0:00

Hi, Andrew Dunkley here and just want

0:02

to say thank you for listening to

0:04

Space Nuts throughout Fred

0:06

and I are taking just a couple of weeks off, but

0:09

we will be back early January. In

0:13

the meantime, here's a repeat episode from

0:15

early 2023, one of our Q&A episodes.

0:21

Space Nuts. Hello and welcome to Space

0:23

Nuts. My name is Andrew Dunkley, your

0:25

host. It's so good to have your

0:27

company. And being episode 345, we

0:29

dedicate the entire show to questions from the audience. And

0:35

we're going to do a bit of a mix of

0:37

audio and text questions today. We'll fit in as many

0:39

as we can. We've got 500 of them here. We

0:41

might get two in, two or three.

0:45

We'll see how we go. We'll be

0:47

looking at the rotation curve of

0:49

galaxies and walking on neutron stars.

0:51

We'll also be chasing up the

0:53

previous episode's talk on asteroids, dark

0:56

matter, dark energy, bright holes, the

0:58

period of inflation and much, much

1:00

more coming up on this episode

1:03

of Space Nuts. 15

1:06

seconds. Guidance

1:09

is internal. 10,

1:14

9, ignition sequence start. Space

1:18

Nuts. As the Nuts

1:20

report, it feels good. And joining me

1:23

to answer all of those questions and

1:25

more is Professor Fred Watson, astronomer at

1:27

large. Hello, Fred. Hello, Andrew.

1:29

It's great to see you again. You too.

1:32

After so long. It's been so long. Yeah.

1:35

Been so very long. Tongue

1:38

in cheek. Yeah, well, actually, we should

1:40

just blow the whistle. We're doing catch up

1:42

episodes because you're going to be away for a bit. I'm going

1:45

to be away for a bit. Adds up

1:47

to a long period of time where we won't be able to

1:49

record. So we're working ahead

1:51

of time. But

1:53

for you who are listening, it is

1:55

the right time anyway. So it

1:58

doesn't really matter that I'm explaining that. like

2:00

I am. We

2:03

might as well get stuck a

2:05

lot to do so we will

2:07

just go straight into question one

2:09

which comes from Rusty in our

2:11

favorite WA town of Donnybrook. Hey

2:14

Fred and Andrew it's Rusty in Donnybrook. I

2:17

hope you are keeping cool in our

2:19

extended summertime here in Australia. Fred

2:22

you once famously remarked

2:26

on the show that

2:28

spiral galaxies when

2:30

viewed in infrared light completely

2:32

lose their spirals. You

2:34

don't see them at all in infrared. So

2:39

I am wondering since most

2:41

of the visible light is

2:44

from the spirals and almost

2:46

all of the ultraviolet light is also

2:48

from the spirals how

2:51

does the rotation curve

2:53

vary with wavelength?

2:57

Thank you. Alright, thank

2:59

you Rusty. Nice to hear from you one

3:01

of our regulars. We

3:04

did talk about that before and

3:06

it became apparent that when you

3:08

view a spiral galaxy through infrared

3:10

there are no spirals and

3:13

yeah it's got Rusty thinking. Rusty has

3:15

an interesting mind. He thinks about a

3:18

lot of things. Yeah

3:21

and actually Andrew and Rusty

3:25

what's given the light to

3:27

my comment about the

3:29

spiral arms disappearing in the infrared is

3:32

some beautiful James Webb Space

3:34

Telescope images of galaxies which

3:37

have sensational spiral arms. What I

3:39

said originally is that if

3:48

you look in the infrared you see galaxies dominated

3:50

by old stars and they tend to be yellowish

3:58

in color rather than. rather

4:00

than in you know rather than blue

4:02

and white as the young stars are

4:05

and so they they do and

4:09

it is true that the

4:11

galaxy itself has this

4:13

underlying population of these elderly

4:16

stars that have been there a long time. So

4:19

what you for you're an elderly star

4:22

is well yes

4:24

no I'm just old Andrew there's

4:26

no bit about the book in

4:28

fact I'm bordering on ancient I

4:31

think I could say. So

4:34

anyway yeah so there's an underlying

4:36

population of old stars including

4:39

me and they

4:41

tend not to delineate

4:44

the spiral arms. Then

4:47

if you look at you know most images

4:50

of galaxies and particularly the early black and

4:52

white ones which were sensitive

4:55

to the blue actually rather than the

4:57

red yeah they show the spiral arms

4:59

because that's where the young energetic

5:01

stars are they're white

5:03

or bluish in color and they show up.

5:07

Now spiral arms are we

5:09

know the host the location of many

5:11

young stars because the spiral arms are

5:13

caused by sound waves effectively

5:15

passing through them and basically

5:20

sparking them into ignition

5:24

and so you get short-lived very

5:26

bright stars which show up

5:28

as bluish objects in the

5:30

spiral arms. Now why does

5:32

the Hubble sorry why does

5:34

the James Webb space telescope show galaxies

5:36

with lovely spiral arms and the

5:39

answer is that what you're seeing there is the

5:41

dust in these in these

5:43

spiral arms. Predominately the

5:46

dust and that dust is

5:48

being also pushed

5:50

into a spiral shape by the shock

5:52

wave the density wave that's passing through

5:55

them and causing the star formation that

5:57

reveals the spiral arms the stars themselves.

