UNSW Centre for Ideas: UNSW Centre for Ideas. 

Sven Rogge: Good evening. Welcome to Science Week. I would like to welcome you to tonight's event, which is Tamara Davis: Dark Energy, the 2024 Einstein Lecture.  

My name is Sven Rogge, and I am the dean of UNSW Science, I’m also the immediate past president of the Australian Institute of Physics. 

But firstly, I would like to acknowledge the Bidjigal People, who are the Traditional Owners of the land we’re on. I would also like to pay my respect to Elders past and present, and extend that respect to any Aboriginal and Torres Strait Islanders with us today.  

The event tonight is presented by the New South Wales branch of the Australian Institute of Physics, by UNSW Science, and also by the Centre of Ideas. And it's all part of the National Science Week.  
Now with us we have today Professor Tamara Davis AM, who is an astrophysicist, and just past ARC Laureate from the University of Queensland. Tam has been studying over 2 decades supernovae, black holes, dark energy. We will hear about that tonight.  

I will not mention the very long list of amazing academic accolades, but I do want to highlight that Tam is also an amazing science communicator, and hosted several ABC TV Catalyst shows, one of them that actually won an award for the American Physical Society, which is an amazing achievement.  
If that wasn't impressive enough, I would like to stress that Tam also played until recently in one of the national teams, and recently came back with gold. Not from Paris. I'm sure we will hear more about that tonight.  

And that, without any further ado, I would like to turn this evening over to the dark side, and invite Tamara up on the stage.  

Applause 

Tamara Davis: Thanks so much Sven /  

Sven Rogge: Thank you.

Tamara Davis: / and thanks to UNSW, and the Australian Institute of Physics for hosting this event. It is fantastic to see so many people here for a talk about science, and about astrophysics.  
I have very fond memories of this building because I was a student at University of New South Wales for 10 years. And… yeah I was a bit slow in getting my degree, you know? But I did get 3 in the end. So I spent a bit of time here, and usually it wasn't up on stage. It's good to be back.  
So, today I was going to talk to you a little bit about the dark side of the universe, the stuff that I have had the privilege to study. I had a really hard time trying to figure out what I was going to talk about, because there is so much exciting stuff going on at the moment, that it was really hard to narrow it down into what I could fit into tonight's talk. Hopefully we will get lots of good questions afterwards as well, and you can quiz me on things I didn't get to cover.  

Before I begin though, I would like to... I am studying the dark side of the universe, things like dark energy and dark matter, which I will tell you all about. But one of the funnest things that I learned about Aboriginal astronomy, is… you know, I grew up in the European tradition of looking at the constellations which are made of the bright points in the sky. Here in the southern hemisphere we have a great view of the centre of the Milky Way, and some of the Aboriginal traditions talk about, there’s pictures of the sky being made of dark patches.  

And as someone who studies the dark side of the universe, this blew my mind, and I thought this is really cool, I love the inverse, the switch of perspective sometimes that you get from looking at things from different cultures’ points of view.  

Now, let's start simple. The universe. You know, it's big. But we can start nearby. This is a picture of the earth, we’ve got the International Space Station in the way. This is a picture slightly further away, hopefully a lot of people have seen this before. This is the Earth Rise picture that was taken by the Apollo astronauts when they went and orbited the moon. This is sort of cool, because this was the first time that we had seen our planet sitting in space, as this little ball, from far away. And you can see the phases of the… you can see where the sun is shining on one side of the planet, which is a perspective we had only really seen of the moon, prior to going off the planet and having a look back at this kind of image. And apparently it inspired a bunch of environmental movements, which is pretty cool. 

This is also a picture of the Earth. It might not look like the Earth that you recognise, because Saturn’s in the way.  

Laughter 

Tamara Davis: But that’s Earth.  

Laughter 

Tamara Davis: So that little tiny dot is what earth would look like if you’re looking from the Cassini mission, that was a satellite that went and viewed Saturn and is looking back through rings at what Earth looks like from there.  

Even further away, this is the famous pale blue dot that was taken by Voyager. The most distant picture of earth ever taken, you can see us there suspended in a sunbeam. If you go look up a quote from Carl Sagan at this, there’s this whole big long quote that he talks about, just everybody you have ever met, kings, conquerors, peasants, anyone, everybody, every couple in love, everything that has ever happened in human history all happened on that pale blue dot. So it’s a really beautiful, interesting perspective that you get from studying astrophysics. But for me, a picture from this far away is still extremely local. I don't study anything that’s that close to Earth.  

So, we live in the galaxy the Milky Way. It might look something like this. This is a mockup where people have tried to imagine, from data, what the actual spiral arms look like. Here you have the, what our galaxy would look like side on. As I mentioned, we get a beautiful view of the centre of the Milky Way from the southern hemisphere. That’s because we are sort of tilted slightly with the south side of the earth pointed a bit towards the centre of the Milky Way. And that makes... that means that we get to see the whole, most of the galaxy. Whereas from the Northern Hemisphere you see more of the outskirts of the galaxy, which is why the Milky Way is so much brighter from the Southern Hemisphere than the North.  

This also is way too local for me, though. I would go and look beyond the galaxy. This is a picture of the galaxy, that’s where the galaxy centre would be. You can see the Magellanic Cloud, some of the nearest galaxies which are actually in the process of being gobbled up by the Milky Way over here on the side.  

What I study though goes much further away from this. This is a picture from the Hubble space telescope, one of these beautiful images where we’re looking really far away. Most of the little dots you see here are galaxies. So this is what you get if you take these the Hubble Space Telescope and point it at a blank piece of sky. A place you can't see any galaxies, you have no stars, there is nothing there. But you leave the shutter open for 11 days, and after that much time of exposing a really sensitive camera, you collect all the light from galaxies that were just too faint to see before. And you see that what seems like empty space is just filled with this beautiful array of galaxies. And we’re looking out almost to the horizon of our universe with these kinds of images. It's sort of the power of modern telescopes that have allowed us to figure out some really amazing fundamental things about our universe, that we would never have figured out just by doing experiments here on Earth. 

Now this is one of the most distant images that we've ever taken, it’s a very similar one, this one’s now from the James Webb space telescope. And you can see a whole bunch of cool things in this image. These are stars, the ones with the spiky things. All of the other dots in the background, these are galaxies. And you can see some which have been lensed by the things in the foreground. The light is being bent due to the gravity of the clusters that it’s passing past.  

