The Future of Gravitational Wave Astronomy

even from earliest times humans stood and looked up and saw the weight from the stars so the you know air list human civilizations looked up and saw the heavens but through all that time the universe has been sending us a completely different set of signals it's been sending us some vibrations and for the first timing of instruments to pick those up and they bring with them entirely different messages about what's out there these other messengers are gravitational waves ripples in the fabric of space-time predicted by Einstein's theory of relativity and spectacularly confirmed by LIGO the laser interferometer gravitational-wave Observatory LIGO works by detecting subatomic sized changes in laser beam arm lengths in four kilometer long detectors Legos already made several remarkable discoveries which resulted in the Nobel Prize in Physics only two years after its first discovery but this is only the beginning ambitious plans are afoot to build new detectors that could find gravitational waves from far further into the cosmos and all the way back to the Big Bang itself I was sitting in a little cabin in Maine which I rent and buy the computer and I see a funny statement on one of the one of the sites there are logs that are kept by the sites there's a site as you know in Hanford is a site in Louisiana and I was looking at the Louisiana site because that's where I gone and it said fix it day is not going to happen what is fix it day fix today's the day we have one day a week when we shut down everything both at both sides and we fix those things I gone broke over the week so I I said huh why would they shut down fix it day so always everything you know it's always on a on a Tuesday and I go to the Hanford log and I find exactly the same thing there we're not going to have fix-it day and then I got an email and the email says go to this site take a look what you see there and I saw this waveform that now is famous okay I look at it it's much too big absolutely never expected that we would see something that big so I figured it was a false injection now let me explain that to you during our prior runs what we did to test the entire system that's both the instrument and the people well we had a secret group that would inject signals into the two detectors simultaneously of some waveform that as could have come from Astrophysical sources and this was to see if they instrument which you know as injected into the at mirada's someplace to move the mirror a little bit and he's got and and so I said yes obviously a you know when he's false signals that was put in the testicle and that's nice in yeah and then I then I began to realize that there was a little early we hadn't yet really it's constituted at the team that would do that and I wrote a li mail to a guy who sent me the email aggressor says isn't this a false objection or in pain or a trial and judgment he said no we've established it's not a trial injection Wow so the next horrible thought many of us had I wasn't the only one maybe we had been hacked it could have been anywhere we're in the data analysis system it could have been in the computer system that stored the data they people have been could have been clever enough to go to the apparatus and put some transmitters and receivers into them that would make believe that they were part of the apparatus and they injected signals right at the app we could think of so many ways that people could hack us so we put a special group of people together a very good man named Matt Evans one of faculty at MIT went to both sites organized the team to look into the hacking and that became very complicated it took almost a month slowly but surely people began to say look it's more natural that maybe it's easier to explain this as that it came to him from nature and some of us began to relax some of us didn't and the thing that finally did it for me was that we had a another event there was a really very different and very good event on December 26th of that year and then all of us who were still doubting said yep we ought to write this thing up for a moment they outshine the entire universe in light but in gravitational waves and that discovery literally shook the world because when gravitational waves pass by they affect the interferometer mirrors and the mood at the very first ones we saw were pretty big 30 solar masses to 30 solar masses objects go around each other smack into each other effectively making a new black hole that isn't quite equal to sum of the masses of the tools in fact it's missing about three solar masses and those three solar masses is what got radiated away most astronomers thought that the black holes that we are going to observe will be at the range of five to ten times more massive than the Sun but the ones that we observed were more like 30 to 35 times the mass of the Sun you might think oh this only about five or six times bigger than what was observed what's the big deal it's a big deal because the usual way of forming these by the evolution of stars it turned out was not it was not possible to produce these heavy black holes but the other interesting thing from the population of the detections that we have made so far is that all these black holes seem to be either how no spin at all they're not spinning or they have spins in all right random directions that they completely cancel out and that seems to be a quite a bit bit of a puzzle