*33C3 preroll music*
Herald Angel: Okay, our next speaker is Michael Büker. He is a science
communicator and an astrophysicist. He is also a science journalist and a writer.
So, he's currently living in Dresden and he wrapped his mind around this very
question so how do you measure these great distances and how do you get an idea of
how huge the cosmos really is, since the universe is like seriously huge.
Michael, your stage.
*applause*
Michael: Okay, thank you very much. Thank you everyone for being here.
While after the kind of year that we've had it's natural to be thinking about where and how
fast you might be able to get away from earth. So let's all be a little bit like
Maddie was a couple of months ago, when she thought that actually the Voyager
probe is winning, because it's quite far away and we're gonna be talking about even
larger distances. But, to think about distances in the universe and how we can
measure them and how we can determine how far away stuff is from each other, it all
starts when we look at the sky, because when we look up at the sky all we see is
basically moving dots. This is a nice picture that shows the very large
telescope and above it there is the moon, Venus, and the planet Jupiter shining.
And these will be moving across the sky in a way that we are familiar with, but if they
are just moving at the sky and every night the pattern repeats, how can we find out
about the distances, how far these are away from us, from anywhere else and we
are gonna be looking at, actually, how that works. Even in antiquity, this sketch
is from 200 years before the common era, so it's more then 2200 years old now, the
answer was clever geometry. If you measure exactly at what point on our sky stuff
appears at certain times instead of just saying, well, it's somewhere up there and
later it's gonna be like over there. If you do this precisely, you can get a grasp
at where stuff is and how far away it is from us and relative to each other.
There was a small break in progress in this, because
*laughter*
for a time people chose to believe that actually the earth was at the center
of the solar system and then none of your measurement make any sense So, okay, we
kind of wasted 1000 years on that question. But then in the 1600s there came
a very important breakthrough, actually 2 of them, first was Johannes Kepler, who
found out that the way that planets move around the sun, including the earth,
follows a very specific mathematical pattern and then this was comprehensively
explained by Isaac Newton when he formulated the general laws of gravitation and how they
work. So it was found out that these all follow a certain law and from this you can
determine the distances relative to each other. So they were able to tell how much
exactly further away from the sun is the average orbit of Mars than earth. So, we
had a relative idea of how far away stuff is from the sun, but we didn't know what
the exact value was. So, if during the 17th century you were to ask an
astronomer, how far away is Jupiter from the sun, he would say, about five times as
much as the earth, but then if you ask him but how much is that in miles or whatever,
they wouldn't be able to tell you. So with this one measurement, if we measured this
AU, which stands for astronomical unit, which we just conveniently define to say
well, the average orbit the earth has around the sun is 1 astronomical unit, if
we found out that one value, we would be able to determine all the distances of all
the planets in the solar system from the sun. And again, the answer was clever
geometry. In a way that I'm not going to go into in much detail, when the planet
Venus transits the star, we saw transits in an earlier talk, is when a planet moves
in front of a star and kind of blocks the light from it a little bit. If you time
this exactly and measure exactly the way that it moves from different points on the
earth, this gives you a clue. But, there is a big problem, is that transits of
Venus as seen from the earth come in pairs 8 years apart - which is okay - but that only
happens every 120 years So, the very first one that was really observed was in 1639,
but that was basically just one guy in England in his backyard and he didn't
really have colleagues, he didn't have good equipment and anything. So the number
that he found was not very precise. Then astronomers spent, after Kepler and Newton
had made their discoveries, astronomers spent decades preparing, they set up
telescopes in different places in the earth, they coordinated, they wrote
letters to each other. But they were trolled by how they didn't really
understand how their telescopes worked very well. So then astronomers said, okay
that didn't really work out. We're gonna doing it real well in 120 years.
