Latest / Space Nuts: Astronomy Insights & Cosmic Discoveries / Probing the Dark Unknowns: Seeking Clarity on Dark Matter and Energy | #385

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Probing the Dark Unknowns: Seeking Clarity on Dark Matter and Energy | #385 · Space Nuts: Astronomy Insights & Cosmic Discoveries

0:00
Hi, Andrew Dunkley here, and just want to say thank you for listening
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to Space Nuts throughout twenty twenty three. Fred and I are taking just a
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couple of weeks off, but we will be back early January. In the
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meantime, here's a repeat episode from early twenty twenty three, one of our
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Q and A episodes, Space Nuts. Hello, and welcome to Space Nuts.
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My name is Andrew Dunkley, your host. It's so good to have
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your company. And being episode three hundred and forty five, we dedicate the
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entire show to questions from the audience, and we're going to do a bit
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of a mix of audio and text questions today. We'll fit in as many
0:39
as we can. We've got five hundred of them here. We might get
0:42
two or three, we'll see how we go. We'll be looking at the
0:47
rotation curve of galaxies and walking on neutron stars. Will also be chasing up
0:53
the previous episodes, talk on asteroids, dark matter, dark energy, white
0:58
holes, the period of inflame, and much much more. Coming up on
1:02
this episode of Space Nuts fifteen in Channel ten nine ignition sequence Space Nuts or
1:14
three two Space Nurse, as the Nights reported, Bils good and joining me
1:22
to answer all of those questions and more is Professor Fred Watson, an astronomer
1:26
at large. Hello Fred, Hello Andrew, it's great to see you again.
1:30
You too, after it's been so long, been so very long.
1:38
Tongue in cheek. Yeah, well, actually we should just blow the whistle.
1:42
We're doing catch up episodes because you're going to be away for a bit.
1:45
I'm going to be away for a bit. Adds up to a long
1:47
period of time where we won't be able to record, so we're working ahead
1:51
of time. But for you who are listening, it is at the right
1:56
time anyway, so it doesn't really matter that I'm explaining that like I am.
2:01
We might as well get stuck straight into it because we've got a lot
2:05
to do, so we will just go straight into question one, which comes
2:08
from Rusty and our favorite wa town of Donnybrook. Hey, Fred, and
2:14
Andrew was Rusty and Dinnybrook. I hope you are keeping cool in our extended
2:19
summertime here in Australia. Fred, you once famously remarked on this show that
2:27
spiral galaxies, when viewed in infrared light, completely lose their spirals. You
2:34
don't see them at all. In infrared. And so I'm wondering, since
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most of the visible light is from the spirals, and almost all of the
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ultra violet light is also from the spirals, how does the rotation curve vary
2:53
with wavelength? Thank you? All right, thank you. Nice to hear
3:00
from you, one of our regulars. Yeah, we did talk about that
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before, and it became apparent that when you view a galaxy spiral galaxy through
3:09
infrared, there are no spirals. And yeah, it's got rusty thinking.
3:15
Rusty has an interesting mind. He thinks about a lot of things. Yeah,
3:21
And actually, Andrew and Rusty, what's given the lie to my comment
3:28
about the spiral arms disappearing in the infrared is some beautiful James Webb's based telescope
3:35
images of galaxies wow, which have sensational spiral arms. Okay, but you're
3:40
you're seeing. So what I said in the originally is that if you look
3:47
in the infrared, you're you're seeing dominant galaxies dominated by old stars, and
3:54
they tend to be yellowish in color rather than rather than in you know,
4:00
rather than blue and white as the young stars are. And so they they
4:06
do. And it is true that the galaxy itself has this underlying population of
4:15
these elderly stars that have been there a long time. So you're an elderly
4:20
star. Well, yes, no, I'm just old. Im there's you
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know, there's just no bitting about the book, in fact, bordering on
4:30
the ancient. I think they could say so anyway. Yeah, so,
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so there's an underlying population of old stars, including me and he, and
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they tend not to delineate the spiral arms. Then if you look at you
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know, most most images of galaxies, and particularly the early black and white
4:53
ones which were sensitive to the blue actually rather than the red, they show
4:59
the spiral arms because because that's where the young energetic stars are, the white
5:02
or bluish in color, and they show up. Now, spiral arms are
5:09
we know, the host the location of many young stars because the spiral arms
5:13
are caused by sound waves effectively passing through them and basically sparking them into ignition.
5:24
And so you get short lived, very bright stars which show up as
5:29
bluish objects in the spiral alarms. Now, why does the Hubble, sorry,
5:33
why does the James Webb space telescope show galaxies with lovely spiral alarms?
5:38
And the answer is that what you're seeing there is the dust in these in
5:43
these spiral arms, predolently the dust, and that dust is being also pushed
5:49
into a spiral shape by the shockwave the density wave that's passing through them and
5:55
causing the style formation that reveals the spiral arms the stars themselves the right.
6:00
So that's just by way of a caveat to what I said, as Rusty
6:08
quoted me as famously having said that the spiral arms disappear, and it's it's
6:12
still true, but it's certain wavelengths of light, which brings me to Russy's
6:18
question, how do the rotation curves vary with wavelength? So if you are
6:27
always looking at stars, you're going to see you know, you're seeing objects
6:35
whose spectrum is going from from the ultraviolet to the infrared, but it's the
6:44
same object and so it's the same moving with the same velocity. So in
6:48
that regard, you know, looking at stars in different wavebands, you're still
6:51
going to see the same velocities. But it extends even further than that.
