10:02:43 Yeah. Okay what why don't we begin.
10:02:47 So Peter Graham Thanks for coming.
10:02:49 Peter has been working in theory.
10:02:53 In this area, long before it became really trendy I think it's fair to say, and will continue and build on the previous talk. Go ahead.
10:03:02 Perfect. Great. Yeah, thank you very much for inviting me and thanks the organizers actually for organizing a really fun workshop I've been, I've been having a great time so far, shame we can't be there in person I always had a great time in Santa Barbara
10:03:14 but hopefully soon next year. Yeah, hopes up. I actually, I brought my Santa Barbara water bottle so I could feel like I'm there.
10:03:24 Yeah so so I got this title I don't even know if I picked it was given it.
10:03:28 But luckily, and I didn't really know what I'm talking about but luckily it was so broad that I could talk about a whole range of different things.
10:03:36 So I think I will actually talk about essentially two separate topics gravitational waves, and then also new physics, as a separate topic, and in particular the two topics I'm mostly in fact focused on talking about gravitational waves and Jason did a
10:03:53 great job, describing some of the efforts using Adam enough rocketry and we heard yesterday also about the use of atomic clocks, but actually I want to talk about a new idea that we Some of us have been kicking around recently for going to even lower
10:04:06 frequencies and using atomic clocks, to try to get at this kind of roughly micro hertz range for gravitational waves.
10:04:14 I'll spend most of the time focusing on that. Think that's that's sort of fun and exciting idea this is a good crowd to talk about it in front of.
10:04:21 That's that's sort of fun and exciting idea this is a good crowd to talk about it in front of. But then, hopefully there's a little bit of time, I'm also happy to talk about some work we're doing right now that I'm excited about looking for detect millet charged particles, using trapped ions.
10:04:31 And I should say both of these topics are very preliminary. They haven't come out yet, but I'd love to hear any feedback or thoughts or thinking, or things like that.
10:04:41 Okay. So to begin with, I want to talk about this new idea we have for using atomic clocks, to look for gravitational waves at this very low frequency region one to 10 megahertz roughly around there.
10:04:53 And this is work with my collaborators might go and search eat.
10:04:58 Um, so, I think it probably don't have to motivate gravitational waves very much, but I really believe that the observation of gravitational waves I mean we've already seen fantastic results coming out of like a really exciting we're learning things about
10:05:10 black holes in the universe.
10:05:12 I think that's gonna be a major part of the future of astronomy astrophysics cosmology, maybe even high energy physics.
10:05:20 And I think it's really just crucial to observe in as many frequency bands that the gravitational spectrum as possible.
10:05:27 We're learning a lot of great things that Lego in some sense that's sort of the tip of the iceberg as we go to ever lower frequencies will learn, I think even, you know even much more.
10:05:36 So here's that strain curve characteristic strain of gravitational wave versus frequency that you were seeing a lot in Jason's talk.
10:05:45 And like I was looking up here and sort of 10s to hundreds of hurts.
10:05:49 And Lisa is down around 10 to the minus to her son of minus three hertz.
10:05:59 And then, at the lowest frequencies that we sort of directly detect are the pulse our timing arrays down at periods of years or so.
10:06:05 Kind of minus eight or 10 minus nine hurts. And we just heard some nice talks, discussing the use of for example Adams, either Adam interferometer is or atomic clocks, to look in this mid frequency range.
10:06:18 And there's also some other proposals.
10:06:20 I think that's very exciting because that's really a sort of open region between Lego and Lisa, that also has a lot of really interesting science, and there's a lot of important things you can do.
10:06:33 Um, and so so I'm, I'm definitely interested in that and excited about that but but actually today I want to talk about something else, which is, you may notice, and it was, it was kind of bugging me and I think several other people for a while, that
10:06:44 there's a, there's sort of another open band here, down below Lisa but above pulse our timing in this roughly what's called 10 to the minus seven hertz attended minus four hertz or so region, where there really isn't any current, you know existing or
10:07:00 plan even detector really focusing in and trying to go after that region.
10:07:08 And in fact, there is I think just as sort of a ton of gravitational wave science as I said really across all bands, roughly maybe following sort of diagonal line like this.
10:07:18 This is kind of telling you the levels of sensitivity you want to get to.
10:07:21 We really want to be able to observe as much of the gravitational wave spectrum as possible.
10:07:27 So I would argue since gravitational waves are so important, it's really important to consider all possible different detection techniques to try to cover the entire spectrum.
10:07:35 So I want to ask what can we do to get into this region. Okay, that's what I want to focus on here.
10:07:44 And to think about that let me actually ask why does that gap exist. Okay, so So in particular, you might say, Why can't Lisa go down to lower frequencies are some, some space space interferometer concept like that go to lower frequencies.
10:07:57 So here from the lease alfre proposal is there a strain sensitivity curve the proposed strain sensitivity curve is this green line here.
10:08:06 And you can see it sort of rising sharply to the left and to the right.
10:08:19 right you have you have the satellites that are floating around is really good inertial proof masses, but you have to measure the distance between them, or if you like do clock synchronization between them or however, however you whatever your concept
10:08:29 What's going on well, very crudely, if you haven't spent a lot of time thinking about gravitational waves on the right side of the curve, you can understand this as essentially photon shot noise or the noise in the the link between the two satellites
10:08:34 is for gravitational wave detection.
10:08:36 You need some link, and actually this is a pretty generic feature that the right side of these curves.