6:00

positive, right? So that's

6:02

just by way of a caveat to

6:05

what I said as Rusty

6:07

quoted me as famously having

6:10

said that the spiral arms

6:12

disappear. And it's still true,

6:14

but it's certain wavelengths of

6:16

light, which brings me to

6:18

Rusty's question, how do

6:21

the rotation curves vary with

6:23

wavelength? So if you

6:26

are always looking at stars,

6:35

you're seeing objects whose

6:37

spectrum is

6:39

going from the ultraviolet to

6:41

the infrared, but

6:44

it's the same object. And so it's the

6:46

same moving with the same

6:48

velocity. So in that regard, looking at stars

6:50

in different wave bands, you're still going to

6:52

see the same velocities. But

6:56

it extends even further than that. And

6:58

that is because, and this was actually some

7:00

of the work that Ken

7:02

Freeman here in Australia and Vera Rubin

7:04

did in the United States, back in

7:07

the 70s, demonstrating the

7:09

rotation curves of galaxies are flat,

7:11

they don't behave as

7:13

you would expect. If

7:15

you look at plans of gas with

7:18

radio telescopes, the sort of, you

7:21

know, cold hydrogen

7:23

in space, which

7:26

emits radiation at

7:28

21 centimetres, it's in

7:31

the radio spectrum, that follows the same

7:33

rotation curve as the stars

7:35

do. So in that regard, the

7:38

rotation curves are independent of

7:40

wavelength. Okay, very good. That

7:42

was simple. Yeah, long

7:45

answer to a short question. But a good

7:47

question, Rusty. As Andrew says, you always think

7:49

outside the box. You do indeed. Thanks, Rusty.

7:52

And now we'll move on to North Carolina,

7:55

which is a long, long way from Donnybrook. And

7:58

one of our... female

8:00

listeners. We don't get too many questions.

8:05

Hello, Nan. I'm confused

8:07

about gravity, she says. You'd

8:10

be the only one. I

8:13

heard it described as the curving of space due

8:15

to the mass of an object. Thus, an

8:17

object in the vicinity of another object

8:19

falls into the curve, causing the object

8:22

to follow the curve. When referring to

8:24

the formation of stars, the description seems

8:26

to be that the gas is squeezed

8:28

until it becomes hot enough to ignite.

8:31

This is also described as gravity

8:33

drifting on the gas. That seems

8:35

to be a different action of

8:37

gravity than the bending of space.

8:39

Help me understand. Thanks, Nan.

8:43

What a great question. Yeah, that's

8:48

a fabulous question. So, yes,

8:52

it was Einstein who

8:54

said that gravity

8:57

is the phenomenon, it's

9:00

a geometrical phenomenon is what he said.

9:02

It's actually about space being bent by

9:04

any mass

9:06

that's within it. And

9:09

that's fairly easy to get your head around for something

9:11

like the Sun, where you've

9:13

got this giant ball of

9:16

gas, which is gravitationally distorting

9:18

the space around it. And that's demonstrated by

9:20

the fact that when you look

9:23

at the Sun in eclipse, you see stars in the

9:25

background looking to be in

9:27

the wrong direction, which is how they proved

9:29

that Einstein's theory was correct. But

9:32

it's probably less easy to get your head

9:34

around that when you're thinking just of a

9:36

giant cloud of gas. So if

9:38

you've got a blob of gas in space, and

9:43

that gas

9:47

is gravitating because it's made

9:49

of matter, then

9:51

even though it's pretty

9:55

tenuous, is that the

9:57

word? Yeah. It's a tenuous

10:00

object is not solid like a

10:02

planet, it will still distort the

10:04

space around it. And

10:06

the effect of that is once again

10:09

that the outer edges of

10:11

that space will be bent less

10:13

than the regions towards the center where

10:16

the mass is concentrated and

10:18

you'll get this compression effect. The

10:20

gas will slide down the bent

10:22

space and the

10:24

effect of it is the temperature

10:27

increasing and eventually the cloud of

10:29

gas turns into a star. It's

10:32

the mantra is that what

10:37

is it? Matter tells space how

10:39

to bend, space tells

10:41

matter how to move. Right. That's

10:44

the, I think it

10:46

might be John Wheeler who said that

10:48

decades ago, but that's the bottom line.

10:51

Very clever. Okay. Gee,

10:54

we're getting through on fast. We

10:58

need to slow down. It's

11:00

too quick for my brain.

11:03

We can easily see. Thank

11:06

you, Nan. Let's go to our

11:08

next questioner and this one's

11:11

a sort of a speculator from

11:13

Russ. Hi guys, Love

11:15

the Show. It's Russ here from Stalebridge

11:17

in the UK. My

11:20

question is more of a journey

11:23

that we could take. Let's take

11:25

out the physics of

11:27

the impossible. I won't

11:29

be able to do it, but let's

11:31

have a walk across the surface

11:34

of a neutron star. What

11:37

words we'd be seeing on the surface.

11:39

What does, what would the surface look

11:41

like? Would it be glowing? Would it

11:43

be white? Would it be

11:48

iridescent? What sorts of colours would we

11:51

be seeing if we bend down and

11:53

touch the surface? What would it feel

11:55

like? If we were able to jump

11:57

off a little step, maybe. looking

14:00

at the sky from the neutron star, it

14:05

probably would look a bit weird because

14:07

there would be definitely gravitational distortion effects

14:09

in the space around you and

14:12

that might cause some strange

14:16

effects, particularly near your horizon, with

14:18

stars compressed

14:22

one way or the other. So it

14:24

would be an environment that is very very

14:26

different, assuming that we could

14:28

magically somehow survive it. It

14:31

would be very very different from

14:33

anything we experience on Earth

14:35

and that is, I guess, typical

14:38

of astronomy. All pretty well,

14:40

all the objects we talk about, if

14:43

you transported yourself from Earth

14:46

to one of those objects, no matter what it

14:48

was, even if it was an asteroid, the phenomena

14:50

that you would encounter will be so different from

14:52

what we have on our own planet that

14:55

it makes for very

14:57

interesting thought experiments and very

14:59

interesting reading and I hope

15:01

very interesting podcasts. Indeed. In

15:04

fact, we are so well adjusted to

15:06

our own planet because we've spent hundreds

15:08

of thousands, more tens of thousands of

15:10

years adapting to this environment. Just about

15:12

anywhere else we could go would not

15:15

be good for us. No,

15:17

that's right. Unless we

15:19

could find another planet exactly the same

15:21

as ours in terms of

15:24

size and proximity.