6:58
And that is because and this was actually some of the work that Ken Freeman
7:01
here in Australia and Vera Rubin did in the United States back in the seventies,
7:08
demonstrating the rotation curves of galaxies are flat. They don't behave as you
7:13
would expect if you look at clouds of gas with radio telescopes, the sort
7:19
of you know, cold hydrogen in space, which emits at its radiation of
7:28
twenty one centimeters. It's in the radio spectrum that follows the same rotation curve
7:33
as the stars do, so in that regard they are the rotation curves are
7:39
independent of wavelength. Okay, very good. That was simple. Yeah,
7:45
a long answer to a short question, but a good question, Rusty,
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as Andrew says, you always think outside the box. You do. Indeed,
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Thanks Rusty, and now we'll move on to North Carolina, which is
7:55
a long long way from Donnybrook. And one about female listeners. We don't
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get too many questions from our female listeners, so it's nice when we do.
8:05
Hello, Nan, I'm confused about gravity, she says, you'd be
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the only one I heard it described as the curving of space due to the
8:15
mass of an object. Thus, an object in the vicinity of another object
8:18
falls into the curve, causing the object to follow the curve. When referring
8:22
to the formation of stars, the description seems to be that the gas is
8:28
squeezed until it becomes hot enough to ignite. This is also described as gravity
8:33
acting on the gas. That seems to be a different action of gravity than
8:37
the bending of space. Help me understand, Thanks, Nan, what a
8:43
great question. Yeah, that's a fabulous question. So, yes, it
8:52
was Einstein who said that gravity is the phenomenon. It's a geometrical phenomenon,
9:01
is what is said. It's actually about space being bent by any mass that's
9:07
within it, and so, and that's fairly easy to get your head around
9:11
for something like the Sun, where you've got this giant ball of gas which
9:16
is gravitationally distorting the space around it. And that's demonstrated by the fact that
9:22
when you look at the Sun in eclipse, you see stars in the background
9:26
looking to be in the wrong direction, which is how they proved that Einstein's
9:28
theory was correct. But it's probably less easy to get your head around that
9:33
when you're thinking just of a giant cloud of gas. So, if you've
9:37
got a blob of gas in space, and that gas is gravitating because it's
9:48
made of matter, then even though it's pretty tenuous, is out the word,
9:56
Yeah, it's a ten us object. It's not solid like a planet,
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it will still distort the space around it, and the effect of that
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is once again that the outer edges of that space will be bent less than
10:13
the regions towards the center where the mass is concentrated, and you'll get this
10:18
compression effect. The gas will slide down the bend space, and the effect
10:24
of it is the temperature increasing and eventually that cloud of gas turns into a
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star. It's the you know, the mantra is that what is it?
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Matter tells space, how to bend space, tells matter how to move right.
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That's the That's the and I can't think it might be John Wheeler who
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said that, Okay, decades ago, but that's the bottom line. Very
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clever. Okay, we're getting through on fast. We need to slide.
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It's just too quick for my brain. We can easily see. Thank you,
11:05
Nan. Let's go to our next question, and this one's a sort
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of a speculator from Russ. Hi. Guys love the show. It's Russ
11:16
here from Stalebridge in the UK. My question is more of a journey that
11:22
we could take. Let's take out the physics of the impossible. I we
11:28
won't be able to do it. But let's have a walk across the surface
11:33
of a neutron star. What would we be seeing on the surface? What
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does what would the surface look like? Would it be glowing, would it
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be white, would it be in redescent? What sort of colors would we
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be seeing? If we bend down and touch the surface, what would it
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feel like if we were able to jump off a little step, maybe your
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foot high? How fast woud we be going when we hit the surface.
12:05
If we looked up into space, what would we see? Just can we
12:09
just have a theoretical walk across the surface of a neutron star? Thanks very
12:18
much, love the show, guys, Take care, Okay, thank you,
12:20
Russ. We have talked about neutron stars before. I think the very
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first thing that we can say is, as soon as you walk on a
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neutron star, you're you're a mountain climber. Yeah, because the mountains are,
12:33
as we discussed before, millimeters high, yeah, a few millimeters.
12:37
Actually, something happens to you before that though, you die of a horrible,
12:41
painful, immediate prispy death. Well your spaghettifying, all right, just
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like because like a black hole, you know, the gradient the gravity gradient
12:52
around a neutron star is very steep, so your head's feeling, you know,
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as you walk, your head is feeling less gravity than your feet,
12:58
and you spaghettified. Basically, it's not very nice, not pretty. So
13:05
but yeah, what an interesting question. And I think it, I think,
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and I ought to check this, but I think the surface of a
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neutron star is very very radiative, so it's beaming out light and I think
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it's probably ultraviolet because it's such high energy. So it's all the good stuff
13:28
like the human body loves exactly. Well, you've got now everything else,
13:35
You've got everything. It's it's not just the gravity and the the blinding intensity
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of the radiation. You've also got intense magnetic fields that I'll probably screw your
13:46
insides up completely. Stepping off a doorstep would happen because the doorsteps already been
13:54
squashed as being something less than a micron high, So there's not much to
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do with looking at the sky from the neutron star. Yeah, you would
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see it probably would look a bit weird because there would be definitely gravitational distortion
14:09
effects in the space around you, and that might cause some strange effects,
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particularly near your horizon with you know, stars compressed one way or the other.