But anyway. To give you a slightly more visceral feel of just how far we’re looking when we look at images like this, here’s a different image from the Hubble Space Telescope. It is superimposed on other images from other telescopes that cover the same patch of sky, but they just have a wider field of view. And as you zoom out and you zoom out, eventually, eventually you get to the constellations that you might recognise.

 
So, thanks to the power of some of these modern telescopes we have discovered some weird things about the universe. And the stuff I’m gonna tell you about tonight are the things that I study, which are dark energy and dark matter. Now these are two different things. We think that together they make up 95% of the universe. The dark matter clumps, it holds galaxies together, it has gravity that pulls. Dark energy, we think, has a gravity that pushes, something out there some sort of antigravity property. And a lot of my career has been trying to figure out what that could possibly be.  

So. Let’s get into it. About 100 years ago now, just over 100 years ago we first discovered the expansion of the universe and the way that was done was by the first time we could measure accurate distances to things that were far away. Now, when you look at those images of the sky, one thing that’s really difficult to figure out is how far away the dots are. Either, you don't know if you're looking at a bright thing far away or a faint thing that’s nearby, unless you have some indication of how intrinsically bright the thing is.  

So, it was Henrietta Swan Leavitt discovered that there’s a type of variable star called a Cepheid variable, that it varies in brightness, and the ones that vary fast are brighter than the ones that vary slow. So if you measure how fast they’re varying, you have a measure of how bright they are intrinsically. And that means you can tell how far they are away. It’s called using a standard candle, and it’s the same sort of principle that if I literally held up a candle, and held it right in front of your face and then I ran down the street 100 m, even in complete blackness you could make a good guess of how far I am away because you know how bright candles are, typically.  

So that was how we started to measure distances for the first time, and it was about that time we saw these stars in distant galaxies and were able to measure that these spirals in the sky weren’t just like spirals of gas close to us, but actual whole galaxies far away. And that just increased our understanding of the scale of the universe enormously.  

At the same time people use spectra, so separating the light into component colours, to measure the velocity of galaxies. If you have a spectrum, you can see that if something is moving away from you it tends to have the lines in the spectrum moved towards the red, and if it's moving towards you the lines are shifted towards the blue. And what they discovered that most of the galaxies are moving away, and the ones further away are moving faster, and that was the discovery of the expansion of the universe, it was made by a couple of people, some of the people like I’ve shown so far. Here's Hubble doing two things that we never do these days with a telescope. One is smoking, and the other is looking through the eyepiece.
 
Laughter 

Tamara Davis: And this is his plot, which has some pretty crappy data on it, admittedly, but this was velocity versus distance, and this was the first-ever Hubble diagram. Lemaître did one earlier, but he published in a French journal in 1927. This was in 1929 and because he published in a French Journal and not much of a hoo ha was made out about it, Hubble got everything named after him, because people noticed his paper. So this was the discovery of expansion. 

Now the discovery of dark matter was hot on the heels of the discovery of expansion. The first paper on dark matter appeared in 1933. This is just a few years after we knew that galaxies were galaxies, and this guy Fritz Zwicky, measured the motion of the galaxies, and galaxies sometimes form clusters and that is what you’re looking for in the background here, it’s a modern simulation of the formation of clusters of galaxies. So in the centre here, all these big fluffy things, are galaxies that are falling into a big cluster.

 
He measured how fast galaxies are orbiting each other, again using the Doppler shift, the shift in the spectrum. And found they’re moving really fast. Far faster than could be explained by the mass that you would expect to see from the bright stuff in the galaxy. So he just speculated there must be a bunch of matter out there that is not glowing, because the gravitational pull is much stronger than can be explained by the stars and gas that we can see. 

So, at the time we people didn't know what the dark matter could be, they thought it was a whole bunch of planets floating around. It wasn't taken seriously massively seriously either, until the 1960s, when Vera Ruben made a similar measurement, but this time of individual galaxies and how they spin on their own axis. Now, if you’re orbiting something, there’s a certain amount of speed that you have to have, in order to not fall into the centre. And the more mass, the faster you have to go round to avoid falling in.  

Now, if you go to the outskirts of the galaxy, you’re quite far away from most of the mass. We think if most of the mass is the really bright stuff in the centre. So you’re not being pulled very strongly by gravity, so you can relax, you can just meander around the outside of the galaxy and it’s gonna be fine, you’re not gonna fall in. 

Now, that's what we expected to see. But, when we went out and measured, this is happening, so the outskirts of the galaxy are moving just as fast as the centre, and this discovery was more evidence there’s something out there that has a gravitational pull that is not just the bright stuff that we can see. So this was the first discoveries and real, sort of, when people took seriously the idea there was a lot of dark matter out there.  

But that wasn't the end of the story of the dark stuff in the universe. This has been measured more precisely since then. I’m not going to have time to go into a lot of it but I’ll give you a glimpse at some of the other things that have been used to measure this more precisely recently. 

But first, the discovery of dark energy. Now this was a bit more subtle. So this needed to wait until the 1990s when we had a much better standard candle than those Cepheid Variables that I was talking about before. Because with Cephied Variables you need to see individual stars in a galaxy and measure how they vary. And you can't do that for galaxies except for the ones that are really quite close to us.  

So we had to wait till we had a better standard candle, a new type of standard candle came along called a Type 1A Supernova. Now these supernovae, while they explode to the approximately the same brightness, so they can be used as a standard candle as well, but they are so bright that the peak brightness, they basically, after they explode they brighten and fade, and they’re really bright for about a month and that…while they’re bright they outshine all the stars in a typical galaxy. So one exploding star is brighter than hundreds of billions of stars combined that make up a galaxy.  

Which means that as long as you can see galaxies, you can see supernovae. So all of a sudden we had a standard candle that could be measured much, much further away. Now, that’s really useful because if you can measure further away you can also look back in time, because in astronomy these things are so far away that the light travel time is extremely significant, we can look at galaxies as they were billions of years ago and see the universe as it was in the past. So we can now, with the supernovae, we can measure distance to things that are far away, and measure how fast they’re moving and that gives us how fast the universe was expanding in the past.  

So with this discovery they tried to go out and measure whether the universe was expanding fast enough to have the escape velocity and expand forever, or whether the gravity of the galaxies was strong enough to slow down the expansion and make it re-collapse. So this what they were looking for. So, I should have had this picture up before, this is an example of a supernova going off in a galaxy, this is an artist impression, but this is how it brightens and fades over about the course of a month and outshines the galaxy.  