*laughter*
So again they coordinated extremely well the telescopes have gotten much better
they distributed around the earth, which was easier due to railways, well you
couldn't fly, but there was, you know, there was the railways and everything, so
communication and transportation was a little easier and they distributed all
around the earth and they did this again in the 1870s and 1880s and they were
trolled by how their clocks were not precise enough. So, because the
comparative measurements were off by as much as a minute in time they didn't get a
value as exact as they were hoping for. I mean, here we see 149 million km and then
there is an uncertainty of 160.000 it's not so bad. Actually in astronomy that's
pretty amazing for accuracy, but it's not enough if you're trying to send stuff to
Venus. So they were probably hoping for the early 2000s to really finally find the
true distance, the true value of the astronomical unit, but then before that
something else happened. So, in the 1960s big radio transmitters, radio antennas,
became good enough to actually beam a radio signal at the planet Venus and then
wait and measure how long it takes to bounce back. So we did a radar ranging
experiment to the planet Venus and that gave a value for this astronomical unit
that was good enough to actually build probes that would fly to Venus. And then
if you have something there which is not just a wave bouncing off of the planet,
but you actually have a spacecraft there you can pretty much exactly time all the
transmissions from the antenna on the spacecraft and everything and that's how
we found that value. So from this, we know, and this is actually the defined
value, so it doesn't change anymore, we just said that this is the astronomical
unit, and we know that very well, and this helps us to establish all the distances in
the solar system. Still, the transit of Venus that happened in 2004 and 2012, it
just gave us amazing pictures like these, taken in Greece in 2004 or this one taken
from a Japanese space probe in 2012. Now, if you weren't around to witness those,
well, next one is up in 2120 or something. So, just wait around.
*laughter*
Now, as we moved towards the stars, so we basically covered the solar system, but we
also wanna know how far away are the stars, which is the next logical step, if
we are looking outwards in the universe we have to talk about the concept of
parallax. And it's a bit complicated, it involves geometry, but we can cover it
sort of in a way of the layout of this Saal. So if there was somewhere, someone
up there on the Rang of Saal 1 and they were looking straight at the stage and see
me here and walking from one side of the Saal to the other, then first I would be
appearing like a little to the left of their field of vision, if they were
looking straight ahead, with their nose pointed at the screen. And then as they
move to the other side of the Saal I would appear in the other direction and there
would be an angle which corresponds to how far they moved. And if they precisely
measured this angle and how far they moved they can calculate the distance towards
me. Now, in this Saal that would mean about 40 meters and it would be a parallax
angle of about 10 to 20 degrees and that would then give you the information that
from up there I'm probably about 50 meters away. We can do that with the stars. Now,
on earth we can move from one place on the earth to the other, but that's
actually a small baseline that doesn't give us an angle that's a lot of fun to
work with. But luckily, since earth moves around the sun all time for free, we can
just use that and measure the position of a star, wait 6 months, and measure it
again. And we will be at a totally different place, well basically 300
million km away and we can use that as a baseline for this measurement. So we look
at a star, we wait half a year, we look at the same star, and precisely measure how
much the star wobbles. Unfortunately, this leads us to the definition of the distance
unit of the parsec, and the parsec is a unit of distance. Please do not confuse it
with other stuff as some might do. So how is the parsec defined? Well, if we have
this angle, I told you that from Saal 1, from there to there it might be something
like 10 to 20 degrees. If a star is a parsec away then over the course of a
year over our geometrical baseline of the earth moving around the sun, 300 million
km apart in the 2 points, it will have to be the angle of an arcsecond. Now what is
an arcsecond? It's just an extremely small angle. You have a full circle
divided into 360 degrees, then each of these degrees is divided into 60 minutes,
and then each of these minutes is divided into 60 arcseconds. An we're looking at
an angle of 1 arc second that these stars would over the course of 1 year be
wobbling in the sky from our movement around the sun. Let's take an example of
looking at the international space station from down on the ground. You might have
seen this, it's actually quite fun to see, you can look it up on websites at what
point in time the international space station will be above you. And the angle
of one arc second would be the size of an astronaut floating next to the
international space station as you're looking at it from the ground. Obviously,
you can't see an astronaut from the ground that's because our eyes can't pick out
the angle that is one arcsecond. Another example might be, again for someone way up
there at the end of Saal 1, looking at me at a distance of about 50 meters, the angle of one
arcsecond would be the width of one the hairs of my beard. And if you could see
that you would have a detector that is capable of distinguishing one arcsecond.
Now, if we do that, and if we manage to do that, the telescopes are actually good
enough to do this, one parsec is the distance to a star that wobbles by
1 arcsecond. But, actually, our closest neighbor is even further away. So, we
don't have any star that does that. 1.3 parsecs is the distance to Proxima
Centauri, and the Alpha and Beta Centauri system, so these are even smaller. And
270.000 astronomical units is the distance to that one, so that means it's way
further away. I mean, in the solar system we can move 2, 3, 5, maybe 10, 20, 30
astronomical units if we are doing well with our rockets and it takes a bunch of
years, but to cover 1000s or even 100s of 1000s of astronomical units tells us that
the propulsion systems and the rockets that we have today are not capable of getting us
to the stars in the way we do it right now, which we also heard, of course, in
the talks before. Telescopes on the ground are nice, but actually telescopes in space
can give us an even better resolution. And the Hipparcos satellite, which was active
in the last couple of decades, measured up to 2 milliarcseconds. Now think of it. The
arcsecond with the astronaut in the sky and my beard and stuff. A 1/1000 of that
as an angular resolution is what the Hipparcos satellite was able to measure
and this gave us the distances to basically all the stars in our field of
view that were up to 100 parsecs away. And we know exactly how far these are away.
