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golo.com. That's golo.com. Again, G-O-L-O

1:30

dot com. My. They thanks for joining

1:32

us again. This is space nuts

1:34

where we talk astronomy and space

1:36

science. My name is Andrew Dunkley

1:38

your host. Coming up on this

1:40

episode will be answering audience questions.

1:42

Ash is looking a Apollo Thirteen.

1:45

Darryl is asking questions about Absolute

1:47

Zero, which seems to be a

1:49

common topic. I'm pretty sure we've

1:51

had this one pop up previous.

1:53

Lisa will have a crack at

1:55

that again. Obvious that we didn't

1:57

do it well enough before hand.

2:00

Alex is focused on

2:02

anti-gravity. That's all

2:04

coming up on this edition of

2:07

Space Nuts. 15 seconds,

2:09

guidance is internal. 10,

2:12

nine, ignition sequence start.

2:14

Space Nuts. Five, four,

2:16

three, two. One, two, three,

2:18

four, five, five, four, three, two, one. astronauts

2:22

reported feels good. Joining

2:24

me to solve all of those

2:27

riddles and puzzles is Professor Fred

2:29

Watson from Atlanta, hello Fred. Hi

2:32

Andrew, how are you doing? Now

2:34

Fred, let's go to our Q&A

2:37

segment. This is where we basically take questions from

2:39

the audience which are always welcome. Don't forget to

2:41

send them in to us and

2:44

we endeavor to answer them or we just pretend

2:46

we know the answer and then move on. And

2:50

I mentioned at the beginning

2:52

that Ash wanted to ask a

2:54

question about Apollo 13. That's

2:57

not quite accurate. What he

2:59

was asking about, he

3:02

used Apollo 13 as an example

3:06

of a situation that he doesn't quite get.

3:08

Let's hand it over to Ash. Yeah,

3:11

what I want to ask Ash here from

3:13

Brisbane again with another question

3:15

for you. I

3:18

was recently watching the movie Apollo 13

3:20

with my daughter and

3:23

coming towards the end of the movie

3:25

where they're talking about their reentry of

3:28

the command module. The

3:31

news reporter said

3:33

that too steep an angle

3:35

and it will burn up on reentry, I get that.

3:39

And then he goes on to say that coming

3:42

too shallow and the spacecraft

3:44

will bounce harmlessly off the atmosphere,

3:47

floating off into space, skipping off the atmosphere

3:49

like a rock off a pond. Don't

3:52

really get this one. Skipping

3:55

off the atmosphere, is this something we've

3:57

observed in the past? Or is it just

3:59

something theoretically? I'm interested to

4:01

hear your thoughts on that. Well,

4:04

the show goes, came up. So Ash

4:06

is bringing up an interesting point because we

4:08

all understand the implications

4:10

of coming in too steep and

4:13

hitting the atmosphere and burning up.

4:15

We've seen that in recent years

4:17

with disastrous effects and

4:20

the loss of lives unfortunately on one

4:23

particular occasion. But we

4:26

don't think much about the bouncing off thing

4:28

and I've always just taken it for granted

4:31

that that's gospel. And

4:33

I suppose he brings

4:35

up a very solid

4:37

question as to have we ever witnessed

4:39

this. So

4:42

yeah, let's try and understand the

4:44

concept a bit more bouncing off

4:46

the atmosphere like a skipping stones

4:48

across a lake. And

4:51

I think that's the problem Andrew that we kind

4:54

of use what

4:57

I think is the wrong terminology. So

5:01

yeah, I mean we've all seen skimming stones

5:03

where you skim across the lake, exactly as

5:05

you've said, and that's what this sort of

5:07

thing catches up for you in your mind.

5:10

But what you're actually doing is

5:13

it's the angle of entry that

5:15

is the critical thing. If

5:19

you get it too shallow,

5:22

sorry too steep, then

5:25

the velocity that you come

5:27

in at is too

5:29

high for the spacecraft's

5:31

heat shield to cope

5:33

with the frictional heat

5:35

that you've got as it passes through the

5:37

atmosphere. Remember the atmosphere is

5:39

just getting steadily more dense as you go down.

5:43

And so that's catastrophic as you've just

5:45

said. And so then

5:48

there's a sort of sweet spot where

5:50

you can use the friction of the

5:52

atmosphere to slow you down, atmospheric breaking.

5:56

It's a balance between the thermal.