So these guys went and tried to measure this. This is Brian Schmidt, from the High-Z Supernova Search team. He was doing this from the Australian National University. And this is Saul Perlmutter, the Supernova Cosmology Project, he was doing this over from Berkely, and I had both of these guys as my bosses simultaneously, at one point after I finish my PhD. Now here they’re pretending to fight at a conference. They were competing, they were both trying to measure the same thing, actually on the same telescope, and they were trading nights and there were a whole bunch of fun stories that you could have about that.  

So anyway! Lo and behold, when they finally figured it out, both teams found the same thing. And they found that none of these are true. We are not going to re-collapse, we’re not just expanding forever, we are accelerating right now, and in more detail, now we know the universe initially decelerated and then accelerated at about half the age of the universe ago. And this was the discovery of dark energy. Something out there is causing gravity to push rather than pull, we don’t know what it is, we give it the name dark energy, and much of my career has been spent trying to measure it more precisely, so we can figure out what it is.  

So, with this, these guys won the Nobel Prize, here they are looking a bit more respectable along with their colleague Adam Riess here. And… this was… I wasn't part of the team. So I started my PhD in 1999, as this discovery was made, and did my PhD in theoretical cosmology and then went and joined the teams after my PhD. But I worked with them for all of those years till they got the Nobel Prize in 2011, and so I got to go to some of the parties in Stockholm. 

Laughter 

Tamara Davis: There were some fun after parties, at the Nobel Prize ceremonies, so, it was pretty good. I didn't get to do the bit where you meet the King though.  
So anyway! What could these things be? Well, what his dark matter? We think it is probably a new type of particle, we have a lot of evidence now that it’s probably some sort of particle, as opposed to some sort of modification to gravity. For a long time there was a debate over whether we needed to change our theories of gravity, and that would help solve the dark matter problem. We’ve now got some more evidence which makes us think it's probably a particle, but we are not closing the door on the possibility we need to do need to still edit our laws of gravity.  

After all, the laws of gravity have been changed before. Newton had a great set of laws and we found out they didn't work so well when you have strong gravity, or if something is moving really fast. For that we need Einstein's law, so, relativity. And so, maybe relativity isn’t the final word, maybe we need a quantum theory of gravity, this is actually one of the motivations of doing this kind of work, because we know there are two theories of physics, quantum physics, which is the theory of particles and general relativity which is the theory of gravity, they’re incompatible. In quantum physics time doesn't warp and bend, but in gravity that’s a fundamental aspect of the theory. 

And so, we know they can't both be the final story. They work beautifully well and have passed so many tests in their own separate domains, and there’s not many situations in which you need both. But maybe dark matter and dark energy are cases of experimental evidence where you do actually need both, and that's one of the reasons that I find this so fascinating, we’re really trying to nail down the fundamental physics here.  

Dark energy, the leading candidate is that it’s the energy of the vacuum itself, so the energy of empty space. And again, that’s something that is predicted by quantum physics, but there’s hand wavy predictions about how much of it there should be. And while the properties are right, it looks like it should have some sort of repulsive gravity because it has negative pressure, which is weird thing.  

But the amount… if you just make, sort of a rough estimate of how much there should be in the universe, it’s about 120 orders of magnitude wrong, which if you know what a magnitude is, that’s a big number. It’s pretty much the worst prediction of all physics except for infinity. So, yeah. Maybe that's not the final story. Maybe we might need to modify gravity for this one, that’s still very open. Or maybe it’s something we haven't thought of yet. So, that’s the situation we are in and what we are trying to solve.  

So, I have been working recently, and by recently I mean for the last 12 years, on something called the Dark Energy Survey, and we… I am very, very excited. I have been giving talks, of, we’re gonna find some exciting stuff, we’ll make the most precise measurements ever! And I've been saying those things for the better part… well, for over a decade, and finally this year we released our final results, all of that’s done, and so now I can tell you what the answer is from all of that effort. But let me tell you what we did first. 

This is the CTIO 4-metre telescope, before I got involved in the project, people had designed and built this fancy new camera to go on it. It’s an absolutely beautiful camera, it takes images like this, which you can't see too well on this screen but it’s a really wide field image of the sky. If you put the moon superimposed, that’s how big the moon would be, so you can fit quite a few moons in one field of view, and that means that we could scan the sky really effectively, really efficiently. And to find supernovae you need to go back to the same patch of sky, night after night and look for things that change.  

So we did that and this is, sort of the resolution you get on that kind of image and we scanned a big patch of sky, as well as looking for supernovae, and we’ve published a catalogue of over half a billion galaxies. Covering an eighth of the sky out to half the age of the universe ago. So it’s an enormous map of the distribution of galaxies in the universe, and we found thousands of supernovae with which we are measuring dark energy.  

So, we followed that up with some measurements on the Anglo Australian telescope to get the spectra we needed to get velocities. So we use the Chilean telescope to get the distances, and this is the 2DF robot on the Anglo Australian telescope, which we use to get velocities. And this is a robot that is putting optical fibres down at interesting positions on a plate so that it can look at an image like this and each fibre would be centred on a galaxy, and you’d get a spectrum of 400 galaxies simultaneously. Really great technology that was pioneered by the Australians.  

This is a visualisation of some of the supernovae we found. So we are sitting at the centre there, looking outwards in 4 different directions. These are the 4 directions that we went back to, night after night, or week after week, for 5 years. And those sparkles that you’re seeing periodically are the supernovae, and the locations of those that we’ve seen. To give you a sense of scale, where it sort of gets a bit fainter there, sort of about here-ish, that’s about half the age of the universe ago. So, the yellow dots, which are positions of galaxies. About here, yeah, those galaxies omitted the light that we’re now seeing, about 7 billion years ago. So, to put that in perspective the earth is about 4 1/2 billion years old. So that light that we are looking at from these supernovae was emitted before the earth even formed. And the first thing that it hit, in all of that time, was the mirror of our telescope. Which is really phenomenal to think about.  

So yeah, so this was Hubble's diagram in the 1920s. This is the diagram that won the Nobel prize in the 1990s. One group had 10 supernovae with 2 colours, the other had 42 supernovae but only one colour. With the Dark Energy Survey, we've now got over 1500 supernovae in 4 colours. And so we were able to make extremely precise measurements. This represents 80% of the known supernovae at high distances. So it’s really a ground breaking change, a step change in our understanding. And because we have measured much higher distances than had been done before, we were able to measure how the expansion of the universe and the dark energy has changed over time.  

