1
00:00:00,000 --> 00:00:15,180
33C3 preroll music
2
00:00:15,180 --> 00:00:20,910
Herald Angel: Okay, our next speaker is
Michael Büker. He is a science
3
00:00:20,910 --> 00:00:27,120
communicator and an astrophysicist. He is
also a science journalist and a writer.
4
00:00:27,120 --> 00:00:34,780
So, he's currently living in Dresden and
he wrapped his mind around this very
5
00:00:34,780 --> 00:00:42,370
question so how do you measure these great
distances and how do you get an idea of
6
00:00:42,370 --> 00:00:49,750
how huge the cosmos really is, since the
universe is like seriously huge.
7
00:00:49,750 --> 00:00:51,550
Michael, your stage.
8
00:00:51,550 --> 00:00:59,339
applause
9
00:00:59,339 --> 00:01:02,040
Michael: Okay, thank you very much. Thank
you everyone for being here.
10
00:01:02,040 --> 00:01:07,960
While after the kind of year that we've had it's
natural to be thinking about where and how
11
00:01:07,960 --> 00:01:13,150
fast you might be able to get away from
earth. So let's all be a little bit like
12
00:01:13,150 --> 00:01:17,140
Maddie was a couple of months ago, when
she thought that actually the Voyager
13
00:01:17,140 --> 00:01:21,880
probe is winning, because it's quite far
away and we're gonna be talking about even
14
00:01:21,880 --> 00:01:27,220
larger distances. But, to think about
distances in the universe and how we can
15
00:01:27,220 --> 00:01:31,060
measure them and how we can determine how
far away stuff is from each other, it all
16
00:01:31,060 --> 00:01:35,729
starts when we look at the sky, because
when we look up at the sky all we see is
17
00:01:35,729 --> 00:01:39,990
basically moving dots. This is a nice
picture that shows the very large
18
00:01:39,990 --> 00:01:45,650
telescope and above it there is the moon,
Venus, and the planet Jupiter shining.
19
00:01:45,650 --> 00:01:50,070
And these will be moving across the sky in a
way that we are familiar with, but if they
20
00:01:50,070 --> 00:01:54,610
are just moving at the sky and every night
the pattern repeats, how can we find out
21
00:01:54,610 --> 00:01:58,740
about the distances, how far these are
away from us, from anywhere else and we
22
00:01:58,740 --> 00:02:03,530
are gonna be looking at, actually, how
that works. Even in antiquity, this sketch
23
00:02:03,530 --> 00:02:09,910
is from 200 years before the common era,
so it's more then 2200 years old now, the
24
00:02:09,910 --> 00:02:16,190
answer was clever geometry. If you measure
exactly at what point on our sky stuff
25
00:02:16,190 --> 00:02:19,620
appears at certain times instead of just
saying, well, it's somewhere up there and
26
00:02:19,620 --> 00:02:23,879
later it's gonna be like over there. If
you do this precisely, you can get a grasp
27
00:02:23,879 --> 00:02:29,480
at where stuff is and how far away it is
from us and relative to each other.
28
00:02:29,480 --> 00:02:32,959
There was a small break in progress in this, because
29
00:02:32,959 --> 00:02:34,079
laughter
30
00:02:34,079 --> 00:02:38,459
for a time people chose to believe
that actually the earth was at the center
31
00:02:38,459 --> 00:02:42,140
of the solar system and then none of your
measurement make any sense So, okay, we
32
00:02:42,140 --> 00:02:49,110
kind of wasted 1000 years on that
question. But then in the 1600s there came
33
00:02:49,110 --> 00:02:53,900
a very important breakthrough, actually 2
of them, first was Johannes Kepler, who
34
00:02:53,900 --> 00:02:58,740
found out that the way that planets move
around the sun, including the earth,
35
00:02:58,740 --> 00:03:03,120
follows a very specific mathematical
pattern and then this was comprehensively
36
00:03:03,120 --> 00:03:08,610
explained by Isaac Newton when he formulated
the general laws of gravitation and how they
37
00:03:08,610 --> 00:03:14,920
work. So it was found out that these all
follow a certain law and from this you can
38
00:03:14,920 --> 00:03:20,769
determine the distances relative to each
other. So they were able to tell how much
39
00:03:20,769 --> 00:03:27,030
exactly further away from the sun is the
average orbit of Mars than earth. So, we
40
00:03:27,030 --> 00:03:32,630
had a relative idea of how far away stuff
is from the sun, but we didn't know what
41
00:03:32,630 --> 00:03:36,960
the exact value was. So, if during the
17th century you were to ask an
42
00:03:36,960 --> 00:03:41,140
astronomer, how far away is Jupiter from
the sun, he would say, about five times as
43
00:03:41,140 --> 00:03:46,090
much as the earth, but then if you ask him
but how much is that in miles or whatever,
44
00:03:46,090 --> 00:03:50,700
they wouldn't be able to tell you. So with
this one measurement, if we measured this
45
00:03:50,700 --> 00:03:55,300
AU, which stands for astronomical unit,
which we just conveniently define to say
46
00:03:55,300 --> 00:03:59,350
well, the average orbit the earth has
around the sun is 1 astronomical unit, if
47
00:03:59,350 --> 00:04:04,470
