[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.93,0:00:04.27,Default,,0000,0000,0000,,Here are some images of clusters of galaxies.
Dialogue: 0,0:00:04.27,0:00:06.10,Default,,0000,0000,0000,,They're exactly what they sound like.
Dialogue: 0,0:00:06.10,0:00:08.65,Default,,0000,0000,0000,,They are these huge collections of galaxies,
Dialogue: 0,0:00:08.65,0:00:10.91,Default,,0000,0000,0000,,bound together by their mutual gravity.
Dialogue: 0,0:00:10.91,0:00:13.57,Default,,0000,0000,0000,,So most of the points that you see on the screen
Dialogue: 0,0:00:13.57,0:00:16.10,Default,,0000,0000,0000,,are not individual stars,
Dialogue: 0,0:00:16.10,0:00:18.94,Default,,0000,0000,0000,,but collections of stars, or galaxies.
Dialogue: 0,0:00:18.94,0:00:21.27,Default,,0000,0000,0000,,Now, by showing you some of these images,
Dialogue: 0,0:00:21.27,0:00:23.01,Default,,0000,0000,0000,,I hope that you will quickly see that
Dialogue: 0,0:00:23.01,0:00:25.69,Default,,0000,0000,0000,,galaxy clusters are these beautiful objects,
Dialogue: 0,0:00:25.69,0:00:27.19,Default,,0000,0000,0000,,but more than that,
Dialogue: 0,0:00:27.19,0:00:29.85,Default,,0000,0000,0000,,I think galaxy clusters are mysterious,
Dialogue: 0,0:00:29.85,0:00:31.40,Default,,0000,0000,0000,,they are surprising,
Dialogue: 0,0:00:31.40,0:00:32.82,Default,,0000,0000,0000,,and they're useful.
Dialogue: 0,0:00:32.82,0:00:36.35,Default,,0000,0000,0000,,Useful as the universe's most massive laboratories.
Dialogue: 0,0:00:36.35,0:00:39.99,Default,,0000,0000,0000,,And as laboratories, to describe galaxy clusters
Dialogue: 0,0:00:39.99,0:00:41.85,Default,,0000,0000,0000,,is to describe the experiments
Dialogue: 0,0:00:41.85,0:00:43.40,Default,,0000,0000,0000,,that you can do with them.
Dialogue: 0,0:00:43.40,0:00:45.68,Default,,0000,0000,0000,,And I think there are four major types,
Dialogue: 0,0:00:45.68,0:00:48.27,Default,,0000,0000,0000,,and the first type that I want to describe
Dialogue: 0,0:00:48.27,0:00:50.49,Default,,0000,0000,0000,,is probing the very big.
Dialogue: 0,0:00:50.49,0:00:52.18,Default,,0000,0000,0000,,So, how big?
Dialogue: 0,0:00:52.18,0:00:56.43,Default,,0000,0000,0000,,Well, here is an image of a particular galaxy cluster.
Dialogue: 0,0:00:56.43,0:00:59.40,Default,,0000,0000,0000,,It is so massive that the light passing through it
Dialogue: 0,0:00:59.40,0:01:02.02,Default,,0000,0000,0000,,is being bent, it's being distorted
Dialogue: 0,0:01:02.02,0:01:04.53,Default,,0000,0000,0000,,by the extreme gravity of this cluster.
Dialogue: 0,0:01:04.53,0:01:06.33,Default,,0000,0000,0000,,And, in fact, if you look very carefully
Dialogue: 0,0:01:06.33,0:01:09.03,Default,,0000,0000,0000,,you'll be able to see rings around this cluster.
Dialogue: 0,0:01:09.03,0:01:10.58,Default,,0000,0000,0000,,Now, to give you a number,
Dialogue: 0,0:01:10.58,0:01:12.36,Default,,0000,0000,0000,,this particular galaxy cluster
Dialogue: 0,0:01:12.36,0:01:16.57,Default,,0000,0000,0000,,has a mass of over one million billion suns.
Dialogue: 0,0:01:16.57,0:01:19.88,Default,,0000,0000,0000,,It's just mind-boggling how \Nmassive these systems can get.
Dialogue: 0,0:01:19.88,0:01:21.38,Default,,0000,0000,0000,,But more than their mass,
Dialogue: 0,0:01:21.38,0:01:23.36,Default,,0000,0000,0000,,they have this additional feature.