15:27

Well, it's, you know, I'm going

15:29

around a star like the Sun rather than

15:31

a red dwarf that's going to spit out

15:34

radiation flares all the time. Yes. I

15:37

mean, it's not surprising, you know, we've evolved

15:40

as creatures of the Earth so we are

15:42

very well adapted to it and you can

15:44

kind of imagine how many million years it

15:47

might take for humans to adapt to being

15:49

a neutron star. I

15:51

think supermodels would adapt well because

15:53

they like being skinny. Yeah,

15:57

skinny is one thing but it's forget if you

18:00

and science or nature. Could you talk

18:02

a little bit more about the background on this dark

18:04

energy, dark matter web? I'd

18:07

like to know a little bit more on the background so I can kind of

18:09

run away from there. Thanks you guys.

18:11

Keep up the good work. Really love

18:13

the show. Thank you. Thank you Jeff. And

18:15

wow, what an astute fellow. He knows

18:18

his stuff about RNA and DNA and

18:21

yeah, very, very clever.

18:25

Brought up some interesting points. I didn't

18:27

know, is he right that the Earth was

18:29

probably more RNA than DNA in the

18:31

beginning and something changed? I'm

18:36

not sufficiently engaged

18:38

with the world of evolutionary biology.

18:40

I haven't heard that before. I'm

18:45

very glad that Jeff put those ideas

18:47

there because we'll follow up on that

18:49

and find out what the story is

18:51

there. But his main question was about

18:54

one of our favourite topics, dark energy

18:56

and dark matter. And yeah, he did

18:58

describe them as the

19:00

web that holds galaxies together. And we

19:02

have said before that if there was

19:05

none of this, galaxies would just spin

19:07

themselves into oblivion. They'd just go in

19:09

all directions I suppose. So

19:11

yeah, how does it work I suppose was what he

19:13

wanted to know. Yeah

19:15

so giant space spiders.

19:20

God, you've cut to the chase. David

19:22

Bowie was right, spiders from Mars. There

19:25

you are. Spiders from Mars, yeah.

19:28

So we need to disentangle dark

19:31

matter and dark energy though because dark

19:34

energy is not something that's

19:36

part of the web that

19:38

Jeff's talking about. Just talking about the

19:40

cosmic web which is structures

19:43

of matter within the

19:45

universe. Now those

19:48

structures of matter we

19:50

think were instrumental in the

19:53

creation, just as you

19:55

said Andrew, of galaxies because

19:57

we find that when you... build

20:00

novels of the way the Big Bang evolves, you

20:03

end up with this web

20:06

of material. It's almost like a foam,

20:09

if I can put it that way, very

20:11

much like cells of a honeycomb with

20:14

the walls between the

20:16

honeycomb forming the structure of

20:18

the web, which is there in both

20:22

dark matter and normal matter. The

20:26

dark matter probably was the first thing to

20:29

crystallize into this web shape after the

20:31

Big Bang, with the normal matter being

20:33

gravitationally attracted to it, because dark

20:35

matter outweighs normal matter by 5 to

20:38

1 or thereabouts. So

20:40

that's the hydrogen that

20:43

followed the dark matter, and

20:45

that hydrogen then collapsing into stars,

20:49

gas clouds, galaxies, and all the stuff that

20:51

we're familiar with now. But dark

20:54

energy is

20:57

probably uniform throughout the universe, so it's

20:59

not part of this web structure. The

21:02

web structure is just for matter, whether it's

21:04

dark matter or what

21:06

we call barionic matter, which is the

21:08

matter that we can detect. That

21:11

forms the web, but dark energy doesn't.

21:13

Dark energy seems to be a property

21:16

of space itself, irrespective

21:18

of what structures you build inside it.

21:20

The dark energy is there. The

21:24

effect of dark energy, of course, is what we

21:26

see with the universe

21:28

accelerating in its expansion,

21:34

as it has been doing for about the

21:36

last 5 billion years. We think that before that,

21:38

it wasn't accelerating in its

21:40

expansion, even though dark energy was

21:43

there. But the

21:45

galaxies were close enough together that

21:48

their mutual gravitational attraction

21:50

resisted the effect of dark energy.

21:53

It was only as the universe continued to

21:55

expand that the galaxies became far enough apart

21:57

that their gravitational pull towards each other.

22:00

was not strong enough to

22:02

overcome the accelerating

22:05

effect of the dark energy. So that

22:07

acceleration is something we've only seen for

22:09

about half the age

22:11

of the universe. Before that, the

22:13

universe's expansion was probably slowing down. Any

22:17

theories as to what changed? Yeah,

22:20

the fact that the galaxies became

22:22

far enough apart that the gravitational

22:24

pull between them wasn't breaking the

22:27

expansion. So that

22:29

allowed the dark energy to become the dominant

22:31

force. We were basically

22:33

holding it back until it

22:35

reached a release point and away

22:37

she went. Away she went.

22:40

Quite gradually. It's sort of like when

22:42

you blow up a balloon. When you first start

22:44

to blow up a balloon, it's a hard thing

22:46

to do and then it suddenly gets

22:49

easier. That's a really good other

22:51

log actually because what you're feeling at first when

22:53

you're puffing hard against

22:55

the resistance of the

22:58

rubber or whatever material it is.

23:01

And that then gets beyond a certain point where

23:03

it's really easy to blow it up and if

23:05

you do it too much it bursts. Which

23:08

is probably what the universe will do in

23:10

the big rip in a few trillion years

23:12

to start. Or next week, whichever is

23:14

longer. Whichever comes sooner, yes, that's right.

