Cosmic Queries: Time, Light, and the Universe
In this engaging episode of Space Nuts, hosts Heidi Campo and Professor Fred Watson dive into a captivating Q&A session, tackling listener questions that span the intricacies of time dilation, the speed of light, and the structure of the universe. With a mix of scientific insight and relatable explanations, this episode promises to enlighten and entertain.
Episode Highlights:
- 3D Mapping the Universe: A listener named Sam poses a thought-provoking question about the complexities of 3D mapping galaxies based on light emitted millions of years ago. Fred explains how astronomers interpret these vast distances and the challenges involved in visualizing the universe's structure over time.
- The Speed of Light in Different Mediums: Mark from Quebec asks about the behavior of light traveling through various materials, like diamonds. Fred clarifies how light slows down in denser media and seamlessly resumes its speed in a vacuum, drawing parallels to wave motion for a clearer understanding.
- Understanding the Heliopause: Regular contributor Rennie Traub inquires about the heliosphere's dimensions and whether all solar systems possess one. Fred discusses the heliosphere's size and its significance in relation to solar and stellar magnetism.
- Time Dilation and the Kelly Twins: Dean from Queensland dives deep into the concept of time dilation, examining the age difference between the Kelly twins and the effects of gravity and speed on time perception. Fred navigates through the complexities of relativity, shedding light on how these factors interplay in the universe.
For more Space Nuts, including our continuously updating newsfeed and to listen to all our episodes, visit our website. Follow us on social media at SpaceNutsPod on Facebook, X, YouTube Music Music, Tumblr, Instagram, and TikTok. We love engaging with our community, so be sure to drop us a message or comment on your favorite platform.
If you’d like to help support Space Nuts and join our growing family of insiders for commercial-free episodes and more, visit spacenutspodcast.com/about
Stay curious, keep looking up, and join us next time for more stellar insights and cosmic wonders. Until then, clear skies and happy stargazing.
Got a question for our Q&A episode? https://spacenutspodcast.com/ama
Become a supporter of this podcast: https://www.spreaker.com/podcast/space-nuts-astronomy-insights-cosmic-discoveries--2631155/support.
00:00:00 --> 00:00:02 Heidi Campo: Welcome back to another fun and exciting Q
00:00:02 --> 00:00:05 and A episode of space duts.
00:00:05 --> 00:00:06 Andrew Dunkley: 15 seconds.
00:00:06 --> 00:00:08 Professor Fred Watson: Guidance is internal. 10,
00:00:08 --> 00:00:11 9. Ignition sequence start.
00:00:12 --> 00:00:14 Space nuts. 5, 4, 3, 2. 1.
00:00:14 --> 00:00:17 Andrew Dunkley: 2, 3, 4, 5, 5, 4, 3, 2,
00:00:17 --> 00:00:18 1. Space nuts.
00:00:19 --> 00:00:20 Professor Fred Watson: Astronauts report it feels good.
00:00:21 --> 00:00:23 Heidi Campo: I'm your host for this episode, Heidi Campo.
00:00:23 --> 00:00:26 And joining us today is our beloved
00:00:26 --> 00:00:29 professor Fred Watson,
00:00:29 --> 00:00:31 astronomer at large. How are you doing today,
00:00:31 --> 00:00:32 Fred?
00:00:32 --> 00:00:35 Professor Fred Watson: Very well, thank you, Heidi. And, um, you
00:00:35 --> 00:00:37 look, uh, as though you're in fit and well
00:00:37 --> 00:00:39 compared with the way you've been the last
00:00:39 --> 00:00:42 week or two. I hope you're feeling better,
00:00:42 --> 00:00:44 but all good here at this end.
00:00:44 --> 00:00:46 Heidi Campo: Yeah, slowly but surely. I
00:00:47 --> 00:00:49 got a little bit of. A little upper
00:00:49 --> 00:00:52 respiratory, just a cough, a little bit of a
00:00:52 --> 00:00:54 fever, but that's. I always just say,
00:00:54 --> 00:00:56 um, I know this isn't like a health and
00:00:56 --> 00:00:58 fitness podcast, but it's so important to
00:00:58 --> 00:01:00 take care of your body. Eat your vitamins.
00:01:01 --> 00:01:03 Um, if you're from my generation, you can
00:01:03 --> 00:01:06 say, eat your Wheaties. I don't
00:01:06 --> 00:01:08 know. They still make those, don't they?
00:01:08 --> 00:01:09 Professor Fred Watson: Um, I don't know.
00:01:11 --> 00:01:13 I'm not sure what we're talking about.
