The Cosmic Q&A: Redshift, Dark Matter & the Shape of the Universe

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Andrew Dunkley: Hello again. Thanks for joining us on Space

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Nuts. This is a Q and A edition. My name is

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Andrew Dunkley. What's a Q and A edition?

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It's an edition where we get Q's and

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give you A's because you're so clever.

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Uh, something like that. Anyway, we're going

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to answer audience questions. That's what I'm

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getting at. We've got questions about

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redshift, We've got questions about dark

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photons.

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Professor Fred Watson: What?

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Andrew Dunkley: Uh, we've got questions about deep space

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astronomy and another one about the expansion

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of the universe. I think we talked about that

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last episode. Anyway, uh, we'll see if we can

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solve all of that on this episode of space

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nuts. 15 seconds.

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Professor Fred Watson: Guidance is internal. 10,

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9, ignition sequence. Star

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space nuts.

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Andrew Dunkley: 5, 4, 3, 2.

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Roger: 1.

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Professor Fred Watson: 2, 3, 4, 5, 5, 4, 3, 2,

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1. Space nuts.

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Andrew Dunkley: Astronauts report it feels good.

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And with us again to kind of

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try to maybe answer some of that is

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Professor Fred Watson Watson, astronomer at

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large. Hello, Fred Watson.

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Professor Fred Watson: Hello, Andrew. Um, kind of is probably the

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best description really, isn't it?

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Andrew Dunkley: Possibly so. Possibly so. Um,

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but you know, it's good to get questions.

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We've got a whole new batch, so, um, let's

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get stuck straight into it.

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Now. First question comes from, um. Uh,

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I love the way he always ends his questions.

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I'm not going to reveal anything, but, um,

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let's hear from Roger.

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Roger: Hey there, Space Nuts. This is Roger

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the truck driver. Tonight I'm in,

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uh, Rutland, Vermont. Got a

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question about the red shift of galaxies.

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Um, if the light that we're seeing from a far

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off galaxy is shifted to the red and it

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started out at a higher frequency,

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doesn't that mean energy's lost somewhere

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between here and there? And is that energy

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just transferred into space? And if it

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is, does that contribute to the

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expansion of space? And I'm not saying it's

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dark energy, but does it

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contribute to it or does that

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energy get dissipated in another way?

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All right. Always digging the show, guys.

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Keep on trucking.

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Andrew Dunkley: I love that. I love that. Uh, we've got

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train drivers that do that. Unfortunately,

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they do it at 3 o' clock in the morning.

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Although today he did it at 10 to 7. I was

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pretty annoyed. Pretty annoyed.

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Professor Fred Watson: This is, uh, the one going past your place?

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Andrew Dunkley: Yeah, behind our place there's a rail line.

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It doesn't get used a heck of a lot, but when

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it does, um.

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Eli: Yes?

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Andrew Dunkley: The glasses rattle. Uh, the ones on my face,

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I mean. Uh, thanks, Roger. Great question.

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Uh, so, um, yeah, the change

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in frequency with the, um,

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energy loss, um, where does the energy go and

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does it contribute to the expansion of the

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universe? And could it possibly be.

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Maybe, maybe not dark matter

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or dark energy or something?

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Professor Fred Watson: Yeah, yeah. Um, there's a lot.

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Andrew Dunkley: He packed a lot into that question.

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Professor Fred Watson: He did. And it's a great question too. Uh,

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and, you know, I mean, it's a,

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uh, project, um, Absolutely right. The

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conservation of energy. Uh, energy

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can't be created or destroyed. That's the

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fundamental rule. Its

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energy is always conserved.

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But, uh, the universe doesn't play

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by the ordinary rules.

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Uh, and, um,

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it's an interesting answer here.

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Um, and I have to say it's changed

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my view of what this, you know, what

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the answer to this problem was because,

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um, when we've been asked this before,

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we haven't been asked it for a long time.

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I just assumed that the energy, uh,

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basically was absorbed by the universe by

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space time, uh, and

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maybe contributed to the expansion.

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Although,

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uh, you can't have it both ways because it's

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the expansion that's causing the photon's

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energy to be lost. Uh,

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and just stepping back, exactly as

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Roger said, uh, you've got light going

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through the universe. It's,

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uh, its wavelength is being stretched by

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the expansion of the universe. Therefore the

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light is losing energy. Because the energy

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of a beam of light is all about the

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frequency of the light, in other words, or

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the wavelength. Putting it another way. So

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if you increase the wavelength, you lose

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energy. And that's, um,

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a given already. Uh, so what I

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used to say was, yes, it kind of goes into

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the universe. But I've done a bit more

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reading on this and I was wrong.

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Um, because when

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you apply general relativity to

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the universe as a whole, and that's the.

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As we've talked about, and we've talked about

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it at length in the last episode, it's, uh,

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the kind of fundamental rule that governs

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everything that we understand in the

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universe. Um, when you

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apply general relativity,

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Andrew Dunkley: uh,

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Professor Fred Watson: that conservation of energy

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that we expect to happen in the

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everyday world, it

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doesn't hold good. So energy, uh,

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is not conserved in an expanding

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universe. Uh, and so

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basically the energy

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simply disappears. It's

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just not there anymore because of the

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expansion of the universe. It's not causing

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the expansion of the universe. It's not

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create contributing to dark energy or dark

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matter, the energy loss, it just vanishes.

