The Supermassive Podcast - 38: Gettin' Gravitational Wave-y

Episode Date: February 24, 2023

The Supermassive team take on their toughest challenge (and most tenuous title) yet…Gravitational Waves. Izzie and Dr Becky explore what they are and ask how the heck to detect something so small? With special thanks to Prof. Mark Hannam from Cardiff University and Prof Sheila Rowan, Director of the Institute for Gravitational Research at the University of Glasgow. Plus Dr Robert Massey takes on your questions and shares his stargazing tips for spring.  Get your copy of our book, The Year in Space, here: https://geni.us/jNcrw To add to the Supermassive Mailbox, email questions to [e-mail], tweet @RoyalAstroSoc or slide into the DMs on Instagram, @SupermassivePod.  The Supermassive Podcast is a Boffin Media Production by Izzie Clarke and Richard Hollingham for the Royal Astronomical Society. 

If you wanted to measure gravitational waves, waving your arms around would be a really bad source. One plus one does not equal two. These ripples in space and time are so small. Hello and welcome to the Supermassive Podcast from the Royal Astronomical Society with me, science journalist Izzy Clark and astrophysicist Dr Becky Smethurst. with me, science journalist Izzy Clark and astrophysicist Dr Becky Smethurst. Yeah, grab your space surfboards because this month it's all about gravitational waves.

We're going to find out what they are and ask how the heck do you detect something so small? And shout out to listener Michael Cleary because he sent a question about gravitational waves a fair few months ago and we decided that the topic needed a little bit more time than just one answer so we'll get to it. I would have been there forever otherwise. You'd have been like shut up. I'm just like the shepherd's crook comes out like shut up. And obviously Dr Robert Massey, Shut up. And obviously, Dr. Robert Massey, the Deputy Director of the Royal Astronomical Society is here. So how excited are you about gravitational waves? You know, one of the great things about being in astronomy for a few decades is you get to see things that you thought might be impossible become reality. And gravitational waves,

the first detection of those in 2015 was one of those. I remember going to scientific meetings in 2000 where people were talking about building detectors that they knew probably wouldn't detect gravitational waves. And they had to do all the engineering, work through it all. And then finally, finally, finally, 2015, you see it happen. And when you think about it, this tiny shift in space-time, I mean, there are huge disturbances in space-time, but by the time they get to the Earth, this teeny tiny shift in the length of a detector that we're able to pick up, it's crazy and we can do it. And it now offers us this completely new way of looking at the universe. So, you know, we think about light radio waves, X-rays, gamma rays, and that's all part of the electromagnetic spectrum and using telescopes and detectors of one type or another.

And then, you know, particle physics neutrinos coming through the earth is a different window and this is a completely different window again so it's slowly but surely opening up an entirely new way of looking at the universe and i think when you'll hear the interviews from today you'll just hear me going like oh my gosh okay okay let me wrap my head around that fine um yeah i love how robert your memories are like from serious meetings that you were in about gravitational wave detectors my memory of like the the very first gravitational wave detector is just everyone going around and greeting everyone in astronomy just like all week because that was like the noise that it made if you like the famous if you if you shifted it to like the the the human hearing, it just made this little pop sound.

So we would just walk around just being like, hey. I don't know. You see, there was me thinking Oxford Astrophysicists were all serious. Not at all. Okay, so gravitational waves are pretty tricky things to understand. So I asked for help from Professor Mark Hannum from Cardiff University. And Mark started by giving me a little lesson in gravity. The way that we think about gravity now, which comes from Einstein, is this really strange idea that he had that space and time are a curve. And that's really hard to picture. But

one way to think about it, which is in some way using gravity to explain gravity, but fine, which is if you're standing on a trampoline and the mat of the trampoline is stretched down, and then someone pushes a ball onto the trampoline, then it will sort of spiral around you and get closer and closer in, rather than rolling just straight across, which is what it would do if the mat was flat. Yeah. And that's kind of like what's happening with gravity, except that with gravity, it's actually space being stretched and time being slowed down. When you have objects moving through space, then the gravity around them is changing. And that change is going out into space as a ripple, as a wave in the stretching of space and time.