00:01:13 --> 00:01:15 Heidi Campo: The Wheaties. The Wheaties cereal, it was
00:01:15 --> 00:01:18 the, uh, it was a. Ah, it was the breakfast
00:01:18 --> 00:01:20 of champions. And they would always put a big
00:01:20 --> 00:01:23 sports superstar on the Wheaties cereal box.
00:01:23 --> 00:01:24 Professor Fred Watson: Okay.
00:01:24 --> 00:01:26 Heidi Campo: And so in the 90s and the early 2000s, people
00:01:26 --> 00:01:28 would always say, eat Wheaties. Yeah, of
00:01:28 --> 00:01:31 course, is the thing of saying, like, you
00:01:31 --> 00:01:32 know, that's what. What you do to be
00:01:32 --> 00:01:35 healthier. My house growing up, we'd watch a
00:01:35 --> 00:01:37 lot of Popeye. And my grandpa. My grandpa
00:01:37 --> 00:01:39 would always read me Popeye, so he would be
00:01:39 --> 00:01:41 like, make sure you're eating your spinach.
00:01:41 --> 00:01:44 Professor Fred Watson: Yes, of course. That's the. Certainly
00:01:44 --> 00:01:46 the secret that Popeye had.
00:01:47 --> 00:01:49 Heidi Campo: Yeah. Eat your Wheaties, eat your spinach,
00:01:49 --> 00:01:52 take your vitamins. Whatever you gotta do to
00:01:52 --> 00:01:53 keep yourself healthy.
00:01:53 --> 00:01:56 All right, well, let's just jump right into
00:01:56 --> 00:01:59 our questions, um, from our listeners.
00:01:59 --> 00:02:02 So in these Q and A episodes, if you are new
00:02:02 --> 00:02:04 here, we do do an episode where Fred
00:02:04 --> 00:02:07 tells us all about everything exciting
00:02:07 --> 00:02:09 happening in space. And then we follow it up
00:02:09 --> 00:02:12 with a Q A episode where you, the
00:02:12 --> 00:02:15 listener, ask us your questions and Fred
00:02:15 --> 00:02:17 answers them. And sometimes I'll chime in,
00:02:17 --> 00:02:20 and when Andrew's back, he'll be chiming in
00:02:20 --> 00:02:22 with his wonderful dad jokes. I have not been
00:02:22 --> 00:02:23 doing good with the dad jokes. I'm sorry.
00:02:25 --> 00:02:27 Professor Fred Watson: It's a relief, actually. It's great not to
00:02:27 --> 00:02:29 have the dad jokes.
00:02:30 --> 00:02:33 Heidi Campo: All right, well, our first question today is
00:02:33 --> 00:02:35 a Written question and it's a bit longer.
00:02:36 --> 00:02:39 And this question is from Sam
00:02:39 --> 00:02:42 and Sam says thank you for your
00:02:42 --> 00:02:44 podcasts. Thank you for inviting listener
00:02:44 --> 00:02:46 questions and for your helpful answers. It
00:02:46 --> 00:02:49 supports making learning a lifelong
00:02:49 --> 00:02:52 adventure. There's been a lot of discussion
00:02:52 --> 00:02:55 about increasing opportunities to 3D map
00:02:55 --> 00:02:58 the universe. With our various new telescopes
00:02:58 --> 00:03:00 coming, uh, online, I am
00:03:00 --> 00:03:02 struggling with trying to understand,
00:03:02 --> 00:03:05 visualize what is being attempted to be
00:03:05 --> 00:03:08 portrayed in the variety of efforts at
00:03:08 --> 00:03:10 3D mapping of the universe or large
00:03:10 --> 00:03:12 subsets thereof.
00:03:13 --> 00:03:15 Although the idea of 3D portrayal seems
00:03:15 --> 00:03:17 obvious, especially when dealing with
00:03:17 --> 00:03:20 something fairly local or close by,
00:03:20 --> 00:03:23 it seems to me it would be problematic when
00:03:23 --> 00:03:26 we are using the light we receive today,
00:03:26 --> 00:03:29 but was, uh, emitted millions or billions of
00:03:29 --> 00:03:31 years ago. Do the 3D map show the locations
00:03:31 --> 00:03:34 of the galaxies and other structures in the
00:03:34 --> 00:03:37 positions they were at when the light we
00:03:37 --> 00:03:40 are now using was actually emitted? Or
00:03:40 --> 00:03:43 are the galaxy locations manipulated to fast
00:03:43 --> 00:03:46 forward them where they would be estimated to
00:03:46 --> 00:03:49 be currently? It seems to me that either view
00:03:49 --> 00:03:52 would have its problems in portraying a 3D
00:03:52 --> 00:03:54 picture attempting to show relative positions
00:03:54 --> 00:03:57 and locations. But relative to what in space
00:03:57 --> 00:04:00 and. Or time? Ooh, this is a really
00:04:00 --> 00:04:01 interesting question.