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Wow. So work that one out.

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Andrew Dunkley: I can't.

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Professor Fred Watson: No, I can't either.

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Um, I kind of really

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need to look at the equations on this.

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Andrew Dunkley: Um, don't show them to me. I mean,

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Professor Fred Watson: yeah, I'M not that keen on looking at them

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myself either. Too much else to do. But, uh,

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um, uh, but yes, that is

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the thinking on this.

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Uh, and I think the conservation

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rule does not work, uh,

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um, when it comes to

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the universe on a whole.

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Andrew Dunkley: Yeah.

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Professor Fred Watson: Wow.

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Andrew Dunkley: Gee, um, that's quite a

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revelation. Who figured that out?

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Professor Fred Watson: Uh, uh, it's on a number of

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different, uh, physics, uh, related websites.

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Andrew Dunkley: There's the reason no one knows about it

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because it's physics and

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who reads that stuff?

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Professor Fred Watson: Yeah, I think the relativistic bit of

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it, uh, comes from the fact

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that the energy of a particle,

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which is what we're talking about, it's an

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observer dependent quantity.

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And so that's why relativity plays a part in

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this because you're the observer

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and you're talking about something that's

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relative to another observer, that is the

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photon. Uh, and that's why you've got,

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uh, a relativistic

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access. Ah, to it.

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Andrew Dunkley: Wow. Okay. Um, great question,

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Roger. I'm not sure you were expecting that

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answer, but, uh, there it is. Uh, the energy

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just gone,

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goes, vanishes, ceases to

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exist. It's a dead poly.

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So anyway, um,

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no one got that joke. I was, um,

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doing a Monty Python skit for some reason.

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Professor Fred Watson: Yeah, you were. That's right.

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Look, I'm pursuing this in a little bit more

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detail and, uh, just trying to, you know, see

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whether we've got alternative. Alternative

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views of this.

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Andrew Dunkley: Well, generally speaking, you do get

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alternative views when it comes to this kind

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of stuff.

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Professor Fred Watson: That's right. Um, yes,

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so

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that's right. Uh, uh,

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I think the standard explanation today is

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that energy is not conserved.

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Okay.

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Andrew Dunkley: We'll leave it at that until somebody throws

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another spanner into the.

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Professor Fred Watson: Yeah, uh, we might be giving a different

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answer next week. It could be.

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Andrew Dunkley: Thanks, Roger. Great to hear from you. Toot,

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toot. Uh, we'll catch you next time.

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Our next question comes from

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Peter. He's from San Diego, California.

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While listening to another astrophysics

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podcast, I heard the term dark

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photon for the first time. Apparently this is

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a particle astrophysicists are, uh, seeking

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in order to explain dark matter and, or dark

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energy. Could you please elaborate on what a

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dark photon could be?

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Um, dad, joke for Andrew. A photon

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travels at the speed of light. Does that mean

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a dark photon travels at the speed of

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dark. I like that.

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That's good. Yeah, that's really good. Uh,

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keep up the great work, he says. Uh, thank

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you, Peter.

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Professor Fred Watson: All as well.

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Andrew Dunkley: In San Diego, California.

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Uh, have you ever heard of a dark photon,

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Fred Watson?

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Professor Fred Watson: Um, yes, I'VE probably got a few in this box

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here. The

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speed of dark. Just, just going back to that,

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that quip, uh, there was

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a storey I read, uh, probably

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a fortnight ago, uh, about

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exactly this. In that dark

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ness can move faster than the speed

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of light.

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Andrew Dunkley: No,

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Professor Fred Watson: but it's ah, an illusory darkness. It's when

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you've got um, light beams

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interfering with one another so that

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you've uh, interference

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light beams can cancel out. So if you've got

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two light waves and you add them up out of

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phase, they can cancel out and you get

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darkness. That's a well known principle

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of interferometry. I used to play with that

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when I was a student a lot. Uh,

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but there are certain circumstances that

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those patterns of darkness can actually

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exceed the speed of light

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because they're not actually real, they're

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not real entities. They're not a thing that's

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carrying any sort of information or energy.

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They're just patterns in an

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interference pattern. They're just dark

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patches in it. And I think under certain

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circumstances they could go faster than the

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speed of light. Darkness might

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be not quite as uh, you know, as twee as

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you thought it was. I guess so

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anyway, anyway, uh, that's not the

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question, uh, because dark photons are

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definitely something different and they're

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basically uh, hypothetical.

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They've been hypothesised by

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physicists and cosmologists as uh,

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being a uh, force carrier

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similar to the ordinary photon

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but related to dark

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matter. In other

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words, you might have. Sorry, somebody's

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trying to phone me. I'm just gonna kill that

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call. Yeah, um,

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that was me.

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Andrew Dunkley: That was me. No it wasn't.

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Professor Fred Watson: You know, they're part of the. There may be.