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So it would be an environment that is very very different, you know,
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assuming that we could magically somehow survive it, it would be very very
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different from anything we experience on Earth. And that is I guess typical of
14:37
astronomy all pretty well, all the objects we talk about. If you transported
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yourself from Earth to one of those objects, no matter what it was,
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even if it's an asteroid, the phenomena that you would encounter will be so
14:52
different from what we have on our own planet that it makes for very interesting
14:58
thought experiments and very interesting really and I hope very interesting podcasts. Indeed,
15:03
in fact, we are so well adjusted to our own planet because we've spent
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hundreds of thousands and more tens of thousands of years adapting to this environment,
15:13
just about anywhere else we could go would not be good for us. No,
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that's right, unless we could find another planet exactly the same as ours
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in terms of every ways and proximity. Yeah, well, it's you know,
15:28
going around a star like the Sun rather than a red dwarf that's going
15:33
to spit out all the time. Yes, No, I mean it's not
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surprising. You know, we've evolved as creatures of the Earth, so we
15:41
are very well adapted to it. And you can kind of imagine how many
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million years it might take for humans to adapt to being on a neutron star
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if they're good. Yes, I think supermodels would adapt well because they like
15:54
being skinny. Yeah, skinny is one thing, but spaghettiveations another. The
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one good thing about a neutron star is that you could walk all the way
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around it in a you know, much of ours. Is that right?
16:08
Because they're not very big? Are they the side of a city? That's
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right? So yeah, yeah, slums down third, it might be thirty
16:15
killing time bus or get mugged. Probably get mugged the neutron bus. Are
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all right? Thank you, Rus, lovely to hear from you, and
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thanks to Rusty and Nan for sending in questions to us on this episode three
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hundred and forty five of Space Nuts. Space Nuts. All right, we'll
16:41
just carry right on, Fred because we have a question from Jeff. This
16:45
is a follow up to something we talked about in the last episode. Hey
16:51
freend Andrew Jeff in Ohio US eight here. They just want to clarify a
16:55
couple of biochemical things from the urosl and an asteroid discussion, and ask a
16:59
question as well about dark matter dark energy. So, yes, biological processes
17:04
on Earth that make proteins use all l amino acids, but some biological organisms
17:11
actually use d amino acids make d amino acids. For example, Anthrax makes
17:15
a polymer out of glutamic acid that's all D or mostly D. And also
17:22
when we're talking about trying to find DNA in an asteroid, there's a leading
17:26
hypothesis that actually RNA was the world before DNA and protein showed up that it
17:32
not only held it genetic material like DNA does, but also catalyze reactions like
17:36
proteins do, and we still see evidence of that today. So my question
17:41
about dark matter dark energy, I'm slightly familiar with these two concepts being described
17:48
as a web that kind of holds galaxies together and keeps them from playing apart.
17:53
And I think there was some kind of modeling that showed that, or
17:56
at least try to model what that web might look like maybe a few years
17:59
ago. And Science or Nature, did you talk a little bit more about
18:03
the background on this dark energy dark matter WAB. I'd like to know a
18:07
little bit more on the background, so I can kind of run of it
18:08
from there. Thanks you guys, keep up the good work. Really love
18:11
the show. Thank you about Thank you Jeff, And wow, what on
18:15
a Stuid fellow? He knows his stuff about RNA and DNA, and yeah,
18:22
very very clever. Brought up some interesting points I didn't know. Is
18:26
he right that the Earth was probably more RNA than DNA in the beginning and
18:32
something changed. I'm not sufficiently engaged with the world of evolutionary biologis and I
18:44
before. I'm very glad that Jeff put those ideas there, because, yeah,
18:48
we'll follow up on that. Yeah, and I find out what the
18:49
story is that. But his main question was about one of our favorite topics,
18:55
dark energy and dark matter. And yeah, he did describe them as
19:00
the web that holds galaxies together. And we have said before that if there
19:03
was none of these galaxies would just spin themselves into oblivion. They just go
19:08
in all directions, I suppose, So yeah, how does it work?
19:11
I suppose was what he wanted to know. Yeah, so giant space spiders.
19:19
God, you've cut to the chase. David Bowie was right, spiders
19:23
from Mars. There you are spiders from Mars. Yeah, So we need
19:30
to disentangle dark matter and dark energy though, because dark energy is not something
19:36
that's part of the web that just talking about, just talking about the cosmic
19:41
web, which is structures of matter within the universe. Now, there were
19:48
structures of matter we think were instrumental in the creation, just as you said,
19:55
Andrew of galaxies, because we find that when you build models of the
20:00
way the Big Bang evolves, you end up with this web of material.
20:06
It's almost like a foam, if I can put it that way, very
20:11
much like cells of a honeycomb, with the walls between the honeycomb forming the
20:18
structure of the web, which is there in both dark matter and normal matter.
20:25
The dark matter probably was the first thing to sort of crystallize into this
20:30
web shape after the Big Bang, with the normal matter being gravitationally attracted to
20:33
it because dark matter outweighs normal matter by five to one or thereabouts. So
20:40
that's the hydrogen that followed the dark matter, and that hydrogen then collapsing into
20:48
stars, gas clouds, galaxies and all the stuff that we're familiar with now.