00:04:02 --> 00:04:04 Professor Fred Watson: It is, it's a great question. Uh, Sam? Um,
00:04:05 --> 00:04:07 and um, the
00:04:07 --> 00:04:10 answer is that when we,
00:04:10 --> 00:04:12 when, you know, particularly when we're
00:04:12 --> 00:04:14 looking at great distances,
00:04:15 --> 00:04:17 uh, at galaxies that are millions of billions
00:04:17 --> 00:04:20 of years ago, uh, light years away,
00:04:20 --> 00:04:23 we think in terms of look back times.
00:04:23 --> 00:04:26 So we're looking back in time
00:04:26 --> 00:04:29 because that's the only thing we can measure.
00:04:29 --> 00:04:31 We measure something called the redshift,
00:04:31 --> 00:04:34 which is a number that relates to,
00:04:34 --> 00:04:37 ah, how basically it
00:04:37 --> 00:04:39 relates to size of the universe when the
00:04:39 --> 00:04:41 light was emitted. Uh, so we measure the
00:04:41 --> 00:04:44 redshift and that tells us how far back in
00:04:44 --> 00:04:46 time we're looking for, uh,
00:04:48 --> 00:04:51 our depictions of these objects. And that's
00:04:51 --> 00:04:53 all we have. Um, it's
00:04:53 --> 00:04:55 nearly all we have. There is one other thing
00:04:55 --> 00:04:58 I'll tell you about in a minute. But um, the
00:04:58 --> 00:05:00 bottom line is that when we build these maps,
00:05:01 --> 00:05:03 basically we're putting in look back times
00:05:03 --> 00:05:05 rather than distances. We think of them as
00:05:05 --> 00:05:08 distances, but they're look back times. And
00:05:08 --> 00:05:11 so yes, we are depicting where that
00:05:11 --> 00:05:13 galaxy was, uh, when the light received,
00:05:14 --> 00:05:17 uh, when the light left it, basically.
00:05:17 --> 00:05:20 So it's the galaxy
00:05:20 --> 00:05:22 positions, ah, not manipulated
00:05:22 --> 00:05:25 in any way. It's directly read from the
00:05:25 --> 00:05:28 look back time. The one caveat to that that
00:05:28 --> 00:05:31 I've mentioned is that um, galaxies
00:05:32 --> 00:05:35 as well as the flow of
00:05:35 --> 00:05:38 uh, what we call the Hubble flow, the fact
00:05:38 --> 00:05:40 that the universe Is expanding.
00:05:41 --> 00:05:43 Heidi Campo: I hear a little rooster in the background.
00:05:44 --> 00:05:47 Professor Fred Watson: Yeah, he's just seen somebody he knows.
00:05:47 --> 00:05:49 That's our dog, believe it or not. Not the
00:05:49 --> 00:05:50 rooster.
00:05:51 --> 00:05:53 Um, um, forgive me if
00:05:53 --> 00:05:55 I just go and check that it's what I think it
00:05:55 --> 00:05:58 is. Sorry, I'll be back in a second. We can
00:05:58 --> 00:06:00 cut this out. Uh, okay.
