Q&A: Cosmic Mapping, Light Speed Anomalies & The Nature of Time

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Heidi Campo: Welcome back to another fun and exciting Q and A

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episode of space duts.

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Andrew Dunkley: 15 seconds.

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Professor Fred Watson: Guidance is internal. 10,

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9. Ignition sequence start.

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Space nuts. 5, 4, 3, 2. 1.

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Andrew Dunkley: 2, 3, 4, 5, 5, 4, 3, 2,

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1. Space nuts.

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Professor Fred Watson: Astronauts report it feels good.

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Heidi Campo: I'm your host for this episode, Heidi Campo. And

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joining us today is our beloved

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professor Fred Watson,

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astronomer at large. How are you doing today, Fred?

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Professor Fred Watson: Very well, thank you, Heidi. And, um, you look,

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uh, as though you're in fit and well compared with

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the way you've been the last week or two. I hope

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you're feeling better, but all good here at this end.

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Heidi Campo: Yeah, slowly but surely. I

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got a little bit of. A little upper respiratory, just

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a cough, a little bit of a fever, but

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that's. I always just say, um, I know this isn't

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like a health and fitness podcast, but it's so important to take care of

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your body. Eat your vitamins. Um, if

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you're from my generation, you can say, eat your Wheaties.

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I don't know. They still make those, don't they?

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Professor Fred Watson: Um, I don't know.

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I'm not sure what we're talking about.

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Heidi Campo: The Wheaties. The Wheaties cereal, it was the, uh,

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it was a. Ah, it was the breakfast of champions.

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And they would always put a big sports superstar on the

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Wheaties cereal box.

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Professor Fred Watson: Okay.

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Heidi Campo: And so in the 90s and the early 2000s, people would always say,

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eat Wheaties. Yeah, of course, is the

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thing of saying, like, you know, that's what. What you do to be healthier.

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My house growing up, we'd watch a lot of Popeye. And my

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grandpa. My grandpa would always read me

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Popeye, so he would be like, make sure you're eating your spinach.

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Professor Fred Watson: Yes, of course. That's the. Certainly

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the secret that Popeye had.

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Heidi Campo: Yeah. Eat your Wheaties, eat your spinach, take your

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vitamins. Whatever you gotta do to keep yourself healthy.

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All right, well, let's just jump right into our

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questions, um, from our listeners.

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So in these Q and A episodes, if you are new here,

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we do do an episode where Fred tells us all

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about everything exciting happening in space. And

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then we follow it up with a Q A episode where

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you, the listener, ask us your questions

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and Fred answers them. And sometimes I'll

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chime in, and when Andrew's back, he'll be chiming in with

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his wonderful dad jokes. I have not been doing good with the dad jokes.

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I'm sorry.

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Professor Fred Watson: It's a relief, actually. It's great not to have the dad

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jokes.

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Heidi Campo: All right, well, our first question today is a

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Written question and it's a bit longer.

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And this question is from Sam

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and Sam says thank you for your

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podcasts. Thank you for inviting listener questions and

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for your helpful answers. It supports making

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learning a lifelong adventure.

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There's been a lot of discussion about increasing

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opportunities to 3D map the universe.

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With our various new telescopes coming, uh, online,

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I am struggling with trying to understand,

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visualize what is being attempted to be

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portrayed in the variety of efforts at

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3D mapping of the universe or large

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subsets thereof.

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Although the idea of 3D portrayal seems obvious,

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especially when dealing with something fairly local

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or close by, it seems to me it would be

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problematic when we are using the light

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we receive today, but was, uh, emitted

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millions or billions of years ago. Do the 3D map

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show the locations of the galaxies and other

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structures in the positions they were at

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when the light we are now using was actually

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emitted? Or are the galaxy locations

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manipulated to fast forward them where

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they would be estimated to be currently? It

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seems to me that either view would have its problems

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in portraying a 3D picture attempting to show

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relative positions and locations. But relative

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to what in space and. Or time?

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Ooh, this is a really interesting question.

