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For the next talk, we will hear
about how to get together
lasers and dark matter.
So our
speaker for the next grant
studied physics in Hanover and taught
astro astronomy in
remote places like Tanzania.
He is a postdoc at the University of
Florida, where he now works on
the apps instrument
or device that he will talk to
you about and will maybe
give you the chance to one
day actually know
that at least where the dark matter
is that you might want to own.
So please welcome with me
Simon Barker
with Eavesdropping on the Dark Cosmos,
given Wylma Plus.
Well, hi, thanks
for having me. Thank you for being here.
And did you know that the screen
behind me has two million
pixels, let's say,
just for fun, let's assume
this screen is all there
is and the entire universe.
So if that was the case,
this screen would be
dark for 95 percent.
95 percent of the screen would be
completely invisible.
There would be another like eighty five
thousand pixels, which are utterly
boring.
Then we have some cool, like 10000
asphyxiates, which are made of stars.
That's nice.
We have elusive neutrinos
making up like 6000 pixels.
And do you know what the small portion
down there is?
622 pixels.
That is you. That is me.
That is this planet.
This is all the higher elements like
oxygen and carbon, like gold and
plutonium.
That is all there is of matter
we care about.
Usually
astrophysicists care
about a little bit more so
they don't care about zero point zero
three percent, but more like about the
five percent over
there on the right.
I myself care about the ninety
five percent.
So I'm interested in the stuff you
can't see in the invisible dark
part of the cosmos.
So welcome to
Eavesdropping on the Dark Cosmos.
I'm here on behalf of the Max Planck
Institute for Gravitation of Physics and
Hanover and the University of Florida
in Gainesville, United States.
My name is Simon Bach.
And before I would
like before I continue to
talk about the dark side of the cosmos,
I would first like to explain to you
what I mean when I talk about Cosmos or
universe, what is our universe?
So I'm pretty sure you've heard that our
universe started in a big bang and
here we have the size of
the universe over it.
It took three hundred eighty thousand
years after the Big Bang
for the universe to expand
to a size where the density
was low enough so that light
could pass through the universe
through the very first events we can
observe happened three hundred eighty
thousand years after the Big Bang.
Since then, thirteen point eight
billion years have passed and
the universe became quite bigger.
Actually, the universe right now
has a radius of forty
six billion
billion billion light years, so diameter
of ninety two billion light years.
And now you may wonder how could
we see something 46
billion light years away
if the light had only thirteen point
eight billion years time to
Treva?
What?
Back then, when the light originated,
like 380000 years after the Big
Bang, the universe was much smaller,
actually just roughly 40
million light years across.
That's when the light from the
edge of the universe started to travel
towards our point in space
and the universe expanded
during the time to try
to reach us.
So it's like the malls on the rubber band
pulling apart and it took the light
thirteen point eight billion years in
order to basically cross 40 million light
years.
And the universe expanded since then
to ninety two billion light
years in diameter.
So that's what I speak about
when I say our universe or more
precisely, my universe.
I am in the center of this universe.
If I moved like five meters to
the left, my universe would
expand five meters to the left and
contract five meters.
Right. So you all have
different local universes around you.
And of course, they are universes
out there far, far away
with like aliens and their centers,
which we could never reach, which
would have no causal connection to us.
We can see there.
We can't interact there.
It's universes of their own, but they are
in our space time continuum.
It's nothing strange, just too far away
to be counted as part of our universe.
Anyway, our universe
looks like that we can do pictures
of it.
We can see that there are billions and
billions of galaxies out there.
Can we yes,
billions and billions of galaxies, each
galaxy contains billions
and billions of stars.
It's a huge space, we can see
planets and nebula, we can
see jets emitted from black holes,
we can do pictures, but
actually that's all we do.
Or we know about the universe as
it looks like we know.
From light electromagnetic
radiation, that's all
we can do.
These are the Maxwell equations,
they describe light.
So one solution of some extra
equations is the differential
differential WAF equation, which
in the end results in periodic
oscillating electric and magnetic
fields that what we call light that
an electromagnetic wife.
And we use this on Earth as well.
We use it to see other.
So a light rain, electromagnetic magnetic
wave will bounce off stuff.
Different materials only reflect
certain frequencies of the
electromagnetic wave.
