 What I want to do is give you a little tour through I went, I looked for a photo of Thibault with your Niel André performing and I couldn't find one I could have given you an audio recording, but without the permission of the artists. I didn't think that would be appropriate Maybe at some other time But now let me give you a little bit tour about where we're going in the future We've heard in the previous few talks how the theory Led to and then from Alessandra a little snippet of the results from the LIGO and Virgo observations Where are we going in the future? I'm actually going to be a bit ambitious and stretch a bit beyond the just the interferometers on the ground and give you a more complete vision and so here is a plot of gravitation wave strain on the vertical Axis and frequency over an absolutely enormous range, of course from once per universe to once per millisecond And a variety of different techniques that are used to look in these different frequency domains now walk through them I think I'll have to note also that my knowledge also progresses from Negligible at these frequencies to rather deep at this range of frequencies And so you'll see a change in the way I present as I go forward But the first thing I want to talk about a bit is the the use of the cosmic microwave background As a probe for looking at primordial gravitational waves It clearly is the holy grail To be able to see the first moments of the universe via gravitational waves It's probably the only way we can get as early a glimpse as we would love to see And probably looking at the influence of those initial primordial gravitational waves on the cosmic microwave background Is the best handle that we have on it? We could imagine building a special purpose say space based detector Focused on a 0.1 Hertz frequency when there might be a minimum of Static from other gravitational wave sources where we may be able to actually see a A directly a cosmic microwave. I'm sorry A cosmic gravitational wave background, but for now, this is the best thing to look at and the measure of success that this This attempt uses is to look at the tensor to scalar ratio in the in the background looking effectively looking at the curl or the b B modes In the relation to the electric field modes And there was just a recent Paper on this from bicep kek w-map plonk Which put a somewhat better limit on the value of this tensor to scalar ratio of An r that ratio of 0.036 It's been inching down or sentimentering down as time goes by Here's a map actually of the b mode spectrum at the frequency 95 gigahertz Which has the least Foreground dust to distract that however it is a really big problem for this method of detection And of course there was one Confused notion that maybe something had been seen when in fact it was nothing but dust Here's the sad truth this ratio scales At least in some theory or another At the fourth power of the energy of the scale of inflation and so well To explore a broad range of energies is probably impossible because our scales so quickly Halfly it looks like some of the cherished theories can be reached even within the range that's feasible So where's the future on this particular? Approach to looking at gravitational waves. It's probably cmb s4 It's a ground-based cosmic microwave background experiment Consisting of 21 telescopes on some at the south pole and some in the Chilean at to comma desert Multiband detectors are used to be able to better remove that contamination from the galactic foregrounds It's a us thing with the department of energy in the nsf as the funding agencies It's going to be commissioned during this decade and then seven years of operations are planned through the 2030s And it should give about a 10 times improvement in sensitivity over as the best numbers to date Here's a plot of the tensor to scalar ratio r on the vertical axis over a range of spectral indices for different models of the Of this cosmic microwave background and you can see the the current models. That's right. The current measurements are up around 0.0 0.03 here and the cmb s4 targets to get down A factor of 10 or more The sensitivity that's planned ensures that a non detection of r would rule out leading inflationary models And motivate alternative models for the origin of the universe If in fact, um r is truly greater than 0.003 It's expected that a measurement could be made at five sigma. That would be convincing If nothing is seen, um, then it sets r down another factor of five or thereabouts So this is a very exciting Place to look Clearly there be I'd say perhaps nothing more revolutionary than seeing traces of this primordial gravitational wave background So I'm now going to move up in frequency. I've got another plot here of strain versus frequency Where I've trimmed off the cosmic microwave background And now we'll talk a bit about Using pulsar timing arrays to look at the frequency range from something like 10 to the minus 10 to 10 to the minus 6 hertz What's the basic notion? Well, first off the prime target is a stochastic background signal From cosmological sources. It's very unlikely that in those in this frequency range That a primordial background would dominate over a cosplay an astrophysical background It may also be possible to use this approach to see some super massive black hole binary inspirals as individual sources Will require some luck, but there may be some there And the technique is to observe well characterized millisecond pulsars. Here's here's one here It's radiating Radio waves due to its magnetic field it spun up due to the accretion that formed the neutron star That scene is a highly periodic