1 00:00:09,269 --> 00:00:11,989 How can astrophysicists study the story of the Universe? 2 00:00:12,690 --> 00:00:17,930 Billions of years ago, when the Big Bang happened, there was no Milky Way galaxy, no Solar System, 3 00:00:17,930 --> 00:00:23,180 no planet Earth, and, especially, no human beings to witness these and all the events that followed. 4 00:00:23,180 --> 00:00:24,990 So how would they know about this stuff? 5 00:00:24,990 --> 00:00:28,900 Well, it turns out that the Universe is, somehow, like a time machine. 6 00:00:28,900 --> 00:00:31,700 When looking at things in the sky, we are looking at that past. 7 00:00:31,700 --> 00:00:34,520 Yeah, it's a bit confusing but try it this way: 8 00:00:34,520 --> 00:00:38,120 When you hear a plane, you probably have a hard time spotting it in the sky. 9 00:00:38,360 --> 00:00:42,060 You look in the direction where the sound came from but the plane is no longer there 10 00:00:42,380 --> 00:00:44,900 That's because its sound took some time to reach you, 11 00:00:44,900 --> 00:00:47,760 and by the time it did, the plane had already moved on. 12 00:00:47,760 --> 00:00:50,400 In a way you were hearing back in time 13 00:00:50,400 --> 00:00:53,900 as the sound you perceived was the one that left the plane seconds before. 14 00:00:53,900 --> 00:00:56,220 With light it's exactly the same. 15 00:00:56,220 --> 00:01:00,080 Even though light is much faster than sound — in fact, it's the fastest thing we know — 16 00:01:00,420 --> 00:01:04,100 it still takes time to get from where it is emitted to where it is seen. 17 00:01:04,320 --> 00:01:08,040 The father the object the longer it takes light to make the journey to the observer. 18 00:01:08,400 --> 00:01:13,220 By looking at galaxies that are very far away, whose light takes billions and billions of years to reach us, 19 00:01:13,220 --> 00:01:15,580 we are seeing them how they looked billions of years ago, 20 00:01:15,780 --> 00:01:19,160 when the universe was much younger and they were just beginning to form. 21 00:01:19,460 --> 00:01:23,820 But as we look at galaxies that are closer and closer to us, studying them throughout time, 22 00:01:24,060 --> 00:01:26,700 it's possible to see how they aged and change, 23 00:01:26,700 --> 00:01:31,740 just like if we were looking at babies, children, teenagers and adults to see how humans develop. 24 00:01:32,040 --> 00:01:34,860 The problem is when things are very far away from you, 25 00:01:34,860 --> 00:01:38,300 it gets to a point where it's impossible for your eyes to distinguish details. 26 00:01:38,300 --> 00:01:42,100 Telescopes, especially the ones that see the same kind of light as we do, also have a limit 27 00:01:42,660 --> 00:01:46,340 and are not able to detect the light emitted by the first galaxies ever formed, 28 00:01:46,340 --> 00:01:49,300 as they are too distant and their light is too faint. 29 00:01:49,300 --> 00:01:52,640 In those galaxies, however, the first stars were born. 30 00:01:52,640 --> 00:01:54,900 And even though there's no telescope powerful enough to see them shine, 31 00:01:54,900 --> 00:01:58,460 ALMA, with its incredible sharpness and ability to see radio light, 32 00:01:58,460 --> 00:02:03,100 can distinguish the dust and gas clouds which formed the first generations of stars in the Universe. 33 00:02:03,100 --> 00:02:07,100 This can help astronomers know a little bit more about these early phases of time and space, 34 00:02:07,100 --> 00:02:09,580 which are fundamental to understand our present. 35 00:02:11,380 --> 00:02:14,220 Transcribed by ESO. Translated by —.