And then we receive this wave
as our eyes and interpret the
different frequencies as colors
in our brain.
So different colors are nothing but
different frequencies of this oscillating
field. But again, all we know about the
universe, we know from light.
Wouldn't it be nice if we could not only
see the universe, but also
hear it?
So we need all these different spacecraft
in order to cover the entire range
of electromagnetic waves there.
But there's no way to listen to
when events happening out there in the
cosmos. It's all still just
electromagnetic radiation.
So how could we listen to
the cosmos here on Earth?
We listen through pressure waves
in air, so
sound waves travel through a medium.
Do we have a medium in space?
No one space. No one can hear you scream.
That's a problem.
We can't transmit sound through space,
but don't we have another medium out
there?
In fact, we do.
Since 100 years we know
from the Einstein field equations
that there is something called space
time.
And the Einstein field equations told
us that gravity
is nothing but curvature of space time.
So you have a massive object and
this massive object is curving
spacetime.
And then smaller objects do nothing
but falling into the curvature of the
space time.
Just bend space time like Schnur's, Earth
is curving space time and I am falling
into the curvature of space time.
I'm attracted by the gravitational force
of the earth. That's what I'm seeing.
But in reality, it's just curved space
time. So we know there's space time
everywhere and space time can be curved.
Country transmit waves through space
time where we would have
to see if this equations, the ancient
feud equations have way solutions.
Yes, they have.
And then we would need to find conditions
under which astrophysical sources
could emit gravitational waves.
So what does a star have to do in
order to emit gravitational waves in the
fabric of space time?
Some years ago we did some
YouTube videos
basically exactly about that, like
what does a star have to do in order to
emit gravitational waves and
just listen to YouTube for a second or
so?
Yeah, normally we
would have to solve the calculations
involved in Einstein's theory in order to
understand it.
Say that for a system to emit
gravitational waves, it only needs a
non-zero third time derivative of the
quadripolar of its energy tensor.
Funnily enough, this is a bit complicated
to intuitively understand.
Yeah, that's a math.
So you have to stress energy tensor,
which basically describes energy and
matter. And if the time derivative
of the quadruple moment of the stress
energy transfer of the ancient field
equations, if that is not zero,
then there will be gravitational waves
easy enough.
Actually, there's the picture
I can give you. It's very easy to
understand. All we need in order to
have gravitational waves are accelerated
objects, massive objects
that made it to stars.
And Robert basically also
me spinning.
I'm accelerating my hands in
a circle.
This is steering up spacetime.
That's a non-zero time derivative
and so on and so forth.
And this gravitational waves are
transmitted throughout the entire
universe. And there are lots of objects
out there that are constantly
accelerated.
So let's take two galaxies
colliding, merging two supermassive
black holes at their centers,
two black holes colliding, huge
amounts of matter accelerated
rapidly.
You have smaller stars or small black
holes, neutron stars falling into
supermassive black holes.
Of course, this is accelerated metter
producing gravitational waves.
Why are they falling?
You have.
Very tight binary star system
so close together that
the companion starts actually sucking off
metter from its bigger one until
it explodes like a huge supernova,
explosions accelerate and Tetragon
should produce gravitational waves.
And you may have like artificial
sources of gravitational waves.
Spaceship's accelerated very
fast should produce gravitational.
All that I just shown you,
it's not science fiction,
no, wait for it.
We see rapidly spinning neutron
stars, Pulsers, we
see these vampyre stars,
we can see we can track
the orbits of stars circling around
supermassive black holes.
We see supernova explosions.
And yes, we even have a theory
on how to build a warp drive.
We cannot do that now and we are not even
sure if it's actually possible.
But this is the only way we know
that could propel a spaceship faster
than the speed of light that is not
forbidden by physical laws.
And that is pretty cool.
And it involves an artificial curvature
of space time and some negative energy.
But that's just a technical issue.
But we know that if a spaceship
would enter this warp bubble, it would
produce gravitational waves.
So when we would detect gravitational
waves, we could at least say, no,
no one out here in our universe is
using warp drive. So maybe it's not
possible at all.
Or we could detect, like we have a warp
drive detect or know if we have
gravitational waves detector.
Let's see.
So
how actually can we detect gravitational
waves? The biggest effect of
gravitational waves on us
is a change in distance.