we found out that one value, we would be
able to determine all the distances of all
48
00:04:04,470 --> 00:04:09,610
the planets in the solar system from the
sun. And again, the answer was clever
49
00:04:09,610 --> 00:04:15,910
geometry. In a way that I'm not going to
go into in much detail, when the planet
50
00:04:15,910 --> 00:04:21,450
Venus transits the star, we saw transits
in an earlier talk, is when a planet moves
51
00:04:21,450 --> 00:04:25,610
in front of a star and kind of blocks the
light from it a little bit. If you time
52
00:04:25,610 --> 00:04:29,920
this exactly and measure exactly the way
that it moves from different points on the
53
00:04:29,920 --> 00:04:35,279
earth, this gives you a clue. But, there
is a big problem, is that transits of
54
00:04:35,279 --> 00:04:40,600
Venus as seen from the earth come in pairs
8 years apart - which is okay - but that only
55
00:04:40,600 --> 00:04:47,490
happens every 120 years So, the very first
one that was really observed was in 1639,
56
00:04:47,490 --> 00:04:52,080
but that was basically just one guy in
England in his backyard and he didn't
57
00:04:52,080 --> 00:04:55,691
really have colleagues, he didn't have
good equipment and anything. So the number
58
00:04:55,691 --> 00:05:00,860
that he found was not very precise. Then
astronomers spent, after Kepler and Newton
59
00:05:00,860 --> 00:05:05,210
had made their discoveries, astronomers
spent decades preparing, they set up
60
00:05:05,210 --> 00:05:08,289
telescopes in different places in the
earth, they coordinated, they wrote
61
00:05:08,289 --> 00:05:11,729
letters to each other. But they were
trolled by how they didn't really
62
00:05:11,729 --> 00:05:16,539
understand how their telescopes worked
very well. So then astronomers said, okay
63
00:05:16,539 --> 00:05:20,570
that didn't really work out. We're gonna
doing it real well in 120 years.
64
00:05:20,570 --> 00:05:21,570
laughter
65
00:05:21,570 --> 00:05:25,159
So again they coordinated extremely well
the telescopes have gotten much better
66
00:05:25,159 --> 00:05:28,940
they distributed around the earth, which
was easier due to railways, well you
67
00:05:28,940 --> 00:05:32,570
couldn't fly, but there was, you know,
there was the railways and everything, so
68
00:05:32,570 --> 00:05:35,840
communication and transportation was a
little easier and they distributed all
69
00:05:35,840 --> 00:05:40,760
around the earth and they did this again
in the 1870s and 1880s and they were
70
00:05:40,760 --> 00:05:44,890
trolled by how their clocks were not
precise enough. So, because the
71
00:05:44,890 --> 00:05:48,970
comparative measurements were off by as
much as a minute in time they didn't get a
72
00:05:48,970 --> 00:05:55,130
value as exact as they were hoping for. I
mean, here we see 149 million km and then
73
00:05:55,130 --> 00:05:59,149
there is an uncertainty of 160.000 it's
not so bad. Actually in astronomy that's
74
00:05:59,149 --> 00:06:04,190
pretty amazing for accuracy, but it's not
enough if you're trying to send stuff to
75
00:06:04,190 --> 00:06:11,089
Venus. So they were probably hoping for
the early 2000s to really finally find the
76
00:06:11,089 --> 00:06:16,409
true distance, the true value of the
astronomical unit, but then before that
77
00:06:16,409 --> 00:06:22,860
something else happened. So, in the 1960s
big radio transmitters, radio antennas,
78
00:06:22,860 --> 00:06:28,839
became good enough to actually beam a
radio signal at the planet Venus and then
79
00:06:28,839 --> 00:06:34,440
wait and measure how long it takes to
bounce back. So we did a radar ranging
80
00:06:34,440 --> 00:06:39,390
experiment to the planet Venus and that
gave a value for this astronomical unit
81
00:06:39,390 --> 00:06:44,540
that was good enough to actually build
probes that would fly to Venus. And then
82
00:06:44,540 --> 00:06:48,190
if you have something there which is not
just a wave bouncing off of the planet,
83
00:06:48,190 --> 00:06:52,160
but you actually have a spacecraft there
you can pretty much exactly time all the
84
00:06:52,160 --> 00:06:55,649
transmissions from the antenna on the
spacecraft and everything and that's how
85
00:06:55,649 --> 00:07:01,190
we found that value. So from this, we
know, and this is actually the defined
86
00:07:01,190 --> 00:07:04,760
value, so it doesn't change anymore, we
just said that this is the astronomical
87
00:07:04,760 --> 00:07:08,070
unit, and we know that very well, and this
helps us to establish all the distances in
88
00:07:08,070 --> 00:07:13,500
the solar system. Still, the transit of
Venus that happened in 2004 and 2012, it
89
00:07:13,500 --> 00:07:18,830
just gave us amazing pictures like these,
taken in Greece in 2004 or this one taken
90
00:07:18,830 --> 00:07:24,020
from a Japanese space probe in 2012. Now,
if you weren't around to witness those,
91
00:07:24,020 --> 00:07:30,409
well, next one is up in 2120 or something.
So, just wait around.
