Latest / Space Nuts: Astronomy Insights & Cosmic Discoveries / From Stopping Light to Space Junk — Your Questions Answered

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From Stopping Light to Space Junk — Your Questions Answered · Space Nuts: Astronomy Insights & Cosmic Discoveries

0:00
Andrew Dunkley: Hi there.
0:01
Andrew Dunkley: This is Space Nuts. It's a Q and A edition.
0:04
Uh, my name is Andrew Dunkley. Thanks for
0:06
your company. In, uh, this episode we will
0:08
endeavour to answer audience
0:11
questions. Uh, Kevin wants to know about
0:14
stopping a photon. Did that really happen?
0:17
Ah, we've got a, uh, duo
0:20
named Reynold and Brian wanting to ask about
0:22
intertwining electromagnetic fields.
0:26
Um, the speed of colliding particles in the
0:29
Large Hadron Collider is a question we've
0:32
received. And Mark is asking us
0:35
about the excess number of satellites in
0:38
space and what can be done about it. He's got
0:40
an idea. We will see what that's all about
0:43
on this episode of space nuts.
0:46
Generic: 15 seconds. Guidance is internal.
0:48
10, 9. Ignition
0:51
sequence start.
0:52
Professor Fred Watson: Space nuts.
0:53
Generic: 5, 4, 3. 2. 1. 2, 3, 4,
0:56
5, 5, 4, 3, 2, 1.
0:58
Professor Fred Watson: Space nuts.
0:59
Generic: Astronauts report it feels good.
1:02
Andrew Dunkley: And he's back again for more.
1:04
Uh, it is Professor Fred Watson Watson,
1:06
Astronomer at large. Hello Fred Watson.
1:08
Professor Fred Watson: Hello Andrew. Um, fancy seeing you here. Yes,
1:12
in my study.
1:13
Andrew Dunkley: Yes, I'm in mine as well. Although it's
1:16
hard to see because the background's all
1:18
blurred. I must have a setting
1:21
that I changed in this thing and I can't
1:23
figure it out how to undo it. But um, it
1:25
doesn't really matter. You probably don't
1:28
want to see all the junk at the back of my
1:29
room anyway. It's not as good as your
1:32
junk.
1:32
Professor Fred Watson: Oh, it's good Chunk. My microscope, uh, there
1:35
as well.
1:35
Andrew Dunkley: Oh yeah, that's nice.
1:37
Professor Fred Watson: If I see anything I need to look at closely,
1:39
I can just turn around in my chair and have a
1:41
look.
1:41
Andrew Dunkley: Yeah, well, your age, that's probably.
1:46
You walked into that one.
1:47
Professor Fred Watson: I did deny. Yes.
1:50
Andrew Dunkley: Um, shall we answer some questions?
1:53
Professor Fred Watson: Uh, no, no, let's
1:57
Andrew Dunkley: uh, let's go to our first question. It's an
1:59
audio question and it comes from Kevin.
2:03
Kevin: Hello, space notes. My name is Kevin. I'm
2:06
from Las Vegas, Nevada and I finally have a
2:08
question to ask you after listening to you
2:11
guys from the beginning. It's regarding
2:14
an article that I came across but didn't get
2:16
to fully read on how we have
2:18
officially docked a particle
2:21
of light. Not just slowed it down but full
2:24
on. Um, stop. My question is kind of a
2:27
two part A, is this a
2:30
legitimate thing? Have we stopped a, uh,
2:32
photon from moving and B,
2:36
if not, this can be posed as a what if
2:38
question. But what's the consequences for
2:41
a photon that come to a complete stop?
2:43
Now, photons don't have rest mass. It's only
2:46
in the mass of their energy. But does
2:49
it Gain rest mass now that it is at a rest
2:52
or is this one of those it enters
2:56
and just ends up going back to the speed of
2:58
light once whatever's holding it lets go?
3:02
Um, Google doesn't quite give me the run
3:04
around for a bunch of stuff so I figured I'd
3:07
ask you guys. Love the show. Thank you for
3:10
listening.
3:11
Professor Fred Watson: Thank you.