You're sitting there where you sit and
you don't move at all and let me
stand over here and not move.
And no gravitational waves is passing
through the earth.
What it does is it periodically changes
the distance between us
by stretching space time between us
and compressing it again.
So you don't move? I don't move, but our
distance is changing periodically.
That's a weird concept.
But now we know how to how to detect
gravitational waves or we need to do
is measure distances like.
Like really. Really.
Exactly.
The big issue is that if
a strong gravitational wave
hits our solar system,
then the distance between Earth and sun
will change by the fraction of the
diameter of an atom.
And that's like distance between Earth
and sun.
So that's what we need to do.
That's how precise we need to become.
We need to measure the distance
between Earth and Sun
with the precision of one atom.
Technical issues.
We actually solve them,
so.
OK, maybe let's start first with
what we expect to detect,
if we could measure that, if
we could measure the distance between us
and stand by the diameter of an atom
and then amplify the signal and convert
the frequencies to audio
waves, we could listen to the
universe. We could listen to start
exploding. We could listen to black holes
merging. And I brought some audio files
of like
artificially generated signals that we
expect to hear.
Pulsars are rapidly spinning neutron
stars and they steer up
space time at a constant motion should
just be assigned signal.
So that's our sine wave.
No.
That's a pattern, these are supernova
explosions, can we turn it up a
little?
Supernovas.
Then we have
binary stars in our galaxy.
Orbiting it so many
of them that they will contribute to a
nice.
If binary stars that
much and collide
gone there, and this could
happen with more massive objects like two
black holes orbiting each other
at low frequencies
coming closer and closer
and merging.
That's what we expect to hear
and then we have smaller stars
falling into supermassive black holes,
and this is more of the really
fascinating thing. There is lots and lots
of details to it.
That's another one.
Oh.
You can hear a spin to lining,
you can put out so much physics
out of these signals to get to Mars
and the orbital velocities and all of
that out of these weird noises from
the universe, if we could detect them.
So let's detect them.
We did build gravitational waves,
detectors. We actually started 10, 20
years ago building these.
The two biggest ones are currently in the
United States, one in Louisiana, one in
Washington state.
And that is like the Laser
Interferometer gravitational waves
detector and
basically consists of two big
lasers at a rectangular
four kilometers long.
And when gravitational waves hits the
detector, the distance
of one arm or the length of one arm
will become longer and the other one will
become shorter.
So all we need to do is to measure the
length of the two arms in order
to detect gravitational waves
with only four km long arms.
We need to do that better than the
fraction of an atomic nucleus.
That's why it took us 20 years to build
the thing.
And then last
year, September 14th, I guess
you need not go too far away from here,
last year, September 14th,
gravitational wave hit the detector.
So what happened was we are measuring
the length of both arms with lasers.
We are sending one laser beam to beam
splitter, reflecting it back from
tumorous. And usually
we don't have light at the airport.
But when the gravitational wave changes
the length of both arms, we see a light
flickering at the lower, lower output
on our detector.
So all we need to look for is this
flickering light.
And since full
brightness and no intensity at
all is only like half
of a wavelength, only 500 nanometer
distance, and we cannot only detect full
brightness and zero, we can detect
a little brightness where we can
go all the way down to the fraction
of an atomic nucleus and measuring
the distance variations between the both
arms.
And then the gravitational wave came like
basically a day after we switched on the
device after a big upgrade, a
very beautiful signal.
And here it is.
This is really a simulation.
That is the very first gravitational
wave ever detected
by a gravitational wave detector.
You see?
It wasn't me, it was thousands and
thousands of physicists working at the
thing for 10, 20 years, but
it's it's an amazing discovery.
We know that the prediction of Einstein
was real. What we have here is time
over amplitude.
And you see that this gravitational
waves, we detect, it only lasted for 200
milliseconds.
You also have the frequency.
So the peak frequency was like 250
hertz.
That kind of means that the two objects
orbiting each other, producing this
gravitational waves, had to orbit each
other 250 times a second
that fast.
We don't do this around Sun.
We can also, like, change
the pitch of the signal a little to make
it.
Uh, that didn't look sorry,
Beck.
One more.
We can change the pitch a bit later.
