WEBVTT 00:00:01.436 --> 00:00:03.296 In the movie "Interstellar," 00:00:03.320 --> 00:00:06.647 we get an up-close look at a supermassive black hole. 00:00:06.671 --> 00:00:08.814 Set against a backdrop of bright gas, 00:00:08.838 --> 00:00:10.956 the black hole's massive gravitational pull 00:00:10.980 --> 00:00:12.415 bends light into a ring. 00:00:12.439 --> 00:00:14.548 However, this isn't a real photograph, 00:00:14.572 --> 00:00:16.358 but a computer graphic rendering -- 00:00:16.382 --> 00:00:19.772 an artistic interpretation of what a black hole might look like. NOTE Paragraph 00:00:20.401 --> 00:00:21.567 A hundred years ago, 00:00:21.591 --> 00:00:25.192 Albert Einstein first published his theory of general relativity. 00:00:25.216 --> 00:00:26.655 In the years since then, 00:00:26.679 --> 00:00:29.652 scientists have provided a lot of evidence in support of it. 00:00:29.676 --> 00:00:32.760 But one thing predicted from this theory, black holes, 00:00:32.784 --> 00:00:35.134 still have not been directly observed. 00:00:35.158 --> 00:00:38.364 Although we have some idea as to what a black hole might look like, 00:00:38.388 --> 00:00:41.167 we've never actually taken a picture of one before. 00:00:41.191 --> 00:00:45.470 However, you might be surprised to know that that may soon change. 00:00:45.494 --> 00:00:49.658 We may be seeing our first picture of a black hole in the next couple years. 00:00:49.682 --> 00:00:53.640 Getting this first picture will come down to an international team of scientists, 00:00:53.664 --> 00:00:55.231 an Earth-sized telescope 00:00:55.255 --> 00:00:58.087 and an algorithm that puts together the final picture. 00:00:58.111 --> 00:01:01.639 Although I won't be able to show you a real picture of a black hole today, 00:01:01.663 --> 00:01:04.574 I'd like to give you a brief glimpse into the effort involved 00:01:04.598 --> 00:01:06.211 in getting that first picture. NOTE Paragraph 00:01:07.477 --> 00:01:08.914 My name is Katie Bouman, 00:01:08.938 --> 00:01:11.504 and I'm a PhD student at MIT. 00:01:11.528 --> 00:01:13.555 I do research in a computer science lab 00:01:13.579 --> 00:01:16.877 that works on making computers see through images and video. 00:01:16.901 --> 00:01:19.063 But although I'm not an astronomer, 00:01:19.087 --> 00:01:20.372 today I'd like to show you 00:01:20.396 --> 00:01:23.299 how I've been able to contribute to this exciting project. NOTE Paragraph 00:01:23.323 --> 00:01:26.154 If you go out past the bright city lights tonight, 00:01:26.178 --> 00:01:28.614 you may just be lucky enough to see a stunning view 00:01:28.638 --> 00:01:30.131 of the Milky Way Galaxy. 00:01:30.155 --> 00:01:32.617 And if you could zoom past millions of stars, 00:01:32.641 --> 00:01:36.396 26,000 light-years toward the heart of the spiraling Milky Way, 00:01:36.420 --> 00:01:39.941 we'd eventually reach a cluster of stars right at the center. 00:01:39.965 --> 00:01:43.171 Peering past all the galactic dust with infrared telescopes, 00:01:43.195 --> 00:01:47.062 astronomers have watched these stars for over 16 years. 00:01:47.086 --> 00:01:50.675 But it's what they don't see that is the most spectacular. 00:01:50.699 --> 00:01:53.765 These stars seem to orbit an invisible object. 00:01:53.789 --> 00:01:56.112 By tracking the paths of these stars, 00:01:56.136 --> 00:01:57.430 astronomers have concluded 00:01:57.454 --> 00:02:00.583 that the only thing small and heavy enough to cause this motion 00:02:00.607 --> 00:02:02.575 is a supermassive black hole -- 00:02:02.599 --> 00:02:06.777 an object so dense that it sucks up anything that ventures too close -- 00:02:06.801 --> 00:02:08.295 even light. NOTE Paragraph 00:02:08.319 --> 00:02:11.380 But what happens if we were to zoom in even further? 