10:08:41 Usually dominated by the link noise, And in particular, would be this rather flat slow but then around here this breakpoints. That's where as you see you're going up in frequency, the wavelength of the gravitational wave actually becomes shorter than
10:08:55 the very long arm length of Lisa, the baseline between the satellites.
10:09:01 And then of course, your gravitational waves signal, sort of cut off you can't you don't get to use the whole baseline, you don't get age times baseline strain times baseline, stretching and squeezing the baseline.
10:09:13 You only get each times lambda, and of course then as frequency goes up, therefore your your sensitivity is you're losing sensitivity as you go to the right.
10:09:22 And of course you can imagine that because one way to say it is as the as the light from one satellite is traveling over the whole one baseline, the gravity wave is actually oscillating many times right that's what it means, if the baseline is larger
10:09:32 than the wavelength the gravitational wave that the period of the gravitational wave is short compared to the light travel time.
10:09:40 And so you're really only in some sense getting the sort of last one canceled period a full a full oscillation doesn't help you. You don't you don't get any stretching or squeezing from that you don't get any signal from that.
10:09:50 That's actually also why they're these little ripples and Lisa sensitivity curve.
10:09:55 Okay actually that'll be useful for something I'm saying later but that's not even really my point here. The point here is what's going on in this left side, and roughly said very sort of crudely what's going on the left side which is true for almost
10:10:06 all gravitational wave detectors, is the proof mass has some acceleration noise there's there's some noise acting on the proof mass making it not a perfect inertial tracker of space time, meaning it's not just perfectly following that gravitational wave
10:10:20 metric, something else is messing with it.
10:10:22 Okay.
10:10:24 And as I said that's that's pretty standard.
10:10:27 That is that is true for like oh two that's the left side of their curve is that by their proof mass acceleration noise.
10:10:33 And it's a, you know, very standard feature of this kind of noise that it would rise at low frequencies it just gets ever harder to control.
10:10:47 Try to make some, some proof mass really inertial at lower and lower frequencies. Right. So here for example is the measured acceleration power spectrum or actually used to be able to special density of the acceleration and meters per second squared,
10:10:55 For hurts measured by the LISA Pathfinder experiment, and they really did a fantastic job even better than the needed spec needed requirement for Lisa was really amazing work.
10:11:09 I'm knocking down this acceleration noise but you can see of course, still, it's always rising as you go to lower frequencies. And in fact, you can see they've only measured it down to about 2000 minus five hurts so far.
10:11:21 And this is rising roughly like one over half which is which is probably not too surprising.
10:11:26 And so translated that into the gravitational wave plot, you get this, this sharp rise in your the start decreasing sensitivity as you go to lower frequencies.
10:11:36 And of course that's not surprising I mean how do you hold a mass and have it really sit there and have just nothing for sure but at this extremely low level, you know, kind of minus 1300 minus 14 meters per second squared over 10 to the five seconds
10:11:47 10 to the six seconds, those are very long time skills.
10:11:54 Similarly, here's this nice paper actually referred to in June stock yesterday about using atomic clocks, to look for gravitational waves also focusing in this kind of minus two ton of minus three hertz frequency band.
10:12:07 And so you can see for example, look at this orange curve for example something you can do with an atomic clock,
10:12:14 it's rising on the right again for similar reasons but but on the left you can see that it's still got the same sort of roughly universal slope or any of these curves the green curve or the purple curve this universal slow, and that's because they've
10:12:25 assumed again, even if you're using atomic clocks you still also you have a you have an excellent clock, right, but you still also need, of course, a very good initial proof mass you need something that's just sitting there and you can measure the distance
10:12:36 between it or do your clock synchronization between your to prove masses.
10:12:52 So I think in this paper they assumed essentially same spec as Lisa, that the same LISA Pathfinder specification. And so you get the same rise to lower frequencies. So that makes it that sort of tells you the problem that's why it's hard to go to lower frequencies that it's hard to build a good enough proof mass. So what could you do, how
10:12:59 enough proof mass. So what could you do, how could you imagine trying to do it. Well one thing of course you could try to just do better than LISA Pathfinder I mean they they worked really hard they did a great job but maybe you could improve on that
10:13:10 right so maybe you could decrease the acceleration noise, especially these low frequencies.
10:13:13 And for example, I'll show you in a second. There's something called them urs concept which is similar to Lisa, where you essentially that's what they're they're sort of relying on that you could do that.
10:13:23 And similarly at the same time you'd also try extending You can also try sending the arm length, extending the arm length would, would you can see, raise the right side of the curve, but it would improve the left side of the curve because the strain this
10:13:35 this acceleration is some noise, acting as some jitter on your proof mess itself you know its measured in meters per second squared. It's how much your proof masses is wiggling around and meters.
10:13:43 If I'm dividing it by longer baseline between my two satellites. Then of course, I without even improving this acceleration noise meter per second squared.
10:13:51 I immediately improved this purple curve in in stream right because I'm dividing by a longer baseline.
10:13:59 So the Mijares concepts relies on both of those.
10:14:02 That's interesting, but obviously you know people did work very hard to to achieve this LISA Pathfinder result. So we wanted to ask it but I should say I mean that's a, it's a really important thing to be able to observe gravitational waves in these lower
10:14:13 frequencies. So we should really be trying all approaches I think that's a that's a really interesting and important approach and that's worth probe that's worth, that's worth really attempting and thinking about.
10:14:24 We wanted to ask is there another way is this the only way to do it, that you just have to basically do better sort of engineering better drag for engineering of your proof mass, or is there another way.
