Einstein's General Relativity, from 1905 to 2005 - Kip Thorne - 11/16/2005

good good evening I'm Tom from brelo I'm chair of the division of physics math and astronomy they've handed me so many announcements to make before the this evenings presentation that I hope I we don't use up most of the evening doing them the next thing you'll see in Beck Beckman is on the evening of Thursday December 1st it's the Lauridsen like lecture it's by Professor Ken do phase of Princeton University it's the peak of world oil production Thanksgiving Day 2005 I think you might be interested in that one the next presentation in Beckman is by Professor William Goddard becoming revolution in pharmaceuticals and that's on January 8th 18th 2006 the series of lectures for the Einstein 100th anniversary of the Einstein miracle year have been put on at Caltech and we want to thank the office of the president and in particular Denise Nelson national events for putting these things together so well well now having gotten through the introductions I've got to try to remember what tonight's about it's the Watson like lecture Kip Thorne is speaking on Einstein's general relativity I think it's up there on the screen from 1950 to 2005 warp space-time black holes gravitational waves and the accelerating universe now you might say that Einstein had a very good year in nineteen five though Kipp is not obviously not talking about what Einstein did in nineteen five but it's also true that in 2005 our speaker tonight also had a very good year he won a Commonwealth award with people that you might have heard of like Colin Powell he's California scientists of the year and all of that is on top of the he wins prizes for writing wins prizes for teaching he's the Fineman professor at Caltech and if I were to go on about Kip Thorne we really would use up the holy Eve evening so at that point I think I'll just introduce our speaker Kip Thorne I always like to begin a lecture with a quotation from my close friend Stephen Hawking can you hear me and good there were two scientists physical scientists in the history of humankind who are the greatest intellects that we have seen in the physical scientists sciences Isaac Newton and Albert Einstein and they tower over all of the rest of us even Stephen Hawking and far far over me Newton in lived 1643 to 17 27 and he gave us a framework for the laws of nature that lasted for 200 years a framework based on absolute space absolute time forces accelerations the things of everyday experience Einstein lived from 1876 to 1955 he gave us a new framework that supplanted Isaac Newton's framework it has now been in place for a hundred years and the fundamental foundation for that is what Einstein called the principle of relativity the principle of relativity is an audacious thing it is a set a law that governs the laws of physics if you can just imagine that somebody conceiving of a law that governs the laws of physics what it says is that each law of nature must be the same in every reference frame and he laid this down in his classic paper on the electrodynamics of moving bodies in June 1905 so here you are running down Colorado Boulevard in your high-speed sports car and you have a reference frame inside there and inside this car you do an experiment to study the laws of nature for example you study the Lorentz force law the force that acts on a charged particle when it's moving in an electric and magnetic field I said outside there and I do out on the street on Colorado Boulevard I do the same experiment and we have to get identically the same answers we have to see that they this what these force laws for electromagnetism must be identically the same for you at high speed in your car and for me out on the street well that's not quite right be in 1905 Einstein did not yet know how to deal with gravity and yet we have gravity on Colorado Boulevard and in your car and so we've got to do what a physicist often does we do thought experiments where we very easily put you the car and me out in interstellar space and now we redo the experiment and so you think about that is a thought experiment then that that's the way it really goes there were some really remarkable consequences in 1905 that Einstein deduced from this fundamental principle quite surprising but they were forced on him just by laying down that principle the laws of physics are the same in every reference frame first of all in your frame your car looks like that but when I look measure your car in my reference frame on Colorado Boulevard as the as the car goes whizzing by it appears to be contracted in length I looking at myself in a mirror I look perfectly normal but you look at me as you go flying by and I appear to be contracted in width in addition as I look at your clock's ticking away an ideal flaw the best atomic clock fit to the world's best clock maker can make I see your clocks running slow but you see my clocks running slow how is this possible what it has to do with the fact that simultaneity is different for you and for me so if you put a bunch of firecrackers on the top of your car and you go running down Colorado Boulevard and you set them all off to explode simultaneously in my reference frame I will see the one at the back explode first then this then this and all the way up to the front so what is simultaneous is seen by you is not simultaneous is seen by me you get a sort of a queasy feeling now how are you going to do physics if if you have if all of these things are so weird well what is this going on how is this possible the key issue is that your time turns out to be a mixture of my time in my space and your space is a mixture of my space in my time this is quite analogous to the following that if you have a compass and it points toward magnetic north that's not true north it differs by about 15 degrees or so and so magnetic north is a mixture of true north and true east and that's what's going on in space time with this mixing of space and time that Einstein discovered from his remarkably simple postulate that the laws of physics must be all the same in every reference frame the bottom line is that time and space are in his words relative I would prefer to use the word personal you have taught your time and you have your space I have my time in my space their mixtures of each other but day but so they are personal to ourselves and they be things look different to you and me depending on how we're moving now all was well and good 9 Stein worked out the consequences and they gladden the hearts of his colleagues who had been working in the same direction and had almost gotten there but not really made the great leap in understanding this mixing of space and time but then Einstein had to face the issue of the laws of gravity Newton's law of gravity says that the Sun attracts the earth gravitationally with a force that's inversely proportional to the separation between the earth and the Sun the separation of man well Newton had an absolute time and so this was an instantaneous separation because there was no issue of a personal time there was an absolute time so it was an instantaneous separation and but Einstein had to ask separation is measured in whose reference frame because he had overthrown or but he had claimed at least to overthrow the idea of an absolute time an absolute simultaneity he also had to ask oh the separation is measuring whose reference frame so separations distances are different as seen than two frames and instant Tenaya T as different as measured in the two frames so the fundamental bottom line was that Newton's laws of gravity because they depended on instant ain't in Tenaya T and on distance being absolute his laws of gravity violated Einstein's principle of relativity and Einstein had a lot of foot spa Newton obviously was wrong and so he said about trying to figure out what should supplant Newton's laws of gravity it took two years for him to have what he later called the happiest thought of my