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When we discover finally what dark matter is,

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there may be a suite of

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dark particles which could include

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dark photons. That's the bottom line.

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Andrew Dunkley: Right?

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Professor Fred Watson: Um, and so you know we mentioned last

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week the, or in the last episode the uh, the

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Large Hadron Collider being upgraded to the

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High Luminosity Large Hadron Collider. Um,

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that's one of the things they'd be looking

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for, will be dark photons.

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Okay.

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Andrew Dunkley: You know, I tried to do

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um, an AI search for an

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explanation on it and um,

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it sort of gave me all this gobbledygook. But

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um, you know, what would a dark

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proton, a photon do? It says it would

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carry a force within the dark sector.

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We call that the government. It might allow

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dark matter particles to interact with each

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other and it could very weakly mix with

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normal photons, giving us a way to Detect it.

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And the reason they reckon that scientists

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care about this, as you said, could explain

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what dark matter is made of. So

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therefore solving some of those gaps in our

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current physics theories.

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That's why people are interested in this and

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that's why they're upgrading the Large Hadron

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Collider. And hopefully we will

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learn more in years to come.

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That's the hope.

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Professor Fred Watson: That's the hope, yeah. So we might be talking

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one day about dark photons, um, having been

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detected, which would be a coup

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for space newts.

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Andrew Dunkley: Yes, it will. Uh, but at this stage they

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are not proven. It's just a theory. So

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that's about as much as we know at this point

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in time. But, uh, very good question. Uh,

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and, uh, thank you, Peter, for sending it in.

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This is Space Nuts with Andrew Dunkley and

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Professor Fred Watson Watson.

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0G and I feel fine. Space Nuts.

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Okay, Fred Watson, we'll move straight on to

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our next question, which is, uh, another

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audio question from Eli.

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Eli: Hello, this is Eli from

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sunny Coachella Valley in

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California. I'm embarrassed to

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admit it, but I still can't get my head

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around deep space astronomy. I get that

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the light from, say, a distant galaxy is a

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billion years old, but why

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that particular point in its time? Is

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it just a matter of whatever light is hitting

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us is the time we get to see.

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But for really early light,

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the JWST, early universe stuff

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that's been travelling for 13 billion years

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and just hitting us now,

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are we looking for the light that hasn't

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passed us by or hasn't made it here yet,

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but is from that one precise

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location long ago?

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This stuff is so difficult to get my head

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around. Love the show and hope

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you guys can clear this up for me.

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Andrew Dunkley: Uh, no, we can't. We just thought we'd, um,

342
00:14:38.590 --> 00:14:41.370
put the question in there. Thanks,

343
00:14:41.370 --> 00:14:44.210
Eli. Uh, this is a deep, um, I'm, um.

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Not only in deep space astronomy terms, but

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it is a deep, deep topic.

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Um, I mean, when we look up into the sky

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at night and we see all those beautiful

348
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coloured dots, we are looking at history.

349
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And it's variable history because some of

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it's 4.41 light years away and

351
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some of it's 400,000 light

352
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years away, some of it's further than that.

353
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Um, but then you've got the cosmic

354
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microwave background radiation, which is kind

355
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of a leftover of,

356
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um, what happened after the

357
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Big Bang and that,

358
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that's a different kettle of fish. And I can

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understand why you've got a headache. Eli,

360
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over to you, Fred Watson.

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Professor Fred Watson: Thanks. Um, so I

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guess uh, you know,

363
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I understand Eli's issue as well.

364
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Um,

365
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you've got to be in the right place at the

366
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right time to see a photon from a distant

367
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galaxy. But I guess the way

368
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to envisage this is if you think

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of the universe, um,

370
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and you've got to perhaps think of it as if

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you were looking at it from the outside,

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which we never can. But, uh, if you can think

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of it that way, then it's full of

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00:16:01.210 --> 00:16:03.370
objects which are radiating light.

375
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Even in its infancy, when the universe was

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very young, the stuff in it was basically

377
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shining. Um, once we got past the Dark Ages,

378
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where no stars were shining, uh,

379
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um, and those are the galaxies that we now

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see. So they constantly radiate, creating

381
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light. And that's just like a river of

382
00:16:23.470 --> 00:16:26.470
light that's flowing down time,

383
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if I can put it that way. Uh, and

384
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a long time in the future it

385
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reaches us. But it's not just

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an individual photon or something that's

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reaching us. It's this stream of stuff that

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is being radiated throughout the

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universe by these galaxies. So we,

390
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um. And we pick it up. We

391
00:16:49.760 --> 00:16:52.520
pick it up sometimes exactly as you've said.

392
00:16:52.520 --> 00:16:54.480
Well, up to 10 billion years after it's been

393
00:16:54.800 --> 00:16:57.760
radiated. I think 12 billion years,

394
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uh, are the oldest or the earliest galaxies

395
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that we now see. We're looking back in time

396
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12 billion years and seeing them as they were

397
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perhaps a billion and a half years after the

398
00:17:08.360 --> 00:17:11.160
Big Bang. Um, and they are shining,

399
00:17:11.160 --> 00:17:13.320
they're radiating light, uh, in the early

400
00:17:13.320 --> 00:17:16.230
universe and down the track that reaches us

401
00:17:16.390 --> 00:17:18.390
because that light's going in all directions.