If a gravitational wave was to pass through the room now, the distance between the walls would get slightly smaller and then slightly bigger and slightly smaller and slightly bigger without them moving. Okay, you just blew my mind just a little bit there. And I think it's fair to that that is a completely bizarre concept yeah i think when when we're working on it we forget how really bizarre it is and the way i think about it is that it it is a completely mad idea and it would have been completely thrown out when einstein suggested it except that every single measurement we've ever done

is consistent with that theory so we just have to live with it. Okay. So are we saying that everything could give off a gravitational wave? If it's just gravity, then everything can give off gravity? Everything that has mass produces gravity. And so, yeah, if you're waving your arms around, that's producing gravitational waves okay just really really weak because gravity is the weakest of forces we know and these gravitational

waves are just this tiny perturbation on top of gravity so they're ridiculously weak so if you wanted to measure gravitational waves waving your arms around would be a really bad source okay so what are some of the better sources then to measure? Because if they are so weak, I'm assuming then that you need something massive to actually be able to even begin to detect these gravitational waves. Right, you want to come up with the most violent accelerations of matter you can think of. And that's why we look into space and we look, for example, collisions of black holes. Black holes have a huge amount of mass compressed into a tiny region.

And then if you take two of them, they can orbit each other very closely, very rapidly. And that's the strongest source of gravitational waves we can imagine. And so that's where we go to look for them. Can you talk me through that event? We talk about the collision of two black holes, but we've also seen them with two neutron stars colliding. Talk me through what's happening with them, that we then pick up these ripples in space-time. Okay, so two black holes, they're in orbit, and they very slowly spiral into each other. But this gets faster and faster. As they get closer, they orbit faster.

They give off more gravitational waves. They go yet faster again. And so this thing speeds up until they finally make contact and merge into one black hole. And I was watching videos of, you know, simulations of what this would look like. And do you know what the movement really reminds me of? I don't know if – I hope listeners did this as children but you'd go into mcdonald's and they had those machines where you drop a penny in and it would start going around the side of the machine

and then slowly circle in and in and it goes as it gets into the center it goes really really really fast that's sort of like the movement that we see of if you put two coins in at the same time and they get into the centre at the same point, that's essentially the movement that we're seeing of these merging, you know, whatever, massive objects, right? Right. That's a really good analogy of what they're doing. You can think of that bowl as like the curvature of space and time and so if we're

talking about waves here does that mean that as they get closer and closer together we're seeing the waves these ripples get bigger and bigger and and frequent as well. No, the waves do get, the signal gets louder, which is the right term to use because they're at, when we detect them, they're actually at frequencies of sound waves. So they really are like sounds and the detectors are like microphones. So yeah, the signals are getting louder as the black holes spiral together. And the signal, this is called a chirp signal. The way in which the sound rises is like a chirp.

And so you can go on the internet and you can find sound bites of people having simulated black holes and they go whoop. Oh my gosh, I love that. That's so good. And so you mentioned at the very beginning of this that this has something to do with Einstein who predicted these in the early 1900s. So how? How did he know that this might be in effect? So he'd come up with his theory of special relativity, which says that nothing can go faster than the speed of light.

And once he'd done that, he realised, well, gravity is a problem because in Newton's theory of gravity gravity just goes pump it's everywhere in the universe instantly and if you move something the gravitational field everywhere just changes instantly so it's obviously something's happening faster than the speed of light so that can't be right so he needed to fix Newton's gravity in some sense and so in doing that he came up with a theory and one of the things that dropped out was that if you have some very small change to your gravitational field and you look how that behaves it will behave like a wave and but he when he did that he thought that they wouldn't be detectable because they are so weak oh that's that's really interesting okay so he

even with all of this he knew that it would be an incredibly weak signal to try and find. And so obviously, we've moved on since the early 1900s. So we have been able to detect gravitational waves. So how did that change over time? You know, what were the efforts that really transformed studying gravitational waves? transformed studying gravitational waves? Well, one of the big things was this observation of these two neutron stars that were in a binary system and they were observed to be very, very slowly moving together