And surprisingly, we found hints that the dark energy might genuinely be changing with time. Which we thought that it was probably constant. Everything up until now, we thought it was constant. But our data has showed that there are hints that the equation of state of dark energy, for the technical people in the audience, the equation of state might be changing with time.  

So that’s… it might not be... that’s sort of inconsistent with it being the energy of the vacuum itself. But we need to doublecheck these results. Ideally we would want to have something else that was able to use a completely different technique and measure the same thing, to confirm whether this is really a true affect or not. And, because you definitely want to work on just one project at a time, we've also been working on a completely separate technique to do just that. So, in my last few minutes I will tell you, quickly, a little bit about that.  

And to introduce that, I want to introduce another concept as well. Which is the size of the observable universe. So, I mentioned before that we made a map of half a billion galaxies, that was a rough map where we don't have some of the distances. But we know that there’s a limit to how far we can see in the universe. And so, if we imagine this stuff in the background is filamentary structure of galaxies and stuff. There is a circle, a sphere around us, which is the patch of the universe that we can see. We know that the universe probably extends beyond that, but there is a patch that we can see.  

And when you look at images like this. So when I go out and I admit to someone that I'm an astrophysicist, I often get asked the question, like, you know, "So what do you do?” and like, you know, “Do you name galaxies?" Or something like that. I am like, well, actually, so we do a lot of interesting and useful stuff. I rarely get asked if, you know, I make new imaging processing techniques that could then be used to, you know, look after fires and floods and that sort of thing, and whether the software used to find supernovae can also be used to make an app that scans skin cancers and tells you whether you have a problematic skin cancer. Or whether the data scientists that we are training up can go into the industry and make clean renewable fuels. That kind of thing. So that's the kind of thing we actually do. But people say, "Do you discover galaxies?" . 

And I’m like, well, discovering galaxies is actually really easy. You just get a bigger telescope than anybody’s had before, and you look at a patch of sky that nobody’s has looked at for that long before, and you look for longer than anyone has done, and you see new galaxies. 

But with an image like this that is almost, well, pretty much no longer true. This is from JWST. You're looking so far back in time with these images that you're looking, along the line of sight, back to before galaxies had even formed. So you’re looking back into the void, where there is no galaxies more to be seen. And I think this is actually a really exciting time for humans as a species, basically, because we don't... we are actually able to observe basically to the edge of the observable universe. And we are at the point where we are going to have the next few generations of telescopes over the next couple of decades, we will basically be able to catalogue all of the galaxies in the observable universe.  

Now, this is not the last thing you can see, though. And if you zoom out beyond this, you can see something called the cosmic microwave background, which is the light which is the light that’s left after the Big Bang. I'm going to have to rush through this bit because I've run out of time, but this is basically looking back to when the universe was a few hundred thousand years old. And these hotspots and cold spots are signatures of a compression wave, like a sound wave, that was travelling back then. Because if you were living back then it would have been like living inside a star, but a star that went everywhere, in every direction.  

And, ah, interestingly those hot and cold spots are actually where there are compressions and refractions and as the universe expanded, they are where the soundwaves couldn’t propagate any more because you got too much vacuum, and those dense spots are where galaxies started to form. And so, if you want to remember one cool thing, I’ll skip over this… it’s also evidence for dark energy and dark matter, and this is if you have no dark energy and dark matter in your model, you don’t fit the data that I’ve run out of time to talk about that. So, someone can ask me if they are interested. 

But this is now a simulation, of, if you start from the initial conditions that we have observed in the cosmic microwave background and just let time run forward and gravity do its thing, you form all these filamentary structures, and these clusters of galaxies and where the galaxies form is basically where the dense points were in the soundwaves. So, if you walk away from anything from tonight, a piece of information that might be cool is that the distribution of galaxies in space is not random, it has a sound wave imprint, from the basics of the beginning of the universe when the universe could propagate sound. So I think that is cool and one of the reasons I think it’s cool, is because we can actually use that and this filamentary structure that’s in there, this is a simulation of the entire observable universe, to measure dark energy and dark matter. We use it as a standard candle, we use it as a standard ruler. The wavelength of those sound waves which is now imprinted in the distribution of galaxies. 

So, in one more minute I will show the last piece of data we have been working with, because we've been working with the Dark Energy Spectroscopic Instrument, it was DES and DESI, and I know, I think my parents were very confused when I said I was working on something called the Dark Energy Survey, and DES and Dark Energy Spectroscopic Instrument, DESI, that these are actually two different things.  

But this is the spectrograph that we use for DESI. And remember that fibre fed spectrograph I was talking about before? That was the Australian technology with the robot putting fibres in particular positions? Well this has come out of that and we helped do some design studies that let the Americans build one of these, that's even bigger and better, and this has 5000 optical fibres, as opposed to the 400 on the AAT, and in contrast to the AAT every single fibre has its own robot. It used to take about 40 minutes to configure the Anglo Australian Telescope, we configure all the fibres on this in about in five seconds. When I moved back to Australia, to the University of Queensland, after some post-docs overseas, I moved back to do something called the Wiggles Dark Energy Survey, with the Anglo Australian Telescope, and we spent five years and we measured the positions, precise positions of 250,000 galaxies. With DESI we measured 100,000 in a night, which is both exciting and also a little bit depressing.  

Laughter. 

Tamara Davis: But this is the focal plane of DESI showing you a little animation of how this works. Now, switch to the punchline, we measured… with this instrument and measured galaxies, use them as a standard ruler, here’s some of the maps of the universe that we made, these are real positions of actual galaxies and you can do a fly through of some of these. And we used these to test dark energy and dark matter, and interestingly found the same thing that we’d found with the supernovae, that dark energy might be changing with time a little bit, in exactly the same direction that the supernovae found. And so, the whole astrological cosmological community is up in arms about that at the moment. This all happened in the last 6 months. DES came out in January, DESI came out in April. And so now everybody is super excited about trying to figure out what this is.  

And here’s a map, one of the maps that we’ve made, and I wanted to put a couple of things on it. Cause’ we’re looking back in time here. And if you look back, we’re looking back to a point that’s 10 billion years ago, when the universe was 3 billion years old. That’s when the first stars formed. So we are really making maps which almost back to the beginning of the universe already.  

And yeah, as I said, we confirmed, DES... The New York Times put this out, but they said "tantalising hint that astronomers got dark energy all wrong!" Which I absolutely hate those kind of titles.  