10:14:33 And in particular, there is another way right that people have already played around with, which is, instead of kind of go the opposite route instead of, you know, putting in some real intelligence and hard work into making it extremely drag free proof
10:14:47 mass with really low acceleration noise. Instead, use what nature gives you, and just take some astrophysical proof mass that for example is how pulse our timing gets to be at such a low frequencies right you just use a pulsar, use a pulsar as your initial
10:14:59 proof mass.
10:15:01 And it's just really big, it's really heavy so not a whole lot can knock a star around can not compulsory around, or for example that's what we realized arranging does right watching the Earth and the Moon fall towards the sun, the Earth and the Moon
10:15:16 your proof masses, they're just really big know when engineered them. Alright, so I'll talk about that. That second idea for most of the talk. Let me just briefly touch on this urs concept though, before I get there.
10:15:28 So here is a figure I stole from this nice paper this new RS paper.
10:15:34 The basic concept is to do another Lisa like configuration but now with these much longer arm length.
10:15:42 And also, in order to draw their This is again, like characteristic strain versus frequency curve and you see Lisa over here and this is SK is a pulse our timing array.
10:15:52 In order to draw this dashed line sensitivity from urs, you're also assuming that actually the acceleration noise is better than than demonstrating Pathfinder and remains flat at low frequencies not rising as one of our F.
10:16:05 m.
10:16:15 I won't go through them all but you can see there's all sorts of black black hole binaries and supermassive black hole binaries even a large read shifts and you know you can learn all sorts of things about cosmology and everything from that.
10:16:25 So, so they're sort of tons of sources and this is telling you about the range we want to get to. So in about the 10 the minus five to 10 of minus six hertz frequency range you can see I want to be at maybe you know 10 to the minus 16 or 10 to the minus
10:16:36 17 or so. Characteristics train.
10:16:40 And if you can get there there's really a lot of science you can do there's really a lot of sources.
10:16:44 Okay, so we want to ask Are there other ways to observe in this band.
10:16:50 So you could ask also now how about coming from the left side, using this astrophysical proof mass motivation.
10:16:55 What about pulse our timing Why, why can't pull their timing do it, why can't that get to higher frequencies. So here's an example strain sensitivity curve for pulse our timing.
10:17:03 And of course pulsars as I said they're, they're very heavy so they're excellent social proof masses. They also function as clocks, that's sort of tangential to this to this discussion.
10:17:12 But of course that's crucial to how you do the gravitational wave discussion detection.
10:17:15 But what's going on here you can see there rising for the right for the same reason I told you earlier that the pulsar is extremely far away right it's parsecs many several parts X and Y or more, meaning that again the wavelength the gravitational wave
10:17:30 is less than the baseline. Since the gravitational wave signals scaling proportional The, the wavelength now, not the whole baseline all the way to the pulse are.
10:17:37 You can see that as the frequency rises your signal gets smaller and smaller. So you're just looking for and ever smaller actual size timing jitter.
10:17:47 Um, and of course you're comparing that to their their pulse time and residuals which are in a nanosecond, in some sense, actually. So you could say that maybe the baseline was too long, that I had something too far away, that's a little bit silly, of
10:17:59 course, the one baseline didn't suppress your signal.
10:18:01 You can ever do better than stream times the gravitational wave wavelength at any given frequency. But what was going on, of course, was that you Only you this the, in some sense, you could say your timing wasn't good enough, right compared to an atomic
10:18:14 clock, this is not great timing, what's happening. Well you only have the pulse that you get from the pulsar, you've got a certain, you know, you only get a certain SNR on that right you have some, some noise in your, in your radio receiver and the pulse
10:18:26 is the pulse are so far away that you're not getting some extremely strong pulse so that's limiting our SNR.
10:18:31 So I'd like to say then maybe this kind of motivates, what do we want to, to push these astrophysical proof masses to the right. Maybe I want some sort of combination of approaches, where I want a shorter baseline, so I can get good SNR for my pulses
10:18:45 so I can really do excellent timing I can leverage the power of these atomic clocks for example how well humans can time and and maybe I want to use a man made clock and man made pulses man made link between my, My astrophysical proof masses.
10:19:00 We do do something like that already, of course, lunar laser arranging does that right, we that was actually a brilliant concept to many decades ago put a wrench some retro reflectors on the moon, right, and then we can use our lasers and our clocks and
10:19:13 everything to range the moon, and we use the earth and the moon as proof masses.
10:19:18 They are fantastic proof masses, at least their centers of mass are fantastic proof masses right not a whole lot knocks around the Earth and the Moon makes them jitter at these kind of frequencies.
10:19:28 But, sitting on the earth is kind of annoying right we have this atmosphere, we have seismic noise right we're sitting on some liquid underneath us, and the mantle.
10:19:36 The plates are moving around. So that really we know from our experience with lunar Laser Ranging for example really strongly limits your sensitivity there, and all the lunar ways ranging is fantastic experiment works great at sort of DC at the zero frequencies
10:19:48 it's, it's something great, you can do.
10:19:51 I would not be sufficient to see gravitational waves with sensitivity we need in our, in our frequency account.
10:19:58 Alright. So in some sense, I'd say the earth is sort of too big and had all these problems from having heat and seismic activity and stuff. So what can we use.
