21st Century Cosmology

VOICEOVER
Welcome to Melbourne University Welcome to Melbourne University Up Close, a fortnightly podcast of research, personalities and cultural offerings of the University of Melbourne, Australia. Up Close is available on the web at upclose.unimelb.edu.au. That’s upclose.u-n-i-m-e-l-b.edu.au.

SHANE HUNTINGTON
Hello and welcome to Up Close coming to you from Melbourne University, Australia.  I’m Dr Shane Huntington and today’s topic is 21st century cosmology.  Astronomers are in many ways like perfect historians; every time observations are made, astronomers peer not only into the far reaches of the universe but also into the distant past.  In this way, they build up a storyline that tells us about the universe we live in today and about how the universe came to evolve into its current form.  This story is complex and there are many obstacles to knowing every chapter of the universe’s journey.  New telescopes are currently being deployed to help fill in the gaps in what is, without a doubt, the most extraordinary story ever told.  Today on Up Close we are joined by an expert in astronomy, Prof Rachel Webster from the School of Physics, the University of Melbourne, Australia.  Welcome to Up Close, Rachel.

RACHEL WEBSTER
Hello.

SHANE HUNTINGTON
Firstly, let’s just consider the history of the universe.  How does looking at the sky help us put that together?  Are we not just looking at what the universe looks like today?

RACHEL WEBSTER
Astronomers always collect light – photons that travel through the universe at a finite speed.  Because light travels at a finite speed, as we look out to great distances we’re actually looking back in time.  Of course, if we look to very great distances we’re looking, effectively, right back to the beginning of the universe.

SHANE HUNTINGTON
Now, the beginning of the universe being the Big Bang – let’s start there.  Tell us what happened?  How did things start?  What did it look like?

RACHEL WEBSTER
Well, I wish I could tell you exactly why it started, that’s one of the questions that we really can't answer today.  But we certainly know that at very, very early times the universe was extremely hot and very, very dense and in some sense – and you have to feel very comfortable with the geometry here – it was much smaller than it is today.

SHANE HUNTINGTON
Right, and we consider it today to be incredibly large, or almost infinite?

RACHEL WEBSTER
Yes.  Well, usually we talk about the observable universe which is really just how far a photon can have travelled in the age of the universe.  So if we take the speed of light and the age of the universe and multiple those two numbers together, we get a distance and that’s the size of the observable universe and, yes, it’s extremely large.

SHANE HUNTINGTON
Now, in the first, say, 300,000 years of the universe certain things were happening.  Give us an idea of the sort of post-Big Bang initial stage.

RACHEL WEBSTER
In those first 300,000 years we probably understand the physics very well, I would say at this stage.  Matter and light, if you like – or energy – were interacting very closely; you know photons or particles of light didn't travel very far before they interacted with an electron and the electrons were coupled to the protons by electromagnetic forces.  So one of the ways that we phrase this is we sort of had a soup of material and energy that was very tightly coupled.  The material at that time was ionised matter, so it was basically protons and electrons and neutrons.  Then another key idea here that we need is that the universe is, in fact, expanding with time.  So, as it expands it cools down and, as it cools, eventually it gets to a temperature where those particles want to combine together to form hydrogen atoms, for example.

SHANE HUNTINGTON
Now, I suppose, prior to some of this happening – I’m trying to get to the point where we talk about the microwave background here, because that’s our image of the very early stage, is that correct?

RACHEL WEBSTER
That's right.  At the present time the only image that we have is from particles of light or photons from what we call the cosmic microwave background, which was essentially formed at a particular point in time.

SHANE HUNTINGTON
This was not long after the Big Bang?

RACHEL WEBSTER
Well, it’s about 300,000 years after the Big Bang.

SHANE HUNTINGTON
Yeah.  What does that look like?  So when we look at this background in different directions in the sky, is it the same everywhere or is it a variation?

RACHEL WEBSTER
It’s essentially the same everywhere.  The light has the form of black body radiation because it was hot at that time.  The temperature that we observe today is about a factor of 1.000 smaller than it was at the time that it was formed, so it’s about 3° Kelvin, so that’s absolute degrees, today.  But back at the time that it formed it was about 3,000 Kelvin but very perfect black body form.

SHANE HUNTINGTON
Now, we get to about the 300,000 year mark and things start to change and we enter what cosmologists call the Dark Ages, which is an unusual term but I guess this is quite literal?

