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LOC | Cosmology from Ancient Greece to Today, with NASA-Goddard’s Dr. Michelle Thaller

Uploaded 02/03/2014

Cosmology from Ancient Greece to Today, with NASA-Goddard’s Dr. Michelle Thaller

Dr. Michelle Thaller discusses how we have perceived own own place in the universe since ancient times.

Speaker Biography: Michelle Thaller is assistant director for science communication and higher education at NASA’s Goddard Space Flight Center.




>> From the Library of Congress in Washington, DC.

[ Silence ]

>> I’m Jennifer Harbster. I’m a science research specialist in the Science, Technology, and Business Division here at the Library of Congress. Today, we conclude the seventh year of talks in our ongoing collaboration with NASA’s Goddard and we’re having a return engagement with Dr. Michelle Thaller. Michelle gave a fantastic talk on Galileo and, now why am I stumbling on this, Sidereus Nuncius here in February 2010. If you’re interested, you can view this lecture online through our webcast page from or through the LOC YouTube channel and we have a “Topics in Science” play list. Right now, it’s my please. Oh whoops, I was going to introduce somebody else but now I’m introducing Michelle. Sorry about that. We had a little change of plans. I’m happy to introduce the final speaker in this year’s series. This year has included talks on the Mars Rover, managing a satellite in space, hot towers and hurricanes, the search for inhabited exoplanets and now, Dr. Michelle Thaller will speak on the big picture, our place in the universe, “Cosmology from the Ancient Greeks to Today.” A nationally recognized spokesperson for astronomy and science, Michelle Thaller is assistant director of science at NASA’s Goddard Space Flight Center. She has a bachelor’s in astrophysics from Harvard and a PhD from Georgia State University. Michelle’s research specialized in the evolution of binary star systems and she has used the Hubble and Spitzer Space Telescopes as well as ground-based observations such as Mount Palomar, Kitt Peak, and Mount Stromlo for her observations. After a postdoctorate research fellowship at Cal Tech, Michelle became particularly interested in public outreach and science communication. In her current position as assistant director for science for communication, she has produced and starred in several broadcast series available on I-Tunes and YouTube and has received the highest honors for online programming. Michelle has been one of the regular hosts of “The Universe” television series on History Channel, National Geo’s “The Known Universe” and Discovery Channel’s “How the Universe Works” and I should note that this week, Science Channel is running “How the Universe Works” and I’ve been watching it all week. Behind the scenes, Michelle has led efforts to develop high quality apps for smart phones and tablets as well as involved NASA missions with social media outlets such as Facebook, Twitter, Second Life. In her current role, Michelle represents all of NASA Science themes from earth sciences and climate change to the Sun, space weather, solar system expiration all the way out to cosmology and the deep universe, which is the subject of today’s talk. Michelle speaks to members of congress and their staff regularly as well as international embassy staff and internal NASA policy makers. Michelle has received numerous high-profile awards for her work including the Robert Goddard Award, the Women in Aerospace Award, and induction into the Space Camp Hall of Fame. So please join me in welcoming back Dr. Michelle Thaller.

[ Applause ]

>> Thank you. I think they gave her the long bio version. I apologize for that. Wow, you know this is an incredibly broad topic and I actually– I’m going to just apologize for a few things first. There’s so many things I wish I could tell. I basically want to teach you all a semester course on this and the other thing is I’m not used to standing behind podiums. I’m very much of a wandering speaker but they’ve asked me to stand here. So, I’m a little bit hidden from you. I apologize for that but I have something on the order of 4,000 Facebook friends. I friend everybody who doesn’t post anything offensive to my site and it’s very obvious to me the people around the world want answers to questions like how did the universe begin, how’s the universe going to end and they seem to think that we actually have answers to that, you know, real answers to that. And this is one of the wonderful things about being a scientist is getting comfortable with the fact that you always have to make the best measurement, take the first guess as to what you data is saying but you have to be steeped in humility that we are limited creatures and we don’t know the full extent of the universe yet. I mean, there’s no way I can tell you exactly how the universe began or ended. We don’t know. And this sort of tension between knowing some really amazing things and not knowing some very important things is something that makes people uncomfortable about science sometimes. I think it makes us all a little bit dangerous too in the sense that we don’t accept answers easily and things have to be followed up with proof. So, this is one of the reasons that personally I enjoy looking back to the past. I’m not an expert in the history of science but when you look at what people knew a long time ago and how they knew it and just how clever they were, also how they got tripped up. Where did ideology and ideas that should have been abandoned long ago, why did they hang around so long. When you look at the patterns of the past, it gives you some idea about how to approach science today. So, we’ll start with some of the amazing things we know about the Greeks, the Greeks in particular because we do have some records of them. The Romans mentioned them in their writings. This was actually rediscovered in the Middle Ages, when the crusades came to the Middle East and found this again. It had been lost to Europe for many, many years. So, starting back to, in some ways, what we can think of as the dawn of our modern idea of science and some of that comes from a region of Greece not talked about very much, Ionia. Ionia is actually on the Turkish coast and the islands right around there. There’s a little inset map there you can see. That’s actually the shape of the country of Turkey on the upper right-hand corner, it shows you Ionia. And Ionia starting in the 6th century BC, we have records of people approaching the universe as something that could be known through experimentation. The first time people really thought of that in kind of non-divine terms, in terms of a science. The universe was made of materials, you know, not just spirit, not just mystery, and we have records of some of the experimentation, some of the thoughts that the ancient Ionians explored. Now, two of the famous ones that I think are really quite amazing are Thales and Anaximander, both born around 600 B.C. and Thales was quite good at predicting solar eclipses. This is actually nothing all that new. The Babylonians also did this quite a ways before these people but specifically the eclipse of 585. Something that I find really intriguing is that Thales found fossils of seashells on the tops of mountains and he realized that there’s no way they could have gotten there, you know, unless something had really changed in the way that the earth was built. And he came up with a hypothesis that the land actually raised itself out of the ocean, basically true. I mean, we know now of things like continental drift. And he and Anaximander, I sorry, Miletus there should read Anaximander. That was a mistake of mine. They produced the first world map that you see and they had this idea of continents and ocean and there being this primordial sea. Now, Anaximander took that idea a little bit further and this is really fascinating. If we all used to be covered by ocean and land emerged from the ocean over time, then humans could not have existed in their current form for the entirety of history. We must have changed somehow or been created at a later date and in the case of Anaximander, he talked about life having to adapt. He hypothesized that humans were descended from fish or similar animals. He said given our extended infancy as children, we couldn’t survive in the ocean in our current form. So, it amazes me that 2600 years ago people were starting to mess with the idea of evolution and that’s from just looking at what’s around you, the fossils, how the earth changes. Now, you compare this school of thought with something a little bit later, the Athenians, and one of course, the most famous one is Plato. Plato was born in Athens around 429 B.C., a student of the famous Socrates. This entire school was hugely influential in the topic of epistemology, which is the study of knowledge. How do we know something? How do we know something is true or not? The foundations of logic, you know, when is an argument sound? When is it not sound? Plato and his students were somewhat disdainful of the idea of materialism. They were very mistrustful of the material world as only a reflection of the true reality and there’s actually a famous analogy called Plato’s Cave, where Plato said that humans and our perceptions are extremely limited. We don’t perceive the true nature of the universe and if you picture us all being deep inside a cave and there’s light shinning down from the entrance of the cave and all we see of the outside world are shadows being cast in our cave on the walls, such is a similar idea of the world around us. There is an ultimate higher divine reality and the reality we see around us is not a true reflection of that.