10:20:10 So I'd like to sort of throw out a fun idea and analyze it, which is, I want something of course a lot bigger than a man made satellites, man made satellites are knocked around too much that's that's what set that acceleration Noise Curve for LISA Pathfinder,
10:20:22 but smaller than the Earth, and I don't have any atmosphere or plate tectonics.
10:20:26 So how about an asteroid, there are all these rocks floating around in the solar system right they can be quite big. Here's a picture of arrows for example some big chunk of rock but they're pretty dead, not a whole lot is going on.
10:20:38 So can we use those as inertial proof masses in some way sort of similar to the way lunar laser arranging put something on the moon and used it.
10:20:47 What I'm mainly going to talk about, okay, for the rest of the talk is we want to evaluate how good asteroids are as an actual proof masses for gravitational wave detection, in particular, I want to evaluate the acceleration noise of an asteroid proof
10:21:02 mass. And we'll try to show, we think that it actually can be naturally, much lower than any human made proof mass in this frequency man they really may be sort of optimal for this frequency pan.
10:21:16 The I won't talk too much about a full design for an experiment I'm focusing first on kind of I would say that the first step is making sure asteroids are even viable proof masses at all, how to turn that into a full gravitational wave detector I won't
10:21:28 say much about except let me just sort of give you a kind of crude cartoon or toy concept here, which is that I would want of course to prove masses, for example two asteroids, with some radio or laser link between them of course I have to be able to
10:21:42 measure the distance or time between them.
10:21:46 As it turns out, as I mentioned on fewer future slides, just so you can have some numbers in mind when we think about the noise of these things, the acceleration noise of the asteroids, it turns out we're going to want sort of asteroids in the in the
10:21:55 greater than one kilometer maybe around 10 kilometer class orbiting near-ish the earth around few way you and you naturally then the distances between them would be sort of order a you also as well.
10:22:07 These are approximate numbers I mean you have a wide range of of numbers that would work.
10:22:12 So you pick these two asteroids I have some link between them. But of course, I need, so they need three elements are good gravitational wave detector right I need a really good proof mass, I need a link and then I also need excellent clocks, so I can
10:22:29 comparison and measure this light travel time if you like across the baseline. And here I'm going to imagine for example that there are atomic clocks on or near these asteroids, and I'm comparing I'm just doing clock synchronization but across this long
10:22:38 distance, using the asteroids as initial proof masses.
10:22:42 Okay, I won't say too much more about that but but let me just to show you there are some asteroids here we pulled a few from the NASA asteroid database which satisfy all the criteria that I'm going to want as I'll show you.
10:22:52 These are all in the few way you orbits from Earth and they're all diameters have around 10 kilometers or so.
10:22:59 Okay, I won't say much more about that.
10:23:01 There's actually lots of asteroids, of course in the solar system so you have a lot of choices, which is nice, you have you have things you can choose.
10:23:07 I also want say much about this except to say, is it crazy to think about using asteroids well I don't really know I'm not a I'm not a satellite engineered but I do know we've landed on asteroids many times, actually there's been a lot of interest in
10:23:17 this recently you see a lot of these this is from Wikipedia. A lot of these landings were very recent people have gotten really interested recently in landing on asteroids for various reason they've been sort of driven rovers actually hops rovers on asteroids
10:23:29 asteroids that this is a picture from one of the rovers, that was driving really hopping on an asteroid, they've collected samples for returned to Earth.
10:23:41 In fact, landing on the asteroid to be maybe a little quick about it landing on the asteroid wasn't really the problem, they have a really low gravity.
10:23:48 So it's not like landing on Mars or something where you're, you're worried about crashing Of course that's a it's a real challenge a real art form to be able to land on Mars landing on asteroid you sort of get near it and park there in fact they had trouble,
10:23:59 sticking, one of the, one of the landers bounced.
10:24:04 Of course it's still a non trivial mission for sure.
10:24:09 But the hope is that sort of nowhere near as challenging as something like landing on Mars which we know required a, you know, big dedicated missions.
10:24:18 I'm not going to talk too much more about these really challenging engineering aspects, I just want to focus on the asteroid is proof mass for now but this is more of a kind of information to say you may be possible to consider using these as proof masses.
10:24:31 masses. Ok so now let me get kind of the heart of the point which is evaluate the asteroid acceleration noise.
10:24:38 The first biggest effect as gravitational perturbations from planets.
10:24:43 Those are of course the sun those of course the biggest forces acting on an asteroid that would that would move it around, but those are all very low frequency these orbits are yours, right for these asteroids and for the planets and of course very well
10:24:57 known we know GM for all the planets very well. So those are outside of our frequency band and not a problem. The probably the biggest remaining external force on an asteroid is the radiation pressure.
10:25:05 So if you just do a quick estimate of the radiation pressure from the sun, you can see it's scaling with the area the asteroid over its mass, and of course scaling down as the distance were from the sun.
10:25:17 This would be the flux of radiation from the sun, so of course you can choose asteroids that are bigger or farther away from the sun, and to reduce this noise and that's actually one of the specifications that goes into I was telling you, our choice of
10:25:29 asteroid.
10:25:31 If you just evaluate this numbers actually it sounds like a small acceleration to the minus 30 meters per second squared, but it's quite large if you think back to those acceleration numbers that was given you earlier.
10:25:39 It's really very large on the scale that I want.
10:25:42 That's also not a problem though it's just a DC acceleration where we actually care about is the fluctuation of this noise in our frequency man's.