23:20

I hope that helps to explain

23:22

some of the confusion

23:24

there, Geoff. Separate

23:27

dark energy and dark matter out in your

23:29

mind because they're quite different things but the

23:31

dark matter is what forms that web-like structure

23:34

that basically is the scaffolding

23:37

on which the objects in the

23:39

universe were built. Yes, and as we've mentioned

23:41

in previous episodes, they're just

23:43

badly named. Dark edges

23:45

should probably be called something else so that

23:47

there's no confusion. That's

23:50

where paper may have crossed up. Dark

23:53

matter would have been better as invisible matter I

23:55

think but dark seems

23:57

to be the buzzword in enough. It

24:00

does. All right. Thank you, Geoff. We

24:03

got a text question from Austin, Texas.

24:05

It's Carlos. He says, Hello, Andrew and

24:07

Professor Watson. I will preface

24:09

this question by saying that it may

24:11

not have a conclusive answer because

24:14

it details in the theoretical. I

24:17

was pondering the concept of white holes

24:19

being mathematically understood but not observed. I

24:22

wonder if white holes could lurk in

24:24

the dark matter spectrum of the universe,

24:27

just like we can't detect or

24:29

understand dark matter slash dark energy.

24:32

Could it be possible that white holes

24:34

exist within this yet to be understood

24:36

spectrum of the universe? Thanks for a

24:38

great show every week. Much love to

24:40

y'all. I hope I said that right.

24:42

From Texas. Yeehaw. That's what

24:45

I did. Not me, him. A good

24:47

browse. That's very flavoursome. Yeah, it

24:49

is. Yeah. And some

24:51

boot scooters lurking somewhere in their arms.

24:56

Probably. Yeah,

25:01

so that's an interesting thought. Let's

25:03

explore that a little bit. The

25:06

idea that maybe in the dark

25:09

matter universe, which we

25:11

can't detect directly,

25:14

there are objects

25:16

akin to black holes

25:18

and white holes. Let's

25:21

do it both ways. Carlos

25:24

is absolutely right that the mathematics of black

25:26

holes or the mathematics of

25:29

gravitation let you conjecture

25:31

that there are such things as

25:33

white holes. When

25:35

you're working in the equations, I think what you do is

25:37

you reverse the sign of time. So

25:40

you put time that's going negative and you've got a

25:42

white hole instead of a black hole. But

25:45

we see nothing in the universe that actually

25:47

could be one of those because

25:50

unlike a black hole where nothing gets out

25:53

with a white hole, nothing gets in. And

25:56

you'd think you'd notice that. But

25:59

the... I guess the bottom line

26:01

here is when you, all right, let's think

26:03

about dark matter. We think it is some

26:06

kind of species of

26:08

subatomic particle and perhaps many

26:12

different species of subatomic particle,

26:16

which doesn't interact with normal

26:18

particles, so it doesn't interact with light.

26:20

We can't see it shining, it doesn't

26:22

interact with matter, it

26:25

doesn't seem to react with normal

26:27

matter. All it does is

26:30

displays gravity. It has gravity

26:33

and that's how we detect it because exactly

26:36

as you said earlier on, when

26:38

we look at the way galaxies work, if

26:41

you spot a rotating galaxy

26:43

and if all that was in

26:45

there is all that you

26:47

can see, if that's all there is, then it should

26:49

have blown itself apart

26:52

a gazillion

26:54

years ago, maybe only millennia ago,

26:56

but a long time ago. It

26:59

can't exist without the

27:01

idea that there is some invisible

27:03

material holding it together. When

27:06

you do the theory, you get the calculation

27:08

or you get almost a

27:10

picture that shows you that these

27:13

galaxies are embedded in halos of

27:16

this mysterious dark matter. Dark

27:18

matter reveals itself by its gravity.

27:22

Gravity behaves normally as far as

27:24

dark matter is concerned, which

27:26

suggests that if you had a

27:31

dark matter black hole, it

27:34

would exhibit its

27:38

forces or exhibit its

27:40

presence in exactly the same way as a

27:42

normal matter black hole does because it would

27:44

be a singularity with intense

27:47

gravitational field around it, which

27:50

would pull other stuff in, whether that was gas

27:53

being accreted like it is at the center of

27:55

a galaxy, whether

27:57

it's a supermassive black hole or

28:00

an x-ray binary where you've got a

28:02

companion star that's leaking material onto the

28:04

black hole and causing it to release

28:06

x-rays. All of that should still hold

28:09

good so that what you

28:11

see in the black hole universe in real

28:13

or normal matter, baryonic

28:15

matter, you should also see in

28:17

dark matter. Right. Okay. Interesting.

28:21

So probably not is what the answer is

28:23

which saved us a lot of time but

28:25

we were going to flow at the start

28:28

so that's fine. I've actually discovered

28:30

a white hole. Where

28:33

is it? It's called my bank account. Nothing

28:35

gets in. Yes.

28:37

Nothing gets

28:40

in. But things get out. Yeah. Sounds

28:42

like a white hole. Yeah.

28:44

It's definitely a white hole. Alright.

28:46

Thanks Carlos. Let us move on to

28:49

Duncan. I think Duncan sent us

28:51

a few questions in recently so

28:53

let's tackle this particular one. I

28:55

think he's looking at the period

28:58

of inflation. Hello.

