From Stopping Light to Space Junk — Your Questions Answered

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Andrew Dunkley: Hi there.

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Andrew Dunkley: This is Space Nuts. It's a Q and A edition.

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Uh, my name is Andrew Dunkley. Thanks for

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your company. In, uh, this episode we will

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endeavour to answer audience

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questions. Uh, Kevin wants to know about

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stopping a photon. Did that really happen?

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Ah, we've got a, uh, duo

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named Reynold and Brian wanting to ask about

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intertwining electromagnetic fields.

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Um, the speed of colliding particles in the

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Large Hadron Collider is a question we've

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received. And Mark is asking us

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about the excess number of satellites in

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space and what can be done about it. He's got

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an idea. We will see what that's all about

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on this episode of space nuts.

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Generic: 15 seconds. Guidance is internal.

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10, 9. Ignition

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sequence start.

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Professor Fred Watson: Space nuts.

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Generic: 5, 4, 3. 2. 1. 2, 3, 4,

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5, 5, 4, 3, 2, 1.

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Professor Fred Watson: Space nuts.

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Generic: Astronauts report it feels good.

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Andrew Dunkley: And he's back again for more.

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Uh, it is Professor Fred Watson Watson,

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Astronomer at large. Hello Fred Watson.

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Professor Fred Watson: Hello Andrew. Um, fancy seeing you here. Yes,

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in my study.

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Andrew Dunkley: Yes, I'm in mine as well. Although it's

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hard to see because the background's all

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blurred. I must have a setting

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that I changed in this thing and I can't

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figure it out how to undo it. But um, it

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doesn't really matter. You probably don't

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want to see all the junk at the back of my

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room anyway. It's not as good as your

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junk.

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Professor Fred Watson: Oh, it's good Chunk. My microscope, uh, there

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as well.

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Andrew Dunkley: Oh yeah, that's nice.

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Professor Fred Watson: If I see anything I need to look at closely,

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I can just turn around in my chair and have a

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look.

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Andrew Dunkley: Yeah, well, your age, that's probably.

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You walked into that one.

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Professor Fred Watson: I did deny. Yes.

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Andrew Dunkley: Um, shall we answer some questions?

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Professor Fred Watson: Uh, no, no, let's

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Andrew Dunkley: uh, let's go to our first question. It's an

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audio question and it comes from Kevin.

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Kevin: Hello, space notes. My name is Kevin. I'm

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from Las Vegas, Nevada and I finally have a

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question to ask you after listening to you

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guys from the beginning. It's regarding

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an article that I came across but didn't get

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to fully read on how we have

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officially docked a particle

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of light. Not just slowed it down but full

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on. Um, stop. My question is kind of a

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two part A, is this a

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legitimate thing? Have we stopped a, uh,

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photon from moving and B,

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if not, this can be posed as a what if

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question. But what's the consequences for

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a photon that come to a complete stop?

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Now, photons don't have rest mass. It's only

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in the mass of their energy. But does

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it Gain rest mass now that it is at a rest

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or is this one of those it enters

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and just ends up going back to the speed of

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light once whatever's holding it lets go?

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Um, Google doesn't quite give me the run

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around for a bunch of stuff so I figured I'd

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ask you guys. Love the show. Thank you for

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listening.

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Professor Fred Watson: Thank you.

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Andrew Dunkley: Kevin. Uh, I love this question. Uh, this is

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a subject that has come up uh, a few times

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over the years and it prompted me to do

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a bit of research. Uh, and I did find uh,

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an article on the Physics World website

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that uh, discusses this.

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Professor Fred Watson: Fred Watson Good.

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Uh, yes, that's right. Look, it's ah,

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it really is an interesting um, process.

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Um, but it's uh, it's,

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there's a bit of subterfuge here in the

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nomenclature

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Andrew Dunkley: because well that's a big word.

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Professor Fred Watson: Uh, there is two big words

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there. Don't know what either of them mean.

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There's a, you're almost

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playing with words here in a way because

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you do stop light. But it's not

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the individual photon

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that stops. It gets

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converted into something else,

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if I can put it that way. So you've got to

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start off with a Bose

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Einstein condensate. A

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condensate which is ultra

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cold atoms, they're a fraction of a

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degree above absolute zero.

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And the thing about one of these, they're

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usually called a bec, a Bose Einstein

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condensate. Um, it is

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basically a whole lot of atoms and usually

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it's sodium, uh, which um,

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are so cold that they behave

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like a single quantum object. So

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it's a bit like entanglement

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where you've got two quantum particles and

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they um, behave like a single particle.

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It's that. But in a, in

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a whole petri dish if you like, a lot

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of um, a lot of uh, these atoms are

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entangled effectively. So you've got this

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bec, the boson condensate. But

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then you've got to uh,

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you sort of excite it with

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a laser and then you send your

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photon in that you want to stop.

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And um, it basically

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the photon,

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it's not a photon anymore. It's now

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interacting with these super cold

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atoms, uh, in a way that

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effectively slows the transfer of energy

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down. So it's not the same photon that

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stopped. It becomes something else. It

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becomes um, uh.

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One um, document I read

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suggests it's actually

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converted into a matter

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based hologram, uh, uh,

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which is a slightly um, odd way of putting it

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but basically it tells you that

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you've changed the photon but

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uh, you can then basically,

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um, there's

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a separate laser that's exciting the BEC

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into this unusual state. If you turn that

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off, uh, the pulse doesn't

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just slow down. Sorry, the

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photon that you're trying to stop actually

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does stop when you turn this energy off.

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And what you've got is

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essentially,

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Kevin: uh,

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Professor Fred Watson: all the information, if I can put it that

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way, contained in the photon is

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transferred into this imprint in

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the bec, in the atoms of the

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Bose Einstein condensate. It

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becomes, as I said earlier, like a hologram.

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But then if you turn that, what's called the

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coupling laser back on, um, the light

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pulse is reconstructed

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and sets off again on its path. I haven't

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explained that very well, but that's

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basically what's happening.

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Andrew Dunkley: Okay, so

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Kevin's right. Uh, we

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have demonstrated that you can

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slow light down. I, uh, think when the storey

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first came out, they actually said they

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stopped it. Uh, but

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second, uh, part of his question was,

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does it reconstitute itself and get on with

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its journey? And the answer is yes, that's

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correct.