Laughter 

Tamara Davis: But sort of, just the level of excitement over the fact that dark energy might be varying.

 
OK. And there is a whole bunch of cool new things that are coming up, that we could chat about. But I will leave you on this picture of a tree, to bring things back down to earth. Because I think one of the most important things that we learned from astronomy, and looping back to the beginning of the talk, is just the fact of how precious our earth is in amongst all of this emptiness of outer space. And there’s, you know, about 100km of air above us, and that is all the air that we’re ever gonna get to breathe. And so, if I've learned anything from astronomy, it’s that this is a really precious place and we should look after it. That, I will leave it there, thanks.  

Applause 

Sven Rogge: Tamara, that was amazing. Mindbending. Looking into the void. Thank you. 

Tamara Davis: Yep, exactly. 

Sven Rogge: Thank you very much.  

I would like to kick off and ask you, how did you get into physics? And then you might want to expand on what got you into the dark side of it all. 

Tamara Davis: Ahh, well, I actually, one of the reasons I came and did physics at University of New South Wales is, I knew that I loved science, but I really didn't know what part of science I could do. And physics gave me the most options, and was the most flexible of the degrees that I could choose. And so, that was one of the motivations. But also I remember, I loved, like all science-fiction sort of things, I loved speculating about space. I loved doing, I remember watching the shuttle launches, and things like that, when I was growing up. And that got me excited.  

My parents are sitting here, they will remember this story. When I was about 10, there was this special space shuttle launch planned. They were going to send... We studied it at school. We studied all the astronauts. First time they were sending a teacher up into space. And I must've been really excited about this, because my parents agreed to wake me up in the middle of the night and watch the launch live at 3 AM. And of course, that was the Challenger disaster. So I got to watch the shuttle explode a couple of minutes after launch, or a minute after launch. So that had a bit of an impact, as a 10-year-old. Prior to that I really wanted to be an astronaut.  

Laughter 

Tamara Davis: But after that, I actually really wanted to be an astronaut! Which is a weird response. But I guess it’s, I dunno, brought home the sort of, the importance of exploration, and the difficulty, and the challenge of it. And, yeah, I remember that as actually being an inspirational moment, even though it was a really sad one.  

Sven Rogge: Thank you. A thrill seeker to a degree.  

Tamara Davis: Laughs. 

Sven Rogge: And understanding why.  

Tamara Davis: Yea. 

Sven Rogge: You hinted in your talk, you wanted to expand on what time and space… We all got here because space is rigid, time is the same everywhere. But you hinted that that is not quite true everywhere. You wanna expand on that?  

Tamara Davis: Yeah, so, I actually I do remember a formative moment in grade 10 as well, when my high school teacher who loved astronomy took me to some talks at the one of the Universities – I think it was at Macquarie actually, this one –  and they had this these public lectures. And they introduced the concept of time dilation and length contraction. And the fact that if you are moving, or if you are in a different gravitational field, your clock will tick different rate to somebody else’s. And this blew my mind. And I do remember at the time, my teacher was apparently just sitting there listening to the talk and going oh my god, what have I done? These kids that I’ve brought here aren’t going to be understanding anything. But then I apparently jumped up afterwards, and I quizzed the lecturer. Because I was like, "and what about this and this? And what about this?" I asked a bunch of questions that I now realise were really difficult to answer and very annoying.  

Laughter 

Tamara Davis: But I was like hooked from the start about this kind of thing. And actually I have bonus slides, can I show a bonus slide? I didn’t think… I was going to put this in my talk, but then I realised, I definitely didn’t have time. But, there’s one with rainbow light colours, could you pull that one up? Oh, actually, I think I can probably get there, because I put it after this. Um, yeah. This one. So this is actually a technical slide, but it’s actually a visualisation of our data. So what you’re looking at here is the supernovae getting brighter and fainter in four different colour spans, four different filters you can put on your camera, so different colours.

We lose, these are as they go up in red shift, they’re separated, the ones that are going higher are further away. And because they are moving faster we expect them to be time dilated. So, if something moves fast its clock should be going more slowly, and the ones at a red shift of one should be twice as wide as the ones at red shift of zero. So, this is actually, this is what we show in our paper, but we have corrected the time dilation in this one, and if you look at especially out here, at these ones up here, if I don't correct for time dilation for these really distant ones, you can see that they are much wider. 

And you can see that the width of these ones is much higher than the width of these ones down here, and that’s what you should be comparing and this is evidence that time dilation is happening. So we actually measured time dilation precisely in these supernovae. And so, this is the first super precise measurement that we made out to high red shift. So that was like one of the bonus added extras that we got out of this dataset, which everyone expected to be there, there there’s no question that this should be there, but it was just like, super cool. 

Laughter 

Sven Rogge: So, you really do blue sky research, dark sky, looking into the void…

Tamara Davis: Laughs. 

Sven Rogge: And that needs no justification whatsoever, it just explains the world we live in. I work in the field where we use quantum technology, we pride ourselves, for example we can make ultra stable clocks / 

Tamara Davis: Mmm hmm. 

Sven Rogge: / that also started just for doing, for the heck of it. But there’s actually a beautiful link between your world and my world, and that all got you – at least a large fraction of you – here, when you stare at your phone you rely on GPS. Do you want to expand on how that works? 

Tamara Davis: Yeah, so this is, people ask me, you know, I’m studying black holes and cosmology and general relativity, what possible practical use would that have? So did anyone come here using a blue dot on their GPS?  

So, the GPS satellites are in a different gravitational field to you are, because they’re up in space, they’re also moving fast, so this is one of the practical situations in which we need to understand those general relativity equations, because the way the GPS works is there are clocks up in the satellite and there’s clocks down here, and it’s the timing of signals tells you where we are on earth. And if we didn't take into account relativity, the fact that the clocks there tick at a different rate to the clocks here, the GPS position would drift and we would fall out of sync very quickly, so it’s an actual critical part of a thing that I use pretty much every day.  

Sven Rogge: Yeah, I think that’s amazing, like atomic clocks were invented because we wanted to understand atomic physics, general relativity came out of the desire to understand the world, and then 100 years later, 50 years later, we get these inventions that really change the way we live out of that knowledge. I find that fascinating and I think it’s very important to remember fundamental science is linked to these breakthroughs but not in a controlled manner. There’s short term application, there’s long term applications. COVID vaccines is one of these, so that’s just fantastic.  