00:06:00 --> 00:06:03 Um, so the. Let me pick up where I
00:06:03 --> 00:06:06 was talking about. The caveat, uh,
00:06:06 --> 00:06:09 the thing that distinguishes, um,
00:06:10 --> 00:06:12 the position of a galaxy from where we
00:06:13 --> 00:06:15 think of it in terms of its look back time,
00:06:15 --> 00:06:18 uh, is that we can for some galaxies,
00:06:18 --> 00:06:20 particularly relatively nearby ones out to
00:06:20 --> 00:06:22 perhaps just, you know, a billion light years
00:06:22 --> 00:06:25 or so, maybe a little bit longer than that, a
00:06:25 --> 00:06:27 bit further than that. Uh, we can also
00:06:27 --> 00:06:30 measure something called the peculiar motion
00:06:30 --> 00:06:33 of the galaxies. The peculiar velocity. And
00:06:33 --> 00:06:36 what this is, is the velocity
00:06:36 --> 00:06:38 a galaxy has that, uh,
00:06:38 --> 00:06:41 is a result of local
00:06:42 --> 00:06:44 gravitational forces. So if you've got a big
00:06:44 --> 00:06:47 cluster of galaxies, they'll be moving around
00:06:47 --> 00:06:50 a sort of center of mass. They'll have what
00:06:50 --> 00:06:53 we call a peculiar motion which is distinct
00:06:53 --> 00:06:55 from their motion because of the
00:06:55 --> 00:06:57 expansion of the universe. I'm not sure
00:06:57 --> 00:07:00 whether I'm making this clear. Um, but the
00:07:00 --> 00:07:02 way we describe it usually is if you think of
00:07:02 --> 00:07:05 a river flowing, uh, and you
00:07:05 --> 00:07:08 imagine boats on that river, they
00:07:08 --> 00:07:11 have their own motion, uh, across the
00:07:11 --> 00:07:13 water, but they're also being carried along
00:07:13 --> 00:07:16 by the motion of the river itself. And that's
00:07:16 --> 00:07:18 an analog with what's happening with the
00:07:18 --> 00:07:20 galaxies. They've got their own individual
00:07:20 --> 00:07:22 motions as well as what we call the Hubble
00:07:22 --> 00:07:24 flow. The fact that they're moving because of
00:07:24 --> 00:07:26 the expansion of, of the universe. And
00:07:27 --> 00:07:30 you could in principle take
00:07:30 --> 00:07:32 those peculiar velocities and
00:07:32 --> 00:07:35 say, well, um, you know,
00:07:35 --> 00:07:38 if you think about where they are now, those
00:07:38 --> 00:07:40 galaxies, their positions will have changed.
00:07:41 --> 00:07:44 But in terms of the change
00:07:44 --> 00:07:46 compared with the distance that we're looking
00:07:46 --> 00:07:49 at, the changes are negligible over the
00:07:49 --> 00:07:51 timescales that we are talking about. Even
00:07:51 --> 00:07:54 though it's billions of years. Um, uh, when,
00:07:54 --> 00:07:55 when you're talking about things billions of
00:07:55 --> 00:07:58 light years away, uh, and you're talking
00:07:58 --> 00:08:00 about, you know, maybe a few,
00:08:00 --> 00:08:03 um, it's more than millions of
00:08:03 --> 00:08:06 kilometers, but it's, it's, it's so small
00:08:06 --> 00:08:08 compared with the size of the universe that
00:08:08 --> 00:08:11 you would never know the difference. So
00:08:11 --> 00:08:13 basically we just take what we get from our
00:08:13 --> 00:08:15 measurement of distance and plot the maps
00:08:15 --> 00:08:18 that way. A long answer to a fairly long
00:08:18 --> 00:08:20 question, Sam. I hope that explains why
00:08:20 --> 00:08:21 what's going on there.
00:08:22 --> 00:08:23 Heidi Campo: Well, that was, that was a really Fun
00:08:23 --> 00:08:26 question. Um, thank you for answering it.
00:08:29 --> 00:08:31 Professor Fred Watson: Roger. Your lot right here also.
00:08:31 --> 00:08:33 Heidi Campo: Space Nuts, our next question
00:08:34 --> 00:08:37 is from Mark, and this is going to
00:08:37 --> 00:08:39 be a audio question. Uh,
00:08:39 --> 00:08:42 Mark, Mark from Quebec. So we're going
00:08:42 --> 00:08:45 to, uh, cue that up and play that for you
00:08:45 --> 00:08:47 guys right now. So Fred and I are going to
00:08:47 --> 00:08:49 get that ready, we'll listen to it, and we'll
00:08:49 --> 00:08:51 play it for you as well. We're going to play
00:08:51 --> 00:08:53 that question you right now.
00:08:54 --> 00:08:56 Andrew Dunkley: Hello, Space Nuts. My name is Mark. I'm
00:08:56 --> 00:08:58 recording from Sherbrooke in the beautiful
00:08:58 --> 00:09:01 province of Quebec. Now, I have a
00:09:01 --> 00:09:04 question about the speed of light. So
00:09:04 --> 00:09:06 when we talk about the speed of light, we
00:09:06 --> 00:09:09 assume it's the speed of light in the vacuum
00:09:09 --> 00:09:11 of space, right? I've heard that,
00:09:12 --> 00:09:14 uh, the speed of light can slow down by
00:09:14 --> 00:09:17 something around like 40%
00:09:18 --> 00:09:21 when, uh, it's traveling through matter like
00:09:21 --> 00:09:23 water or diamonds. Now, if an
00:09:23 --> 00:09:26 astronaut in space would shine a
00:09:26 --> 00:09:28 laser beam through a diamond.
00:09:28 --> 00:09:29 Professor Fred Watson: Held.