402
00:17:18.390 --> 00:17:20.310
So it wouldn't matter where in the universe

403
00:17:20.310 --> 00:17:22.710
we were, we would still see them.

404
00:17:23.510 --> 00:17:25.670
Uh, we'd just see them in a, you know, in a

405
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different position in the sky. If we're a

406
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long way from where we are now. Yeah, but,

407
00:17:30.589 --> 00:17:33.350
yeah, so I guess it's, you

408
00:17:33.350 --> 00:17:35.950
know, in a way, one way of thinking about

409
00:17:35.950 --> 00:17:38.910
this is if you imagine us on planet

410
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Earth here and imagine us being

411
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surrounded by a whole series of

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shells which, uh, we're at the centre

413
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of. And this is a bit like the crystalline

414
00:17:49.340 --> 00:17:51.820
spheres that people used to think, uh, the

415
00:17:51.820 --> 00:17:54.100
universe was made of. Uh, but

416
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these shells, uh, spherical shells,

417
00:17:57.340 --> 00:17:59.700
all centred on the Earth, but each one

418
00:18:00.020 --> 00:18:02.740
clicks over to a time

419
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further in the past, uh, because the

420
00:18:05.660 --> 00:18:08.660
light's coming to us from the whole cosmos,

421
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which is full of stuff. Uh, and that's why

422
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we, these shells sort of being

423
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illuminated in a way by the objects that, uh,

424
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radiated them at that time. Uh,

425
00:18:20.100 --> 00:18:22.880
um, that we see them because of

426
00:18:23.120 --> 00:18:25.520
the distance that they are away from us means

427
00:18:25.520 --> 00:18:28.520
that the light has taken that long to get to

428
00:18:28.520 --> 00:18:31.040
us, whether that helps or not. In fact, I

429
00:18:31.040 --> 00:18:33.040
think I've just confused it completely. But,

430
00:18:35.080 --> 00:18:36.560
Andrew Dunkley: um, I

431
00:18:38.570 --> 00:18:41.330
just doing a little experimental search here

432
00:18:41.330 --> 00:18:41.930
for a sec.

433
00:18:44.090 --> 00:18:46.970
What I agree

434
00:18:46.970 --> 00:18:49.690
with in terms of Eli's question and getting

435
00:18:49.690 --> 00:18:52.650
your head around it is, um, if

436
00:18:52.650 --> 00:18:54.730
Betelgeuse, or however you want to pronounce

437
00:18:54.730 --> 00:18:57.570
it, went supernova right now as we

438
00:18:57.570 --> 00:18:58.170
were speaking,

439
00:19:00.410 --> 00:19:02.010
we wouldn't see it for

440
00:19:03.700 --> 00:19:05.140
640 years.

441
00:19:05.780 --> 00:19:06.340
Roger: Yeah.

442
00:19:07.220 --> 00:19:09.700
Andrew Dunkley: So for it to have gone

443
00:19:09.700 --> 00:19:12.700
supernova in the past and us to witness

444
00:19:12.700 --> 00:19:14.420
it, it has to have happened

445
00:19:15.940 --> 00:19:18.660
pretty close to 640 years ago.

446
00:19:19.220 --> 00:19:20.260
Does that make sense?

447
00:19:20.420 --> 00:19:23.260
Professor Fred Watson: Yes. Um, so you could think of that in

448
00:19:23.260 --> 00:19:25.460
another way. Um, you know,

449
00:19:26.300 --> 00:19:29.060
um, anywhere between us and 640

450
00:19:29.060 --> 00:19:31.620
light years away, there could be this pulse

451
00:19:31.620 --> 00:19:33.540
of light that's on its way to us

452
00:19:34.260 --> 00:19:37.220
from Betelgeuse. Uh, it would spread

453
00:19:37.220 --> 00:19:39.940
out in a sphere, and as that sphere

454
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expanded, eventually it would wash over the

455
00:19:42.140 --> 00:19:44.980
Earth and we'd see it, um, and perhaps

456
00:19:44.980 --> 00:19:46.740
see it during the day as well, because it

457
00:19:46.740 --> 00:19:49.700
might get bright enough to do that. Uh, and

458
00:19:49.700 --> 00:19:51.220
I think that's a really good way of putting

459
00:19:51.220 --> 00:19:53.820
it, Andrew, because thinking, um, about the

460
00:19:53.820 --> 00:19:55.500
galaxies, they're just streaming light out

461
00:19:55.500 --> 00:19:58.300
all the time, but something like a, uh,

462
00:19:58.380 --> 00:20:01.140
supernova explosion, which gives a big pulse

463
00:20:01.140 --> 00:20:04.140
of light, um, that's perhaps easier to get

464
00:20:04.140 --> 00:20:06.180
your head around because that's. That's just

465
00:20:06.180 --> 00:20:08.940
gotta, um. It'll

466
00:20:08.940 --> 00:20:11.500
take whatever time is

467
00:20:11.500 --> 00:20:14.420
represented by the distance away. So 640

468
00:20:14.420 --> 00:20:17.260
light years away. It'll take 640 years

469
00:20:17.260 --> 00:20:19.340
to get here for that pulse to get here. But

470
00:20:19.340 --> 00:20:22.260
then it will sweep over us and we'll see the

471
00:20:22.260 --> 00:20:24.220
light. The light fading away.

