure the dust at a few different
frequencies you can subtract it out of the
measurement. And then most likely there will
be some polarization that survives and then we
believe that should be from primordial gravitational
radiation. So that's a long answer but I hope
it kind of gives you a picture a sense of
what was going on.
Barbara Kennedy: We have more than one person who's worried
about the next question How are they planning
to isolate the detector in a geologically active
location like Japan or the Washington observatory
how do the observatory technicians manage
the earth quakes!
Nergis Mavalvala: Excellent question. So it turns out that it's a geologically pretty active region but geological
activity comes in bursts. And the rest of
the time it's a actually a fantastic location
it's got a lot of bedrock and as a result
the seismic waves attenuate pretty quickly and
so it's actually systemically a very quiet
area. Except when there's geological activity,
like a few years ago Mt Saint Helen's was
rumbling again and but at those moments in
time are detector is off the air anyway. So
most of the time it's a fanatic it turns out
that most people don't appreciate this but
our Louisiana observatory is actually much
much more problematic in terms of systemic noise
because the systemic waves travel travel pretty
unattenuated and it's quite close to the
ocean and the ocean waves when they crash
onto the shore than the wave just travels
right through our detector. So it's actually
a much more problematic place to do this kind
of vibration sensitive experiment than the
Washington site. And the Japanese have a even
nicer thing going on, yes it is a geologically
active but for the same reasons its not gonna be
you know a lot of the time. Their detector
is underground. It's actually going to be
in a mine tunnel. And when you go underground
your systemic externalizations actually decrease
by a factor of a few. So ti's actually going
to be geologically you know seismically pretty
a pretty nice place to build an observatory
like this. Except for the times when there
is earthquake or seismic activity and the duty
cycle people expect for these to just lose
a few percent of operating time. So.
These two questions may be related so I will
read them together. One after the other. How
does this spinning in the black hole get started
after the supernova. That's one question.
And why do objects swirl around the black
hole before they fall in the marble just goes
straight into the bowling ball on the sheet.
Okay, let me answer the last question first.
If I -- Okay it is true if i just put a bowling
ball and a put the marble at the edge all
it will do is fall in. But imagine now that
instead of just putting it at the edge I put
it at the edge of the cushion and I give it
a little bit of velocity. Then in the transverse
direction, at the inverse angle at which it
would fall in. Then this marble would just
orbit around the bowling ball, it won't fall
in. And you probably have gone to museums
before where you have these uh little black
wishing wells where you put pennies at the
edge if you just put the penny at the edge
it just falls right down into the hole, but
if you get it going into a circle it will
be taking many man orbits before it falls
in. And that's the reason. So that's the first
part of the question, the second part I already
forgot Barbara. What was it?
Barbara Kennedy: I'm getting there! Alright, um hold on a second.
How does the spinning in the black hole get
started after the supernova
Nergis Mavalvala: Right, thank you. Yeah so typically the way
that objects get out to spinning is when you
have these explosions what is the requirement
for something to spin. It has to have some
angler momentum. And so somehow the motion
of the ejecta and the explosion has to impart
some angler momentum in the system and angler
momentum in the system and there is no way
to lose it. So once it's there the object
will spin. So that's typically one of the
ways that the original explosion imparted
some angler momentum. Another way that it
could happen and we don't have complete evidence
of which dominates is that these particles
that these stars can meet other stars and
as they go by they get disturbed by the gravitational
interaction with other objects. Sometimes
they even get captured and even if they don't
get captured it changes their direction of
motion and they can acquire spin that way.
Barbara Kennedy: Could you build a gravitational wave observatory
in space?