Tamara Davis: Yeah, like the, you know, people are playing with wires and magnets, and like, hey! There’s this electricity thing, what on earth will we use that for in the future? Who knows? And it really is genuinely one of my motivations that doing these fundamental physics, we’ve discovered something that’s causing the entire expansion of the universe to accelerate, right? There’s something out there we really don't understand, but we don't know whether we can harness that. Is that something we can we use for propulsion, is that something we can use as a clean source of energy? Quite possibly not, maybe? But, cause it’s very, very weak compared to normal gravity here on earth. But maybe we can, and maybe if we understand the link between that and quantum physics, maybe we’ll be able to do something that humans really need to do at some point.  

And even apart of those fundamental advances in understanding, we also get a whole bunch of spin-offs, which is sort of cool. So, I did, I mentioned a couple there flippantly, but some of my colleagues who were looking for supernovae, really did make an app that you can use to take pictures of your skin cancers to see if they change over time or look at pictures of your moles. And there’s, one of the ex-astronomers, Alana Fein, made a better radiotherapy machine that’s cheaper by using some adaptive optics techniques, that was used to get rid of atmospheric effects at telescopes. And, yeah we’re looking at different imaging processing techniques that help control, not control floods, but monitor floods and crops, all these sorts of things. Just the number of jobs that there after you've done a physics degree, you don’t have to go into research, there are practical applications that you can do, it’s really sorta cool.  

Sven Rogge: I guess that brings us back to your earlier statement as to why physics is exciting, because all the choice you have afterwards.  

Tamara Davis: Yeah that is, actually, I also worked in one of my family's companies doing steel manufacturing over in Canada, while I was doing my undergrad, and as a physicist I helped them design the order in which they built things and saved them some like, crane time and stuff. Like that sort of stuff is actually also really fun. I can get excited about all sorts of things! 

Laughter 

Tamara Davis: But it’s fun because my uncles who I was working for over there were like “Wow, we've never had anyone with your skills working in this sort of business. So I changed the profit margin for them from 5% on a job to 10% on a job, and they were like, “Please, please stay!”  

Laughter 

Sven Rogge: We’re very happy to take questions from the audience, maybe a student? Someone from the younger generation would like to jump in? While you think about your questions I’ll read out one of the ones that have been submitted by Slido. What are the filaments in the universe made of – I guess you showed them earlier – and are they the highways across the universe that are just linked to the sci-fi movies we said we have seen?

Tamara Davis: Ha ha! Great question! I love it. So those filaments that you saw on those simulations, most of those simulations are based on dark matter. So they’re showing where we think the dark matter is.

The normal matter also forms… like falls into the same gravitational wells as the dark matter, and so there will be normal matter on there as well, like the icing on the cake. The dark matter’s the dominant thing though, it will be the heaviest thing. You see that things fall, basically it falls in sort of a pancake, which forms a filament, which funnels down the filament into the clusters of galaxies, and the pipelines through the universe, that I think you might be referring to, might be wormholes? Which are different to these things. Wormholes would be tunnels through space, but these filaments are, sort of the scaffolding upon which all of the galaxies form.  

Sven Rogge: Thank you. Do we have an in-audience question? 

Audience Question 1: You’ve probably been asked this a lot of times but one of my favourite quotes is a quote that says, there’s two possibilities, either we’re alone in the universe or we’re not. And both are equally as terrifying. 

Tamara Davis: Laughs. 

Audience Question 1: So I don’t want empirical data, but just based on your feelings, like, do you think we’re alone in the universe? 

Tamara Davis: There’s a great quote from Carl Sagan saying that a scientist should never think with their gut, so we shouldn’t say our feelings. But that’s ok I’ll say my feelings anyway. I would be astonished if there was no life elsewhere in the universe. And so actually while I was here at UNSW and doing my PhD, we wrote a paper called Does the Rapid Appearance of Life on Earth Suggest Life in the Universe is Common? I’m surprised I remembered that title.
 
But the question is, if you look back at the geological history of Earth, basically as soon as we had solid rocks there is evidence very soon there after, of life in the fossils of those rocks. And so, it looks like life appeared here quickly. And so, does that mean that life is common? Maybe it’s easy to form if it formed here quickly. Or maybe it  was actually elsewhere first and came to Earth. So, the long and short of it, is as long as you don't need this long to evolve intelligence, then you would say, yeah it probably life would be common.  

But I think, empirical evidence, I think it's really an interesting question right now, because telescopes like James Webb are looking at the atmospheres of exoplanets. We now know of thousands of planets around other stars, a lot of them we know from the transit technique, because you see these little eclipses happening where you’ve got the star and the planet in between you and the star repeatedly, and that periodic dipping is evidence that there’s a planet there. But the, when it passes in front, some of the light will pass through the atmosphere, just like skimming the planet and we can measure what the atmosphere is made of, it's not accurate yet, but we’re getting there. 

And that’s the kind of thing where people are looking further traces of stuff like oxygen. Here on Earth oxygen is evidence of life because it is made by trees etc. and it is very reactive, you don't expect oxygen to be just floating  around in air usually, because it burns at once, basically if there’s O2 in the atmosphere it will be get used up by something. So if you see it there, something has to be generating it.  

So we’re really, again, the next few generations of telescopes might give hints that there is molecular life, at least, on planets, if we discover something like that in some of the exoplanets. 

Audience Question 1: Cool, thank you very much.

Audience Question 2: I’ve got two whole questions. Since your subject is a mapping of the universe and dark matter and dark energy over there. Since you mentioned that along with the time, dark energy is generating or the universe is expanding at an accelerated rate. So do you mean, that dark energy being generated more in the distant past compared to the recent past, like you know when you map it? So why is the universe expanding, because it is of the quantity of the so called dark energy, is it generating more and more? Is it just with the time? Or because it is distributed unevenly across the spectrum of the universe?
 
Tamara Davis: So the dark energy we believe, if it was vacuum energy, it would just be constant. But because the universe is expanding, essentially more vacuum is being made as time goes on, so that's why went for a decelerating universe when the universe was very dense, still in it’s youth, everything was still close together, it hadn't expanded enough to let dark energy dominate, but as it expanded and the vacuum became more and more of the universe was just empty space, then dark energy could show up, like show it’s face, and it started dominating the dynamics and started pushing the universe apart.  

Now if we have dynamical dark energy, it might be that that is not just a constant, that there is actual change that is in addition to just more vacuum being out there. But we’re trying to measure that more precisely now.  

Audience Question 2: Does it ever impact the stretching of the space-time fabric of the universe?  