6:00

construction of the heat shield,

6:03

how much temperature that will withstand it and for

6:05

how long and how

6:08

much of that heat is conducted

6:11

through to the interior of the

6:14

spacecraft. So that balancing act is

6:16

very much sort

6:20

of – it's judging

6:23

many different factors,

6:26

steepness, temperature, resilience of the

6:28

spacecraft, heat shield, all of

6:31

that to get the

6:35

right angle of entry. But

6:37

if you then change that to

6:39

make it shallower, remember

6:42

you're still

6:46

in a gravitational situation. When the

6:48

spacecraft is outside the atmosphere, generally

6:51

the only force acting on it is

6:53

gravity and that dictates its motion exactly.

6:56

So when it enters the

6:58

atmosphere, that's when the thing is going to

7:01

start slowing down. So if you

7:03

enter at an angle that

7:05

is too shallow, the gravitational

7:08

pull of

7:10

the earth, which the thing

7:12

is feeling and it's going downwards, it

7:15

will also – as it hits the outer

7:18

parts of the atmosphere, it will basically

7:20

feel the deceleration of the

7:22

atmospheric breaking. But

7:25

there won't be enough if you're not

7:27

at a steep enough angle. There won't

7:29

be enough gravitational breaking and

7:31

eventually, even though

7:34

the heat shield will heat up and everything, but

7:36

eventually it won't actually come

7:39

down to earth. It will keep

7:41

going through the upper atmosphere. Its

7:43

orbit will be altered dramatically. In

7:46

fact, it may even, as a result of

7:48

that, go into orbit around the earth because

7:50

it's experienced sun breaking, but it's still not

7:53

being captured by the earth in

7:55

the sense that you want it to be. You

7:57

want it to come in at about 11 kilometres

7:59

per second. it's got to hit the Earth's

8:01

atmosphere out to slow down enough to come

8:04

back in from the Moon.

8:09

So it's not a bounce, it's

8:12

that gravity wins over

8:14

atmospheric braking. And what would happen, as I

8:16

said, it's likely that it would come out

8:19

of the atmosphere but now

8:21

be in an elliptical orbit around the

8:23

Earth and so its orbit,

8:25

depending on just what the circumstances

8:27

were, might turn into a long

8:29

ellipse and go back down. Now

8:31

the half being, contrary

8:34

to popular belief, you're not going to

8:36

be speared off into oblivion. Well, you

8:39

would be basically. Oh, okay. Because you'll

8:41

be in the wrong orbit and you

8:44

don't have any means of changing the orbit. You're

8:48

probably still… Let's

8:51

say a spacecraft does make that mistake

8:53

and gets sort of bounced off. Is

8:56

it recoverable if you've got the power? If

9:00

you've got an engine, surely you can… Yeah,

9:02

but they didn't have. That's a command

9:04

module. It's basically an inert lump of

9:06

metal with an… Oh, you're right. Apollo

9:09

13 was. They only had one shot at

9:11

it. I mean,

9:13

with something like a space shuttle or the

9:16

secrets, space planes and all those

9:18

things, they've got their

9:21

own power so they would be

9:23

able to potentially recover. I should

9:25

qualify something I said earlier. I

9:27

said we've seen this happen with

9:30

people involved in that terrible

9:33

space shuttle tragedy. They actually had the

9:36

angle right as far as I'm aware.

9:38

It was a failed tile that caused

9:41

the craft to burn up. So it

9:43

wasn't actually the wrong

9:46

angle and speed because it did

9:48

actually reenter. It just reentered cataclysmically.

9:53

Unfortunately, there were gaps in the wings

9:55

which were caused by damage in the

9:57

wings. It

10:00

didn't damage on lift off I think it was. But

10:03

the shuttle, Andrew, on

10:06

re-entry is not powered. You

10:08

might remember it's got three huge rocket motors on

10:11

the back but it also has a huge fuel

10:13

tank to feed them. So they

10:15

can't actually run those motors on

10:17

re-entry. It was an inert

10:19

amount of metal for re-entry that turned

10:21

into a glider. Apollo, of course, had

10:23

parachutes. What I

10:26

was going to say was that

10:28

we had several instances of

10:31

asteroid samples being dropped to Earth by

10:34

Spacecraft. Sirius

10:37

Rex is the most recent one that

10:39

comes to mind because

10:42

you remember it's content

10:45

of asteroid sample from

10:48

Bennu were dropped

10:50

in Utah last year. It

10:53

took them a long time to open the capsule,

10:55

the canister this year because they had a bolt

10:57

that was stuck. But that was

10:59

dropped by a Sirius Rex. It

11:01

was a mother spacecraft. It dropped the sample

11:03

capsule and then went on its

11:06

way. And I would guess that

11:08

it was close enough to Earth when it dropped

11:10

that to be within at

11:13

least the outer layers of the atmosphere. And

11:16

so those calculations, that physics would have

11:18

been very precisely done so that the

11:20

spacecraft, perhaps it

11:22

did need some breaking to put it into a new

11:24

trajectory because it's on its way to a new satellite,

11:28

sorry, a new asteroid now

11:30

to investigate. So

11:32

yeah, complicated answer. But

11:35

it and bouncing is the wrong

11:37

word, but it certainly in a movie is

11:39

as good a word as any to use.