472
00:20:24.460 --> 00:20:25.770
Andrew Dunkley: Yeah. And, um,

473
00:20:27.340 --> 00:20:29.500
the reason I chose that target is because

474
00:20:29.740 --> 00:20:32.500
there's a lot of conjecture about

475
00:20:32.500 --> 00:20:35.220
its future and the possibility that it's

476
00:20:35.220 --> 00:20:36.940
reaching that critical mass point.

477
00:20:37.480 --> 00:20:37.800
Professor Fred Watson: Yes.

478
00:20:38.190 --> 00:20:39.720
Andrew Dunkley: Um, but it could have already happened.

479
00:20:39.720 --> 00:20:41.240
That's the other thing.

480
00:20:42.040 --> 00:20:45.040
Professor Fred Watson: But that's something we can have no knowledge

481
00:20:45.040 --> 00:20:47.400
of. That's the key thing, because, um,

482
00:20:47.880 --> 00:20:50.360
we are limited by the speed of light. That's

483
00:20:50.440 --> 00:20:52.320
the thing that always limits our view of the

484
00:20:52.320 --> 00:20:52.760
universe.

485
00:20:52.760 --> 00:20:55.640
Andrew Dunkley: And just to confuse Eli a little bit more,

486
00:20:56.440 --> 00:20:59.040
there are, ah, probably things in the

487
00:20:59.040 --> 00:21:01.040
universe we will never witness because the

488
00:21:01.040 --> 00:21:04.000
light is just too far away to reach us in any

489
00:21:04.000 --> 00:21:05.960
reasonable amount of time. Even

490
00:21:06.910 --> 00:21:09.830
beyond the life of the Earth itself or

491
00:21:09.830 --> 00:21:12.180
our sun. Uh,

492
00:21:13.230 --> 00:21:15.750
there are things we will never, ever know

493
00:21:15.750 --> 00:21:16.030
about.

494
00:21:16.670 --> 00:21:17.310
Professor Fred Watson: Correct.

495
00:21:18.200 --> 00:21:21.040
Andrew Dunkley: Um, and that's where it just gives you, um,

496
00:21:22.430 --> 00:21:24.830
one of those Headaches that requires, uh, you

497
00:21:24.830 --> 00:21:27.630
to take paracetamol and ibuprofen at the same

498
00:21:27.630 --> 00:21:27.950
time.

499
00:21:32.100 --> 00:21:34.720
Um, deep, deep headaches. But Eli, great

500
00:21:34.720 --> 00:21:36.440
question. I'm not sure we solved your

501
00:21:36.440 --> 00:21:39.420
problem, but, um, anyway, uh,

502
00:21:40.800 --> 00:21:42.600
I try to explain this sort of stuff to my

503
00:21:42.600 --> 00:21:45.520
grandson, uh, and, uh, my granddaughters.

504
00:21:45.520 --> 00:21:48.280
And, you know, how do you

505
00:21:48.280 --> 00:21:50.160
explain time and distance

506
00:21:51.040 --> 00:21:53.970
to a young child? And, um,

507
00:21:53.970 --> 00:21:55.360
when you're trying to get through traffic,

508
00:21:57.200 --> 00:21:58.840
Professor Fred Watson: that might not be the best time to do it.

509
00:21:58.840 --> 00:22:00.720
Andrew Dunkley: Probably not, but they're very interested.

510
00:22:01.280 --> 00:22:03.240
Very interested. Thanks, Eli.

511
00:22:03.240 --> 00:22:03.840
Great question.

512
00:22:06.540 --> 00:22:09.180
Professor Fred Watson: The crew of Artemis 2 now bound for the moon,

513
00:22:09.420 --> 00:22:11.980
humanity's next great voyage begins.

514
00:22:12.620 --> 00:22:13.820
Space nuts.

515
00:22:14.140 --> 00:22:16.190
Andrew Dunkley: Our final question comes, uh,

516
00:22:16.780 --> 00:22:19.740
from Nova Scotia. It's from Ken.

517
00:22:19.910 --> 00:22:21.940
Uh, look, this is an old chestnut. We've,

518
00:22:21.940 --> 00:22:24.660
we've probably spoken about this many times,

519
00:22:24.660 --> 00:22:27.620
but it's always good to, um, to revisit. If

520
00:22:27.620 --> 00:22:30.340
the universe is expanding, what is it

521
00:22:30.340 --> 00:22:32.700
expanding into? And also,

522
00:22:33.330 --> 00:22:35.090
is the universe spherical?

523
00:22:36.770 --> 00:22:39.010
Professor Fred Watson: So, um, yes. What's it expanding into?