29:00

Duncan here from Weymouth in

29:02

the UK. Question

29:04

about a period of inflation after the

29:06

Big Bang. When

29:09

the universe expanded faster than the speed

29:12

of light was that faster than the

29:16

actual speed of light or was it that

29:18

the speed of light at that time was

29:20

faster than it was now? I'm

29:23

just thinking that if the speed of

29:25

light in itself at that time was

29:27

faster could it be

29:29

that there is some property

29:32

of the universe in which

29:35

light is able to travel faster than

29:37

what it does currently in the current

29:39

vacuum and if

29:41

we could discover what that

29:43

particular property of the universe back

29:46

then was then maybe

29:48

there would be some way

29:50

that obviously in the

29:52

distant future will current technology to

29:56

create a drive that goes faster

29:58

than it. I

30:02

don't know. It's just

30:05

that obviously we're limited to the speed of

30:07

light but if the speed of light in

30:09

itself could be increased then

30:12

who knows. Anyway, thanks for your

30:15

help. Keep up the good work. Well,

30:18

okay. Thank you Duncan. Always good

30:20

to hear from you and now

30:22

I understand how the Americans have

30:26

learned to pronounce things differently to us

30:28

because of Duncan's

30:30

accent. I picked up something, an

30:32

American pronunciation in there. I

30:35

can't remember what the word was now but... That's

30:37

what I was going to ask you.

30:39

Yeah, I can't. I just went straight

30:41

out of my head. It's very late

30:43

on a Friday here so my

30:46

brain decides to give up once I've

30:48

walked out of the office. A period

30:51

of inflation, we know immediately

30:55

after the Big Bang the universe expanded it

30:57

faster than the speed of light and then

30:59

it slowed down and now it's accelerating again.

31:03

Where does Duncan's theory sit? There

31:06

are two different things we're talking about

31:09

here, Andrew and Duncan. When you think

31:14

about inflation, the speed of light doesn't

31:16

matter because it's

31:19

the fabric of space, whatever

31:22

that is. It's basically itself

31:24

that's expanding. You could only

31:27

talk about being faster than the

31:30

speed of light if you think of two points within that

31:32

space. How fast are they

31:34

receding from one another and it

31:36

may well be faster than the

31:38

speed of light. In fact, it

31:40

would have to be just because

31:42

of the way the inflation took

31:44

place. It was an extraordinary period

31:46

in the universe's history but it

31:48

is the space that's expanding very

31:51

fast and that

31:53

doesn't impact the speed

31:55

of things going through it. One

31:58

of the basic foundations of the universe is the space that's expanding very fast. of

32:01

cosmology as we understand

32:03

it, our theory of the origin and

32:06

evolution of the universe. One of

32:08

its basic principles is that the speed of

32:10

light is a constant, that it has always

32:14

been the same. Ever since the beginning it

32:16

was 300,000 kilometres per second. There

32:20

are probably still

32:23

people, I haven't

32:26

really caught up with this work yet, but

32:29

recently I haven't caught up with it recently.

32:31

This is work that was done a decade

32:33

or more ago by

32:35

colleagues here in Australia, in fact

32:37

principally at the University of New

32:39

South Wales, who were

32:42

observing different distant quasars. There

32:47

was just some evidence in

32:49

those, they were spectra, they were taking the rainbow

32:52

spectra of these quasars and looking at the features

32:54

in them. There was evidence

32:57

that hinted that something

33:00

was varying, that

33:02

one of the fundamental physics

33:04

principles was different than it

33:07

is now. Because when you're

33:09

looking at quasars you're looking a long time

33:11

back into the past. The

33:14

inference was that it was either

33:16

the charge on the electron or

33:18

the speed of light that was different. That

33:22

work was always

33:24

greeted with a reception

33:27

that was less than warm by the astrophysical

33:30

community. I don't know why, because I've

33:32

seen the data and it was right

33:34

on the limit of detectability, this

33:41

effect that they were highlighting.

33:44

And I suspect that more recent

33:46

observations, because we've now observed quasars

33:48

to death in the last 20

33:50

years or so, I think with

33:52

those more recent observations, it might

34:00

have gone away. However, it might

34:02

not have done. And I would

34:04

not be surprised if we hear from

34:06

one of the proponents of that work

34:09

and one of the people who carried it out who

34:12

is a good

34:14

friend. I'm going

34:17

to tell the standard joke about this gentleman.

34:19

I hope if he's listening, he won't mind.

34:21

His name is John Webb. And the thing

34:24

about John Webb was you never met up with him

34:26

at the University of New South Wales. It was always

34:29

in New York or Cambridge or Paris

34:31

or somewhere. It was always somewhere else, which

34:33

is why he became known as the worldwide

34:35

one. Yes. I remember you

34:37

telling me this once before. That's a

34:39

great nickname. Yeah. Great

34:42

nickname. It is a great nickname. It's a great

34:44

guy as well. And it'd be nice to try

34:47

and catch up with him

34:49

in Cairo or somewhere to find out

34:51

whether those ideas are still prevalent. Yeah,

34:57

I should look it up. I

34:59

have a listener from Cunha

35:01

Barabran who emails

35:03

me quite regularly and

35:06

listens to space. And I tell her, Barry, he sent

35:08

me some nicknames the other day. Keth,

35:11

K-E-T-H. It's the

35:13

nickname of a bloke with

35:16

names Keith, but he only has one eye. So

35:20

he's lost his eye. Keth.

35:25

Well, Keith. I love it. That's a very

35:27

clever nickname. Very clever nickname. It is. It's

35:30

a good one. Yeah. It's nearly as good

35:32

as we go with the shovel on his

35:34

shoulder, isn't it? What's that? Doug.

35:37

Doug. Yeah. Yeah. Something.

35:40

The guy floating in the ocean bob. There's

35:42

a minute. There's a minute of shovel on

35:44

his shoulder. Douglas. We

35:48

could go on forever, but we probably lose

35:50

our entire audience. See what

35:52

you've done, Duncan. Yes. Just

35:55

to return to it, I think it really is very much

35:58

a pleasure. principle

36:01

of our understanding of the engineering

36:09

the speed of life itself down

36:12

the track is something that I

36:15

suspect we would never get to. We

36:17

are trying ways of speeding up our capacity

36:19

to move through the universe but

36:22

getting to the speed of light. If we can

36:24

get to a fraction of it that'll be an

36:26

achievement Full

36:29

speed of light probably way out of

36:31

our realm given how much energy is

36:34

required. Thank you Duncan. Loved the question.