11:42

Yeah, yeah. Never let the truth get in the way of

11:44

a good story, Fred. That's all they always say. But

11:47

it was a good question to ask because it sort

11:49

of cleared up what probably a lot of us misinterpreted

11:52

in terms of bouncing

11:55

off the atmosphere. Yeah, good question.

11:58

Thank you very much, Ash. Now we've got

12:00

a... question from Darryl and our

12:02

brains tell us that we have sort

12:04

of come across this type of question

12:06

before and Darryl's

12:09

in South Australia. This

12:12

question is from

12:15

a long time listener who is also a patron

12:17

so thank you Darryl I think we've had a

12:20

few patrons sending questions lately. Why

12:22

in a universe of such extremes

12:24

and vast emptiness does absolute zero

12:26

273.15 degrees Celsius or 459.67 degrees

12:32

Fahrenheit even exist? Given

12:34

that a star is thousands of

12:36

thousands to millions of degrees why

12:38

is there a limit on cold

12:41

temperature? Is there a limit on

12:43

hot temperature? Absolute hot and

12:45

while I'm in the question asking mode

12:47

is there an absolute heavy and an

12:49

absolute light? Keep

12:52

up the adequate job

12:54

Darryl. Thanks Darryl. Yes

12:59

so Darryl's

13:01

point is well made certainly

13:03

absolute zero has a physical meaning

13:06

it's not just a random temperature

13:08

it's the temperature which atomic motion

13:10

stops. So you

13:12

know on the level of atoms all

13:15

motion stops at that temperature because temperature

13:17

is the motion of atoms you

13:21

know and depending on

13:23

how hot you are the

13:26

faster the atoms move. Is

13:28

there an absolute heart? Probably

13:32

not. It's you

13:34

know things happen atoms fall to pieces

13:36

at various temperatures we

13:38

don't know whether some of the

13:40

fundamental particles of the universe fall

13:43

to pieces at certain temperatures it's very likely

13:45

they don't. I

13:48

think I'm probably right in saying that the

13:50

hottest temperature ever reached in the universe was

13:52

in the Big Bang where

13:54

we were talking about maybe

13:57

even hundreds of millions of degrees. But

14:00

I don't think there's a barrier

14:03

to more

14:07

extreme temperatures in terms of the upward

14:09

temperature rather than the low temperature. Absolute

14:12

heavy, probably a black hole. I mean,

14:15

we've got black holes that are up

14:17

to four and a half billion solar

14:19

masses now. And

14:21

that doesn't seem to have a

14:23

limit on it. We

14:26

can't, you know, we're going to find ones that

14:28

are even more massive than that. So you

14:31

can't say there's a limit

14:34

on mass either. Wow,

14:36

what about an absolute light? It's

14:39

probably nothing, isn't it really? Yeah, that's what

14:42

I was thinking. Empty

14:44

space. As Monty Python

14:46

said, nothing comes from nothing. Yeah,

14:50

the trouble is it's not

14:52

true. Well

14:55

that's the story of the universe. In

14:57

the beginning was nothing and then it exploded. Yeah,

15:00

very true. So

15:04

yes, no, no, no. Daryl?

15:08

Vic, in terms of all those

15:10

absolutes. And thank you for your question. Let's

15:13

move on to our final question for

15:15

this week. And this one comes from

15:17

Alex. Hello, Alex

15:20

Marshall from London, UK. Yes,

15:23

I'm from the States, Indiana to be

15:26

precise. Question

15:29

I have is, is dark

15:31

energy, more appropriately

15:34

invisible energy, anti-gravity?

15:38

Space not expanding, but

15:40

that it's pushing back against

15:43

the gravity of each one of

15:45

the galaxies and that it's

15:47

hovering around the outside of a galaxy

15:50

is what makes the gravity

15:52

work stronger for a galaxy.