The Gaia satellite, which is now just coming into operation, commissioned by the
European space agency, this is about to have an even better performance, it will
look at a billion stars, that's what it's called, the Billion Stars Surveyor, it
will be good for distances of up to 5000 parsecs and it's gonna tell us the
distances to all these stars, it's gonna be an amazing step in looking at how far
away the stars are and forming a map of all the stars around us. And, there is
something missing? No. Let's talk about standard candles now, because that's
another important tool apart from the geometry that we saw before. A standard
candle is just something where you know exactly how bright it is. And then you can
calculate how far away. A standard candle would be, well, like any, let's image a
set of candles and all of them burn at the same brightness. So if you measured the
brightness of one of these candles, you could tell how far apart it was. Actually,
maybe a better picture is streetlights in the night. If you see a car coming towards
you, you can kind of estimate by how brightly you see the light if the car is
still far away, or if it is close to you, because you have an intuitive
understanding of how bright the lights of a car should be if it is right next to you
or a couple of 100 meters away or many kilometers away, if it's a clear night.
And so we want standard candles in space. We want stuff in space, where we have a
good idea of how bright it should be. And then from how bright we see it, how much
of the light actually reaches us, we can calculate the distance. And this we can do
with the help of these, one of the most important diagrams and all of
astrophysics, which is the Hertzsprung-Russel diagram. It basically
sorts stars by their colors and by how bright they are. And because of the way that stars
work, the color and the brightness are also intermittently connected to their
mass and what's happening inside the stars and then if we see a bunch of stars, we
can do this very well with clusters, which are groups of 10s or 100s up to 1000s of
stars in one place, at basically the same distance, and they have sort of a standard
population, then we can estimate how far away they're. Let's think of it like this,
we jut had the picture of the car and the night, which was light, but let's think of
it as sound. Think of groups of children in maybe preschool and let's imagine that
every preschool group of children always had 20 children in it, just because. And
now, you can estimate how loud 20 preschool children just playing around actually
are and from the sound of when you hear the children you can tell how far away
that group is from you. If we have a group of stars and we know the light, the
different colors that they have, we can actually match it to this graph and see
how far away this group is by estimating the properties that they have in this way.
And so this then gives us an overview of basically our galactic neighborhood, so
the other stars in our galaxy. The number of stars in our galaxy is about 200 billion,
but before I bombard you with more numbers, we have a chance to get a
great overview of what that's like from the artists of Monty Python.
Song: Just remember that you standing on a planet that's evolving,
revolving at 900 miles an hour.
Michael: Sorry.
*applause*
Thank you Monty Python. Now, the numbers that they present have changed over time.
Now scientists speak of 200 billion stars in the galaxy instead of 100 billion, but
still it gives you an amazingly good overall idea. And whenever I try to think of the
parameters of the milky way galaxy, like 100.000 light-years side to side, I just
have the song in my head. And it works amazingly well. Except also for the one
part where it says that the universe is expanding at the speed of light, like we
heard in the talk before, that's not actually true. The expansion of the
universe actually exceeds the speed of light, but common, they are comedians, so.