Interesting idea, and this school advocated pure logic in mathematics can help overcome this handicap. Logic can take you through some of the illusions of the material world. They did a lot of thinking about the stars. They were some of the first people to realize that both philosophically and through experimentation that celestial objects were spheres, the most perfect shape. Everything below the orbit of the moon, they believed was made of the corruptible elements, earth, water, fire, and air, and above that everything was made of a perfect fifth element, the quintessence, the fifth element, the essence of spirit. It may interest you to know that there’s actually a reason they thought there were five elements and that had to do with geometry. It shows you how much they loved the idea of pure logic. You can only make five solids out of regular polygons, shapes where each of the shape has the same sized size and the same angle between the sides. There are five of those and, therefore, there had to be five elements in the universe, so a real grounding in geometry. That’s not true actually, a lovely theory. I mean, it’s not actually true at all but they had a wonderful consistent model. Plato encouraged the idea that the universe was perfect and, therefore, everything in the heavens had to move in perfect circles and the circles had to have uniform motion, no speeding up or stopping. Now, probably the most famous pupil of Plato was Aristotle and Aristotle codified a lot of this, so he was famously the tutor of Alexander the Great, one of the reasons we know so much about him, and the father our current formal logic and the idea of axioms or universal truths proven through logic. He had a wonderfully encompassing philosophical system. Natural science ethics are to politics, he had laws for whether these were done well or not. And he was heavily influential all the way up until basically the renaissance. The idea that the universe was made of nested perfect spheres that the planets traveled on and everything in the sky moved in perfect motion. Now, there’s one problem with this and this has been known about for a long time. These are actual observations of the planet Saturn over the course of a few years from 2008, I guess from 2006 to 2008, and you’re seeing pictures of Saturn taken night to night against the background of stars. For those of you that are astronomers, you probably can pick out the constellation Leo. It’s one of the easier ones to pick out in the sky.  Planets, the word planet is derived from the Greek work for wanderer and this was one of the reasons the planets were first associated with gods because they seemed to wander around the sky, unlike everything else in the sky that went overhead, you know, once every day. These things kind of wandered around. And that doesn’t look very much like perfect motion. And this is actually a wonderful sort of sequence. This is from the website “Astronomy Picture of the Day” that NASA Goddard manages and these are pictures of Mars taken over a couple of different months in 2011 to 2012. Again, you can actually see the constellation Leo in the background and Mars is doing one of these loops. It actually appears to go backwards and kind of move around the sky. This was called retrograde motion because things were moving backwards in the sky. And one of the big deals with the Greeks was trying to explain what was going on here because this didn’t look very perfect by any means at all. And I have a somewhat long, well it’s only a couple minutes long but this is an animation of some of the ideas we’ve had about retrograde motion and I’ll kind of put this through. You start with the Earth in the middle. You know, that’s kind of reasonable to assume that when you’re an ancient person. The earth seems huge and the middle of everything is going on in the skies. Now, the little ball you see is Mars and this is a model that was proposed by a man called Eudoxus of Cnidus and Eudoxus was actually a friend of Aristotle’s. They were both students of Plato and Eudoxus was trying to figure out how you could get Mars to move backwards and forwards while still having everything be perfect circles, moving at the same velocity all the time and there is a way to do it if you nest rotating rings one inside the other and then put all of that on a ring that rotates it around during the course of the year and what Eudoxus thought he had discovered here were sort of the supporting mechanisms under these crystalline spheres, under these perfect spheres the Greeks believed in. It works fairly well for what the Greeks were able to measure back then in terms of planetary positions. Honestly, it never worked all that well even for them and fairly quickly after that, we go to an idea called epicycles, which probably most of you have heard of. The first person we know that actually came up with this idea was Apollonius of Perga and this was refined later by astronomers called Hipparchus and Ptolemy. Ptolemy was an Egyptian who was born in about 90 A.D., actually I think that, so this was right around the turn of the millennium we’re talking about. And but when Ptolemy described this motion, he said, “Well, it actually gets a lot easier.” If you assume that Mars is on another little circle that goes around the orbit of Mars we see in the sky and from the perspective of Earth you see that as you look out from earth, you see Mars do these loop-de-loops on the sky as it goes around its little circle there. That circle was actually called the deferent; that was the word they used for it. Now, this model worked fairly well and actually, you know, that was something that in my last talk about Galileo, people were arguing about, you know, even as late as the 1600s. Galileo was the person who proved beyond a shadow of a doubt this could not work. He had very, very good proof for why it doesn’t work. And, of course, now we understand why Mars makes this motion. You take Earth away from the center. Now you put the Sun in the center, and both the Earth and Mars are going around their orbits. Earth is going a bit faster than Mars is. Both Mars and Earth are moving forward in their orbit all the time but as we’re going a little faster, we overtake Mars and as that happens, you know, just like if you’re driving in a car on a highway and you’re driving a little faster than another car, even though that car and you are both moving forward, the car seems to move backwards to you. That’s really what’s going on. So, there’s a little bit about epicycles and how different people have described that through the ages. All right, now the Greeks were getting really good and doing some measurements of important things and one of the most amazing things they were able to do was measure the size of the Earth very, very correctly. And the record we have of this being done first is a man called Eratosthenes, again around 276 to 195 B.C. and Eratosthenes realized that there was a day of the year where there was a well, a water well that you get water out of in a town called Syene and the Sun actually shown directly down that well, the Sun was directly overhead on that day, and on the same day in Alexandria, that wasn’t the case. The Sun didn’t shin directly down the well. It was a slight angle away from overhead. And Eratosthenes realized that that difference in angle from being overhead to not quite overhead, that very small change in angle, if you pace out the distance between Alexandria and Syene, which he hired somebody to do, some poor person walking through the desert, pacing out exactly how far away that is. That distance is to that angle as 360 degrees is to the whole circle, the whole circumference of Earth. And so he measured that difference in angle and then deduced that same relationship applied all the way around the earth and in fact he measured the correct circumference of the Earth accurate to better than 1% and this is actually one of the things doing TV shows, there was one time on the Discovery Channel, they wanted me to give the throwaway line, “Okay, well when Columbus proved the Earth was round,” and they wanted me to go on from there and I refused to say that because that’s not true. Columbus knew the Earth was round. Columbus actually redid this calculation and made a mistake and thought the Earth was smaller than Eratosthenes did. The Greeks were right. Now, once you have the size of the Earth, there are a lot of interesting things that fall into place and a person that is one of my personal heroes of Aristarchus of Samos, who you may not of heard of. This person lived about 300 years B.C. and he’s the first person we know that had proof that the Sun was the center of the solar system, not the Earth, born about 12 years after Aristotle died, so in defense of Aristotle, Aristotle didn’t know about this. He wasn’t much of a formal philosopher, didn’t have these grand ethical theories and all, so he wasn’t actually much liked by the Romans. The interesting thing that I didn’t know when I was researching my last talk is that Galileo did know of Aristarchus and he quoted his measurements in the famous letter to Archduchess Christina. Okay, so what did Aristarchus do? Aristarchus looked at lunar eclipses, times when the Earth’s shadow is actually cast onto the Moon and he figured out that it was the Earth’s shadow because lunar eclipses only occur when the Sun and the Moon are on opposite sides of the horizon  and the Earth is in the way. So, he realized that the light source of the Sun was casting the shadow of the Earth onto the Moon. And what he saw was that lunar eclipses happen, you know, at many different times, always during full moon of course, but they happen at many different angles and you see this curved shadow of the Moon, sorry, the curved shadow of the Earth crossing the Moon in many different places on the Moon. It doesn’t always go the same way and he realized that the only shape that could cast a curved shadow like that at very different perspective, every different angle was a sphere, so he realized that the Earth was a sphere and then what he was able to do, this is actually a picture that kind of shows you.