life I was sit he said later I was sitting in a chair in the Patent Office where he was working in Bern Switzerland when all of a sudden the thought occurred to me if a person Falls freely he would not feel his own way in other words if I climb up on a table and I fall freely while I'm falling I don't feel gravity I have no sense that gravity is there gravity is gone and so I then know while I'm falling I know how to analyze the laws of nature because gravity is gone and I fi mine Stein I've worked out the fundamental principles of the laws of nature in my special relativity theory in the absence of gravity and so Einstein was with from this key idea he was able to analyze then the following question if you sit there with an ideal clock of the best world's best atomic clock and you've got one attached to the ceiling how do the ticking rates of those clocks compare and what he concluded was that the time is measured by an ideal clock on the floor with you flows slower I'm sorry on the ceiling it flows flows slower than on the floor do I have the right way around well we'll see the bottom line was that time is warped okay I know I have it right on the next slide and when I'm in the middle of a lecture having to have trouble getting myself confused okay so let's go to the next slide where I know I have it right because I have to make an argument in the next slide I have to argue from this warping of time that the rate of flow of time on the ceiling is different than on the floor which he deduced from the idea that he could do the calculation when he was freely falling and he knew how the laws of physics behaved he then deduced then this idea that time was warped and so I want to look at the issue of warping of time as being associated with gravity then it's gravity that is responsible for their different rate of flow of time on the ceiling than on the floor so I want to think about the following experiment I take an apple or I have you taken out an apple and you're sitting here on the in this room and you take an apple and you throw it in the air in just such a way that it hits the floor two seconds later and the question is why did it go in this arcing parabola and then hit the floor and Einstein gives us an answer he says that the Apple takes the path of longest time that is the fastest ticking as seen in its own reference frame I'll return to why he says this but he asserts that he says that the Apple finds a route that will cause it to take have the fastest ticking so it takes the longest time to get from here to there now let's think through what kind of a path that should be to take the longest time so I have it right this time that that the clocks that you have on the floor here are ticking slowly the clocks up there on the ceiling or ticking fast so if the Apple wants to take along the time that is it has to have a fastest average ticking of its clock then it wants to get up to the ceiling where time is flowing fast and then get back down to the floor but it has to do it in two seconds as measured by your clocks on the floor two seconds of its own clock ticking so it just wants to jump up the ceiling stay there and come back down but no it can't do that because it's also true that the faster it moves the swift current moves the slower it ticks is seen by you that was Justin Stein's principle from special relativity so it doesn't want to go up to the ceiling too fast because then it kick too slowly while I was getting up to the ceiling so there's an optimal path where it goes up not too fast but it tries to get to the ceiling where it can tick I rapidly and then back down and there is an optimal path and so this Apple it feels its way finding the path that will enable it to have it sticking be the fastest that it ages the most on that trajectory now this sounds like a crazy crazy idea but this was Einstein's idea and why was it einstein's idea because he asserted that time is warped at this point he did not have space orbit time has warped and the trajectory of longest time he said is a straight line now you're accustomed to the idea that between this point and that point the line of shortest length is a straight line he's saying the opposite thing says the trajectory of longest time is measured by my ideal clock as I go sailing up and back down that's a straight line and that's the difference between space and time Einstein understood at this point the space and time were a little weird and the in space time in the combination of space and time if you want to go along a straight line it's the line on which your clock ticks the fastest ticks the most that's the straight line and so he said this is a straight line you say well it's obvious not a straight line that's a parabola Einstein says I'm sorry but you have just been trained to think in a rather weird way if you will just look at that from a freely falling reference frame it's moving along a straight line as seen by you while you're falling and it is falling and Einstein says that straight lines as seen by freely falling observers those are the straight lines of space-time and he built his theory on that so this is then the essence of his building a theory in 1912 in which he said that gravity is due to warp warp time and that theory as he developed it nicely described all that we know about the solar system the orbits of the planets around the Sun the orbit of the moon around the earth it worked beautifully but there was something wrong with it Einstein realized fairly quickly the problem of course is that my space is a mixture of your time in your space and so if your time is warped then my space has got to be worked since it's a mixture and so you can't have just a warping of time you have to have a warping at least as seen by most people however they're moving through the universe a warping of both space and time and so in 1913 then he modified his theory it took him about a year with the help of his friend Marcel Grossman learning the mathematics that he needed mathematics of what today we call differential geometry to develop his theory with warp space-time and in 1913 he laid down a version of this theory of warp space-time explaining gravity but the theory that he laid down had problems it wasn't totally logically self-consistent he soon realized and he struggled for two years of very hard work trying to figure out how to deal with this finally November 11 1915 he gave us the mathematical law called Einsteins field equation that tells us precisely how the matter and the energy that live in the universe the matter that your body is made of the energy of the heat that's coming off of the lights in the ceiling how they all combine together that matter and energy to warp space-time so 1915 he had his final general theory of relativity with gravity associated with a curvature with a warping of space-time let me I give you a final little description of this law of general relativity in the following way suppose that we have a child who throws two apples up in the air absolutely parallel they go up and then they go down now physicists do thought experiments like this every day and what the physicists will say is I want to explore the trajectories of those apples and I don't want to worry about the atmosphere I don't want to worry about the apples running into the earth and the rock and so I just imagine the apples are made of something that doesn't interact with the atmosphere or the earth in the rock or I imagine that a hole is drilled through the earth so that the apples don't run into the material so the apples fall they just fall down into the earth and of course Newton says the apples get pulled together because the gravitational pull is toward the center of the earth and they will crash into each other but Einstein says those apples were initially moving along absolutely parallel lines and then those lines cross and if you have absolutely parallel lines and then they cross that's not possible in Euclidean and a Euclidean