00:02:11.404 --> 00:02:16.137 Is it possible to see something that, by definition, is impossible to see? 00:02:16.719 --> 00:02:19.963 Well, it turns out that if we were to zoom in at radio wavelengths, 00:02:19.987 --> 00:02:21.669 we'd expect to see a ring of light 00:02:21.693 --> 00:02:24.104 caused by the gravitational lensing of hot plasma 00:02:24.128 --> 00:02:25.957 zipping around the black hole. 00:02:25.981 --> 00:02:27.141 In other words, 00:02:27.165 --> 00:02:30.336 the black hole casts a shadow on this backdrop of bright material, 00:02:30.360 --> 00:02:32.202 carving out a sphere of darkness. 00:02:32.226 --> 00:02:35.565 This bright ring reveals the black hole's event horizon, 00:02:35.589 --> 00:02:37.989 where the gravitational pull becomes so great 00:02:38.013 --> 00:02:39.639 that not even light can escape. 00:02:39.663 --> 00:02:42.522 Einstein's equations predict the size and shape of this ring, 00:02:42.546 --> 00:02:45.754 so taking a picture of it wouldn't only be really cool, 00:02:45.778 --> 00:02:48.396 it would also help to verify that these equations hold 00:02:48.420 --> 00:02:50.886 in the extreme conditions around the black hole. NOTE Paragraph 00:02:50.910 --> 00:02:53.468 However, this black hole is so far away from us, 00:02:53.492 --> 00:02:56.590 that from Earth, this ring appears incredibly small -- 00:02:56.614 --> 00:03:00.204 the same size to us as an orange on the surface of the moon. 00:03:00.758 --> 00:03:03.582 That makes taking a picture of it extremely difficult. 00:03:04.645 --> 00:03:05.947 Why is that? 00:03:06.512 --> 00:03:09.700 Well, it all comes down to a simple equation. 00:03:09.724 --> 00:03:12.140 Due to a phenomenon called diffraction, 00:03:12.164 --> 00:03:13.519 there are fundamental limits 00:03:13.543 --> 00:03:16.213 to the smallest objects that we can possibly see. 00:03:16.789 --> 00:03:20.461 This governing equation says that in order to see smaller and smaller, 00:03:20.485 --> 00:03:23.072 we need to make our telescope bigger and bigger. 00:03:23.096 --> 00:03:26.165 But even with the most powerful optical telescopes here on Earth, 00:03:26.189 --> 00:03:28.608 we can't even get close to the resolution necessary 00:03:28.632 --> 00:03:30.830 to image on the surface of the moon. 00:03:30.854 --> 00:03:34.471 In fact, here I show one of the highest resolution images ever taken 00:03:34.495 --> 00:03:35.892 of the moon from Earth. 00:03:35.916 --> 00:03:38.473 It contains roughly 13,000 pixels, 00:03:38.497 --> 00:03:42.547 and yet each pixel would contain over 1.5 million oranges. 00:03:43.396 --> 00:03:45.368 So how big of a telescope do we need 00:03:45.392 --> 00:03:48.157 in order to see an orange on the surface of the moon 00:03:48.181 --> 00:03:50.395 and, by extension, our black hole? 00:03:50.419 --> 00:03:52.759 Well, it turns out that by crunching the numbers, 00:03:52.783 --> 00:03:55.393 you can easily calculate that we would need a telescope 00:03:55.417 --> 00:03:56.810 the size of the entire Earth. NOTE Paragraph 00:03:56.834 --> 00:03:57.858 (Laughter) NOTE Paragraph 00:03:57.882 --> 00:04:00.001 If we could build this Earth-sized telescope, 00:04:00.025 --> 00:04:02.950 we could just start to make out that distinctive ring of light 00:04:02.974 --> 00:04:05.157 indicative of the black hole's event horizon. 00:04:05.181 --> 00:04:08.099 Although this picture wouldn't contain all the detail we see 00:04:08.123 --> 00:04:09.629 in computer graphic renderings, 00:04:09.653 --> 00:04:11.952 it would allow us to safely get our first glimpse 00:04:11.976 --> 00:04:14.463 of the immediate environment around a black hole. NOTE Paragraph 00:04:14.487 --> 00:04:16.100 However, as you can imagine, 00:04:16.124 --> 00:04:19.748 building a single-dish telescope the size of the Earth is impossible. 