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Professor Fred Watson: Yeah. So this is. It's not, um, a

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particular, you know, it's not a specific

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piece of research. This. There's a whole lot

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of research going on. It's almost like

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becoming, um, uh, just a

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everyday tool of physicists to do this, to

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stop pulses of light, uh, and

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tinker around and see what they can learn

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from it. Making that grossly

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oversimplified. So I apologise to all my

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physicist friends. Um, but it's, um,

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almost a routine process to do this. Now. I

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think I'm right in saying that not just.

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Although I suspect it's only a few labs in

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the world that have got the equipment

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necessary, uh, to do it. Because

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it's not just your everyday microscope or

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anything like that. It's, uh, quite a

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specific piece of, uh, infrastructure,

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including the Bose Einstein condensate, which

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I think we're all actually made in the. Was

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it in the 1980s? Um, they were predicted by

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Bose and Einstein, two physicists. Uh,

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but I don't think we actually managed to make

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one until maybe 40 years ago. I might have

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that date wrong, but that sticks in my mind.

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Andrew Dunkley: Yeah, that's fascinating. I wonder why we're

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so keen to learn how to do this with light. I

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mean, what do we gain from it?

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Professor Fred Watson: Well, um, uh, it

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teaches you about the properties of the Bose

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Einstein condensate. And

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being able to stop a photon and store its

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energy is quite an

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interesting thing. Particularly if

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you think, well, maybe we can apply this to

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quantum computing. I think that's

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uh, one of the reasons why this is a hot

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topic, uh, that it does have

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applications for quantum,

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uh, information. It also,

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um, you know, it relates to

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our understanding of physics at the most

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basic level. Uh, it's, uh.

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Yes, it's extraordinary. I think it is a very

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useful line of research and, um.

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Sounds like it, I think. Yes, I think I

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should understand it better. That's the

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bottom line.

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Andrew Dunkley: Kevin might also be interested to know the

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revival process after you switch the laser

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back on is quite slow. It's not like it

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instantly goes back to its 300 million

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metres per second. Um, light speed,

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uh, takes a little bit, and

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I'm talking a little bit of time to, to sort

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of rev its engines back up again.

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Professor Fred Watson: Yeah, so, so that's not. I mean, photons

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in a vacuum always travel at that 300

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or 300,000 kilometres per second, the way we

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usually put it, 300 million kilometres

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per second. Um, uh, but that's only

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the speed in a vacuum. The speed in

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different, um, other media is

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different.

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Andrew Dunkley: Thanks for the question, Kevin. That's um,

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that's a really interesting one.

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Our next question, Fred Watson, comes from.

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Uh, Now I'm going to assume this is two

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people. And the reason I say that is because

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the other day we read a note from Rennie in

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California about, uh, one of his grandsons

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being inspired to perhaps study astronomy in

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the future. And these two fellows

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sport the same surname as Rennie. So I'm

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going to assume these are two people,

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Reynold and who've sent this question in.

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And if I'm wrong, I'm sorry, but, uh, I just

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got that gut feeling about it. They haven't

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actually said these are from two different

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people, but, um, uh, the fabric

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of space time consists of different

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fields. An example is the Higgs field,

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uh, electromagnetic field, et cetera.

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So my question is, theoretically, could any

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of these fields intertwine and become

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a new type of field, or could the

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intertwining effect a, uh, field

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to interfere with its behaviour?

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That's getting really into the,

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00:11:30.980 --> 00:11:33.550
um, big complexities of,

264
00:11:34.240 --> 00:11:35.470
uh, studying

265
00:11:38.430 --> 00:11:40.430
these particles.

266
00:11:41.550 --> 00:11:43.630
It's the smallest level of anything really,

267
00:11:43.630 --> 00:11:44.190
isn't it?

268
00:11:45.310 --> 00:11:47.310
Professor Fred Watson: That's correct, yes. So we're talking about

269
00:11:47.390 --> 00:11:49.860
fundamental particles which equally, uh,

270
00:11:50.510 --> 00:11:53.210
well, can be seen as, um, uh,

271
00:11:53.540 --> 00:11:55.700
as disturbances

272
00:11:56.580 --> 00:11:59.140
or eddies if you like, in, in the field, in

273
00:11:59.140 --> 00:12:01.980
the force field. Uh, so, you

274
00:12:01.980 --> 00:12:04.860
know, whatever that force field is. But I

275
00:12:04.860 --> 00:12:06.660
think there's a fairly straightforward answer

276
00:12:06.660 --> 00:12:09.260
to this question though. Uh, um.

277
00:12:09.860 --> 00:12:12.060
Exactly. As Reynolds and Brian say, the

278
00:12:12.060 --> 00:12:13.860
fabric of space time consists of different

279
00:12:13.940 --> 00:12:16.700
fields, such as the Higgs field. And the

280
00:12:16.700 --> 00:12:18.900
Higgs boson is a disturbance within the Higgs

281
00:12:18.900 --> 00:12:21.060
field. But, um,

282
00:12:21.900 --> 00:12:23.860
uh, and so the question is, theoretically,

283
00:12:23.860 --> 00:12:25.580
could any of these fields intertwine and

284
00:12:25.580 --> 00:12:28.180
become a new type of field or could the

285
00:12:28.180 --> 00:12:30.620
intertwining affect a field to interfere with

286
00:12:30.620 --> 00:12:33.580
its behaviour? And the answer is yes to the

287
00:12:33.580 --> 00:12:36.020
first part. They don't exactly

288
00:12:36.020 --> 00:12:38.660
intertwine, they superimpose. And

289
00:12:39.140 --> 00:12:41.900
you've actually, um, Reynold and Brian

290
00:12:41.900 --> 00:12:43.860
already named one because the

291
00:12:43.860 --> 00:12:46.140
electromagnetic field is actually a

292
00:12:46.140 --> 00:12:49.140
superposition of the electric field and the

293
00:12:49.140 --> 00:12:50.860
magnetic field, which are themselves

294
00:12:50.860 --> 00:12:52.880
separate. And there are other, there are

295
00:12:52.880 --> 00:12:55.200
other superpositions as well.

296
00:12:55.280 --> 00:12:58.280
Um, uh, the weak

297
00:12:58.280 --> 00:13:01.120
nuclear force intertwines with

298
00:13:01.120 --> 00:13:03.240
the electromagnetic force to become the

299
00:13:03.240 --> 00:13:05.960
electroweak force, which is something we

300
00:13:05.960 --> 00:13:08.320
think was present in the early universe.