3:12
Andrew Dunkley: Kevin. Uh, I love this question. Uh, this is
3:14
a subject that has come up uh, a few times
3:17
over the years and it prompted me to do
3:20
a bit of research. Uh, and I did find uh,
3:23
an article on the Physics World website
3:26
that uh, discusses this.
3:27
Professor Fred Watson: Fred Watson Good.
3:32
Uh, yes, that's right. Look, it's ah,
3:36
it really is an interesting um, process.
3:39
Um, but it's uh, it's,
3:43
there's a bit of subterfuge here in the
3:46
nomenclature
3:47
Andrew Dunkley: because well that's a big word.
3:50
Professor Fred Watson: Uh, there is two big words
3:53
there. Don't know what either of them mean.
3:57
There's a, you're almost
4:00
playing with words here in a way because
4:03
you do stop light. But it's not
4:06
the individual photon
4:09
that stops. It gets
4:11
converted into something else,
4:14
if I can put it that way. So you've got to
4:16
start off with a Bose
4:19
Einstein condensate. A
4:21
condensate which is ultra
4:24
cold atoms, they're a fraction of a
4:27
degree above absolute zero.
4:30
And the thing about one of these, they're
4:33
usually called a bec, a Bose Einstein
4:35
condensate. Um, it is
4:38
basically a whole lot of atoms and usually
4:41
it's sodium, uh, which um,
4:44
are so cold that they behave
4:47
like a single quantum object. So
4:50
it's a bit like entanglement
4:53
where you've got two quantum particles and
4:55
they um, behave like a single particle.
4:58
It's that. But in a, in
5:01
a whole petri dish if you like, a lot
5:04
of um, a lot of uh, these atoms are
5:07
entangled effectively. So you've got this
5:09
bec, the boson condensate. But
5:12
then you've got to uh,
5:14
you sort of excite it with
5:17
a laser and then you send your
5:20
photon in that you want to stop.
5:23
And um, it basically
5:26
the photon,
5:30
it's not a photon anymore. It's now
5:32
interacting with these super cold
5:35
atoms, uh, in a way that
5:39
effectively slows the transfer of energy
5:42
down. So it's not the same photon that
5:45
stopped. It becomes something else. It
5:48
becomes um, uh.
5:50
One um, document I read
5:54
suggests it's actually
5:56
converted into a matter
5:59
based hologram, uh, uh,
6:02
which is a slightly um, odd way of putting it
6:05
but basically it tells you that
6:08
you've changed the photon but
6:11
uh, you can then basically,
6:14
um, there's
6:17
a separate laser that's exciting the BEC
6:20
into this unusual state. If you turn that
6:23
off, uh, the pulse doesn't
6:26
just slow down. Sorry, the
6:29
photon that you're trying to stop actually
6:31
does stop when you turn this energy off.
6:34
And what you've got is
6:37
essentially,
6:40
Kevin: uh,
6:41
Professor Fred Watson: all the information, if I can put it that
6:42
way, contained in the photon is
6:45
transferred into this imprint in
6:48
the bec, in the atoms of the
6:51
Bose Einstein condensate. It
6:54
becomes, as I said earlier, like a hologram.
6:57
But then if you turn that, what's called the
6:59
coupling laser back on, um, the light
7:02
pulse is reconstructed
7:05
and sets off again on its path. I haven't
7:08
explained that very well, but that's
7:11
basically what's happening.
7:12
Andrew Dunkley: Okay, so
7:15
Kevin's right. Uh, we
7:17
have demonstrated that you can
7:20
slow light down. I, uh, think when the storey
7:23
first came out, they actually said they
7:25
stopped it. Uh, but
7:28
second, uh, part of his question was,
7:31
does it reconstitute itself and get on with
7:34
its journey? And the answer is yes, that's
7:36
correct.
7:36
Professor Fred Watson: Yeah. So this is. It's not, um, a
7:39
particular, you know, it's not a specific
7:41
piece of research. This. There's a whole lot
7:43
of research going on. It's almost like
7:46
becoming, um, uh, just a
7:50
everyday tool of physicists to do this, to
7:53
stop pulses of light, uh, and
7:56
tinker around and see what they can learn
7:58
from it. Making that grossly
8:00
oversimplified. So I apologise to all my
8:03
physicist friends. Um, but it's, um,
8:06
almost a routine process to do this. Now. I
8:09
think I'm right in saying that not just.