00:09:31 --> 00:09:34 Andrew Dunkley: At the top of his fingertips,
00:09:34 --> 00:09:36 let's say the light would travel through the
00:09:36 --> 00:09:38 diamond at a reduced speed, right?
00:09:39 --> 00:09:41 But once the light exits the diamond
00:09:42 --> 00:09:45 and is back in the vacuum of space, would
00:09:45 --> 00:09:47 it continue traveling at a reduced speed or
00:09:47 --> 00:09:50 would it resume its initial speed?
00:09:50 --> 00:09:53 And if it did resume its initial
00:09:53 --> 00:09:56 speed, where would it get the energy
00:09:56 --> 00:09:59 to accelerate again? Now, I know that the
00:09:59 --> 00:10:02 light has no mass, but I
00:10:02 --> 00:10:05 kind of can't imagine how light could travel
00:10:05 --> 00:10:08 at the reduced speed or how it
00:10:08 --> 00:10:10 could automatically, uh, return to its
00:10:10 --> 00:10:12 original speed after being slowed down.
00:10:13 --> 00:10:16 So I would really like if you could help me
00:10:16 --> 00:10:19 understand this, uh, how
00:10:19 --> 00:10:22 this works. So thank you very much. Great,
00:10:22 --> 00:10:24 great show. Thank you for all, uh, your
00:10:24 --> 00:10:25 work, guys.
00:10:25 --> 00:10:26 Andrew Dunkley: Bye bye.
00:10:26 --> 00:10:29 Professor Fred Watson: That's a great, great question. Um,
00:10:29 --> 00:10:31 and it's a little bit
00:10:32 --> 00:10:34 like, it's kind of related to a question that
00:10:34 --> 00:10:37 we, we've had some time ago, um,
00:10:37 --> 00:10:40 which is about, um,
00:10:41 --> 00:10:43 when photons are emitted,
00:10:43 --> 00:10:46 uh, how long does it take them to accelerate
00:10:46 --> 00:10:49 to the speed of light? Um, and the
00:10:49 --> 00:10:52 answer is they're emitted at the
00:10:52 --> 00:10:55 speed of light. And so, um,
00:10:55 --> 00:10:58 this question, uh, I think I
00:10:58 --> 00:11:00 would tackle it in the same way as I tackled
00:11:00 --> 00:11:03 that other question. And that is that light
00:11:03 --> 00:11:06 is not just a stream of particles, uh,
00:11:06 --> 00:11:09 which, as, uh, Mark says, are massless.
00:11:09 --> 00:11:11 Effectively, they've got no rest mass, um,
00:11:11 --> 00:11:14 but it's also a wave motion. And
00:11:14 --> 00:11:16 that's perhaps the easier way to understand
00:11:16 --> 00:11:19 what's going on here. Uh, you've got
00:11:19 --> 00:11:21 these waves, um, which
00:11:21 --> 00:11:24 encounter a surface, perhaps a diamond
00:11:24 --> 00:11:27 or a water surface, and indeed they do slow
00:11:27 --> 00:11:30 down, uh, the propagation of the wave slows
00:11:30 --> 00:11:33 down. Uh, but then when
00:11:33 --> 00:11:35 they leave that surface, when they leave that
00:11:35 --> 00:11:38 material on the other side, they go back to
00:11:38 --> 00:11:40 the same speed. And that's
00:11:41 --> 00:11:44 much easier to understand from the point
00:11:44 --> 00:11:46 of view of wave motion than it is from the
00:11:46 --> 00:11:49 idea of streams of particles. Uh, because the
00:11:49 --> 00:11:52 same thing happens, uh, um, in water
00:11:52 --> 00:11:54 waves. If you have water waves that are
00:11:54 --> 00:11:57 propagating on a surface and they come to
00:11:57 --> 00:11:59 a shallow region, their velocity will change.
00:11:59 --> 00:12:01 And then if they come to a deeper region,
00:12:01 --> 00:12:04 they go back to where they were before. Um,
00:12:04 --> 00:12:06 so the speed of light in a vacuum is one of
00:12:06 --> 00:12:09 these strange things. It's immutable. It does
00:12:09 --> 00:12:11 not change. It's always 300 kilometers
00:12:11 --> 00:12:13 per second. I think we discussed this in the
00:12:13 --> 00:12:16 last Q and A session. Uh, we talked at length
00:12:16 --> 00:12:18 about it. So, um, quite
00:12:18 --> 00:12:21 counterintuitive. And I can understand
00:12:21 --> 00:12:24 why your question arises, Mark. But think of
00:12:24 --> 00:12:26 it as waves, and it's much easier to
00:12:26 --> 00:12:27 understand what's going on.
00:12:27 --> 00:12:29 Heidi Campo: Excellent, Fred. Thank you.