geometry and acquittee in space and so Newton says gravity did it gravity pulled them together Einstein says it was the fact that space-time is warped that did it more precisely if you have two parallel lines on a flat sheet of paper they won't ever cross but if you have them on a curved surface like the surface of the earth and they go up from the equator they cross at the North Pole I'm Stein says the crossing is due to Newton says the crossing is due to gravity Einstein says space-time did it the bottom line is matter warped space-time and that warping causes gravity in that design Stein's general theory of relativity and that was the step in in modern language of a physicist those are the steps that Einstein went through in order to deduce it one of the wonderful things about being at Caltech is what you have really interesting people to talk to and oh and I want to understand about the history of work in my field of general relativity and the further development so beyond Einstein's early work I can go just down the street to the office of the Einstein papers project which is led by a Diana farm us book Wald and with the Tilghman Sauer being the other scene senior the most senior editor along with her and I can talk with them I can see Einstein's original papers and I can get a real understanding of the history of my subject and Diana and I have even supervised the PhD thesis together of somebody kept an kenefick who is one of the editors on this particular volume who did both a physics PhD and a and PhD research in the history of relativity so this is just one of the beautiful things about about Caltech is all these interesting people to talk to let me go on now from 1915 and talk about the consequences of general relativity from 1915 to 2005 the past 90 years an initial issue is that space is warped inside and around the Sun and in any other massive body that's a prediction of Einstein's general relativity theory and we can understand that prediction by imagining taking an equatorial slice through the Sun just a slice of two-dimensional slice that bifurcates the Sun between the northern half and the southern half and the assertion is that the geometry of that slice will not be the geometry of a flat sheet of paper it will be warped because space is warped inside the Sun the warping is depicted here much exaggerated you can think of this as being what that slice would look like by somebody who is looking in from a higher dimensional space a higher dimensional flat space and so this stuff around here is this higher dimensional the higher dimensions of the flat space and this equatorial slice is warped in it alternatively you can imagine taking the equatorial slice out move it into interstellar space and it will have to be bent like this in order to accommodate itself to the flat flatness of interstellar space the thing that you notice is circumference around here is less than pi times diameter on that surface and that is the nature of the warping around the Sun though it is much much exaggerated here now one of the predictions about this warping that Einstein gave us in 1915 is the prediction of the deflection of starlight by the if you have the Sun here and a star near it here is a picture of the Warped space the Sun is seen from hyperspace the star is there and the light ray from the star moving toward our eye moves along the straightest line it can travel on on this warped surface but that straightest line that can travel on the Warped surface if we project our eye backward it that makes us think that the star is at this location and so the star appears to be here when really it was much closer to the Sun well somewhat closer to the Sun and so this was the prediction Einstein gave us and in 1919 in a famous Eclipse expedition I I to test this prediction when the Sun was blotted out by the moon so that day the astronomers could see the star nearby the prediction was beautifully confirmed to within an accuracy of O so by 1955 there had been a number of Eclipse expeditions and the accuracy was thought to be rather better than 20% but the answer was coming out too big and this is the first example of what I'm going to give you that in the history of the development of Einstein's the consequences of Einstein's ideas it has taken decades to get to where one could test them with high precision and here 1955 that's 40 years later the precision is not much better and the answer seems to be coming out wrong and that was the year in which nine Stein died but he had firm confidence in his prediction and maintained that there had to be something wrong with the observations in 1970 there was pioneered at Caltech a new technique for making these measurements a technique based on radio astronomy radio interferometry and that technique by 2005 has given us an accuracy of one part in 10,000 on this deflection of starlight beautifully confirming general relativity just a wonderful confirmation - very high accuracy so we know Einstein was right with an accuracy of a part in thousand looking on toward the future there is a space mission called the space interferometry mission that is being developed at JPL I has been tenderly scheduled for launch in 2009 but that the launch date is being pushed back along with everything else in terms of space science at NASA because NASA is in total shambles at the present time with regard to its science program which is a separate topic from this this lecture but you'll hear me say this several times again the the what sim is going to be capable of doing is mapping stars on the sky to an accuracy in their positions to an accuracy of four micro arc seconds that's for one millionth of an arc second accuracy that is an accuracy a thousand times better than the deflection of starlight by the Sun not when the star's rays are coming close to the Sun when the star is way off in a different part of the sky and so sim will see the whole sky warped in terms of positions of the stars by amounts that are a thousand times stronger than its accuracy and so that shows you where the technology is taking us to the point where this will have to be dealt with in order to understand the observation you've got to correct for all this warping another example of the influence of warping is what is called gravitational lensing these are photographs taken by the Hubble Space Telescope in the 1980s and you see a strange pattern of galaxies here sort of a circular pattern and that turns out to be because there is a massive cluster of galaxies down here in the center that is whose gravitational field is or whose mass is warping space and that warped space is acting like a lens and that lens is distorting all the images in this complicated but very pretty pattern so warped space shows up in a high-precision astronomy in astronomy measurements looking out at great distances warped space produced by intervening galaxies clusters of galaxies in the 2000s they say this warping of space gravitational lensing is being used to search for exotic objects in the sky called cosmic strings and macho's it's being used to map something called dark matter in galaxies and clusters of galaxies it's being used to measure the cosmological properties of the universe so we've come around to where the warping of space is a key tool for studying exotic phenomena in the universe one of the greatest challenges of this past century the 20th century has been to measure the overall shape of the universe is the universe overall when you average over the lumps associated with galaxies and clusters of galaxies is it shaped like the surface of a sphere or like the surface of a saddle or is it too flat and the prime goal of the Palomar Mountain 200-inch telescope Kalas Caltex big 200 telescope when it went into operation in 1948 was to deter measure the geometry of the universe in this way by looking at the sizes and brightnesses of distant galaxies and seeing whether they are blown up to larger sides and they ought to be or not by