8:12
Although I suspect it's only a few labs in
8:14
the world that have got the equipment
8:15
necessary, uh, to do it. Because
8:18
it's not just your everyday microscope or
8:20
anything like that. It's, uh, quite a
8:22
specific piece of, uh, infrastructure,
8:25
including the Bose Einstein condensate, which
8:27
I think we're all actually made in the. Was
8:30
it in the 1980s? Um, they were predicted by
8:32
Bose and Einstein, two physicists. Uh,
8:35
but I don't think we actually managed to make
8:38
one until maybe 40 years ago. I might have
8:40
that date wrong, but that sticks in my mind.
8:43
Andrew Dunkley: Yeah, that's fascinating. I wonder why we're
8:45
so keen to learn how to do this with light. I
8:48
mean, what do we gain from it?
8:51
Professor Fred Watson: Well, um, uh, it
8:54
teaches you about the properties of the Bose
8:57
Einstein condensate. And
9:00
being able to stop a photon and store its
9:02
energy is quite an
9:05
interesting thing. Particularly if
9:07
you think, well, maybe we can apply this to
9:10
quantum computing. I think that's
9:14
uh, one of the reasons why this is a hot
9:16
topic, uh, that it does have
9:19
applications for quantum,
9:21
uh, information. It also,
9:25
um, you know, it relates to
9:28
our understanding of physics at the most
9:30
basic level. Uh, it's, uh.
9:32
Yes, it's extraordinary. I think it is a very
9:35
useful line of research and, um.
9:38
Sounds like it, I think. Yes, I think I
9:41
should understand it better. That's the
9:43
bottom line.
9:44
Andrew Dunkley: Kevin might also be interested to know the
9:46
revival process after you switch the laser
9:49
back on is quite slow. It's not like it
9:52
instantly goes back to its 300 million
9:54
metres per second. Um, light speed,
9:57
uh, takes a little bit, and
10:00
I'm talking a little bit of time to, to sort
10:03
of rev its engines back up again.
10:05
Professor Fred Watson: Yeah, so, so that's not. I mean, photons
10:08
in a vacuum always travel at that 300
10:11
or 300,000 kilometres per second, the way we
10:13
usually put it, 300 million kilometres
10:16
per second. Um, uh, but that's only
10:19
the speed in a vacuum. The speed in
10:21
different, um, other media is
10:24
different.
10:26
Andrew Dunkley: Thanks for the question, Kevin. That's um,
10:28
that's a really interesting one.
10:30
Our next question, Fred Watson, comes from.
10:33
Uh, Now I'm going to assume this is two
10:35
people. And the reason I say that is because
10:37
the other day we read a note from Rennie in
10:39
California about, uh, one of his grandsons
10:41
being inspired to perhaps study astronomy in
10:44
the future. And these two fellows
10:47
sport the same surname as Rennie. So I'm
10:49
going to assume these are two people,
10:52
Reynold and who've sent this question in.
10:55
And if I'm wrong, I'm sorry, but, uh, I just
10:58
got that gut feeling about it. They haven't
11:00
actually said these are from two different
11:02
people, but, um, uh, the fabric
11:05
of space time consists of different
11:07
fields. An example is the Higgs field,
11:11
uh, electromagnetic field, et cetera.
11:14
So my question is, theoretically, could any
11:16
of these fields intertwine and become
11:19
a new type of field, or could the
11:21
intertwining effect a, uh, field
11:24
to interfere with its behaviour?
11:28
That's getting really into the,
11:30
um, big complexities of,
11:34
uh, studying
11:38
these particles.
11:41
It's the smallest level of anything really,
11:43
isn't it?
11:45
Professor Fred Watson: That's correct, yes. So we're talking about
11:47
fundamental particles which equally, uh,
11:50
well, can be seen as, um, uh,
11:53
as disturbances
11:56
or eddies if you like, in, in the field, in
11:59
the force field. Uh, so, you
12:01
know, whatever that force field is. But I
12:04
think there's a fairly straightforward answer
12:06
to this question though. Uh, um.