00:12:29 --> 00:12:32 Um, our next question is from Rennie
00:12:32 --> 00:12:34 Traub from Sunny Hills, California.
00:12:35 --> 00:12:38 And Rennie has a short and sweet question.
00:12:38 --> 00:12:40 And it is, how great is the
00:12:40 --> 00:12:42 heliosphere around our solar system?
00:12:43 --> 00:12:45 And do all or most solar systems
00:12:45 --> 00:12:46 have one?
00:12:48 --> 00:12:50 Professor Fred Watson: Um, yeah. Great questions,
00:12:50 --> 00:12:53 Rennie, one of our regular questioners. There
00:12:53 --> 00:12:54 are always good questions from Rennie. This
00:12:54 --> 00:12:57 is a good one too. Um, uh,
00:12:57 --> 00:13:00 so it's only an estimate,
00:13:00 --> 00:13:03 uh, although we do have some measurements
00:13:03 --> 00:13:06 that lead us to believe this estimate is
00:13:06 --> 00:13:08 somewhere near the truth. Because we've got,
00:13:09 --> 00:13:11 uh, five spacecraft which are leaving the
00:13:11 --> 00:13:14 solar system. Uh, and they are, I
00:13:14 --> 00:13:16 think, all equipped with magnetometers. The
00:13:16 --> 00:13:18 two pioneers, the Voyagers and New, uh,
00:13:19 --> 00:13:20 Horizons, I think they've all got
00:13:20 --> 00:13:23 magnetometers on board. And the heliosphere
00:13:23 --> 00:13:25 is the Sun's, uh, sphere of
00:13:25 --> 00:13:28 magnetic influence. Uh, and so those magnetic
00:13:29 --> 00:13:31 magnetometers can basically give you.
00:13:32 --> 00:13:34 Give, uh, you an idea of what,
00:13:34 --> 00:13:37 uh, what, you know, what the dimensions of
00:13:37 --> 00:13:40 the heliosphere are. And it's in the
00:13:40 --> 00:13:41 region of.
00:13:44 --> 00:13:46 It's basically
00:13:47 --> 00:13:49 measured in astronomical units. An
00:13:49 --> 00:13:51 astronomical unit is the distance between the
00:13:51 --> 00:13:54 Earth and the sun. Something in the region
00:13:54 --> 00:13:57 of 100 astronomical units,
00:13:59 --> 00:14:02 uh, is the radius. Um, and
00:14:02 --> 00:14:05 so, uh, it's
00:14:05 --> 00:14:07 not spherical. It's got a
00:14:07 --> 00:14:10 peculiar shape, which is probably because
00:14:10 --> 00:14:13 of the sun's motion through
00:14:13 --> 00:14:16 the galaxy's magnetic field. That distorts
00:14:16 --> 00:14:19 the shape of the heliosphere. Uh, but, um,
00:14:19 --> 00:14:22 it's roughly, as I said, a radius
00:14:22 --> 00:14:25 of, uh, about 100 astronomical units. So
00:14:25 --> 00:14:27 what is that? It's 100 times 150. 50 million
00:14:28 --> 00:14:30 kilometers, uh, which
00:14:30 --> 00:14:33 is um, if my
00:14:33 --> 00:14:35 mathematics is right it's about 15 billion.
00:14:35 --> 00:14:38 Is that right? Thereabouts, yeah. 15 billion
00:14:38 --> 00:14:41 kilometers. Something of that size. So it's,
00:14:41 --> 00:14:43 it's and the voyagers uh,
00:14:43 --> 00:14:46 are both uh, further than that
00:14:46 --> 00:14:49 distance and so they have ah,
00:14:49 --> 00:14:52 sensed the edge of the magnetosphere. Uh,
00:14:52 --> 00:14:55 um, we keep seeing headlines.
00:14:55 --> 00:14:57 Um, they're leaving the solar system. Well
00:14:57 --> 00:15:00 that's not really quite the case because the
00:15:00 --> 00:15:02 solar system encompasses the Oort cloud which
00:15:02 --> 00:15:04 is a lot further out. But they are probably
00:15:04 --> 00:15:07 leaving the heliosphere, the region of the
00:15:07 --> 00:15:09 Sun's magnetic influence. And uh, to
00:15:10 --> 00:15:13 answer your question Renny, fully, uh,
00:15:13 --> 00:15:15 yes, uh, sun like stars, like ours would
00:15:15 --> 00:15:18 have a heliosphere. Some stars are far more
00:15:18 --> 00:15:21 magnetic, uh, uh, than the sun is
00:15:21 --> 00:15:23 and so they would probably have a bigger
00:15:23 --> 00:15:25 heliosphere depending on the type of star it
00:15:25 --> 00:15:27 is. Uh, but yet they'll be common to all
00:15:27 --> 00:15:29 stars we think because magnetism plays such a
00:15:29 --> 00:15:31 huge role in the way stars work.
