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The Cosmic Q&A: Redshift, Dark Matter & the Shape of the Universe · Space Nuts: Astronomy Insights & Cosmic Discoveries

0:00
Andrew Dunkley: Hello again. Thanks for joining us on Space
0:02
Nuts. This is a Q and A edition. My name is
0:04
Andrew Dunkley. What's a Q and A edition?
0:06
It's an edition where we get Q's and
0:09
give you A's because you're so clever.
0:12
Uh, something like that. Anyway, we're going
0:14
to answer audience questions. That's what I'm
0:16
getting at. We've got questions about
0:17
redshift, We've got questions about dark
0:20
photons.
0:20
Professor Fred Watson: What?
0:21
Andrew Dunkley: Uh, we've got questions about deep space
0:24
astronomy and another one about the expansion
0:26
of the universe. I think we talked about that
0:29
last episode. Anyway, uh, we'll see if we can
0:31
solve all of that on this episode of space
0:33
nuts. 15 seconds.
0:35
Professor Fred Watson: Guidance is internal. 10,
0:38
9, ignition sequence. Star
0:41
space nuts.
0:41
Andrew Dunkley: 5, 4, 3, 2.
0:43
Roger: 1.
0:43
Professor Fred Watson: 2, 3, 4, 5, 5, 4, 3, 2,
0:46
1. Space nuts.
0:48
Andrew Dunkley: Astronauts report it feels good.
0:51
And with us again to kind of
0:54
try to maybe answer some of that is
0:56
Professor Fred Watson Watson, astronomer at
0:58
large. Hello, Fred Watson.
1:00
Professor Fred Watson: Hello, Andrew. Um, kind of is probably the
1:02
best description really, isn't it?
1:05
Andrew Dunkley: Possibly so. Possibly so. Um,
1:08
but you know, it's good to get questions.
1:10
We've got a whole new batch, so, um, let's
1:13
get stuck straight into it.
1:14
Now. First question comes from, um. Uh,
1:18
I love the way he always ends his questions.
1:20
I'm not going to reveal anything, but, um,
1:23
let's hear from Roger.
1:24
Roger: Hey there, Space Nuts. This is Roger
1:27
the truck driver. Tonight I'm in,
1:30
uh, Rutland, Vermont. Got a
1:33
question about the red shift of galaxies.
1:36
Um, if the light that we're seeing from a far
1:38
off galaxy is shifted to the red and it
1:41
started out at a higher frequency,
1:44
doesn't that mean energy's lost somewhere
1:46
between here and there? And is that energy
1:49
just transferred into space? And if it
1:52
is, does that contribute to the
1:55
expansion of space? And I'm not saying it's
1:57
dark energy, but does it
1:59
contribute to it or does that
2:02
energy get dissipated in another way?
2:06
All right. Always digging the show, guys.
2:08
Keep on trucking.
2:11
Andrew Dunkley: I love that. I love that. Uh, we've got
2:14
train drivers that do that. Unfortunately,
2:15
they do it at 3 o' clock in the morning.
2:18
Although today he did it at 10 to 7. I was
2:21
pretty annoyed. Pretty annoyed.
2:23
Professor Fred Watson: This is, uh, the one going past your place?
2:25
Andrew Dunkley: Yeah, behind our place there's a rail line.
2:27
It doesn't get used a heck of a lot, but when
2:29
it does, um.
2:30
Eli: Yes?
2:31
Andrew Dunkley: The glasses rattle. Uh, the ones on my face,
2:33
I mean. Uh, thanks, Roger. Great question.
2:36
Uh, so, um, yeah, the change
2:39
in frequency with the, um,
2:43
energy loss, um, where does the energy go and
2:46
does it contribute to the expansion of the
2:48
universe? And could it possibly be.
2:51
Maybe, maybe not dark matter
2:54
or dark energy or something?
2:56
Professor Fred Watson: Yeah, yeah. Um, there's a lot.
