 Grazie. No, effettivamente noi in comunità scientifica qualche problema con i nomi ce l'abbiamo, ma non soltanto per la morte termica o il gas di genere. Quando abbiamo costruito un telescopio molto grande in Cile per esempio costituito da quattro telescopi ciascuno con uno specchio primario di otto metri, l'abbiamo chiamato con un acronimo inglese che è VLT. T sta per telescopio, VL sta per veri, molto grande, abbiamo costruito un telescopio molto grande l'abbiamo chiamato telescopione, va bene? Va bene. Secondo la teoria della relatività del generale di Einstein noi siamo immersi in uno spaziotempo. Bene questo spaziotempo non è rigido, è deformabile. Che cosa lo può deformare? Una massa dell'energia che lo percorre, che lo attraversa. Ed essendo deformabile in certe condizioni le deformazioni possono propagarsi. Queste sono le onde gravitazionali. Bene io conosco gente che non ha mai creduto che le onde gravitazionali potessero essere rivelate. Abbiamo l'onore, il privilegio, il piacere di ospitare invece qui una persona che ha pensato che non soltanto si potessero a rivelare le onde gravitazionali ma ha convinto una comunità intera insieme ad altri colleghi naturalmente a costruire uno strumento gli strumenti per farlo. Abbiamo con noi Ray Weiss, premio Nobel per la fisica nel 2017 per il contributo per il contributo fondamentale alla costruzione di LIGO e per aver rivelato le onde gravitazionali. In mio piccolo parco con te, spero che potessi mostrare un esempio molto bello di un astronome multimessager che è stato passato a tutti noi un anno fa, un po' di anni fa, un po' di anni fa, e ci chiederò in il medio del mio parco. Però prima voglio dire un po' motivare cosa è la gravitazionale, cosa è la gravitazionale, l'astronome e cosa è la gravitazionale. Perciò, torniamo immediatamente e vediamo se questa persona, vediamo se il mio pointero funziona, andiamo a provare. Ah, buono, ha funzionato. Ma comunque, l'ultima gravitazionale che mostri di noi sapevano viene da quello che abbiamo imparato nella scuola in, probabilmente, i corsi di colleggio su la gravitazionale di Newton. E la gravitazionale di Newton è un'esponenza wonderfule di quello che è andato all'earth, sembra anche andare in i tempi. È una sintesis meravigliosa che è stata creata, e ha avuto un po' di storico e, in realtà, anche delle esperienze religiei. Ma Einstein, dopo l'anno, ha un po' di complesso con l'utilizzazione di Newton in fisica, per esplorare certe cose in gravitazionale, e due di loro, l'un di loro è che non ha lavorato per molto, molto velocità, quando le cose vengono velocemente, e non ha una funzione di notte, in modo inoltre, una cosa che ha avuto informazione che era in modo più rapido di la velocità di lucia. Inoltre, per esempio, in Newton, come interpretato dopo, da persone che hanno fatto Newton, probabilmente non come intelligente come Newton, è che se avete l'earth, e ti plugga l'earth, cioè, avete l'earth, e ti plugga l'earth, l'earth away da l'earth, è una cosa di 9 minuti per te per sapere. Ora, se calcolate in Newton's theory, cosa succede quando hai l'orbito di l'earth all'interno di l'earth, in Newton's theory, molti persone avrebbero interpretato che se ti plugga l'earth away, immediatamente l'earth avrebbe avuto un tangente, e questo non può essere vero, perché ha di prendere almeno 9 minuti, anche in gravitazione, per l'earth, per sapere che l'earth non è più l'earth. E questo è l'inizio di qualunque gravitazione è. Ora, Einstein, in 1916, ha scritto un paese, dopo che ha sviluppato l'earth in general, che ha replicato Newton's theory per avere una relazione tra la geometria e la geometria di spazio, e il modo in cui il tempo è mescolato, tanto il spazio e il tempo, come si è mescolato. Ora, in la nuova teoria che Einstein ha fatto relato con la distribuzione della mattera e dell'energia in il universo. In other words, in Einstein's theory, non è più una gravitazione forza, almeno nel modo in cui ha interpretato, e c'è una distorsione di spazio e una distorsione del tempo due alla distribuzione massima. E ora voglio mostrare il modo in cui il gravitazione è così, quindi potete avere un'immagine di come lo detecta e come diventa qualcosa che è utile. Ora, su la strada, e vi faccio pulire un altro punto, ho un altro problema che ho bisogno di qui, è che spero che puoi vedere questo. Se non puoi, puoi potere vedere il verde se puoi dire sì se puoi vedere? Ah, è meraviglioso, buono. Siamo rischiati di questo. Allora, quindi, per esempio, i sources di gravitazione sono massi accelerati, muchi come nell'electricità e il magnetismo, i sources di gravi electromagnetiche sono accelerati. I certi classi di moti sono gravitati, sono non sferici e simetrici. In other words, cose che smasciano a un altro, sono gravitazioni, o cose che guadano su un altro, sono gravitazioni. Ma cose che spasciano uniformemente, sferici e simetrici, non sono gravitazioni. E' qualcosa di che Einstein ha scoperto nel suo primo paese, nel 1916, e poi lo ha fixato nel 1918. Ma nel suo primo paese ha anche detto che gravitazioni sono kinematici. In other words, hanno propagato la velocità di litro, che è quello che ha ipothesizzato. E come vedete in circa 5 o 10 minuti, noi now know that exquisitely well that indeed they propagate at the speed of light. The other kind of, the other attribute of the wave is that they are waves very much like water waves on a pond. A water wave travels in, let's say, that direction, but the excitation of the height of the