the warping of the space in the entire universe that quest failed completely and it failed completely because what people didn't realize at the time that the plan was laid out was that galaxies eat each other and they eat each other a lot they're very cannibalistic our own galaxy is in the process of eating the Large Magellanic Cloud it's a satellite galaxy and when they eat each other they change their properties and so if you see a very distant galaxy it's also a much younger than galaxies today are and you really don't know what it would look like if you got up close to it and so this this approach completely failed however Mark kamionkowski a professor here at Caltech in cosmology came to the rescue along with a couple of other colleagues but come in Cal skee said is the following what I'm showing you here is the history of the expansion of the universe on one diagram running from 10 to the minus 43 seconds the big bang up to something like 15 billion years today we the quest of the Palomar telescope to measure the shape of the universe was out here in the modern era and the universe is very complicated in the modern era but if we go back to when the universe is about 300 thousand years old the universe was very simple it was just consisted of hot gas plasma with very weak sound waves large em large wavelength sound waves but very weak propagating through it and one can and we know a great deal about the properties of those sound waves because they were so simple that it doesn't involve the kind of complicated physics of galaxies and stars and so forth and so what Mark kamionkowski said is look here at those sound waves and see whether the sizes of the sound waves are amplified or not by the gravitational lensing by the intervening universe how do you look well with something calls them called the cosmic microwave radiation which was emitted by this gas and redshifted into the microwave frequency band as it traveled out to earth so this quest was then taken up by Andrew Lang and his colleagues Andrew Lang is another professor here at Caltech I and Andrew and his colleagues flew a a microwave telescope to look at the sky on a flight around Antarctica the telescope is called boomerang and the prediction was that if the universe is closed like the surface of a sphere then you would have the sound waves on the sky would be amplified you would see a phat pattern like this with pretty big lumps if it's flat you'd see a pattern like that with smaller lumps and if it's shaped like a saddle you would see a pattern like this there is the pattern that was seen that Andrew and his colleagues saw and he found they found that the universe is flat so the Palomar quest Palomar failed but it did lots of other wonderful things but Andrew Lang and his team of scientists with boomerang I succeeded where Palomar failed by following kamionkowski x' a suggestion of looking where the universe is simple in order to be looking at something that that one understood very well and we turn to the warping of time Einstein also in 1915 predicted that time has warped time slows near any massive body and for example near the surface of the Sun by 1955 many attempts had been made to measure the slowing of time near the surface of the Sun and they had not really succeeded the attempt is made by looking at the spectral lines of light that's emitted from the Sun and those spectral lines tell you about the ticking rate of atoms so it's sort of like atomic clocks in the near the surface of the Sun and when the radiation reaches the earth you compare them with the spectral lines of the same kind of material here on the surface of the earth and by looking at the redshift you can infer the difference between the ticking rate or the ratio of the ticking rates on the surface of the Sun and on earth but it was the Sun is so messy that these measurements were very controversial in 1955 when Einstein died 1976 Marching technology comes to the rescue Robert Vesco at the Harvard Smithsonian Astrophysical Observatory and his team built a set of atomic clock clocks hydrogen maser clocks they flew several of them in a rocket up to a height of 10,000 kilometers had identical atomic clocks down at the Kennedy Space Center and they telemetered back down to the kennedy space center the ticking rates of the clocks up here and thereby they were able to compare the ticking rate of time the rate of flow of time at 10,000 kilometers altitude with that on the surface of the earth the prediction was that time slows near the earth by four parts and ten billion and they confirmed this to an accuracy of one hundredths of a percent one part in 10 to the 4 again a beautiful confirmation of Einstein's predictions but it didn't come until 1976 that says 60 years after Einstein made the prediction it took that long for technology to catch up today we have the global positioning system with satellites above the surface of the earth that send down signals that are basically the ticking rates of clocks up there in the satellites and tick and time markers earth clocks up there in the satellites and down on the surface of the earth you have a GPS receiver and the receiver triangulates on these satellites to determine where you are in the surface of the earth these radio signals have to be corrected for the slowing of time on the earth otherwise the GPS system would fail if you didn't do the correction right and a former student of mine cliff Will was asked by the Defense Department to chair a committee to look at whether they were doing the corrections right very early on because there were questions where they were really doing it right and whether the system would really work properly and they got it all straightened out and so those Corrections are put into something that is part of everyday technology now the correction for the slowing of time is part of everyday technology that's what has happened with Einstein's ideas not only is there a warping of space and warping of time and general relativity there is also a tornado like whirling motion of space around any rotating body so if the earth is the Earth rotates it according to general relativity grabs space and sets space into a whirling tornado like motion the earth of course rotates at run-run revolution a day and that drags space into motion at one revolution every 6 million years that's some tornado nevertheless it's an interesting effect and it deserves to be tested and there is a bank of superconducting gyroscopes now in orbit a project led by Francis Everett at Stanford University something called gravity probe B which is currently collecting data and what gravity probe B does is these gyroscopes they're sitting here spinning on their axes and the whirling motion of space here grabs that at the end of the gyroscope and pulls it around faster than this end because this end is farther away and so the whirling motion is a little lower and it's sort of like a leaf sitting on in a stream near a bank where their leaf turns because of the differential motion the water is moving faster out in the center of the bank of the river then it de is near the near the bank and the leaf turns because of that and that's what happens to these gyroscopes and gravity probe be a very tiny effect but they expect to measure this with an accuracy of 1% or better they're hoping for an accuracy of about one part in a thousand well let me turn to the most interesting of all things associated with warped space-time and that is black holes and whenever I talk about black holes I always have to bring my favorite black hole out so this black hole if it were a black hole would not be made from rubber but rather it's made from warped space and time and in particular one way to understand the warpage is that the circumference around this black hole looks like it's about 3 feet so you would expect that the diameter is 3 feet divided by pi which it would be about 1 foot but in fact the diameter is not about one foot it is enormous ly