00:04:19.772 --> 00:04:21.659 But in the famous words of Mick Jagger, 00:04:21.683 --> 00:04:23.474 "You can't always get what you want, 00:04:23.498 --> 00:04:25.685 but if you try sometimes, you just might find 00:04:25.709 --> 00:04:26.924 you get what you need." 00:04:26.948 --> 00:04:29.412 And by connecting telescopes from around the world, 00:04:29.436 --> 00:04:32.974 an international collaboration called the Event Horizon Telescope 00:04:32.998 --> 00:04:36.107 is creating a computational telescope the size of the Earth, 00:04:36.131 --> 00:04:37.668 capable of resolving structure 00:04:37.692 --> 00:04:39.891 on the scale of a black hole's event horizon. 00:04:39.915 --> 00:04:43.302 This network of telescopes is scheduled to take its very first picture 00:04:43.326 --> 00:04:45.141 of a black hole next year. 00:04:45.165 --> 00:04:48.503 Each telescope in the worldwide network works together. 00:04:48.527 --> 00:04:51.239 Linked through the precise timing of atomic clocks, 00:04:51.263 --> 00:04:53.920 teams of researchers at each of the sights freeze light 00:04:53.944 --> 00:04:56.906 by collecting thousands of terabytes of data. 00:04:56.930 --> 00:05:01.947 This data is then processed in a lab right here in Massachusetts. NOTE Paragraph 00:05:01.971 --> 00:05:03.765 So how does this even work? 00:05:03.789 --> 00:05:07.192 Remember if we want to see the black hole in the center of our galaxy, 00:05:07.216 --> 00:05:10.198 we need to build this impossibly large Earth-sized telescope? 00:05:10.222 --> 00:05:12.454 For just a second, let's pretend we could build 00:05:12.478 --> 00:05:14.320 a telescope the size of the Earth. 00:05:14.344 --> 00:05:16.799 This would be a little bit like turning the Earth 00:05:16.823 --> 00:05:18.570 into a giant spinning disco ball. 00:05:18.594 --> 00:05:20.794 Each individual mirror would collect light 00:05:20.818 --> 00:05:23.415 that we could then combine together to make a picture. 00:05:23.439 --> 00:05:26.100 However, now let's say we remove most of those mirrors 00:05:26.124 --> 00:05:28.096 so only a few remained. 00:05:28.120 --> 00:05:30.997 We could still try to combine this information together, 00:05:31.021 --> 00:05:33.014 but now there are a lot of holes. 00:05:33.038 --> 00:05:37.411 These remaining mirrors represent the locations where we have telescopes. 00:05:37.435 --> 00:05:41.514 This is an incredibly small number of measurements to make a picture from. 00:05:41.538 --> 00:05:45.376 But although we only collect light at a few telescope locations, 00:05:45.400 --> 00:05:48.823 as the Earth rotates, we get to see other new measurements. 00:05:48.847 --> 00:05:52.666 In other words, as the disco ball spins, those mirrors change locations 00:05:52.690 --> 00:05:55.589 and we get to observe different parts of the image. NOTE Paragraph 00:05:55.613 --> 00:05:59.631 The imaging algorithms we develop fill in the missing gaps of the disco ball 00:05:59.655 --> 00:06:02.688 in order to reconstruct the underlying black hole image. 00:06:02.712 --> 00:06:05.348 If we had telescopes located everywhere on the globe -- 00:06:05.372 --> 00:06:07.313 in other words, the entire disco ball -- 00:06:07.337 --> 00:06:08.621 this would be trivial. 00:06:08.645 --> 00:06:11.967 However, we only see a few samples, and for that reason, 00:06:11.991 --> 00:06:14.379 there are an infinite number of possible images 00:06:14.403 --> 00:06:17.367 that are perfectly consistent with our telescope measurements. 