as well it's not only just the masses but their spins seem to be somewhat unusual and understanding the origin of those two will be something that is important for the future we took data in to observing runs in 2015 and 2016 and 17 and those delivered 11 detections 10 from black hole mergers and one from neutron star mergers we began taking date again in our third observing run on April 1st and today is June 24th I think 2015 and we have alerted astronomers about 14 different events 11 of which are black hole mergers so that's more than what we had before that was ten and three events that they have low probability so they might stay away but one is a neutron star a binary neutron star murdered another one it's half 50% probably of being a big neutron star merger and the other one seems to be a neutron star black hole merger so that would be a first but that one actually has also false alarm and large false alarm probability so it's very exciting LIGO first went into operation in 2002 but for years detected nothing when the system was upgraded to become advanced LIGO in 2015 the first discovery was made almost immediately after switching it on but new upgrades will push the system even further culminating in LIGO Voyager which is planned for the late 2020s pushing the boundaries further actually takes us back to the lab it takes us back to developing novel meadows the actual portions of the instrument that a gravitational wave moves when it arrives he daenerys currently an advanced LIGO those are are formed from 40 kilogram chunks of ultra-pure glass fused silica super low absorption with optical coatings of light to the front we invested that for the next generations perhaps of our instruments rather than room-temperature fused silica we actually might switch to silicon which we can cool down to cryogenic temperatures to reduce the vibrations of the very atoms and molecules and those mirrors which set there as a background noise source but we might need 100 kilograms 150 kilograms of silicon material so that's a challenge understanding the optical properties of that material because it has to act as a metal substrate in the end and most importantly understanding the properties of the materials that we apply to the front a very thin layer a few microns thick to turn these chunks of material into mirrors that's also very important because and we believe for the current generation of detectors it's actually the vibration of the atoms and molecules in that few micron thick metal coating on the front of the substrates that actually will limit the sensitivity of these large observatories so actually like many problems and science many challenges in experimental physics material science underlies a lot of our future developments LIGO will be upgraded we will roughly increase the distance up to which we can see by a factor of two that means that we can observe sources by a factor of eight greater in volume so we will observe events at the rate of something like ten times eight to ten times more than what we have been doing so far so it's a truly global endeavor in terms of gravitational waves and Europe there's currently the advanced vertical project involving France Italy the Netherlands and other countries in Japan there's a detector called car graph this under construction and commissioning currently and there are of course plans quite firm plans to have another like like instrument in India having those detectors distributed around the globe is important for the science that we want to do because to know where in the sky a gravitational you signal is coming from we effectively time its arrival at the different gravitational wave observatory x' and with only one observatory with us wouldn't have significant directional information we didn't know where our signal would come from in the sky with two we start to have directional information but with three four or five we're really able to pen down weight on the sky our signals are coming from and that's information we can share with our colleagues of telescopes you may wish to point and examine that portion of the sky for light of an electron it takes a fill in one of our previous films we covered one of the most intriguing mysteries of cosmology the hubble tension one way of measuring the expansion rate of the universe is to look at the Cosmic Microwave Background but another way is to look at distant supernovae which are standard candles as they have a known brightness these two methods do not agree and the disparity is getting worse so does this mean that new physics is needed or is it just a measuring error Barnard shoots recently was awarded the Eddington prize for showing that gravitational waves from black hole collisions which act as standard sirens can become a new way to probe the Hubble parameter and potentially resolve this problem we don't know if this represents a difficulty in in one or the other way of measuring things and they're not doing it right or if there's some unexplained new part of cosmology that we don't understand yet which creates a difference between these two groups because they're measuring the expansion in quite different ways if we with our standard siren measurements we're measuring also something quite local we're measuring black hole coalescence Azure neutron star coalescence --is in the near neighbourhood of our universe so in principle if this is some new physics we should agree with the people who measure the