Dialogue: 0,0:01:23.36,0:01:25.70,Default,,0000,0000,0000,,They are essentially isolated systems,
Dialogue: 0,0:01:25.70,0:01:27.92,Default,,0000,0000,0000,,so if we like, we can think of them
Dialogue: 0,0:01:27.92,0:01:31.20,Default,,0000,0000,0000,,as a scaled-down version of the entire universe.
Dialogue: 0,0:01:31.20,0:01:33.20,Default,,0000,0000,0000,,And many of the questions that we might have
Dialogue: 0,0:01:33.20,0:01:35.16,Default,,0000,0000,0000,,about the universe at large scales,
Dialogue: 0,0:01:35.16,0:01:37.08,Default,,0000,0000,0000,,such as, how does gravity work?
Dialogue: 0,0:01:37.08,0:01:40.11,Default,,0000,0000,0000,,might be answered by studying these systems.
Dialogue: 0,0:01:40.11,0:01:41.44,Default,,0000,0000,0000,,So that was very big.
Dialogue: 0,0:01:41.44,0:01:43.33,Default,,0000,0000,0000,,The second things is very hot.
Dialogue: 0,0:01:43.33,0:01:46.11,Default,,0000,0000,0000,,Okay, if I take an image of a galaxy cluster,
Dialogue: 0,0:01:46.11,0:01:49.03,Default,,0000,0000,0000,,and I subtract away all of the starlight,
Dialogue: 0,0:01:49.03,0:01:51.82,Default,,0000,0000,0000,,what I'm left with is this big, blue blob.
Dialogue: 0,0:01:51.82,0:01:53.31,Default,,0000,0000,0000,,This is in false color.
Dialogue: 0,0:01:53.31,0:01:55.66,Default,,0000,0000,0000,,It's actually X-ray light that we're seeing.
Dialogue: 0,0:01:55.66,0:01:58.32,Default,,0000,0000,0000,,And the question is, if it's not galaxies,
Dialogue: 0,0:01:58.32,0:02:00.52,Default,,0000,0000,0000,,what is emitting this light?
Dialogue: 0,0:02:00.52,0:02:02.42,Default,,0000,0000,0000,,The answer is hot gas,
Dialogue: 0,0:02:02.42,0:02:04.24,Default,,0000,0000,0000,,million-degree gas --
Dialogue: 0,0:02:04.24,0:02:05.90,Default,,0000,0000,0000,,in fact, it's plasma.
Dialogue: 0,0:02:05.90,0:02:07.56,Default,,0000,0000,0000,,And the reason why it's so hot
Dialogue: 0,0:02:07.56,0:02:09.54,Default,,0000,0000,0000,,goes back to the previous slide.
Dialogue: 0,0:02:09.54,0:02:12.28,Default,,0000,0000,0000,,The extreme gravity of these systems
Dialogue: 0,0:02:12.28,0:02:15.32,Default,,0000,0000,0000,,is accelerating particles of gas to great speeds,
Dialogue: 0,0:02:15.32,0:02:17.90,Default,,0000,0000,0000,,and great speeds means great temperatures.
Dialogue: 0,0:02:17.90,0:02:19.62,Default,,0000,0000,0000,,So this is the main idea,
Dialogue: 0,0:02:19.62,0:02:21.99,Default,,0000,0000,0000,,but science is a rough draft.
Dialogue: 0,0:02:21.99,0:02:24.54,Default,,0000,0000,0000,,There are many basic properties about this plasma
Dialogue: 0,0:02:24.54,0:02:26.24,Default,,0000,0000,0000,,that still confuse us,
Dialogue: 0,0:02:26.24,0:02:27.57,Default,,0000,0000,0000,,still puzzle us,
Dialogue: 0,0:02:27.57,0:02:29.66,Default,,0000,0000,0000,,and still push our understanding
Dialogue: 0,0:02:29.66,0:02:31.69,Default,,0000,0000,0000,,of the physics of the very hot.
Dialogue: 0,0:02:31.69,0:02:35.12,Default,,0000,0000,0000,,Third thing: probing the very small.
Dialogue: 0,0:02:35.12,0:02:37.97,Default,,0000,0000,0000,,Now, to explain this, I need to tell you
Dialogue: 0,0:02:37.97,0:02:39.99,Default,,0000,0000,0000,,a very disturbing fact.