00:06:17.391 --> 00:06:20.407 However, not all images are created equal. 00:06:20.849 --> 00:06:25.307 Some of those images look more like what we think of as images than others. 00:06:25.331 --> 00:06:28.553 And so, my role in helping to take the first image of a black hole 00:06:28.577 --> 00:06:31.509 is to design algorithms that find the most reasonable image 00:06:31.533 --> 00:06:33.755 that also fits the telescope measurements. NOTE Paragraph 00:06:34.727 --> 00:06:38.669 Just as a forensic sketch artist uses limited descriptions 00:06:38.693 --> 00:06:42.207 to piece together a picture using their knowledge of face structure, 00:06:42.231 --> 00:06:45.546 the imaging algorithms I develop use our limited telescope data 00:06:45.570 --> 00:06:49.892 to guide us to a picture that also looks like stuff in our universe. 00:06:49.916 --> 00:06:53.567 Using these algorithms, we're able to piece together pictures 00:06:53.591 --> 00:06:55.771 from this sparse, noisy data. 00:06:55.795 --> 00:07:00.324 So here I show a sample reconstruction done using simulated data, 00:07:00.348 --> 00:07:02.281 when we pretend to point our telescopes 00:07:02.305 --> 00:07:04.890 to the black hole in the center of our galaxy. 00:07:04.914 --> 00:07:09.369 Although this is just a simulation, reconstruction such as this give us hope 00:07:09.393 --> 00:07:12.846 that we'll soon be able to reliably take the first image of a black hole 00:07:12.870 --> 00:07:15.465 and from it, determine the size of its ring. 00:07:16.118 --> 00:07:19.317 Although I'd love to go on about all the details of this algorithm, 00:07:19.341 --> 00:07:21.515 luckily for you, I don't have the time. NOTE Paragraph 00:07:21.539 --> 00:07:23.540 But I'd still like to give you a brief idea 00:07:23.564 --> 00:07:25.866 of how we define what our universe looks like, 00:07:25.890 --> 00:07:30.356 and how we use this to reconstruct and verify our results. 00:07:30.380 --> 00:07:32.876 Since there are an infinite number of possible images 00:07:32.900 --> 00:07:35.265 that perfectly explain our telescope measurements, 00:07:35.289 --> 00:07:37.894 we have to choose between them in some way. 00:07:37.918 --> 00:07:39.756 We do this by ranking the images 00:07:39.780 --> 00:07:42.614 based upon how likely they are to be the black hole image, 00:07:42.638 --> 00:07:45.120 and then choosing the one that's most likely. NOTE Paragraph 00:07:45.144 --> 00:07:47.339 So what do I mean by this exactly? 00:07:47.862 --> 00:07:49.840 Let's say we were trying to make a model 00:07:49.864 --> 00:07:53.047 that told us how likely an image were to appear on Facebook. 00:07:53.071 --> 00:07:54.772 We'd probably want the model to say 00:07:54.796 --> 00:07:58.353 it's pretty unlikely that someone would post this noise image on the left, 00:07:58.377 --> 00:08:00.796 and pretty likely that someone would post a selfie 00:08:00.820 --> 00:08:02.154 like this one on the right. 00:08:02.178 --> 00:08:03.817 The image in the middle is blurry, 00:08:03.841 --> 00:08:06.480 so even though it's more likely we'd see it on Facebook 00:08:06.504 --> 00:08:07.864 compared to the noise image, 00:08:07.888 --> 00:08:10.848 it's probably less likely we'd see it compared to the selfie. NOTE Paragraph 00:08:10.872 --> 00:08:13.162 But when it comes to images from the black hole, 00:08:13.186 --> 00:08:16.688 we're posed with a real conundrum: we've never seen a black hole before. 00:08:16.712 --> 00:08:19.003 In that case, what is a likely black hole image, 00:08:19.027 --> 00:08:21.965 and what should we assume about the structure of black holes? 