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