This is actually real images, again from “Astronomy Picture of the Day,” of different lunar eclipses all put together so you can actually see the Earth’s shadow and the true shape of it. So, you see that this object is casting a spherical shadow. Now, what was really noticed here before that wasn’t noticed is that the light shines all the way around the Earth, so the Sun must be larger than the Earth. If the Earth is the thing casting the shadow at all these different angles, you actually get light shinning all the way around this thing, so it must be bigger. And, in fact, Aristarchus thought he’d measured the true relationship of the size between the Moon and the Earth based on this too. He was a bit off because he didn’t realize that light diffracts, that light actually bends around a corner, but he had a pretty good estimation. So, doing this, he actually started estimating the size of the solar system and if light shown all around the Earth’s shadow, the Sun must be larger. He estimated it was about five times larger than the Earth and about 5 million miles away. Now, of course, that’s way off but not bad for, you know, 2300 years ago. Right? I mean we were starting to get an idea of the true scale of the solar system long ago and, amazingly to me, he also estimated the distances to the stars assuming they were as bright as the Sun, assuming they were objects like the Sun. That was happening 2300 years ago. And in the case of the estimating the stars as bright as the Sun, he actually had a disk of bronze that he held up to the Sun during the day and he had tiny little holes he drilled in them and he tried to compare them to the brightness of the stars. He didn’t know that the human eye is not actually a very good measurement, that our sensitivities change, but still, I mean, a wonderful experimental technique. And just in passing, it’s worth mentioning that once you put the Sun in the middle of the solar system, the retrograde motion thing goes pretty easily and, in fact, Aristarchus advocated exactly the right reason for retrograde motion, that we were going around in different speeds in our orbits around the Sun. Now, I want to take a little bit of a detour. That’s a bit about the theory and the observation of the Greeks. Another thing that really amazes me is the state of technology and I was actually on a Smithsonian tour recently, where I was lecturing about this while we were going through the Aegean Sea, and I want to talk to you about something called the Antikythera mechanism, which I think a lot of you know about. Antikythera sounds kind of sinister. It’s sort of a weird sounding word. It’s actually just the name of an island. It’s a very, very small island designated on Google Maps by that A and between the Ionian Sea and the Aegean Sea and Greece and in 1900 some pearl divers, sorry, sponge divers– Say that again.  In 1900 some sponge divers found the remains of a Roman galley that had wrecked that was carrying lots of different interesting treasures. There were all kinds of statuary, you know, they have coins, lots of neat things, and one of the things that they dragged up from that wreck was this rusted, corroded bit of bronze and if you look closely, this is actually from the museum in Athens. If you look closely, there appear to be a bit of a wheel in there. There’s kind of a wheel shape and so it looked like it might have been some type of a machine, some type of a mechanism. People were curious about this, but honestly it didn’t get a lot of very serious attention until the 1970s, when they began to x-ray it. And this is an x-ray of that actual device and it turns out it was a complex computer, a gear-based mechanical computer. And one of the amazing things and actually Goddard Space Flight Center has been involved, we had these people come and give a talk that blew the top of my head off. It was amazing. People have been building models, trying to piece together what these gears did and this is actually one of the models that they brought to show us. What this was, was an astronomical calculator that could calculate the phases of the Moon, the position of the planets, the position of the Sun forward and backward in time by turning the gears. And the sort of gear work that you see, the sort of complexity, if I just go back there, that sort of gear work was not seen again until the early renaissance. So, it’s amazing that in ancient Greece, they had this clockwork-based thing and I have an animation, which actually takes apart all the gears and shows you what this thing did. So let me start that and we can talk a bit about it as it goes through. A lot of the Antikythera mechanism is missing in a sense that we don’t have all of the gears but we do have at least the faces and we know what should have been moving around. So as the animation begins, the captions, this was done by the planetarium in Milan, the captions are in Italian and English, that’s a lucky thing about speaking English. Most people do it as the second language. But they have the hand crank there starting. They have a wheel that shows you the position of the Sun. That even was corrected because the Sun doesn’t move across the sky at the same rate all the time. It slows, it speeds up and slows down during the course of