92
00:07:30,409 --> 00:07:31,690
laughter
93
00:07:31,690 --> 00:07:36,780
Now, as we moved towards the stars, so we
basically covered the solar system, but we
94
00:07:36,780 --> 00:07:40,029
also wanna know how far away are the
stars, which is the next logical step, if
95
00:07:40,029 --> 00:07:43,480
we are looking outwards in the universe we
have to talk about the concept of
96
00:07:43,480 --> 00:07:49,330
parallax. And it's a bit complicated, it
involves geometry, but we can cover it
97
00:07:49,330 --> 00:07:54,770
sort of in a way of the layout of this
Saal. So if there was somewhere, someone
98
00:07:54,770 --> 00:07:59,640
up there on the Rang of Saal 1 and they
were looking straight at the stage and see
99
00:07:59,640 --> 00:08:04,930
me here and walking from one side of the
Saal to the other, then first I would be
100
00:08:04,930 --> 00:08:08,029
appearing like a little to the left of
their field of vision, if they were
101
00:08:08,029 --> 00:08:13,730
looking straight ahead, with their nose
pointed at the screen. And then as they
102
00:08:13,730 --> 00:08:17,380
move to the other side of the Saal I would
appear in the other direction and there
103
00:08:17,380 --> 00:08:21,939
would be an angle which corresponds to how
far they moved. And if they precisely
104
00:08:21,939 --> 00:08:26,680
measured this angle and how far they moved
they can calculate the distance towards
105
00:08:26,680 --> 00:08:32,929
me. Now, in this Saal that would mean
about 40 meters and it would be a parallax
106
00:08:32,929 --> 00:08:37,130
angle of about 10 to 20 degrees and that
would then give you the information that
107
00:08:37,130 --> 00:08:43,600
from up there I'm probably about 50 meters
away. We can do that with the stars. Now,
108
00:08:43,600 --> 00:08:46,370
on earth we can move from one place on
the earth to the other, but that's
109
00:08:46,370 --> 00:08:50,090
actually a small baseline that doesn't
give us an angle that's a lot of fun to
110
00:08:50,090 --> 00:08:56,801
work with. But luckily, since earth moves
around the sun all time for free, we can
111
00:08:56,801 --> 00:09:02,630
just use that and measure the position of
a star, wait 6 months, and measure it
112
00:09:02,630 --> 00:09:07,020
again. And we will be at a totally
different place, well basically 300
113
00:09:07,020 --> 00:09:11,760
million km away and we can use that as a
baseline for this measurement. So we look
114
00:09:11,760 --> 00:09:17,020
at a star, we wait half a year, we look at
the same star, and precisely measure how
115
00:09:17,020 --> 00:09:25,430
much the star wobbles. Unfortunately, this
leads us to the definition of the distance
116
00:09:25,430 --> 00:09:31,320
unit of the parsec, and the parsec is a
unit of distance. Please do not confuse it
117
00:09:31,320 --> 00:09:37,770
with other stuff as some might do. So how
is the parsec defined? Well, if we have
118
00:09:37,770 --> 00:09:41,690
this angle, I told you that from Saal 1,
from there to there it might be something
119
00:09:41,690 --> 00:09:47,940
like 10 to 20 degrees. If a star is a
parsec away then over the course of a
120
00:09:47,940 --> 00:09:52,930
year over our geometrical baseline of the
earth moving around the sun, 300 million
121
00:09:52,930 --> 00:09:58,420
km apart in the 2 points, it will have to
be the angle of an arcsecond. Now what is
122
00:09:58,420 --> 00:10:04,250
an arcsecond? It's just an extremely
small angle. You have a full circle
123
00:10:04,250 --> 00:10:10,540
divided into 360 degrees, then each of
these degrees is divided into 60 minutes,
124
00:10:10,540 --> 00:10:16,210
and then each of these minutes is divided
into 60 arcseconds. An we're looking at
125
00:10:16,210 --> 00:10:22,180
an angle of 1 arc second that these stars
would over the course of 1 year be
126
00:10:22,180 --> 00:10:27,060
wobbling in the sky from our movement
around the sun. Let's take an example of
127
00:10:27,060 --> 00:10:30,140
looking at the international space station
from down on the ground. You might have
128
00:10:30,140 --> 00:10:33,980
seen this, it's actually quite fun to see,
you can look it up on websites at what
129
00:10:33,980 --> 00:10:38,020
point in time the international space
station will be above you. And the angle
130
00:10:38,020 --> 00:10:42,980
of one arc second would be the size of an
astronaut floating next to the
131
00:10:42,980 --> 00:10:47,210
international space station as you're
looking at it from the ground. Obviously,
132
00:10:47,210 --> 00:10:51,750
you can't see an astronaut from the ground
that's because our eyes can't pick out
133
00:10:51,750 --> 00:10:56,450
the angle that is one arcsecond. Another
example might be, again for someone way up
134
00:10:56,450 --> 00:11:02,140
there at the end of Saal 1, looking at me at
a distance of about 50 meters, the angle of one
135
00:11:02,140 --> 00:11:06,590
arcsecond would be the width of one the
hairs of my beard. And if you could see
136
00:11:06,590 --> 00:11:11,670
that you would have a detector that is
capable of distinguishing one arcsecond.