524
00:22:39.010 --> 00:22:41.130
Andrew Dunkley: Well, we don't know.

525
00:22:41.130 --> 00:22:43.250
Professor Fred Watson: And yes, that's.

526
00:22:43.650 --> 00:22:45.970
Yes. Uh, it's actually, we don't know. And

527
00:22:45.970 --> 00:22:48.930
maybe, maybe, maybe. So,

528
00:22:49.000 --> 00:22:51.570
um, the universe

529
00:22:52.210 --> 00:22:55.090
is everything that we can detect. That's

530
00:22:55.090 --> 00:22:56.850
the definition of the universe. Everything we

531
00:22:56.850 --> 00:22:59.490
can measure or detect. And that means,

532
00:23:00.370 --> 00:23:02.450
and we observe the expansion,

533
00:23:03.250 --> 00:23:06.210
but we don't know whether there's an edge

534
00:23:06.210 --> 00:23:08.050
to the universe. We don't know whether it's

535
00:23:08.050 --> 00:23:10.410
infinite. We don't know anything beyond the

536
00:23:10.410 --> 00:23:13.130
horizons that we see. And um, the most

537
00:23:13.130 --> 00:23:14.850
obvious one is the cosmic microwave

538
00:23:14.850 --> 00:23:16.900
background radiation, um,

539
00:23:17.730 --> 00:23:19.570
beyond which we can't see. But the universe

540
00:23:19.570 --> 00:23:21.570
almost certainly goes on beyond that,

541
00:23:22.130 --> 00:23:24.610
probably for a very long way, maybe very big.

542
00:23:24.930 --> 00:23:27.330
But we've got no knowledge of a boundary or

543
00:23:28.190 --> 00:23:30.510
any other medium that it might be expanding

544
00:23:30.510 --> 00:23:33.230
into. So, um,

545
00:23:33.610 --> 00:23:36.430
uh, one possibility is the idea of multiple

546
00:23:36.430 --> 00:23:38.830
universes. And they might

547
00:23:38.830 --> 00:23:40.990
exist maybe

548
00:23:41.630 --> 00:23:44.080
in a higher dimensional, uh,

549
00:23:45.390 --> 00:23:48.270
arena, if I can put it that way. You know,

550
00:23:48.750 --> 00:23:51.670
if you can, um, find that

551
00:23:51.670 --> 00:23:54.670
there are extra dimensions, we know the

552
00:23:54.830 --> 00:23:56.870
three dimensions of space and one of time.

553
00:23:56.870 --> 00:23:58.550
That's what we've got now.

554
00:23:59.830 --> 00:24:02.230
But, uh, if there are hidden

555
00:24:02.630 --> 00:24:04.870
extra dimensions, maybe they provide

556
00:24:05.830 --> 00:24:08.150
a venue for the universe to expand into.

557
00:24:08.970 --> 00:24:11.750
Uh, and there are various theories

558
00:24:11.750 --> 00:24:14.750
that accept that, um, M. M theory is one of

559
00:24:14.750 --> 00:24:17.710
them, where M is probably an abbreviation

560
00:24:17.710 --> 00:24:19.990
for membrane. The idea is that the universe

561
00:24:20.470 --> 00:24:22.590
can be collapsed onto a two dimensional

562
00:24:22.590 --> 00:24:24.390
membrane, and there are lots of these

563
00:24:24.390 --> 00:24:27.300
membranes in the kind

564
00:24:27.300 --> 00:24:29.580
of higher dimensional universe. But that's

565
00:24:29.580 --> 00:24:31.420
just conjecture and we've got no

566
00:24:32.060 --> 00:24:34.420
mechanism for proving that at the moment. The

567
00:24:34.420 --> 00:24:36.700
only thing we know with certainty with

568
00:24:36.700 --> 00:24:38.740
absolute certainty is that the universe is

569
00:24:38.740 --> 00:24:39.340
expanding.

570
00:24:39.500 --> 00:24:41.940
Andrew Dunkley: Yes. Uh, at an accelerating rate. Although

571
00:24:41.940 --> 00:24:43.900
the accelerating rate's not as accelerating

572
00:24:43.900 --> 00:24:45.580
as it once was. Possibly.

573
00:24:45.740 --> 00:24:46.380
Professor Fred Watson: Possibly.

574
00:24:46.530 --> 00:24:49.100
Andrew Dunkley: Um, yeah. There's three possible

575
00:24:49.980 --> 00:24:52.900
shapes of the universe. He asks if it's

576
00:24:52.900 --> 00:24:55.860
a sphere. Um, there's, uh, the flat

577
00:24:55.860 --> 00:24:58.470
universe theory. Do we have to go there? Uh,

578
00:24:58.470 --> 00:25:00.360
there's the closed universe

579
00:25:01.160 --> 00:25:04.080
theory, which is the positive curvature, so a

580
00:25:04.080 --> 00:25:06.960
sphere. Or the open universe theory,

581
00:25:06.960 --> 00:25:09.040
which is negative curvature. Huh. So it's

582
00:25:09.040 --> 00:25:11.800
more like the shape of a saddle. From what

583
00:25:11.800 --> 00:25:13.720
I'm reading, the most popular,

584
00:25:15.170 --> 00:25:17.800
uh, likelihood is the flat universe theory.