301
00:13:09.120 --> 00:13:10.870
Uh, so, uh,

302
00:13:12.720 --> 00:13:15.720
yes, it's interesting the way that these

303
00:13:15.720 --> 00:13:17.760
superpositions happen. So they're absolutely

304
00:13:17.760 --> 00:13:20.750
right. They can entwine, uh, and, uh,

305
00:13:22.040 --> 00:13:24.090
um, at least maybe intertwines the wrong

306
00:13:24.090 --> 00:13:27.090
word. But, uh, superimpose at least so that

307
00:13:27.090 --> 00:13:29.690
you have multiple fields becoming

308
00:13:30.570 --> 00:13:32.890
something different, a new type of field.

309
00:13:32.890 --> 00:13:34.780
Exactly as they say. Okay, yeah.

310
00:13:34.780 --> 00:13:36.730
Andrew Dunkley: Ah, it's a strange world, isn't it, when you

311
00:13:36.730 --> 00:13:39.210
get down to the. It is

312
00:13:39.530 --> 00:13:42.050
tiny, tiny objects and, um,

313
00:13:42.890 --> 00:13:44.650
Professor Fred Watson: strange in the big objects as well.

314
00:13:45.130 --> 00:13:48.030
Andrew Dunkley: I suppose so. I mean, if you

315
00:13:48.030 --> 00:13:50.270
really sit back and drink a few scotches and

316
00:13:50.270 --> 00:13:53.150
start looking up and thinking about it, your

317
00:13:53.150 --> 00:13:55.670
brain just explodes. It's probably the scotch

318
00:13:55.670 --> 00:13:57.590
more so than the problems of the universe.

319
00:13:59.980 --> 00:14:01.910
Um, it is so

320
00:14:02.710 --> 00:14:04.870
out there when you're, you know, just

321
00:14:05.110 --> 00:14:08.030
contemplating existence itself is one

322
00:14:08.030 --> 00:14:10.630
of the things I find myself thinking about

323
00:14:10.710 --> 00:14:13.350
from time to time. How is existence

324
00:14:14.910 --> 00:14:16.990
not, not just why, but how.

325
00:14:18.250 --> 00:14:19.710
Uh, it's all very weird.

326
00:14:21.190 --> 00:14:22.990
Uh, and thank you to Reynold and Brian for

327
00:14:23.070 --> 00:14:25.580
sending in that question. And, um,

328
00:14:27.310 --> 00:14:29.469
we wish you well. Uh, and please send some

329
00:14:29.469 --> 00:14:29.790
more.

330
00:14:30.330 --> 00:14:32.430
Uh, this is Space Nuts, a Q and A edition

331
00:14:32.430 --> 00:14:34.750
with Andrew Dunkley and Professor Fred Watson

332
00:14:34.750 --> 00:14:35.470
Watson.

333
00:14:36.830 --> 00:14:38.710
Andrew Dunkley: Let's take a short break from the show to

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Kevin: Space Nuts.

376
00:16:28.870 --> 00:16:30.900
Andrew Dunkley: Uh, I think we've got another audio question.

377
00:16:30.900 --> 00:16:33.470
We seem to be on a bit of a, um, um,

378
00:16:33.810 --> 00:16:36.680
um, you know, particle

379
00:16:36.680 --> 00:16:39.560
type of bender at the moment with this

380
00:16:39.560 --> 00:16:41.840
episode. Uh, this, this question comes from

381
00:16:41.840 --> 00:16:42.360
Andy.

382
00:16:43.160 --> 00:16:45.480
Andy: Hi guys. Andy again, from uk,

383
00:16:45.960 --> 00:16:47.600
actually from Cheshire, just down the road

384
00:16:47.600 --> 00:16:50.319
from the beautiful Jodrell Bank. Although

385
00:16:50.319 --> 00:16:52.320
I've never forgiven them since they took out

386
00:16:52.320 --> 00:16:55.320
the planetarium. Um, just a quick question.

387
00:16:55.810 --> 00:16:58.440
Um, the lhc, um,

388
00:16:58.760 --> 00:17:00.680
we're told that it

389
00:17:01.320 --> 00:17:03.320
accelerates particles to

390
00:17:04.120 --> 00:17:06.520
very close to the speed of light, about 0.9 C

391
00:17:06.520 --> 00:17:09.080
or whatever the actual figure is.

392
00:17:09.650 --> 00:17:12.520
Um, but they also say that

393
00:17:12.520 --> 00:17:14.720
they're colliding particles at close to the

394
00:17:14.720 --> 00:17:17.440
speed of light. Now if they're colliding

395
00:17:17.440 --> 00:17:18.920
particles that they're accelerating in

396
00:17:18.920 --> 00:17:21.560
opposite directions, surely that means they

397
00:17:21.560 --> 00:17:24.040
should be the collisions. The impact

398
00:17:24.280 --> 00:17:27.229
should be at close to twice

399
00:17:27.549 --> 00:17:29.080
the speed of light. Um,

400
00:17:30.749 --> 00:17:32.949
if you just clear that one up, I'd be very

401
00:17:32.949 --> 00:17:34.749
happy. Um, I,

402
00:17:36.429 --> 00:17:38.109
I think I'm right and I think the collisions

403
00:17:38.109 --> 00:17:39.749
are happening at greater than the speed of

404
00:17:39.749 --> 00:17:42.189
light. But prove me wrong

405
00:17:42.669 --> 00:17:45.149
again, fantastic show. Speak to you soon.

406
00:17:46.109 --> 00:17:49.069
Andrew Dunkley: Thanks, Andy. Um, reminds me of all

407
00:17:49.069 --> 00:17:49.389
those,

408
00:17:52.340 --> 00:17:52.460
Andrew Dunkley: I

409
00:17:52.460 --> 00:17:53.940
Andrew Dunkley: suppose, when they're teaching you to drive

410
00:17:53.940 --> 00:17:56.780
and they're saying, um, look, you're

411
00:17:56.780 --> 00:17:58.820
driving along the highway at 100 kilometres

412
00:17:58.820 --> 00:18:00.500
an hour and a car's coming in the opposite

413
00:18:00.500 --> 00:18:02.820
direction at 100 kilometres an hour and you,

414
00:18:03.360 --> 00:18:06.140
uh, sadly, hit each other. The

415
00:18:06.140 --> 00:18:08.660
impact speed is 200 kilometres an hour. I

416
00:18:08.660 --> 00:18:09.860
guess that's what he's getting at.