10:25:49 Right. So here for example is power spectrum or this is really the amplitude spectral density of the strain noise that would come from this fluctuating fluctuations in the solar intensity, and in particular what we don't worry too much about the formula
10:26:02 but we really care about is this year SP is the is the power spectrum of the Sun solar intensity, which is of course but measured very well for many decades because a lot of people care about this in our frequency band right it's only noise if it's fluctuating
10:26:16 in our frequency band.
10:26:18 There are also other things. For example, the asteroids are below or area effective cross sectional area fluctuates changes as it rotates and things like that.
10:26:27 But that would definitely be at the rotation period of the asteroid, which, again, we will choose to be out of our frequency band will choose asteroids that don't rotate it in our frequency band, or that would be a lot of large noise source.
10:26:40 And, and as I'll see you in a second. We'll see and just on the next slide. So long as I choose a big enough asteroid roughly bigger than about a kilometer.
10:26:47 You have a significant suppression of this noise sufficient for good gravitational wave measurement.
10:26:53 Alright so now let me just show you some plots.
10:26:59 To summarize, so here's the strain again versus frequency here's Lisa and here's a mammogram which is perfect timing right.
10:27:07 Nancy Roman and guy us astrometry carefully metric precision positions of stars to look for gravitational waves.
10:27:14 But of course, we want to do much better in this low frequency when we want to sort of get down to here.
10:27:19 If you estimate the solar intensity fluctuation noise. Using these measures fillers intensities.
10:27:25 We took the real data and and use this transfer function to put it on the plot here, you can see you're already getting to an interesting strange sensitivity level.
10:27:34 Okay.
10:27:35 and of course it's falling off rapidly at higher frequency.
10:27:41 This isn't however the only noise. There's also the solar wind, that's smaller flux smaller momentum flux from the solar wind, but it has a larger variation in our frequency band of interest, we can of course estimated very similarly so let me just put
10:27:54 that on the plot now too.
10:27:57 So if you use now these measurements of the solar wind power spectrum of course people also care a lot about the solar wind, and so they've measured it over decades, so we can get a good estimate for the solar wind noise and this is I should have said
10:28:10 for for a particular size asteroid we picked some particular numbers obviously these would move around depending on your choice of asteroid.
10:28:18 It is bigger in fact in our frequency band of interest but still low enough that we get a really interesting sensitivity.
10:28:26 One more so now I'm just going to kind of go fast that I won't go through all the sources of noise.
10:28:31 But I want to kind of hit some of the most important ones, another one which you may be thinking about is the asteroid is heated by the sun, and the fluctuations in the solar intensity, cause a fluctuations of the temperature of asteroid, the asteroid
10:28:50 which caused it to expand and contract right and the thermal expansion noise is actually often a problem for these kind of high precision experiments that could potentially be a big problem for us.
10:28:59 There's of course huge day night variations on the asteroid as it rotates, those can be hundred kelvin. But again, those are outside our frequency band of interest.
10:29:07 So again, we really care about is the solar fluctuations of the intensity, the amount the sun's intensity itself fluctuate in are relevant frequency band of interest
10:29:17 over these timescales. They only heat a sort of roughly one meter layer of the asteroid intend to the five or 10 of the six seconds. So it's the fluctuation of just that surface layer that you care about.
10:29:27 And if we translate again those measured solar intensity to the thermal expansion noise you get roughly this kind of pink curve here.
10:29:45 Finally, we want to choose an asteroid, a lot in fact a lot of these asteroids that you have naturally have rotation periods around a few hours, we definitely want to stay far away from the rotation period there will be a lot of noise that rotation period.
10:29:47 That's kind of maybe likely to be your dominant acceleration noise source of these higher frequencies but still allows a very interesting strange sensitivity.
10:29:56 I've marked out here where this rotation period would be, these would presumably we just be blind in those and then the harmonics I should say of that rotation period presumably we just be blind in those frequencies.
10:30:07 Although possibly you'd even be able to pick up a little bit of space past the first time on it, but roughly that would cut off that would that would set the high frequency cut off for your asteroid proof mass, and you can see that's kind of around there
10:30:18 a few hours so it's around 10 minus four hertz or so. So it's really letting us get into the frequency band of interest.
10:30:25 There's a lot of other acceleration noise sources, I don't want to go through them all of them I'm happy to discuss them.
10:30:31 Things like collisions and title heating seismic noise etc. Actually a lot of these are known and measured from things like the moon and Mars.
10:30:39 These appear sufficiently small though I said preliminarily where we are still thinking about these things but they appear sufficiently small for a large enough asteroids bigger than about a kilometer so.
10:30:48 So it appears that as an initial proof mass the asteroid is really an excellent inertial proof mass that lets us go make significant improvement in gravitational wave detection at low frequencies.
10:30:58 I want this is more or less the the main point that I wanted to make.
10:31:02 But, but I did want to just briefly mentioned I think I just have maybe a couple minutes, hopefully.
10:31:09 How would you turn this into a full gravitational wave experiment, like I said, I sort of showed you that cartoon.
10:31:15 I want an atomic clock so here if I take this curve is the the best published atomic clock from from June each group from a couple years ago.
10:31:23 So if I just put that curve and actually we extrapolated sort of flat to higher frequencies here to tire to lower frequencies here to longer timescales.
10:31:32 If I put that curve on this on this plot, you can see it's already actually already the existing atomic clocks now this is existing terrestrial atomic clocks would be good enough to get you excellent gravitational wave sensitivity in the frequency man
10:31:46 of interest.
10:31:47 And of course if it can be improved by an order of magnitude or so then they're not even the limits at all.