at a rate that exactly agreed with Einstein's theory. And so that showed that gravitational waves were real. And then, of course, much more recently, we've now directly detected gravitational waves with the LIGO and Virgo detectors since 2015. So that was the real transformation. Yeah. And what was that like in 2015 when that measurement came through for you, you know, in particular working in this field? through for you you know in particular working in this field it was amazing because the detectors had been upgraded over a few years to be more sensitive and they were about to be turned on and we thought okay this time we might see something but probably it will take a few years before that happens and a day after they were turned on the first signal came through so it was just incredible i didn't believe it lots of people didn't believe it. We thought, okay, they've just turned these on,

there's going to be problems, there's going to be confusion. And it was really only a few weeks later that I was finally convinced and that everyone had checked everything and they were real. And then it was just incredible. Now, I don't mean to seem rude when I ask this, but what is the point of measuring gravitational waves? That's a good question because, I mean, gravitational waves are really the least significant thing we have ever measured in human history because they've made the smallest effect we've ever measured. But what they're telling us about is about black holes and out in the universe and neutron stars and from that we can learn how those stars formed and that tells us about how the universe evolved from neutron stars we'll eventually be able to measure the signals from those from neutron star mergers we'll have

to measure the signals so well that they will tell us about nuclear physics inside the neutron stars to densities that we can't dream of producing in the laboratory. We've learned a lot from gravitational waves so far, but we haven't yet had our understanding of the universe overturned. But it's sure to come. That was Mark Hannum from cardiff university i love that he said what a mad idea gravitational waves are i think that i was just fully there in that interview like okay don't worry about shifts in space time that's totally fine i agree and actually we have the sound of a gravitational wave chirp. This is what happens when two black holes collided.

See, sounds just like... Yes, exactly. They should have done that in the press briefing, shouldn't they, really? So we are going to get onto how we detect gravitational waves in a moment. But Becky, what have we actually learnt from detecting them?

I mean, a lot. How long is a piece of really is he like first of all we've been able to test you know general relativity einstein's best theory of gravity within an inch of its life with all of these detections that we've made you know we've been taking predictions from models on what the shape of sort of these waves look like by the time they reach earth like what we should actually uh detect and all those models seem to hold up. They're based on gender relativity. We've confirmed that, and I like to express this as one plus one does not equal two. It's always confirmed because when you measure two black holes merging, they could have a mass of like, say one has a mass of 10 times the mass of the sun and one has 15 times the mass of the sun. You think you'd get out a

black hole of 25 times the mass of the sun, but you don times the mass of the sun you think you'd get out a black hole of 25 times the mass of the sun but you don't you get one out that's just a bit less than that because some of the mass and energy equivalent e equals mc squared so some of the mass of the two black holes goes into the energy that's needed to radiate away the gravitational waves which i just love that one yeah okay time we've also learned the speed of gravity is the same as the speed of light so one of the events that lego detected was 170817 a famous number now for astronomers so it's called a kilonova so it wasn't black hole mergers but two neutron stars that merged together and so we detected actually light from that merger across the entire sort of electromagnetic spectrum,

you know, x-rays, optical gamma, everything, but then also gravitational waves. And we wouldn't have ID'd it for what it was if it wasn't for the gravitational waves. And if we study it across all of these wavelengths, we learn a lot about, you know, like heavy element production, like where does all the gold come from?

And it's from neutron star mergers and also these neutron star mergers are what's known as a standard candle if you remember your cosmology izzy they're the same oh my god i have not heard that term for so long yeah so they're the same brightness wherever they go off so you can use them to get at the distance of whatever galaxy they went off in so in this case it was ngc993. And so you can get the distance to that galaxy independent of any other method, which means you can get an expansion rate of the universe independent of any other method.

And if you remember, there was a bit of a hoo-ha going on over there that two of the main ways that we measure that do not agree at the minute. So people got excited like, oh, we can use this gravitational wave discovery to measure the expansion rate of the universe. Of of course it turned out to be smack bang in the middle of the two that don't oh good it's a bit annoying but it can't help us teach us about that

but this idea that gravitational waves have sort of traversed the speed of light so gravity has the same speed as the speed of light it means they they're also affected, you know, by the expansion of the universe as well, the curvature of space-time, you know, caused by other heavy objects. They experience time dilation as well. And the implications of all that is that essentially there must be this quantum theory of gravity where you have this particle that sort of communicates what is the strength of gravity. And we call that a graviton, seems like the photon for light behaving as this quantum particle. So it has really interesting implications, all of these stuff that we've learned from gravitational waves about what is gravity and how we describe it. I mean,

quantum theory of gravity has been like physics bucket list for a very long time. Yeah time and i think it's incredible that you can take something so massive like the most massive objects in our universe to then come down and it then takes it down onto the tiniest level you know quantum level i don't think we're gonna do an episode on that uh tbc a bit out of mine and robert's wheelhouse uh Someone else can cover that topic. We'll leave that to Brian. Yeah, exactly. But do they tell us anything? Have we learned anything new about,