00:08:21.989 --> 00:08:24.621 We could try to use images from simulations we've done, 00:08:24.645 --> 00:08:27.175 like the image of the black hole from "Interstellar," 00:08:27.199 --> 00:08:30.137 but if we did this, it could cause some serious problems. 00:08:30.161 --> 00:08:33.541 What would happen if Einstein's theories didn't hold? 00:08:33.565 --> 00:08:37.526 We'd still want to reconstruct an accurate picture of what was going on. 00:08:37.550 --> 00:08:40.921 If we bake Einstein's equations too much into our algorithms, 00:08:40.945 --> 00:08:43.700 we'll just end up seeing what we expect to see. 00:08:43.724 --> 00:08:46.000 In other words, we want to leave the option open 00:08:46.024 --> 00:08:48.947 for there being a giant elephant at the center of our galaxy. NOTE Paragraph 00:08:48.971 --> 00:08:50.028 (Laughter) NOTE Paragraph 00:08:50.052 --> 00:08:53.041 Different types of images have very distinct features. 00:08:53.065 --> 00:08:56.613 We can easily tell the difference between black hole simulation images 00:08:56.637 --> 00:08:58.913 and images we take every day here on Earth. 00:08:58.937 --> 00:09:02.041 We need a way to tell our algorithms what images look like 00:09:02.065 --> 00:09:05.314 without imposing one type of image's features too much. 00:09:05.865 --> 00:09:07.758 One way we can try to get around this 00:09:07.782 --> 00:09:10.844 is by imposing the features of different kinds of images 00:09:10.868 --> 00:09:14.998 and seeing how the type of image we assume affects our reconstructions. 00:09:15.712 --> 00:09:19.203 If all images' types produce a very similar-looking image, 00:09:19.227 --> 00:09:21.284 then we can start to become more confident 00:09:21.308 --> 00:09:25.481 that the image assumptions we're making are not biasing this picture that much. NOTE Paragraph 00:09:25.505 --> 00:09:28.495 This is a little bit like giving the same description 00:09:28.519 --> 00:09:31.515 to three different sketch artists from all around the world. 00:09:31.539 --> 00:09:34.399 If they all produce a very similar-looking face, 00:09:34.423 --> 00:09:36.216 then we can start to become confident 00:09:36.240 --> 00:09:39.856 that they're not imposing their own cultural biases on the drawings. 00:09:39.880 --> 00:09:43.195 One way we can try to impose different image features 00:09:43.219 --> 00:09:45.660 is by using pieces of existing images. 00:09:46.214 --> 00:09:48.374 So we take a large collection of images, 00:09:48.398 --> 00:09:51.116 and we break them down into their little image patches. 00:09:51.140 --> 00:09:55.425 We then can treat each image patch a little bit like pieces of a puzzle. 00:09:55.449 --> 00:09:59.727 And we use commonly seen puzzle pieces to piece together an image 00:09:59.751 --> 00:10:02.203 that also fits our telescope measurements. NOTE Paragraph 00:10:03.040 --> 00:10:06.783 Different types of images have very distinctive sets of puzzle pieces. 00:10:06.807 --> 00:10:09.613 So what happens when we take the same data 00:10:09.637 --> 00:10:13.767 but we use different sets of puzzle pieces to reconstruct the image? 00:10:13.791 --> 00:10:18.557 Let's first start with black hole image simulation puzzle pieces. 00:10:18.581 --> 00:10:20.172 OK, this looks reasonable. 00:10:20.196 --> 00:10:22.890 This looks like what we expect a black hole to look like. 00:10:22.914 --> 00:10:24.107 But did we just get it 00:10:24.131 --> 00:10:27.445 because we just fed it little pieces of black hole simulation images? 00:10:27.469 --> 00:10:29.349 Let's try another set of puzzle pieces 00:10:29.373 --> 00:10:31.882 from astronomical, non-black hole objects. 00:10:32.914 --> 00:10:35.040 OK, we get a similar-looking image. 