Dialogue: 0,0:02:39.99,0:02:42.78,Default,,0000,0000,0000,,Most of the universe's matter
Dialogue: 0,0:02:42.78,0:02:44.59,Default,,0000,0000,0000,,is not made up of atoms.
Dialogue: 0,0:02:44.59,0:02:46.54,Default,,0000,0000,0000,,You were lied to.
Dialogue: 0,0:02:46.54,0:02:49.66,Default,,0000,0000,0000,,Most of it is made up of something \Nvery, very mysterious,
Dialogue: 0,0:02:49.66,0:02:51.79,Default,,0000,0000,0000,,which we call dark matter.
Dialogue: 0,0:02:51.79,0:02:55.45,Default,,0000,0000,0000,,Dark matter is something that \Ndoesn't like to interact very much,
Dialogue: 0,0:02:55.45,0:02:57.12,Default,,0000,0000,0000,,except through gravity,
Dialogue: 0,0:02:57.12,0:02:58.73,Default,,0000,0000,0000,,and of course we would like to learn more about it.
Dialogue: 0,0:02:58.73,0:03:00.28,Default,,0000,0000,0000,,If you're a particle physicist,
Dialogue: 0,0:03:00.28,0:03:02.79,Default,,0000,0000,0000,,you want to know what happens \Nwhen we smash things together.
Dialogue: 0,0:03:02.79,0:03:04.78,Default,,0000,0000,0000,,And dark matter is no exception.
Dialogue: 0,0:03:04.78,0:03:06.44,Default,,0000,0000,0000,,Well, how do we do this?
Dialogue: 0,0:03:06.44,0:03:07.93,Default,,0000,0000,0000,,To answer that question,
Dialogue: 0,0:03:07.93,0:03:09.32,Default,,0000,0000,0000,,I'm going to have to ask another one,
Dialogue: 0,0:03:09.32,0:03:12.49,Default,,0000,0000,0000,,which is, what happens when galaxy clusters collide?
Dialogue: 0,0:03:12.49,0:03:14.80,Default,,0000,0000,0000,,Here is an image.
Dialogue: 0,0:03:14.80,0:03:17.99,Default,,0000,0000,0000,,Since galaxy clusters are representative
Dialogue: 0,0:03:17.99,0:03:21.11,Default,,0000,0000,0000,,slices of the universe, scaled-down versions.
Dialogue: 0,0:03:21.11,0:03:23.23,Default,,0000,0000,0000,,They are mostly made up of dark matter,
Dialogue: 0,0:03:23.23,0:03:25.79,Default,,0000,0000,0000,,and that's what you see in this bluish purple.
Dialogue: 0,0:03:25.79,0:03:27.40,Default,,0000,0000,0000,,The red represents the hot gas,
Dialogue: 0,0:03:27.40,0:03:29.37,Default,,0000,0000,0000,,and, of course, you can see many galaxies.
Dialogue: 0,0:03:29.37,0:03:31.74,Default,,0000,0000,0000,,What's happened is a particle accelerator
Dialogue: 0,0:03:31.74,0:03:33.63,Default,,0000,0000,0000,,at a huge, huge scale.
Dialogue: 0,0:03:33.63,0:03:35.40,Default,,0000,0000,0000,,And this is very important,
Dialogue: 0,0:03:35.40,0:03:37.29,Default,,0000,0000,0000,,because what it means is that very, very small
Dialogue: 0,0:03:37.29,0:03:40.37,Default,,0000,0000,0000,,effects that might be difficult to detect in the lab,
Dialogue: 0,0:03:40.37,0:03:42.55,Default,,0000,0000,0000,,might be compounded and compounded
Dialogue: 0,0:03:42.55,0:03:46.36,Default,,0000,0000,0000,,into something that we could \Npossibly observe in nature.
Dialogue: 0,0:03:46.36,0:03:47.87,Default,,0000,0000,0000,,So, it's very funny.
Dialogue: 0,0:03:47.87,0:03:49.82,Default,,0000,0000,0000,,The reason why galaxy clusters
Dialogue: 0,0:03:49.82,0:03:51.48,Default,,0000,0000,0000,,can teach us about dark matter,
Dialogue: 0,0:03:51.48,0:03:53.24,Default,,0000,0000,0000,,the reason why galaxy clusters
Dialogue: 0,0:03:53.24,0:03:55.79,Default,,0000,0000,0000,,can teach us about the physics of the very small,
Dialogue: 0,0:03:55.79,0:03:58.82,Default,,0000,0000,0000,,is precisely because they are so very big.