I don't know, characterising massive objects themselves? More like massive and very dense rather than just massive because obviously a galaxy is a massive object, right? But it's very, very dense. So it's very much sort of

neutron stars and black holes. We can sort of ask questions like, you know, does the curvature of space around them behave the same as sort of mass or gradient, or does becoming a black hole change it completely? You know, a black hole is different in some way. But the thing is, we're still really limited with LIGO to this certain mass range of black holes and neutron stars

that we can look at. You know, we look at what we call the stellar mass range. So similar in mass to stars. So anywhere from sort of one times the mass of the sun if you're sort of an up if you're a neutron star up to like a hundred times the mass of the sun not like super massive black holes yeah okay which is stuff you know that i don't really think about that's the thing that you're waiting for you're like exactly and i am waiting fairly impatiently um for that because we need a bigger detector for this.

So I think we're going to hear in a little bit about, you know, how we actually detect gravitational waves. But essentially the size of your detector limits the frequency of the waves you can detect. And the bigger the object you get, the frequency that that changes. So as I discussed with Mark earlier, on the 14th of September 2015, scientists detected a gravitational wave signal for the very first time from two merging black

holes 100 years on from Albert Einstein's prediction of gravitational waves. But these ripples in space and time are so small. We're talking fractions of the width of a proton small. So how do scientists detect them? And just how difficult is it? It's something that I put to Professor Sheila Rowan, Director of the Institute for Gravitational Research at the University of Glasgow. The fact that they're tiny, they are very hard to detect because they don't interact with very much. And so that means that the challenge for us is being able to build instruments in the end that are sensitive enough to detect stretching and squashing of space-time, what feels to us like changes in distance of isolated objects, the mirrors in our detectors,

that are less than a thousandth of the diameter of a subatomic particle. These signals are just so tiny. So how do you go about measuring them and detecting them? Because fundamentally, we're talking about tiny ripples in space and time the way we detect gravitational waves is using a technique called laser interferometry and based on what's called a michelson type interferometer something that folks who've studied physics at university will recognize from their undergraduate physics classes yeah i'm having flashbacks and the the principle is that we take light from a laser highly stabilized in intensity and in frequency we send that towards a beam splitter the beam splitter splits that light in

two directs it along two paths that are at right angles to one another so you can think of the light wave traveling distances along those arms the light waves reach mirrors at the ends of the interferometer arms and the light wave is then reflected back and traveling back towards the beam splitter and as those waves arrive at the beam splitter they either add up together two peaks arrive together and two peaks in the light of course makes a bright spot or if something has changed differentially the length of the arms of our instrument the waves may for instance arrive back from one arm with a peak and the other arm with a trough those then cancel out and we'd get a dark spot. So what that kind of device does, it uses light to accurately measure the length of the paths that the light travel. If the mirrors at

the ends of our arms move, then we see that by looking at the changes in the intensity of the light detected. Gravitational waves have the effect, as they pass through our instrument, of differentially changing the lengths of the arms of the instrument. That's the signature of a gravitational wave. So effectively, one arm length would be stretched, the other would be squashed, and we would look for that signature, that change in arm length by looking at the intensity of the light at the output of the detector so that's the principle in which they work in truth there's a lot of instrumentation in there a lot of other tricks to make that

even more sensitive so on a really basic level and i mean really, we're looking at is this laser still in sync or has something, gravitational waves, changed it. But the difference with any laser experiments that I ever did at undergrad was that I could fit them on a table. And LIGO and observatories like it are massive. So do you want to explain what they look like? So our instruments are large. explain what they look like? So our instruments are large. In this case, the longer our arm lengths, the more sensitive our instruments are to gravitational waves. So there are a number of these instruments, these observatories around the world. In the US, there are the LIGO observatories. So there are two instruments, one in Hanford in Washington State, one in Livingston in Louisiana, and their arms are four kilometres long. So if you approach one of these observatories, you would see a big building in the