supernovae if on the other hand we agree with the people who measure Hubble constant with the Cosmic Microwave Background and we disagree with the local supernovae people that would be very strong evidence that the supernovae people are leaving something out in their measurements of distances because it's a very complicated thing to measure the distance to a supernova it's much much easier for us to measure the distance to our standard sirens we have dreams expensive dreams but we have dreams because we know how to build better detectors what we call third-generation detectors of course we want to make them a bit cheaper and more affordable but we have concepts and we are working on those and those will be built eventually I hope in my lifetime in the next decade or so we know what the noises are in our detectors now we are fighting it we can make it a bit better but even with the same noise if you make the detectors ten times longer then they are ten times more sensitive and of course you can make them even more sensitive if you reduce the noise so the main trick is making them longer the concept of cosmic Explorer is making it 10 times longer 40 kilometers long the concept of Einstein telescope which is a European concept is to make them 10 kilometers long but in a triangular configuration instead of l-shape that gives you a bit more information it doesn't help you to localize the source but it gives you more information about the polarization now because they're bigger that makes them a bit more complicated too because you have to use larger mirrors and those are heavier and so you need to work on the suspension system you need because they they are longer than they are farther apart so you need to work not just on horizontal seismic isolation which is what we do best but also some vertical seismic isolation because vertical is different on the two extremes because the earth is curved so there are lots of things that need to be worked out but we know how to do that why do we think that that's the right way to go well for a couple of reasons we know it'll work it costs money that's there's no doubt doing something like that cost money but we know it will work and and the little of our experiences now say that we will probably not be able to make such a dramatic improvement by 10 with all the little things we can think of that are the fixing things that we can think of because all of them are hard to do both of these should improve the present detectives by more than a factor of 10 in in their reach in how far away and if you can imagine a factor of 10 in radius means a factor of a thousand and volume and so they'll be they'll be able basically working together to observe every black hole coalescence that's happening in in the universe the incredible reach of third-generation detectors will have huge implications for our understanding of the cosmos but before they are built we may have the first-ever gravitational wave detector in space called Lisa for gravitational wave detectors on the ground we observe across a range of different frequencies from about you know one to ten Hertz up to a few kilohertz we can pick up signals in that range but at low frequencies there's a noise source that becomes troublesome and ground-based detectors called gravity gradient noise the way our detectors work we have a suspended manner whose possession we monitor low frequencies local things people walking around cars driving past all exert a straight gravitational pull on our suspended matter that that's not something we can shield against you can't shield against gravity so we become sensitive to local gravitational effects here on the earth rather than the gravitational signals traveling in from across the universe we can't shield against it but what we can do is fly instruments in space where there are no people walking paths that are no cars driving past so that gravitational gradient noise is greatly greatly reduced and that opens up a whole new set of gravitational wave sources for us to detect Lisa is as old as LIGO almost I mean you know that everybody thinks it's just new thing people been more thinking about Lisa at least since 1975 the first guy who really began to think about it hard was a guy named Peter bender he was on a committee with me that was trying to see what could the space program do for a tional physics and cosmology and we knew right away as soon as you put something into space you could have very much longer arms yeah I mean if in fact we silly to make something with short arms because you gain the signal gains with the arm beautifully a Peter bender came up with once he came up with something which was sort of five million kilometers on the side a triangle if you do it right and he came up with an absolutely magnificent orbit the orbit of that equilateral triangle if you inclined it to the ecliptic a good client inclined it to the plane of the orbit it would have if you got it just right it wouldn't need much rocketry to keep it there one of the decadence studies these things up every 10 years I think that the Cadle study of 2010 gave it very high billing and and shortly after that NASA found out that it was in trouble and they had to get James Webb was in the way and all sorts of hell broke loose and they gave up on it now they didn't give up on it entirely and now slowly but surely it's coming back and the Americans will have to make some investment and they intend to but the