20:52
But dark energy is probably uniform throughout the universe, so it's not part
20:59
of this web structure. The web structure is just for matter, whether it's
21:03
dark matter or what we call baryonic matter, which is the matter that we
21:08
can detect that forms the web. But dark energy doesn't. Dark energy seems
21:14
to be a property of space itself, irrespective of what structures you build inside
21:19
it. The dark energy is there, and the effect of dark energy,
21:25
of course, is what we see with the galaxy. Sorry, with the
21:29
universe accelerating in its expansion, as it has been doing for about the last
21:36
five billion years. We think that before that it wasn't accelerating in its expansion,
21:41
even though dark energy was there. But the galaxies were close enough together
21:47
that their mutual gravitational attraction resisted the effect of dark energy. And it was
21:52
only as the universe continued to expand that the galaxies became far enough apart that
21:57
their gravitational pulled towards each other was not strong enough to overcome the accelerating effect
22:04
of the dark energy. So that acceleration is something we've only seen for about,
22:10
you know, half the age of the universe. Before that, it
22:12
were the universe's expansion was probably slowing down any furious as to what changed.
22:19
Yeah, the fact that the galaxies became far enough apart that the gravitational pull
22:23
between them wasn't breaking the yes, the expansion, and so that allowed the
22:29
dark energy to so we were we were dominant. We were basically holding it
22:33
back until it reached a release point. And ye, where she went where
22:38
she went quite gradually. But it's sort of like when you blow up a
22:41
balloon. When you first start to blow up a balloon, it's really it's
22:45
a hard thing to do, and then it suddenly gets easier. That's a
22:49
really good analogue actually, because what you're feeling at first, when you're puffing
22:53
hard against the resist resistance of the of the of the you know, the
22:57
rubber or whatever really it is, and that then gets beyond a certain point
23:03
where it's really easy to blow it up, and if you do it too
23:06
much, it bursts, which is probably what the universe will do in the
23:10
big Rip in a few trillion years time or next week, whichever is longer,
23:15
whichever comes sooner. Yes, that's right. Yeah, Well I hope
23:19
that explain or helps to explain some of the you know, the confusion there.
23:25
Jeff separate dark energy and dark matter out in your mind, because they're
23:29
quite different things. But the dark matter is what forms that web like structure
23:33
that basically is the scaffolding, scaffolding on which the objects in the universe were
23:38
built. Yes, and as we've mentioned in previous episodes, they're just badly
23:44
named dark edge. You'll probably be called something else so that there's no confusion.
23:48
But that yeah, that's where the sort of crossed up dark matter would
23:52
have been better as invisible matter. I think, yeah, but dark seems
23:56
to be the buzzword it does, all right, Thank you, Jeff.
24:02
We've got a text question from Austin, Texas. It's kaos. He says,
24:06
Hello Andrew and Professor Watson. I will preface this question by saying that
24:10
it may not have a conclusive answer because it details in the theoretical I was
24:17
pondering the concept of white holes being mathematically understood but not observed. I wonder
24:22
if white holes could lurk in the dark matter spectrum of the universe. Just
24:26
like we can't detect the or understand dark matter slash dark energy, could it
24:32
be possible that white holes exist within this yet to be understood spectrum of the
24:37
universe. Thanks for a great show. Every week. Much love to y'all.
24:41
I hope I said that right from Texas. Yehare, that's what it
24:45
had not me him. Good bro, that's very flavorous of it. And
24:52
yeah, some bootscooters are lurking somewhere. There are probably, Yeah, so
25:02
that's an interesting thought. Let's explore that a little bit, the idea that
25:06
maybe in the dark matter universe, which we can't detect directly, there are
25:15
objects akin to black holes and white holes. Let's let's do it both ways,
25:22
okay, And Carlos is absolutely right that the mathematics of black holes or
25:26
the mathematics of gravitation, let you conjecture that there are such things as white
25:33
holes. And when you're working in the equations, I think what you do
25:37
is you reverse the sign of time, so you put times going negative,
25:41
and you've got a white hole instead of a black hole. But we see
25:45
nothing in the universe that actually could be one of those, because unlike a
25:51
black hole where nothing gets out, with a white hole, nothing gets in.
25:55
Yeah, and you'd think you'd notice that, but I guess that the
26:00
bottom line here is when you all right, let's think about dark matter,
26:03
we think it is some kind of species of sub atomic particle and perhaps many
26:11
different species of sub atomic particle excuse me, which doesn't interact with normal particles.
26:18
So it doesn't interact with light. We can't see it shining. It
26:21
doesn't interact with matter, you know, it doesn't seem to react with that
26:26
with normal matter. All it does is displays gravity. It has gravity,
26:33
and that's how we detect it because as exactly as you said earlier on,
26:37
when we look at the way galaxies work, if you spot a rotating galaxy
26:42
and if all that you can all that was in there is all that you
26:47
can see, if that's all there is, then it should have flown itself
26:52
apart gazillion years ago, maybe on a millennia ago, but a long time
26:57
ago. It should. It should can't exist without the idea that there is
27:02
some invisible material holding it together. And when you do the theory, you
27:07
get the calculation or you get the almost a picture that shows you that these
27:12
galaxies are embedded in halos of this mysterious dark matter. Now, dark matter
27:18
reveals itself by its gravity, and so gravity behaves normally as far as dark
27:23
matter is concerned, which suggests that if you had a dark matter black hole,
27:33
it would exhibit its forces or exhibit its present in exactly the same way
27:41
as a normal matter black hole does, because it would be a singularity with
27:47
intense gravitational field around it, which would pull other stuff in, whether that
27:51
was gas being accreted like it is at the center of a galaxy, whether
27:56
it's a supermassive black hole, or you know an x red binary where you've
28:00
got a companion star that's leaking material onto the black hole and causing it to
28:06
release X rays. All of that should still hold good, so that what
28:10
you see in the black hole universe in real normal matter burialic matter, you
28:15
should also see in dark matter. Right, okay, interesting, sobly probably
28:22
not is what the answer is, which saved us a lot of time.