signal by a radio telescope Using techniques to add signals together remove the dispersion You can come up with an extremely accurate measurement of the time arrival of the clock ticks here The thing is that as the gravitational wave passes The apparent distance between us and to that clock will change And that would lead to a shift in the arrival of the clock ticks that could be due to a passing gravitational wave It does require a search for and a very deep understanding of very stable pulsars Where are we going with this particular search? The most recent pulsar timing results are from nanograv's analysis Um, again, it's a us outfit that's leading. I hope I don't sound too nationalistic I'll be mostly talking about you as activities here They're recent analysis of 12.5 years of precision timing data from 47 pull out pulsars They see a strong evidence for Some kind of red noise process some color in the noise spectrum that seemed however, it's not correlated spatially Hellings and downs demonstrated that for a gravitation gravitational wave due to the quadrupole or form that you expect to see On the sky a distribution of correlation which is characteristic and that's not there yet So so far they could either be seeing the first bits of evidence of a true signal or they just may be looking at noisy pulsars They're already considering galaxy formation with the level of sensitivity there's antennas are They really every there are two pieces to this of course. There's understanding the pulsars Which is a may requires a lot of detailed understanding of the Of those strange objects But then there's also the need for a very good very sensitive radio telescopes distributed around the earth our SIBO was the really the prime source of data for nanograv And one can't say our SIBO without thinking of chibo, of course And the way that he used the data from that and the observations by holster and others to put really remarkable constraints on 30s of Reputivity and I'm sure we'll hear more about that as we go forward in this meeting Meanwhile back to pulsar timing arrays for gravitational waves We do have the new chinese radio antenna, which is coming online and looks like we'll share data Chime up in british columbia will also be a source ska will come online in a while The team's working on this think that they can see a factor of 10 improvement in the next 10 years This is some kind of graphical representation of that over This is years on the horizontal scale and and a measure of the amplitude sensitivity on the vertical scale And their notion is that they can push down by about a factor of 10 by 2030 And this team is the team's working on pulsar timing not only the us team, but the international pulsar timing array Folks in australia and michael kramer in in germany and in europe in general All believe they can pull together an international pulsar timing array analysis Which will make a detection in the coming years. My guess is that this will be the next method And domain that will show a gravitational wave signal So let's move up one more step in frequency From 10 to the minus 4 hertz to about zero point one hertz Um space-based interferometric measurements are the ones that look like the best approach So this notion of using space-based Inter interferometers as a means of detecting gravitational waves Dates from 1974, which is just a couple of years after ray wises groundbreaking Analysis that made it look like In 1972 that made it look like ground-based interferometry had some ghost of a chance of working Ray wise and peter bender were having dinner and In those days one used napkin technology as a way of noting what was Going to be planned And the basic notion is that as a gravitational wave passes this array of free-floating satellites For one phase of the gravitational wave this arm lengths would be stretched And these two would be slightly shrunken And of course the converse for the other half of the periodic gravitational wave And it's basically a timing measurement between test masses in space Where these test masses are explicitly isolated from external forces Not only by being very far from the earth and That bothers some planet planetoid the moon But also inside a shield a satellite which is slaved to follow the free-floating test mass Protecting it from solar wind and micrometeorites and so forth and so on One can take advantage of the vacuum in space to make very long arms The signal that we perceive a delta l a change in length Is proportional to the gravitational wave strain h times the length of the arms l In space one can imagine making arms of I say a million Or I'm sorry a billion meters million kilometers This can lead to for sensible gravitational wave signals when you could hope to see frequently A delta l is sometimes the minus 11 meters I notice that that's actually a much more generous motion than what the ground based interferometers have to deal with because of their much shorter arms There are other challenges in putting things up in space A triangular configuration is used This has a few advantages Some indifferences are taken around the loop in both directions all three arms all six links are instrumented That allows both polarizations of gravitational waves to be measured Provide signals to remove the laser frequency noise And generation also of a null stream for a test of Of the noise performance The earth trailing orbit Here demonstrated here's the sun This triangle cartwheels around the sun at one astronomical unit Making a scan of space and allowing long-lived sources to be looked at from various different perspectives Improving the ability to do localization The status