Our Place in the Universe: Cosmology from Ancient Greece to Today

from the Library of Congress in Washington DC you I'm Jennifer Harpster 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 Goddard and we're having a return engagement with dr. Michelle thaller Michelle gave a fantastic talk on Galileo and now why my stumbling on this Siderius monkey is here in February of 2010 if you're interested you can view this lecture online through our web cast page from Loc gov or through the LS the LC YouTube channel and we have a topics in science playlist right now it's my pleasure whoops I was going to introduce somebody else but now I'm introducing myself sorry about that we had a little change of plans I'm happy to introduce the final speaker speaker in this year in this year 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 spokes spokesperson for astronomy and science Michelle thaller is assistant director of science at NASA's NASA's Goddard Space Flight Center she is 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 Telescope's as well as ground-based observations such as mount Mount Palomar Palomar Kitt Peak and Mount strum-strum low for her observations after a post-doctorate research fellowship at Caltech 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 podcast series available on iTunes and YouTube and has received the highest honors for online programming michelle has been one of the regular hosts of the universe telephone 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's Science Channel is running how the universe works and I've been watching it all week behind the scenes michelle has left has led efforts to develop high quality apps for smartphones and tablets as well as involve NASA missions with social media outlets such as Facebook Twitter Second Life in her current role Michelle represents all of NASA's science names from Earth Sciences and climate change to the Sun space weather solar system exploration all the way out to cosmology in 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 and house of policy makers michelle has received numerous high-profile awards for her work including the Robert Robert Goddard award the women in aerospace award an induction into the Space Camp Hall of Fame so please join me in welcoming back dr. Michelle thaller thank you III think they gave her the the long bio version III apologize for that Wow you know this is an incredibly broad topic and I actually I'm gonna just apologize for a few things first there are so many things I wish I could tell I want to teach you all 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 from that but um I have something on the order of 4,000 Facebook friends I friend everybody who doesn't supposed anything offensive to my site and it's it's an it's very obvious to me the people around the world want answers to questions like how did the universe begin how is the universe going to end and they seem to think that we actually have answers to that you know real answers to that and 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 gasp as to what your data is saying but you have to be steeped in humility that we are limited creatures and 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 a little bit dangerous too and in the sense that we don't accept answers easily and we know 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 just how clever they were also how they got tripped up where did ideology and ideas that should have been abandoned long ago why do 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 well the Greeks in particular because we do have some records of them the Romans mentioned them in their writings that this was actually rediscovered in the Middle Ages when the Crusades came to the Middle East and found this again have 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 I owe Nia Ionia is actually on the the Turkish coast and the islands right around there there's a little inset map there you can see that that's actually the shape of the country of Turkey on the upper right hand corner and shows you Ionia and I only uh starting in the sixth 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 not just spirit and 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 fail E's and Anaximander both born around 600 BC and Phaleas 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 clips of 585 something that I find really intriguing is that families 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 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'm sorry m'lady 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 that humans were too 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 the 2600 years ago people were starting to mess with the idea of evolution and 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 they give the athenians and one of course the most famous one is Plato Plato's born in Athens around 429 BC 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 we 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 shining 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 as 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 and 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 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 shows you how about how much they love the idea of pure logic you can only make five solids out of regular polygons shapes where each of the shape has the same size side 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 that's not true actually the lovely theory I mean it's it's not actually true at all but 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 of 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 arts politics he had laws for whether these were done well or not and he had he was heavily influential all the way up until basically the Renaissance the idea that the 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 a 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 taking not-taken night tonight 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 word 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 yeah 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 so this is from the website Astronomy Picture of the Day the nasa goddard manages and these are picture 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 but this is an animation of some of the ideas we've had about retrograde motion and I'll I'll kind of put this through you started with the earth in the middle I mean that's kind of reasonable to assume that when you're an ancient person the earth seems huge and the middle of everything that's going on in the skies now the little ball you see is Mars and this is a model that was produc proposed by a man called Eudoxus of tinnitus 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 you DOCSIS thought he had discovered here we're sort of the supporting mechanisms under these crystalline spheres under these perfect spheres that Greeks believed in it works fairly well for for what the Greeks were able to measure a back event 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 her parkus and ptolemy ptolemy was an Egyptian who was born in about but 90 AD I actually think that so this is right around the turn of the millennium we're talking about and but what 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 deference that was the word they they used for it now um this model worked fairly well and and actually you