project has become a European project we proposed back in 1994-95 to put a - the European Space Agency to put a gravitational wave detector into space they liked the idea and they've encouraged us to develop it and in order to support it they launched a satellite which was a very difficult satellite to build to test the new technologies that we knew we have to have in order to detect gravitational waves in space if you can imagine it's very difficult to build the detectors on the ground also takes new technology in space and that's that spacecraft was called Lisa Pathfinder and it was one of the most successful spacecraft that eisa has ever launched it was launched in at the end of 2015 and so in 2016 and 17 it made fantastic measurements it didn't detect any gravitational waves wasn't designed to do that it was designed to show that we could build the the gravitational wave detectors the key technology components that we could do that and it performed practice of 10 or 20 better than it was expected to better than the European Space Agency wanted it to that cleared the path and now now ISA the European Space Agency is ready to go and has approved our space gravitational wave detector which is called Lisa these are interferometer space antenna Lisa is on adopted mission by the European Space Agency with planned launch date currently I think of 20 34 they are hoping somehow to accelerate it and get it launched in 2028 I hope they can do it but it's getting later in later eight years to develop this is something it says you have to there's a lot of work involved in getting a thing like that together there are three satellites to 1/2 million kilometres away from each other are it like in a triangular in a configuration and there's the laser going from each satellite to each other satellites so from each satellite we have 2 lasers and in measures like Lego does gravitational waves measuring the distance between the satellites now the difference is that because it's so much longer the noise is higher so the sensitivity to gravitational waves is about the same as as like a wheel is now but because it's so much longer it's going to be detecting gravitational waves of much much longer wavelength and those are produced by bigger systems of those bigger systems are these massive black holes at the center of galaxies smaller black holes falling into these black holes we call those embrace 6-3 mass ratio in spirals and white dwarfs in our galaxy white dwarfs that these big stars so they're not very massive they're actually less than the mass of the Sun but they're very big so they produce when they merge they are producing gravitational waves of a long wavelength so it's like a completely different science than like it's like comparing a radio telescope an x-ray telescope they will see little or black holes being eaten by the big black holes and those are very good sensitive tests for the general theory of relativity because you can do the problem so easily it's a nice problem like a little thing going into a great big thing a lot of the complexity of two things being equal close to equal it falls away so it turns out you can do very sharp tests of general relativity with us and you will certainly discover all sorts of new things there's no question it is not just about black holes and neutron stars which we know they exist but there are other things probably in the universe and this is an opportunity by building the next generation of detectors we will be able to observe such phenomena what they are I don't know if I knew I would have told you immediately but I don't know what they are and that's what the you know exciting thing about Sciences and that region of the spectrum sort of from minutes to hours is something you can't do it all from the ground and so their technique is a very different technique than the one by use by the people on the ground they send signals between the satellites all three of them as they send them between them in pairs but along the arms and then look and then have them re-- send them in other words the signal comes in from one that's a laser that said one micron laser probably it's from a mirror a little telescope it's gets its gets detected by a detector and that gets amplified put back into a into another laser which add to drive that laser and gets sent back to that other to the satellite where it came from and then they look at the frequency difference and that's a way of measuring the change of the spacing between the satellites is like it's a different technique and it measures instant where we're measuring 10 to the minus 18 meters they don't need to do better than 10 to the minus 12 meters because they're dealing with baselines that are 10 to the 6 bigger than the ones we have on the ground now darkest mini Hertz gravitational waves there are also now efforts to observe gravitational waves of even lower something like nano Hertz gravitational waves and they are done by using what are called pulsar timing arrays the basic idea is that you monitor the arrival times of pulses from neutron stars that are distributed around the galaxy and they will be a systematic change in their arrival times in response to a passing gravitational wave near Earth and so by observing those systematic changes we should be able to observe nano Hertz gravitational waves so that is called pulsar timing array and that will observe in a different window as well oh these will also be supermassive