10:31:53 Of course that that's what the big caveat is as many people have said you have to actually translate the terrestrial clock to space that's an extremely important that's extremely important work will assume for now There won't be a limit, though, you can
10:32:06 see that even with existing clocks it's already very good.
10:32:09 And then finally we we put on, it may be harder to run a Lisa style at least a silent, of course will be down here and would be much better than we need, so we can do something much easier or with less precision than that.
10:32:22 Maybe that's hard though because the asteroids do have significant uncontrolled relative motion but even a laser pulsing system or a radio system could probably get you the, the sensitivity you need.
10:32:31 I didn't want to kind of briefly mentioned, the last piece of noise which is actually crucial and which we we actually wrote a separate paper on which has come out already because this applies to all kinds of detectors.
10:32:44 Is this sort of gravity grading noise the Jason mentioned, there are a lot of asteroids and the solar system.
10:32:50 It's good for us because we can use find something we like but there's a ton of them so actually just the gravity, as you know, we know where the planets are but the asteroids there tons of them and as they move around you get essentially a stochastic
10:33:00 Newtonian gravitational noise.
10:33:03 This is worse than low frequencies where the right roughly the rotation period of the asteroids is around a few years, but this certainly would apply them urs concept and cut it off as well.
10:33:11 This would apply to anything and you can see this this blue Noise Curve here is what we estimate when we calculate with a dedicated simulation from the NASA JPL catalog for this asteroid Newtonian gravitational noise and this would really cut you off
10:33:24 or doing any one of these kinds of experiments around maybe few 10s of my seven hertz or so.
10:33:30 Okay. So with that, let me kind of wrap up and say this is our full sensitivity curve.
10:33:37 Just put all those noise sources together and you get these green or red sort of markets little more conservative or a little more optimistic projections.
10:33:44 And you can see we're getting a good sensitivity with asteroids in the frequency man we want.
10:33:50 I think this is really just sort of motivation hopefully for further study, in particular, hopefully motivates space qualifying atomic clocks I think that's a really interesting direction for a lot of reasons that a lot of speakers that pointed out, and
10:34:02 I think also now motivated by gravitational wave detection in this low frequency band. And even if you could just get a 10 to the minus, 18, or so clock in space, you would already be able you know if you if you could just put it on an asteroid which
10:34:14 is which is certainly not trivial, but that level of clock to the minus 18 and space would already be good enough to do excellent job excellent gravitational wave sensitivity in this band.
10:34:25 And I think it also motivates further the sort of landings on asteroids we really like to see them do seismic measurements like they recently put a seismometer in the with the Mars rover measure seismic activity on Mars that done on the moon for a long
10:34:37 time.
10:34:38 I think it would be really interesting just to see measurements of that on the asteroid, to really confirm, is this going to be a good proof mass for this band.
10:34:46 So I'll stop there. I won't go into the next topic that I can talk about very briefly if you're interested.
10:34:51 Yeah, thanks very much. Yeah Do upload your slides about the millet charged particles that'd be great.
10:34:57 So open for questions about gravitational waves and asteroids.
10:35:08 john Mark Russell.
10:35:12 You're muted.
10:35:28 Why do we have to go to the trouble of using asteroids couldn't be used the moon and one other body rather than, for instance Mars, since we're probably gonna go to both places in the near future.
10:35:39 That's a great question and absolutely i mean that's something we were thinking a little bit about I think that should be thought more about so I don't want to say we can't, maybe we can let me turn around and say, why we focused on asteroids, so the
10:36:00 is very interesting absolutely as you say that's been mentioned it is very seismically quiet actually that's part of what gives us our confidence that we think the asteroids will be even, you know, also very good. You might be able to use the moon actually as one of your test objects, perhaps to an
10:36:05 asteroid, for example, the moon annoyingly does rotate right in the speakeasy band of interest.
10:36:11 So, I'm, you always would get a large noise around the rotation period so I'm the rotation frequency so I'm a little worried about that but the moon may be good.
10:36:23 Mars potentially but it does have an atmosphere, you know they've just been flying helicopters in it. And the atmosphere can be pretty bad for us. So, so I would be, let's say very nervous about using Mars, also I think it is a lot easier to land on asteroid
10:36:35 than on Mars. So I don't know that it's purely the thought that we're going to send equipment to Mars anyway and maybe we can piggyback.
10:36:47 But
10:36:47 you don't hear about as much they're not as big missions but but we do keep actually sending lots of things asteroids actually been a lot of interest in landing on asteroids as well but but yeah exactly all of any of those objects are interesting.
10:36:55 You just want to make sure they have low enough seismic noise and things like that. Yeah. Okay, great. Thank you.
10:37:00 On Yeah.
10:37:03 Thanks for that delightful talk.
10:37:07 This might be off topic but if you wouldn't mind indulging me Could you sketch out how a pulse our timing array works I've never heard of such a thing.
10:37:15 Sure, yeah.
10:37:17 Let me go back
10:37:20 to the beginning here.
10:37:23 Sorry.
10:37:24 So, so, for example, let me say kind of how they work and why you get a sensitivity curve like this.
10:37:29 The basic idea is you have pulsars distributed around and they are as I said excellent proof masters and also excellent clocks because they're really heavy so they spend with a very constant rotation rate.
10:37:39 And then you just time you so you have your radio telescope, measuring your pulsar, and you just time, the the arrival time of the pulses.