12:09
Exactly. As Reynolds and Brian say, the
12:12
fabric of space time consists of different
12:13
fields, such as the Higgs field. And the
12:16
Higgs boson is a disturbance within the Higgs
12:18
field. But, um,
12:21
uh, and so the question is, theoretically,
12:23
could any of these fields intertwine and
12:25
become a new type of field or could the
12:28
intertwining affect a field to interfere with
12:30
its behaviour? And the answer is yes to the
12:33
first part. They don't exactly
12:36
intertwine, they superimpose. And
12:39
you've actually, um, Reynold and Brian
12:41
already named one because the
12:43
electromagnetic field is actually a
12:46
superposition of the electric field and the
12:49
magnetic field, which are themselves
12:50
separate. And there are other, there are
12:52
other superpositions as well.
12:55
Um, uh, the weak
12:58
nuclear force intertwines with
13:01
the electromagnetic force to become the
13:03
electroweak force, which is something we
13:05
think was present in the early universe.
13:09
Uh, so, uh,
13:12
yes, it's interesting the way that these
13:15
superpositions happen. So they're absolutely
13:17
right. They can entwine, uh, and, uh,
13:22
um, at least maybe intertwines the wrong
13:24
word. But, uh, superimpose at least so that
13:27
you have multiple fields becoming
13:30
something different, a new type of field.
13:32
Exactly as they say. Okay, yeah.
13:34
Andrew Dunkley: Ah, it's a strange world, isn't it, when you
13:36
get down to the. It is
13:39
tiny, tiny objects and, um,
13:42
Professor Fred Watson: strange in the big objects as well.
13:45
Andrew Dunkley: I suppose so. I mean, if you
13:48
really sit back and drink a few scotches and
13:50
start looking up and thinking about it, your
13:53
brain just explodes. It's probably the scotch
13:55
more so than the problems of the universe.
13:59
Um, it is so
14:02
out there when you're, you know, just
14:05
contemplating existence itself is one
14:08
of the things I find myself thinking about
14:10
from time to time. How is existence
14:14
not, not just why, but how.
14:18
Uh, it's all very weird.
14:21
Uh, and thank you to Reynold and Brian for
14:23
sending in that question. And, um,
14:27
we wish you well. Uh, and please send some
14:29
more.
14:30
Uh, this is Space Nuts, a Q and A edition
14:32
with Andrew Dunkley and Professor Fred Watson
14:34
Watson.
14:36
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16:27
Kevin: Space Nuts.
16:28
Andrew Dunkley: Uh, I think we've got another audio question.
16:30
We seem to be on a bit of a, um, um,
16:33
um, you know, particle
16:36
type of bender at the moment with this
16:39
episode. Uh, this, this question comes from
16:41
Andy.
16:43
Andy: Hi guys. Andy again, from uk,
16:45
actually from Cheshire, just down the road
16:47
from the beautiful Jodrell Bank. Although
16:50
I've never forgiven them since they took out
16:52
the planetarium. Um, just a quick question.
16:55
Um, the lhc, um,
16:58
we're told that it
17:01
accelerates particles to
17:04
very close to the speed of light, about 0.9 C
17:06
or whatever the actual figure is.
17:09
Um, but they also say that
17:12
they're colliding particles at close to the
17:14
speed of light. Now if they're colliding
17:17
particles that they're accelerating in
17:18
opposite directions, surely that means they
17:21
should be the collisions. The impact
17:24
should be at close to twice
17:27
the speed of light. Um,
17:30
if you just clear that one up, I'd be very
17:32
happy. Um, I,
17:36
I think I'm right and I think the collisions
17:38
are happening at greater than the speed of
17:39
light. But prove me wrong
17:42
again, fantastic show. Speak to you soon.
17:46
Andrew Dunkley: Thanks, Andy. Um, reminds me of all
17:49
those,
17:52
Andrew Dunkley: I
17:52
Andrew Dunkley: suppose, when they're teaching you to drive
17:53
and they're saying, um, look, you're
17:56
driving along the highway at 100 kilometres
17:58
an hour and a car's coming in the opposite
18:00
direction at 100 kilometres an hour and you,
18:03
uh, sadly, hit each other. The
18:06
impact speed is 200 kilometres an hour. I
18:08
guess that's what he's getting at.