2:58
Andrew Dunkley: He packed a lot into that question.
3:00
Professor Fred Watson: He did. And it's a great question too. Uh,
3:02
and, you know, I mean, it's a,
3:04
uh, project, um, Absolutely right. The
3:07
conservation of energy. Uh, energy
3:10
can't be created or destroyed. That's the
3:12
fundamental rule. Its
3:15
energy is always conserved.
3:18
But, uh, the universe doesn't play
3:21
by the ordinary rules.
3:24
Uh, and, um,
3:28
it's an interesting answer here.
3:31
Um, and I have to say it's changed
3:34
my view of what this, you know, what
3:37
the answer to this problem was because,
3:40
um, when we've been asked this before,
3:43
we haven't been asked it for a long time.
3:46
I just assumed that the energy, uh,
3:49
basically was absorbed by the universe by
3:51
space time, uh, and
3:55
maybe contributed to the expansion.
3:57
Although,
4:00
uh, you can't have it both ways because it's
4:02
the expansion that's causing the photon's
4:05
energy to be lost. Uh,
4:08
and just stepping back, exactly as
4:11
Roger said, uh, you've got light going
4:13
through the universe. It's,
4:15
uh, its wavelength is being stretched by
4:18
the expansion of the universe. Therefore the
4:21
light is losing energy. Because the energy
4:24
of a beam of light is all about the
4:26
frequency of the light, in other words, or
4:28
the wavelength. Putting it another way. So
4:31
if you increase the wavelength, you lose
4:34
energy. And that's, um,
4:37
a given already. Uh, so what I
4:40
used to say was, yes, it kind of goes into
4:42
the universe. But I've done a bit more
4:44
reading on this and I was wrong.
4:48
Um, because when
4:51
you apply general relativity to
4:54
the universe as a whole, and that's the.
4:57
As we've talked about, and we've talked about
4:59
it at length in the last episode, it's, uh,
5:01
the kind of fundamental rule that governs
5:04
everything that we understand in the
5:06
universe. Um, when you
5:09
apply general relativity,
5:12
Andrew Dunkley: uh,
5:12
Professor Fred Watson: that conservation of energy
5:16
that we expect to happen in the
5:19
everyday world, it
5:22
doesn't hold good. So energy, uh,
5:25
is not conserved in an expanding
5:27
universe. Uh, and so
5:31
basically the energy
5:33
simply disappears. It's
5:36
just not there anymore because of the
5:39
expansion of the universe. It's not causing
5:41
the expansion of the universe. It's not
5:43
create contributing to dark energy or dark
5:45
matter, the energy loss, it just vanishes.
5:49
Wow. So work that one out.
5:51
Andrew Dunkley: I can't.
5:53
Professor Fred Watson: No, I can't either.
5:56
Um, I kind of really
5:59
need to look at the equations on this.
6:02
Andrew Dunkley: Um, don't show them to me. I mean,
6:06
Professor Fred Watson: yeah, I'M not that keen on looking at them
6:08
myself either. Too much else to do. But, uh,
6:11
um, uh, but yes, that is
6:14
the thinking on this.
6:17
Uh, and I think the conservation
6:19
rule does not work, uh,
6:24
um, when it comes to
6:28
the universe on a whole.
6:30
Andrew Dunkley: Yeah.
6:30
Professor Fred Watson: Wow.
6:30
Andrew Dunkley: Gee, um, that's quite a
6:33
revelation. Who figured that out?
6:37
Professor Fred Watson: Uh, uh, it's on a number of
6:40
different, uh, physics, uh, related websites.
6:43
Andrew Dunkley: There's the reason no one knows about it
6:45
because it's physics and
6:48
who reads that stuff?
6:50
Professor Fred Watson: Yeah, I think the relativistic bit of
6:53
it, uh, comes from the fact
6:57
that the energy of a particle,
7:00
which is what we're talking about, it's an
7:02
observer dependent quantity.