417
00:18:10.100 --> 00:18:12.170
Professor Fred Watson: Exactly that, yes. Um,

418
00:18:13.660 --> 00:18:16.340
um, and it's a natural thing and it's a

419
00:18:16.340 --> 00:18:19.340
question that we often get, uh, because it's

420
00:18:19.340 --> 00:18:20.740
completely counterintuitive.

421
00:18:22.440 --> 00:18:25.400
Uh, exactly as, um, as Andy's saying. Uh,

422
00:18:25.520 --> 00:18:28.200
and yeah, Cheshire's lovely. He's right. And

423
00:18:28.200 --> 00:18:31.090
so is Jodrell Bank. Um, uh, uh,

424
00:18:31.120 --> 00:18:33.920
as Andy's saying, you're colliding these

425
00:18:33.920 --> 00:18:36.320
things. If I remember rightly, the, uh,

426
00:18:36.320 --> 00:18:38.720
proton, uh, speed

427
00:18:39.439 --> 00:18:41.760
within the Large Hadron Collider,

428
00:18:42.320 --> 00:18:42.960
I think it's

429
00:18:42.960 --> 00:18:46.520
99.99998%

430
00:18:46.520 --> 00:18:49.320
of the speed of light. So that's how fast

431
00:18:49.320 --> 00:18:51.320
these things are going, almost the speed of

432
00:18:51.320 --> 00:18:54.160
light. And you've got two, uh, streams of

433
00:18:54.160 --> 00:18:56.920
them going in opposite directions. You bring

434
00:18:56.920 --> 00:18:58.880
them together at the various experiment

435
00:18:58.880 --> 00:19:01.480
points. Um, I've been to some of those. I've

436
00:19:01.480 --> 00:19:03.400
been in the cavity at the cavern, actually,

437
00:19:03.400 --> 00:19:05.840
where the compact muon solenoid lives.

438
00:19:06.270 --> 00:19:08.400
Uh, and that's where they collide. So

439
00:19:08.400 --> 00:19:10.080
shouldn't they collide at nearly twice the

440
00:19:10.080 --> 00:19:12.160
speed of light? And the answer is no,

441
00:19:13.040 --> 00:19:13.840
because then

442
00:19:13.840 --> 00:19:14.640
Andrew Dunkley: you ought to be no.

443
00:19:14.800 --> 00:19:17.600
Professor Fred Watson: Yeah, that only works in classical mechanics,

444
00:19:18.290 --> 00:19:20.880
uh, where, as you said, the velocities just

445
00:19:20.880 --> 00:19:23.400
add together. Uh, if these things were

446
00:19:23.400 --> 00:19:26.110
moving, you know, in the, what we call the

447
00:19:26.110 --> 00:19:29.030
classical realm, in other words, slow stuff,

448
00:19:29.190 --> 00:19:31.750
you would add the velocities together. Uh,

449
00:19:31.830 --> 00:19:33.510
but when you get to

450
00:19:33.990 --> 00:19:36.710
relativistic speeds, as we call them, speeds

451
00:19:36.710 --> 00:19:39.310
close to the speed of light, you have to

452
00:19:39.310 --> 00:19:42.150
account for two other relativistic

453
00:19:42.150 --> 00:19:44.550
factors, which are, uh, time dilation

454
00:19:44.870 --> 00:19:47.750
and length contraction. And both of those

455
00:19:47.750 --> 00:19:50.070
things are things, uh, that become very

456
00:19:50.070 --> 00:19:52.270
significant at, uh, nearly the speed of

457
00:19:52.270 --> 00:19:54.920
light. And so when you take those into

458
00:19:54.920 --> 00:19:57.520
account, you get a different formula. And

459
00:19:58.240 --> 00:19:59.760
I don't know whether listeners are going to

460
00:19:59.760 --> 00:20:02.200
turn off here, but, uh, I'm going to give you

461
00:20:02.200 --> 00:20:04.920
the formula. So in the

462
00:20:04.920 --> 00:20:07.440
classical case, if you've got two

463
00:20:07.440 --> 00:20:10.000
velocities, U and V, it's always U and V,

464
00:20:10.240 --> 00:20:12.360
not you and me, U and V. Um,

465
00:20:13.260 --> 00:20:16.160
uh, and yes, in classical case, U plus

466
00:20:16.160 --> 00:20:18.920
V is

467
00:20:18.920 --> 00:20:21.770
the closing speed, but in the relativistic

468
00:20:21.770 --> 00:20:24.450
case, the Closing speed is u

469
00:20:24.450 --> 00:20:26.570
+v divided by

470
00:20:27.210 --> 00:20:28.650
1 over u

471
00:20:29.850 --> 00:20:32.170
times v over c squared.

472
00:20:33.690 --> 00:20:36.449
So u +v divided by 1 over

473
00:20:36.449 --> 00:20:38.850
UV over c squared. That's the

474
00:20:38.850 --> 00:20:41.250
relativistic formula. And when you put the

475
00:20:41.250 --> 00:20:44.170
numbers in, uh, you realise

476
00:20:44.250 --> 00:20:47.180
that you can never, uh, exceed the speed

477
00:20:47.180 --> 00:20:48.420
of light by this.

478
00:20:50.310 --> 00:20:53.180
Um, you just get, uh, an answer

479
00:20:53.180 --> 00:20:55.500
that's even closer to the speed of light than

480
00:20:55.500 --> 00:20:58.500
your two initial, uh, colliders.

481
00:20:58.580 --> 00:21:01.310
So, um, here's an example. Uh,

482
00:21:01.310 --> 00:21:03.620
you've got two things travelling,

483
00:21:04.100 --> 00:21:07.100
hitting each other or travelling towards each

484
00:21:07.100 --> 00:21:09.620
other at 0.8 of the speed of light.

485
00:21:09.940 --> 00:21:12.500
In the classical situation, they would be

486
00:21:13.140 --> 00:21:15.580
coming together at 1.6 times the speed of

487
00:21:15.580 --> 00:21:17.880
light. That will be their relative veloc. But

488
00:21:17.880 --> 00:21:20.550
when you do the relativistic calculation, uh,

489
00:21:20.550 --> 00:21:22.240
their Closing velocity is

490
00:21:22.240 --> 00:21:25.240
0.975 times the

491
00:21:25.240 --> 00:21:26.000
speed of light.