18:10
Professor Fred Watson: Exactly that, yes. Um,
18:13
um, and it's a natural thing and it's a
18:16
question that we often get, uh, because it's
18:19
completely counterintuitive.
18:22
Uh, exactly as, um, as Andy's saying. Uh,
18:25
and yeah, Cheshire's lovely. He's right. And
18:28
so is Jodrell Bank. Um, uh, uh,
18:31
as Andy's saying, you're colliding these
18:33
things. If I remember rightly, the, uh,
18:36
proton, uh, speed
18:39
within the Large Hadron Collider,
18:42
I think it's
18:42
99.99998%
18:46
of the speed of light. So that's how fast
18:49
these things are going, almost the speed of
18:51
light. And you've got two, uh, streams of
18:54
them going in opposite directions. You bring
18:56
them together at the various experiment
18:58
points. Um, I've been to some of those. I've
19:01
been in the cavity at the cavern, actually,
19:03
where the compact muon solenoid lives.
19:06
Uh, and that's where they collide. So
19:08
shouldn't they collide at nearly twice the
19:10
speed of light? And the answer is no,
19:13
because then
19:13
Andrew Dunkley: you ought to be no.
19:14
Professor Fred Watson: Yeah, that only works in classical mechanics,
19:18
uh, where, as you said, the velocities just
19:20
add together. Uh, if these things were
19:23
moving, you know, in the, what we call the
19:26
classical realm, in other words, slow stuff,
19:29
you would add the velocities together. Uh,
19:31
but when you get to
19:33
relativistic speeds, as we call them, speeds
19:36
close to the speed of light, you have to
19:39
account for two other relativistic
19:42
factors, which are, uh, time dilation
19:44
and length contraction. And both of those
19:47
things are things, uh, that become very
19:50
significant at, uh, nearly the speed of
19:52
light. And so when you take those into
19:54
account, you get a different formula. And
19:58
I don't know whether listeners are going to
19:59
turn off here, but, uh, I'm going to give you
20:02
the formula. So in the
20:04
classical case, if you've got two
20:07
velocities, U and V, it's always U and V,
20:10
not you and me, U and V. Um,
20:13
uh, and yes, in classical case, U plus
20:16
V is
20:18
the closing speed, but in the relativistic
20:21
case, the Closing speed is u
20:24
+v divided by
20:27
1 over u
20:29
times v over c squared.
20:33
So u +v divided by 1 over
20:36
UV over c squared. That's the
20:38
relativistic formula. And when you put the
20:41
numbers in, uh, you realise
20:44
that you can never, uh, exceed the speed
20:47
of light by this.
20:50
Um, you just get, uh, an answer
20:53
that's even closer to the speed of light than
20:55
your two initial, uh, colliders.
20:58
So, um, here's an example. Uh,
21:01
you've got two things travelling,
21:04
hitting each other or travelling towards each
21:07
other at 0.8 of the speed of light.
21:09
In the classical situation, they would be
21:13
coming together at 1.6 times the speed of
21:15
light. That will be their relative veloc. But
21:17
when you do the relativistic calculation, uh,
21:20
their Closing velocity is
21:22
0.975 times the
21:25
speed of light.
21:26
Andrea: Okay.
21:31
Andrew Dunkley: Okay.
21:33
Professor Fred Watson: I hope that makes sense. It's all
21:36
about the weird things that happen when you
21:38
get near the speed of light. You know, time
21:40
dilation itself, time slowing down for,
21:43
uh, you know, for the. For as
21:45
a difference between the observer and the
21:47
person moving at the speed of light and
21:49
length contraction. These are all weird
21:50
things. So it shouldn't be a surprise that
21:53
they don't just. The velocities don't just
21:55
add together, they combine in that
21:56
relativistic sense. Sorry about the equation.
21:59
It's an equation I quite like, which is why I
22:01
threw it in there.
22:04
Andrew Dunkley: It's fair enough, too. And, uh, hopefully
22:06
that's solved, uh, Andy's dilemma.