00:10:35.064 --> 00:10:37.300 And then how about pieces from everyday images, 00:10:37.324 --> 00:10:40.109 like the images you take with your own personal camera? 00:10:41.312 --> 00:10:43.427 Great, we see the same image. 00:10:43.451 --> 00:10:46.817 When we get the same image from all different sets of puzzle pieces, 00:10:46.841 --> 00:10:48.887 then we can start to become more confident 00:10:48.911 --> 00:10:50.877 that the image assumptions we're making 00:10:50.901 --> 00:10:53.822 aren't biasing the final image we get too much. NOTE Paragraph 00:10:53.846 --> 00:10:57.099 Another thing we can do is take the same set of puzzle pieces, 00:10:57.123 --> 00:10:59.612 such as the ones derived from everyday images, 00:10:59.636 --> 00:11:03.236 and use them to reconstruct many different kinds of source images. 00:11:03.260 --> 00:11:04.531 So in our simulations, 00:11:04.555 --> 00:11:08.330 we pretend a black hole looks like astronomical non-black hole objects, 00:11:08.354 --> 00:11:12.203 as well as everyday images like the elephant in the center of our galaxy. 00:11:12.227 --> 00:11:15.395 When the results of our algorithms on the bottom look very similar 00:11:15.419 --> 00:11:17.515 to the simulation's truth image on top, 00:11:17.539 --> 00:11:20.885 then we can start to become more confident in our algorithms. 00:11:20.909 --> 00:11:22.776 And I really want to emphasize here 00:11:22.800 --> 00:11:24.734 that all of these pictures were created 00:11:24.758 --> 00:11:27.694 by piecing together little pieces of everyday photographs, 00:11:27.718 --> 00:11:29.933 like you'd take with your own personal camera. 00:11:29.957 --> 00:11:33.233 So an image of a black hole we've never seen before 00:11:33.257 --> 00:11:37.200 may eventually be created by piecing together pictures we see all the time 00:11:37.224 --> 00:11:39.969 of people, buildings, trees, cats and dogs. 00:11:39.993 --> 00:11:42.638 Imaging ideas like this will make it possible for us 00:11:42.662 --> 00:11:45.281 to take our very first pictures of a black hole, 00:11:45.305 --> 00:11:47.752 and hopefully, verify those famous theories 00:11:47.776 --> 00:11:50.197 on which scientists rely on a daily basis. NOTE Paragraph 00:11:50.221 --> 00:11:52.829 But of course, getting imaging ideas like this working 00:11:52.853 --> 00:11:56.175 would never have been possible without the amazing team of researchers 00:11:56.199 --> 00:11:58.086 that I have the privilege to work with. 00:11:58.110 --> 00:11:59.273 It still amazes me 00:11:59.297 --> 00:12:02.648 that although I began this project with no background in astrophysics, 00:12:02.672 --> 00:12:05.291 what we have achieved through this unique collaboration 00:12:05.315 --> 00:12:08.074 could result in the very first images of a black hole. 00:12:08.098 --> 00:12:10.796 But big projects like the Event Horizon Telescope 00:12:10.820 --> 00:12:13.634 are successful due to all the interdisciplinary expertise 00:12:13.658 --> 00:12:15.448 different people bring to the table. 00:12:15.472 --> 00:12:17.178 We're a melting pot of astronomers, 00:12:17.202 --> 00:12:19.434 physicists, mathematicians and engineers. 00:12:19.458 --> 00:12:22.012 This is what will make it soon possible 00:12:22.036 --> 00:12:24.889 to achieve something once thought impossible. NOTE Paragraph 00:12:24.913 --> 00:12:27.169 I'd like to encourage all of you to go out 00:12:27.193 --> 00:12:29.289 and help push the boundaries of science, 00:12:29.313 --> 00:12:33.214 even if it may at first seem as mysterious to you as a black hole. NOTE Paragraph 00:12:33.238 --> 00:12:34.412 Thank you. NOTE Paragraph 00:12:34.436 --> 00:12:36.833 (Applause)