know that was something that 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 on 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 that there's a little bit about epicycles and how different people have described that through the ages right now the Greeks were getting really good at 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 Aristophanes again R and B up to 76 to 195 BC and Aristophanes realized that there was a day of the year where there was a well a well a water well that you get water out of a town called Syene and the Sun actually shone 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 shine directly down the well it was a slight angle away from overhead and Aristophanes realized that that difference in angle from being overhead - not quite overhead that very small change in angle if you pace out the distance between Alexandria and sang in when she hired somebody to do some 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 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 with doing TV shows there was one time on the Discovery Channel where 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 did redid this calculation made a mistake and thought the earth was smaller than Aristophanes dudes the Greeks were right now the UH once you have the size of the earth there are a lot of interesting things that fall into place and and a person that is one of my personal heroes is Aristarchus of Samos so you may not have heard of this person lived about 300 years bc 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 also 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 and the famous letter to Archduchess Cristina okay so what did Aristarchus do um Aristarchus looked at lunar eclipses times when the earth shadow is actually cast onto the moon and he figured out that it was the Earth's shadow because litter 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 that the light source of the Sun was casting the shadow of the earth onto the moon and what he saw was that lunar eclipse has happened you know in at many different times always during full moon of course but they happen in many different angles and you see this curved shadow of the moon sorry the curved shadow of the earth crossing the moon in 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 curb shadow like that at every 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 the true shape of it so you see that this object is casting a spherical shadow now what would have those 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 shining all the way around this thing so it must be bigger and in fact Aristarchus thought he'd measured the the true relationship of the size between the moon and the earth based on this - he was a bit off because he didn't realize that like to diffract the 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 if light shone all around the Earth shadow the Sun must be larger he estimated it was about 5 times larger than the earth and about 5 million miles away now of course that's way off but not bad for po4 2,300 years ago right I mean we were 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 2,300 years ago and in the case of the estimating the stars as bright as the Sun yikes she 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 he tried to compare them to the brightness of the stars he didn't know that the the human eye is not actually a very good measurement that our our sensitivities change but still I mean 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 goes pretty easily Aristarchus advocated exactly the right reason for retrograde motion that we were going around at different speeds and our orbits around the Sun now I want to take a little bit of a detour that's a bit about the theory in 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 bout something called the Antikythera mechanism which I think a lot of you know about Antikythera sounds kind of sinister sort of a weird sounding word it's actually just the name of an island it's it's a very very small island designated on Google Maps by that a and between the Ionian Sea and the Aegean Sea in 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 were coins lots of neat things and one of the things that they they dragged up from that wreck was this rusted corroded bit of bronze and it if you look closely this is actually from the museum in Athens if you look closely there appeared to be a bit of a wheel in there this 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 but honestly it didn't get a lot of very serious attention until the 1970s when they began to x-ray it and well this is an x-ray of an actual device and it turns out it was a complex computer a gear based mechanical computer and one of the the amazing things an actually Goddard Space Flight Center has been involved where these people come and get give give us a talk the blue the top of my head off is 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 to 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 I we it's amazing that in ancient Greece they had this 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 the a lot of the Antikythera mechanism is missing in in sense that we don't have all of the gears but we do have at least the phases and we know what should have been moving around so as the animation begins the the captions this is done by the planetarium in Milan the captions are in Italian and English it's a lucky thing about speaking English most people do it as the second language but they they have the hand-crank they're starting they have a wheel that shows you the position of the Sun that way even was corrected because the Sun doesn't move across the sky at the same rate all the time it slows and speeds up and slows down during the course of the year that's actually due because of our orbit is elliptical but 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 this mechanism most of the Sun cycle and the moon cycle we actually have intact when you start getting out you can see some of the cycles of calculates the Panhellenic games that's the olympic games when the olympic games would fall the the metonic cycle is is an even division of lunar months into the year the sarah 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 read of this area in the late 1970s looking for anymore of the gears and plates he could find while he fired he found other things that helped us date the wreck he didn't find anymore 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 Andy mechanism was like and as we bring in the plates that on the display would show you the position of the planets relative to the Stars nothing it'll end there this is amazing this is technology that that almost shouldn't have been there 20 20 100 years ago is about when we date this too so there we go putting it all together you'll see that the moon going around with a little moon phases calculator and and we actually don't know what sort of housing it was in you'll see it's 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 the Olympic cycle is kind of fun because that's actually made people wonder what they use this for it could have been for betting that if you eye yeah that if you 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 there actually may have been something like that the 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 the just the rusted outer shells of this thing and they believe