black holes but of much heavier nature billions to tens or hundreds of billions of solar mass black holes that are going around each other when galaxies come together and merge the black holes at their centers are likely to merge as well and those are the sources of these nano Hertz gravitational waves one mystery that future gravitational wave missions hope to solve is how supermassive black holes form but there are perhaps more fundamental mysteries that Lisa and other missions may be able to address that matter we don't know what it is but if it is present in around black holes for instance that could be detected because it could drag the orbits of black holes and therefore change the way they are going to in spiral and merge moreover certain kind of accion ik matter could extract energy from black holes if there are black holes are rotating there is a phenomena called superradiance by which this accion ik matter can extract the rotational energy of black holes and we might be able to detect them as well these are two ways but some dark matter can actually fall into the course of neutron stars and convert neutron stars into black holes this will be a fantastic opportunity because if you start to detect something like you know neutron star size objects but they turn out to be black holes how do we know that they're black holes well we can measure what is called the tidal deformability of these objects that signature will be present in the gravitational waves that they emit if this title deformability is 0 then the apply calls and if you have something like neutron star masses but they are black holes the only way they could have been produced is because of dark matter accumulation which converts neutron stars into black holes some have suggested that there is no dark matter and instead we need to modify our theories of gravity to account for the anomalous observations that lead most cosmologists to accept the existence of dark matter we already actually have contributed to the discussion of theories of modified gravity and how that affects some consideration of dark matter through our observation of the gravitational wave signals from colliding neutron stars and combining that with the observation of in fact the gamma-ray signals that came from those that collision and you don't know the gravitational wave signal and the gamma ray the electromagnetic signal arrived within 1.7 seconds of one another picked up here around the earth and they had travelled 130 million years before arriving with us so that tells us that if you like the speed of gravity and the speed of light are the same to an accuracy of 1.7 seconds and 130 million years now relativity predicts indeed that M gravitational waves should travel at the speed of light and that 1.7 second discrepancy is actually probably real and that there's astrophysics involved it takes time when those neutron stars smash into one another for the mechanism that produces gamma rays to actually kick in and happen and without measurement the bones set by that actually relate a whole class of series of modified gravity which made predictions that gravitational waves and light should travel rather different speeds the dark matter is a mystery and what we don't even know about it is if it's just one thing the simplest ideas is just one kind of elementary particle but we haven't been able to find that and it may not be because those elementary particles don't exist it may be because the dark matter is a mixture of different kinds of things and so we have to go another factor of ten or something before we begin to see any one of them and and that's kind of discouraging but it could be that one of the components of this mixture is the the black holes that were detecting using Bonnie black holes and neutron stars we can very accurately measure distances to the sources of the host galaxies of these objects once you know the distance combined with electromagnetic observation which could give you redshift you will be able to map out what is the expansion history of the universe now the expansion history of the universe depends on dark energy and not only dark energy but also the nature of dark energy whether it is dynamical whether it is simply a cosmological constant so we'll be able to address these questions with the next generation of gravitational wave detectors if dark energy is related to a deviation of general relativity and that deviation is shown in the signal in the signals that we see from these massive black holes then that would give us a clue Kennedy could be something very simple it could be just be part of the laws of physics Einstein put in his cosmological constant and that describes the dark energy that we see right now but we don't have a very good measurement of it we don't have a very accurate measurement of it one of the problems is getting a long enough range into the universe to see how the dark energy might be changing if the dark energy hasn't changed at all out to redshifts of two or three then maybe it is a simple Einstein cosmological constant most businesses would prefer to see the dark energy as something that comes out of quantum theory quantum electrodynamics or maybe something from quantum gravity and that would suggest that there would be some dynamics in the dark energy that it would change with time a little bit at least with gravitational waves with the Lisa mission there's a very big possibility that we can measure the