137
00:11:11,670 --> 00:11:16,370
Now, if we do that, and if we manage to do
that, the telescopes are actually good
138
00:11:16,370 --> 00:11:21,470
enough to do this, one parsec is the
distance to a star that wobbles by
139
00:11:21,470 --> 00:11:26,180
1 arcsecond. But, actually, our closest
neighbor is even further away. So, we
140
00:11:26,180 --> 00:11:33,210
don't have any star that does that. 1.3
parsecs is the distance to Proxima
141
00:11:33,210 --> 00:11:39,260
Centauri, and the Alpha and Beta Centauri
system, so these are even smaller. And
142
00:11:39,260 --> 00:11:45,550
270.000 astronomical units is the distance
to that one, so that means it's way
143
00:11:45,550 --> 00:11:52,560
further away. I mean, in the solar system
we can move 2, 3, 5, maybe 10, 20, 30
144
00:11:52,560 --> 00:11:56,290
astronomical units if we are doing well
with our rockets and it takes a bunch of
145
00:11:56,290 --> 00:12:01,830
years, but to cover 1000s or even 100s of
1000s of astronomical units tells us that
146
00:12:01,830 --> 00:12:06,080
the propulsion systems and the rockets that
we have today are not capable of getting us
147
00:12:06,080 --> 00:12:09,920
to the stars in the way we do it right
now, which we also heard, of course, in
148
00:12:09,920 --> 00:12:15,320
the talks before. Telescopes on the ground
are nice, but actually telescopes in space
149
00:12:15,320 --> 00:12:21,110
can give us an even better resolution. And
the Hipparcos satellite, which was active
150
00:12:21,110 --> 00:12:26,710
in the last couple of decades, measured up
to 2 milliarcseconds. Now think of it. The
151
00:12:26,710 --> 00:12:32,110
arcsecond with the astronaut in the sky
and my beard and stuff. A 1/1000 of that
152
00:12:32,110 --> 00:12:36,110
as an angular resolution is what the
Hipparcos satellite was able to measure
153
00:12:36,110 --> 00:12:40,370
and this gave us the distances to
basically all the stars in our field of
154
00:12:40,370 --> 00:12:46,560
view that were up to 100 parsecs away. And
we know exactly how far these are away.
155
00:12:46,560 --> 00:12:51,590
The Gaia satellite, which is now just
coming into operation, commissioned by the
156
00:12:51,590 --> 00:12:56,980
European space agency, this is about to
have an even better performance, it will
157
00:12:56,980 --> 00:13:01,040
look at a billion stars, that's what it's
called, the Billion Stars Surveyor, it
158
00:13:01,040 --> 00:13:06,230
will be good for distances of up to 5000
parsecs and it's gonna tell us the
159
00:13:06,230 --> 00:13:11,090
distances to all these stars, it's gonna
be an amazing step in looking at how far
160
00:13:11,090 --> 00:13:17,711
away the stars are and forming a map of
all the stars around us. And, there is
161
00:13:17,711 --> 00:13:21,660
something missing? No. Let's talk about
standard candles now, because that's
162
00:13:21,660 --> 00:13:26,210
another important tool apart from the
geometry that we saw before. A standard
163
00:13:26,210 --> 00:13:30,610
candle is just something where you know
exactly how bright it is. And then you can
164
00:13:30,610 --> 00:13:36,890
calculate how far away. A standard candle
would be, well, like any, let's image a
165
00:13:36,890 --> 00:13:42,080
set of candles and all of them burn at the
same brightness. So if you measured the
166
00:13:42,080 --> 00:13:47,760
brightness of one of these candles, you
could tell how far apart it was. Actually,
167
00:13:47,760 --> 00:13:53,300
maybe a better picture is streetlights in
the night. If you see a car coming towards
168
00:13:53,300 --> 00:13:57,461
you, you can kind of estimate by how
brightly you see the light if the car is
169
00:13:57,461 --> 00:14:01,470
still far away, or if it is close to you,
because you have an intuitive
170
00:14:01,470 --> 00:14:05,970
understanding of how bright the lights of
a car should be if it is right next to you
171
00:14:05,970 --> 00:14:11,190
or a couple of 100 meters away or many
kilometers away, if it's a clear night.
172
00:14:11,190 --> 00:14:15,720
And so we want standard candles in space.
We want stuff in space, where we have a
173
00:14:15,720 --> 00:14:19,930
good idea of how bright it should be. And
then from how bright we see it, how much
174
00:14:19,930 --> 00:14:26,170
of the light actually reaches us, we can
calculate the distance. And this we can do
175
00:14:26,170 --> 00:14:29,770
with the help of these, one of the most
important diagrams and all of
176
00:14:29,770 --> 00:14:33,820
astrophysics, which is the
Hertzsprung-Russel diagram. It basically
177
00:14:33,820 --> 00:14:40,440
sorts stars by their colors and by how bright
they are. And because of the way that stars
178
00:14:40,440 --> 00:14:44,690
work, the color and the brightness are
also intermittently connected to their
179
00:14:44,690 --> 00:14:50,230
mass and what's happening inside the stars
and then if we see a bunch of stars, we
180
00:14:50,230 --> 00:14:55,040
can do this very well with clusters, which
are groups of 10s or 100s up to 1000s of
181
00:14:55,040 --> 00:14:59,780
stars in one place, at basically the same
distance, and they have sort of a standard
182
00:14:59,780 --> 00:15:04,790
population, then we can estimate how far
away they're. Let's think of it like this,
183
00:15:04,790 --> 00:15:08,130
we jut had the picture of the car and the
night, which was light, but let's think of
184
00:15:08,130 --> 00:15:13,460
it as sound. Think of groups of children
in maybe preschool and let's imagine that
185
00:15:13,460 --> 00:15:20,010
every preschool group of children always
had 20 children in it, just because. And
186
00:15:20,010 --> 00:15:25,060
now, you can estimate how loud 20
preschool children just playing around actually
187
00:15:25,060 --> 00:15:28,900
are and from the sound of when you hear
the children you can tell how far away
188
00:15:28,900 --> 00:15:32,500
that group is from you. If we have a group
of stars and we know the light, the
189
00:15:32,500 --> 00:15:38,030
different colors that they have, we can
actually match it to this graph and see
190
00:15:38,030 --> 00:15:45,080
how far away this group is by estimating
the properties that they have in this way.