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Professor Fred Watson: It is, it's a great question. Uh, Sam? Um,

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and um, the

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answer is that when we,

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when, you know, particularly when we're looking at

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great distances, uh, at galaxies

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that are millions of billions of years ago, uh,

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light years away, we think in terms of

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look back times. So we're

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looking back in time because that's the only thing

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we can measure. We measure something called the redshift,

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which is a number that relates to,

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ah, how basically it

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relates to size of the universe when the light was emitted.

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Uh, so we measure the redshift and that tells us how

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far back in time we're looking for,

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uh, our depictions of

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these objects. And that's all we have. Um,

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it's nearly all we have. There is one

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other thing I'll tell you about in a minute. But um,

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the bottom line is that when we build these maps,

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basically we're putting in look back times rather than

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distances. We think of them as distances, but they're look

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back times. And so yes, we are

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depicting where that galaxy was,

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uh, when the light received, uh,

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when the light left it, basically. So

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it's the galaxy positions, ah,

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not manipulated in any way. It's directly

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read from the look back time. The one

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caveat to that that I've mentioned is that

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um, galaxies as well as

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the flow of uh,

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what we call the Hubble flow, the fact that the universe Is

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expanding.

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Heidi Campo: I hear a little rooster in the background.

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Professor Fred Watson: Yeah, he's just seen somebody he knows.

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That's our dog, believe it or not. Not the rooster.

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Um, um, forgive me if

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I just go and check that it's what I think it is. Sorry, I'll be back

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in a second. We can cut this out.

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Uh, okay. Um, so the. Let me

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pick up where I was talking about. The caveat,

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uh, the thing that distinguishes,

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um, the position of a galaxy from

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where we think of it in terms of its look

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back time, uh, is that we can

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for some galaxies, particularly relatively nearby ones out

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to perhaps just, you know, a billion light years or so,

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maybe a little bit longer than that, a bit further than that.

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Uh, we can also measure something called the peculiar

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motion of the galaxies. The peculiar velocity.

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And what this is, is the

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velocity a galaxy has that,

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uh, is a result of

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local gravitational forces. So if

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you've got a big cluster of galaxies, they'll be moving around

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a sort of center of mass. They'll have what we call a

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peculiar motion which is distinct from

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their motion because of the expansion of the universe. I'm

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not sure whether I'm making this clear. Um, but the

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way we describe it usually is if you think of a river

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flowing, uh, and you imagine

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boats on that river, they have their

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own motion, uh, across the water,

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but they're also being carried along by the motion

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of the river itself. And that's an analog

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with what's happening with the galaxies. They've got their own individual

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motions as well as what we call the Hubble flow. The fact

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that they're moving because of the expansion of, of the universe.

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And you could in principle

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take those peculiar velocities

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and say, well, um,

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you know, if you think about where they are now,

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those galaxies, their positions will have changed.

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But in terms of the change

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compared with the distance that we're looking at, the changes are

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negligible over the timescales that we are

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talking about. Even though it's billions of years.

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Um, uh, when, when you're talking about things billions of light

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years away, uh, and you're talking about, you

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know, maybe a few,

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um, it's more than millions of

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kilometers, but it's, it's, it's so small

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compared with the size of the universe that you would never

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know the difference. So basically we just take

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what we get from our measurement of distance and plot

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the maps that way. A long answer to a fairly long

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question, Sam. I hope that explains why what's going on

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there.

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Heidi Campo: Well, that was, that was a really Fun question.

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Um, thank you for answering it.

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Professor Fred Watson: Roger. Your lot right here also.

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Heidi Campo: Space Nuts, our next question

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is from Mark, and this is going to

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be a audio question. Uh,

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Mark, Mark from Quebec. So we're going

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to, uh, cue that up and play that for you guys

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right now. So Fred and I are going to get that ready, we'll

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listen to it, and we'll play it for you as well. We're going to play

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that question you right now.