7:05
And so that's why relativity plays a part in
7:08
this because you're the observer
7:11
and you're talking about something that's
7:13
relative to another observer, that is the
7:15
photon. Uh, and that's why you've got,
7:18
uh, a relativistic
7:22
access. Ah, to it.
7:24
Andrew Dunkley: Wow. Okay. Um, great question,
7:26
Roger. I'm not sure you were expecting that
7:29
answer, but, uh, there it is. Uh, the energy
7:31
just gone,
7:35
goes, vanishes, ceases to
7:38
exist. It's a dead poly.
7:41
So anyway, um,
7:45
no one got that joke. I was, um,
7:48
doing a Monty Python skit for some reason.
7:50
Professor Fred Watson: Yeah, you were. That's right.
7:53
Look, I'm pursuing this in a little bit more
7:55
detail and, uh, just trying to, you know, see
7:58
whether we've got alternative. Alternative
8:00
views of this.
8:02
Andrew Dunkley: Well, generally speaking, you do get
8:04
alternative views when it comes to this kind
8:06
of stuff.
8:06
Professor Fred Watson: That's right. Um, yes,
8:09
so
8:12
that's right. Uh, uh,
8:15
I think the standard explanation today is
8:18
that energy is not conserved.
8:21
Okay.
8:23
Andrew Dunkley: We'll leave it at that until somebody throws
8:24
another spanner into the.
8:26
Professor Fred Watson: Yeah, uh, we might be giving a different
8:27
answer next week. It could be.
8:29
Andrew Dunkley: Thanks, Roger. Great to hear from you. Toot,
8:31
toot. Uh, we'll catch you next time.
8:33
Our next question comes from
8:36
Peter. He's from San Diego, California.
8:39
While listening to another astrophysics
8:41
podcast, I heard the term dark
8:43
photon for the first time. Apparently this is
8:46
a particle astrophysicists are, uh, seeking
8:49
in order to explain dark matter and, or dark
8:51
energy. Could you please elaborate on what a
8:54
dark photon could be?
8:57
Um, dad, joke for Andrew. A photon
8:59
travels at the speed of light. Does that mean
9:02
a dark photon travels at the speed of
9:04
dark. I like that.
9:07
That's good. Yeah, that's really good. Uh,
9:09
keep up the great work, he says. Uh, thank
9:12
you, Peter.
9:13
Professor Fred Watson: All as well.
9:13
Andrew Dunkley: In San Diego, California.
9:16
Uh, have you ever heard of a dark photon,
9:18
Fred Watson?
9:19
Professor Fred Watson: Um, yes, I'VE probably got a few in this box
9:21
here. The
9:24
speed of dark. Just, just going back to that,
9:26
that quip, uh, there was
9:29
a storey I read, uh, probably
9:32
a fortnight ago, uh, about
9:36
exactly this. In that dark
9:39
ness can move faster than the speed
9:42
of light.
9:43
Andrew Dunkley: No,
9:46
Professor Fred Watson: but it's ah, an illusory darkness. It's when
9:49
you've got um, light beams
9:52
interfering with one another so that
9:55
you've uh, interference
9:58
light beams can cancel out. So if you've got
10:00
two light waves and you add them up out of
10:03
phase, they can cancel out and you get
10:04
darkness. That's a well known principle
10:07
of interferometry. I used to play with that
10:09
when I was a student a lot. Uh,
10:12
but there are certain circumstances that
10:14
those patterns of darkness can actually
10:17
exceed the speed of light
10:20
because they're not actually real, they're
10:22
not real entities. They're not a thing that's
10:24
carrying any sort of information or energy.