changes in the cosmological constant which then wouldn't be a constant out at redshifts are of two because we have very very high precision in measuring the standard sirens so just like we would measure standard sirens with ground-based detectors to measure local Hubble constant we can use the standard sirens that Lisa will observe to go much much deeper into the cosmology and and perhaps measure the the changes in the dark energy and that would be fantastic there are some speculative ideas about how black holes might behave with regard to the unification of quantum mechanics and gravity there is a prediction that the horizons of black holes might have flank scale sub structure even on the whole you know horizon scale which is kilometre or tens of kilometers or hundreds of kilometers depending on the size of the black hole but if these Planck scale substructure exists on horizon of black holes then we might be able to detect those signatures with future observations of correlating black holes because they will be present in the swansong that is emitted by two black holes that merge together they don't they die very smoothly in the sense that the final radiation that comes out is an exponentially damped sinusoid but it is a spectrum of gravitational waves that comes out and that spectrum has different signatures depending on whether that substructure is present or it is just a classical black hole without any sub structure if you had a theory what might it predict about gravitational waves for example and one of the things is that might predict new kinds of polarizations of gravitational waves in Einstein's theory it's very simple there are two polarizations it's very like in electromagnetism there are only two polarizations but in gravity itself you could have up to six different kinds of polarizations and so with enough detectors on earth for example when we have five detectors we will actually be looking for different polarizations another thing we might be able to see is some kind of dispersion we predict the signals that we get from standard sirens and the standard science we've we've been observing that that whose radiation was emitted whose gravitational waves were emitted something like billions of years ago and we are detecting so they've traveled for over billions of light years they still have the same signal shape and that means that higher frequencies and lower frequencies are traveling at the same speed that doesn't happen and sound it doesn't happen in any other material that for where we have waves the usually there's a different speed of propagation for for high frequencies and low frequencies and even for electromagnetic waves going through a plasma or something there's dispersion if there were dispersion of gravitational waves it would not be part of Einstein's theory that would be a hint at something quantum and it just can be a very tiny thing because we're measuring over such big distances it doesn't need the very much dispersion to produce an observable effect so there are things like that dispersion there are also things that have to do with the difference between left and right left handed and right handed we call these chiral effects in physics and when we get a gravitational waves we typically get grabbed a mixture of both certain low secular polarization one-way and circular polarization the other way and again if they fall out of step with one another then that's a different kind of effect in in in gravity and that would be another indication of a modification of Einstein's theory that could lead us to a quantum gravity so we're always monitoring these things whether we'll find something is just a matter of discovery so far Einstein's theory has passed every test the future of the field took a dramatic turn in 2017 when the merger of neutron stars was detected in this case it wasn't just gravitational waves that were observed but other signals - and this is heralded a new field of astronomy combining light and potentially neutrinos and cosmic rays in what has become known as multi messenger astronomy so multi messenger astronomy is looking at the universe in different ways at the same time the obvious way to look at the universe is with your eyes and that would detect optical photons but there are lots of other things ordinary people can't see and even special people can't like neutrinos gravitational waves things like that but with specialized instruments we can see those two and that combining them gives us much more information what we saw in August of 2017 was the merger of two neutron stars and that signal came as gravitational waves because of the current detectors a gravitational wave the location of that merger was very large in the sky so the uncertainty was very large he's like I tell you you know there's been a merger of neutron stars and you asked me where and I tell you well somewhere around that region in the sky instead at the same time we have what we call a gamma-ray burst which is a big flare of gamma rays that was detected with the satellite experiment and that is very precise is like looking at stars in an in a telescope so you have a very precise location and that allows all the different follow-up experiments to go in that particular direction and follow that for many many days and study what happened with that murder you must have long been fascinated by the idea that there are invisible messengers all around us and one of those kinds of