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Andrew Dunkley: Hello, Space Nuts. My name is Mark. I'm recording

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from Sherbrooke in the beautiful province of

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Quebec. Now, I have a question

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about the speed of light. So when we

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talk about the speed of light, we assume it's the speed

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of light in the vacuum of space, right?

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I've heard that, uh, the speed of light can slow

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down by something around

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like 40% when, uh,

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it's traveling through matter like water or diamonds.

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Now, if an astronaut in space would shine

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a laser beam through a diamond.

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Professor Fred Watson: Held.

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Andrew Dunkley: At the top of his fingertips,

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let's say the light would travel through the diamond

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at a reduced speed, right? But once the

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light exits the diamond and is

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back in the vacuum of space, would it continue

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traveling at a reduced speed or would it

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resume its initial speed? And if

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it did resume its initial speed,

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where would it get the energy to accelerate

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again? Now, I know that the light has no

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mass, but I kind

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of can't imagine how light could travel at the

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reduced speed or how it could

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automatically, uh, return to its original speed after being

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slowed down. So I would really

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like if you could help me understand this, uh,

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how this works. So thank you very much.

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Great, great show. Thank you for all, uh,

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your work, guys.

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Andrew Dunkley: Bye bye.

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Professor Fred Watson: That's a great, great question. Um,

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and it's a little bit

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like, it's kind of related to a question that

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we, we've had some time ago, um,

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which is about, um,

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when photons are emitted,

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uh, how long does it take them to accelerate to

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the speed of light? Um, and the answer

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is they're emitted at the speed of

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light. And so, um,

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this question, uh, I think I

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would tackle it in the same way as I tackled that other

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question. And that is that light is not just

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a stream of particles, uh, which, as, uh,

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Mark says, are massless. Effectively, they've got no

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rest mass, um, but it's also a wave

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motion. And that's perhaps the

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easier way to understand what's going on here.

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Uh, you've got these waves, um, which

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encounter a surface, perhaps a diamond

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or a water surface, and indeed they do slow

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down, uh, the propagation of the wave slows down.

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Uh, but then when they leave that

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surface, when they leave that material on the other side,

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they go back to the same speed.

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And that's much easier to understand

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from the point of view of wave motion than it is

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from the idea of streams of particles. Uh,

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because the same thing happens, uh, um, in

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water waves. If you have water waves that are

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propagating on a surface and they come to

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a shallow region, their velocity will change. And then if they come to

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a deeper region, they go back to where they were before.

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Um, so the speed of light in a vacuum is one of these

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strange things. It's immutable. It does not change. It's

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always 300,000 kilometers per second. I think we

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discussed this in the last Q and A session. Uh, we

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talked at length about it. So, um, quite

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counterintuitive. And I can understand

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why your question arises, Mark. But think of it as

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waves, and it's much easier to understand what's going on.

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Heidi Campo: Excellent, Fred. Thank you.

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Um, our next question is from Rennie

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Traub from Sunny Hills, California.

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And Rennie has a short and sweet question. And it

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is, how great is the heliosphere

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around our solar system? And do all or

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most solar systems have one?

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Professor Fred Watson: Um, yeah. Great questions,

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Rennie, one of our regular questioners. There are always

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good questions from Rennie. This is a good one too.

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Um, uh, so

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it's only an estimate, uh, although we do

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have some measurements that lead us

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to believe this estimate is somewhere near the

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truth. Because we've got, uh, five

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spacecraft which are leaving the solar system. Uh,

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and they are, I think, all equipped with

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magnetometers. The two pioneers, the Voyagers and

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New, uh, Horizons, I think they've all got magnetometers on board.

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And the heliosphere is the Sun's,

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uh, sphere of magnetic influence. Uh, and

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so those magnetic magnetometers can basically

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give you. Give, uh, you an idea of

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what, uh, what, you know, what the

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dimensions of the heliosphere are. And it's

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in the region of.

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It's basically

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measured in astronomical units. An astronomical unit is the

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distance between the Earth and the sun.