the year. That’s actually because our orbit is elliptical. They also had the position of the Moon. So, you can see here they’re actually putting together all the gears that were in this mechanism. Most of the Sun’s cycle and the Moon’s cycle we actually have intact. When you start getting out, you can see some of the cycles it calculates. The Panhellenic games, that’s the Olympic games, when the Olympic games would fall. The Metonic cycle is an even division of lunar months into the year. The [inaudible] cycle is an eclipse predictor. This was able to predict lunar and solar eclipses. And going farther back in there, we actually have plates, we think, for the motions of Mercury and Venus, what they call the inferior planets, and the Sun, and then you’ll see them putting together the plates that we believe gave the motions of Mars and the outer planets including retrograde motion. Most of the outer planet plates have not been found but remnants of the gear have. One of the things I thought was kind of cool was Jacques Cousteau actually re-dove this area in the late 1970s looking for any more of the gears and plates he could find. While he found other things that helped us date the wreck, he didn’t find any more. So, unfortunately, we don’t have all of this. But based on what the face is like and what things were written, this is what we think the Antikythera mechanism was like and as we bring in the plates that on the display, which show you the position of the planets relative to the stars at the little end there. This is amazing. This is technology that almost shouldn’t have been there 2100 years ago, is about when we date this to. So, there we go putting it all together. You’ll see the Moon going around with the little Moon phases calculator and we actually don’t know what sort of housing it was in. You’ll see it sort of drawing I think a bit of a wooden housing around it but this accurately calculated the position of the Sun, Moon, planets, eclipses, all of that. The Olympic cycle is kind of fun because that’s actually made people wonder what they used this for. It could’ve been for betting, that if you, [laughing] yeah, if you scroll this ahead, you know, 50 years’ time, you’ll know what the stars would be like during the Olympic games and the stars might favor one side over another. So, [laughing] there actually may have been something like that. The thing that sort of puts this into context– At Goddard, they were talking about this during their talk. They’ve been doing very, very high imaging resolution of just the rusted outer shells of this thing and they believe they’ve uncovered an instruction manual and an instruction manual is very interesting because that means there probably more than one of these. It wasn’t a single object made for a single expert. It was something that you would acquire and then learn to set and there were instructions as to how to do that. So, what an amazing state of technology by the ancient Greeks as well, better than we thought. I will mention, however, that one of the reasons I don’t like working with the History Channel much anymore is they would always have my show “The Universe” on immediately before the show “Ancient Aliens” and then this guy comes around and everything we’ve been talking about for a half an hour about astronomy is like it’s alien. It’s aliens. And so I mean he’s on record as saying the Antikythera mechanism was done by aliens. So, you know, this is from but it’s true. I mean, if the aliens are going to come many light years in crafts that can travel interstellar distances to give us bronze gears. It like, “Okay, thanks guys.” So, as amazing as the Antikythera mechanism is, there’s no reason to think that it’s anything other than human ingenuity and it shows us the state of sophistication in the ancient world. Just a little bit of a side, there’s sort of a cottage industry in building models of the Antikythera mechanism for science fairs including out of Lego so if you want to go to the Lego website, you can see all of that. All right, so that’s a bit about the sophistication of the technology, the theory, and the observation of the ancient world but also a bit of a caution about how some of the models like the Aristotelian view of perfection also stuck us up for a while and kept things moving forward. So, where are we today? And in the second half of the talk, I want to talk a bit about our current views of the universe, how much we know and how much we don’t know and so, you know, how much is out there? Well, let me just do a couple of things at first. Whenever I start talking about space, I just want to make sure everybody’s up to speed on this, I’ll use terms like light years because the distances get so big that it becomes pretty useless to start talking about kilometers or anything like that. The speed of light is about 186,000 miles per second. A light year is the distance you would travel at that speed if you went for one year. That’s about 6 trillion miles. So a light year is a unit of distance, approximately 6 trillion miles. The neat thing is that this actually means that everything we see very far away in the universe, we see in the past. The nearest large galaxy to us, Andromeda is 2 million light years away; that’s the nearest one.