of laser The projected science capabilities are truly breathtaking The mapping of for massive black holes by intermediate mass tiny Test particles understanding galaxy formation Unprecedented tests of general relativity Where our t-vose waveforms will have to be pushed to ever higher precision This is a snapshot from the proposal to isa for the lisa mission Which in tries to encapsulate the range of things that can be shown here I won't spend much time with it once again. It's strain versus frequency Here are the arcs of the path of several different scales of supermassive black holes Here are some sources which can be seen both in space and on the ground Here is a huge number of white dwarfs, which will form a static background, but which can be regressed out to some measure The key freefall technology of lisa was beautifully demonstrated by lisa pathfinder The telescope is the principal untested instrument of development element But we think we know how to build telescopes now 37 meters in diameter. It's modest There are lots of systems challenges But in fact, you know, it's not so easy to build three satellites with six Transponders and get them all into space and get them to work So a lot of it is pretty practical a matter of making the space mission go This is an isa l mission with broad european number of state participation. NASA is a junior partner The mission formulation review is underway. We're on track for a 2025 adoption A mid 2030s launch that start to observe in late 2030s With a four year Guaranteed mission and 10 year consumables. So this is something that I'm looking forward to I'm going to eat carefully and exercise to make sure I'm around for it when it's actually observing So let's move on to the last domain of frequency space from about Couple of hertz up to maybe a couple kilohertz or the ground based interferometric detectors are the ones that are the best choice There are three epochs relevant for this future discussion One is building out the network of current advanced detectors Then a full exploitation of the of the present observatories three and four kilometer observatories And then comes the next generation instruments in new observatories All he mentioned binary reach the neutron star is a couple of times as a way to indicate sensitivities Obviously, there's a wide range of gr astrophysics cosmology that can be explored. We'd love to see say cosmic strings um I mostly want to see things that Are guaranteed sources from the fact that they appear as in high signal to noise ratio in multiple detectors And for which there is no obvious Explanation that's what I really want to see but let me talk a bit about building out the network This is a pictorial representation of where the ground based detectors currently stand We have advanced ligo handford and livingston that came on around 2015 I had the pleasure to leave the project that led to these instruments. What a what a what a team What a nice result Advanced virgo came on a year later. They got started a couple of years later but quickly caught up and of course virgo and ligo have been observing together and Have shown that what really matters is the network individual detectors are cool You need a network if you want to do science Kagura, which is a very ambitious technically project in japan Has already observed although at a rather low sensitivity or poor sensory have to say And I think they still have a number of years to go Because they were ambitious about picking up some technologies that will certainly be useful for future detectors building underground Using cryogenics using a different wavelength of light using a different test mass material There are a lot of commissioning challenges to bring this instrument to its full astrophysical sensitivity Then there's ligo india when we built advanced ligo. We built actually three detectors and put one in boxes and ligo india is an india government funded project to build an infrastructure That can receive this third detector and when it is installed probably in the mid to late 2020s It will come online with the same configuration and we expect the same sensitivity as the ligo detectors And so by the end of this Decade we should have an incredibly broad and robust high sensitivity network of ground-based interferometers in the current observatories What can we do in a four kilometer infrastructure? Well ligo and virgo as I said will continue to interleave observing and improving the sensitivity Until the next generation detectors in place Maybe we can keep on observing if there's a good enough scientific reason and we can get enough money from The funding agencies to keep the infrastructure going Using ligo as an example in the near term just sort of 2028 We have a well-defined program leading to about a 20 times greater event rate That comes from about a 2.7 times better signal to noise ratio for a given event We get to cube this of course to know what the rate is because the volume of the Sphere with which we can reach gross is the cube This is a pictorial representation of the evolution of frequency Strain on the vertical axis frequency and the horizontal axis and now we're talking about audio frequencies Where we can see the progressions through the various observing runs already executed 0101 0203 And then heading into 04 which we expect to start about a year from now And with a somewhat better sensitivity than the previous run And then the ultimate sensitivity of the detectors which are currently installed in ligo and we expect to see in Ligo india comparable for virgo of something like if you reach to 330 make a par six for neutron star binaries On the longer