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Something in the region of 100

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astronomical units,

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uh, is the radius. Um, and

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so, uh, it's

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not spherical. It's got a

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peculiar shape, which is probably because

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of the sun's motion through

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the galaxy's magnetic field. That distorts the

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shape of the heliosphere. Uh, but, um,

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it's roughly, as I said, a radius

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of, uh, about 100 astronomical units. So

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what is that? It's 100 times 150. 50 million

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kilometers, uh, which

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is um, if my

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mathematics is right it's about 15 billion. Is

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that right? Thereabouts, yeah. 15 billion kilometers.

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Something of that size. So it's, it's and

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the voyagers uh, are

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both uh, further than that distance

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and so they have ah, sensed the edge of

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the magnetosphere. Uh, um,

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we keep seeing headlines. Um, they're leaving the

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solar system. Well that's not really quite the

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case because the solar system encompasses the Oort cloud which

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is a lot further out. But they are probably leaving

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the heliosphere, the region of the Sun's

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magnetic influence. And uh, to

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answer your question Renny, fully, uh,

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yes, uh, sun like stars, like ours would

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have a heliosphere. Some stars are far more

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magnetic, uh, uh, than the sun is

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and so they would probably have a bigger heliosphere depending on the type

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of star it is. Uh, but yet they'll be common to all

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stars we think because magnetism plays such a huge role

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in the way stars work.

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Heidi Campo: Another good high impact question from Rennie.

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Andrew Dunkley: 0G and I feel fine Space nuts.

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Heidi Campo: Um, our very last question today is

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another audio question and this one is from Dean

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in Queensland. And we are

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going to go ahead and play the audio question for you all

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now.

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Andrew Dunkley: Hi Fred, Heidi and Andrea. My question is about

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time dilation, but I've had to break it into three parts. I

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hope that's okay. First part concerns um,

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the Kelly twins, whose ages diverge slightly

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because of time dilation when one of them spent a year on the

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ISS orbiting the Earth. I've read that a

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person moving at high speed experiences times slower than

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a slow moving person. However, speed is

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relative. If two people in space were moving away

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from each other at a constant rate, then each one

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would perceive the other to be the one doing the moving.

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In that case, what determines which one

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would have the slower time? This question

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makes me wonder whether it's acceleration that

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causes the time dilation rather than just speed.

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This could explain the Kelly twin's age difference as the

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the ISS orbital motion is a form of

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acceleration. Plus there was also a linear

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acceleration to get into orbit in the first place.

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Part two is about the idea that an object in

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a high gravity field experiences time slower

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than an object in low gravity. If this is

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correct, is it independent from speed

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induced time dilation? And could these two

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effects add together if an object

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is moving very fast and it's within a

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uh, high gravity field? Part three

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is about uh, descriptions of time

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spans in the early uh, universe. Certain

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events Are, uh, described as happening within a

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specific number of years of the Big Bang.

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However, if time runs slower in a high

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gravity field, then it must have generally

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run slower when all the baryonic matter

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in the early universe was densely packed in a

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smaller space time. And if that is true,

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then the period of 100,000 years from the Big

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Bang would not be equivalent to a period

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of 100,000 years here on Earth. Is that

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correct? I probably have a lot of this

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wrong. Can you explain it for me? Thanks again

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for the podcast.

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Professor Fred Watson: Um, Dean, you don't have a lot of it wrong. I think

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you've got a lot of it right. Um,

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so, um, the first and second parts

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of your question, I think really merge into one.

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Uh, because I think the difference in ages with the Kelly

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twins, I think it was the gravitational time dilation

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that was being taken into account rather than the velocity time

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dilation. I'm not sure about that.

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Uh, but both of those effect. You're quite right that

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accelerations also play a role in this

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too. Um, certainly for the velocity time

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dilation, it's what allows the twins

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paradox to work. Uh, because you've got

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accelerations at, uh, the beginning and end of the twin

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one twins voyage to the nearest star and

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back again. Um, but yes, the

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gravitational and, um, velocity

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time dilations, they're both caused by

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relativity. The two different relativity

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theories. Special, uh, relativity in

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1905 talked about velocities. When

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you get velocities going near the speed of light, all

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kinds of weird things happen, including the phenomenon

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of time dilation. A stationary observer will see somebody

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else's clock moving slower, ah, as they whiz

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by at nearly the speed of light. And then in,

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um, 1915, uh, the

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general theory of relativity, which was about

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the way gravitation works. And it turns out that

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gravity does the same thing. Uh, gravitational

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time dilation. If you're in a gravitational field, your

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clocks are running slower than if you're outside it.