larger than one foot and that's because space is so highly warped around and inside of a black hole and we can understand this warping if I can find my here we go we can understand this in the following way this is a little analogy suppose that we take a sheet of rubber say a child's trampoline we put it up on stilts and we sink put a rock in the center and the rock sinks the rubber down like this and then suppose that you're an and you live on this rubber this rubber is your entire universe you're a blind ant so you can't look out and see what's going on here all you can do is measure the shape of your universe you will marching around and measure the circumference and then you go and measure the diameter and the diameter is huge compared to the circumference and you say how is that possible and of course I know how it's possible I can see the rock that's distorting the sheet it's because your universe is warped and this warping is identical to the warping around a black hole all I do is change the labels now I have a the shape of an equatorial slice through a black hole and I have it down at the center I don't know what oh there and I don't know where it went so I have and this is a shape in a hyperspace now and down at the center where I had a rock before I now have something called a singularity which I'll talk about near the end of my talk now the thing that you all know about black holes is when something falls in it can't get back out and it can't send signals out and the reason for that is the following that if you fall in and you're living in this space so it's now a little two dimensional you or me falling ins trying to send microwave signals out of a little microwave transmitter once you or I fall through and the surface of the black hole which is called the horizon the signals get pulled down with me toward the singularity now what is the physics that causes that what forces what gives rise to everything being pulled down it's a warping of time we have the curvature of space that I talked about before but we also have a warping of time time slows as you near a massive body if you remain at rest just above the surface of a black hole time at that location slows to a halt compared to time far away and as soon as you're inside the surface time is still flowing but it's flowing in a direction you would have thought was a space direction it's flowing toward the center toward the singularity down here and that's why nothing can get out because nothing in travel backward in time at least locally backward in time at the very end I'll talk about doing backward in time by going out into the universe and coming back but locally you can't go backward in time and so it is the downward flow of time that prevents anything from getting out of a black hole of course the black hole can also spin on its axis and its angular momentum of rotation drag space into a whirlpool tornado-like motion but in this case it can be a very fast motion compared to the contrasted with the motion of space around the Earth it can be a motion about many revolutions per second around a spinning black hole a real tornado type motion a challenge for the coming decade is to probe black holes in exquisite detail to map out all three aspects of warped space-time around a black hole the warping of space the warping of time and the whirling motion of space this is what the map should look like according to general relativity a very precise depiction of that map is seen looking in from hyperspace this is showing the warping of space and then the color coding is the warping of time when you get down to the transition between the purple into the yellow in here time is flowing at about twenty percent the rate that it is far away down here at the beginning of the red is 10% and down there at the black it is completely halted and below that you're inside the horizon I've cut off the interior the horizon in this diagram so the horizon is there remember this is an equatorial slice I've lost one dimension and so this is the dimension of space if I cut right through the black hole take an equatorial slice I have this shape and the rainbow colors showing the rate of flow of time if the black hole is spinning that black hole is not spinning but the black hole is spinning the throat is predicted to be much longer and here coated in with arrows is the rate of motion of space the tornado-like motion of space caused by the spin of the black hole so those are the predictions they're very precise predictions from general relativity and we would like to test them so how can we see a black hole and at this space-time warpage well the problem is that a black hole is black genome it's no light no x-rays no radio waves so if you want to see this I think the very best way to go about doing it is by using a form of radiation that's made from the same stuff as the black hole itself made from Warped space and time and these are gravitational waves a phenomenon predicted by Einstein using his general relativity equations in 1916 so for a concrete example suppose that I have a small black hole orbiting around a large black hole and this small black hole goes around and around and gradually spirals in and ultimately plunges through the horizon of the large black hole why does it spiral in because it's losing energy where is it losing energy to well as you see there are ripples here those ripples are caused by the warping of the small black hole's warpage the small black hole goes around and around it creates ripples in the geometry of space and those ripples travel out like ripples traveling out from your finger if you stir your finger around and around in a pond or in a bathtub and those ripples are gravitational waves they're carrying away energy and so the small black hole spirals into the big black hole as it loses energy but they are also are carrying a map a full map in complete detail one of my graduate students Fenton Ryan proved just before he went off to all Wall Street - I used the tools of stochastic differential equations which he had learned at Caltech to predict the motion of money markets so just before that he did a superb piece of work in which he predicted that a full map of the big holes spacetime warpage is encoded in these waves as they come out so we have the challenge of monitoring those waves and making the map well how can we monitor these gravitational waves well let me use an analogy again suppose that you have waves on the surface of a pond and you are intelligent insect lives on the surface of a pond with some decent technology and you decide you want to what measure those waves so you get a couple of quarks and you get a laser and a laser metrology beam and you let use the laser to monitor the separation the precise distance between those quarks and as the waves go by those quarks move back and forth and the laser use the laser beam to monitor them moving back and forth and you can see that the waves are passing well this is what we do with gravitational waves here is a picture of what the waves actually do in the gravitational wave case if the waves are propagating into the screen what they do is they stretch and squeeze space in the pattern that you see there when stretching in one direction squeezing in the other direction transverse to the direction of propagation of the of the wave so this is one aspect of the warped space-time of a gravitational wave so we here at the a superb experimental team that I'll talk about in a few minutes that is a headquarter here at Caltech has built earth-based laser interferometer gravitational wave detectors that work on the that monitor passing gravitational waves are trying to detect and monitor passing gravitational waves by just looking at the stretching and squeezing of space and what is done is to hang four mirrors from overhead supports by steel wires they're steel at the present time and when the wave passes these two mirrors will be pushed apart they basically ride on space as it's