term in the four kilometer infrastructure We can make a bit more progress. We're just starting to think about what's possible and what's practical It looks like improvements of about another factor of two insensitivity or eight in rate will be feasible This is a little map of doing some modeling the current a plus that's installed We can see probably to about 340 mega par six for binary neutron stars when it's fully commissioned That is by the way for binary black holes a greater reach of about 2.5 pick a par six A plus plus which we Think we know how to build that would not be too ambitious We'd be given my mild increase we can either change the Kind of coatings that we use or perhaps install some mild cryogenics and get even further out So there's still some future in the current observatories And one which we hope will bridge to beyond the four kilometer infrastructure Just want to show a sky map with that five detector array and the kinds of sensitivities We expect to have toward the end of this Um this decade we can expect to see better than Square 10 square degrees of localization over most all of the sky It will be great for doing multi messenger astrophysics So what's after that next generation observatories is something that's gotten A great deal of work over the last decade and is now starting to take on an aura of reality First, let me say a bit about the european concept the einstein telescope There's been a significant study design under study design study undertaken for both facilities and instruments Underground construction is proposed to reduce the newtonian background Of course, we can do a good job with engineering of reducing the stray forces Which are applied mechanically to the test masses But the time-varying newtonian attraction of the test mass due to the fact that the density of material around the test mass Is changing from seismic waves or from people walking nearby Is is a very difficult and in fact ultimately irreducible limit to how low in frequency one can go on the ground If you go underground That seismic noise is reduced and it reduces that newtonian background It's also nice because if it's underground it doesn't keep the cows from roaming on the surface of the of the earth in europe It a triangular format is proposed which is shown in this really fantastic Rendering here of about a 10 kilometer long arm this triangular system allows again multiple instruments in a xylophone configuration To look at different frequency ranges Because of the three interferometers one localized at each one of the corners here And one site polarization is possible polarization measurement is possible It's also designed to accommodate a range of topologies for future growth There's really big news that took place this summer It was this was placed on the european How what in the world does this stand for it's it is a roadmap of the research? infrastructures of the largest scale in europe and this project was placed on that roadmap which gives it a high likelihood Of funding in the long term. That's a really wonderful thing I can't help but show this computer generator rendering of what the underground facility might look like And I you have to realize the size scale here. I don't know if you can make out on your screen this human It's an absolutely enormous Magnificent cavern that will be dug to house the detector In the u.s. There's also a concept for a next generation detector This approach is actually more brute force Make it more american The notion is to make advanced LIGO some 10 times longer And that will lead to a 10 times greater sensitivity thermal noise radiation pressure seismic noise newtonian noise background are all unchanged as forces on the test mass But the signal grows with length once again l larger l leads to a larger delta l And this is the measurable for us in our interferometry That's true, of course up to the point where the wavelengths are shorter than the arms. Half wavelength is the optimal And you could note that a 20 kilometer long antenna is ideal For looking at the neutron star neutron star tidal signal detection, which would happen at a few kilohertz This gives you a sense of the scale that we're talking about Here's a sketch of the four kilometer LIGO facility and that's what it looks like against the 40 kilometer arms of the cosmic explorer concept In fact, cosmic explorer consists of two sites 40 kilometers and 20 kilometers. It's on the earth's surface We look for something which is truly flat, which we would call a bowl But there was still to be some earth moving involved 40 kilometers is ideal for that reaching the maximum distance to increase the reach of To a larger and larger black hole and black hole distances This concept offers sensitivity without new measurement challenges We can start it from temperature, modest laser power and so forth and so on That's a recently completed cosmic explorer horizon study which brings together and Refines a lot of the ideas for this concept I would say that the the group in the us is eager to catch up with Einstein telescope, which is clearly much more Refined and also further along in identifying a path to funding. Here's A notion of what the corner station might look like with the tubes hitting off into the horizon So what can you do with these new instruments? One more time here is a plot of strain noise versus frequency over sort of a few hertz up to a few kilohertz For the present LIGO and Virgo sensitivities are up here somewhere The best that we can do in the four kilometer and three kilometer installations of LIGO and Virgo were sketched out here And then these next generation instruments with their