22:09
Um, he thought it would be twice the
22:12
speed of light or something to that effect if
22:13
you got two objects at the speed of light
22:16
impacting each other head on. But no, can't
22:19
be done is what you're saying.
22:22
Professor Fred Watson: Yeah, they're close. I mean, only light
22:25
can go at the speed of light. So you're
22:26
talking about things going at nearly the
22:28
speed of light. Uh, they're not colliding at
22:31
nearly twice the speed of light. They're
22:32
colliding at even more nearly the speed of
22:35
light than they were to start with. But it
22:37
never exceeds the speed of light.
22:39
Andrew Dunkley: I get it. There you go, Andy. Uh, solved.
22:45
Professor Fred Watson: The crew of Artemis 2 now bound for the moon.
22:48
Humanity's next great voyage begins.
22:51
Andrew Dunkley: Space Nuts.
22:52
Andrew Dunkley: And our final question today comes, uh,
22:55
from. Mark. Hi, Fred Watson, Andrew, uh,
22:58
and team. It's, uh, Mark again from Sunny,
23:01
is it Cece.
23:04
Professor Fred Watson: Yes, it's where Patrick Moore used to live.
23:07
He used to visit him.
23:08
Andrew Dunkley: I really have to use a bigger font size with
23:11
these questions. Sunny, uh, Selsey on the
23:14
south coast of England. Um, in more
23:17
than one of your podcasts, you mentioned the
23:19
growing problem of excess satellites in space
23:22
and what to do with them. That got me
23:24
thinking. Would it be possible to use the
23:26
action reaction principle to place a new
23:29
satellite in the same place as an old
23:31
one and move the old one into a higher
23:34
graveyard orbit? Uh, Then at a later date,
23:37
collect them to be dismantled safely. The way
23:40
I look at it, if they want to put more
23:42
satellites into space, they should also pay
23:44
to clean the space up. Uh, I know this
23:47
sounds, uh, a, uh, bit space
23:50
snook, a bit like space space snooker. Yes,
23:53
it does. Uh, but would it be possible. By the
23:55
way, I broke the TV in the Globe Pub as a
23:58
young man playing snooker, so probably not a
24:01
good idea to ask me to work out the
24:03
trajectories for all of this. Keep, uh, up
24:05
the great work. It means a lot to everyone
24:07
listening. And those, uh, that don't, well,
24:09
you just gotta pity them,
24:12
says Mark. Thanks, Mark, for the question.
24:15
Uh, I'd love to, I'd love to have been the
24:17
night he broke the tv.
24:18
Professor Fred Watson: That would have been spectacular.
24:20
Generic: Yeah.
24:20
Andy: Gosh.
24:22
Andrew Dunkley: Now what I want to know is, was that he's
24:24
backswing, getting ready for the, the,
24:27
the move of the queue that hit the screen, or
24:29
did he actually fire a ball,
24:32
uh, across the, across the room and hit the
24:35
tv? Uh, you're gonna have to clarify that
24:38
one, Mark. Um, look,
24:41
uh, in, in regard to, um,
24:43
cleaning up your own mess, there's actually
24:45
a. Isn't there an international law
24:48
that requires you to deal with your own
24:51
stuff up there?
24:52
Professor Fred Watson: Yes, there is now. Um, I think it was added
24:55
to the, uh, the
24:57
approvals given by the International
24:59
Telecommunications Union, which is a
25:01
governing body of all this stuff, um,
25:04
that you. I think this came in
25:06
probably five, 10 years ago. You have to
25:09
demonstrate, uh, before they'll give you
25:12
permission to launch, that you've got a way
25:15
of removing your spacecraft from
25:17
orbit. Um, in other words,
25:20
you've got to be able to clean up your own
25:22
junk. Uh, now that's
25:25
fine for new stuff, but there's a lot of
25:27
stuff up there that didn't
25:30
qualify for that. And no thought was given to
25:32
the idea of trashing space that you, you
25:35
know, your spacecraft would
25:38
just continue in orbit, um, after
25:41
its useful life was over. And
25:44
indeed for many of them, for objects,
25:47
uh, especially ones with solar panels which
25:50
are big and act as a drag on the residual
25:52
atmosphere up there. Uh, even if you're up
25:55
at, uh, uh, four or five hundred
25:57
kilometres, there's enough atmosphere that
26:00
if you do nothing, your spacecraft will,
26:03
uh, the orbit will decay. It will
26:06
hit the atmosphere and slow down and that
26:08
brings it down lower and then it slows down
26:11
more. And that is how
26:15
space is kind of almost automatically cleaned
26:18
up.