stretched and squeezed while these two mirrors are pushed together in the next half cycle these two mirrors are pushed apart and those are pushed together and a technique called laser interferometry that I won't go into is use then to monitor the difference in the separation between these two mirrors and those two mirrors and this difference Delta L general relativity predicts is proportional to L because it's a stretching and squeezing of space the farther apart you are the greater will be the motions ISO Delta L is some dimensionless gravitational wave field which is associate with the warping of space times L the magnitude that we expect for this gravitational wave field is less than or of order 10 to the minus 20 10.2 NT zeros and a 1 after it this is a dimensionless magnitude you multiply that by the arm length for the instruments that our experimental team has built for kilometers and you find that these mirrors are moving back and forth by an amount of 4 times 10 to the minus 16 centimeters and so we have now operational instruments capable of monitoring this looking at motions of mirrors for kilometers apart to this precision now what is that precision let's talk about 1 times 10 to the minus 16 centimeters which is closer to where the noise is in these instruments well 1 centimeters about half an inch oops I let's do it one step at a time a human hair is a hundred microns that's a hundred times smaller than half an inch the wavelength of the light that is being used to monitor the motion of those mirrors is a hundred times smaller than that it's one micron you go down by a factor of 10,000 you reach the diameter of an atom you going down by another factor of a hundred thousand you reach the diameter of the nucleus at the center of the atom you go down by another factor of a thousand you reach LIGO sensitivity now this is a tour de force in high precision technology it is really remarkable in fact I co-authored a textbook classic textbook on general relativity yeah in the early 1970s with John Wheeler and Charlie Messner and then there there's an exercise for the student to show that this technique of measuring gravitational waves is crazy it'll never work well this is the way the way our team is doing it now in fact LIGO is a reality it has one site in Hanford Washington with the laser beams running up and down these tubes it is a collaboration of about 500 scientists and 40 institutions in eight nations with Caltech and MIT the lead institutions and it's headquartered here at Caltech it is led by Barry bearish and Stan Whitcomb here at Cal Tech and the spokesman for the scientific collaboration those those 40 institutions is Peter salsa at Syracuse University it was originally ray Weiss who started the project ray Weiss Ronde Reaver here at Caltech and I started the project back in the 1980s and it the project owes a great deal to the ingenuity of both Ronde River here at Caltech and Ray Weiss here is the second side in Livingston Louisiana and here is the noise curve that we said in 1989 when we submitted our construction proposal that we expected to get for our first interferometers when they went into operation plotting frequency from 10 cycles per second 10 Hertz here up to 10,000 Hertz you notice these numbers these are the gravitational wave strain and for those of you who are scientists or engineers it's the noise so it's strain per square root of Hertz frequency these numbers are 10 to the minus 23 down in here this is many orders of magnitude the blue is where our noise was in August 2005 almost right on except for a little corner down here it's superb performance on a tour de force on the part of the experimental team 12 days ago ly who began its first long search for gravitational waves with these interferometers these gravity wave detectors a search that will last for a year or so have maybe 18 months in order to collect a full year years worth of data and we are eagerly awaiting the results of this search LIGO is designed to look at small black holes in distant galaxies black holes with masses between 10 and a hundreds times the mass of the Sun sizes of order a hundred kilometers something like the size of the Los Angeles area we also have in the early in their planning stages intermediate planning stages a different gravitational wave detection system called Lisa the laser interferometer space antenna Lisa is going at it consists of three spacecraft which track each other with laser beams just like the Wii U's laser beams to track the motion of these mirrors in LIGO but these spacecraft are five million kilometres apart so instead of four kilometres five million kilometres and correspondingly they go after gravitational waves with much longer wavelength instead of wavelengths that are ordered the size of North America is like Oh does or the size of the state of California they go after wavelengths that have sizes of order the distance between the Earth and the moon or the distance between the moon and the Sun much longer wavelengths a very different frequency band correspondingly they will study Lisa will study giant black holes and distant galaxies black holes that weigh a million times what the Sun the Sun weighs weighs JPL and Caltech leases as you see by these symbols up here it's a joint mission of the European Space Agency and NASA and JPL and Caltech are in charge of the science from the American n Tom Prince is the mission scientist for Lisa stirol' Finney headed the mission design team that before at least it became a real mission and he now and these are both professors at Caltech he now is in charge of the data analysis and the characterization of gravity wave sources for Lisa I'm also involved a number of people at Caltech and JPL are involved in Lisa as we are in LIGO Lisa was currently scheduled for launch in 2014 and it will probably get pushed out because of the chaos that's going on with regard to the whole science program in NASA at the present time but Lisa has a very high rating with regard to scientific priorities and so we remain quite confident that it is going to fly let's return to what Lisa and Lyle might do one of the pieces of science mapping a black hole a spacetime warpage what happens that the map comes out wrong well one possibility is we may have discovered a new type of inhabitant of the dark side of the universe that is a new kind of object with highly warped space that emits little or no light little or no electromagnetic radiation there are two longshot possibilities you might have a dense object that's made from cold dark matter and has a very different kind of a warped space conceivably you have a singularity like the one at the center of the black hole but it's not at the center of a black hole sitting out in the external universe for all the world to see and has some wildly shaped warped space I just made these shapes up out of my mind these are not predictions they're just icons to indicate that there we could have big surprises when we look out at the universe and start doing these maps we also will have the possibility to probe the very horizon of a black hole that point of no-return down which things fall out which nothing can come because this little hole raises it tied on the horizon of the big hole is it orbits around that tide pulls back on the little hole and changes its orbit and changes its orbit by a fairly large amount and that large enough amount that very easily Lisa should be able to see this when Lisa looks at the gravitational waves from such systems and so we actually expect with Lisa to be able to probe the horizons of black holes and study what their properties are more interesting than that to me is the study of two black holes with comparable masses that come crashing together and liberate in explosive energy 10% of the mass of the black hole converted into radiation into gravitational waves there is no electromagnetic radiation emitted whatsoever it's all in the form of gravitational waves these are the