28:26
But we were going slow at the start, so that's fine. I've actually
28:30
discovered a white hole. Where is it? It's called my bank account.
28:34
Nothing gets in, yest in, but things get out. Yeah, yes,
28:41
that sounds like a white hole. It's definitely a white hole. All
28:45
right, thanks Carlos. Let us move on to Duncan. I think Duncan's
28:49
sent us a few questions in recently, so let's tackle this particular one.
28:56
I think he's looking at the period of inflation. Hello Duncan here from Weymouth
29:02
in the UK, questioned about a period of inflation after the Big Bang when
29:08
the universe expanded faster than the speed of light. Was that faster than the
29:15
actual speed of light? Or was it that the speed of light at that
29:18
time was faster than it was now. I'm just thinking that if the speed
29:25
of light in itself at that time was faster, could it be that there
29:30
is some property of the universe in which light is able to travel faster than
29:37
what it does currently in the current vacuum. And if we could discover what
29:42
that particular property of the universe back then was, then maybe there would be
29:48
some way that obviously in the distance future or current technology to create a drive
29:56
that goes faster than it. I don't know, it's just the obviously were
30:06
limited to the speed of light. But if the speed of light in itself
30:08
could be increased, then who knows? Anyway, Thanks for you help keep
30:15
up the good work. Well, okay, thank you, Duncan. Always
30:19
good to hear from you. And now I understand how the Americans have learned
30:26
to pronounce things differently to us because of Duncan's accent. I picked up something
30:32
an American pronunciation in there. I can't remember what the word was now,
30:36
but yeah, that's what I was going to ask you. Yeah, I
30:41
just went straight out of my head. It's very late on a Friday here,
30:45
so my brain decides to give up once I've once I've walked out of
30:48
the office. But a period of inflation, yeah, we know, you
30:52
know more, immediately after the Big Bang, the universe expanded, it faster
30:56
than the speed of light, and then it slowed down, and now it's
31:00
accelerating again. Weird does Duncan's theories sit. There's two different things we're talking
31:07
about here, Andrew and Duncan. So the when you think about inflation,
31:15
the speed of light doesn't matter because it's the fabric of space, whatever that
31:21
is. It's you know, it's space itself that's expanding. And you know,
31:26
you could only talk about being faster than the speed of light if you
31:30
think of two points within that space, how fast are they receding from one
31:34
another? And it may well be faster than the speed of light. In
31:37
fact, it would have to be just because of the way the inflation took
31:41
place. It was an extraordinary period in the universe's history. But it is
31:45
the space that's that's that's that's expanding very fast, and that doesn't impact the
31:55
speed of things going through it. So one of the basic foundations of cosmology
32:01
as we understand it, our theory of the origin and evolution of the universe.
32:07
One of its basic principles is that the speed of light is a constant,
32:13
that it has always been the same ever since the beginning it was three
32:16
hundred thousand kilometers per second. There are probably still people I hadn't really course
32:25
up with this work yet, but sorry recently, I haven't caught up with
32:30
it recently. This is work that was done a decade or more ago by
32:35
colleagues here in Australia, in fact, principally at the University of New South
32:39
Wales, who were observing different distant quasars and there was just some evidence in
32:49
those there were spectra. They were taking the rainbow spectra of these quasars and
32:52
look at the features in them. There was evidence that hinted that some thing
33:00
was varying, that one of the fundamental physics principles was different then than it
33:07
is now. Because when you're looking at as you're looking a long time back
33:10
into the past, and the inference was that it was either the charge on
33:16
the electron or the speed of light that was different. That work was always
33:23
greeted with a reception that was less than worn by the astrophysical community. And
33:31
I know why because I've seen the data and it is really, it was
33:36
really, you know, it was right on the limit of detectability, this
33:40
this effect that they were highlighting. And I suspect that more recent observations because
33:47
we've now observed quais as to death in that, you know, in the
33:52
last twenty years or so, I think with those more recent observations it might
34:00
have gone away. However, might not have done. And I would not
34:04
be surprised if we hear from one of the proponents of that that work and
34:08
one of the people who carried it out, who is a good friend.
34:15
I'm going to tell the standard joke about this gentleman. I hope if he's
34:19
listening you won't mind. His name is John Webb. And the thing about
34:23
John Webb was you never met up with him at the University of New South
34:27
Wales. It was always in New York, of Cambridge or Paris or somewhere.
34:30
It was always somewhere else, which is why he became known as the
34:35
Worldwide One. Yes, I remember this once before. That's a great Yeah,
34:39
that's a great nickname. Yeah, great, it is a great nickname.