10:26
They're just patterns in an
10:29
interference pattern. They're just dark
10:31
patches in it. And I think under certain
10:32
circumstances they could go faster than the
10:35
speed of light. Darkness might
10:38
be not quite as uh, you know, as twee as
10:41
you thought it was. I guess so
10:43
anyway, anyway, uh, that's not the
10:47
question, uh, because dark photons are
10:49
definitely something different and they're
10:52
basically uh, hypothetical.
10:55
They've been hypothesised by
10:58
physicists and cosmologists as uh,
11:01
being a uh, force carrier
11:04
similar to the ordinary photon
11:07
but related to dark
11:10
matter. In other
11:13
words, you might have. Sorry, somebody's
11:15
trying to phone me. I'm just gonna kill that
11:17
call. Yeah, um,
11:21
that was me.
11:21
Andrew Dunkley: That was me. No it wasn't.
11:26
Professor Fred Watson: You know, they're part of the. There may be.
11:29
When we discover finally what dark matter is,
11:33
there may be a suite of
11:36
dark particles which could include
11:39
dark photons. That's the bottom line.
11:41
Andrew Dunkley: Right?
11:42
Professor Fred Watson: Um, and so you know we mentioned last
11:45
week the, or in the last episode the uh, the
11:48
Large Hadron Collider being upgraded to the
11:50
High Luminosity Large Hadron Collider. Um,
11:53
that's one of the things they'd be looking
11:56
for, will be dark photons.
11:58
Okay.
11:59
Andrew Dunkley: You know, I tried to do
12:02
um, an AI search for an
12:04
explanation on it and um,
12:07
it sort of gave me all this gobbledygook. But
12:10
um, you know, what would a dark
12:12
proton, a photon do? It says it would
12:15
carry a force within the dark sector.
12:19
We call that the government. It might allow
12:21
dark matter particles to interact with each
12:23
other and it could very weakly mix with
12:25
normal photons, giving us a way to Detect it.
12:28
And the reason they reckon that scientists
12:31
care about this, as you said, could explain
12:34
what dark matter is made of. So
12:36
therefore solving some of those gaps in our
12:39
current physics theories.
12:43
That's why people are interested in this and
12:45
that's why they're upgrading the Large Hadron
12:47
Collider. And hopefully we will
12:50
learn more in years to come.
12:54
That's the hope.
12:55
Professor Fred Watson: That's the hope, yeah. So we might be talking
12:58
one day about dark photons, um, having been
13:01
detected, which would be a coup
13:03
for space newts.
13:05
Andrew Dunkley: Yes, it will. Uh, but at this stage they
13:08
are not proven. It's just a theory. So
13:11
that's about as much as we know at this point
13:13
in time. But, uh, very good question. Uh,
13:16
and, uh, thank you, Peter, for sending it in.
13:19
This is Space Nuts with Andrew Dunkley and
13:22
Professor Fred Watson Watson.
13:26
0G and I feel fine. Space Nuts.
13:29
Okay, Fred Watson, we'll move straight on to
13:31
our next question, which is, uh, another
13:33
audio question from Eli.
13:36
Eli: Hello, this is Eli from
13:39
sunny Coachella Valley in
13:42
California. I'm embarrassed to
13:45
admit it, but I still can't get my head
13:47
around deep space astronomy. I get that
13:50
the light from, say, a distant galaxy is a
13:53
billion years old, but why
13:56
that particular point in its time? Is
13:59
it just a matter of whatever light is hitting
14:01
us is the time we get to see.
14:05
But for really early light,
14:07
the JWST, early universe stuff
14:10
that's been travelling for 13 billion years
14:13
and just hitting us now,
14:16
are we looking for the light that hasn't
14:19
passed us by or hasn't made it here yet,
14:22
but is from that one precise
14:24
location long ago?
14:27
This stuff is so difficult to get my head
14:30
around. Love the show and hope
14:33
you guys can clear this up for me.
14:36
Andrew Dunkley: Uh, no, we can't. We just thought we'd, um,
14:38
put the question in there. Thanks,
14:41
Eli. Uh, this is a deep, um, I'm, um.