Tamara Davis: Yes. So it does accelerate the expansion of the universe. So it is having an effect on the fabric of the universe, even though there’s a whole different debate we could have about what that, what it means to say fabric of the universe  

Audience Question 3: Hi Tamara, I’m Kye, I love the universe. I’ve actually got a note in my phone from 11 February 2023, and I wrote down, "dark matter is negative energy." Which when you think about our conscious thought and all the things that we think about that actually, you know, goes out into the universe, what if we are actually our purpose and the things we do are contributing to a lot of this? 

Tamara Davis: There’s a part of quantum physics that is all about the observer. Yeah, but negative energy is more likely to be a component of dark energy than dark matter because if you have some sort of negative energy, we think it’s actually negative pressure, that’s the kind of thing that would give you repulsion, it would cause gravity to work in the opposite direction. But yeah, thanks… 

Audience Question 3: Well, I often find lights flickering and I’m like, ooh, that’s negative energy, and then when I follow them, I actually end up in a negative position, there will be like, somebody around and I’m not safe, and I actually feel the light going a bit funny. And I’m like, ooh, is this a sign of some negative energy here? Maybe we are contributing in some way?  

Tamara Davis: I don’t know anything about that! But yeah… 

Audience Question 3: I mean, think of… I mean, the universe is expanding, what about our mind and our consciousness is also expanding? 

Tamara Davis: I certainly hope that I am learning more and more every day, that’s true. 

Audience Question 3: Yeah. 

Tamara Davis: Thank you very much. 

Audience Question 3: That’s ok. 

Sven Rogge: Thank you. Please. 

Audience Question 4: Do you think that physics will be able to explain the origin of cellular life?  

Tamara Davis: I would love to think that it could, and the big question of how life began is something I find fascinating. One of my Catalyst episodes I got to interview a whole bunch of experts on this topic – there’s a few of them here at UNSW as well – who are looking at how cells can form just naturally by the polarity of lipids and things you can make, basically sort of soap bubbles that can align things and make cells, and sort of looking at different ways where you can get structures that could protect amino acids or the components of DNA. So I am hoping that possibly we can explain it one day. And I think the emergence both of life and of consciousness from there are both fascinating topics. 

Audience Question 5: Is it possible that the dark matter or dark energy would have had a different set of properties in the early universe compared to what they are now? And if so, how would we test them and compare them?  

Tamara Davis: So that’s exactly the kind of question that we’re trying to answer with these more detailed observations, by using, with the Dark Energy Survey and DESI, we’re looking further back in time than had been possible before. So we’re able to look for time variations of both dark energy and dark matter, and that would show up as different curves. If you would, like would appear as some of the stuff we are seeing, where we are seeing some time variation.  

We also make a point at looking in different directions of the sky, and seeing if we can see any clustering or any directional dependence of our measurements. And so far we can't see any directional dependence of the dark energy. There is inhomogeneity’s in the universe, you saw, like the clusters and filaments that form and stuff. But beyond those local inhomogeneities, on average once you take big patches of the sky, it looks like it's the same everywhere. And the laws of physics have been consistent throughout time.  

But I know there’s also some people in the audience who are looking, whether there are things like the time variations of the constants of nature. So we actually also look for, you know, things like the speed of light, the fine structure constant, the charge of the electron. Are they changing with time? And we can look at distant galaxies and see if the physics that’s going on there matches the physics here. And uh, yeah, so we question everything, if we’re physicists. We don't take anything for granted.  

Audience Question 5: Gotcha, thank you. 

Audience Question 6: Hello, I also found your talk very fascinating and interesting. Sorry if this is an annoying or difficult to answer question, I have an annoying and difficult to answer curiosity. But do we know where dark energy came from? Did it come from before the Big Bang, from the Big Bang? And furthermore, do we know what was there before the Big Bang?  

Tamara Davis: Oh! Just the easy questions you give me, isn't it? Laughs  

Laughter 

Audience Question 6: Apologies.  

Tamara Davis: Ah, well, it’s sort of asking the question of, where did all of the matter in the universe come from? And that’s a really interesting and somewhat open question. We have theories about how that could have happened. There is a particular theory of the inflationary universe. If there was something that caused a rapid acceleration in the early universe, and then that acceleration turned off, that could dump a bunch of energy that would make all the particles in the universe. And that’s actually our leading theory for how matter initially formed. There was some quantum fluctuation that caused an inflationary period, and then that energy got dumped into matter. 

But we don't really know, beyond maybe it's even a fundamental property of the vacuum. Where dark energy, et cetera, would come from. So that question - you are really asking about the origin of the universe, and the origin of everything, and that is one of the ultimate questions that we are trying to answer with this kind of stuff.  

Audience Question 6: And, also you mentioned earlier in your slideshow that at one point the acceleration of the universe slowed down. Do we have any theories on why it slowed down at that point?  

Tamara Davis: Yeah so, I think what you are referring to is that initially is that the universe was decelerating, then it started to accelerate. Yeah so that’s… if you have... imagine you have a constant force pushing outwards, but you have a variable force pulling inwards. So when the universe was really dense and all of the matter was really close together, the gravitational pull of the galaxies on each other was really strong. Because they were just neighbours, they were really, really close. So the gravitational pull was dominating, and it was winning. Dark energy might have been there and going, "I'm trying to push, but I can't do it, you guys are too strong!" Dark Matter is like, "I am so strong!"  And then universe got bigger and the space between the galaxies got bigger. And the galaxies were like "Oh, I can't hang on to you anymore! My gravity is getting weaker!" And dark energy is like, "Yes! victory!" And it started accelerating the universe. So that’s how we think it worked, with all of that drama and personification as well.  

Audience Question 6: Thank you for answering my question. 

Applause  

Sven Rogge: Fantastic question. Please, on this side.  

Audience Question 7: Thank you, I’ve always been confused about how the universe can be expanding without a known centre. On top of that we have cosmic background radiation which is isotropic. But how can it be isotropic, if it’s coming from a central point? If the universe used to be smaller?  

And another thing, for Hubble’s constant, does that change over time? Because if velocity’s proportional to distance, that implies that the velocity is increasing exponentially?  

