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 *laughter**applause* 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!