34:43
Is a great guy as well. Yeah, you know, and I'd
34:46
be nice to try to catch up with him in Cairo or somewhere to find
34:51
out whether he's still whether whether those ideas are still prevalent. Yeah, I
34:57
should look it up. I have a listener from Kune Barrabin who emails me
35:04
quite regularly and listens to Space, and that's H Barry. He sent me
35:07
some nicknames the other day. Keith kat E t H. It's the nickname
35:14
of a bloke with named Keith, but he only has one eye, so
35:20
he's lost his eye. Keith. Well, I love it. That's a
35:28
very clever nickname, very clever nicknase. It's a good one. Yeah.
35:30
It's nearly as good as the guy with the shovel on his shoulder, isn't
35:35
it. What's that Doug Dog? Yeah, yeah, yeah, the guy
35:39
floating in the ocean, Bob, there's a shovel on his shoulder, Douglas.
35:47
We could go on forever, but we probably lose our entire audience.
35:52
You've done, Duncan, Yes, just to return to it. I think
35:57
you know, it really is very principle of our understanding of the universe that
36:02
the speed of light hasn't there, and so engineering the speed of light itself
36:09
down the truck is something that I suspect we would never get to. Okay,
36:15
and not for want of trying. We're trying ways of speeding up our
36:19
capacity to move through the universe. But yeah, getting to the speed of
36:23
light, I mean, if we can get to a fraction of it,
36:24
that'll be an achievement. But yeah, full speed of light probably way out
36:30
of our realm, given how much energy is required. Thank you. Duncan
36:35
loved the question. This is space Nuts Andrew Dunkley here with Professor Fred Watson,
36:44
Spacenuts. Okay, let us continue and our next audio question comes from
36:50
Mark. Hey, guys, this is Mark from Baton Rouge, Louisiana.
36:55
I really love your shirt. I understand that one of the lines of reasoning
37:00
pointing toward the existence of dark matter has to do with the comparison of the
37:06
rotational period of galaxies to the amount of matter that they contain. However,
37:12
I've seen various estimates of the number of stars in the Milky Way galaxy,
37:16
ranging anywhere from one hundred to about four hundred billion stars. This is quite
37:22
a large Arab war, I would say, and I'm curious how they can
37:27
make this comparison if astronomers are this unsure of the number of stars in our
37:31
own galaxy, much less other galaxies. Thanks, guys, I hope to
37:37
get an answer. We hope to give you on one day. Actually you're
37:44
asking the right block because Fred has been counting stars for all of his career.
37:49
Pretty well, that's right, And yes they you know, the way
37:54
you estimate the number of stars in a galaxy is certainly in our own galaxy.
38:05
You're what you're trying to do is find a way of measuring its mass
38:10
and then you turn that into stellar masses. But one stellar mass does not
38:17
necessarily equal one star. So some of the work, in fact, I
38:22
was involved with this work decade or so ago, by trying to measure the
38:28
mass of our galaxy by using the escape velocity of stars. If you think
38:37
about the way stars some stars might escape from the galaxy, then you can
38:44
use that if you this is we did this with the rave experiment, the
38:46
radio velocity experiment, you can actually deduce back what the mass of the galaxy
38:52
is within that radius with it where the particular star is. Actually it's within
38:59
the radi of the Sun, the Sun's distance from the center of the galaxy,
39:02
and you get if I remember Odi, we got one point for trillion
39:10
trillion solar masses for the mass of the galaxy. But that includes dark matter,
39:19
so it's not individual stars. So you know, you've got to know
39:23
something about the universe before you make these calculations, and looking at other galaxies,
39:30
it's easier you don't count the individual stars in the galaxy. And it's
39:36
only recently that we've been able to see the individual stars in the galaxy,
39:39
although back in the nineteen twenties Hubble was observing Cepheid variable stars in the Andromeda
39:47
galaxy and that was an early step in that direction. But most of the
39:51
stars in a galaxy are too faint to do that, and Allly sees this
39:54
glow which collects them together. But by observing so what you're doing is you're
40:01
looking at the luminous characteristics of a galaxy, the stuff that is emitting lines.
40:09
Even if you can't see the individual stars, and from that you can
40:15
deduce the stellar mass content that is emitting the light. In other words,
40:20
you've got some handle on the normal matter. And it turns out that that
40:23
is far too little to keep the galaxy held together. And so that difference
40:31
between one hundred and four hundred so you know, stars in our own sorry,
40:36
four one hundred and four hundred billion stars in our own galaxy. Yes,
40:39
it's a four to one error, but it's still well within the limits
40:45
that would be imposed by dark matter. The dark matter itself is much more
40:50
than that, is what I'm trying to say. It doesn't matter whether it's
40:52
one one hundred billion or four hundred billion, the dark matter content has to
40:57
be still much more. Okay, so it is. It's a good question
41:00
mark, and you know, it goes to the heart of how we understand
41:05
these things. The it's not just the rotation of galaxies, of course,
41:10
that leads us to believe dark matter is real. Another very strong pointer to
41:17
the existence of dark matter is the distortion of space by clusters of galaxies and
41:22
galaxies themselves. Once Again, if you look at a galaxy, the space
41:25
around it is distorted to the far more than you could account for simply by
41:32
the luminous matter in the galaxy. It's it's got much more to it.
41:37
And that's why we're so booked on the idea of dark matter, because all
41:42
the tests seems to should suggest it's there. Yeah. Wow, Okay,
41:45
I've been trying to count the stars. I'm up to five. So you've
41:51
been observing the Southern Cross then, yeah, I've been. That's as far
41:52
as I got. Yeah, oh, hang on to the sun six.
41:59
There you've making progress. Well done, you are, Thank you Mark.