36:36

This is Space Nuts. Andrew

36:38

Duncley here with Professor Fred Watson. 0J

36:43

and I feel fine. Space nuts.

36:45

Okay let us continue and our

36:47

next audio question comes from Mark.

36:52

Hi guys. This is Mark from

36:54

Baton Rouge, Louisiana. I

36:56

really love your shirt. I

36:59

understand that one of the lines of

37:01

reasoning pointing toward the existence of dark

37:03

matter has to do with

37:05

the comparison of the rotational period of

37:07

galaxies to the amount of matter

37:09

that they contain. However,

37:12

I have seen various estimates of the

37:14

number of stars in the Milky Way

37:16

galaxy ranging anywhere from 100 to

37:18

about 400 billion stars. This

37:22

is quite a large air war I would

37:25

say and I am curious how

37:27

they can make this comparison if astronomers are

37:29

this unsure of the number of stars in

37:31

our own galaxy much

37:34

less other galaxies. Thanks

37:36

guys. I hope to get an

37:38

answer. We

37:40

hope to give you one one

37:43

day. Actually you're asking the right

37:45

bloke because Fred has been counting stars for

37:47

all of his career. Pretty

37:49

well that's right. The

37:51

way you estimate the number of stars in

37:54

a galaxy is

38:01

certainly in our own

38:03

galaxy, what

38:07

you're trying to do is find a way

38:09

of measuring its mass, and then you

38:12

turn that into stellar masses.

38:16

But one stellar mass does

38:18

not necessarily equal one star. So

38:22

some of the work, in fact I was involved with this work

38:25

a decade or so ago, by

38:27

trying to measure the mass of our

38:29

galaxy by

38:32

using the escape

38:34

velocity of stars. If

38:37

you think about the way some

38:39

stars might escape from the galaxy, then

38:43

you can use that. We did this

38:46

with the Rave experiment, the radial velocity experiment.

38:49

You can actually deduce

38:52

what the mass of the galaxy is within that

38:55

radius where the particular star is.

38:57

Actually, it's within the radius of

39:00

the Sun's distance from the center

39:02

of the galaxy. If

39:04

I remember earlier, we got 1.4 trillion

39:13

solar masses for the mass of

39:15

the galaxy, but that includes dark

39:18

matter. So it's

39:20

not individual stars. You've got

39:22

to know something about the

39:25

universe before you make these

39:27

calculations. Looking at other galaxies,

39:30

it's easier. You don't

39:32

count the individual stars in

39:35

a galaxy. It's only recently that

39:37

we've been able to see the individual stars in

39:39

the galaxy, although back

39:41

in the 1920s

39:44

Hubble was observing cepheid variable stars

39:46

in the Andromeda galaxy, which was

39:48

an early step in that direction.

39:50

But most of the stars in

39:52

a galaxy are too fine to do that. All

39:54

you see is this glow which collects them together.

40:00

So what you're doing is

40:02

you're looking at the luminous

40:05

characteristics of a galaxy, the

40:08

stuff that is emitting light,

40:10

even if you can't see the individual stars.

40:13

And from that, you can

40:15

deduce the stellar mass

40:17

content that is emitting the light. In

40:19

other words, you've got some handle on

40:21

the normal matter. And it turns

40:23

out that that is far

40:26

too little to keep

40:28

the galaxy held together. And so

40:30

that difference between 100 and 400

40:33

stars in our own galaxy, yes,

40:35

it's a four-to-one error,

40:42

but it's still well within the

40:45

limits that would be imposed by dark

40:47

matter. The dark matter itself is much

40:49

more than that, is what I'm trying

40:52

to say. It doesn't matter whether it's

40:54

100 billion or 400 billion, the dark

40:56

matter content has to be still much

40:58

more. OK. So

41:00

it's a good question mark and

41:03

goes to the heart of how we understand these

41:05

things. It's

41:08

not just the rotation of galaxies, of course, that

41:11

leads us to believe dark matter

41:13

is real. Another very

41:16

strong pointer to the

41:18

existence of dark matter is the

41:20

distortion of space by clusters of

41:22

galaxies and galaxies themselves. Once

41:24

again, if you look at a galaxy, the

41:26

space around it is distorted to

41:29

the far more than

41:31

you could account for simply by the

41:33

luminous matter in the galaxy. It's

41:37

got much more to it. And that's

41:39

why we're so hooked on the idea of dark

41:41

matter, because all the tests seem

41:43

to suggest it's there. Yeah. Wow.

41:46

OK. I've been trying to count the stars. I'm

41:49

up to five. So you've

41:51

been observing the Southern Cross then. Yeah, I've been. That's

41:53

as far as I got. Yeah. Oh,

41:55

hang on. The sun six. There

41:58

you go. Well

42:00

done. Well done. You

42:02

are. Thank you Mark. And

42:04

now we've got a question from Nick

42:06

who is another sandgroper. Do you know

42:08

the term sandgroper for it? I

42:11

don't. No. That's what we

42:13

call West Australians. They're sandgroppers. So South

42:15

Australians are crow eaters. I

42:17

know where that comes from. Crow eaters because

42:20

back in the day during the Gold Rush I think

42:22

or something around that era, there

42:24

wasn't much food. So they used to eat crows. They

42:28

used to shoot them. They called them something else. They called

42:30

them desert pigeons or something.

42:33

But they used to shoot crows

42:35

and cook them and eat them. So they

42:37

became crow eaters. I'm still to find out

42:40

why West Australian is called a sandgroper though.