longer baselines allow this very significant roughly factor of 10 step Forward in terms of the sensitivities that can be achieved A different and probably more informative way of looking at the sensitivity of these detectors Is given in looking at a plot of redshift Versus total source frame mass where again the current detectors are down here you can see these new detectors can reach out to the Almost inconceivable notion of a redshift of 100 This donut plot gives a visual representation of that. I won't talk through it in detail, but for both binary black holes And for neutron stars It's expected that these next generation observatories cosmic explorer and Einstein telescope should be able to see To the edge of the population of those of the binaries that could be formed from those objects When could this new wave of ground instruments come into play looks like 15 years is about what it takes based on LIGO and virgo experience If the funding holds up Einstein telescope could be observing in the early 2030s and cosmic explorer in the mid 2030s We should hope and strive and plan to have the great instruments ready to catch the end phase of binary scene in lisa It looks like the timing is not impossible What's crucial for all these endeavors is to grow the scientific community planned on exploiting these instruments far beyond general relativity and gravitational wave affectionati and This is because the costs are like the giant telescopes on the ground billions of accounting units So my last page They're wonderful gravitational. We've signed opportunities within the reach of technology Let's hope and conspire to cause our funding agencies to to support these initiatives And then I didn't say an awful lot about debo's contributions because others will certainly But I do want to say thanks to debo for contributing in so many ways This is the two of us in casual attire at a dinner event that we had the pleasure to attend up in stock home Maybe we'll have other reasons to get up there and put on a tuxedo Thank you very much What are the prospects of observing at still higher frequency a few kilohertz five kilohertz With a detector which will be tuned To observe the merger and post merger of two neutron stars because there is a lot of physics Associated with the nuclear matter inside neutron stars and to be compared with gamma rebirth model and and so on Hmm. Yes, it's it's a challenge It certainly is a challenge for the interferometric detectors as they're currently made to have a very high sensitivity up with those high frequencies And there are a few approaches that are being studied Simply increasing the laser power very significantly Even if one's doing a good job of using prepared states of light squeezing and so forth That creates noise at low frequencies, but it can increase the sensitivity at high frequencies If we can manage the technical limitations due to absorption in the test mass substrates and coatings Also, there's the question of the dynamics of the test mass of the the photon pressure is really formidable once you get up to megawatts of power But between those approaches and also using Detuned interferometers that concentrate their sensitivity there. We think that with these New interferometers these long baseline interferometers and the kinds of technology we'll have in the mid 30s We have a good chance where we to see for instance another neutron star neutron star binary at the same distance of the very well-studied gw Binary neutron star that we saw in 2017 It should be possible for us to study in detail that Coalescence and be able to extract from it parameters about the the neutron star material Perhaps others will say more about that in later in the in the meeting But we think we have technologies that we can develop to the point where we can make that measurement Thank you. Other questions No, uh jump here Hi, David Oh, I would like to make a prediction that I won't be around to to verify, but I bet That the cosmic explorer will be observing 10 years before the Iceland telescope I hope I hope and pray that is not the case I hope they both Exceed our expectations for when they come online and I think what one of the things that the ground-based Instrument building community needs to do is make sure that we work as a team So that we get these new detectors online as quickly as we possibly can and have the proper network Like I I'll bet against you, but we can make a dollar bet or a euro bet if you prefer David, the reason is very simple as usual americans choose something simple And europeans have something so complicated. It will never work like it's We see I want I want you to be proven wrong Okay, there is one more question coping back to To the question about to the binary Certainly now we know many binary neutron stars will set them And and the observation in that again in the jet that they give mass And a lot of details of this system I wonder what the complementary information Could be Because we already have a lot of data Well, I think that it's clear that there there are things that happen You can read out the response to the tidal forces in the gravitational wave And I think it's very likely that the data that can be a change from that Is orthogonal to that which can be seen from the electromagnetic radiation And the two can be put together in a synergistic way to build a more complete model Of nuclear matter in those very extreme circumstances But now we're getting well beyond what I call my My my expertise and I'm sure others in the audience over coffee can give you a richer answer to your question Indeed, I think this is a very good point to stop and to thank David