Nergis Mavalvala: Fantastic question. The answer is yes. And
in fact there has for a long time been a plan
to build such a one that was also very much
studied and supported by both NASA and the
European Space Agency, it's called LISA which
is Laser Interferometer Space Antenna and it's
a beautiful concept. you have three space
crafts and they are separated by five million
kilometers. Okay so we're not talking about
a kilometer or 2 like we have to do on earth
but by a million kilometers and they shoot
laser beams at..each space craft shoots laser
beams at the other space craft and they measure
the light travel time of those laser beams
and from that they can reconstruct over the
spacing of five million kilometers what the
distance between the space craft is. Now why
is that doable in space? Well once you get
up your L your length getting up to 500 kilometers
your Delta L you have to measure is only and
I say only you know it's only a picometer
it's 10 to the minus 12 meters so if you're
thinking about it in comparison to the terrestrial
detectors that have to measure 10 to the 18th
10 to the 19th meters I mean if we could make
such a long detector on the earth we'd have
to the same luxury. Now of course in space
everything is harder. So even picometre level
geometry is very challenging. Uh but this
program has been around for a long time and
it was only in the last year or so that has
actually been sort of demoted to sort of very
futuristic things, mostly because everything
in the pipeline of NASA is sort of on hold
until the successor of the Hubble telescope
the James Webb telescope goes up. So NASA is
very busy with James Webb and everything else
is on hold or LISA would be I think its a fantastic
..no why would you want to do that? Let me
just answer that even though it's not a question.
So it turns out that if you want to measure
gravitational waves that are lower frequency
than about 10Hz maybe 3Hz and there are many
man sources that radiate at very low frequencies
like super massive black holes like the ones
we know are at the center of many galaxies.
They are so so massive they are not vibrating
at 100Hz or at kilohertz they are just lumbering
around. K? And the radiation from them would
be at these very low frequencies and we have
really no hope of measuring at those frequencies
on the planet. The planet is too active at
these very low frequencies. That's too much
vibration so you really have to get off the
planet to do that. So when you think abut
LISA and the terrestrial observatories like
LIGO they're very complimentary. You can think
of almost as they are look the same way as
in light you have X-rays for looking at very
high frequency light and radio telescopes
for looking at very low frequency light, it's
kind of the same thing. LISA and LIGO are
two completely different frequency band for
gravitational waves. So there is really is
many many reasons to do it. It's just expensive.
Barbara Kennedy: What does it mean to measure its position
oh I'm sorry I should read the first question
first. How polished is the surface of the
mirror what does it mean to measure it's position
to person of 10 to the minus 18 meters much
smaller than an atom.
Nergis Mavalvala: Yeah, that's actually another fantastic question.You
guys have really either done you're homework
or are very thoughtful. Um so the question
being asked is look what does it mean when
you say you are going to measure the position
of your mirrors surface down to a thousandth
of a proton. You know the mirror is not flat
at that level. And the reason why that works
is that the mirror is actually flat at the
level of nanometer. So it's a little bit less
maybe a tenth of a nanometer. So the bumps
on the mirror are thousands if not millions
of times bigger than the average position
of the mirror that we can to measure. The
reason why this works is that our laser beam
is very big. And it's averaging over the whole
surface of the mirror, so the average over
all those pumps, What we are interested in
is the average position of the mirror not
the given single bump here which would be
11 million times bigger than what we are trying
to measure. So it's this averaging effect
that allows us to make mirrors that are a
tenth of a nanometer flat which by the way
our also really a tour-DE-force in mirrors
but you don't have to make them flat at the
level smaller than protons.
Barbara Kennedy: Giving you a moment to take a breath. [ laughing ]
Nergis Mavalvala: Do I look like I need to? [laughing]
Barbara Kennedy: No no. Would you need three interferometers
to reconstruct a 3d map of gravity.
Nergis Mavalvala: Okay so that is another fantastic question.
So I showed you a picture about half way in
my talk of a global network of observatories
I showed you there were two for LIGO two in
Europe in Japan and India, why do you need
all of these? Alright, you need them all for
many reasons but the two main ones are the
first one is and the most important one is
that these observatories their these big L
shaped detectors. Now most telescopes if you
want to look at an object in the sky your
telescope is on a little swivel mount and
you swivel it over and it points. Now you
take something that is 4 kilometers long on
the ground it's not pointing. The only way
that points is by the rotation of the earth.