492
00:21:26.320 --> 00:21:26.960
Andrea: Okay.

493
00:21:31.200 --> 00:21:31.760
Andrew Dunkley: Okay.

494
00:21:33.760 --> 00:21:36.760
Professor Fred Watson: I hope that makes sense. It's all

495
00:21:36.760 --> 00:21:38.840
about the weird things that happen when you

496
00:21:38.840 --> 00:21:40.320
get near the speed of light. You know, time

497
00:21:40.320 --> 00:21:42.560
dilation itself, time slowing down for,

498
00:21:43.120 --> 00:21:45.990
uh, you know, for the. For as

499
00:21:45.990 --> 00:21:47.630
a difference between the observer and the

500
00:21:47.630 --> 00:21:49.270
person moving at the speed of light and

501
00:21:49.270 --> 00:21:50.830
length contraction. These are all weird

502
00:21:50.830 --> 00:21:53.750
things. So it shouldn't be a surprise that

503
00:21:53.750 --> 00:21:55.390
they don't just. The velocities don't just

504
00:21:55.390 --> 00:21:56.910
add together, they combine in that

505
00:21:56.910 --> 00:21:59.190
relativistic sense. Sorry about the equation.

506
00:21:59.830 --> 00:22:01.950
It's an equation I quite like, which is why I

507
00:22:01.950 --> 00:22:02.790
threw it in there.

508
00:22:04.230 --> 00:22:06.510
Andrew Dunkley: It's fair enough, too. And, uh, hopefully

509
00:22:06.510 --> 00:22:09.100
that's solved, uh, Andy's dilemma.

510
00:22:09.100 --> 00:22:12.030
Um, he thought it would be twice the

511
00:22:12.030 --> 00:22:13.950
speed of light or something to that effect if

512
00:22:13.950 --> 00:22:16.730
you got two objects at the speed of light

513
00:22:16.730 --> 00:22:19.610
impacting each other head on. But no, can't

514
00:22:19.610 --> 00:22:21.810
be done is what you're saying.

515
00:22:22.530 --> 00:22:25.490
Professor Fred Watson: Yeah, they're close. I mean, only light

516
00:22:25.490 --> 00:22:26.930
can go at the speed of light. So you're

517
00:22:26.930 --> 00:22:28.290
talking about things going at nearly the

518
00:22:28.290 --> 00:22:31.289
speed of light. Uh, they're not colliding at

519
00:22:31.289 --> 00:22:32.810
nearly twice the speed of light. They're

520
00:22:32.810 --> 00:22:35.050
colliding at even more nearly the speed of

521
00:22:35.050 --> 00:22:37.570
light than they were to start with. But it

522
00:22:37.570 --> 00:22:39.090
never exceeds the speed of light.

523
00:22:39.570 --> 00:22:42.530
Andrew Dunkley: I get it. There you go, Andy. Uh, solved.

524
00:22:45.180 --> 00:22:47.820
Professor Fred Watson: The crew of Artemis 2 now bound for the moon.

525
00:22:48.060 --> 00:22:50.620
Humanity's next great voyage begins.

526
00:22:51.260 --> 00:22:52.380
Andrew Dunkley: Space Nuts.

527
00:22:52.540 --> 00:22:55.150
Andrew Dunkley: And our final question today comes, uh,

528
00:22:55.500 --> 00:22:58.030
from. Mark. Hi, Fred Watson, Andrew, uh,

529
00:22:58.420 --> 00:23:01.420
and team. It's, uh, Mark again from Sunny,

530
00:23:01.660 --> 00:23:02.700
is it Cece.

531
00:23:04.060 --> 00:23:06.460
Professor Fred Watson: Yes, it's where Patrick Moore used to live.

532
00:23:07.580 --> 00:23:08.620
He used to visit him.

533
00:23:08.620 --> 00:23:11.580
Andrew Dunkley: I really have to use a bigger font size with

534
00:23:11.580 --> 00:23:14.300
these questions. Sunny, uh, Selsey on the

535
00:23:14.300 --> 00:23:17.250
south coast of England. Um, in more

536
00:23:17.250 --> 00:23:19.490
than one of your podcasts, you mentioned the

537
00:23:19.490 --> 00:23:22.170
growing problem of excess satellites in space

538
00:23:22.170 --> 00:23:24.210
and what to do with them. That got me

539
00:23:24.210 --> 00:23:26.770
thinking. Would it be possible to use the

540
00:23:26.770 --> 00:23:29.170
action reaction principle to place a new

541
00:23:29.170 --> 00:23:31.849
satellite in the same place as an old

542
00:23:31.849 --> 00:23:34.730
one and move the old one into a higher

543
00:23:34.730 --> 00:23:37.610
graveyard orbit? Uh, Then at a later date,

544
00:23:37.610 --> 00:23:40.130
collect them to be dismantled safely. The way

545
00:23:40.130 --> 00:23:42.250
I look at it, if they want to put more

546
00:23:42.250 --> 00:23:44.330
satellites into space, they should also pay

547
00:23:44.330 --> 00:23:47.230
to clean the space up. Uh, I know this

548
00:23:47.230 --> 00:23:50.030
sounds, uh, a, uh, bit space

549
00:23:50.190 --> 00:23:53.110
snook, a bit like space space snooker. Yes,

550
00:23:53.110 --> 00:23:55.870
it does. Uh, but would it be possible. By the

551
00:23:55.870 --> 00:23:58.830
way, I broke the TV in the Globe Pub as a

552
00:23:58.830 --> 00:24:01.230
young man playing snooker, so probably not a

553
00:24:01.230 --> 00:24:03.110
good idea to ask me to work out the

554
00:24:03.110 --> 00:24:05.590
trajectories for all of this. Keep, uh, up

555
00:24:05.590 --> 00:24:07.150
the great work. It means a lot to everyone

556
00:24:07.150 --> 00:24:09.470
listening. And those, uh, that don't, well,

557
00:24:09.710 --> 00:24:11.390
you just gotta pity them,

558
00:24:12.830 --> 00:24:14.670
says Mark. Thanks, Mark, for the question.

559
00:24:15.410 --> 00:24:17.850
Uh, I'd love to, I'd love to have been the

560
00:24:17.850 --> 00:24:18.850
night he broke the tv.

561
00:24:18.850 --> 00:24:20.410
Professor Fred Watson: That would have been spectacular.