water is perpendicular to the direction in which the wave is traveling. It's called a transverse wave. And that's also true of electromagnetic waves. And now I want to show you what it actually does. Now let's see if this animation works. If I hit this, let's see, ah, good, wonderful. What you're looking at is a gravitation wave that's coming out at you. You're standing right there where that red little mark is. And this is a distribution of matter that's been put out in space and the gravitation wave, as I say, is coming to you. Now you'll notice two things in that pattern right away. You'll notice that when there is an expansion of space, let's say in this direction, the east-west direction, there's a contraction of space in a north-south direction and that keeps flipping back and forth. I hope you see that. That's very important in the detection. There's some space get stretched in one dimension and compressed in the other perpendicular direction in which the wave is traveling. The other thing you'll notice is something as important and that is that the two dots, let's say next to you, here you are again, this dot and that dot, they don't move very much. But look at the dots that are very far away from you. That one and that one, they're moving an awful lot. And that's true in the other direction as well. And that is a motion that's very much like you would make if you made a rubber band with a friend of yours, you take a rubber band and put marks on it and pull it. And as you pull the rubber band and look at the way the marks are, you'll see that that is very much exactly that motion in one dimension. It's given and expressed by the idea that it's a strain in that space and a strain is a change in the position. Let's say the change of this point with respect to that point, how much they change, but divided by their separation. So the change in position divided by their separation is a constant, at any one instant in one dimension in this picture. And that's the way you want to look at a gravitational wave. The reason why I make a big fuss about this is the instrument I'm going to quickly tell you about very shortly is an instrument that actually measures the motion of those dots and compares a motion going in this dimension and with one that goes in that dimension by using light and timing light as it leaves from here goes out and comes back again and then it does the same thing going in this direction and the time will change. The time by the light spends in those two paths changes because of the gravitational wave. When that's standing still they don't get changed. And so here is the guy who actually told us how difficult this all would be. This is Kip Thorne at a younger age when he was probably in his 40s and he had a fancy symbol I don't know what that is. Many of you might know what that is. By the way, he said look if you're ever going to succeed with measuring gravitational waves you're going to have to measure h which is this thing I just told you about that's the strain which is the change in length divided by the length you're going to have to be able to measure things that are smaller than 10 to the minus 21. Now that's a terribly small number and many engineers who would look at that number if you brought them the idea that you should measure such a small amount of things they would ask you what you've been smoking. Okay, but let's translate it into what actually had to be done. Namely we built instruments and there are now instruments I'll show you where they all are. The ones in the United States are four kilometers the ones in Italy are three kilometers the ones in Japan are three kilometers but anyway of order four kilometers the change in length that you have to measure if you want to satisfy Kipp's condition is you have to measure a motion that's 10 to the minus 18 meters big and let me give you a feel for that that's one thousandth the size of the nucleus of an atom I mean it's just infinitesimal and that's when the engineers really will throw you out the door okay they'll understand that right away and now let's the challenge then that Kipp threw at the experimenters was that if you want to measure a gravitational wave if you want to use light to do it you're going to have to measure 10 to the minus 12 of the wavelength of light to get a meaningful result that's 10 to the 12 times smaller than the wavelength of the light that you're using and that turns out to be the easier of the two problems the other problem is you're going to have to also make measurements in an earth that's wiggling right here in this room the earth is shaking by about 10 to the minus 6 meters everywhere in the world is shaking by that there's not no place that is shaking less than that and so consequently you're going to have to get to 10 to the minus 18 isolate the motion of whatever you're going to look at to 10 to the minus 12 of the motion of the earth and that's the real tall order okay so this is Kipp's statement of how hard it was going to be and here is I won't walk you through this diagram completely but I do want to walk you through it a little bit so you will understand the nature of what was done okay and um the so now to relate that picture with the dots this device right there which we call the beam splitter which will be a source which will break light from this laser break it up so half the light goes to that mirror and the other half the light goes to that mirror so this will be that place where I put the red