00:15:32 --> 00:15:34 Heidi Campo: Another good high impact question from
00:15:34 --> 00:15:35 Rennie.
00:15:37 --> 00:15:40 Andrew Dunkley: 0G and I feel fine Space nuts.
00:15:40 --> 00:15:43 Heidi Campo: Um, our very last question today is
00:15:43 --> 00:15:45 another audio question and this one is from
00:15:45 --> 00:15:48 Dean in Queensland. And
00:15:48 --> 00:15:50 we are going to go ahead and play the audio
00:15:50 --> 00:15:52 question for you all now.
00:15:52 --> 00:15:55 Andrew Dunkley: Hi Fred, Heidi and Andrea. My question is
00:15:55 --> 00:15:57 about time dilation, but I've had to break it
00:15:57 --> 00:16:00 into three parts. I hope that's okay. First
00:16:00 --> 00:16:03 part concerns um, the Kelly twins, whose ages
00:16:03 --> 00:16:05 diverge slightly because of time dilation
00:16:05 --> 00:16:07 when one of them spent a year on the ISS
00:16:07 --> 00:16:10 orbiting the Earth. I've read that a person
00:16:10 --> 00:16:12 moving at high speed experiences times slower
00:16:12 --> 00:16:15 than a slow moving person. However, speed is
00:16:15 --> 00:16:18 relative. If two people in space were moving
00:16:18 --> 00:16:20 away from each other at a constant rate, then
00:16:20 --> 00:16:23 each one would perceive the other to be the
00:16:23 --> 00:16:25 one doing the moving. In that case, what
00:16:25 --> 00:16:28 determines which one would have the slower
00:16:28 --> 00:16:31 time? This question makes me wonder whether
00:16:31 --> 00:16:33 it's acceleration that causes the time
00:16:33 --> 00:16:36 dilation rather than just speed. This could
00:16:36 --> 00:16:38 explain the Kelly twin's age difference as
00:16:38 --> 00:16:41 the the ISS orbital motion is a form of
00:16:41 --> 00:16:44 acceleration. Plus there was also a linear
00:16:44 --> 00:16:46 acceleration to get into orbit in the first
00:16:46 --> 00:16:49 place. Part two is about the
00:16:49 --> 00:16:51 idea that an object in a high gravity field
00:16:51 --> 00:16:54 experiences time slower than an object in low
00:16:54 --> 00:16:57 gravity. If this is correct, is
00:16:57 --> 00:16:59 it independent from speed induced time
00:16:59 --> 00:17:02 dilation? And could these two effects add
00:17:02 --> 00:17:04 together if an object is
00:17:05 --> 00:17:07 moving very fast and it's within a uh, high
00:17:07 --> 00:17:10 gravity field? Part three is
00:17:10 --> 00:17:12 about uh, descriptions of time
00:17:12 --> 00:17:15 spans in the early uh, universe. Certain
00:17:15 --> 00:17:18 events Are, uh, described as happening within
00:17:18 --> 00:17:20 a specific number of years of the Big Bang.
00:17:21 --> 00:17:24 However, if time runs slower in a high
00:17:24 --> 00:17:26 gravity field, then it must have generally
00:17:26 --> 00:17:29 run slower when all the baryonic matter
00:17:29 --> 00:17:32 in the early universe was densely packed in a
00:17:32 --> 00:17:35 smaller space time. And if that is true,
00:17:35 --> 00:17:38 then the period of 100 years from the Big
00:17:38 --> 00:17:41 Bang would not be equivalent to a period
00:17:42 --> 00:17:45 of 100 years here on Earth. Is that
00:17:45 --> 00:17:47 correct? I probably have a lot of this
00:17:47 --> 00:17:50 wrong. Can you explain it for me? Thanks
00:17:50 --> 00:17:51 again for the podcast.
00:17:52 --> 00:17:55 Professor Fred Watson: Um, Dean, you don't have a lot of it wrong. I
00:17:55 --> 00:17:57 think you've got a lot of it right. Um,
00:17:58 --> 00:18:01 so, um, the first and second parts
00:18:01 --> 00:18:03 of your question, I think really merge into
00:18:03 --> 00:18:05 one. Uh, because I think the difference in
00:18:05 --> 00:18:08 ages with the Kelly twins, I think it was the
00:18:08 --> 00:18:11 gravitational time dilation that was being
00:18:11 --> 00:18:13 taken into account rather than the velocity
00:18:13 --> 00:18:15 time dilation. I'm not sure about that.