26:19
Andrew Dunkley: And that's what's happening to the Swift.
26:21
Professor Fred Watson: Uh, yes, that we talked about a couple of
26:23
episodes ago. Exactly right. That's right.
26:25
And that one's worth saving, which is why a
26:28
mission's been mounted to do that, to boost
26:30
it into a higher orbit. So in a way, what
26:32
that's doing is actually what Mark is
26:34
suggesting. You, uh, can go, uh,
26:37
attach another rocket to it and push it up to
26:38
a higher orbit to safeguard it. Um,
26:42
um, so for low Earth
26:45
orbit, There's below about 5,
26:48
600 kilometres. There is this natural
26:50
sweeping up as things decay
26:53
unless you do something about it. Many
26:55
spacecraft have got thrusters that lets you
26:58
lift its orbit. Um, but if you switch the
27:01
thrusters off, that means they're going to
27:03
come back to Earth anyway. And that might be
27:04
enough to satisfy the international
27:06
Telecommunications Unit, uh, going higher
27:09
up, though.
27:10
Andrew Dunkley: Except.
27:11
Andrew Dunkley: Yes, one more point. Uh, when these things
27:13
are burning up, they're putting all those
27:15
metals into our atmosphere.
27:17
Professor Fred Watson: Yeah, you're still getting contamination.
27:19
That's right. We're getting aluminium oxide
27:21
and all sorts of stuff up there that
27:23
shouldn't be there. Uh, but,
27:25
um, yes, for higher orbits,
27:30
these are the ones, what you might call mid
27:32
earth orbits above 1,000 kilometres,
27:35
uh, they're not gonna decay so readily. And
27:38
so they are an. And then,
27:41
uh, the, um, geostationary
27:45
satellites. So the geostationary orbits are
27:47
very, very specific. Um, in fact,
27:50
all the satellites are in the same orbit,
27:52
more or less, um, because it's the one that
27:55
keeps them over the equator and keeps them
27:57
going, uh, round once in a day.
28:00
Um, those geostationary orbits, they're at
28:03
36,000 kilometres. They have to have
28:05
mechanisms to push them into what's called
28:08
exactly as, uh, Malik mentions, a grave
28:12
orbit, which just gets them out of the way so
28:15
that when they become defunct and you can't
28:16
control them anymore, they're not going to
28:18
bang into one of the active geostationary
28:20
satellites. So it is a game of snooker up
28:23
there, um, in a perhaps more gentle way than
28:26
knocking one satellite into another, um, and
28:29
replacing its position in space.
28:32
All you do, if you do that is
28:35
you've got another one that's going to decay
28:37
at the same rate. If it's in low Earth orbit,
28:38
it.
28:39
Andrew Dunkley: Yeah, they reckon there's somewhere between
28:41
three and four and a half thousand inactive
28:44
or defunct satellites in orbit at the moment.
28:47
Professor Fred Watson: That's correct, yes. Um, but
28:49
then on top of that there's a, uh, host
28:52
of, uh, upper stages, launch,
28:55
you know, the launch vehicles. Lots of bits
28:58
and pieces, bits of fairing, bits of junk,
29:00
debris from previous collisions. It's a
29:03
fleck of paint, flecks of Paint. That's
29:05
right. There's even a glove.
29:08
Andrew Dunkley: And a spanner with a spanner too. Yeah,
29:10
there's all sorts of stuff floating around.
29:13
Professor Fred Watson: It's all going at 8 kilometres per second.
29:15
That's the dangerous bit.
29:17
Andrew Dunkley: So I think that, uh, was another part to his
29:20
question. Could you replace a satellite in
29:23
its exact position, move the
29:26
defunct one out and put a new one in the
29:28
exact spot that its predecessor was?
29:31
Professor Fred Watson: Well, you could, and, uh, indeed that's done.