Dialogue: 0,0:03:58.82,0:04:02.90,Default,,0000,0000,0000,,Fourth thing: the physics of the very strange.
Dialogue: 0,0:04:02.90,0:04:05.95,Default,,0000,0000,0000,,Certainly what I've said so far is crazy.
Dialogue: 0,0:04:05.95,0:04:08.24,Default,,0000,0000,0000,,Okay, if there's anything stranger
Dialogue: 0,0:04:08.24,0:04:10.65,Default,,0000,0000,0000,,I think it has to be dark energy.
Dialogue: 0,0:04:10.65,0:04:12.37,Default,,0000,0000,0000,,If I throw a ball into the air,
Dialogue: 0,0:04:12.37,0:04:14.17,Default,,0000,0000,0000,,I expect it to go up.
Dialogue: 0,0:04:14.17,0:04:16.29,Default,,0000,0000,0000,,What I don't expect is that it go up
Dialogue: 0,0:04:16.29,0:04:18.46,Default,,0000,0000,0000,,at an ever-increasing rate.
Dialogue: 0,0:04:18.46,0:04:21.20,Default,,0000,0000,0000,,Similarly, cosmologists understand why
Dialogue: 0,0:04:21.20,0:04:22.79,Default,,0000,0000,0000,,the universe is expanding.
Dialogue: 0,0:04:22.79,0:04:24.95,Default,,0000,0000,0000,,They don't understand why it's expanding
Dialogue: 0,0:04:24.95,0:04:26.89,Default,,0000,0000,0000,,at an ever-increasing rate.
Dialogue: 0,0:04:26.89,0:04:28.57,Default,,0000,0000,0000,,They give the cause of this
Dialogue: 0,0:04:28.57,0:04:30.16,Default,,0000,0000,0000,,accelerated expansion a name,
Dialogue: 0,0:04:30.16,0:04:32.05,Default,,0000,0000,0000,,and they call it dark energy.
Dialogue: 0,0:04:32.05,0:04:34.73,Default,,0000,0000,0000,,And, again, we want to learn more about it.
Dialogue: 0,0:04:34.73,0:04:37.12,Default,,0000,0000,0000,,So, one particular question that we have is,
Dialogue: 0,0:04:37.12,0:04:39.82,Default,,0000,0000,0000,,how does dark energy affect the universe
Dialogue: 0,0:04:39.82,0:04:41.43,Default,,0000,0000,0000,,at the largest scales?
Dialogue: 0,0:04:41.43,0:04:42.89,Default,,0000,0000,0000,,Depending on how strong it is,
Dialogue: 0,0:04:42.89,0:04:46.15,Default,,0000,0000,0000,,maybe structure forms faster or slower.
Dialogue: 0,0:04:46.15,0:04:48.70,Default,,0000,0000,0000,,Well, the problem with the large-scale structure
Dialogue: 0,0:04:48.70,0:04:51.04,Default,,0000,0000,0000,,of the universe is that it's horribly complicated.
Dialogue: 0,0:04:51.04,0:04:53.37,Default,,0000,0000,0000,,Here is a computer simulation.
Dialogue: 0,0:04:53.37,0:04:55.50,Default,,0000,0000,0000,,And we need a way to simplify it.
Dialogue: 0,0:04:55.50,0:04:59.07,Default,,0000,0000,0000,,Well, I like to think about this using an analogy.
Dialogue: 0,0:04:59.07,0:05:01.79,Default,,0000,0000,0000,,If I want to understand the sinking of the Titanic,
Dialogue: 0,0:05:01.79,0:05:03.45,Default,,0000,0000,0000,,the most important thing to do
Dialogue: 0,0:05:03.45,0:05:05.23,Default,,0000,0000,0000,,is not to model the little positions
Dialogue: 0,0:05:05.23,0:05:08.16,Default,,0000,0000,0000,,of every single little piece of the boat that broke off.