42:02
And now we've got a question from Nick. Who is another sandgroper? Do
42:07
you know the term sandgroper fruit? They don't. That's what we call West
42:12
Australians. They're sand gropers. So South Australians are crow eaters. I know
42:16
where that comes from. Crow eaters because back in the day, during the
42:21
gold Rush I think or something around that era, there wasn't much food,
42:24
so they used to eat crows. They used to shoot them. They called
42:29
them something else, they called them desert pigeons or something, but they used
42:34
to shoot crows and cook them and eat them, so they became crows.
42:37
I'm still to find out why West Australian is called a sandgroper though, but
42:43
I'm going to find out. I'm sure it's on the interwebs somewhere anyway.
42:45
This sandgroper is Nick from Perth, who has a question about planetary diversity.
42:52
It is a given that the planets of our Solar system formed by accretion from
42:58
a disc of dust and gas circling around the young Sun, that's the sixth
43:01
star in the sky. Gravity inspired differentiation leading to more dust on the inner
43:07
disk and gas of the outer of the outer resulting in the inner rocky planets
43:14
and the outer gas giants all good. Aside from those groupings, what fascinates
43:17
me is the lack of homogeneity between the planets and moons around the gas giants
43:23
within these two groupings. They are so different, all of them. How
43:28
did that happen? Can Professor Watson recommend some reading on the matter. Should
43:31
I buy his books? Well? That's simple answer is yes, Nick.
43:37
But it's an interesting observation though, because we've got rocky planets inside, we've
43:44
got gas giants further out, and yet they've got rocky moons surrounding them,
43:51
and ice moons and all this other weird stuff. Why is it, so
43:58
yeah, and which book is it in? The best one actually is probably
44:02
the Kids book. It's the one where I think I went into the most
44:08
detail about planet formation, which I probably shouldn't have done in the Kids but
44:12
but never mind, it was it was fun to write. So we think
44:17
we understand why there is this differentiation between the inner rocky planets and the outer
44:27
gassy ones because of the existence of the frost line. So if you look
44:34
at the distance from the Sun where water freezes, basically, it's it's kind
44:45
of beyond it's the outer edge of the gold what you might call the outer
44:47
edge of the Goldilocks zone. Yees too hot and it's not too called for
44:51
liquid water to exist, and so you've got and it's between the old bits
44:54
of Mars and Jupiter basically, And that's what you'd expect because the we think
45:00
that the idea of water, which is by far the commonest to element molecule
45:07
in the universe, freezing and causing an increase in the mass of the outer
45:14
worlds as the planets were forming. We think that's why they were able to
45:17
hold onto a gas assemblop and become gas giants, whereas that the inner rocket
45:22
planets were within the frost line, and so it was you know, they
45:28
weren't able to do that. So so that's a neat explanation. But then
45:35
the moons themselves, you know, Nick is quite right that the moons themselves
45:43
are diverse, but they are all basically rocky bodies, rather like asteroids,
45:51
with some of them have gotten over an over layer of water and an overlayer
45:57
of ice on top of that. Many of them, which we've talked about
45:59
many times, for some are just rock like Eo, Some are just lumps
46:04
of In fact, some are probably more like Pommis Phobos. The moon of
46:08
Mars is diverse in that regard, in that more than fifty percent of its
46:15
his mass is empty space, which is what gives it that low density.
46:21
So there is still diversity among the moons even when you consider that. Yes,
46:27
they're all basically made of rock, but maybe the gas giants are as
46:31
well. We don't know whether they have a rocky core. Yes, yeah,
46:36
that's one of the mysteries, isn't it. So it's possible that guest
46:38
giants are something of an illusion in some respects. That's right. They might
46:44
be just rocky planet's masquerading as something else. Yeah, just got massive atmospheres.
46:51
Yeah, big atmosphere. Yeah, it's like a big hairdo really his
46:54
which you don't know anything about. Actually I did once. I'm rapidly catching
47:00
up to you as you can see. Yes, all right, Thank you,
47:04
Nick, and enjoy groping the sand whatever that means in Western Australia.
47:08
Love Western Australia. Beautiful, beautiful place. To our final question, Fred,
47:14
and it comes from one of our favorite terraforming experts and sci fi writers.
47:22
I'm going to introduce him the way he introduces us. Hello Martin,
47:28
Hello space. That markin Berming Gorvain here writer extraordinaire in many genres. Today
47:38
we're going to terror form a completely theoretical object. And I would just like
47:45
to know what you would see if you were on a tiplar cylinder and a
47:55
circling around it overhead was a a space ship that Professor Tepplai tells you would
48:08
be going back in time. Love your show. I can't wait for the
48:14
answer, Berman Borvain in Potnic, Maryland, USA, over and out.
48:20
Thank you Martin. He's really stretching now, isn't he. Now. I
48:23
just tried to look up what a tipless cylinder is also known as a tiplar
48:28
time machine. It's a hypothetical object theorized to be a potential mode of time
48:31
travel, although results have shown that a tipless cylinder could only allow time travel
48:37
if its length were infinite with the existence of negative energy. So yeah,
48:44
I'm actually looking at the same page as right and true if it's if its
48:49
length were infinite or with the existence of negative energies. So you've got two
48:54
alternatives there, and infinite length is tricky, does a bit make negative energy
49:01
is even trickier. That's why we're probably never going to build one. But
49:07
what an interesting idea it was. It was it actually is something that falls
49:14
out of the equations of relativity, and in fact, it was mathematicians looking
49:20
at those equations back in the nineteen twenties that produced this idea of as you
49:28
said, a hypothetical object theory ez to be a potential mode of time travel,
49:35
and it's because of its effect on the closure of off space time.