29:33
You don't move the other one out. You. Once
29:36
its orbit's decayed, you, uh, just let it
29:38
drop. Yeah, you've got that orbit, uh, freed
29:41
up and you put another
29:43
spacecraft there. That's what's happening
29:44
with Starlink. Actually, it's exactly what's
29:46
happening. The Starlink satellites are all at
29:49
round about 500 kilometres. They were
29:51
planning another shell at, uh, 1200
29:54
kilometres. But, uh, for once, um, SpaceX
29:57
listened to the astronomy lobby. Because
29:59
those outer ones can be visible all night in
30:01
some parts of the world, um, even though
30:04
they're fainter because they're higher up,
30:06
uh, it means that they're visible for much
30:08
longer during twilight.
30:10
Andrew Dunkley: Yeah, and that's a real problem, isn't
30:13
it? There you go, Mark. Uh, everything you
30:16
said, um, is possible. And
30:19
uh, yes, there is a law requiring people to
30:22
clean up their messes, but at the moment,
30:24
letting them burn up in the atmosphere is
30:26
okay until we all die of some
30:29
kind of metallic poisoning. Then, um, they'll
30:32
go, ah, yeah, we should have done, done
30:33
something about that.
30:35
Professor Fred Watson: Unintended consequences. Yeah.
30:37
Andrew Dunkley: Uh, lovely to hear from you, Mark.
30:38
Um, uh, we've been talking a lot
30:41
about particle science today, and, uh, Andrea
30:44
in Western Australia sent, uh, something in
30:47
a while back and I've kind of been sitting on
30:49
it, trying to find the appropriate moment.
30:51
And because of the, the fact that three of
30:53
our four questions were focused on, on
30:56
particles, I thought it was appropriate
30:59
to play, um, uh,
31:01
Andrea's little voice piece today.
31:05
Andrea: Hey, you two. The joke for the day.
31:09
Two neutrinos walked through a bar.
31:14
Andrew Dunkley: Thanks folks.
31:15
Andrea: Really enjoy your show and I hope you guys
31:17
found that really fun.
31:18
Professor Fred Watson: We did.
31:21
Andrew Dunkley: Uh, that's a good one.
31:22
Professor Fred Watson: That is excellent. Yeah, perfect.
31:24
Andrew Dunkley: Perfect timing. Well, actually, I've been
31:27
sitting on it for months, but it,
31:30
um, seemed appropriate. Appropriate today.
31:32
Professor Fred Watson: Yes, that's the, um, one.
31:34
Andrew Dunkley: Now a reminder, if you have questions for us,
31:36
we would love to get them. Uh, you need to go
31:39
to our website to send them in, uh, which is
31:41
easy, spacenutspodcast.com or spacenuts
31:44
IO. Click on the Ask me anything button at
31:46
the top, it's labelled ama.
31:49
And that's also the logo for the Australian
31:51
Medical Association. But don't get confused.
31:54
Uh, they might answer it too, though. You
31:56
never know. Uh, but send your questions into
31:58
us because, um, there's so much stuff that
32:01
people want to know and if you want to know
32:02
something, the best way to find out is to ask
32:05
us and then we'll refer it to somebody else.
32:07
But, uh, it is, um, uh, text and audio.
32:10
Don't forget to tell us who you are and where
32:13
you're from. Thank you so much, Fred Watson.
32:15
It's been a pleasure.
32:16
Professor Fred Watson: Always a pleasure, Andrew. Great to talk.
32:19
Andrew Dunkley: Catch you soon. Professor Fred Watson Watson,
32:20
astronomer at large. And, uh, thanks to Huw
32:23
in the studio, who puts everything together
32:25
with Blu Tack. Couldn't be with us today
32:27
though, because he drives a proton and it
32:30
does not do the speed of light. And so he was
32:33
late. And from me, Andrew Dunkley. Thanks for
32:35
your company. We'll catch you on the next
32:37
episode of Space Nuts.
32:38
Professor Fred Watson: Bye. Bye.
32:40
Andrew Dunkley: You've been listening to the Space Nuts
32:42
podcast, available at
32:45
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32:48
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32:50
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32:54
Andrew Dunkley: this has been another quality podcast
32:56
production from bytes.com.