191
00:15:45,080 --> 00:15:50,149
And so this then gives us an overview of
basically our galactic neighborhood, so
192
00:15:50,149 --> 00:15:56,269
the other stars in our galaxy. The number
of stars in our galaxy is about 200 billion,
193
00:15:56,269 --> 00:15:59,900
but before I bombard you with
more numbers, we have a chance to get a
194
00:15:59,900 --> 00:16:05,610
great overview of what that's like from
the artists of Monty Python.
195
00:16:07,500 --> 00:16:13,500
Song: Just remember that you standing
on a planet that's evolving,
196
00:16:13,500 --> 00:16:17,238
revolving at 900
miles an hour.
197
00:16:20,743 --> 00:16:22,055
Michael: Sorry.
198
00:18:10,277 --> 00:18:18,217
applause
199
00:18:18,217 --> 00:18:23,550
Thank you Monty Python. Now, the numbers
that they present have changed over time.
200
00:18:23,550 --> 00:18:27,660
Now scientists speak of 200 billion stars
in the galaxy instead of 100 billion, but
201
00:18:27,660 --> 00:18:31,990
still it gives you an amazingly good overall
idea. And whenever I try to think of the
202
00:18:31,990 --> 00:18:36,050
parameters of the milky way galaxy, like
100.000 light-years side to side, I just
203
00:18:36,050 --> 00:18:41,770
have the song in my head. And it works
amazingly well. Except also for the one
204
00:18:41,770 --> 00:18:45,341
part where it says that the universe is
expanding at the speed of light, like we
205
00:18:45,341 --> 00:18:48,890
heard in the talk before, that's not
actually true. The expansion of the
206
00:18:48,890 --> 00:18:51,809
universe actually exceeds the speed of
light, but common, they are comedians, so.
207
00:18:51,809 --> 00:18:52,809
laughing
208
00:18:52,809 --> 00:18:58,150
Cut them a little slack on that one. Other
galaxies, the milky way galaxy that we
209
00:18:58,150 --> 00:19:01,710
have just gotten this nice overview over
is by far not the only one, there are
210
00:19:01,710 --> 00:19:06,040
other galaxies and we are part of groups
of galaxies, actually the one that's
211
00:19:06,040 --> 00:19:11,070
called the local group, which has 3 very
large galaxies, which is ours, the milky
212
00:19:11,070 --> 00:19:16,450
way, the Andromeda galaxy, which is
actually larger, and another one which is
213
00:19:16,450 --> 00:19:19,920
a bit smaller. And then there's a bunch of
dwarf galaxies also moving around there
214
00:19:19,920 --> 00:19:25,450
and we gonna be looking at how we find
about distances in that regard. Now again,
215
00:19:25,450 --> 00:19:29,750
we have a sort of standard candle here,
and these are stars called Cepheids, and
216
00:19:29,750 --> 00:19:33,640
what you see here is the brightness of the
star pulsating. So you look at the star
217
00:19:33,640 --> 00:19:36,680
and you say, okay it's this bright, oh no
wait, it's dimmer again, oh wait, it's
218
00:19:36,680 --> 00:19:40,800
getting brighter again, over the course of
a couple days. And if you measure this
219
00:19:40,800 --> 00:19:44,430
brightness very precisely, you just have
to wait a few days, it's not a difficult
220
00:19:44,430 --> 00:19:52,250
measurement in that regard, you can find
out that the duration of these variations
221
00:19:52,250 --> 00:19:57,650
is actually closely linked to how bright
they are. So, calculating or measuring the
222
00:19:57,650 --> 00:20:02,410
period of these oscillations gives you the
brightness and then these stars, called
223
00:20:02,410 --> 00:20:07,950
Cepheids, can work for you as a standard
candle and this works out into other
224
00:20:07,950 --> 00:20:11,530
galaxies. So, we look at like the
Andromeda galaxy, which is a couple of
225
00:20:11,530 --> 00:20:15,960
million light-years away, and we see a
Cepheids star in there somewhere, we
226
00:20:15,960 --> 00:20:20,760
measure the period of it's oscillations
and then we can tell how far apart it is
227
00:20:20,760 --> 00:20:25,730
and this gives us a good idea of how away
that galaxy actually is. That doesn't work
228
00:20:25,730 --> 00:20:31,350
for galaxies where they appear so small in
our field of view that we can't point out
229
00:20:31,350 --> 00:20:39,750
a single Cepheid star. So these groups of
galaxies also form together into something
230
00:20:39,750 --> 00:20:44,290
called Superclusters. And the Virgo
Supercluster is an idea of what our group
231
00:20:44,290 --> 00:20:48,640
is actually in. So I mentioned the local
group of a couple of maybe 100 dwarf
232
00:20:48,640 --> 00:20:54,820
galaxies and three large ones. And this is
actually orbiting something called the
233
00:20:54,820 --> 00:21:03,310
Virgo cluster. So we are a bit out, but I
mean this is an abstract graphic. What
234
00:21:03,310 --> 00:21:07,420
does it look like to look at the Virgo