most powerful explosive events in the unit modern universe the only thing more powerful according to theory the only thing more powerful was the Big Bang birth of the universe itself and the details of this collision are encoded in the wave forms the up and down oscillations of the gravitational waves that are emitted and so I would very much like to see those waveforms and see the details of these kinds of collisions and let me describe this a little more graphically each black hole is rotating so it drags space into motion around itself so you have like a tornado so you have two tornadoes they're orbiting each other their orbital angular momentum drags space into motion so you have two tornadoes embedded in a third larger tornado and you want to know what happens when they come crashing together when they're made from Warped space and time and not made from air and we don't know we don't know because we haven't been clever enough to solve Einstein's equations to figure it out we will figure it out through a combination of the observations of these collisions and supercomputer simulations they'll indicate in a moment now how far can LIGO see such black hole collisions well today with this present sensitivity you can see out about 250 million light years out to a distance where there are about 50,000 galaxies that distance there is predicted to be about one collision every 10 years but this is a very uncertain prediction it could be bigger it could be smaller but we have to be lucky in order to see black hole collisions with our current instruments a very exciting development in the last week or so has been a deduction from new observations of something called short gamma-ray bursts that although we might have not be lucky with seeing black holes that we could be lucky with something a different kind of a source two neutron stars spiraling together and crashing together or possibly a neutron star being torn apart by a black all new estimates for event rates for that just in the last week by a car and gallium who are a young astrophysicists here at Caltech and Derek Fox at penn state new number of three per year the first time we've had such an optimistic prediction for initial LIGO but I don't believe theorists capability of making these predictions even when they're guided as these are by observation and we will look out and we will see but we're all very excited about the fact that these these observations are now underway the search is underway in 2010 we will upgrade to advanced gravity wave detectors which can see 18 times farther through 300 million galaxies to a distance where the best estimates are a 1 blackhole collision per day and so this upgrade was really the instrument we wanted to build in the first place but it was much too big a leap to go from our 40 meter prototype here on the Caltech campus that was built originally by Stan Whitcomb and Ron driver to these big instruments with a very sophisticated advanced detector so we had to do it in two steps and we're now in the first step and then we will do the second step and do very rich science we're quite sure after the upgrade to interpret the observed gravitational waves we've got to compute compared with supercomputer simulations and so we have developed here at Caltech in collaboration with Cornell a project for simulation of extreme space times led by Leland blue mark she'll friends Pretorius I I'm sorry Lee Lyndon March she'll and Harold Pfeiffer I got the wrong person on here I apologize for Harold is in the audience Salta Kolski and Larry Kidder at Cornell and interestingly funded jointly by NSF NASA and the Sherman Fairchild Foundation we are now in an era where when you have an exciting new piece of science that you want to get done NSF and NASA are no longer nimble like they used to be and they can't move quickly in and provide funding at the level that's required to really pick off the great science and so the Sherman Fairchild foundation a private foundation has stepped in and provided the necessary funding to really bring this fully to fruition the best simulations to date by anyone in the world are by Franz Pretorius so who was a postdoc in the group and I this is just a picture of a simulation then of the warped time around a colliding two black holes that are orbiting each other and collide so with the black areas where time is slowed right to a halt that's the center of the black hole and these other regions are where time is flow is flowing more slowly these are this was the first successful simulation of a collision of two black holes the black holes go around each other a couple of times and collide and the calculated is stable and computes all the way to the end this was just done this past spring here at Caltech here is a picture of the gravitational waves produced in that collision again from the simulation you see the waves flowing out as the two black holes merge in a pattern much like the patterns spiral pattern of ways you would produce if you were to stir your finger in the water so we're just at the beginning of being able to do these kinds of simulations there's still a long way to go but these are going to be key to getting the science out of Lyell well in the last few minutes I want to move into some other aspects of warped space-time that are more speculative let me begin with the singularity of the center of a black hole general activity tells me that if I fall into the black hole the singularity will stretch me from head to foot squeeze me from the sides then stretch me from the sides and squeeze me from head to foot and do an axillary stretching and squeezing in a pattern that is chaotic in the technical sense of chaos and mathematics until I die and then it will stretch and squeeze the atoms of which my body are made until they are distorted beyond recognition and until all matter of which I made is completely destroyed in this singularity in other words the laws of physics as we know them break down in the singularity the singularity is the domain of the laws of quantum gravity and the best candidate for the laws of quantum gravity a new branch of theoretical physics is string theory or m-theory of aerion more modern variant of string theory we have here at Caltech a superb group working in string theory John Schwarz Hiroshi Oguri I'm Tom Kapusta and Sergey grew cough and pushing hard trying to understand understand the unification of general relativity with quantum theory in order to be able to discuss such things as singularities the center of a black hole is there any hope to ever do experimental studies of singularities well there's a bumper sticker that you sometimes see on cars it says the Big Bang is a naked singularity the Big Bang is a singularity that you can see it's not inside a black hole and indeed the Big Bang if we think of the universe as being like the surface of a balloon blowing up as it expands coming out of the singularity there also should have been gravitational waves and so I show the surfaces of the balloon with little bumps on at the gravitational waves and the holy grail of gravitational wave science is to probe the Big Bang singularity with the gravitational waves that came from the Big Bang and from the early inflationary era of the Big Bang gravitational waves are the only form of radiation that can travel unscathed through the matter of the hot primordial universe to today and bring us direct information about the Big Bang and so Andrew Lang by a technique involving the Cosmic Microwave Background polarization and his group is going after this holy grail at its next incarnation of gravity wave detectors on the earth and in space the regular gravity wave experimenters will be going after this holy grail and I expect it within the next twenty years or so we will be probing the very birth of the universe a tional ways but that's a time in the future and that singularity is very far away is there any hope to find or make and study singularities in the present