So, when you see Andromeda, which is actually up in the night sky tonight, you will see as it was 2 million years ago because it took light that long to get to us at light speed and there is no physical way I can show you what Andromeda looks like today. Right? Light has to travel from one place to another for us to get any information. So, this becomes very important when we look out billions of light years because there’s actually, this is the last bullet point, but that means there’s a limit to how far we can see just because of how old the universe is. We think the universe began 13.7 billion years ago. That means that in any direction on the sky, anywhere you look, the farthest away you can look is 13.7 billion light years because light hasn’t had time to get to you from anywhere farther than that. So, around us, there is a sphere of observability. We call this the observable universe. We do not think that is the extent of the universe. We think the universe is much, much larger than that and there are actually good reasons but I can’t go in to them. But there’s a limit to what we can see because of light travel time. So, everything I can possibly take a picture of or show you or measure is in this sphere around us, 13.7 billion light years in every direction. That’s just as much time as light has had. Now, when you start talking about the scale of the universe, even a relatively small component like an entire galaxy, here’s a galaxy. This is a spiral galaxy very similar to our own home, the Milky Way. One of these galaxies has on the order of, you know, 500 billion stars in it and it is about 100,000 light years across. So, edge to edge, light takes about 100,000 years to get across one galaxy. And the scale of stars compared to a galaxy is literally microscopic. I’ll let you in on a little secret. I kind of lie about the size. The way I usually describe the size of a galaxy is if you think about the dot of an i on a page of regular text. Just open a book, the dot of an i. If the Sun were that dot, the Sun’s about a million miles across, you could fit a million Earths inside the volume of the Sun. If the Sun were the size of that dot, that a galaxy like this I usually would say would be about the distance from New York to Los Angeles. So, you know, picture flying from New York to LA. Somebody has left a book on the ground.  The dot of an i. That’s the Sun just to our Milky Way Galaxy. But the reason I told you that’s a little bit of a lie is because it’s actually bigger than that. I realize that I was losing lock on people. The actual size of our galaxy is closer to the distance from the Earth to the Moon if the Sun were the size of the dot of an i. There are some smaller galaxies that are about the size of the United States, so I use that because people sort of lose lock. The distance from the Earth to the Moon is not understandable but the distance from New York to LA is kind of, so they’re huge. So, how many galaxies are there? Well, this is a picture from the Hubble Space Telescope called the Hubble Ultra Deep Field, where Hubble looked at a relatively empty part of space for the better part of a month. It just stared at the same part of the sky for a long, long time. And to give you an idea, there are about 2,000 galaxies that you can count in this image in the original data and the amount of sky that this represents, I mean, it amazes me. Every little dot you see there is a galaxy, right, a galaxy of hundreds of billions of stars, 100,000 light years across, and the amount of sky that this represents– I have a prop. This is a quarter and if you look at the eye of George Washington, I realize, yeah, difficult for you to see, but if you look at the eye of George Washington and you hold it at arm’s length, that’s the amount of sky that this image represents. So, we find about 2,000 galaxies in every tiny little pinprick dot on the sky. Each of those galaxies has billions of stars. Based on our current estimates of how many planets are in our own galaxy, the Milky Way, we think that each of these galaxies has up to 100 billion planets. So that’s a lot of stuff and this is actually a little close-up of that image. You can see that when you close-up on those tiny little dots, you begin to tease out that they really are galaxies and that’s amazing. But it may surprise you to know that we think that’s almost a tiny little fraction of what’s out there and this is where we find ourselves today. In the universe right now, we think that about as a whole, if you look at the energy that makes up the entire universe, you see that 0.4% stars, et cetera, that’s everything I just showed you. All of the galaxies, all of the planets, all of the stars, all of us, we think make up about 0.4% of the universe. There’s a decent amount of just intergalactic hydrogen gas floating around and then there are these two things called dark matter and dark energy and I can give you at least a quick description of what these are and how they’re really changing our view of what the universe is made of. It always amazes me to realize that we didn’t even know there were other galaxies until the 1920s. This is Edwin Hubble and in the 20s, Edwin Hubble was able to show that the Andromeda galaxy, the nearest galaxy to us, was actually made of lots of little stars. It was another galaxy like the Milky Way. We haven’t known that for very long, less than 100 years, and Hubble famously realized something else, that the galaxies all over the sky were expanding away from us. Everywhere you look, they were moving away from us. And the way he did that was a technique called the redshift. This is basically a rainbow, a spectrum of light, and the little lines that you see in the rainbow are caused when light passes through a gas like hydrogen and the atoms actually absorb bits of that light. It’s actually a chemical process. You can pick out what chemicals light shines through by looking at those little lines. And if something is moving away from you, the light gets stretched out by the motion away from you and these lines shift to a redder part of the spectrum. So, you see there, these are actually, you know, lines of hydrogen. They shift towards the red if something is moving away from you and that’s an actual image from Hubble’s paper, where he showed the galaxies that are farther away are moving faster and faster away from us. He discovered that the entire universe was expanding. The actual lines are a little hard to see. I won’t go point them out but there’s actually an arrow. They’re at the end of the little white arrow that you see there. So he was looking at galaxies all the way from about 78 million light years away to about the bottom one about 3.9 billion light years away and you can see the lines shifting towards different parts of the spectrum. Now, he realized there was a law to this. We call this Hubble’s Law, the farther away a galaxy is, the faster it’s moving away from us, and the rate that that happens is 71 kilometers per second per megaparsec. A megaparsec is about 3 million light years. It’s a convenient unit of measure. I’d be happy to discuss why we use that but 71 kilometers per second, every element of 3 million light years away, you go 71 kilometers per second faster. So if you’re 3 million light years ago, you’re moving about 71 kilometers per second away from us. If you’re 6 million light years ago, you’re moving about 142 and so on and so on. So the universe is expanding. Now, it kind of makes sense that if the universe is expanding, was it all much closer together in the past and this was actually something that was debated by famous people. Here we have George Lemaitre, who was a Jesuit priest and astronomer, of course, Albert Einstein, and it was at a meeting actually that George Lemaitre proposed the idea of what he called a primeval atom that everything in the universe is now expanding away from everything else. Back in the past, that implies there was a time that everything was a whole, one big clump of something, and then it expanded. And the smiling guy there is Fred Hoyle, an English astronomer, a bit of a gadfly and Fred Hoyle said, “Well, wait a minute. Do you mean to suggest everything began in a big bang?” It was actually meant as a joke and Lemaitre said, “Well, yeah.” And that’s where the word Big Bang comes from. The term Big Bang was actually sort of a criticism as to what George Lemaitre thought and so you do a search these days. You do a search these days on Big Bang theory and, of course, you know exactly what you’re going to get and I actually, I encourage people to go to the web and look at videos about the Big Bang but this is always the first thing that– It’s not so bad though because you may have heard from the bio that I actually was a postdoc at Cal Tech, so these people portrayed in the show are my friends and I will say that personally, you know, I don’t know how many science fiction costumes I have. We have had the problem of everybody trying to wear the same science fiction costume, that happened. This was actually my research group at Cal Tech. One time instead of being regular Star Trek people, we all wanted to be mirror universe Star Trek people, where if you’re a science fiction fan, you get the joke. Everybody has a goatee. I loved my goatee. I had so much fun. But at any rate, so some basics of the Big Bang and this is something that I would like to spend a whole hour talking to you about, everything is expanding from everything all at once. There’s no empty center to the universe. All of space is getting bigger in every direction. So no matter where you are in the universe, you’ll see things expanding away from you because space itself is stretching in every direction. The universe includes all space and time. I’m very often trying to talk to people that we’re not expanding into something. We’re not expanding into empty space. The galaxies are not rushing through space into emptiness. That’s not how we see it happening. The universe is absolutely full of galaxies. The whole volume is expanding at once and that’s a semester of general relativity if you want to explain how that’s possible. But if you run the physics backwards, you may get some idea about what conditions near the Big Bang were like and we do that but this is kind of cool. Does a beginning for the universe imply an end as well?