*laughing*
Cut them a little slack on that one. Other galaxies, the milky way galaxy that we
have just gotten this nice overview over is by far not the only one, there are
other galaxies and we are part of groups of galaxies, actually the one that's
called the local group, which has 3 very large galaxies, which is ours, the milky
way, the Andromeda galaxy, which is actually larger, and another one which is
a bit smaller. And then there's a bunch of dwarf galaxies also moving around there
and we gonna be looking at how we find about distances in that regard. Now again,
we have a sort of standard candle here, and these are stars called Cepheids, and
what you see here is the brightness of the star pulsating. So you look at the star
and you say, okay it's this bright, oh no wait, it's dimmer again, oh wait, it's
getting brighter again, over the course of a couple days. And if you measure this
brightness very precisely, you just have to wait a few days, it's not a difficult
measurement in that regard, you can find out that the duration of these variations
is actually closely linked to how bright they are. So, calculating or measuring the
period of these oscillations gives you the brightness and then these stars, called
Cepheids, can work for you as a standard candle and this works out into other
galaxies. So, we look at like the Andromeda galaxy, which is a couple of
million light-years away, and we see a Cepheids star in there somewhere, we
measure the period of it's oscillations and then we can tell how far apart it is
and this gives us a good idea of how away that galaxy actually is. That doesn't work
for galaxies where they appear so small in our field of view that we can't point out
a single Cepheid star. So these groups of galaxies also form together into something
called Superclusters. And the Virgo Supercluster is an idea of what our group
is actually in. So I mentioned the local group of a couple of maybe 100 dwarf
galaxies and three large ones. And this is actually orbiting something called the
Virgo cluster. So we are a bit out, but I mean this is an abstract graphic. What
does it look like to look at the Virgo cluster? Well, We can look at that. And
you see that we look at the sky and there's just a bunch of large galaxies
there. You're looking at something that's probably pretty similar to what our own
galaxy is like, and it's just hanging there in the sky. And by, for example,
this Cepheid measurement method, we can get an idea of how far away it is. But these
local galaxies are not the only ones we see. There is an example that's called the
Hubble Extreme Deep Field, where the Hubble space telescope, that's orbiting the
earth, took pictures of a very small patch of the sky. Here, the moon is shown to
scale. So, if you look at the moon, the photograph that I'm about to show you
right now, shows this small part that's marked by the XDF. And if you look at it
long enough and collect a lot of light, that's why it's called a Deep Field, it
actually looks like this. And there's a huge amount of galaxies and they all look
different. Some are spiral galaxies, some are elliptical galaxies, and they even
have different colors. Some appear red, some appear blue, and this all has to do
with the way that they evolve and we not even done quite in understanding how they
come to look like that. You can actually help with this. There are so many galaxies
just recorded in pictures that we don't have good catalogs of them all. So you can
visit galaxyzoo.org and they will show you a picture of a galaxy somewhat like this
and you have to click, is it a spiral galaxy, is it an elliptical galaxy. Does
it look like blue color, does it look like red color. It's crowdsourced citizen
science and you can help classify a whole bunch of galaxies, and it's a lot of fun,
just click through while you should be working.
*laughter**applause*
Now, also when we look at these galaxies, similar to the way we can look at stars
with the Cepheids and their variation, there is a bunch of methods I'm not going
to get into a lot of detail, but if you look at galaxies and the way they move and
the way that the light emanates from them, and someway you can correlate that
to the distance, and so examining these galaxies very closely can give us an idea
of how far away they are from us. But actually everyone's favorite standard
candle, the one thing that astronomers and astrophysicists really love to use, is
supernovae of the 1a type. Now in the talk before we saw that sometimes little white
dwarf stars can gain mass from their companion stars, so stuff is falling onto
them, until the mass of the white dwarf star that's gaining weight becomes so
large that it explodes in a thermal nuclear explosion and this then is a
supernova of type A. And what's amazing about these explosions is that basically
they are almost the same brightness. Or you can determine the brightness very well
if you look at how quickly the light fades out. So, whenever we see, like you see
here on the top-left picture, whenever we see a galaxy and there is a supernova 1a
happening right at that moment, and they only are visible for a couple of days
mostly, hours to days. So if we look at that closely and we measure how the light
fades away, then we can get a very good idea of how far away that galaxy is. And
even larger structures emerge then, and we think about the Virgo Supercluster that I
just showed you, which was groups of galaxies around groups of other galaxies
and the latest idea of the sort of the large scale structure that the earth and
our milky way is part of, is the Laniakea Supercluster that was proposed just 2 or 3
years ago. And here you don't even see individual galaxies. It's more like the
density of stuff in the universe that's grouped together. And you see these lines,
they represent sort of the way that gravity is pulling everything. And yeah,
that's a pretty amazing idea. And like we've heard in the talk before, the
universe is expanding and this also affects the light, the light gets
redshifted. If there is a lightwave traveling through the universe, and while