42:42

But I'm going to find out. I'm sure it's on

42:45

the interwebs somewhere. Anyway, this

42:47

sandgroper is Nick from Perth who

42:49

has a question about planetary diversity. It

42:54

is a given that the planets of

42:56

our solar system formed by accretion from a

42:58

disk of dust and gas circling around

43:00

the young sun. That's the sixth

43:02

star in the sky. Gravity

43:05

inspired differentiation leading to more dust on

43:07

the inner disk and gas of the

43:09

outer, of the outer

43:11

resulting in the inner rocky planets and

43:14

the outer gas giants. All good. Aside

43:16

from those groupings, what fascinates me

43:19

is the lack of homogeneity between

43:22

the planets and moons around the

43:24

gas giants within these two groupings. They are

43:26

so different, all of them. How

43:28

did that happen? Can Professor Watson recommend

43:30

some reading on the matter? Should I

43:32

buy his books? Well, the simple answer

43:34

is yes. But

43:40

it's an interesting observation though because we've

43:42

got rocky planets inside. We've got

43:45

gas giants further out and

43:48

yet they've got rocky moons surrounding

43:50

them and ice moons and all

43:52

this other weird stuff. Why

43:55

is it so? Yeah,

43:58

and which book is it in? The

44:02

best one actually is probably the Kids Book. It's

44:06

the one where I think I went into the

44:08

most detail about planet formation, which I probably shouldn't

44:10

have done in the Kids Book, but never mind.

44:14

It was fun to write. We

44:17

think we understand why

44:21

there is this differentiation between

44:23

the inner rocky

44:25

planets and the outer gassy

44:28

ones because of

44:30

the existence of the frost line.

44:34

If you look at the distance from the

44:36

Sun where

44:39

water freezes

44:41

basically, it's

44:44

kind of beyond the outer edge of the

44:46

gold. What you might call the outer edge of the gold

44:49

is not too hot and it's not too cold for

44:51

liquid water to exist. It's

44:54

between the orbits of Mars and Jupiter

44:56

basically. That's what you'd

44:59

expect because we think that

45:02

the idea of water, which

45:04

is by far the commonest two

45:06

element molecule in the universe, freezing

45:09

and causing an

45:11

increase in the mass of the

45:14

outer worlds as the planets were forming. We

45:16

think that's why they were able to

45:18

hold onto a gaseous envelope and become

45:20

gas giants. Whereas the inner rocky

45:22

planets were within the frost

45:24

line and they weren't able to do that.

45:31

That's a neat explanation. The

45:35

moons themselves, Nick

45:40

is quite right that the moons

45:43

themselves are diverse, but they are

45:45

all basically rocky

45:47

bodies rather like asteroids.

45:52

Some of them have got an oval

45:55

layer of water and an oval layer of ice

45:57

on top of that. Many of them which we

45:59

talked about many times. before. Some are

46:01

just rock like EO, some are just

46:03

lumps of, in fact, some are probably

46:05

more like POMIS. Phobos,

46:08

the moon of Mars, is

46:11

diverse in that regard in that more

46:13

than 50% of its

46:16

mass is empty space, which

46:19

is what gives it that low

46:21

density. So there is still diversity

46:24

among the moons, even when you

46:26

consider that, yes, they're all basically

46:28

made of rock. Maybe

46:31

the gas giants are as well, we

46:33

don't know whether they have a rocky core. Yes, that's

46:36

one of the mysteries, isn't it? So it's

46:38

possible the gas giants are something of an

46:41

illusion in some respects.

46:43

That's right, they might be just rocky

46:46

planets masquerading as something else. Yeah,

46:49

just got massive atmospheres, like

46:51

atmosphere. Yeah, like a big

46:53

head, which you don't

46:55

know anything about, actually. I did

46:58

one. I'm rapidly

47:00

catching up to you, as you can see. Yes,

47:03

all right. Thank you, Nick, and

47:05

enjoy groping the sand, whatever that

47:07

means, in Western

47:09

Australia. Love Western Australia, beautiful, beautiful place.

47:12

To our final question, Fred, and

47:14

it comes

47:16

from one of our favourite

47:18

terraforming experts and sci-fi writers.

47:22

I'm going to introduce him the

47:24

way he introduces us. Hello,

47:27

Martin. Hello,

47:29

Space Nut. Marc

47:32

and Berman Gorevine here, writer

47:34

extraordinaire in many

47:36

genres. Today,

47:39

we're going to terraform

47:41

a completely theoretical object,

47:44

and I would just like to know

47:46

what you would

47:48

see if you were on

47:51

a tippler cylinder, and

47:53

a circling

47:57

around it overhead was a...

48:04

spaceship that

48:07

Professor Chippler tells you would be

48:09

going back in time. Love

48:12

your show, can't wait for the

48:15

answer. Berman-Corvine in

48:17

Patonic, Maryland, USA. Over and

48:19

out. Thank you, Matt. And he's

48:22

really stretching now, isn't he? Now

48:24

I just tried to look up what

48:26

a tippler cylinder is, also known as

48:28

a tippler time machine. It's a hypothetical

48:30

object theorized to be a potential mode

48:32

of time travel. Although results have shown

48:34

that a tippler cylinder could only allow

48:36

time travel if its length were infinite

48:39

with the existence of negative

48:41

energy. So yeah,

48:44

I'm actually looking at the same page

48:46

as you. Right. If its length

48:50

were infinite or with the

48:52

existence of negative energy. You've

48:54

got two alternatives there. Yeah.

48:57

And infinite length is tricky to make.