585
00:25:18.520 --> 00:25:21.080
Professor Fred Watson: But it's only flat in a Euclidean sense.

586
00:25:21.400 --> 00:25:23.960
It doesn't mean it's shaped like a

587
00:25:23.960 --> 00:25:26.920
tabletop. Uh, it means that parallel

588
00:25:26.920 --> 00:25:29.670
lines never meet. Basically, that's what we

589
00:25:29.670 --> 00:25:31.950
mean by flat. It's the shape of the geometry.

590
00:25:32.510 --> 00:25:35.030
Andrew Dunkley: And the other thing that they suggest is

591
00:25:35.030 --> 00:25:37.870
that, um, it can be flat and still

592
00:25:37.870 --> 00:25:39.790
expanding. As you said, uh, it might be

593
00:25:39.790 --> 00:25:42.510
infinite. We've talked about that before.

594
00:25:42.590 --> 00:25:45.230
And there is likely no centre and no edge.

595
00:25:46.190 --> 00:25:48.270
Professor Fred Watson: Correct. That's what we believe

596
00:25:49.070 --> 00:25:51.710
now, um, to its shape.

597
00:25:52.110 --> 00:25:54.920
So, uh, so

598
00:25:56.120 --> 00:25:58.720
basically, I think Ken's question is, is it

599
00:25:58.720 --> 00:26:00.920
spherical? And

600
00:26:01.480 --> 00:26:03.960
we don't know the answer to that. We know

601
00:26:03.960 --> 00:26:06.560
that the volume within which we can

602
00:26:06.560 --> 00:26:08.760
detect is spherical because

603
00:26:09.720 --> 00:26:12.360
the cosmic microwave background radiation

604
00:26:12.760 --> 00:26:15.160
forms an imaginary shell,

605
00:26:16.100 --> 00:26:19.080
uh, all around our galaxy. And it's

606
00:26:19.080 --> 00:26:21.440
the same distance in every direction. So in

607
00:26:21.440 --> 00:26:24.000
that regard, it's what we call isotropic, the

608
00:26:24.000 --> 00:26:26.870
same in all directions. Uh, and

609
00:26:26.870 --> 00:26:28.790
that's really the only thing we can

610
00:26:29.670 --> 00:26:32.350
lay it down to. But there are ideas that if

611
00:26:32.350 --> 00:26:34.270
you looked at the universe on a bigger scale

612
00:26:34.270 --> 00:26:36.390
than we could see, it wouldn't be. That it

613
00:26:36.390 --> 00:26:38.870
might be different in different directions.

614
00:26:39.820 --> 00:26:42.070
Um, and that, in fact, has been

615
00:26:42.390 --> 00:26:44.950
hypothesised as one of the sources of dark

616
00:26:44.950 --> 00:26:47.270
energy, that we're just seeing a local bit of

617
00:26:47.270 --> 00:26:49.400
the universe that's expanding, whose, uh,

618
00:26:49.750 --> 00:26:51.790
expansion is increasing, whereas somewhere

619
00:26:51.790 --> 00:26:54.750
else it might be slowing down

620
00:26:54.750 --> 00:26:56.800
the expansion of the universe. Um,

621
00:26:58.990 --> 00:27:00.190
Andrew Dunkley: yeah, sorry, go on.

622
00:27:00.350 --> 00:27:02.910
Professor Fred Watson: No, that would be a universe that's not

623
00:27:02.910 --> 00:27:04.550
isotropic. It's not the same in all

624
00:27:04.550 --> 00:27:06.810
directions, but we assume it's isotropic. So,

625
00:27:06.810 --> 00:27:09.190
uh, that's all we can do in our assumptions

626
00:27:09.190 --> 00:27:10.030
in cosmology.

627
00:27:10.190 --> 00:27:13.150
Andrew Dunkley: We just can't see beyond

628
00:27:13.310 --> 00:27:15.310
what we can see. Which sounds stupid, but

629
00:27:15.470 --> 00:27:18.190
that's the way the universe is. Um,

630
00:27:18.430 --> 00:27:20.630
we've got the known universe and then the

631
00:27:20.630 --> 00:27:20.990
rest of the.

632
00:27:21.940 --> 00:27:24.140
Professor Fred Watson: That's right, basically. And the rest might

633
00:27:24.140 --> 00:27:25.700
be a lot bigger than the known universe.

634
00:27:25.940 --> 00:27:27.440
Andrew Dunkley: Yeah, but we just don't know. Um,

635
00:27:29.060 --> 00:27:30.940
the only thing I thought of is, like, you

636
00:27:30.940 --> 00:27:32.820
look at Earth's atmosphere and as you go out,

637
00:27:32.820 --> 00:27:35.460
it fins. And so there's no defined

638
00:27:35.540 --> 00:27:38.260
line between space and

639
00:27:38.660 --> 00:27:41.180
the Earth proper. Could the

640
00:27:41.180 --> 00:27:43.060
universe be of the same ilk?