562
00:24:20.410 --> 00:24:20.970
Generic: Yeah.

563
00:24:20.970 --> 00:24:21.450
Andy: Gosh.

564
00:24:22.650 --> 00:24:24.930
Andrew Dunkley: Now what I want to know is, was that he's

565
00:24:24.930 --> 00:24:27.810
backswing, getting ready for the, the,

566
00:24:27.810 --> 00:24:29.970
the move of the queue that hit the screen, or

567
00:24:29.970 --> 00:24:31.450
did he actually fire a ball,

568
00:24:32.790 --> 00:24:35.090
uh, across the, across the room and hit the

569
00:24:35.090 --> 00:24:38.090
tv? Uh, you're gonna have to clarify that

570
00:24:38.090 --> 00:24:40.810
one, Mark. Um, look,

571
00:24:41.110 --> 00:24:42.960
uh, in, in regard to, um,

572
00:24:43.950 --> 00:24:45.910
cleaning up your own mess, there's actually

573
00:24:45.910 --> 00:24:48.670
a. Isn't there an international law

574
00:24:48.750 --> 00:24:51.070
that requires you to deal with your own

575
00:24:51.390 --> 00:24:52.430
stuff up there?

576
00:24:52.590 --> 00:24:55.270
Professor Fred Watson: Yes, there is now. Um, I think it was added

577
00:24:55.270 --> 00:24:57.550
to the, uh, the

578
00:24:57.710 --> 00:24:59.230
approvals given by the International

579
00:24:59.390 --> 00:25:01.310
Telecommunications Union, which is a

580
00:25:01.310 --> 00:25:04.000
governing body of all this stuff, um,

581
00:25:04.110 --> 00:25:06.590
that you. I think this came in

582
00:25:06.910 --> 00:25:09.590
probably five, 10 years ago. You have to

583
00:25:09.590 --> 00:25:12.350
demonstrate, uh, before they'll give you

584
00:25:12.810 --> 00:25:15.170
permission to launch, that you've got a way

585
00:25:15.170 --> 00:25:17.930
of removing your spacecraft from

586
00:25:17.930 --> 00:25:20.850
orbit. Um, in other words,

587
00:25:20.850 --> 00:25:22.250
you've got to be able to clean up your own

588
00:25:22.250 --> 00:25:24.810
junk. Uh, now that's

589
00:25:25.210 --> 00:25:27.330
fine for new stuff, but there's a lot of

590
00:25:27.330 --> 00:25:30.050
stuff up there that didn't

591
00:25:30.050 --> 00:25:32.770
qualify for that. And no thought was given to

592
00:25:32.770 --> 00:25:35.250
the idea of trashing space that you, you

593
00:25:35.250 --> 00:25:38.030
know, your spacecraft would

594
00:25:38.420 --> 00:25:41.300
just continue in orbit, um, after

595
00:25:41.300 --> 00:25:44.020
its useful life was over. And

596
00:25:44.020 --> 00:25:46.420
indeed for many of them, for objects,

597
00:25:47.310 --> 00:25:50.180
uh, especially ones with solar panels which

598
00:25:50.180 --> 00:25:52.820
are big and act as a drag on the residual

599
00:25:52.820 --> 00:25:55.340
atmosphere up there. Uh, even if you're up

600
00:25:55.340 --> 00:25:57.740
at, uh, uh, four or five hundred

601
00:25:57.740 --> 00:26:00.700
kilometres, there's enough atmosphere that

602
00:26:00.700 --> 00:26:03.140
if you do nothing, your spacecraft will,

603
00:26:03.670 --> 00:26:06.180
uh, the orbit will decay. It will

604
00:26:06.500 --> 00:26:08.980
hit the atmosphere and slow down and that

605
00:26:08.980 --> 00:26:11.760
brings it down lower and then it slows down

606
00:26:11.760 --> 00:26:14.640
more. And that is how

607
00:26:15.600 --> 00:26:18.320
space is kind of almost automatically cleaned

608
00:26:18.320 --> 00:26:18.560
up.

609
00:26:19.440 --> 00:26:21.040
Andrew Dunkley: And that's what's happening to the Swift.

610
00:26:21.630 --> 00:26:23.520
Professor Fred Watson: Uh, yes, that we talked about a couple of

611
00:26:23.520 --> 00:26:25.520
episodes ago. Exactly right. That's right.

612
00:26:25.839 --> 00:26:28.400
And that one's worth saving, which is why a

613
00:26:28.400 --> 00:26:30.280
mission's been mounted to do that, to boost

614
00:26:30.280 --> 00:26:32.360
it into a higher orbit. So in a way, what

615
00:26:32.360 --> 00:26:34.240
that's doing is actually what Mark is

616
00:26:34.240 --> 00:26:37.110
suggesting. You, uh, can go, uh,

617
00:26:37.140 --> 00:26:38.940
attach another rocket to it and push it up to

618
00:26:38.940 --> 00:26:41.590
a higher orbit to safeguard it. Um,

619
00:26:42.970 --> 00:26:45.820
um, so for low Earth

620
00:26:45.820 --> 00:26:48.466
orbit, There's below about 5,

621
00:26:48.574 --> 00:26:50.460
600 kilometres. There is this natural

622
00:26:50.460 --> 00:26:53.260
sweeping up as things decay

623
00:26:53.260 --> 00:26:55.780
unless you do something about it. Many

624
00:26:55.780 --> 00:26:58.340
spacecraft have got thrusters that lets you

625
00:26:58.340 --> 00:27:01.220
lift its orbit. Um, but if you switch the

626
00:27:01.220 --> 00:27:03.180
thrusters off, that means they're going to

627
00:27:03.180 --> 00:27:04.940
come back to Earth anyway. And that might be

628
00:27:04.940 --> 00:27:06.740
enough to satisfy the international

629
00:27:06.900 --> 00:27:09.760
Telecommunications Unit, uh, going higher

630
00:27:09.760 --> 00:27:10.320
up, though.

631
00:27:10.480 --> 00:27:11.120
Andrew Dunkley: Except.

632
00:27:11.440 --> 00:27:13.960
Andrew Dunkley: Yes, one more point. Uh, when these things

633
00:27:13.960 --> 00:27:15.880
are burning up, they're putting all those

634
00:27:15.880 --> 00:27:17.360
metals into our atmosphere.