it's traveling space expands, that also means that the light changes it's
wavelength. It just becomes a different color. And it shifts towards the red,
which is why this thing is called redshift. And so galaxies that are very
far away, because between us and where that galaxy is space is expanding and has
been expanding for a while, these galaxies appear to look red. And we can actually see
that in the pictures, like this one. Yeah, you can see it on the screen, it's this
very faint red dot, and that actually tells us that this is a galaxy which
should actually have blue light, like most of the other galaxies, but because it's so
far away and space has stretched while the lightwaves were traveling in our direction
it now appears red. And 4 gigaparsecs, so we're looking at 4 billion parsecs of
distance towards this, which we can kind of extrapolate of how far it's redshifted,
so how far the light has been reddened, is how we can get an idea of this. And it's
not just the one, this, at least a couple of years ago, was the furthest away galaxy
that had ever been observed, but actually there's a whole bunch of those and they
are everywhere, and like we saw there is a very large number of galaxies to be seen
everywhere. And to give us a final idea of how matter is really distributed in the
universe, I have another video which is a simulation of how these super galaxy
clusters are actually distributed. So let me pull that up. Now we're looking at some
generic super galaxy cluster and we're kind of circling it. And as the camera is
moving out and the picture is getting larger, we see that this one super galaxy
cluster is actually sort of connected to other regions where there is a high
density of galaxies. Remember, this is not stars, we're looking at galaxies. And they
are sort of strung together in something that's called filaments. And these
filaments stretch along the lines of regions where there is almost no galaxies
which are called voids, and these voids are between 10 and 50 million light-years
in diameter, more or less. And this is just the way that everything stretches
out. So, super galaxy clusters are gathered in filaments around voids and it
looks like a sort of a soap bubble or maybe a bee hive structure. And okay, this
is a simulation, it looks nice, and this is gathered from data that we have about how
far away these galaxies are, how we think the universe evolved, but how about real data.
Can we look out there and actually measure galaxies, and actually measure how stuff
looks, and see the structure in the universe? Turns out, we can. And it looks
like this. And it just blows my mind. Because you see this whole bee hive
structure, you see the voids, you see the filaments of super galaxy cluster
structures sort of strung together. And that's just real data. That is the largest
scale structure of all the galaxies, of the observable universe, that have ever
been recorded. And this relies on the measurements of type 1a supernovae, and of
the galaxies which relies on measurements of, for example, the Cepheids stars, which
rely on measurements of the parallax, of the geometrical parallax, like we
discussed here in this room. So, the way of looking at the universe like this, of
all the super galaxy clusters, actually begins when we string together these to
form what's called the cosmological distance ladder of all these different
methods building upon each other. And it starts right here, when we look up at the
sky. So, I hope you enjoy that, thanks for your attention.
*applause*
Herald: Thank you very much, Michael. So, we still have time for questions. Line up
at the microphones if you want to ask any here and now. And we get a little
preference on the Internet, are there any questions, Signal Angel?
That doesn't seem to be the case, and we start with microphone 3, please.
Mic 3: Regarding the redshift of the further away galaxy, red light has less
energy than blue light, where does the energy go?
M: It's lost. In the process of the universe expanding, energy is not
conserved. And that's a big headache for physics.
*laughter* Herald: Microphone 4.
Mic 4: So, I was thinking that in the case that you try to measure the distance to a
far away galaxy, where we are talking in the scale that there is not sufficent
accuracy via parallax, so you rely on supernovas. So, you point the telescope in
a patch of the sky and you pick up a supernova. But you cannot really know, I
suppose, that the supernova belongs to the galaxy where all the other stars around
that are, or perhaps it's very far away on the z-axis in a different galaxy that's
just behind. Is that possible? How do you go around that?
M: Yes, you're right. You may find pictures, and I may find a picture of this
where galaxies are actually overlapping. So in this thing that I showed you from
the galaxy zoo, yeah, I think you see some galaxies overlapping now. This might mean
that they are close together and actually colliding, but it might also mean that
they just happen to be in the same direction. But then the type 1a supernova,
if you measure it, gives you an idea of how far away it is and then hopefully you
can estimate if it was the front galaxy or the back galaxy. But you can't be exactly
sure, you're right.
Herald: Okay, microphone 1, please.
Mic 1: Okay. Thanks, this is really fascinating. This might be a stupid
question. If the outer edges of our observable universe are expanding at
faster than the speed of light and we detect very far away galaxies with light,
how is the light ever reaching us?
M: We see only as far as the expansion of the universe will allow us. And, like we
heard in the talk before, stuff is falling behind the horizon. There are regions in
the universe now, where at a later point, because space is expanding, the light from
these regions will not be able to reach us. So if we look way out into the
universe to the very edge of what we can see, there is stuff disappearing there and
there is just no getting around there, if it's gone, it's gone.
Herald: Okay, this concludes the Q & A. A warm round of applause for Michael Büker.
*applause*
*postroll music*
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