If the universe began and is expanding, well what does that mean? Will the expansion continue forever? Will the expansion stop some day? Will everything come crushing back together? These were some of the big questions that were being asked about 50 years ago. If the universe had a beginning, what can we tell about the end of it? So, the rush was on to do a census of the universe. How much material was out there and how is it behaving and this is actually a cluster of galaxies called the Coma Cluster. It’s a very rich cluster of galaxies, about 3,000 galaxies. We’re in another cluster of galaxies on the edge of this one and people started to look at clusters of galaxies, trying to figure out how much mass there was in the universe, how much material, would it eventually stop this expansion, would it not, and when we started to make the census of the universe, you know, as far as we could see, how many galaxies, where were they, we started noticing some pretty odd things. And this is a picture of Fritz Zwicky, a famous astronomer, somebody who was very active in the 40s and 50s. Fritz Zwicky was studying these clusters of galaxies and he found something difficult to explain. The galaxies were all orbiting around each other. You know, they have a lot of gravity in a collection of many billions of stars. All of these galaxies were orbiting around each other but the orbits were too fast. The galaxy clusters were moving so quickly that they should’ve flown apart. And if you added up all of the mass of the galaxies, it came nowhere near the mass needed to keep the clusters together. In fact, it was a factor that you needed about 80% more mass than you could see. So, all of the visible light only accounted for about 20% of the mass that he saw from these clusters of galaxies. And the problem was closer to home, too. This is a picture of Vera Rubin, who’s actually still here in Washington, DC, and very active. Vera Rubin in the 1960s looked at galaxies individually and realized they were rotating so fast, this is true of the Milky Way as well, that our galaxy should fly apart. You know, Vera Rubin said, “Picture a quickly spinning plate and put a bunch of peas on it and watch the peas fly off the plate.” Our galaxy is rotating so fast, the stars shouldn’t stick together and once again, the number was about the same, about 80% more mass is needed. So, at first nobody thought that this missing mass was going to be all that exotic. Maybe there were stars we hadn’t seen yet. Maybe there were more black holes. Maybe there was a lot of cold gas between the stars we hadn’t seen. The problem is, is that as our observations got better and better, we’ve eliminated all of the easy answers and so we now call this stuff dark matter and the dark just means we know so little about it. There is more mass in the galaxy clusters than we can account for and here’s where things get really amazing. This is a real picture from the Hubble Space Telescope. It has not been altered and you’ll notice all of these streaky lines going around a cluster of galaxies. When we first saw that we had no idea what that could be, you know, what was making these huge streaky structures and we realized that what we had to do was call on another old friend from physics, Albert Einstein. Albert Einstein talked about how gravity has the ability to bend light. This is what he’s most famous for. It’s called the Theory of General Relativity, which says that if you have a massive object, for example the Sun, the Sun actually bends space around it. Gravity, what gravity really is in a deep sense is a bending of space in time. That’s what Einstein’s biggest contribution to us is. And this was actually observed during a solar eclipse in 1911, I believe. I’m trying to remember. It was 1918 [inaudible].