middle, which is about the size of a big supermarket, looks about that size. And going out from that central building, you would see two arms with sort of concrete covers each of which disappears off four kilometers into the distance with another little buildings at the end that contain the the mirrors in them. Okay so that's the LIGO observatories in America but we see similar observatories around the world don't we? So there are several gravitational wave observatories around the globe and there are good scientific reasons for that actually. So in Europe there's the Virgo observatory in Italy but actually is operated by a consortium of European partners various different countries and in fact there's another observatory too there's the Kagura observatory in Japan and that's important

and it's important we have multiple observatories and that they are geographically separated. Multiple reasons for that first of all for that first detection it helped us a lot to see it in multiple instruments but actually scientifically one observatory has some sensitivity to gravitational waves from almost everywhere in the sky not quite but actually it's more like a microphone than a telescope which is good in some ways but on the other hand it means you don't know exactly where your gravitational wave signal came from in the sky if you have two observatories then you can start to time when a gravitational wave signal arrived first at one observatory and then the other. So knowing the timing, we can start to use triangulation to work backwards to point. You don't do terribly well, though, only with two observatories.

There's still quite a bit of uncertainty about where in the sky. with two observatories, there's still quite a bit of uncertainty about where in the sky. So the more observatories you have, you then can pin down with higher and higher accuracy where in the sky a gravitational wave signal has come from and give that information usefully to observers with telescopes. You can then turn their telescopes to point and look for any corresponding electromagnetic signal. So it's scientifically important that we have multiple instruments. And because you're looking for such small signals, do you have to be really careful of how these instruments are isolated? I imagine, you know, if someone goes stomping around near the detectors, that's going to create a vibration that will then change the signal so how do you protect

these instruments so we work very hard to isolate our mirrors in the instrument from external things that might disturb them and there's a lot of technology involved. So we talked about how tiny these changes are in the relative positions of these mirrors. To help you visualise, in the LIGO observatories, they are 40 kilogram mirrors. They are right circular cylinders. They look like big pieces of glass. It's very pure fused silica. And we do need to isolate those. You can imagine if you just put one on the ground, the ground shakes. It shakes naturally, background seismic

vibrations, or someone could, you know, as you see, drop something nearby, cause the ground to shake. So we have to make sure that the mirrors are isolated from those kinds of seismic disturbances. So one of the things we do is we suspend those mirrors at the bottom of pendulums. The laser beams that we send out don't travel through air, they actually are going along inside vacuum pipes so that air molecules passing through the laser beams don't disturb the laser beams as they travel along the arms. The mirrors have to point in a particular direction. We're using laser light that can be absorbed by the mirrors themselves. So we have to put highly reflective coatings on the mirrors to make sure that the laser light is reflected back. So there's a whole set of technological developments that have been research carried out over decades.

And this is the case where bigger is very much better. So will we see even more gravitational wave observatories with even longer arms in the future, do you think? For quite a long time in the field, colleagues both in Europe and the US and internationally have been thinking about a next step by building new instruments, tackling some of those noise sources in different ways we could do much better. So in Europe, for quite a long time now, there's been a vision for a next generation observatory called the Einstein Telescope, which instead of a three kilometre arms would be up to

10 kilometre arms. That enhances the sensitivity of the instrument, potentially underground, actually to reduce the effects of some of those low frequency noise sources, the seismic noise, because that decreases as you go underground. Part of that instrument might be cooled to low temperatures. And in the US, there's a vision again for a future generation instrument called Cosmic Explorer, which could be up to 40 kilometers. And these would have a step change in terms of the capabilities of detecting gravitational waves, potentially detecting the collision of stellar mass black holes out to the edge of the universe. No black hole left behind.