square that's where you're going to be standing and these are the distant points that are those most distant dots this in the y direction that in the x direction and down comes the gravitational wave now before the gravitational wave comes along you have arranged something very interesting here let's not worry about these three mirrors that that's something we'll talk or these four mirrors these four mirrors are all needed to trick it up so that you can get this very high sensitivity on the other hand what you have now is you're going to make it so that the light spends equal time in this from here to there and from here to there and when that is the case no light goes to the photo detector none and when the gravitation wave comes down and disturbs us by pulling this guy in a little bit and pushing that guy out a little bit that puts light at the photo detector and that is the basis of the detection of LIGO all these other mirrors which I'm not going to describe you can ask me about them in the questions later are to enhance the ability to do that but the basic idea is to use the laser light split at the beam splitter have it go down to that mirror spend time in here have it go through that mirror spend time in there and then come back to the detector and if you see light at the detector that means something has disturbed the system so that's the way it works I wish I could spend more time on that with you but maybe if you want to ask me questions we can we can go a little better so here are now the detectors that are around the world that are built on this principle there are two in the united states one is in the northwest corner of the united states there's another one in the southeast that's in louisiana that's in washington state and then there are detectors in europe there's a research detector in hanover germany which is about 600 meters long these are both four kilometers long then there's a detector in kashina which is very close to pisa which is three kilometers long it's probably of all the sites the prettiest one of all the sites and then there is a detector that has just been built and is being commissioned now in the mountain the same mountain that you heard was in which the neutrinos were detected this is now in the it's called kagra and it's in that same mountain and they're gonna try some new ideas there especially cold things and being inside of a mountain which might help a lot and then there's a detector being planned in india which is very much based on the american detectors so those are the number of detectors and now the story I'm gonna tell at for the moment is mostly associated with these two detectors because they made the initial discovery but I do want to say a good bit about Virgo because they have made an enormous contribution also so let's start by showing you what we detected what we detected back in about September of 2015 on a morning early morning was this we saw this signal this is the strain and here is a number that is like kip's number 10 to the minus 21 and this is the signal we'll get to that here is time this is time about 0.2 seconds is from here to there and here is the signal in Livingston that's in the south of the United States this is the north of the United States northwest and you'll see this is junk this is absolute noise and if something begins to emerge out of the signal and it becomes coherent and it gets bigger and bigger and then this is junk again unfortunately those two regions are junk say a very similar thing happens in Hanford in Pacific Northwest this is junk and again something emerges out of the junk and you wind up again with junk at the end and now you can superpose these two and you get what made us somewhat confident that we detected something very interesting because now what has been done we've taken the two signals and we delayed the signal from from Hanford by we made it no we delayed the signal from Louisiana by seven thousandth of a second so we could put the two signals on top of each other and now they're on top of each other this is junk but now you can see both signals they're not perfect there's noise they look like they have very similar signals and this is junk again this is the first discovery of gravitational waves and it was interpreted by well before I say interpreted that's the next slide but at first I want to say we there's another way to think about it because it's important for you to understand this second way of thinking about it and that is that this is now expressing the same thing in in time again and here is that same time series as you saw before this is southern this is the western united states but on top of that now the axis is the frequency of the of the light in here and now you plot this is plotted the brighter this is the more of that frequency is in this signal so for example right here 256 is middle c on the piano and here is middle c on the piano in this same and you can see something quite similar in these two things they're not perfectly the same and what if you could hear this it would go like that that's all you'd hear nothing very long be a little chirp but very very short one and what did we interpret that to be is actually this picture this picture and now this has a story associated with this picture although the experimental development was very profound to get to the point where we could measure 10 to the minus 21 the thing is there was another development that was just as important which was the ability