RACHEL WEBSTER
It is quite literal.  So, apart from the photons of the cosmic microwave background which are relatively low energy photos – they’re at radio wavelengths – any higher energy photons that might have been around at that time are essentially absorbed and re-emitted by the matter.  So, in other words, if we wanted to look back at sources at that time – well, in fact, there weren't any existing at the time of the cosmic microwave background.  But even if we want to look back to somewhat earlier times we would have trouble, because there’s a sort of veil across the universe of neutral hydrogen which absorbs those photons and makes it very difficult to see what’s going on if we look at optical wavelengths or ultraviolet wavelengths.

SHANE HUNTINGTON
So this is, I guess, the area of conventional astronomy where you take a conventional optical telescope and you look at what we can see with the naked eye.  In that particular period of time, it literally was dark; there was nothing for us to observe.

RACHEL WEBSTER
That's correct.  I mean, it was actually dark for two reasons; first of all, there were no sources very early on so there was no light being produced.  Then, secondly, when the first sources did turn on, there was this veil across then which made it difficult for us to see the sources at these wavelengths.

SHANE HUNTINGTON
Now, we know when we look at the microwave background we’re obviously not looking in the normal visible optical region.  So in this dark patch of history, you mentioned radio waves; there’s obviously a whole range of things that we can look at that did emit light at wavelengths that certain instruments can see?

RACHEL WEBSTER
That's right.  So astronomers have had to think much harder about the physics of what’s going on at those times and then start to figure our where the best opportunities might be to actually observe the birth of these first stars and galaxies.  It turns out that, instead of looking in optical wavebands, if we go to longer wavelengths – which is into the infrared and radio wavelengths – then the opportunities are much, much better.  These wavelengths will travel through this veil of neutral hydrogen and then, hopefully, we’re going to be able to see what’s going on.

SHANE HUNTINGTON
I find it incredible that light has just been, I guess, zipping around from that period to the point where we can detect it now.

RACHEL WEBSTER
That's right.  It’s been travelling through space for more than 10 billion years.

SHANE HUNTINGTON
You're listening to Melbourne University Up Close.  I’m Dr Shane Huntington and we’re speaking with Prof Rachel Webster about 21st century cosmology.  Rachel, we’re in the realm now of radio astronomy; very different to normal optical astronomy but, of course, light nonetheless, in a sense.  What is different about radio astronomy?  What makes radio astronomy harder or different to perform than normal optical astronomy?

RACHEL WEBSTER
Well, the wavelength of radio light is much, much longer than optical light.  Typically the surfaces we use to collect light of any sort, the smoothness of the surface, if you like, is related to the wavelength of the light.  So, for example, if you want to look in optical light you look at a mirror, which has got a very smooth surface.  But if you go to a wavelength of light which is one metre, for example, then the surface that collects that light doesn't need to be a mirror, it can be a much rougher surface so long as it appropriately reflects the light and allows you to collect it in some way.

SHANE HUNTINGTON
Now, you're involved in some of the most adventurous new telescopes that are being constructed worldwide and there are two key areas being looked at currently in Western Australia here, obviously on the western side of the Australian continent; one being the Wide Field Array and the other being called ASKAP.  Let’s start with the Wide Field Array – what will this look like and what will it be there to do?

RACHEL WEBSTER:
The Wide Field Array is a low frequency telescope.  This is low radio frequency now, so the wavelengths really are literally about a metre long.  Because they’re so large, we’re able to use quite a different technology to catch the radio waves.  We, in fact, have flat tiles.  So instead of the dishes that you're used to seeing that look a bit like TV dishes, we use a flat array that doesn't move, it just sits on the ground.  Of course, this is much cheaper than the conventional dish that has to be able to move around and track an object.  It has a number of other advantages – it’s obviously cheap but we can also image a large fraction of the sky at any one time.  We do all the combining of the images in computer space rather than in physical space, so we can be quite clever about how we actually image the sky.

SHANE HUNTINGTON
You mentioned a large area of the sky.  Presumably, you're still getting an extraordinary level of detail.  We’re talking about massive quantities of data and data processing in this type of telescope.

RACHEL WEBSTER
That's right.  This telescope is still what we call an interferometer which means that it’s not a filled aperture, it’s like having a number of different mirrors separated in space and then combining the signals from those mirrors to get a sharper image.  So we’ll have in the first telescope that we build about 500 of these tiles spread out over a couple of square kilometres and then we’ll combine the signals from all of these tiles to get the image that we want.  But each tile sees half the sky and we won’t process all of that information because there’s just too much, but we’ll be imaging an area of sky which is many hundreds of square degrees at a single time.