they have uncovered an instruction manual and an instruction manual is very interesting because that means there probably was 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 half an hour but astronomy is like it's aliens it's aliens and so I mean he's he's on record as saying the Antikythera mechanism was was done by aliens so it you know that this is from I haz Cheezburger comedy but it's true I mean if the aliens are gonna come many light years and crafts that could travel interstellar distances that give us bronze gears it's like okay thanks guys so the 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 an aside there there's sort of a a cottage industry and 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 you can see all of that all right so that's a bit about the 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 and kept things moving forward so so where are we today and in the in the 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 lightyears because the distances gets 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 six trillion miles so a Lightyear is a unit of distance approximately six trillion miles the 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 two 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 it as it was two 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 bright light has to travel from one place to another for us to get any information so this becomes very important when we look about 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 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's 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 into 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 the sphere around us 13.7 billion light years in every direction that's just as much time as light as Han 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's about a hundred thousand light years across so edge to edge light takes about a hundred thousand years to get across one galaxy and the scale of stars compared to a galaxy is is literally microscopic I'll let you in on a little secret I kind of lie about the size well the way I usually describe the size of a galaxy is if you think about the dot of an eye on a page of regular text I just open a book the dot of an eye if the Sun were that dot the Sun is 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 say would be about the distance from New York to Los Angeles so you have picture flying from New York to LA somebody's left a book on the ground the dot of an eye that's the Sun just to our own 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 realized 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 eye 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 and 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 a hundred thousand light-years across the amount of sky that this represents I have a prop this is a 1/4 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 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 etc that's everything I just showed you all of the galaxies is all of the planets all 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 galaxies 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 a hundred 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 a 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 that 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 it I won't go point them out but but he could is actually an arrow there at the end of a 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 lot of 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 km/h mega parsec a mega parsec is about three million light years it's it's a convenient unit of measurement I'd be happy to discuss why we use that but 71 km/h 3 million light years away you go 71 km/h you're moving about 71 km/h 6 million light years away you're moving about a 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 out here we have George Lemaitre who was a Jesuit priest an 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 in a bit of a gadfly and Fred Hoyle said well wait a minute I mean do you mean to suggest everything began in a Big Bang it was actually meant as a joke and Lemaitre said well yeah and 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 uh 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 gonna 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 Caltech so these people portrayed in the show are my friends and I will say that that personally you know I 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 Caltech 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 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 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 there 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 new the Big Bang were like and we do that but this is kind of cool so there's a beginning for the universe imply an end as well if the universe began and is expanding well what does that mean is that the will the expansion continued forever well the expansion stopped someday well everything come crashing 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 is called the Coma Cluster it's a very rich cluster of galaxies about 3,000 galaxies were sort of law we're in another cluster of galaxies on the edge of this one and people started to look at clusters of galaxies try to figure out how much mass there was in the universe how much material would it eventually stopped this expansion would have not and when we started to make this census of the universe as far as we could see how many galaxies is where were they we started know as noticing some pretty odd things and this is a picture of Fritz Zwicky a famous astronomer somebody who's very active in the 40s and 50s Fritz Zwicky was studying these clusters of galaxies and he found something difficult to explain the the galaxies were all orbiting around each other you know they had 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 have 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 of but you needed about 80 percent more mass than he 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 that the problem was closer to home - this is a picture 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 Vera Rubin said you know pictured a quickly spinning plate to 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 percent 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 um this is a real picture from the Hubble Space Telescope has not been altered and you'll notice there all of these streaky lines going around a cluster of galaxies when we first saw that we had no idea what that could be and what was making these huge streaky structures and we realized that what we had to do was call on another old friend from physics at Albert Einstein Albert Einstein talked about how gravity has the ability to bend light this is what he's most famous for us called the other 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 isn't a deep sense is a bending of space and 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 his 1918 even though 1919 thank you 1919 so an eclipse in 1919 I 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 was 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 your name is Jane Rigby this was made just a couple years ago and what you're looking at here is that the what you're looking at here is the the yellowish blobs are actually galaxies is a cluster of galaxies all orbiting