>> 19.

>> 1919. Thank you. 1919. So an eclipse in 1919, they were actually able to observe stars that were physically behind the disk of the Sun. The light bent around the gravity, bent around the space of the Sun and you could actually see all of these images of stars kind of crowded up around the edge of the sun. There’s a proof of his theory of General Relativity. We now know when we see images like this– This is an image taken by a friend of mine. Her name is Jane Rigby. This was made just a couple years ago and what you’re looking at here is that the– I don’t know, I’ve got. What you’re looking at here is the yellowish blobs are actually galaxies, a cluster of galaxies all orbiting around each other, and you’ll notice there’s a blue sort of galaxy shape thing here and a big streak. There’s another thing here and another streak. What this really is, is that this is a nearer-by cluster of galaxies and it’s lensing and warping light from something behind it. So, here’s what’s happening. Here’s the Hubble Space Telescope and there’s a nearby cluster of galaxies. I should go up here. This is what the Hubble sees. So there’s a nearer-by cluster of galaxies that’s actually lensing light around it. The light is bending around it and what you see is that these are all the same galaxy but the light’s been smeared out. Again, these images are not modified. If you were able to take a picture of this on the sky tonight, this is what you would see. Space itself can act like a lens and all the sudden we realized that this dark matter could bend light around it. It has gravity even if nothing else appears to be there. And so we set about mapping these warps. And this is actually an amazing thing. This is a group of galaxies that are all colliding together. This area of the universe is so dense that the gravity between the galaxies overcomes the expansion and these galaxy clusters are colliding together. And we actually noticed a couple of really odd things. You can see some lensing. You can see some areas that are rather small on this image but areas where some of the lenses are kind of smeared out. In x-ray light, if you take a picture of this cluster, x-ray light is actually light that’s emitted by very, very hot gas and these two clusters are colliding together and all of the gas in between the clusters is getting compressed and heated by the collision of these thousands of galaxies all together. Now, this gives us some idea where the gas of the galaxy is, you know, where all these clusters are going together but then we combined it to make a map and it’s a little weird but I’ll describe this. You can see the images of all the galaxies in white and where you see the pink color is where we see hot gas being shot together as these clusters of galaxies collide and where we’ve put blue coloring in, this is false coloring. We put blue coloring in to show where we see this lensing effect, where we see this gravity warping space itself and actually warping the light and what appears to have happened is that as these two galaxy clusters collided, the galaxy clusters are sticking together, the gas is sticking together and heating up and getting shocked but there’s some material that’s going all the way through and just drifting away on either side, passing right through like a ghost through a wall. We think this is dark matter being stripped off a cluster of galaxies. Dark matter is really weird. It doesn’t heat up when you shock it. It doesn’t interact with regular matter. It doesn’t reflect light. It doesn’t give off any light at any wavelength even gas that’s only a couple degrees above absolute zero gives off radio and microwave light, we could easily measure that. There’s something here that has gravity and literally nothing else. So, we love to make jokes about this and of course this is one of these, you know, fake inspiration posters. So if you ever feel like, you know, somebody’s got too big of an ego, remember dark matter most of the universe can’t even be bothered to interact with you. We really find this to be true 80% of the universe we think is in a form that we do not know what it is. We have no idea. We’ve made computer models based on very deep observations of the sky what dark matter should look like in the universe. We think it should actually group together, sorry, group together in filaments and, like I said, this was based on a huge computer run that was done at several universities that NASA was involved in as well and based on our observations of the early universe, this should be the shape of dark matter. It should form a web, a structure that actually takes up a whole volume of the universe. So, obviously this much dark material with gravity should influence regular matter like us. We still feel its gravitational pull even if it doesn’t interact with us. And this is another huge computer run where what you can see– Just set that off here. There we go. This is a computer simulation of how regular matter over billions of years starting about, you know, 10 billion years ago or more would actually start mapping itself, attracted to the gravity of this large underlying web of dark matter in the universe. All of the little things you see here are galaxies, galaxies that are colliding, they’re forming bigger galaxies, clusters of galaxies even colliding but the collisions are only happening where these filaments of dark matter direct everything together by the gravity. It’s an amazing idea that there’s a hidden underlying scaffolding to the entire universe. Is there any evidence of this? Well, it actually goes back to– This was an advisor of mine at Harvard back in the late 80s, a guy named John Huchra. I was around when John was doing the first maps of galaxies very far away from the Earth. Actually, the position of Earth is right here, right at this little apex and we are observing out into the universe many, many millions of light years and this is just a plot of a slice of galaxies in two dimensions looking away from the Earth where our galaxy is positioned.