SHANE HUNTINGTON
The wavelength that you spoke about around several metres, we spoke before briefly about the way the universe is expanding.  Given this light is from such a long time ago, has the light changed as well as the universe?

RACHEL WEBSTER
Well, it has.  The most important experiment that we’re going to be doing is trying to image the universe in a particular emission line of hydrogen called the 21-centimetre line which, not surprisingly, has a wavelength of 21 centimetres.  Because the universe is expanded by a factor of six or seven since the time that the light was emitted, that wavelength has multiplied by a factor of six or seven and so it’s now in excess of a metre.

SHANE HUNTINGTON
Okay, so you actually have to compensate for the time that we’ve sort of been waiting around before we do the observation, essentially?

RACHEL WEBSTER
That's right.  The technical term we use is redshift, but we’re basically compensating for the expansion of the universe.

SHANE HUNTINGTON
I understand the Array can be used for other things like looking out for coronal mass ejections.  For our listeners I’m going to first ask you, what are coronal mass ejections and then why we would want to have some sort of early warning system against them?

RACHEL WEBSTER
For a cosmologist, this is actually very exciting because usually we’re just contemplating the far reaches of the universe and this time our telescope will be able to do something of practical use as well.  But a coronal mass ejection is emission of charge particles from the sun.  These are basically happening all the time but sometimes they’re stronger and more vigorous than other times and when these particles reach the earth they perturb the magnetic fields around the earth.  These can play havoc with, in particular, things like telecommunications, satellites, electrical transmission lines and so on.  So it’s actually of quite major importance commercially to understand when one of these big coronal mass ejections is coming towards us and then to take appropriate action.

SHANE HUNTINGTON
Amazing that we’re going to be using the exactly same instrument to look at the early stage of the universe development and protecting our communications system, which is quite a phenomenal balance, I find.  When will the Array be operational?

RACHEL WEBSTER
We expect to have the Array fully deployed out in the desert in Western Australia in the middle of 2010.  There’ll be a preliminary Array operating by the middle of 2009 but the full Array should be operational by then.

SHANE HUNTINGTON
Now you mention in the desert in Western Australia.  Why was this particular site chosen?

RACHEL WEBSTER
Well, the very short answer is that there are about 100 people living in an area about the size of Massachusetts.  Essentially, all human activity produces emission at these long wavelengths of radio waves.  In particular, FM radio stations produce the sort of emission that we don’t want to see.  But almost everything else – even driving your truck or car or something will produce sporadic emission at these wavelengths.  So the only way to get away from this is to go somewhere where there are basically no people and this turns out to be one of the best sites on the planet.

SHANE HUNTINGTON
Excellent.  The other project you referred to as ASKAP, which I assume is an acronym for something.

RACHEL WEBSTER
It is.

SHANE HUNTINGTON
Tell us more about that.

RACHEL WEBSTER
It’s the Australian SKA Pathfinder and the SKA is the square kilometre array, which is a vision that radio astronomers have to produce the next generation radio telescope; an international collaboration between everybody in the world which will essentially have a square kilometre of collecting area.  So on the same site there will be a mid frequency telescope which will be the Pathfinder towards the SKA.  

SHANE HUNTINGTON
Every time we move to a different frequency or a different wavelength we’re looking at a different period in history, is that correct?

RACHEL WEBSTER
Well, we’re collecting a different wavelength and at each wavelength there are things that you preferentially see.  So it’s not necessarily explicitly related to time but it’s just you're looking at a different sort of object generally.

SHANE HUNTINGTON
When you're looking at – this is a very dim source that we’re looking at out – how do you filter out all the things that happened before and after that particular event in addition to what we’re seeing today from current stars and other objects?

RACHEL WEBSTER
Most sources that we see across the universe, when we see them, the light has actually travelled to us almost unaffected by anything in time or space between that object and us.  Now sometimes there’s something in the way and we can see the imprint of that object in the light that we see – you know, there might be an absorption line or something like that – but, surprisingly, a lot of the light just comes to us directly as it was emitted.  Often we have to try and disentangle objects from the other objects around them and that requires us to understand a little bit about the physics of what’s going on in the objects and the objects that are confusing the observation. But astronomers are like detectives; they collect information and then they try and sift through, with the tools that they have available – some of which is physics and mathematics – to try and understand exactly what’s going on.

SHANE HUNTINGTON
You mentioned the Square Kilometre Array.  Will this be a similar sort of construct physically to the types of telescopes, talking about getting away from the dish sort of version of radio telescopes?