14:44
Not only in deep space astronomy terms, but
14:46
it is a deep, deep topic.
14:48
Um, I mean, when we look up into the sky
14:51
at night and we see all those beautiful
14:53
coloured dots, we are looking at history.
14:56
And it's variable history because some of
14:59
it's 4.41 light years away and
15:01
some of it's 400,000 light
15:04
years away, some of it's further than that.
15:07
Um, but then you've got the cosmic
15:10
microwave background radiation, which is kind
15:12
of a leftover of,
15:14
um, what happened after the
15:17
Big Bang and that,
15:20
that's a different kettle of fish. And I can
15:23
understand why you've got a headache. Eli,
15:25
over to you, Fred Watson.
15:27
Professor Fred Watson: Thanks. Um, so I
15:30
guess uh, you know,
15:33
I understand Eli's issue as well.
15:36
Um,
15:38
you've got to be in the right place at the
15:40
right time to see a photon from a distant
15:43
galaxy. But I guess the way
15:46
to envisage this is if you think
15:48
of the universe, um,
15:51
and you've got to perhaps think of it as if
15:54
you were looking at it from the outside,
15:55
which we never can. But, uh, if you can think
15:58
of it that way, then it's full of
16:01
objects which are radiating light.
16:04
Even in its infancy, when the universe was
16:06
very young, the stuff in it was basically
16:09
shining. Um, once we got past the Dark Ages,
16:12
where no stars were shining, uh,
16:15
um, and those are the galaxies that we now
16:18
see. So they constantly radiate, creating
16:20
light. And that's just like a river of
16:23
light that's flowing down time,
16:26
if I can put it that way. Uh, and
16:30
a long time in the future it
16:33
reaches us. But it's not just
16:36
an individual photon or something that's
16:38
reaching us. It's this stream of stuff that
16:41
is being radiated throughout the
16:43
universe by these galaxies. So we,
16:46
um. And we pick it up. We
16:49
pick it up sometimes exactly as you've said.
16:52
Well, up to 10 billion years after it's been
16:54
radiated. I think 12 billion years,
16:58
uh, are the oldest or the earliest galaxies
17:00
that we now see. We're looking back in time
17:02
12 billion years and seeing them as they were
17:05
perhaps a billion and a half years after the
17:08
Big Bang. Um, and they are shining,
17:11
they're radiating light, uh, in the early
17:13
universe and down the track that reaches us
17:16
because that light's going in all directions.
17:18
So it wouldn't matter where in the universe
17:20
we were, we would still see them.
17:23
Uh, we'd just see them in a, you know, in a
17:25
different position in the sky. If we're a
17:27
long way from where we are now. Yeah, but,
17:30
yeah, so I guess it's, you
17:33
know, in a way, one way of thinking about
17:35
this is if you imagine us on planet
17:38
Earth here and imagine us being
17:41
surrounded by a whole series of
17:44
shells which, uh, we're at the centre
17:47
of. And this is a bit like the crystalline
17:49
spheres that people used to think, uh, the
17:51
universe was made of. Uh, but
17:54
these shells, uh, spherical shells,
17:57
all centred on the Earth, but each one
18:00
clicks over to a time
18:02
further in the past, uh, because the
18:05
light's coming to us from the whole cosmos,
18:08
which is full of stuff. Uh, and that's why
18:11
we, these shells sort of being
18:13
illuminated in a way by the objects that, uh,
18:16
radiated them at that time. Uh,
18:20
um, that we see them because of
18:23
the distance that they are away from us means
18:25
that the light has taken that long to get to
18:28
us, whether that helps or not. In fact, I
18:31
think I've just confused it completely. But,
18:35
Andrew Dunkley: um, I
18:38
just doing a little experimental search here
18:41
for a sec.