messengers is real and it's neutrinos and these are tiny tiny subatomic particles that are produced abundantly in stars and other things like supernovae and pass right through us all the time but very rarely it's possible to catch one of them in a specialized detector ahman is the Astrophysical multi messenger Observatory Network and the idea is to combine all these data from all these observatories in one single database so you could say well it's already happening people are working together so there are two main features of what we're doing here at Penn State the first one is that we are concentrating all the signals in the same spot in the same database and everybody hears at the same time from everybody else it's not the one-to-one so instead of having 10 different observatories and and you just talked to me and I talked to him and not to you and so on the communication is centralized in one place so that's a big change in the paradigm of the multi messenger communication you could say the other big difference what everybody else is doing is that we're looking at what we call sub-threshold events and what does it mean substrate so it looks a little jargony so we are looking for particular signals that are weak enough that each individual detector cannot do anything with it so for example there are signals that like us detects for gravitational waves but they are too weak for them to tell them apart so they don't tell anybody else because those signals they are not so sure that that's a real merger instead they tell us look I got a signal but it's a little weak we have all the information from all the other observatories and maybe at the same time from the same location we got a weak GRB signal to that Fermilab for example could not tell yeah this looks like a big grv I'm telling everybody so by combining these signals we get a discovery now because the chances of having a weak signal in gravitational waves independently a weak gamma-ray bursts from the same location at exactly the same time it's from background it's it's zero Multi messenger astronomy has the potential to answer one of the biggest questions the field how do these black hole binaries form so maybe they were formed since here's sort of the puzzle we now have I think the aha these pairs how they made when a star collapses maybe are they made in places where there are lots and lots of stars that are creating on top of each other maybe are they probably are they the result of the collapse of us very very first stars made in the universe possibly are they primordial if a massive star and it collapses and it makes a neutron star and the material bounces and it makes an optical supernova and everybody's happy and you get neutrinos but what could happen a lot of the time is the whole thing collapses and instead of bouncing it just keeps going and then the whole star makes a black hole and then there could be little to no optical emission but there still is neutrino emission and so that is something that you can only do with the neutrinos is to find that whole population of collapses that lead to black holes is to capture the neutrinos now those black holes as they form they could make gravitational waves but it's not guaranteed if they explode if the collapse is very round spherically symmetric they don't make gravitational waves and we know that something is making lots and lots of black holes in the universe and that's what LIGO is finding and so one of the ways to find out what's making them is to capture the neutrinos from their production and the neutrinos have come from the black hole forming case as opposed to the neutron star forming case the spectrum here is a little bit more energetic and by capturing a lot of these supernovae neutrinos we could eventually tease out the balance between the neutron star forming supernovae and the black hole forming supernal Cosmic Microwave Background was emitted about three or 400,000 years after the Big Bang but the cosmic neutrino background was emitted about one second after the Big Bang so if we ever detected that it's the deepest look-back we've ever had and its probes the universe at its earliest time in its highest temperature cosmic neutrino background is something that every physicist dreams of detecting and there have been lots of great ideas and all of them have crashed on the rocks and so far nobody really has a good idea where something like fifteen orders of magnitude away from being able to detect that there's an experiment based out of Princeton called Ptolemy that I think claims to get within several orders of magnitude of detection I consider that a miracle to go from 15 to only to several because that's a pathfinder towards eventually getting there and the technique used is to look at tritium tritium is the third isotope of hydrogen it's radioactive and what you can do is you can wait for tritium to decay and when it decays it makes a certain electron spectrum and a neutrino that's not seen but another thing that can happen is a neutrino can call me and a cosmic neutrino can come in and hit the tritium and stimulate the decay and then the electron comes out with a different spectrum that can be identified as a stimulated decay as opposed to a spontaneous decay so the spontaneous decay gives from your perspective and electron spectrum this is spectrum versus energy that looks like this and the stimulated decay gives an electron spectrum that's a line at the end and if you