Dialogue: 0,0:05:08.16,0:05:09.82,Default,,0000,0000,0000,,The most important thing to do is
Dialogue: 0,0:05:09.82,0:05:11.82,Default,,0000,0000,0000,,to track the two biggest parts.
Dialogue: 0,0:05:11.82,0:05:15.65,Default,,0000,0000,0000,,Similarly, I can learn a lot about the universe
Dialogue: 0,0:05:15.65,0:05:17.12,Default,,0000,0000,0000,,at the largest scales
Dialogue: 0,0:05:17.12,0:05:18.87,Default,,0000,0000,0000,,by tracking its biggest pieces
Dialogue: 0,0:05:18.87,0:05:22.86,Default,,0000,0000,0000,,and those biggest pieces are clusters of galaxies.
Dialogue: 0,0:05:22.86,0:05:25.82,Default,,0000,0000,0000,,So, as I come to a close,
Dialogue: 0,0:05:25.82,0:05:27.82,Default,,0000,0000,0000,,you might feel slightly cheated.
Dialogue: 0,0:05:27.82,0:05:30.07,Default,,0000,0000,0000,,I mean, I began by talking about
Dialogue: 0,0:05:30.07,0:05:32.15,Default,,0000,0000,0000,,how galaxy clusters are useful,
Dialogue: 0,0:05:32.15,0:05:33.65,Default,,0000,0000,0000,,and I've given some reasons,
Dialogue: 0,0:05:33.65,0:05:36.25,Default,,0000,0000,0000,,but what is their use really?
Dialogue: 0,0:05:36.25,0:05:38.37,Default,,0000,0000,0000,,Well, to answer this,
Dialogue: 0,0:05:38.37,0:05:40.99,Default,,0000,0000,0000,,I want to give you a quote by Henry Ford
Dialogue: 0,0:05:40.99,0:05:42.47,Default,,0000,0000,0000,,when he was asked about cars.
Dialogue: 0,0:05:42.47,0:05:43.83,Default,,0000,0000,0000,,He had this to say:
Dialogue: 0,0:05:43.83,0:05:46.12,Default,,0000,0000,0000,,"If I had asked people what they wanted,
Dialogue: 0,0:05:46.12,0:05:48.90,Default,,0000,0000,0000,,they would have said faster horses."
Dialogue: 0,0:05:48.90,0:05:51.40,Default,,0000,0000,0000,,Today, we as a society are faced
Dialogue: 0,0:05:51.40,0:05:53.62,Default,,0000,0000,0000,,with many, many difficult problems.
Dialogue: 0,0:05:53.62,0:05:57.45,Default,,0000,0000,0000,,And the solutions to these \Nproblems are not obvious.
Dialogue: 0,0:05:57.45,0:05:59.62,Default,,0000,0000,0000,,They are not faster horses.
Dialogue: 0,0:05:59.62,0:06:01.86,Default,,0000,0000,0000,,They will require an enormous amount of
Dialogue: 0,0:06:01.86,0:06:03.57,Default,,0000,0000,0000,,scientific ingenuity.
Dialogue: 0,0:06:03.57,0:06:05.15,Default,,0000,0000,0000,,So, yes, we need to focus,
Dialogue: 0,0:06:05.15,0:06:06.90,Default,,0000,0000,0000,,yes, we need to concentrate,
Dialogue: 0,0:06:06.90,0:06:08.87,Default,,0000,0000,0000,,but we also need to remember that
Dialogue: 0,0:06:08.87,0:06:11.70,Default,,0000,0000,0000,,innovation, ingenuity, inspiration --
Dialogue: 0,0:06:11.70,0:06:13.04,Default,,0000,0000,0000,,these things come
Dialogue: 0,0:06:13.04,0:06:14.72,Default,,0000,0000,0000,,when we broaden our field of vision
Dialogue: 0,0:06:14.72,0:06:16.06,Default,,0000,0000,0000,,when we step back
Dialogue: 0,0:06:16.06,0:06:17.41,Default,,0000,0000,0000,,when we zoom out.
Dialogue: 0,0:06:17.41,0:06:19.24,Default,,0000,0000,0000,,And I can't think of a better way to do this than
Dialogue: 0,0:06:19.24,0:06:22.99,Default,,0000,0000,0000,,by studying the universe around us. Thanks.
Dialogue: 0,0:06:22.99,0:06:25.94,Default,,0000,0000,0000,,(Applause)