cluster? Well, We can look at that. And
235
00:21:07,420 --> 00:21:11,060
you see that we look at the sky and
there's just a bunch of large galaxies
236
00:21:11,060 --> 00:21:15,630
there. You're looking at something that's
probably pretty similar to what our own
237
00:21:15,630 --> 00:21:19,770
galaxy is like, and it's just hanging
there in the sky. And by, for example,
238
00:21:19,770 --> 00:21:25,420
this Cepheid measurement method, we can
get an idea of how far away it is. But these
239
00:21:25,420 --> 00:21:32,090
local galaxies are not the only ones we
see. There is an example that's called the
240
00:21:32,090 --> 00:21:36,290
Hubble Extreme Deep Field, where the
Hubble space telescope, that's orbiting the
241
00:21:36,290 --> 00:21:40,390
earth, took pictures of a very small patch
of the sky. Here, the moon is shown to
242
00:21:40,390 --> 00:21:44,520
scale. So, if you look at the moon, the
photograph that I'm about to show you
243
00:21:44,520 --> 00:21:50,020
right now, shows this small part that's
marked by the XDF. And if you look at it
244
00:21:50,020 --> 00:21:54,530
long enough and collect a lot of light,
that's why it's called a Deep Field, it
245
00:21:54,530 --> 00:21:58,640
actually looks like this. And there's a
huge amount of galaxies and they all look
246
00:21:58,640 --> 00:22:03,740
different. Some are spiral galaxies, some
are elliptical galaxies, and they even
247
00:22:03,740 --> 00:22:07,830
have different colors. Some appear red,
some appear blue, and this all has to do
248
00:22:07,830 --> 00:22:12,780
with the way that they evolve and we not
even done quite in understanding how they
249
00:22:12,780 --> 00:22:18,210
come to look like that. You can actually
help with this. There are so many galaxies
250
00:22:18,210 --> 00:22:23,190
just recorded in pictures that we don't
have good catalogs of them all. So you can
251
00:22:23,190 --> 00:22:28,490
visit galaxyzoo.org and they will show you
a picture of a galaxy somewhat like this
252
00:22:28,490 --> 00:22:32,770
and you have to click, is it a spiral
galaxy, is it an elliptical galaxy. Does
253
00:22:32,770 --> 00:22:36,340
it look like blue color, does it look like
red color. It's crowdsourced citizen
254
00:22:36,340 --> 00:22:40,750
science and you can help classify a whole
bunch of galaxies, and it's a lot of fun,
255
00:22:40,750 --> 00:22:43,670
just click through while
you should be working.
256
00:22:43,670 --> 00:22:51,230
laughterapplause
257
00:22:51,230 --> 00:22:54,990
Now, also when we look at these galaxies,
similar to the way we can look at stars
258
00:22:54,990 --> 00:22:58,559
with the Cepheids and their variation,
there is a bunch of methods I'm not going
259
00:22:58,559 --> 00:23:03,650
to get into a lot of detail, but if you
look at galaxies and the way they move and
260
00:23:03,650 --> 00:23:07,220
the way that the light emanates from
them, and someway you can correlate that
261
00:23:07,220 --> 00:23:12,100
to the distance, and so examining these
galaxies very closely can give us an idea
262
00:23:12,100 --> 00:23:17,240
of how far away they are from us. But
actually everyone's favorite standard
263
00:23:17,240 --> 00:23:22,130
candle, the one thing that astronomers and
astrophysicists really love to use, is
264
00:23:22,130 --> 00:23:27,299
supernovae of the 1a type. Now in the talk
before we saw that sometimes little white
265
00:23:27,299 --> 00:23:31,550
dwarf stars can gain mass from their
companion stars, so stuff is falling onto
266
00:23:31,550 --> 00:23:36,240
them, until the mass of the white dwarf
star that's gaining weight becomes so
267
00:23:36,240 --> 00:23:39,960
large that it explodes in a thermal
nuclear explosion and this then is a
268
00:23:39,960 --> 00:23:45,210
supernova of type A. And what's amazing
about these explosions is that basically
269
00:23:45,210 --> 00:23:50,490
they are almost the same brightness. Or
you can determine the brightness very well
270
00:23:50,490 --> 00:23:56,940
if you look at how quickly the light fades
out. So, whenever we see, like you see
271
00:23:56,940 --> 00:24:01,280
here on the top-left picture, whenever we
see a galaxy and there is a supernova 1a
272
00:24:01,280 --> 00:24:05,090
happening right at that moment, and they
only are visible for a couple of days
273
00:24:05,090 --> 00:24:09,330
mostly, hours to days. So if we look at
that closely and we measure how the light
274
00:24:09,330 --> 00:24:16,769
fades away, then we can get a very good
idea of how far away that galaxy is. And
275
00:24:16,769 --> 00:24:22,430
even larger structures emerge then, and we
think about the Virgo Supercluster that I
276
00:24:22,430 --> 00:24:27,630
just showed you, which was groups of