So these are exciting prospects for the future of the field. Big thanks to Sheila Rowan from the University of Glasgow. So far we've talked about ground-based observatories, but what about having one out in space you know away from any noise and disruption? There are plans in the work for a space-based gravitational wave detector from ESA the European Space Agency which is called LISA and that'll have a detector as long as 2.5 million kilometers for context that's about 6.5 times the earth moon distance so it's going to be very very big it's not going to launch until 2037

still in the design phase and everything so we do have to be fairly patient um but then we'll learn really about sort of what happens when the most massive and dense objects in the universe merge with supermassive black holes. This is the Supermassive Podcast from the Royal Astronomical Society with me, astrophysicist Dr. Becky Southerst, and with science journalist Izzy Clark. This month, it's all about gravitational waves. So let's get to our listener questions and just a little caveat from me quite a few of our questions referred to calling them gravity waves but i feel like it's better to call them gravitational waves that's more correct becky can you explain that yeah yeah that's like they're actually two completely different things gravitational waves are the ripples through space times from these cataclysmic events but a gravity wave

would almost be not really a wave necessarily but almost like a a stronger field of gravity moving through space for whatever reason like you almost hear about it in sci-fi more than you do in actual scientific okay gross necessarily um it's like oh there's a gravity wave coming where the gravity is going to increase and everyone sort of gets flattened to the floor or whatever yeah so gravity wave gravitational wave then not really interchangeable okay so gravitational waves it is and i think we have to start with the one that kicked off the entire reason for us doing this episode um michael i am so sorry that it's taken us so long to get to this one question. So Becky, Michael Cleary asks, do gravitational waves interact with each other like intersecting

waves on an ocean? Could large numbers of very big things moving around form standing gravitational waves like in a fancy wave chamber? Is that a factor in why galaxies are so weird well michael it's been a long time coming but here we go now you would think so that this could happen that gravitational waves can interfere with each other sort of cancel each other out or add together to make like a wave twice as big as the ones that that came in And that is true to a point, but they won't pass through each other and add together like waves on an ocean will, just interfering with each other because they will also interact. So remember before I was talking about how we think that the best way of describing gravity would be this quantum theory of gravity with this particle

called the graviton. Now, I basically haven't worked this out yet. We don't have a sort of legit theory of quantum gravity yet. People are still working on it. We'll people get there eventually, but we don't have it yet. TBC, TBC. TBC. But we know, at least from what we've learned about gravitational waves so far, that it's very likely that there is this quantum theory of gravity with these gravitons. So because we have gravitons, we know that there's this particle that's responsible for creating gravity and causing sort of the strength of gravity and doing all this interaction that communicates that. It means that as gravitational waves meet, you don't just get a wave interacting with each other and adding together you would also get graviton

graviton interactions so you'd get scattering and you'd get collisions as well and that would affect how the two waves would interfere with each other so it wouldn't be like the sort of sound wave constructive interference that we're used to in sort of like noise cancelling headphones or like michael gave the example of like ocean waves or anything like that. What actually would happen, we don't have a full picture yet because we don't have a quantum theory of gravity to tell us.

But at least by detecting gravitational waves, it could give us more constraints for our theories of quantum gravity for people trying to track this so i think that's a no unfortunately to standing waves standing gravitational waves michael and no that i think that would mean it wouldn't have any issue in terms of like the weirdness of galaxies i don't know what you're talking about in terms of the weirdness of galaxies it's very lots of weird but you know i think i don't think it might be gravitational waves in the end okay all right

thank you becky i hope that was worth it after so many months i thought that the answer was no sorry okay so robert david charlotte asks are gravitational wave detectors just for black hole and supernova collisions or are there other things detectable yeah i mean the main reason we talk about those things well actually you talk about black hole and neutron stars colliding in the main but the main reason we talk about things like that is because these gravitational waves by the time they get to the vicinity of the earth they're so teeny tiny that you need these massively dramatic events to generate them in the first place so you know they have to be incredibly powerful to generate something we can actually detect here on

earth that so in theory lots of other things will generate gravitational waves it's just that they're so tiny we've got virtually no chance of ever picking them up so but there are other examples i mean one of the one thing is a supernova explosion which if it happens in the right way if it's not perfectly symmetric which which seems rather unlikely, then that would generate a load of gravitational waves as well. It should be possible to pick those up. I don't think we've done that yet. Becky, feel free to dive in here if I'm wrong about that. I don't think anything's happened yet, but it should be possible if you get a very powerful supernova. But we can also see more subtle influence of them. Now, that doesn't mean we're detecting them directly, but the example I could think of was that when you look at neutron star binaries that we saw quite a long time ago,