49:00

Negative energy

49:02

is even trickier. That's

49:05

why we're probably never going to

49:07

build one. But what an interesting

49:10

idea it was. It actually is

49:13

something that falls out of the

49:15

equations of relativity. And

49:18

in fact it was mathematicians looking at

49:20

those equations back in the 1920s that

49:22

produced this idea

49:25

of, as you said, a hypothetical

49:29

object, theorized

49:31

to be a potential mode of time travel. And

49:34

it's because of

49:36

its effect on the

49:39

closure of space

49:43

time. You might put it that way. Gravitational

49:46

potential is such that

49:48

you get, instead of space

49:51

time being a nice

49:53

lattice of stuff, a bit like I

49:55

always think of space time as being like one of those

49:57

climbing crêpes that you find in kids. parks.

50:01

They're old-fashioned ones anyway. They're not like that anymore, but

50:04

they were just a

50:06

regular set of

50:09

things arranged in right

50:11

angles and it gave

50:13

you a three-dimensional structure.

50:15

That's normal space-time. Bend

50:18

space-time is when somebody every stands

50:20

on one of those. That's

50:22

what the equations of relativity show

50:24

us, that when

50:26

you put matter in there, they bend.

50:28

But when you think of all this

50:31

happening around an infinitely long cylinder, you

50:33

get the structure

50:36

of space itself closes on itself, if

50:38

I can put it that way, so

50:40

that you've got a way

50:42

of moving around in time as

50:44

well as space. That's the idea. There's

50:49

also a phenomenon called frame dragging,

50:51

which we know is a real

50:53

phenomenon of relativity. There was certain

50:56

... I forgot which spacecraft it

50:58

was. It won't

51:01

come back to me. There was

51:03

one particular spacecraft that was put

51:06

into orbit around the Earth that

51:08

was designed to demonstrate that

51:10

the Earth as it rotates,

51:12

drags space-time with it. This

51:15

frame dragging phenomenon. I think we did a

51:17

story on that a while back. I think

51:20

we did too. I think we did too.

51:23

The cylinder itself, if it's spinning along

51:25

its long axis, will

51:27

create this frame dragging

51:30

effect, warping space-time in

51:32

such a way that you might be

51:35

able to travel backwards in time. That's

51:37

the bottom line. I forgot

51:40

what Martin's question was. What would a

51:42

spacecraft look like if it was going

51:44

backwards in time? Probably

51:47

just like playing a movie in reverse.

51:49

Yeah, probably. Sadly,

51:52

the boo was put in by a

51:54

number of people, including

51:57

a fellow called Stephen Hawking. He

52:00

threw a relativistic

52:03

argument at an

52:06

idea of a tip-less cylinder

52:08

suggesting that it would never be

52:10

able to be built. Which

52:13

means you couldn't terraform one, basically.

52:16

That's right. Forgotten terraforming

52:18

was at the heart of Martin's question, as

52:21

he always is. And

52:24

terraforming a tip-less cylinder, yeah, that would be

52:26

tricky. That would be very tricky. You're

52:29

a sci-fi writer, Martin. Yeah,

52:32

just do it. Just do it. You

52:35

can do anything in science fiction. Well

52:38

you know that's the case Andrew.

52:40

Yeah, you do, I'm currently reading the

52:42

latest John Birmingham series, John's an English

52:46

author, but he's Australian based and he's just

52:48

released. He always releases books

52:51

in three, all

52:53

his stories have three volumes. And

52:56

I went halfway through the second of three

52:58

books in his latest series and

53:01

it's just a classic

53:03

outer space war story. He

53:07

hasn't done ones like that before. He's

53:09

done other really interesting stories about monsters coming

53:11

out of other dimensions and eating humans and

53:15

he did one about a big blob that came

53:17

from outer space and wiped out half of America

53:19

and half of Canada and what happened to the

53:21

world. That one

53:23

was called Without America. He writes brilliantly and

53:25

I'm really enjoying this latest

53:27

series which hasn't released

53:30

the third book yet, but

53:32

it's due out this year. I'm

53:34

slowly reading the second one so I can get straight

53:36

into the third one when it comes out. It's

53:39

great stuff. It's fun. I

53:41

once did a gig with him. I did you. In

53:44

Brisbane. Yeah, I love his writing style,

53:46

I really do. My

53:50

favorite character of his is Super Dave. Super

53:54

Dave. And then that

53:56

series has since been renamed

53:59

the Super Dave. series because... Okay,

54:01

I thought I took over. So

54:04

we've got to look out for

54:06

the Super Dunk series. Super Dunk

54:08

series. If you're

54:10

listening, John, this is

54:12

it. Super Dunkly. Yeah, yeah. Give

54:15

me it. Put in a

54:17

kind word to your publishers for

54:19

me. That'd be nice. That will

54:21

never happen. Alright, thank

54:23

you very much Martin. Always good to hear from

54:26

you. We're gonna wrap it up there Fred. I

54:28

think we got through a fair bit today but

54:30

again I'll remind people because we've now exhausted quite

54:32

a few of our questions to send them in

54:34

by our website space nuts podcast

54:36

com click on the AMA link to send

54:38

text or audio questions or just click on

54:40

the tab on the right hand side of

54:42

the home page where you can send audio

54:44

questions. Don't forget to tell us

54:46

who you are and where you're from. You

54:49

can record your questions via any device with

54:51

a microphone basically it's that simple. And

54:53

check out all the other stuff on the website while

54:55

you're there. Fred, thank you as always. It's a great

54:57

pleasure and it's good to get through some of the

55:00

questions and hear from the audience. Indeed.

55:03

They talk far more sense than we do.

55:07

Sounds great. Thanks Andrew. We'll see you next

55:09

time. Indeed we will. Fred Watson, astronomer at

55:11

large part of the team here at Space

55:13

Nuts and thanks to Hugh in the studio

55:16

who actually turned up for work today. And

55:18

from me, Andrew Dunkley, catch

55:20

you on the very next episode of Space Nuts. Bye

55:23

bye. Space

55:26

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55:40

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55:42

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