RACHEL WEBSTER
ASKAP, the mid frequency telescope, will in fact have dishes – or probably have dishes – very similar to the ones that we’re used to seeing.  Part of the challenge has been to figure out how to build hundreds, if not thousands, of those very cheaply and optimise the technology.

SHANE HUNTINGTON
You're listening to Melbourne University Up Close.  I’m Dr Shane Huntington and we’re speaking with Prof Rachel Webster about 21st century cosmology.  Rachel, I’d like to talk to you a bit about the Hubble Space Telescope because you've had some involvement in this over the years.  What are the highlights of Hubble?  Everyone knows about the sort of minor flaws or significant flaws that happened in the early 1990s but it has had an incredible history of discovery since then.  What are some of the highlights of that period?

RACHEL WEBSTER
As recently as last year, for example, Hubble discovered that Pluto has not only one moon called Charon, which we’ve known about for a long time, but it’s got two other little moons as well which are called Nix and Hydra.  You just need the superb resolution of Hubble Space Telescope to see things like this so it really has changed the way we look at every aspect of the universe.  I think perhaps the two programs that I would highlight are where it has made an enormous difference.  The first is to measure a parameter that we call the Hubble Parameter and, not surprisingly, this is called the Hubble Space Telescope.  So this was one of the key projects of the Hubble Space Telescope.  The aim here was to measure the rate at which the universe is expanding.  Surprisingly, when Hubble went up we didn't know what this value was and Hubble has provided superb data to, in fact, pin that value down to within, you know, about 5 per cent.  So we do understand now how fast the universe is expanding.

SHANE HUNTINGTON
Hubble is optimised in the visible bands?  Is that correct?

RACHEL WEBSTER
The visible and the ultraviolet bands.

SHANE HUNTINGTON
Hubble is soon to be decommissioned.

RACHEL WEBSTER
Yes.

SHANE HUNTINGTON
Hopefully to be replaced by the James Webb Space Telescope – what will be different and, I guess, what will be the advantages of this new space telescope?

RACHEL WEBSTER
The James Webb Space Telescope will be optimised to image at longer wavelengths, so into the infrared.  In fact, some of the key science is, in fact, to try and probe the Dark Ages – just the topic that we’ve been talking about – but at infrared wavelength instead of radio wavelength.  So this is the science that people are very keen to do.  It will, of course, be a larger telescope than the Hubble; Hubble has a mirror of 2½ metres and James Webb is probably going to be about 6 metres, so it’s a bigger telescope.  Also, it’s going to be located at a different position.  Instead of orbiting the earth, as Hubble does, it will be located at a distant point which we call a Lagrange point in the earth’s orbit.  So if they stuff up the technology this time they won't be able to go and visit it and fix it.

SHANE HUNTINGTON
Right, a long way off?

RACHEL WEBSTER
It’ll be a long way off.

SHANE HUNTINGTON
The Space Shuttle won't be able to make a quick repair call to.

RACHEL WEBSTER
That's right.

SHANE HUNTINGTON
What is particularly interesting in the infrared that will sort of shed light on this story we’ve been talking about?

RACHEL WEBSTER
Well, in the radio we’re looking at a particular emission line of hydrogen.  But in the infrared they will, in fact, be able to look at the emission from molecules and from dust and so it will be a different part of the equation, if you like.  So it’s quite complementary to what we’re doing in the radio.

SHANE HUNTINGTON
Rachel, just to finish; what big cosmological news should we be expecting as a result of all these technological changes in the next few years?

RACHEL WEBSTER
I think that’s quite straightforward.  We’re going to see the first stars in the universe.

SHANE HUNTINGTON
Rachel, thanks very much for being out guest on Up Close today.  That was Prof Rachel Webster from the School of Physics, University of Melbourne, Australia.  Melbourne University Up Close is brought to you by the Marketing and Communications Division in association with Asia Institute of the University of Melbourne, Australia.  Our producers for this episode were Kelvin Param and Eric van Bemmel.  Audio recording by Russell Evans.  Theme music performed by Sergio Ercole.  Melbourne University Up Close is created by Eric van Bemmel and Kelvin Param.  I’m Dr Shane Huntington and, until next time, goodbye.

VOICEOVER
You’ve been listening to Melbourne University Up Close, a fortnightly podcast of research, personalities and cultural offerings of the University of Melbourne, Australia. Up Close is available on the web at www.upclose.unimelb.edu.au, that’s www.upclose.u-n-i-m-e-l-b.edu.au.  Copyright 2008 University of Melbourne.