18:44
What I agree
18:46
with in terms of Eli's question and getting
18:49
your head around it is, um, if
18:52
Betelgeuse, or however you want to pronounce
18:54
it, went supernova right now as we
18:57
were speaking,
19:00
we wouldn't see it for
19:03
640 years.
19:05
Roger: Yeah.
19:07
Andrew Dunkley: So for it to have gone
19:09
supernova in the past and us to witness
19:12
it, it has to have happened
19:15
pretty close to 640 years ago.
19:19
Does that make sense?
19:20
Professor Fred Watson: Yes. Um, so you could think of that in
19:23
another way. Um, you know,
19:26
um, anywhere between us and 640
19:29
light years away, there could be this pulse
19:31
of light that's on its way to us
19:34
from Betelgeuse. Uh, it would spread
19:37
out in a sphere, and as that sphere
19:39
expanded, eventually it would wash over the
19:42
Earth and we'd see it, um, and perhaps
19:44
see it during the day as well, because it
19:46
might get bright enough to do that. Uh, and
19:49
I think that's a really good way of putting
19:51
it, Andrew, because thinking, um, about the
19:53
galaxies, they're just streaming light out
19:55
all the time, but something like a, uh,
19:58
supernova explosion, which gives a big pulse
20:01
of light, um, that's perhaps easier to get
20:04
your head around because that's. That's just
20:06
gotta, um. It'll
20:08
take whatever time is
20:11
represented by the distance away. So 640
20:14
light years away. It'll take 640 years
20:17
to get here for that pulse to get here. But
20:19
then it will sweep over us and we'll see the
20:22
light. The light fading away.
20:24
Andrew Dunkley: Yeah. And, um,
20:27
the reason I chose that target is because
20:29
there's a lot of conjecture about
20:32
its future and the possibility that it's
20:35
reaching that critical mass point.
20:37
Professor Fred Watson: Yes.
20:38
Andrew Dunkley: Um, but it could have already happened.
20:39
That's the other thing.
20:42
Professor Fred Watson: But that's something we can have no knowledge
20:45
of. That's the key thing, because, um,
20:47
we are limited by the speed of light. That's
20:50
the thing that always limits our view of the
20:52
universe.
20:52
Andrew Dunkley: And just to confuse Eli a little bit more,
20:56
there are, ah, probably things in the
20:59
universe we will never witness because the
21:01
light is just too far away to reach us in any
21:04
reasonable amount of time. Even
21:06
beyond the life of the Earth itself or
21:09
our sun. Uh,
21:13
there are things we will never, ever know
21:15
about.
21:16
Professor Fred Watson: Correct.
21:18
Andrew Dunkley: Um, and that's where it just gives you, um,
21:22
one of those Headaches that requires, uh, you
21:24
to take paracetamol and ibuprofen at the same
21:27
time.
21:32
Um, deep, deep headaches. But Eli, great
21:34
question. I'm not sure we solved your
21:36
problem, but, um, anyway, uh,
21:40
I try to explain this sort of stuff to my
21:42
grandson, uh, and, uh, my granddaughters.
21:45
And, you know, how do you
21:48
explain time and distance
21:51
to a young child? And, um,
21:53
when you're trying to get through traffic,
21:57
Professor Fred Watson: that might not be the best time to do it.
21:58
Andrew Dunkley: Probably not, but they're very interested.
22:01
Very interested. Thanks, Eli.
22:03
Great question.
22:06
Professor Fred Watson: The crew of Artemis 2 now bound for the moon,
22:09
humanity's next great voyage begins.
22:12
Space nuts.
22:14
Andrew Dunkley: Our final question comes, uh,
22:16
from Nova Scotia. It's from Ken.
22:19
Uh, look, this is an old chestnut. We've,
22:21
we've probably spoken about this many times,
22:24
but it's always good to, um, to revisit. If
22:27
the universe is expanding, what is it
22:30
expanding into? And also,
22:33
is the universe spherical?
22:36
Professor Fred Watson: So, um, yes. What's it expanding into?