day universe the establishment has an answer probably not and that's embodied in the cosmic censorship conjecture due to Roger Penrose a great physicist at Oxford University which says that all singularities except the big banger hidden inside black holes where you cannot see them unless you pay the ultimate price of going into the black hole to explore them the ultimate price that you can't publish your results so all all singularities then are closed by horizons is that what this conjecture says there are no naked singularities so John Prescott and Stephen Hawking and I made a bet about naked singularities back in 1991 on one of Hawking's many visits here to Caltech says where as Hawking firmly believes that naked singularities are in anathema Hawking is the defender of the establishment and should be prohibited by the gloss of classical physics press : Florin regard them as quantum gravitational objects that might exist unclothed by horizon for all the universe to see therefore we make a wager with Hawking put in some gobbledygook to protect his side of the bet the loser will reward the winner with clothing to cover the winners nakedness clothing is to be embroidered with a suitable concessionary message well this was the event here in Beckman auditorium at which Stephen Hawking conceded though not graciously this is the t-shirt he gave us embroidered with what he regarded as a suitable concessionary message really a challenge you may be a nature may be allowed to have naked singularities but nature absorbs them anyway now why did he concede because of supercomputer simulations numerical relativity solving Einstein's equations on supercomputers is really the wave of the future in understanding warped space-time supercomputer simulations in this case done by Matthew chopped ooook at the University of Texas in which he sent waves in these were actually something called scalar waves but another group a little later did it with gravitational waves let me talk about as gravitational waves so send gravitational waves in with almost enough energy in them to make a black hole but not quite right on the borderline between making a black hole and not and what happened in the super computer simulations was the wave came in waves came in they interacted with each other non linearly in space and time began to boil and froth a sort of an organized frothing creating right at the center ultimately a naked singularity with infinitesimally small mass that lived for an infinitesimally short period of time but enough to force Hawking to concede and so now the challenge is to find out whether or not naked singularities are allowed with big sizes long durations formed in generic situations and we have a new hot bet with Steven over that wormholes you can't talk about warp space-time without talking briefly about wormholes you all know about wormholes at least those of you watch TV or go to movies from the movie contact Star Trek Stargate and other science fiction shows basic idea is that we are here near Earth our universe and somehow in hyperspace wrapped around like that so that you can have a wormhole so-called it goes through hyperspace that will take us from Earth to the vicinity of a distant star in contact it was the star Vega you can travel through a distance that might just be a kilometer for example instead of going around 26 light years well together with a students with a student of mine Mike Morris I worked out the prediction that in order to hold a wormhole open you have to thread it with a material that has negative energy and so there has been a great considerable effort over the past 15 years since we figured that out to determine whether or not you can get together in principle if you're an arbitrarily advanced civilization enough negative energy to hold a wormhole open in practice so that you can go through it the answer is not yet in but things are looking more pessimistic than they did ten years ago and this is not our work here at Caltech about the time that we did this seminal work on wormholes LIGO got funded and we put everything behind us to focus our research groups effort on Lyle and let those at other institutions pursue the wormholes then there's the question of backward time travel and this is something that I've gone back and forth with Stephen Hawking on in nineteen ninety eight ninety I realized that if I have a wormhole and in principle it's easy to make a time machine with the wormhole I have my mouth of the wormhole here my wife Carol Lee has her mouth of the wormhole she goes out in a rocket ship at high speed around the universe and comes back and because of something called the twins paradox that I won't go into in detail it turns out that when she goes out and comes back it takes an hour as seen by her to go out and back but it takes say a couple of years is seen by me the bottom line because we're actually holding hands through the wormhole at the same time is that the wormhole gets converted into a time machine in such a way that if I go in this mouth and come out her mouth I go forward in time by two years if she goes in that mouth and comes back this mouth she goes back in time by two years I won't go into the details those of you who want to see the details of this and some of the other things I've talked about you can buy my book it's a little out of date 1994 but there's a discussion of this and these drawings are from it 1990 I did a calculation of the postdoc son one Kim which showed that something called vacuum fluctuations will always course through a time machine right at the moment that you try to activate it and may destroy the time machine time machines self-destruct when you activate them we look more closely at the strength of the explosion and then concluded that the explosion was too weak that the time machines would not be destroyed Stephen Hawking upon getting a preprint of our article before we had day the ink was hardly dry wrote a paper and submit it for publication saying we were completely wrong that the time machine would self construct and he proposed the ecology protection conjecture that Nature has a way to keep the universe safe for historians over that period there's been a growing consensus that only the laws of quantum gravity know for sure whether or not you can make a time machine and going back go back in time and so Stephen Hawking five years ago on my 60th birthday gave me as a birthday gift and his first attempt to estimate using the laws of quantum gravity the probability that a time machine can be created that is sufficiently big that I could go back in time through it and that probability he calculated quantum mechanically is one part in ten to the 60th I responded on his 60th birthday two years later with a promise that Lyell tests his black hole predictions for his 70th birthday and let me end up then just with a state a description of our extreme ignorant of warped space-time today in 2005 we don't know does a black hole have the precise shapes of warping that general relativity predicts we don't know for sure what happens when black holes collide what other objects made from warped space-time exist in our universe what about singularities what are their structures their behaviors the Big Bang singularity the singularity in the core of a black hole can wormholes exist and be made is it possible to travel backward in time the answers will come from gravitational wave observations numerical relativity simulations and the new laws of quantum gravity string or m-theory we're still exploring Einstein's legacy and we will continue to do so for many years to come thank you

Channel: caltech

Views: 178,017

Rating: 4.8678303 out of 5

Keywords: Caltech, science, technology, research, kip thorne, Albert Einstein (Academic), General Relativity (Field Of Study), Black Hole (Celestial Object Category), gravitational Waves, Universe, Physics (Field Of Study)

Id: JXaukctamdQ

Length: 74min 5sec (4445 seconds)

Published: Tue Dec 09 2014