And every little dot here is a galaxy. And we realized that things were not very random looking. Things appeared to be filling in, in sort of like little bubbles, and there were voids. They called this the Great Wall. It was actually this huge sort of wall of galaxies that stretched millions and millions of light years. Even in the late 80s, there was an inkling of this and now, of course, we have much better surveys going much farther away. This is from a survey called the Sloan Digital Sky Survey. At the very center here is actually our cluster of galaxies, a cluster called the Virgo Cluster, about 2,000 galaxies. Looking out into space, we actually see elements, we see these filaments. We see the structure in the universe that all of the galaxies appear to be attracted to. So, yes indeed, we actually think there is now evidence of dark matter being the real structure of the universe and everything that we are is sort of a dusting on it; 80% of the mass of the universe is something we don’t know what it is. It’s not made of atoms the same way we are. It is completely influencing the shape, structure, density, everything of the rest of the universe. And talk about humility, when you ask about how much we understand the Big Bang, currently we have no idea what dark matter was doing during the Big Bang, what 80% the mass of the universe was doing. So, I know I need to wrap up pretty soon so I’ll end on the thought, what could this stuff be? One of the things that we’re really hoping happens in the next few years is we get some idea what this dark matter is made out of.  One of the things that might help us is CERN, the Large Hadron Collider. We are looking for particles we have never seen before. There are actually three events at CERN–. The people are wondering if they might have seen a dark matter particle, three events out of trillions and trillions and trillions of collisions. Some of the energy these mysterious particles are coming in at implies there might be something called supersymmetric particles and I’m afraid I don’t have a lot of time to explain what that is but it could be particles moving in other dimensions in our three dimensions that we’re aware of and the theorists are hot on that right now. Gravity may actually be the only force of nature that can go between dimensions in space, basically between different universes. This theory works if you assume there are eleven dimensions in space and time and the only force, and there are reasons to believe this, the only force that can travel between them is gravity and, in fact, what dark matter is, is gravity coming from different dimensions. That’s really one of the best ideas theoretically right now as to where this stuff stands. Now, this kind of brings me back to the Greeks because we talked about the idea of epistemology and knowledge and how much of the universe is knowable. The idea that Plato had that we see shadows on a cave that our perception, our senses, our ability to measure is so limited by what we are that we cannot perceive the true nature of the universe. I would love to show you what an eleven-dimensional geometry looks like. There is no way as a three-dimensional creature I can. I will say that mathematics is so elegant that I know I’m getting a little Aristotelian here, it’s so beautiful, it’s so elegant, it fits so well, the mathematics works so well, the electromagnetic forces and more commonly understood force in nature, if you assume eleven dimensions, gravity falls into exactly the same equations as electromagnetic force. Gravity is a force acting in other dimensions but just the same as the other forces we’re familiar with. It’s intriguing. So, you know, I’m not quite sure where to go here. And you’ll notice I didn’t even have time to talk about dark energy. I’m happy to answer questions about dark energy. That was another piece of this puzzle too. But we now have pretty solid proof that the majority of the universe is something we’ve never even guessed what it is and our theory will take us somewhere, our experimental results will also us somewhere but I’m a little amazed at how much back we are in the days of Plato and how much of the universe is even knowable. It’s a fascinating question. Thank you.

[ Applause ]

Do we have time for questions or– I can also go outside if people–

>> Yeah. We’ll take one or two I think.

>> Yeah. I’ll take one or two questions and I think somebody else needs the auditorium but I’ll be right outside. So, if you have questions you didn’t have time to ask, feel free to come up and see me. Can I answer any questions? So, it’s a lot of stuff for, yeah [inaudible].

>> Do you think dark energy and dark matter interact with each other?

>> Repeat the question.

>> Yeah. The question is do I think dark energy and dark matter interact with each other. Boy, that’s not an easy question to do yes and no. So, the unfortunate thing about astronomers is never let them name anything. They see the beautiful giant swirling storm on Jupiter, they call it the Red Spot. I mean, I could go on. But dark energy and dark matter, at the moment we do not believe are connected in any direct way. The dark energy was–  A friend of mine actually got the Nobel Prize for this, a friend of mine from grad school. That’ll make you feel old. He got the Nobel Prize last year for discovering that the universe isn’t only expanding, it’s actually accelerating and the amount of energy needed to actually accelerate the expansion of the universe is huge. And we talked about the fate of the universe, will the expansion stop some day or will it keep going. It used to be that we discovered all this new dark matter and so we were thinking, “A-ha, there’s more mass than we assumed.” So, the expansion will either stop or maybe even collapse. We now have very good evidence that the universe is expanding faster and faster all the time. So, right now the answer is the universe will expand forever. So, dark matter and dark energy have some effect on our view of the end of the universe. Both of them will be major factors and right now it definitely looks like dark energy is winning. The universe is ripping apart, but we don’t necessarily think they’re the same thing. Dark matter will probably turn out to be some particle, some sort of transdimensional gravity whereas dark energy, we have no idea what’s dumping that energy into the universe yet. It could be influence from outside, could be pressure of space. So at the moment, it’s probably safer to assume them as being two different things.

>> Does that mean that energy is being created?

>> Yeah. Well, you know, one of the, one of the big mysteries right now is the rate of acceleration constant. I mean, you probably know your calculus, right? We’re now talking about, you know, second derivatives and third derivatives. You know, I’m sorry if you don’t know your calculus, but there’s some evidence in the past that– This was a Nobel Prize last year, the universe actually does seem to have been slowing down for a while. All of the matter in dark matter gravitationally held things together and the rate of expansion was actually slowing down until about 5 billion years ago and 5 billion years ago, we reached some critical density as we expanded, where dark energy took over and everything started flying apart faster and faster and faster. It could be that the dark energy is an innate pressure of space that was always there. So, some people would say that’s not actually adding energy, that there was an intrinsic pressure of space to expand. We didn’t really see it until the universe got sparse enough that the gravity was weak enough and this other force took over. It became dominant. So, I think right now people aren’t really looking at it as a problem of conservation of energy but it seems like that we been talking about a property of space. Space has a property that wants to make it accelerate.

>> Like compressing a spring.

>> Yeah. Oh yeah, and people talk about things like false vacuum states. I mean, there’s a whole quantum mechanical underpinning of this. The problem is how little proof we have of that. I actually did a lecture tour this summer partially with Brian Green, who’s sort of one of the leading string theory people, and he has his own take on what would cause this dark energy and all that and dark matter. So, yeah.

>> Thank you.

>> Thank you.

>> This has been a presentation of the Library of Congress. Visit us at

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1 Comment for LOC: Cosmology from Ancient Greece to Today, with NASA-Goddard’s Dr. Michelle Thaller
  1. Grab Attention says:

    I see you’ve succeeed in addressing several critical indicators I didn’t have on my list. Good work!

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