as long ago as the 1970s, there was the Horst Taylor pulsar detected, so pulsars are pulsating neutron stars. And the researchers looking at that were able to measure the fact that the two neutron stars were slowly spiraling in towards each other because they were losing energy as gravitational waves and that was in line with Einstein's general theory of relativity as well so we sort of knew they were there and that was why there was such a huge or part of the reason I guess why there was a huge effort to build all these detectors because they're very difficult things to do but that kind of evidence led us to believe it was possible to pick them up so we see their influence indirectly quite a lot as well.

Okay. Do you know what I love as well? The history, like after that discovery in the 70s and 80s, the amount of people that were like, I have built a gravitational wave detector. I have detected gravitational waves. And you're like, no, no, you haven't. No one can replicate what you've done.

Like it was so, like the amount of people that, you know, in false claims there were just because that discovery just kick-started just this like like for all yeah yeah and it is that craziness isn't it you know just imagine i mean you know i know a long time ago but sitting in meetings with people were building this generation of detectors but they won't detect anything so we're just getting a better and better and then eventually we'll get some that work. Yeah. Okay. Becky, Samir wants to know, are there gravitational waves that are resonating continuously from the expansion of the Big Bang? Yes, Samir, we think so. We call them cosmological gravitational waves. And like the cosmic microwave background, that sort of radiation that we detect from all regions of the sky sky we think they would come from every single direction of the sky should

be arriving at us constantly we never detected them before but they are a prediction of the big bang theory of how the universe has evolved the problem is they're a very different frequency from what our current detectors are sensitive to so a very high frequency with a smaller wavelength and then by the time they get to us obviously they're very low amplitude they've been traversing through the entire universe the frequency is actually proportional as well to the size of the universe when the gravitational waves were emitted so if you have a smaller universe you have a smaller wavelength and therefore a higher frequency. And so there are actually plans for LISA, the space-based gravitational wave detector, to be sensitive to some of these frequencies,

and in particular to the ones that would be given out in the era of inflation. So I think we've covered this on the podcast before, but this is the idea that within a fraction of a second, like at the tiniest of billionths of a second, the universe expanded to billions of billions of billions of times its current size very early on in sort of the very first, you know, three seconds of the universe, we think this would happen. And that's what sort of imprinted the same conditions across the entire universe and makes it sort of so looking the same in every direction when we look out. So I think if you consider what classes as a cataclysmic event inflation, you know, definitely comes under that in the way that, you know, black hole mergers do as well. So

it's really important to understand inflation. It's been a sort of, you know, a theory for a while to explain what we see. But if we could detect gravitational waves from it, that would be the first sort of observational, you know, direct observational evidence we have of it, not just like an indirect evidence. And it's really important because the universe at that time was opaque to light. We're never gonna get light from that time. It's absorbed by all the material around it. So gravitational waves would be the only way that we could probe this. So I think that's another reason why people are very excited about LISA. Yeah yeah and we definitely did cover the beginning of the universe and inflation oh yeah new year new universe our 13th ever episode so go back through the archive and

find that one you want to know more about inflation there we go um robert chatty chooks on twitter asks do you think it's possible for two gravitational waves to cancel each other out should we use a word other than waves to describe them well chatty chooks i'm going to refer you to dr smith's earlier answer about the complexity of the interaction of gravitational waves here so i think the caveat is probably not from everything she was describing uh should we use a word other than waves to describe them well i i mean you could certainly think of it as this kind of propagating disturbance. So just as maybe we think about, you know, a tidal wave as being like a wave, it seems reasonable to talk about them in those terms to me.

Who knows, maybe we'll come up with a better word. But I don't know, a lot of the other alternatives just don't seem to cut it really, do they? I mean, pulse or something or disturbance is a bit boring, isn't it it it sounds like a bit of noise on a friday night or something like that i can see becky's got her her thinking face on she's like looking into the distance like what would i see she's exactly she's thinking about a paper and a new term right what is it space is hard words are harder right wave is the best analogy we probably could come up with ah and breathe questions down i think my mind has bent so many times this episode and thank you for everyone who sent in questions um if you want to send any in for a future episode

maybe a bit easier than this topic then you can email podcast at ras.ac.uk, tweet at Royal Astro Sock, or slide into the DMs on Instagram. It's at supermassivepod. Yeah, I like that idea. Slide into the DMs, the supermassivepod box. Yes. This supermassive just inserts it into so many things. The supermassive mailbox. Anyway.