22:39
Andrew Dunkley: Well, we don't know.
22:41
Professor Fred Watson: And yes, that's.
22:43
Yes. Uh, it's actually, we don't know. And
22:45
maybe, maybe, maybe. So,
22:49
um, the universe
22:52
is everything that we can detect. That's
22:55
the definition of the universe. Everything we
22:56
can measure or detect. And that means,
23:00
and we observe the expansion,
23:03
but we don't know whether there's an edge
23:06
to the universe. We don't know whether it's
23:08
infinite. We don't know anything beyond the
23:10
horizons that we see. And um, the most
23:13
obvious one is the cosmic microwave
23:14
background radiation, um,
23:17
beyond which we can't see. But the universe
23:19
almost certainly goes on beyond that,
23:22
probably for a very long way, maybe very big.
23:24
But we've got no knowledge of a boundary or
23:28
any other medium that it might be expanding
23:30
into. So, um,
23:33
uh, one possibility is the idea of multiple
23:36
universes. And they might
23:38
exist maybe
23:41
in a higher dimensional, uh,
23:45
arena, if I can put it that way. You know,
23:48
if you can, um, find that
23:51
there are extra dimensions, we know the
23:54
three dimensions of space and one of time.
23:56
That's what we've got now.
23:59
But, uh, if there are hidden
24:02
extra dimensions, maybe they provide
24:05
a venue for the universe to expand into.
24:08
Uh, and there are various theories
24:11
that accept that, um, M. M theory is one of
24:14
them, where M is probably an abbreviation
24:17
for membrane. The idea is that the universe
24:20
can be collapsed onto a two dimensional
24:22
membrane, and there are lots of these
24:24
membranes in the kind
24:27
of higher dimensional universe. But that's
24:29
just conjecture and we've got no
24:32
mechanism for proving that at the moment. The
24:34
only thing we know with certainty with
24:36
absolute certainty is that the universe is
24:38
expanding.
24:39
Andrew Dunkley: Yes. Uh, at an accelerating rate. Although
24:41
the accelerating rate's not as accelerating
24:43
as it once was. Possibly.
24:45
Professor Fred Watson: Possibly.
24:46
Andrew Dunkley: Um, yeah. There's three possible
24:49
shapes of the universe. He asks if it's
24:52
a sphere. Um, there's, uh, the flat
24:55
universe theory. Do we have to go there? Uh,
24:58
there's the closed universe
25:01
theory, which is the positive curvature, so a
25:04
sphere. Or the open universe theory,
25:06
which is negative curvature. Huh. So it's
25:09
more like the shape of a saddle. From what
25:11
I'm reading, the most popular,
25:15
uh, likelihood is the flat universe theory.
25:18
Professor Fred Watson: But it's only flat in a Euclidean sense.
25:21
It doesn't mean it's shaped like a
25:23
tabletop. Uh, it means that parallel
25:26
lines never meet. Basically, that's what we
25:29
mean by flat. It's the shape of the geometry.
25:32
Andrew Dunkley: And the other thing that they suggest is
25:35
that, um, it can be flat and still
25:37
expanding. As you said, uh, it might be
25:39
infinite. We've talked about that before.
25:42
And there is likely no centre and no edge.
25:46
Professor Fred Watson: Correct. That's what we believe
25:49
now, um, to its shape.
25:52
So, uh, so
25:56
basically, I think Ken's question is, is it
25:58
spherical? And
26:01
we don't know the answer to that. We know
26:03
that the volume within which we can
26:06
detect is spherical because
26:09
the cosmic microwave background radiation
26:12
forms an imaginary shell,
26:16
uh, all around our galaxy. And it's
26:19
the same distance in every direction. So in
26:21
that regard, it's what we call isotropic, the
26:24
same in all directions. Uh, and
26:26
that's really the only thing we can
26:29
lay it down to. But there are ideas that if
26:32
you looked at the universe on a bigger scale
26:34
than we could see, it wouldn't be. That it
26:36
might be different in different directions.