15:57

I'd love to hear the answer. I'm sure we

15:59

don't know. exactly what dark

16:02

energy is but is that thank

16:09

you Alex so the

16:11

question was is dark

16:13

energy anti-gravity it is tempting

16:16

to think of it in those terms because

16:21

it's a repulsive force pushing

16:24

things away much my

16:26

watch is I'm one of those two yeah

16:31

she's probably on the money there

16:39

and it but it doesn't behave

16:41

anything like gravity that's that's the

16:43

reason why we don't think it's

16:46

basically anti-gravity needs

16:48

behaviour is quite different

16:51

it seems to be uniform

16:53

throughout the universe whereas gravity

16:57

hangs around any anything

16:59

that's massive basically any

17:02

object with mass generates

17:04

gravity even you and me so there

17:07

you are there's the opposite pull for your

17:09

wife all right I hate to say a

17:11

friend but wait for it that's heavy but

17:17

I give you an opportunity to use

17:19

yeah so yeah gravity behaves in a

17:21

well-known well

17:26

understood way even though we really don't know what it

17:28

is but we we know

17:30

very precisely how it behaves and

17:33

what we're working on is similar

17:36

precision to know how how

17:38

dark energy behaves and you might remember

17:40

our discussion about the equation of state

17:42

last couple of weeks ago which

17:45

is the basically

17:47

the number that astrophysicists used to

17:49

to identify how dark energy behaves

17:51

but it seems to behave the

17:54

same everywhere it may be something

17:56

that evolves with time but

17:59

by and large it relate

18:02

to objects. In other words, it doesn't

18:04

relate to matter. So its

18:06

behaviour is very much different from

18:08

gravity and it's

18:11

a property of space itself. That's the bottom line. If

18:13

you took all the matter out of the universe,

18:16

you'd still have dark energy. And

18:19

indeed cosmologists who look at these

18:21

large scale galaxy surveys to kind

18:24

of determine the geometry of the universe, which

18:26

is what gives you insights into dark

18:29

energy and dark matter and various

18:31

proportions, they see them as

18:33

quite separate things with quite

18:36

different characteristics. And so

18:38

our anti-gravity whilst in

18:40

a sense, it's, as

18:43

I said, it's tempting to think of it that way

18:45

because it's pushing stuff apart, but that's

18:47

not what it is. It's something different and

18:49

it's something we don't know and we don't

18:51

understand. But Andrew, we're working

18:53

on it. We

18:56

are. I think it's one of the

18:58

great mysteries of the modern era in

19:00

astronomy and space science is to solve

19:03

the dark matter and dark energy

19:06

conundrums and they're working

19:08

on it, but keeps

19:10

throwing up extra questions, which it's

19:14

like a formula.

19:16

You've got to break it up into workable

19:18

parts and figure out every keystone bit by

19:20

bit until you finally get an answer. And

19:23

even that might be wrong. That's the problem

19:25

with it, isn't it? Time will

19:27

tell how

19:30

much time can't tell you.

19:33

Thank you, Alex. To answer

19:35

everybody's questions. Yeah,

19:37

well, that's another thing, isn't it? To

19:40

answer everyone's questions, the answers were not

19:43

quite yes, no, no, no, and not really.

19:47

That would have done it. Just

19:50

a reminder too, if you have questions for

19:52

us, please send them in. Just jump on

19:55

our website, space nuts podcast.com or

19:57

space nuts.io. There's a couple of. links

20:00

on there, the AMA tab or the little

20:03

part of the homepage where you can send

20:05

us your questions in text or

20:07

audio form. Don't forget to tell

20:10

us who you are and where you're from and we'll do

20:12

our very best to not

20:14

ever answer them at all. But if we run

20:16

out of stuff to talk about, we might. Now

20:19

we will try. We will try. We get a lot

20:21

of duplicate questions. So if we miss you, it's not

20:23

because we don't like your question or we're too dumb

20:25

to answer it. We just, someone

20:28

else has probably already covered it. Although we did double

20:30

down on the absolute zero question

20:32

this week. And

20:35

while you're on our website, have a bit

20:37

of a squeeze around and see what you

20:39

can see. Don't forget the Space Nuts shop.

20:43

You might be someone who buys presents for Easter.

20:46

There's no Easter eggs on it but

20:48

you might find something in there.

20:50

I mean Easter does have some

20:52

kind of astronomical relevance. So anyway,

20:56

lots to see and do and don't forget if you'd like

20:58

to become a patron. And if you're a YouTube viewer, don't

21:01

forget to hit the subscribe button below.

21:04

That's what we want. More subscribers

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the better. And we certainly

21:08

got a growing family on YouTube and

21:11

they're starting to get really involved as well

21:13

which we greatly appreciate. Fred,

21:15

that's a wrap for this episode. Thank you

21:17

very much. Yeah.

21:19

Simple as that. Thanks Fred. We'll

21:21

see you soon. Thanks Fred. We'll see you.

21:23

And to Hugh in the studio, I wish

21:26

you all the very best with your editing

21:28

on that one. But you are an editing

21:30

magician unlike myself who avoids it like the

21:33

plague. And from me, Andrew Duncley,

21:35

thanks for your company. We'll catch you on the

21:37

next episode of Space Nuts. Until then, bye-bye. Space

21:39

Nuts. You'll be listening to the Space Nuts podcast. Look

21:42

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21:54

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