635
00:27:17.440 --> 00:27:19.160
Professor Fred Watson: Yeah, you're still getting contamination.

636
00:27:19.160 --> 00:27:21.080
That's right. We're getting aluminium oxide

637
00:27:21.080 --> 00:27:23.000
and all sorts of stuff up there that

638
00:27:23.000 --> 00:27:25.760
shouldn't be there. Uh, but,

639
00:27:25.800 --> 00:27:27.840
um, yes, for higher orbits,

640
00:27:30.400 --> 00:27:32.440
these are the ones, what you might call mid

641
00:27:32.440 --> 00:27:34.800
earth orbits above 1,000 kilometres,

642
00:27:35.400 --> 00:27:38.320
uh, they're not gonna decay so readily. And

643
00:27:38.320 --> 00:27:40.620
so they are an. And then,

644
00:27:41.440 --> 00:27:44.380
uh, the, um, geostationary

645
00:27:45.020 --> 00:27:47.460
satellites. So the geostationary orbits are

646
00:27:47.460 --> 00:27:50.060
very, very specific. Um, in fact,

647
00:27:50.220 --> 00:27:52.180
all the satellites are in the same orbit,

648
00:27:52.180 --> 00:27:54.780
more or less, um, because it's the one that

649
00:27:55.020 --> 00:27:57.660
keeps them over the equator and keeps them

650
00:27:57.660 --> 00:28:00.140
going, uh, round once in a day.

651
00:28:00.620 --> 00:28:03.060
Um, those geostationary orbits, they're at

652
00:28:03.060 --> 00:28:05.980
36,000 kilometres. They have to have

653
00:28:05.980 --> 00:28:08.900
mechanisms to push them into what's called

654
00:28:08.900 --> 00:28:11.820
exactly as, uh, Malik mentions, a grave

655
00:28:12.200 --> 00:28:15.080
orbit, which just gets them out of the way so

656
00:28:15.080 --> 00:28:16.960
that when they become defunct and you can't

657
00:28:16.960 --> 00:28:18.280
control them anymore, they're not going to

658
00:28:18.280 --> 00:28:20.880
bang into one of the active geostationary

659
00:28:20.880 --> 00:28:23.760
satellites. So it is a game of snooker up

660
00:28:23.760 --> 00:28:26.440
there, um, in a perhaps more gentle way than

661
00:28:26.600 --> 00:28:29.200
knocking one satellite into another, um, and

662
00:28:29.200 --> 00:28:31.960
replacing its position in space.

663
00:28:32.360 --> 00:28:34.040
All you do, if you do that is

664
00:28:35.080 --> 00:28:37.040
you've got another one that's going to decay

665
00:28:37.040 --> 00:28:38.790
at the same rate. If it's in low Earth orbit,

666
00:28:38.940 --> 00:28:39.180
it.

667
00:28:39.500 --> 00:28:41.420
Andrew Dunkley: Yeah, they reckon there's somewhere between

668
00:28:41.500 --> 00:28:44.220
three and four and a half thousand inactive

669
00:28:44.380 --> 00:28:46.700
or defunct satellites in orbit at the moment.

670
00:28:47.100 --> 00:28:49.900
Professor Fred Watson: That's correct, yes. Um, but

671
00:28:49.900 --> 00:28:52.900
then on top of that there's a, uh, host

672
00:28:52.900 --> 00:28:55.740
of, uh, upper stages, launch,

673
00:28:55.740 --> 00:28:58.380
you know, the launch vehicles. Lots of bits

674
00:28:58.380 --> 00:29:00.660
and pieces, bits of fairing, bits of junk,

675
00:29:00.660 --> 00:29:03.180
debris from previous collisions. It's a

676
00:29:03.340 --> 00:29:05.900
fleck of paint, flecks of Paint. That's

677
00:29:05.900 --> 00:29:06.860
right. There's even a glove.

678
00:29:08.320 --> 00:29:10.800
Andrew Dunkley: And a spanner with a spanner too. Yeah,

679
00:29:10.880 --> 00:29:13.360
there's all sorts of stuff floating around.

680
00:29:13.920 --> 00:29:15.800
Professor Fred Watson: It's all going at 8 kilometres per second.

681
00:29:15.800 --> 00:29:17.040
That's the dangerous bit.

682
00:29:17.760 --> 00:29:20.640
Andrew Dunkley: So I think that, uh, was another part to his

683
00:29:20.640 --> 00:29:23.640
question. Could you replace a satellite in

684
00:29:23.640 --> 00:29:26.320
its exact position, move the

685
00:29:26.320 --> 00:29:28.680
defunct one out and put a new one in the

686
00:29:28.680 --> 00:29:31.600
exact spot that its predecessor was?

687
00:29:31.600 --> 00:29:33.760
Professor Fred Watson: Well, you could, and, uh, indeed that's done.

688
00:29:33.760 --> 00:29:36.010
You don't move the other one out. You. Once

689
00:29:36.010 --> 00:29:38.130
its orbit's decayed, you, uh, just let it

690
00:29:38.130 --> 00:29:41.090
drop. Yeah, you've got that orbit, uh, freed

691
00:29:41.090 --> 00:29:43.610
up and you put another

692
00:29:43.610 --> 00:29:44.930
spacecraft there. That's what's happening

693
00:29:44.930 --> 00:29:46.810
with Starlink. Actually, it's exactly what's

694
00:29:46.810 --> 00:29:49.210
happening. The Starlink satellites are all at

695
00:29:49.210 --> 00:29:51.730
round about 500 kilometres. They were

696
00:29:51.730 --> 00:29:54.250
planning another shell at, uh, 1200

697
00:29:54.250 --> 00:29:57.250
kilometres. But, uh, for once, um, SpaceX

698
00:29:57.250 --> 00:29:59.410
listened to the astronomy lobby. Because

699
00:29:59.410 --> 00:30:01.830
those outer ones can be visible all night in

700
00:30:01.980 --> 00:30:04.820
some parts of the world, um, even though

701
00:30:04.820 --> 00:30:06.380
they're fainter because they're higher up,

702
00:30:06.750 --> 00:30:08.860
uh, it means that they're visible for much

703
00:30:08.860 --> 00:30:10.380
longer during twilight.