26:39
Um, and that, in fact, has been
26:42
hypothesised as one of the sources of dark
26:44
energy, that we're just seeing a local bit of
26:47
the universe that's expanding, whose, uh,
26:49
expansion is increasing, whereas somewhere
26:51
else it might be slowing down
26:54
the expansion of the universe. Um,
26:58
Andrew Dunkley: yeah, sorry, go on.
27:00
Professor Fred Watson: No, that would be a universe that's not
27:02
isotropic. It's not the same in all
27:04
directions, but we assume it's isotropic. So,
27:06
uh, that's all we can do in our assumptions
27:09
in cosmology.
27:10
Andrew Dunkley: We just can't see beyond
27:13
what we can see. Which sounds stupid, but
27:15
that's the way the universe is. Um,
27:18
we've got the known universe and then the
27:20
rest of the.
27:21
Professor Fred Watson: That's right, basically. And the rest might
27:24
be a lot bigger than the known universe.
27:25
Andrew Dunkley: Yeah, but we just don't know. Um,
27:29
the only thing I thought of is, like, you
27:30
look at Earth's atmosphere and as you go out,
27:32
it fins. And so there's no defined
27:35
line between space and
27:38
the Earth proper. Could the
27:41
universe be of the same ilk?
27:44
Professor Fred Watson: Yes, but that would imply that space time
27:47
just sort of keeps. Just keeps on going. It
27:49
just might be empty.
27:51
Uh, yeah,
27:53
uh, we don't know.
27:56
Andrew Dunkley: We don't know.
27:57
Professor Fred Watson: Why are you asking us? We don't know.
28:02
Andrew Dunkley: Uh, um, thank you, Ken. Uh, very
28:05
thought provoking question and thanks for
28:07
sending it in.
28:08
If you have questions for us, please send
28:10
them to us via our website,
28:12
spacenutspodcast.com spacenuts
28:14
IO there's a little button at the top called
28:16
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28:20
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28:22
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28:23
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28:26
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28:29
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28:31
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28:32
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28:34
blanks. And while you're there, have a look
28:37
around, visit the shop, get something from
28:39
yourself. Um, you know, whatever you like.
28:42
And we're done. Fred Watson, thank you so
28:44
much. That was a tough one.
28:47
Professor Fred Watson: Yeah, well, we, you know, uh, Space
28:50
Nuts always probes the limits of knowledge.
28:52
We. It does. Ah, that's what we.
28:54
Andrew Dunkley: Unfortunately, I have such limited knowledge,
28:56
I'm not very helpful. But I'm glad you're
28:58
here.
28:59
Professor Fred Watson: No, you are very helpful and, um, so are our
29:01
listeners because they keep on probing, which
29:04
is great.
29:04
Andrew Dunkley: They do indeed. All right, Fred Watson,
29:06
thanks very much. We'll catch you on the next
29:07
episode.
29:08
Professor Fred Watson: Sounds great. Thanks, Andrew.
29:10
Andrew Dunkley: Professor Fred Watson Watson, astronomer at
29:11
large. And thanks to Huw in the studio, who
29:13
couldn't be with us today because he's been
29:15
expanding at an accelerating rate. So he was.
29:17
Enter the gym. And from me, Andrew Dunkley.
29:19
Thanks for your company. We'll see you on the
29:21
next episode of Space Nuts.
29:23
Professor Fred Watson: Bye. Bye.
29:24
Andrew Dunkley: Uh, you'll be listening to the Space Nuts
29:27
podcast, available at
29:30
Apple Podcasts, Spotify,
29:32
iHeartRadio or your favourite podcast
29:34
player. You can also stream on
29:36
demand@bytes.comm this
29:38
Professor Fred Watson: has been another quality podcast production
29:41
from bytes.um.com.