10:37:49 And then it should be, you know, if there was no kind of noise or signal, it would be dead, constant and you could compare it to your atomic clock and and really see that it was constant, that there's a gravitational wave that's coming through.
10:38:01 That's stretching and squeezing the baseline that'll that'll Doppler shift if you like the rate of receiving pulses. And so you'll see that in the, in the timing of the pulses and actually want to look at multiple pulse hours, so you're not confused by
10:38:13 And actually you want to look at multiple pulse hours, so you're not confused by any weird thing that might be going on with a single pulse arm. And so you can subtract out noise of your receiving station and things like that.
10:38:20 Because that is on the earth and not too good and social proof mass. So you're really just comparing multiple pulses to each other.
10:38:26 So that's basically how it works and then as I said you were an extremely long baselines the pollsters are your proof masses.
10:38:33 So it's much larger than the wavelength of gravitational waves you're talking about larger than the wavelength gravitational waves you're talking about that's why you get this kind of rapid rise to the right.
10:38:42 Cut off basically the lowest frequency. Humans have the patience to observe.
10:38:47 I don't know if that answered the question.
10:38:50 That was great. Thank you.
10:38:52 Yeah, Jason.
10:38:56 Hey, Peter. I'm so for the gravity gradient noise. I'm wondering is there, is it helpful to have more than to, like, play the same trick Can you can you measure them to any fluctuation if you had an array of these are not.
10:39:08 Yeah, that's a great question, you know, so, so I should say first, you know it's an interesting idea and I, we haven't like carefully evaluated it.
10:39:15 But I'm worried because this is really kind of what's the right thing to say.
10:39:24 you probably could reduce it some.
10:39:28 This is this is very near field noise right so it's not going to be.
10:39:33 It's, it's not going to be tremendous reduction as in the, the biggest noise Well, let me let me think about the right thing to say depends what a little bit what frequency band you're in
10:39:46 the so so so maybe, so maybe you could you would you get some reduction.
10:39:51 Look for the gravitational wave being, you know, a dead.
10:39:58 playing wave.
10:39:59 I think it might be a little harder than with the majors case, because you don't have them you know sort of arranged exactly in a line or something.
10:40:07 But in principle, maybe yes, it's of course harder to add stations here.
10:40:14 Right and majors, you can you can just more easily add more items sources along the line.
10:40:19 Whereas here you really have to be adding a whole separate proof masses.
10:40:24 And and as you know you know the wind wouldn't be quick. So I think it would probably be more expensive than you'd want.
10:40:30 Maybe there are other ways to go after that frequency band but but potentially maybe yes, I like that.
10:40:36 Well, thanks.
10:40:39 Sam you along.
10:40:41 Um, I think you mentioned somewhere that an ideal asteroids to au or something, distance. Why don't we go further and further you so there's less noise.
10:40:51 Ah, the so there'll be less noise from the sun and solar fluctuations things like that so it'll reduce these kind of noise sources I've colored in here.
10:41:02 It does make this blue noise source much worse.
10:41:06 You can see what we've done actually I should have sort of said it, we've attempted to remain well inside in the inner solar system not in the asteroid belt here.
10:41:15 When you're in the asteroid belt, this blue Noise Curve gets much worse. I'm in fact this light blue is close passes, that's roughly when asteroids pass so the dark blue is, is the whole sort of gravitational effect of a whole belt acting on you have
10:41:26 all the asteroids, the light blue is things that pass close quote unquote to you in the asteroid belt, you can imagine that's a lot worse. And that is our dominant a source of lowest frequencies.
10:41:36 So, I think you have a lot more of those you also have more collisions, which I didn't, I didn't discuss but that's irrelevant noise source. So I'd be very worried about actually getting into the asteroid belt we were, we were particularly picking out
10:41:47 asteroids that remained in the inner solar system away, far enough away from the asteroid.
10:41:54 Not thinking.
10:41:59 Yeah, Eric Cornell, if you had any sort of tracking device that would probably be noisy. So if you have a dish or a telescope on this rotating planet it's only going to point at the other asteroid.
10:42:12 Very, very short duty cycle is that something you worry about. Definitely, and and exactly and I would say that's exactly one of the really challenging issues that we've you know only thought a little about so far.
10:42:24 That's one of the things I go, you know, it goes into the challenging engineering aspects of making this a real gravitational a detector.
10:42:31 But, but absolutely That's right, you'd have to be to be re pointing this, your your your your telescope.
10:42:41 Of course other gravitational wave detectors do too, but, you know, all the any gravitational detector in space does have to reorient, but it is a little different on the asteroid obviously you can't control the asteroids you just control a piece of your
10:42:53 detector. Right. And so that I think does lead to some of different engineering challenges.
10:43:00 You know it is of course something we saw on the other people thought a lot about how to, how to, you know, reorient and station keep without messing up you know without introducing extra noise is highly non trivial.
10:43:09 And I certainly wouldn't you know, what can I say, I mean that's that's absolutely one of the crucial points that's worthy of careful study, I don't know whether it would be worse on an asteroid harder than in a satellite.
10:43:20 But yes, definitely.
10:43:23 Also, with, with the post arrays.
10:43:29 I'll be sorry sure I thought I may feel very sure that all sorts are good professors are we going to learn about the presence of loans and asteroids around pulsars or do they never have modes and asteroids.
10:43:39 That's a great question. Actually I think a little bit about similar questions recently, um, let me say the following Yeah, the, the, I think the the base thing to say is you to get around noise sources like that you do want to look at many Paul size.