49:44
You might put it that way. The gravitational potential is such that you get
49:49
instead of space time being a nice you know, a nice lattice of stuff,
49:54
a bit. I always think of space time as being like one of
49:57
those climbing frames that you find in kids kids parks, the old fashioned ones.
50:01
Anyway, they're not like that anymore. But they were just a you
50:06
know, a regular set of things are arranged in right angles, and it
50:09
gave you a three dimensional structure that's you know, that's normal space time.
50:16
Ben space time is when somebody every stands on one of those and that's what
50:21
that's what the what The equations of relativity shows that when you put matter in
50:27
there, they bend. But when you think of all this happening around an
50:30
infinitely long cylinder, you get the the structure of space itself closes on its
50:37
on itself. If I can put it that way so that you you've got
50:42
a way of moving around in time as well as space, that's the that's
50:45
the idea. There's there's also a phenomenon called frame dragging, which we know
50:52
is a real phenomenon of relativity. It's there was certain I forgot which spacecraft
50:58
it was. Won't come back to me. There was one particular spacecraft that
51:05
was put into orbits around the Earth that was designed to demonstrate that the Earth
51:09
as it rotates drags space time with it. This frame dragging phenomenon. So
51:17
we needed to give a story on that a while back. I think we
51:20
did two. Yeah, I think we did two. And so the cylinder
51:23
itself is it's spinning along its long axis, will create this frame dragging effect,
51:29
warping space time in such a way that you might be able to travel
51:35
backwards in time. That's the bottom line, okay, And so I forgot
51:39
what Martian's question was. What would a spacecraft look like it was going backwards
51:45
in time? It probably just like playing a movie in reverse. Probably.
51:52
Sadly, the boot was put in by a number of people, including a
51:57
follow called Stephen Hawking. He through a relativistic argument the idea of a tipless
52:07
cylinder, suggesting that it would never it would never be able to be built,
52:13
which means you couldn't terraform one. Basically, that's right, it's forgotten,
52:17
forgotten. Terr reforming was at the heart of Martin's question, as it
52:21
always is. And terr reforming a tipless cylinder, Yeah, that would be
52:25
tricky. That would be very tricky. You know, you're a sci fi
52:30
writer, Martin, I'm just do it, just do it. It can
52:35
do anything in science fiction. Well, you know that. You know that's
52:38
the candise, Sandra you doing. I'm currently reading the latest John Birmingham series.
52:44
Johnson, Oh yeah, an English author, but he's Australian based and
52:47
he's just released He always releases books in threes. All his stories have three
52:54
volumes, and I mean halfway through the second of three books in his latest
53:00
series, and it's a it's just a classic outer space war story, which
53:05
is he he hasn't done ones like that before. He's done other really interesting
53:09
stories about monsters coming out of other dimensions and eating humans. And he did
53:15
one about a big blob that came from out of space and wiped out half
53:17
of America and half of Canada and what happened to the world. That one
53:22
was called Without America. He writes brilliantly, and I'm really enjoying this,
53:25
this latest series, which is he hasn't released the third book yet, but
53:31
it's due out this year, so I'm slowly reading the second one so I
53:36
can get straight into the third one when it comes out. It's great stuff.
53:40
Once did a gig with him. Oh did you in Brisbane? Yeah?
53:46
Yeah? I love his writing style, really do. My favorite character
53:51
of his is super Dave, Super Dave. Yeah, and then that series
53:57
has since been recalled renamed the Super Day Series because it sort of took over.
54:02
So we've got to look out for the super dunk theory. Oh go
54:07
superdum series. Enough. If you're listening, John, this is it super
54:13
dumply Yeah, yeah, yeah. Give me put in a kind word to
54:16
your publishers for me. That'd be nice. That will never happen. All
54:22
right, Thank you very much, Martin. Always good to hear from you.
54:25
We're going to wrap it up there, Fred, I think we got
54:28
through a fair bit today. But again i'll remind people, because we've now
54:30
exhausted quite a few of our questions to send them in via our website,
54:35
Space nuts podcast dot com. Click on the AMA link to send text or
54:38
audio questions, or just click on the tab on the right hand side of
54:42
the homepage where you can send audio questions. Don't forget to tell us who
54:46
you are and where you're from. You can record your questions via any device
54:49
with a microphone. Basically, it's that simple. And check out all the
54:53
other stuff on the website while you're there, Fred, thank you as always.
54:57
It's a great pleasure, and yeah, it's good to get through some
54:59
of the questions and hear from the audience. Indeed, the top five or
55:04
sence than we did sounds great. Thanks Andrew, we'll see you next time.
55:08
Indeed we will Fred Watson, astronomer at large part of the team here
55:13
at Space Nuts. And thanks to Hugh in the studio who actually turned up
55:16
for work today, and from me Andred Hunkley, get you on the very
55:21
next episode of Space Nuts. Bye byepauts. You'll be listening to the Space
55:25
Nuts podcast available at Apple Podcasts, Google Podcasts, Spotify, iHeartRadio, or
55:35
your favorite podcast player. You can also stream on demand at bites dot com.
55:39
This has been another quality podcast production from nights dot com.