galaxies around groups of other galaxies
277
00:24:27,630 --> 00:24:32,299
and the latest idea of the sort of the
large scale structure that the earth and
278
00:24:32,299 --> 00:24:37,700
our milky way is part of, is the Laniakea
Supercluster that was proposed just 2 or 3
279
00:24:37,700 --> 00:24:43,020
years ago. And here you don't even see
individual galaxies. It's more like the
280
00:24:43,020 --> 00:24:48,620
density of stuff in the universe that's
grouped together. And you see these lines,
281
00:24:48,620 --> 00:24:54,530
they represent sort of the way that
gravity is pulling everything. And yeah,
282
00:24:54,530 --> 00:24:58,530
that's a pretty amazing idea. And like
we've heard in the talk before, the
283
00:24:58,530 --> 00:25:01,970
universe is expanding and this also
affects the light, the light gets
284
00:25:01,970 --> 00:25:07,280
redshifted. If there is a lightwave
traveling through the universe, and while
285
00:25:07,280 --> 00:25:12,160
it's traveling space expands, that also
means that the light changes it's
286
00:25:12,160 --> 00:25:17,480
wavelength. It just becomes a different
color. And it shifts towards the red,
287
00:25:17,480 --> 00:25:21,820
which is why this thing is called
redshift. And so galaxies that are very
288
00:25:21,820 --> 00:25:27,179
far away, because between us and where
that galaxy is space is expanding and has
289
00:25:27,179 --> 00:25:31,870
been expanding for a while, these galaxies
appear to look red. And we can actually see
290
00:25:31,870 --> 00:25:36,510
that in the pictures, like this one. Yeah,
you can see it on the screen, it's this
291
00:25:36,510 --> 00:25:40,540
very faint red dot, and that actually
tells us that this is a galaxy which
292
00:25:40,540 --> 00:25:44,650
should actually have blue light, like most
of the other galaxies, but because it's so
293
00:25:44,650 --> 00:25:49,710
far away and space has stretched while the
lightwaves were traveling in our direction
294
00:25:49,710 --> 00:25:54,980
it now appears red. And 4 gigaparsecs, so
we're looking at 4 billion parsecs of
295
00:25:54,980 --> 00:26:00,490
distance towards this, which we can kind
of extrapolate of how far it's redshifted,
296
00:26:00,490 --> 00:26:06,600
so how far the light has been reddened, is
how we can get an idea of this. And it's
297
00:26:06,600 --> 00:26:09,910
not just the one, this, at least a couple
of years ago, was the furthest away galaxy
298
00:26:09,910 --> 00:26:14,660
that had ever been observed, but actually
there's a whole bunch of those and they
299
00:26:14,660 --> 00:26:19,140
are everywhere, and like we saw there is a
very large number of galaxies to be seen
300
00:26:19,140 --> 00:26:24,480
everywhere. And to give us a final idea of
how matter is really distributed in the
301
00:26:24,480 --> 00:26:29,509
universe, I have another video which is a
simulation of how these super galaxy
302
00:26:29,509 --> 00:26:39,620
clusters are actually distributed. So let
me pull that up. Now we're looking at some
303
00:26:39,620 --> 00:26:44,800
generic super galaxy cluster and we're
kind of circling it. And as the camera is
304
00:26:44,800 --> 00:26:51,210
moving out and the picture is getting
larger, we see that this one super galaxy
305
00:26:51,210 --> 00:26:55,660
cluster is actually sort of connected to
other regions where there is a high
306
00:26:55,660 --> 00:27:01,300
density of galaxies. Remember, this is not
stars, we're looking at galaxies. And they
307
00:27:01,300 --> 00:27:05,040
are sort of strung together in something
that's called filaments. And these
308
00:27:05,040 --> 00:27:09,679
filaments stretch along the lines of
regions where there is almost no galaxies
309
00:27:09,679 --> 00:27:15,390
which are called voids, and these voids
are between 10 and 50 million light-years
310
00:27:15,390 --> 00:27:20,080
in diameter, more or less. And this is
just the way that everything stretches
311
00:27:20,080 --> 00:27:27,220
out. So, super galaxy clusters are
gathered in filaments around voids and it
312
00:27:27,220 --> 00:27:32,471
looks like a sort of a soap bubble or
maybe a bee hive structure. And okay, this
313
00:27:32,471 --> 00:27:38,640
is a simulation, it looks nice, and this is
gathered from data that we have about how
314
00:27:38,640 --> 00:27:43,820
far away these galaxies are, how we think the
universe evolved, but how about real data.
315
00:27:43,820 --> 00:27:47,870
Can we look out there and actually measure
galaxies, and actually measure how stuff
316
00:27:47,870 --> 00:27:52,870
looks, and see the structure in the
universe? Turns out, we can. And it looks
317
00:27:52,870 --> 00:27:58,540
like this. And it just blows my mind.