to solve the Einstein equations by computer that's called numerical relativity and it turns out the experimenter development of these instruments was about parallel with the people learning how to program computers to do the Einstein equations so it turns out here is the Einstein solution of a thing which is two black holes about 30 solar mass black holes going around each other at a distance from the earth of about a billion light years 10 to the 9 light years away and here is the waveform that's made we begin to see it out in here and here at the end point the two black holes have gotten close enough so they smash into each other and they make a new black hole and this then is a waveform which matches the signal the best and this comes from numerical relativity as well as also analytic calculations down in here and so one of the g whiz things about this is this curve right there which shows you the vola this is now the time of the collision and this tells you the velocity of the the relative velocity between the two black holes as a function of time and in units of the velocity of light so when they crash into each other these two objects which are bigger than our sun are moving very close to the velocity of light it's sort of unbelievable when you get to this the magnitude of what's going on in this collision and that was our first experience and what happened is none of us really believed it it was too big we didn't really expect it and luckily there were others and this is what later I mean this is the event we this is the event we've been talking about this is again 10 to minus 21 up in here and this is the event we just been talking about there's another event and you can identify when they were this was in September of 14th of 2015 and in October 12th of 15 we had another event we were not so sure of but then by Christmas of that year this is November this is December 26th the day after Christmas in the United States they celebrate on the 25th you had a signal that we all believed again and now over here are the parameters of these signals for example the first one had masses of 36 and 29 solar masses in those individual black holes and three solar masses were thrown out into gravitational waves at that moment that collision for the very time it lasted that point two seconds in which it lasted it was brighter than the entire universe which is sort of amazing brighter in terms of the energy per unit time that was being emitted so that was an enormously powerful thing and then you can see this for other ones we've seen now different masses and the different amounts of radiation that went away and we've now seen something like 10 of these and there's so it's not that it's ordinary it's still pretty spectacular but there's one that is really very profound and very important to the whole field and here is where one begins to get a feeling for multi-messenger astronomy because an event that we saw in October 14th of 2017 was seen not only by the United States detector but was also seen by the Virgo detector and the Virgo and that made a profound difference in a place that we hadn't been paying enough attention to or we couldn't do much with and that's shown in this picture right here this picture shows you sort of a sky map where in the sky was this kind where did this black hole collision take place it still took place 10 to the nine years ago but still we could not determine where it is better with LIGO alone with this sort of banana-shaped thing right here and then when we found that you could add now the fact that Virgo also saw it and look at the timing differences between Virgo and the United States detectors you could make a much smaller error bar right in here you could this was about a thousand square degrees in the sky of uncertainty this had now come down to the size of about 30 square degrees now that's still for most astronomers a terribly big unknown ma è una grande scelta avanti e vedete in la prossima cosa che parliamo è stato profondo e fondamentale che Virgo era sull'errore quindi questa è la prima deteczione con tre detectori e ha fatto l'obbilità di vedere la sorsa dove era in il cielo sempre così meglio e nessuno ancora che ha avuto un telescopo ha avuto in alcuni di questi per esempio persone avuto in questo erroro bar in qui e non avevano visto niente ora magari non deve essere niente visto da black holes colliding io spero in futuro magari ci vedremo qualcosa da black holes colliding e magari ci vedremo qualcosa per esempio da qualcosa di cui mi sono andato a raccogliere la prossima che è, credo, uno dei più spettacoli cose che hanno avuto in tua vita certamente in mine ma ora è ora che vedete un po' di cosa come interpretare questi signoli questo è il tempo e questo è la frequenza di la gravitazione e ora guarda questo questo è per 10 secondi tra qui e lì e c'è un signolo che fa molto, molto tempo e avventually it goes off the chart we can't see it anymore and it goes from like that like that that's what it does I wish I could play it for you but I can't and so now here is what happens it was also seen in a gamma ray telescope that was on a satellite the Fermi satellite and here's where we thought the collision happened right there and the gamma ray telescope saw a gamma ray burst about 1.7 seconds later there it is and another instrument on the same satellite saw the same thing and then a completely different satellite with another instrument also saw this so now all of a sudden we had an