As the earth rotates it's pointing at different
parts of the sky. So that's the first thing
so if you cover all parts of the sky at any
given time you need to have them scattered
all over the earth. Okay? The other thing
that happens with these detectors a telescope
when you point a telescope you see a teeny
tiny patch of sky and that's what you see.
These detectors are not like that. They are
pointing, they are beaming angle is really
big. You actually see a big swatch of sky
at any given time and in fact both above you
and below you because the gravitational wave
comes right through the earth as well and
as a result you with a single detector you
can't really tell where the source was. You
can just tell it was somewhere in this big
globe. But if you have multiple detectors
you can start triangulating. You can say from
the time of arrival of the signal you can
start to tell where in the sky it was. So
that's another reason you want and you want
the biggest coverage you can get so if you
ask why are the US detectors separated geographically
by 3000 kilometers it's for this reason we
want the baseline to be able to triangulate.
The last reason why you have so many is so
there's this location in the sky question
but the other thing is that we know we know
even with these new improved detectors that
our single to noise is going to be ya know
not huge in the early going. And as a result
what we require is coincidence in all detectors.
Every deco-- because as many man other things
on the earth that go ping and make it look
like a gravitational wave just hit your detector.
but those would be different in the different
detectors on the earth so this coincidence
part is very important where you require that
a signal that a comic signal arrives within
a certain coincidence window um in the different
detectors. So with all of those put together
- and that's part of why this is actually
a really fantastically cooperative field to
work in because all of these observatories
know that they rely on every other observatory
to construct the full picture and so we work
a lot together.
Barbara Kennedy: The person that asked this question is making
an assumption. The question is what is the
one question/mystery you are trying to answer?
and then what?
Nergis Mavalvala: Okay, So actually I think that that's a fair
and good question.There are many mysteries
so let me tell you the one that I'm most excited
about that i told you was the early universe.
The gravitational waves from the time of the
big bang. I don't believe that this generation
of detectors of even the next unless our understanding
of the early universe is not what we think
it is will detect those. Uh will it happen
in my lifetime that we can actually look back
farther into the universe than light as allowed
us to, I hope so! Now that's one excitement.
If we want to know what was going on in the
universe before the photons escaped we would
do that. But lets' not go so far back so far
out in time -- let's just look at our more
local universe we know that black hole proliferate
in our vicinity of the universe we know very
little about them. We know very little about
what does the space-time around a black hole
look like we know very little about how do
black holes interact with each other and we
have no way of measuring that with light because
there black! And so that's the kind of thing
so what is gonna be -- if you're asking me
what to I precinct will be the first discoveries
in these terrestrial detectors? I think it
will be the coalescence the crash of the
binary neutron star or binary black hole system.
It will be that will be the first things we'll
look for because know they're out there. We've
seen them with light and the ones that can,
the black holes we can't, but the neutron
stars we can. But then I think there will
come a time when we will be scratching our
heads there will signals in our detectors
that we just won' know what they are because
we don't know everything that's out there.
Thank goodness or we'd be bored! We'd have
nothing more to do! So I think there will be
a period of time when there will be what i
would call discoveries of objects that we
didn't expect. Every time we open up a new
wavelength of light that happened to astronomers.
And I think that will be the same with this
new tool.
Barbara Kennedy: Why do you give black holes such strange names
as GR0j1655-40?
Nergis Mavalvala: Oh you were really listening! That's fantastic!
The GR0 in this case I think just stands for
gamma ray observatory it think it was i just
the observatory that happened to measure it
even I don't know where all these names come
from. But astronomers are famous for naming
things in strange ways, and the only people
who have us beat at this are people in biology.