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Um, and the closer you are, for

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example, to the Earth, the slower your clocks will run compared with

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somebody who is in orbit. I think that was the issue with the Kelly

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twin winds. Um, it's

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microseconds. It's tiny, tiny amount of time.

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Uh, when you consider the distance between the Earth's surface and the

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height of the International space station at 400 kilometers,

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uh, it's a very small difference, but it is measurable.

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Um, in fact, I think it is even measurable, uh, with

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aircraft. If you fly an atomic clock on board an aircraft,

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I think from a Ground based observer, it looks as though,

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um, it's going faster than what we measure time

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here on Earth. Uh, so, um,

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that's basically sorting out those issues.

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Uh, your third part of the question. It's certainly true

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that when we look back at phenomena that

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are sort of time tagged, if I can put it that way,

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in the early universe, we do see time dilation.

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Um, and, uh, I'm thinking

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particularly of supernova

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explosions where a star explodes, its

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brilliance goes up and then decays slowly

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afterwards. Uh, it turns out that you see

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the decay time changing from our

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perspective, uh,

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on the gravitational, you know, on

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um, Earth, uh, 13.8 or however many

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billion years later when we observe

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these phenomena. So, um, the same

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would be true of, uh, the early universe. And

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I think that's taken into account with people's

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calculations about this. I think time dilation

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falls directly within the province of cosmologists

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who understand it obviously a lot better than, than I

440
00:21:05.100 --> 00:21:07.420
do. Um, but, yeah, that's the bottom line.

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Heidi Campo: Yeah. And the time dilation is always, uh,

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it's always so hard to wrap your head around, but you do a

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great job of explaining it to us.

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Professor Fred Watson: Um, I just try and put it into terms that

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I can understand myself, which is not always

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the cleverest way to do it, but that's all right.

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Heidi Campo: Well, that, that wraps up all of

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our questions for today. Um, Fred,

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thank you so much for always being available to

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help us out with all of our questions. And to you, the

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00:21:37.260 --> 00:21:40.100
listeners, please keep sending in your awesome,

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00:21:40.260 --> 00:21:43.180
well thought out questions. You guys are really so smart.

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Every time I read your questions, I'm like, how are you guys even

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00:21:46.099 --> 00:21:48.180
thinking of this stuff? Uh, you guys are brilliant.

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So keep sending in your questions. Um, you only

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have, like I said, you only have a few more weeks with me before

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Andrew is back, and so take advantage

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of that.

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And I guess without further ado,

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Fred, do you want to sign us off? Do you have anything else you want to

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say?

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Professor Fred Watson: No, just keep the questions coming exactly as you've said, Heidi.

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And, uh, thanks again to all of our great

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00:22:11.080 --> 00:22:13.880
listeners who sent in questions. Thanks to you, Heidi,

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for keeping the show going and we'll, uh, see

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00:22:16.760 --> 00:22:19.720
you next time. You'll be listening

467
00:22:19.720 --> 00:22:21.440
to the SpaceNuts podcast.

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00:22:23.180 --> 00:22:25.740
Andrew Dunkley: Available at Apple Podcasts, Spotify,

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00:22:25.900 --> 00:22:28.700
iHeartRadio, or your favorite podcast

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00:22:28.700 --> 00:22:29.020
player.

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00:22:29.100 --> 00:22:31.740
Professor Fred Watson: You can also stream on demand at Bytes.

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00:22:31.740 --> 00:22:34.540
Com. This has been another quality podcast

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00:22:34.540 --> 00:22:36.350
production from Bytes. Com.

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Heidi Campo: Um.