Make it
easier to hear and then you can download
all the raw data from the
Open Science Center.
They also provide Pisin scripts for you
so you can get the raw
data and play with it a little to make it
sound cooler. Many people did music.
Was it actually that was surprising.
Doesn't sound that good.
But what we can do from the data, what
you could actually do with the raw data
is figure out what kind of objects
exactly emitted these gravitational
waves.
So.
The sum of Shiatsus.
Here we go. So
what we found out was
that these gravitational waves were
emitted somewhere
from the direction of the derartu
constellation.
One point three billion light years away
by two black holes,
129 solar masses, the other
34 solar, 36
months, and then
again, we only courts of last
orbit. So this is written here for.
Two black holes more
massive than our sun, orbiting each other
250 times a second
and producing one giant black hole,
liger is actually
tuned to detect these high frequency
gravitational waves.
That's not surprising because
on Earth everything is shaking
at lower frequencies.
So let's take a
car or me walking.
That's a hertz.
So I'm shaking the ground floor
with a hertz, a cloud moving over the
detectors like a few hertz,
attracting one mirror.
Why its gravity and then pulling it to
the other direction.
So all the noise sources on Earth,
ocean waves at the shore
are covering up all the gravitational
waves we could detect at lower
frequencies.
So all the stuff which
is slower than the universe we could
never detect on ground and
like in classic astronomy.
What we can't measure on ground, we
measure in space where there are no cars,
no waves, no clouds, no me walking,
and that is a lesser mission, so.
The extra proposal
for the mission concept is due
in January.
So we are writing the mission proposal
right now and
leaser consists of three spacecraft
that will be launched before 2030
for like 2030, 32
ish, and they will build a giant
laser interferometer in space.
It's like playing Star Wars.
You have three spacecraft separated
by millions of kilometers,
sending lasers back and forth and doing
the very same thing LEGO does.
They measure the distance between
spacecraft and if gravitational wave
passes the constellation, the distance
changes without the satellites moving
and we can detect gravitational waves,
this time at much lower frequency
since a million hertz range.
And the entire constellation is so big,
like two times, three times the diameter
of the sun that we can't have it in
Earth's orbit anymore.
It's trailing the Earth on an orbit
around the Sun.
And you see it up there if you want
your name to be listed on the official
mission concept proposal to
just visit this website, fill out
information like name and your
affiliation, press enter and your name
will be next to names like Stephen
Hawking, who is already supporting us.
So that's like a historic chance
to have your name, it says is a document
that would be nice and we would
appreciate it very much.
Thank you.
Why do we do all that?
Why do you want to detect
gravitational waves where
gravity is the dominating force and the
universe?
Gravity is cool because it's everywhere.
It's not only in stars and neutrinos.
It's not only in the heavy elements.
Gravity is not only emitted
by the free helium and hydrogen
in our universe.
That's the five percent of normal matter
we can see.
Gravity is also emitted by dark matter
stuff we cannot see.
Dark matter is completely invisible to
us, but we know it is there
because it does emit
gravity.
If you look at to have a deep
space, that's an image
taken by habit and you see all
these galaxies.
You also see distortions
like these rings, these arcs, as
if someone put a lens in front of your
picture.
This is gravitational lensing.
These are strong gravitational fields
like curvatures in space time
where light is like curved around
this gravitational field.
And then it's like you have these ghost
images of galaxies which are actually
behind the gravitational field now
seen as arcs.
And by doing data analysis on these
pictures, we can calculate the amount of
gravity in our universe.
That's easy.
Then we can also like count the dots
and get an estimate on the matter and our
universe.
And then we find out
that it does not add up.
There's much more gravity
than death metal.
So very easy solution is
well, there must be some matter.
We can't see some invisible matter.
And this is not the only
the only hint we have that there must be
more matter than we can see.
There are ruban detected.
By observation that spiral
galaxies do not rotate as they should
like. You can calculate the the outer
star orbital velocity from
Spiral Galaxies, how they should be
on the left hand side, but
they actually rotate like they are shown
on the right hand side.
And you can only reproduce, like
theoretically, the right hand curves
by adding more mass to your galaxy.
So spiral galaxies must be much heavier
than we see there.
So there must be more invisible
matter in there.
Again, there's more
gravity than could be explained
with the matter we see.