So but, yeah, but I don't have a good expiation
I think that GRB0702012 was actually really
reasonable and then if you look at something
like Andromeda so Andromeda in astronomer
speak is called M31 and why? because M was
Messier and he sat down and a century ago
and he started to catalog all of the objects
in the sky and this was the 31st one he cataloged.
K so look, I can't give you a good explanation
it's part of the lore. I guess and I'm not
making an excuse for it it confuses me too.
Barbara Kennedy: How did we see the stars zipping around the
black hole at the center of our galaxy years
ago there was a big controversy about weather
or not we had a black hole at the center of
our galaxy.
Nergis Mavalvala: Yes you are right, there was and I believe
that has been put to rest now by further measurements.
So in the group for example at UCLA for example
and many others people literally are looking
at orbits of stars so you know you have some
region of sky and we happen to know where
the center of our galaxy is it's pointing
in the direction of the constellation Sagittarius
and they look at stars and they notice that
these stars -- they look look at them not
over one night or two night but you know months,
years, and they notice that the stars are
moving in the sky. and they are moving with
trajectories that you can not explain in any
other way than that they are orbiting some
object that you can't see. You can't see it.
Then you know by measuring the orbital dynamics
you can infer what should this object in the
middle be and to your horror you find that
this is something that had to be a million
or ten million times the mass of our sun.
Then you look at it and say okay, but it only
occupies this rather small volume it doesn't
occupy the volume that 10 million suns would
then you can conclude that it has to be a
black hole because that's the only way you
can take that much mass and compact it into
the volume that you see given the orbits of
stars. That's how they know and in fact if
you go online and do a search for this there
are actually now some beautiful movies these
are actual real movies that measure where
the star is and do it over many years and
then they make a movie out of that and you'll
see the star zipping around -- not just one
many zipping around in trajectories that are
only explainable if there is this black hole
sitting there. So I think that controversy
is gone I think it's on pretty good footing
that there is and we know this also from many
other galaxies ours is not unique to have
this black hole. We know from measurements
of other galaxies where we can see the whole
galaxy so we can see the star population in
the galaxy from the outside and we have the
same evidence. We also see galaxies with those
jets remember I said black holes are sloppy
eaters so they actually sort of belch things
out at the poles? And you see galaxies with
large jets and that's again the signature
of a black hole. So, I think the evidence
is really mounting.
Barbara Kennedy:  This will be our last question. There was
one other question but it feels a little too
personal to ask in a public space so if you
have that personal question you can come speak
with Nergis later.
Nergis Mavalvala:  I'm terrified! [ laughter ]
Barbara Kennedy:  So our last question. What is the energy source
that propels the light for billions of years?
Nergis Mavalvala: Oh yeah that's a great question. I think that
the way that you have think of it is that
some process -- some energetic process gives
birth to a photon. And once that photon aquries
that energy it travels at the speed of light
with that same energy. It doesn't lose it
until it meets something else that it can
give the energy to. It doesn't give the energy
to the vacuum. and so it keeps it's energy
until it meets something that it can exchange
energy with. Now the processes that give that
allow us to make all these different energies
of photons are itself a very interesting question.
So remember I told you the very simple minded
and it is simple minded way that you take
light is that you take an electron and you
accelerate it. Right? So the simple way to
think about it is that if you accelerate
it fast or if it has great acceleration you
will get more energetic photons out so that's
heuristic way, but in astronomy in the universe
when we see say X-rays verses radio ways which
are very different in energy we know that
the X-rays were .. originate from some very
violate process because that's where you can
get at that much acceleration to generate
X-rays or in some region where there were
ridiculous magnetic fields or electric fields.
Something has to ..something energetic has
to happen to give rise to these energetic
photons but once they have them they travel
along until they give it up to something else.
Barbara Kennedy: Professor Nergis Mavalvala, we give you our big
thanks.
Nergis Mavalvala:  Thank you everyone for coming!
[ applause ]