10:44:03 these pulse of timing arrays look at, you know, 10s and ultimately I think aiming it even, you know, hundreds of pulse hours. So then you can see okay you know a particular object like a planet or any rock and asteroid whatever.
10:44:10 Is that a very particular frequency right so it's an air frequency band, and it'll be you know it'll be different, even if they all have them it'll be different frequency bands for the different ones, and then it should be removable so I think there's
10:44:28 Yeah, I knew Pam.
10:44:29 whenever there's more to say about that for pulsar timing, but I think that's the that's the sort of trick there.
10:44:32 Thanks, thanks.
10:44:40 So, so you have computed this gravity getting noise from the asteroids but also I mean, do, do what extent can you sense the acceleration Can you really go up to the Kuiper Belt.
10:44:47 Grandma's lovely talk I really enjoyed your talk very much, so just a silly question perhaps it.
10:44:52 Part of the reason I'm asking because even, as you know, as we all know that the solar system itself is sweeping past to the, you know, almost like empty space but if you have some small disturbances that will also induce some innovative acceleration,
10:45:06 maybe very very tiny.
10:45:09 So, whether is any proposal to detect such a you know how, how much can we push the technology, the acceleration.
10:45:17 Yeah, good well so so excellent so so actually could be asking a couple things. So let me ask you, but but in particular yeah if you look at these other colored bands I've got here not the blue, right.
10:45:29 So in other words if you took the blue sort of that signal.
10:45:33 If I want to look for things in the solar system, right, then these other bands are kind of telling you now, now I should say this, we haven't thought super careful about it's a very interesting question.
10:45:42 We just haven't thought about it yet and we were focusing in the spirit man.
10:45:45 And we were sort of viewing ourselves as cut off so I wouldn't want to extrapolate this plot too far, because we just haven't thought of those other frequency bands, but but roughly I would say Yeah right, it looks like these energies of these asteroids
10:45:56 and inertial proof masses would have excellent acceleration sensitivity even download Ilona frequencies to really see a lot of gravitational disturbances from, you know, at least this was dominant at the asteroid belt and things like that but you can
10:46:08 see it sort of orders of magnitude there.
10:46:12 But let me say, let me let me, let me say I haven't thought more than that, I don't know if you have specific.
10:46:19 Other things you're thinking about or I mean it's very interesting topic.
10:46:22 Now just because part of the reason we have we've analyzing similar kind of problem for a matter of interferometer that, to what extent can I really team, the relative acceleration.
10:46:35 And I think the problem is very similar in essence in the spirit. So that's why I was asking that To what extent, maybe one can prove to lease our in future experiments.
10:46:49 Yeah, no, I think you're exactly right that exactly the problem at that point becomes not so much the quality of your you know Adam optics or something, but exactly the quality of improvements and and so exactly as you said that's exactly what motivated
10:46:59 us was was okay I if I just want to better improve mass How do I get it, and then yeah this these well might be good proof masses to consider for those kind of exactly low frequency effects.
10:47:11 Thank you.
10:47:13 Lance.
10:47:15 Thanks Peter for a great talk very thought provoking.
10:47:19 So, how does the grave gravity gradient noise work if you are, if you're in orbit around a larger body particular of Phobos and Deimos, which are asteroids size but there are orbiting Mars, and so did you think about Phobos and Deimos or Phobos to the
10:47:47 depending on whether you want longer or shorter baselines. Yeah, we talked about a little bit, but again, that's I think still something that's very much worth think more thinking about Absolutely.
10:47:47 So what's the right thing to say, I think that, in, in principle, this asteroid gravity graded noise would certainly still be there it would certainly still be in effect.
10:47:58 It might get somewhat modified by the fact that you're orbiting it especially if the orbital like let's let me, let me say this if the orbital period was not in the frequency band of interest.
10:48:09 Then, off the top of my head I suspected won't do too much to it.
10:48:14 So long as the orbit was was short, in fact, maybe I should have said, What setting this frequency bands here is predominantly orbital period is sort of the relative orbital frequency of your detector versus your asteroids, since most of the asteroids
10:48:28 are out in the asteroid belt they've got a lower orbital frequency so actually predominantly this blue is actually being set by the orbital period of the detector around the sun.
10:48:36 That's because of the sweeps around the sun and sees a whole lot of different asteroids that are closer to it.
10:48:42 If it was just sweeping around the Earth, that's a very short orbit. And so I suspect that wouldn't do too much to this noise.
10:48:55 Although, although definitely worth the thought but I think in principle yes like you could, those are those are very worth worth considering those as proof masses Yes.
10:49:02 As I said I'd be worried about anything that had orbital frequencies in our frequency band, because I'd be worried about making a detector looking at the frequencies that you already have a big, big, a big noise source but
10:49:15 also maybe a separate question you showed this guy, I guess that's a proposed bound for Gaia, right, because there's been these reports of excess power and very, very long time or a short little frequencies from nano graph right yeah this guy is going
10:49:33 to be able to say something about that before law.
10:49:37 That's an interesting question i. So, so, possible let me let me say possibly, but I haven't studied that question in detail so so let me not actually try to answer whether I can address the particular nanogram phenomena in fact maybe someone else even
10:49:50 I mean it's a very long baseline anomaly so it takes a lot of watching for a long time, I think, I mean a long time anomaly.
10:49:57 Yeah, it's very low frequency Yeah, yeah.
10:50:01 Okay, thanks for a great talk a lot of discussion time to move on.