Because you see this whole bee hive
318
00:27:58,540 --> 00:28:02,930
structure, you see the voids, you see the
filaments of super galaxy cluster
319
00:28:02,930 --> 00:28:08,700
structures sort of strung together. And
that's just real data. That is the largest
320
00:28:08,700 --> 00:28:14,190
scale structure of all the galaxies, of
the observable universe, that have ever
321
00:28:14,190 --> 00:28:21,539
been recorded. And this relies on the
measurements of type 1a supernovae, and of
322
00:28:21,539 --> 00:28:26,789
the galaxies which relies on measurements
of, for example, the Cepheids stars, which
323
00:28:26,789 --> 00:28:29,991
rely on measurements of the parallax, of
the geometrical parallax, like we
324
00:28:29,991 --> 00:28:35,930
discussed here in this room. So, the way
of looking at the universe like this, of
325
00:28:35,930 --> 00:28:42,620
all the super galaxy clusters, actually
begins when we string together these to
326
00:28:42,620 --> 00:28:46,610
form what's called the cosmological
distance ladder of all these different
327
00:28:46,610 --> 00:28:51,540
methods building upon each other. And it
starts right here, when we look up at the
328
00:28:51,540 --> 00:28:55,820
sky. So, I hope you enjoy that,
thanks for your attention.
329
00:28:55,820 --> 00:29:06,030
applause
330
00:29:06,030 --> 00:29:12,899
Herald: Thank you very much, Michael. So,
we still have time for questions. Line up
331
00:29:12,899 --> 00:29:18,530
at the microphones if you want to ask any
here and now. And we get a little
332
00:29:18,530 --> 00:29:26,559
preference on the Internet, are there any
questions, Signal Angel?
333
00:29:26,559 --> 00:29:31,810
That doesn't seem to be the case,
and we start with microphone 3, please.
334
00:29:31,810 --> 00:29:37,250
Mic 3: Regarding the redshift of the
further away galaxy, red light has less
335
00:29:37,250 --> 00:29:41,240
energy than blue light, where
does the energy go?
336
00:29:41,240 --> 00:29:45,650
M: It's lost. In the process of the
universe expanding, energy is not
337
00:29:45,650 --> 00:29:48,970
conserved. And that's a big
headache for physics.
338
00:29:48,970 --> 00:29:53,749
laughter
Herald: Microphone 4.
339
00:29:53,749 --> 00:29:58,650
Mic 4: So, I was thinking that in the case
that you try to measure the distance to a
340
00:29:58,650 --> 00:30:04,970
far away galaxy, where we are talking in
the scale that there is not sufficent
341
00:30:04,970 --> 00:30:12,220
accuracy via parallax, so you rely on
supernovas. So, you point the telescope in
342
00:30:12,220 --> 00:30:18,990
a patch of the sky and you pick up a
supernova. But you cannot really know, I
343
00:30:18,990 --> 00:30:25,650
suppose, that the supernova belongs to the
galaxy where all the other stars around
344
00:30:25,650 --> 00:30:30,309
that are, or perhaps it's very far away on
the z-axis in a different galaxy that's
345
00:30:30,309 --> 00:30:33,620
just behind. Is that possible?
How do you go around that?
346
00:30:33,620 --> 00:30:38,429
M: Yes, you're right. You may find
pictures, and I may find a picture of this
347
00:30:38,429 --> 00:30:43,900
where galaxies are actually overlapping.
So in this thing that I showed you from
348
00:30:43,900 --> 00:30:48,530
the galaxy zoo, yeah, I think you see some
galaxies overlapping now. This might mean
349
00:30:48,530 --> 00:30:51,299
that they are close together and actually
colliding, but it might also mean that
350
00:30:51,299 --> 00:30:57,610
they just happen to be in the same
direction. But then the type 1a supernova,
351
00:30:57,610 --> 00:31:01,710
if you measure it, gives you an idea of
how far away it is and then hopefully you
352
00:31:01,710 --> 00:31:06,720
can estimate if it was the front galaxy or
the back galaxy. But you can't be exactly
353
00:31:06,720 --> 00:31:09,550
sure, you're right.
354
00:31:09,550 --> 00:31:11,799
Herald: Okay, microphone 1, please.
355
00:31:11,799 --> 00:31:17,719
Mic 1: Okay. Thanks, this is really
fascinating. This might be a stupid
356
00:31:17,719 --> 00:31:26,880
question. If the outer edges of our
observable universe are expanding at
357
00:31:26,880 --> 00:31:33,510
faster than the speed of light and we
detect very far away galaxies with light,
358
00:31:33,510 --> 00:31:37,250
how is the light ever reaching us?
359
00:31:37,250 --> 00:31:43,331
M: We see only as far as the expansion of
the universe will allow us. And, like we
360
00:31:43,331 --> 00:31:49,300
heard in the talk before, stuff is falling
behind the horizon. There are regions in
361
00:31:49,300 --> 00:31:54,350
the universe now, where at a later point,
because space is expanding, the light from
362
00:31:54,350 --> 00:31:58,960
these regions will not be able to reach
us. So if we look way out into the
363
00:31:58,960 --> 00:32:05,690
universe to the very edge of what we can
see, there is stuff disappearing there and
364
00:32:05,690 --> 00:32:10,260
there is just no getting around there,
if it's gone, it's gone.
365
00:32:10,260 --> 00:32:16,020
Herald: Okay, this concludes the Q & A. A
warm round of applause for Michael Büker.
366
00:32:16,020 --> 00:32:22,130
applause
367
00:32:22,130 --> 00:32:29,400
postroll music
368
00:32:29,400 --> 00:32:46,000
subtitles created by c3subtitles.de
in the year 2017. Join, and help us!