saw that line you would know you've seen the stimulated decay it's incredibly hard you asked me earlier if we could conceive of being able to detect this at the moment nobody really has a good idea but we can conceive that people will eventually be able to detect this we just don't know how so cosmic rays are nuclei going from protons all the way to the heavier particles of nucleus that we know so elements that we know and they are bombarding us constantly all the time so in these few minutes that we are here we are bombarded constantly by these subatomic particles and they cover all kinds of energies from very low energies that we know their cap they could come from the Sun for example that's what we call low energy is a nuclear reactor kind of energy that's very low for us all the way to the highest energies which is what we call 10 to a 20 electron volts so that sounds very weird but to have an idea the largest machine that we can build is the Large Hadron Collider which is in Geneva in Switzerland and that produces accelerates protons to an energy of 10 to the 12 electron volts these particles we have no idea where they're coming from they will try high energy cosmic rays that we have detected can reach a hundred million times higher energy that what we can do in the Large Hadron Collider if we wanted to build a particle accelerator similar to the Large Hadron Collider with the technology that we have to reach 10 to a 20 electron volts the ring has to go from here to Saturn and come back probably the most interesting most important gravitational wave signal we don't know how to measure yet is gravitational waves that were created in the Big Bang and are kind of a very low amplitude hiss that's really in the universe the trouble with trying to detect that is that every binary system in the universe is also radiating its own gravitational waves and creating a random background and that background is usually larger than we expect has come from from the Big Bang so we have to develop very special space missions to look in exactly the right frequency band where we can expect that the universe itself is kind of quiet and quiet enough for us to to hear this very low hiss that comes from the Big Bang and now there's a project called Big Bang observer there's another a couple of projects of people that proposed that come come close to that the the technology is not yet completely mature there are many proposals for other kinds of detector tech oh geez that may may function better in space I think there's going to be a long time coming but I would hope maybe in another 10 or 15 years we'll have a concrete proposal worked out that the space agencies can can work with and can look at and and start developing them and eventually we'll get a mission because looking at the gravitational waves from the Big Bang is the most fundamental thing we can do with gravitational ways because these gravitational waves were emitted a fraction of a second after the universe formed we can look back now to the Cosmic Microwave Background in electromagnetic radiation but that happened to two that was emitted at something like 300,000 years after the Big Bang to go right back to the Big Bang and actually get information coming from the tiny fraction of a second before after the Big Bang itself that would be absolutely astonishing and tremendously fundamental and that's the ultimate goal of this field but it's still going to be a long time coming so what is this Big Bang observer it's doing all the bells and whistles well it's not on the ground in space in other words you would now have to take all the sensitivity you have on the ground that 10-18 meters and the fact a little better than that stick it in space not 10 to minus 12 meters 10 to minus 18 meters has to be foot in the space over large baselines it's measure and measure the motions of 10 to minus 18 meters over 10 to the 6 kilometers okay I mean it's just wild idea it's way way far from everything that's being done right now it's using the technology that we're doing on the ground applying it to the scales of Lisa ok and the people who proposed that said look gotta do Lisa first nobody in his right mind at NASA or in Russian space centers or anybody well let you contemplate this thing until you've tried that interferometer on a scale or a gravitational wave detector that on a scale of 10 demise 12 meter sensitivity rather than 10 to minus 18 okay so that's sort of very very distant future but suppose that word eventually to happen maybe if it's true and we saw something how are we the most interesting gravitational wave detection ever made well my god come on you learn how the university here [Music] they can't ask for more than that you

Channel: skydivephil

Views: 111,977

Rating: 4.817822 out of 5

Keywords: astronomy, physics, space, nasa, gravity, black holes, ligo, gravitational waves, Cmb, universe, big bang, quantum physics, relativity, science, cosmology, quantum gravity, nobel prize, rai weiss, LISA, dark energy, dark matter, neutrinos, cosmic rays, cosmic, inflation, esa, stephen hawking, cosmic microwave background, black hole, event horizon, interstellar, ad astra, einstein

Id: jKrOy4mC4wg

Length: 49min 47sec (2987 seconds)

Published: Thu Aug 08 2019

Reddit Comments

[u/lookin_joocy_brah]

This is a really great video giving a forward look on what's to come for gravitational wave astronomy. Worth a watch if you're at all interested in the field.