So we have no idea what documentaries
yet, but we have many ideas.
One idea is there could be
there's a theory that says that could
be an interaction between photons,
normal light particles
and virtual photons
from electric or magnetic fields.
So you have a strong magnetic field, the
VirTra photons in there
and you have a normal photon.
And these two photons may sometimes
on off channels interact
and produce something we call action
or action like particle.
And these axon particles would have
like very similar properties
then what we expect from dark matter,
like they don't interact with anything
else.
And all we need in order to detect them
is another strong magnetic field.
So these actions oscillate back into
photons and then we can detect the
photons there like these solar acciÃ³n
telescopes out already.
What I am working on right now is another
project. We are building a dark matter
generator.
So this is GPS.
It sounds really cool.
And thanks again.
There are many, many physicists working
on this. It's constructed in D.C.,
in Hamburg, but I'm actually working
on Florida on that.
So it's all international.
We are on 100 meter time
scale. We are building a vacuum system
with strong lasers and really strong
magnetic fields, superconducting
magnets. And we want to
have exactly this interaction between
light particles and VirTra photons and
the magnetic field.
Our laser cannot escape the generator,
but the dark matter, if it's generated,
can and will enter our recombination
cavity.
Same device, same magnetic field,
same properties, same resonant
cavity, but this time no
light at all.
But if a dark matter particle enters
there, it is perfectly match
to the cavity and would oscillate back
into light particles.
And then we can detect the light.
And when we switch off our generator and
don't see this light particles anymore,
we know what happened.
We detect the dark matter and the first
place we generated it.
This project is
hopefully finished by 2019, it's
more complex than I showed it to you
again. It's an international effort.
I would like to use my final minute
with the last part of
our universe, which is dark energy.
So dark energy actually makes
up almost 70 percent of everything there
is. What is dark energy and how do
we know it exists?
Again, we can't see it.
You can't really feel it.
But remember, our universe showed
us thirteen point
eight billion years after the Big Bang.
We can measure the speed of acceleration
of the universe and we can actually
see that it's accelerating
in expansion.
So the expansion of the universe is
going faster and faster and faster.
And if something is speeding up, there
must be energy pushing it forward.
And you can calculate pretty easy
actually calculate the amount of energy
necessary to speed up the acceleration
of the universe and that matter.
And this turns out to be equivalent
to 70 percent of all the
and our universe.
And no, we have no idea what dark energy
is or where it come from.
We really don't. And that's like an open
field where come to do research
on that.
The future of the universe actually is
not very bright due to the accelerated
expansion of the universe and the very
end galaxies will be pulled
apart so fast, faster than
the speed of light. Actually, that light
from our neighboring galaxy could not
reach us anymore.
Even faster, our solar system will be
ripped apart because the space
between Earth and Mars is
expanding so fast that
light from Mars cannot reach us anymore.
We will be isolated.
The bonds and our
molecules and our bodies
will be ripped apart because the space
between carbon atoms and oxygen atoms
will expand faster than the speed of
light.
So before we all evaporate and a few
billion of years, remember,
the universe needs you in order to
understand itself.
So.
If you're interested in any
of the projects I showed you, just visit
the different rules of the Lisa Mission
of the legal cooperation of the Dark
Cosmos experiment.
There are so many different
universities doing research on that, and
they all need engineers and physicists
and computer scientists and so on and so
forth. If you have questions, email me or
see me later on the
speaker's culture.
Thank you very much.
Have a great night.
Go,
OK, thank you very much, Simon
Barker s
he already mentioned there will be a
question of arms before, gee,
I would allow a question from the
Internet if there are any.
Yes, there's a question.
It's about the detection of gravitational
waves.
If gravitational waves change spacetime,
does it not also change the detection
device? So we wouldn't detect them at
all? Why does it work?
Well, what basically happens
is that the travel time of light
from the beam splitter to the end
mirror changes.
And yes, everything
in there changes.
The entire device becomes longer and
shorter. But that's exactly what we want
to measure. We want to measure that the
light bounce back and forth.
It's not a little bit faster than in the
other direction.
So we compress entire apparatus and
stretch it when the gravitational waves
pass through. But that's exactly the
effect we are measuring.
OK, that wraps it up for today.
Give another round of applause for
our speaker.