electromagnetic counterpart to the gravitational wave signal and now we know what that is we believe it to be two neutron stars that have collided and I'll get to that in a minute a little more but first I want to show you the importance of Virgo and LIGO together and what happened here here's again a picture of the sky and this picture of the sky has the uncertainties from here's the bananas from LIGO alone that's banana and that banana and here is the uncertainty of and it's very interesting story here and you should have people Virgo tell you this story they did not see anything that's sort of but there is a circle of zero where you can't detect gravitational waves that there's a certain pattern of the antenna pattern of such a detector that's a big L and it turns out what we guessed and they guessed too is that they should have been sensitive enough to see it and it must have thereby been in that zone of silence and knowing that you could make a circle now for where this source was now adding Virgo's non detection which should have been there because we knew they were sensitive enough in here that spot was identified right in there someplace somewhere in there and here is sort of the uncertainty of the Fermi satellite and it was much bigger than the uncertainty from the gravitational waves that was enough information to have a whole bunch of telescopes start looking at it and one of the most important ones was a telescope in the southern hemisphere that 20 days had before this event had taken a picture of a galaxy either the galaxy's name is important to some people I don't understand it that's okay and here is this galaxy and then here are stars in our own galaxy and there you can see the three stars and then you look up about some number of hours 10 hours after we made announcement that Virgo and Lego had seen this lo and behold they're the same stars here's that same galaxy and now there is a hot spot right there and that made all the difference and people looked at that hot spot and they found out a lot of information a tremendous amount of information again and this is the example what I must say where multi-messenger astronomy became a powerful tool because every element of that message came from different places and all of it when put together made a much better understanding of what was actually being found and so here's the thing that is the model for what was being seen here are two neutron stars by the way I didn't explain neutron stars to you neutron stars are stars that are about the mass of the sun but they're only about the size of a city like Bologna I mean imagine something they are enormously dense they have a density of 10 to the 14 grams per centimeter cubed at least maybe a little more than that you couldn't put teaspoon into it and measure its weight you couldn't lift it you couldn't lift the teaspoon just out of question so here these two neutron stars they have collided they're about to make a new black hole but before they do that they emit a gamma ray burst at an angle and on top of that they have this huge mess of nuclear material that's all around them and they make something called a kilonova and that kilonova is a place where a lot of things were discovered people watched this kilonova for a while with telescopes for a couple of weeks they watched it they watched it decay sent people with radio telescopes saw a jet form so they knew that was a black hole and then people gamma ray telescopes again x-ray telescopes excuse me saw the same thing so the whole evolution of that picture was sort of seen but here's sort of an interesting one and this is something people ought to know just because it's a standard piece of chemistry but this is the periodic table and the periodic table which you probably learned in chemistry or maybe you've learned in high school in grade school maybe in the United States kids learned about this in high school so they have a color code which you don't normally see on a periodic table everything that's blue was made in the big explosion that made the universe and everything green and yellow was made subsequently in stars and you'll see stuff that is purple in here and that was made in merging neutron stars and now you'll notice something interesting the things that were made in the initial explosion where we know about is hydrogen and helium that's the two things we know about but then most of the rest of the stuff all the stuff a little bit of lithium but most of the stuff we're made of and interesting stuff is all made in the stars and then thrown out in supernova as you heard before in the other lecture but people did not have a good concept how you made the things heavier than iron and here for example some favorite things that men adore you know gold and platinum seem to be all of it well at least we think right now much of it maybe not maybe all of it is made in neutron star explosion and that's where the density of neutrons would be high enough to do this so that's one discovery I think I'm gonna go over this the hell with this one and I wanna go to the where we're gonna wind up and this is actually so you can imagine where will gravitational wave astronomy be at the time when the K'sharankov telescope array is actually operating so this is a picture which is a little more subtle it's ready for the experts but I'll just quickly tell you the better the detector is the better you go down in this the more sensitive it is the more you go down here is the frequency of