Tamara Davis: Okay, now I will start an hour-long lecture... Laughs 

Laughter  

Tamara Davis: Great questions! Hubble's constant is the rate of expansion right now, so it doesn't change with time. But the expansion rate has been different in the past. There is a Hubble parameter which does change with time, and if we found ourselves in the past or in the future it would have been a different value. So yes that is a number which does change with time, depending on what your now is.  
I actually have some slides. You asked about the centre of the universe. Can I get my slides back up? Because I think the very next slide might even be about where the centre of the universe. Because I get – this is like, "Here is one I prepared earlier" – I get that question a lot.  

So, we do think that everything is expanding away from everything else. We don't necessarily think there is an edge, that there is nothing, and things are expanding into that. It's more like everything is expanding away from everything else. And it might even be just like ancient mariners who went looking for the edge of the earth, didn't realise you could make it all the way around. Maybe we can go all the way around our universe as well. Or maybe it's infinite, we don't know.  

There is a patch of the universe we can see, and that is really all we can say stuff about. The centre question. We know that there is no source, and this is my cartoon diagram of the universe, with some red galaxies, some blue galaxies, some white galaxies. I’ve done a very, very fancy thing in keynote of expanding it a bit.  

So, there is a slightly smaller version, and a slightly larger version. Then I superimposed them on top of each other, and voila! Everything is emanating from the central point. Now I’m going to take this set of dots, and I’m going to move it such that I’ve chosen a different centre. And now it looks like everything is emanating from that other point up in the corner. I think I can do it one more time and I’d choose a different centre down here. And now everything is emanating from that point.  

Basically, if the distances are proportional to the velocities, you just get everything’s moving away from everything else. It's like blowing up a balloon. If the balloon has a bunch of dots in it, you can put your finger on any dot on the balloon, and you will find that all of the dots are moving away from the one you have chosen. There is nothing special about the one you've chosen, it's just, you choose another one and everything is moving away from that. It’s just everything is moving away from everything else. Does that make sense?  

Audience Question 7: Kind of.  

Laughter 

Audience Question 7:  Like, if I look at this and you show the different perspectives, that makes me think that the red dots that we’re seeing in the front are now the centre. Because if we look around, it looks like everything there is being brought out. So maybe this could be the centre? Or there’s a centre behind the screen that’s pushing everything outwards. 

Tamara Davis: Yeah, so I’ve done this in two dimensions, where you’re actually seeing it moving outwards this way. But I don't have the diagram of it because it’s much harder to visualise, but the same thing works in three dimensions. And so, if you have a conclusion, there’s no particular centre to the universe, but you can also choose anything at the centre of the universe. If you want to have another take-home message... You are at the centre of the universe.  

Laughter 

Sven Rogge: We are over time. We will take two more questions from our young colleagues now at the microphone, and then we have to draw it to a conclusion. Please.  

Audience Question 8: Earlier you said that at the start of the universe there was a sound wave background. Anyways, I was wondering, if you travel through time using, say, neutron stars or wormholes or whatever, it’s in a Dr Carl book somewhere. Anyways. If you did that and travelled back in time wearing some fancy headgear and stuck your head outside of the spaceship, or whatever you were using to travel back in time, and just listened, what would it sound like?  

Laughter 

Tamara Davis: Ha ha! Fantastic. It would be really noisy! So if you could go back to the time when soundwaves were travelling, you would jump out of your spaceship, and it would be like literally jumping out of your spaceship into the middle of the sun.  

It would be that hot and dense. And I wouldn't recommend it. Interestingly, the soundwaves at that time were travelling at more than half the speed of light, because what was there was this plasma. You have protons, electrons, neutrons, all bouncing around together with photons. And so the light was participating in the soundwave, and making the sound speed really, really fast. And so, it would have been extremely noisy, and somewhat deadly. It would have sounded a lot like white noise, like SSH! It wouldn't have sounded very coherent.  

Audience Question 8: Ok so, sorry, it would sound like radio static? Because I read somewhere that a little bit of radio static is actually from the Big Bang. So it would just sound like radio static, 17 bajillion or whatever, times louder?  

Tamara Davis: Basically, Yeah. You would definitely lose your eardrums.  

Laughter  

Tamara Davis: It was actually.., when we used to have old analog televisions, the kind that had radios, before we had digital televisions, a bunch of the static that you saw on the television, a few percentage of that static that you saw, was actually the light, the microwaves that were coming from the Big Bang that we were seeing there. 

Audience Question 8: Okay.Thanks, bye!  

Tamara Davis: Thanks haha! 

Applause  

Sven Rogge: And now, last but not least.  

Audience Question 9: It's quite funny, I actually just had the same question.  

Tamara Davis: Laughs  

Audience Question 9: Laughs  

Laughter 

But, I was also wondering, this might be a whole different can of worms, but is anti-matter different to dark matter? Like, is there a big difference between them?  

Tamara Davis: That's very insightful question, and I’m really, really glad you asked. Yes, anti-matter is different to dark matter.  So, anti-matter is essentially normal matter. It's the stuff that sort-of appears in the periodic table, it just has opposite charge. So it has positive mass, so it still has attractive gravity. And, we don't see much of it naturally occurring in the universe, but you can make atoms out of anti-matter if you wanted to. You would have an anti-proton and an anti-electron, and they could make an anti-atom. Yeah, it sort of like, can have its own chemistry, and all that sort of stuff.   

And so we think dark matter... we call it dark because it doesn't interact electromagnetically, so it doesn't interact with light, it doesn't glow. And we think it just passes straight through normal matter without bouncing off it. So anti-matter, in contrast, if it encounters normal matter, boom, bad news for lots of people. Yeah, so it has an annihilating effect if it hits normal matter. They are very different things. But I should have mentioned that, because that is a question I also get asked relatively frequently. So thanks for bringing that one up.  

Audience Question 9: Thank you for answering.  

Applause 

Sven Rogge: On that big ba-da-boom question, I think we end here. I would like to thank you all for joining us here tonight. It’s fantastic to see so many of you and I hope you enjoy more of Science Week. 

I think that was a really fantastic gaze into the void, mind bending Tamara dark energy. Thank you very much for sharing that all with us. If you are interested to hear more about science, please subscribe to our podcast. And keep an eye on what the Centre for Ideas will bring. There’s amazing things going on, not only in Science Week.  

With that, I wish you all a very safe travel home. And thank you very much.  

Applause 

Tamara Davis: Thanks guys! Thanks for having me!  

Centre for Ideas: Thanks for Listening. This event is presented by the UNSW Centre for Ideas, Australian Institute of Physics and UNSW Science as a part of National Science Week. For more information visit unswcentreforideas.com, and don’t forget to subscribe wherever you get your podcasts.