641
00:27:44.180 --> 00:27:47.060
Professor Fred Watson: Yes, but that would imply that space time

642
00:27:47.060 --> 00:27:49.700
just sort of keeps. Just keeps on going. It

643
00:27:49.700 --> 00:27:50.700
just might be empty.

644
00:27:51.400 --> 00:27:53.420
Uh, yeah,

645
00:27:53.880 --> 00:27:56.060
uh, we don't know.

646
00:27:56.220 --> 00:27:57.100
Andrew Dunkley: We don't know.

647
00:27:57.500 --> 00:27:59.500
Professor Fred Watson: Why are you asking us? We don't know.

648
00:28:02.580 --> 00:28:05.500
Andrew Dunkley: Uh, um, thank you, Ken. Uh, very

649
00:28:05.500 --> 00:28:07.460
thought provoking question and thanks for

650
00:28:07.460 --> 00:28:08.060
sending it in.

651
00:28:08.060 --> 00:28:10.100
If you have questions for us, please send

652
00:28:10.100 --> 00:28:11.980
them to us via our website,

653
00:28:12.060 --> 00:28:14.700
spacenutspodcast.com spacenuts

654
00:28:14.700 --> 00:28:16.980
IO there's a little button at the top called

655
00:28:16.980 --> 00:28:19.900
AMA M and that's what you click on to

656
00:28:20.200 --> 00:28:22.080
send us text and audio questions. If you've

657
00:28:22.080 --> 00:28:23.880
got a device with a microphone, you're all

658
00:28:23.880 --> 00:28:26.720
set. Uh, most smartphones and smart devices

659
00:28:26.720 --> 00:28:29.080
have that and you can send it to us

660
00:28:29.560 --> 00:28:31.520
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661
00:28:31.520 --> 00:28:32.880
you are and where you're from. Or you can

662
00:28:32.880 --> 00:28:34.480
send us a text question. Just fill in the

663
00:28:34.480 --> 00:28:37.280
blanks. And while you're there, have a look

664
00:28:37.280 --> 00:28:39.080
around, visit the shop, get something from

665
00:28:39.400 --> 00:28:42.360
yourself. Um, you know, whatever you like.

666
00:28:42.920 --> 00:28:44.480
And we're done. Fred Watson, thank you so

667
00:28:44.480 --> 00:28:45.660
much. That was a tough one.

668
00:28:47.010 --> 00:28:50.010
Professor Fred Watson: Yeah, well, we, you know, uh, Space

669
00:28:50.010 --> 00:28:52.290
Nuts always probes the limits of knowledge.

670
00:28:52.290 --> 00:28:54.010
We. It does. Ah, that's what we.

671
00:28:54.010 --> 00:28:56.570
Andrew Dunkley: Unfortunately, I have such limited knowledge,

672
00:28:56.570 --> 00:28:58.650
I'm not very helpful. But I'm glad you're

673
00:28:58.650 --> 00:28:58.930
here.

674
00:28:59.250 --> 00:29:01.929
Professor Fred Watson: No, you are very helpful and, um, so are our

675
00:29:01.929 --> 00:29:04.170
listeners because they keep on probing, which

676
00:29:04.170 --> 00:29:04.450
is great.

677
00:29:04.450 --> 00:29:06.570
Andrew Dunkley: They do indeed. All right, Fred Watson,

678
00:29:06.570 --> 00:29:07.890
thanks very much. We'll catch you on the next

679
00:29:07.890 --> 00:29:08.370
episode.

680
00:29:08.690 --> 00:29:10.170
Professor Fred Watson: Sounds great. Thanks, Andrew.

681
00:29:10.170 --> 00:29:11.770
Andrew Dunkley: Professor Fred Watson Watson, astronomer at

682
00:29:11.770 --> 00:29:13.850
large. And thanks to Huw in the studio, who

683
00:29:13.850 --> 00:29:15.530
couldn't be with us today because he's been

684
00:29:15.530 --> 00:29:17.560
expanding at an accelerating rate. So he was.

685
00:29:17.710 --> 00:29:19.910
Enter the gym. And from me, Andrew Dunkley.

686
00:29:19.910 --> 00:29:21.550
Thanks for your company. We'll see you on the

687
00:29:21.550 --> 00:29:23.070
next episode of Space Nuts.

688
00:29:23.070 --> 00:29:23.710
Professor Fred Watson: Bye. Bye.

689
00:29:24.330 --> 00:29:27.110
Andrew Dunkley: Uh, you'll be listening to the Space Nuts

690
00:29:27.110 --> 00:29:30.070
podcast, available at

691
00:29:30.070 --> 00:29:32.030
Apple Podcasts, Spotify,

692
00:29:32.190 --> 00:29:34.950
iHeartRadio or your favourite podcast

693
00:29:34.950 --> 00:29:36.670
player. You can also stream on

694
00:29:36.670 --> 00:29:38.990
demand@bytes.comm this

695
00:29:38.990 --> 00:29:41.390
Professor Fred Watson: has been another quality podcast production

696
00:29:41.390 --> 00:29:42.910
from bytes.um.com.