the signal you might be looking at and here is here is here is a 1 kilohertz here is 100 hertz middle C is right about there and you can see that here is for example with the current state of Virgo and it's making detections right now as is LIGO but it's up in here and they're getting better here is where LIGO was in 2017 where we made all these discoveries and we worked very very hard in the last two years to try to make an improvement and here is where we are now on LIGO but we made no improvement at low frequencies and we made some improvement here by using techniques which I'll go into in a lecture tomorrow here is the design sensitivity for LIGO it's below that's where it's supposed to be and we're not there yet and here is something we have planned for the future in about middle 20s of this next decade called LIGO plus and Virgo has a plan for Virgo plus and down in here way below this is now a huge factor down it's a factor almost 10 down are two ideas that are both emergent in Italy and in France as well as in the United States and that is to make a gravitational wave detector that it's not 4 kilometers long but 40 kilometers long and those are the curves for this and I'll show you some of the things that would come from having made such a detector and this is a very pretty little picture that shows this this is a picture which shows you the redshift is a radial distance so for example a redshift of 1 is about there 10 over here 100 over there and this picture over here are all the black holes that we believe are in the universe they end right about at a redshift of about 10 we think we're not sure of that but here are the detectors here's A plus this is the best we can do now we get some of them but if you go to A plus which is that which is being done both by Virgo and by Blago you would get right into the middle of this distribution of black holes but if you build these 40 kilometer things you're way outside you will have detected all the black hole binaries in the universe that's spectacular and over here are the neutron stars the things that made all the fuss just recently and again here you have to build a little better you have to go even better than the first cosmic explorer which is the 40 kilometer you have to do the very best we can to get all the black all the neutron stars that's a very pretty picture to show what the future might have and here is the last slide and this is sort of a give you feeling of where the field is right now and what we've been talking about is this is all let me tell you what this is first this is frequency of gravitational waves this way here for example is 10 kilohertz there's 1 hertz here is 10 to the minus 4 hertz so you can do it up here with time minutes, hours, years, age of the universe all the way over here so this is time going older and older this is frequency getting smaller and smaller and here is strain so for example here's what we've been talking about and these are the sources you know a little about now there's another project which is a space project called lisa which is the laser interferometer space antenna which has sort of sensitivity from hours to minutes and it will look at the black holes like the one in the middle of our galaxy a million mass black hole things falling into it it will also look at white dwarf stars going around each other and it's a very completely different frequency this is a short wavelength these are much longer wavelengths then there's another project going on right now which is using pulsars in our own galaxy to measure gravitational waves that are coming through our galaxy and for example the measurement consists of looking at all the pulsars in the northern sky and all the pulsars in the southern sky and if you notice that all the ones in the northern sky and the southern sky have speeded up a little bit in their pulsing and the ones in the east and west have slowed down in their pulsing you may have detected a gravitational wave of a very long period that's coming through our own galaxy and they're looking like that with radio telescopes and that hasn't yet succeeded but it's a very nice experiment and then this experiment is probably the most dramatic of all this is an experiment that thought they had a result about three four years ago they were looking at attributes of the big explosion that made the universe and the electromagnetic radiation come from that very early days and people were looking at the way the electric fields point in that radiation and there would be patterns in the way the electric field go points namely the polarization of those waves which would look like little spirals and that if they have that pattern or more what are the things that people when they blow on them they turn I can't get the word right now for a thing that kids blow into and they spin spinning wheels okay never mind anyway that pattern would be seen in these and they thought they had seen this pattern and they and what would that pattern be due to it would be due to primordial gravitational waves that were made very very long ago way before anything was any matter was created way before any stars were made and hopefully we might some day see that it coming from the origin the very moment the universe was created now these people thought they saw this about two three years ago and unfortunately what they were seeing is the polarization by dust in our own galaxy but they're still working on it and I hope they see something so thank you