around each other and you'll notice there's a there's a blue sort of galaxy shape thing here in a big streak that's another thing here and another streak what this really is is that this is a nearby cluster of galaxies and it's lensing and warping light from something behind it so here here's what's happening here's the Hubble Space Telescope and there's a nearby cluster of galaxies so I should I should go up here this is what the Hubble sees so there's a nearby 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 galaxies but the lights 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 of a sudden we realize 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 there they're rather small on this image but areas where some of the lenses are kind of smeared out in an x-ray light if you take a picture of this cluster x-ray light is uh 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 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 it's a little weird they'll describe this you can see the images of all the galaxies in white and where do you see the pink color is where we see hot gas being shocked together as these clusters of galaxies collide and where we've put blue coloring in this is false coloring you 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 would love to make jokes about this of course this is one of these you know fake inspiration posters so if you have 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 grouped together in filaments and like I said this was based on a huge computer run that was done in a 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 the 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 set that off here this is a computer simulation of how regular matter over billions of years starting about you know ten 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 a amazing idea that there's a 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 hakura I was around when John was doing the first maps of galaxies very far away from the earth via the actually the position of Earth is right here we're 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 and in two dimensions looking away from the earth where our galaxies 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 that they call this the great wall it was actually this huge sort of wall of galaxies that stretched millions of millions of light years even in the late 80s there was an inkling of this and and now of course we have much better surveys going much farther away now this is from a survey called the Sloan Digital Sky Survey at the at the very center here is actually our cluster of galaxies a cluster called the Virgo cluster about two thousand galaxies looking out into space we actually see elements of we see these filaments we see this structure in the universe that all of the galaxies appear to be attracted to so so yes and 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 to 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 percent the mass of the universe was doing so I know I need to wrap up pretty soon so I'll end on the fog what 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 line the Large Hadron Collider we are looking for particles we have never seen before there there are actually three events at CERN that people are wondering if they might have seen a Dark Matter particle three events out of trillions and trillions and trillions of collisions I some of the the energy is 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 a particles moving in in other dimensions than our three dimensions that were 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 and space basically between different universes this theory works if you assume there are eleven dimensions and space and time and the only force and their 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 a knowledge and and how much of the universe is knowable the idea that Plato had that we seeds shadows on a cave that our perception our sense 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 11 dimensional geometry looks like there is no way as a three-dimensional creature I can I will say the mathematics is so elegant that I know I'm getting a little Aristotelian here because it's so beautiful it's so elegant it fits so well the mathematics works so well the electromagnetic force is a more commonly understood force in nature if you assume 11 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 were familiar with it's intriguing so you know I 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 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 experiment experimental results will also take 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 I do we have time for questions or I can also go outside if people 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 that's a lot of stuff er yeah that's area yeah the question is do I think darkman energy and Dark Matter interact with each other um boy that that's not an easy question to do yes and no so we the unfortunate thing about astronomers is never let them name anything they 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 we at the moment we do not believe are connected in any direct way the the dark energy was a friend of mine actually got the Nobel Prize for this friend of mine from grad school that'll make you feel old I think 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 while the expansion stopped someday or will it keep going it used to be that we discovered all this new dark matter and so we were thinking AHA 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 that the same thing dark matter probably will turn out to be some particle some sort of transdimensional gravity where as dark energy we have no idea what's dumping that energy into the universe yet could be influenced from outside could be pressure of space so they at the moment is probably safer to assume them as being two different things yeah well you know one of the one of the the big mysteries right now is is is the rate of acceleration constant I mean you you probably know your calculus right we're now talking about yeah this second derivatives and third derivatives you know I'm sorry if you don't account but but there's some evidence in the past that this was the Nobel Prize last year the universe actually does seem to have been slowing down for a while all of the matter and dark matter gravitationally held things together and the rate of expansion was actually slowing down until about five billion years ago and five 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 it is it an eight pressure of space that was always there so some people would say that's not actually adding energy but 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 it that we were talking about a property of space space has a property that wants to make it accelerate yeah oh yeah people people talk about things like false vacuum States and 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 the summer parsley with Brian Greene who served one of the leading string theory people and he has his own take on what would cause this dark energy and all of that in Dark Matter so yeah thank thank you this has been a presentation of the Library of Congress visit us at loc.gov

Channel: Library of Congress

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Id: l3Sh9IjoPzQ

Length: 58min 31sec (3511 seconds)

Published: Fri Jan 31 2014