704
00:30:10.860 --> 00:30:13.620
Andrew Dunkley: Yeah, and that's a real problem, isn't

705
00:30:13.620 --> 00:30:16.300
it? There you go, Mark. Uh, everything you

706
00:30:16.300 --> 00:30:19.020
said, um, is possible. And

707
00:30:19.410 --> 00:30:22.340
uh, yes, there is a law requiring people to

708
00:30:22.340 --> 00:30:24.140
clean up their messes, but at the moment,

709
00:30:24.540 --> 00:30:26.620
letting them burn up in the atmosphere is

710
00:30:26.860 --> 00:30:29.740
okay until we all die of some

711
00:30:29.740 --> 00:30:32.620
kind of metallic poisoning. Then, um, they'll

712
00:30:32.620 --> 00:30:33.960
go, ah, yeah, we should have done, done

713
00:30:33.960 --> 00:30:34.760
something about that.

714
00:30:35.080 --> 00:30:37.400
Professor Fred Watson: Unintended consequences. Yeah.

715
00:30:37.550 --> 00:30:38.920
Andrew Dunkley: Uh, lovely to hear from you, Mark.

716
00:30:38.990 --> 00:30:41.960
Um, uh, we've been talking a lot

717
00:30:41.960 --> 00:30:44.800
about particle science today, and, uh, Andrea

718
00:30:44.800 --> 00:30:47.240
in Western Australia sent, uh, something in

719
00:30:47.640 --> 00:30:49.520
a while back and I've kind of been sitting on

720
00:30:49.520 --> 00:30:51.440
it, trying to find the appropriate moment.

721
00:30:51.440 --> 00:30:53.840
And because of the, the fact that three of

722
00:30:53.840 --> 00:30:56.200
our four questions were focused on, on

723
00:30:56.200 --> 00:30:59.040
particles, I thought it was appropriate

724
00:30:59.040 --> 00:31:00.990
to play, um, uh,

725
00:31:01.450 --> 00:31:03.530
Andrea's little voice piece today.

726
00:31:05.930 --> 00:31:08.410
Andrea: Hey, you two. The joke for the day.

727
00:31:09.690 --> 00:31:12.090
Two neutrinos walked through a bar.

728
00:31:14.890 --> 00:31:15.690
Andrew Dunkley: Thanks folks.

729
00:31:15.770 --> 00:31:17.570
Andrea: Really enjoy your show and I hope you guys

730
00:31:17.570 --> 00:31:18.490
found that really fun.

731
00:31:18.490 --> 00:31:19.050
Professor Fred Watson: We did.

732
00:31:21.110 --> 00:31:22.330
Andrew Dunkley: Uh, that's a good one.

733
00:31:22.490 --> 00:31:24.370
Professor Fred Watson: That is excellent. Yeah, perfect.

734
00:31:24.370 --> 00:31:27.170
Andrew Dunkley: Perfect timing. Well, actually, I've been

735
00:31:27.170 --> 00:31:30.030
sitting on it for months, but it,

736
00:31:30.030 --> 00:31:32.390
um, seemed appropriate. Appropriate today.

737
00:31:32.630 --> 00:31:33.830
Professor Fred Watson: Yes, that's the, um, one.

738
00:31:34.390 --> 00:31:36.830
Andrew Dunkley: Now a reminder, if you have questions for us,

739
00:31:36.830 --> 00:31:39.270
we would love to get them. Uh, you need to go

740
00:31:39.270 --> 00:31:41.310
to our website to send them in, uh, which is

741
00:31:41.310 --> 00:31:44.310
easy, spacenutspodcast.com or spacenuts

742
00:31:44.310 --> 00:31:46.630
IO. Click on the Ask me anything button at

743
00:31:46.630 --> 00:31:48.310
the top, it's labelled ama.

744
00:31:49.350 --> 00:31:51.910
And that's also the logo for the Australian

745
00:31:51.910 --> 00:31:53.830
Medical Association. But don't get confused.

746
00:31:54.460 --> 00:31:56.030
Uh, they might answer it too, though. You

747
00:31:56.030 --> 00:31:58.190
never know. Uh, but send your questions into

748
00:31:58.190 --> 00:32:01.060
us because, um, there's so much stuff that

749
00:32:01.060 --> 00:32:02.780
people want to know and if you want to know

750
00:32:02.780 --> 00:32:05.740
something, the best way to find out is to ask

751
00:32:05.740 --> 00:32:07.580
us and then we'll refer it to somebody else.

752
00:32:07.740 --> 00:32:10.740
But, uh, it is, um, uh, text and audio.

753
00:32:10.740 --> 00:32:13.220
Don't forget to tell us who you are and where

754
00:32:13.220 --> 00:32:15.260
you're from. Thank you so much, Fred Watson.

755
00:32:15.260 --> 00:32:16.220
It's been a pleasure.

756
00:32:16.619 --> 00:32:18.460
Professor Fred Watson: Always a pleasure, Andrew. Great to talk.

757
00:32:19.100 --> 00:32:20.980
Andrew Dunkley: Catch you soon. Professor Fred Watson Watson,

758
00:32:20.980 --> 00:32:23.220
astronomer at large. And, uh, thanks to Huw

759
00:32:23.220 --> 00:32:25.340
in the studio, who puts everything together

760
00:32:25.340 --> 00:32:27.940
with Blu Tack. Couldn't be with us today

761
00:32:27.940 --> 00:32:30.870
though, because he drives a proton and it

762
00:32:30.870 --> 00:32:33.750
does not do the speed of light. And so he was

763
00:32:33.750 --> 00:32:35.990
late. And from me, Andrew Dunkley. Thanks for

764
00:32:35.990 --> 00:32:37.590
your company. We'll catch you on the next

765
00:32:37.590 --> 00:32:38.950
episode of Space Nuts.

766
00:32:38.950 --> 00:32:39.590
Professor Fred Watson: Bye. Bye.

767
00:32:40.710 --> 00:32:42.910
Andrew Dunkley: You've been listening to the Space Nuts

768
00:32:42.910 --> 00:32:45.910
podcast, available at

769
00:32:45.910 --> 00:32:47.910
Apple Podcasts, Spotify,

770
00:32:48.070 --> 00:32:50.830
iHeartRadio or your favourite podcast

771
00:32:50.830 --> 00:32:52.550
player. You can also stream on

772
00:32:52.550 --> 00:32:54.230
demand@bytes.com.

773
00:32:54.550 --> 00:32:56.630
Andrew Dunkley: this has been another quality podcast

774
00:32:56.630 --> 00:32:58.710
production from bytes.com.