I think, Robert, we should probably move on to something a bit easier than gravitational waves what can we see in the night sky this month couldn't agree more probably somewhat easier you know bending bending our mind as well as the fabric of the universe so what can we see well look it's we're finally moving into spring and so you've still got the the winter constellations like Orion is still there but we start to see more stuff too and if you look above Orion for example you've got Gemini the zodiac constellations really obvious above it. It looks like a sort of long box with the bright stars Castor and Pollux at one end. And I thought, I was thinking about things to look at. Actually, Castor, if you have a small telescope, is a fabulous example of

no fewer than six stars in a multiple star system, all moving around each other at different rates. And it's actually sort of three binary stars in orbit around each other as well a fiendishly complicated system and you can actually see them you can see the three pairs you don't see them resolved as pairs but you three see three stars and then you can look at them knowing that they're also pairs too one of them is this red dwarf star further out but most small telescopes will help you find that quite easily and then a bit beyond Gemini further to the east is the quite faint constellation of cancer which i mentioned because it's got this beautiful open star cluster messier 44 or precipi the beehive and that's visible actually with the naked eye if it's sufficiently dark where you are and it's one of

those objects where actually having a pair of binoculars rather than a telescope is an advantage because you you see the whole sort of dual box of stars and if you have a telescope you're only able to see a bit of it because it's quite a big thing and over in the western sky we're losing we're slowly using we're losing pretty much now saturn mars is fading out and it's moving down towards the west as well as the seasons go on and Jupiter the same but Venus is becoming much more obvious and that will be you know clearer and clearer higher in the skies than over the next few months and if you're you know if you're driving home at sunset and you see this ridiculous bright thing on the horizon that's all that's that's Venus and it's going to get better and better and but before Jupiter goes completely on the first and second of March the two planets will be really close together it should be very photogenic it's going to get better and better. But before Jupiter goes completely, on the 1st and 2nd of March,

the two planets will be really close together. It should be very photogenic. It's the kind of thing where they won't look like a single object to your eye, but they'll be really close. And if you pick up a pair of binoculars, you'll see the moons around Jupiter and Venus next to it. The two brightest planets, pretty much, so a really nice sight then. And spring is also a really really good time to be looking out looking at the moon because it's really nice in the evening sky in the spring

months because of the way because we're in the northern hemisphere and that's how it moves through the zodiac so if you're looking out the next few months but for example the next week in or so late february early march it'll be there is a beautiful crescent coming to the first quarter moon. And you can see things like the earth shine. So do look out for that too. That's a phenomenon where you get the crescent moon, the brightly lit thing, thinking of Becky's reference to a particular type of moon.

Move on quick. The darker bit of it, the bit that's not in sunlight at that point, is lit up by the light from the earth. So sunlight reflects off the earth onto it in this lovely thing called Earthshine, which is sometimes referred to as the new moon in the old moon's arms. I've never heard that before. That's beautiful. Lovely. And I also want to say thank you to listener Chris, who also goes by Catching Photons,

because he attempted to look at the comet that we've had in our night skies recently. And it's brilliant. And that was all because we talked about it last month so I'm I will put that on Instagram at some point I will do that it will be there soon you have got I should say you've got a little bit of time left to see the comet as well although it's getting fainter now it's going down memory it's going down near Ryan yeah you definitely need a good pair of binoculars now and he's fading out but there will be more well i think that's it for this month in that case and we'll be back next time with a look at jupiter you just were we just not looking at saturn on purpose now or yeah i'll see how i feel see how i feel. Is it? You're teasing me.

You're teasing me, Izzy. When will we look at... No, I'm excited to look at Jupiter. I'm very, very excited. I'm excited for the experts we're going to have as well. So get in touch if you have a question for the team. It's at Royal Astrosoc on Twitter or you can email your questions to podcast at ras.ac.uk

and we'll try and cover them in a future episode. But until then, everybody, happy stargazing.