00:18:16 --> 00:18:18 Uh, but both of those effect. You're quite
00:18:18 --> 00:18:21 right that accelerations also play a role in
00:18:21 --> 00:18:24 this too. Um, certainly for the
00:18:24 --> 00:18:27 velocity time dilation, it's what allows
00:18:27 --> 00:18:29 the twins paradox to work. Uh, because you've
00:18:29 --> 00:18:31 got accelerations at, uh, the beginning and
00:18:31 --> 00:18:34 end of the twin one twins voyage to
00:18:34 --> 00:18:36 the nearest star and back again.
00:18:37 --> 00:18:40 Um, but yes, the gravitational and,
00:18:40 --> 00:18:43 um, velocity time dilations, they're both
00:18:43 --> 00:18:46 caused by relativity. The two different
00:18:46 --> 00:18:49 relativity theories. Special, uh, relativity
00:18:49 --> 00:18:51 in 1905 talked about velocities.
00:18:52 --> 00:18:54 When you get velocities going near the speed
00:18:54 --> 00:18:56 of light, all kinds of weird things happen,
00:18:56 --> 00:18:59 including the phenomenon of time dilation. A
00:18:59 --> 00:19:01 stationary observer will see somebody else's
00:19:01 --> 00:19:04 clock moving slower, ah, as they whiz by
00:19:04 --> 00:19:06 at nearly the speed of light. And then in,
00:19:07 --> 00:19:09 um, 1915, uh, the
00:19:10 --> 00:19:12 general theory of relativity, which was about
00:19:12 --> 00:19:15 the way gravitation works. And it turns out
00:19:15 --> 00:19:17 that gravity does the same thing. Uh,
00:19:17 --> 00:19:20 gravitational time dilation. If you're in
00:19:20 --> 00:19:22 a gravitational field, your clocks are
00:19:22 --> 00:19:24 running slower than if you're outside it. Um,
00:19:24 --> 00:19:27 and the closer you are, for example,
00:19:27 --> 00:19:29 to the Earth, the slower your clocks will run
00:19:29 --> 00:19:31 compared with somebody who is in orbit. I
00:19:31 --> 00:19:33 think that was the issue with the Kelly twin
00:19:33 --> 00:19:35 winds. Um, it's
00:19:35 --> 00:19:38 microseconds. It's tiny, tiny amount of time.
00:19:38 --> 00:19:40 Uh, when you consider the distance between
00:19:40 --> 00:19:42 the Earth's surface and the height of the
00:19:42 --> 00:19:43 International space station at 400
00:19:43 --> 00:19:46 kilometers, uh, it's a very small difference,
00:19:46 --> 00:19:49 but it is measurable. Um, in fact, I think it
00:19:49 --> 00:19:51 is even measurable, uh, with aircraft. If you
00:19:51 --> 00:19:54 fly an atomic clock on board an aircraft, I
00:19:54 --> 00:19:56 think from a Ground based observer, it looks
00:19:56 --> 00:19:59 as though, um, it's going faster than what
00:19:59 --> 00:20:01 we measure time here on Earth. Uh,
00:20:02 --> 00:20:04 so, um, that's basically sorting
00:20:04 --> 00:20:07 out those issues. Uh, your third part of
00:20:07 --> 00:20:10 the question. It's certainly true that when
00:20:10 --> 00:20:12 we look back at phenomena that are
00:20:12 --> 00:20:15 sort of time tagged, if I can put it that
00:20:15 --> 00:20:17 way, in the early universe, we do see time
00:20:17 --> 00:20:20 dilation. Um, and, uh,
00:20:21 --> 00:20:23 I'm thinking particularly of
00:20:23 --> 00:20:26 supernova explosions where a star
00:20:26 --> 00:20:28 explodes, its brilliance goes up and
00:20:28 --> 00:20:31 then decays slowly afterwards. Uh,
00:20:31 --> 00:20:34 it turns out that you see the decay time
00:20:34 --> 00:20:37 changing from our perspective, uh,
00:20:38 --> 00:20:41 on the gravitational, you know, on
00:20:42 --> 00:20:45 um, Earth, uh, 13.8 or however many
00:20:45 --> 00:20:48 billion years later when we observe
00:20:48 --> 00:20:51 these phenomena. So, um, the same
00:20:51 --> 00:20:54 would be true of, uh, the early universe. And
00:20:54 --> 00:20:55 I think that's taken into account with
00:20:56 --> 00:20:58 people's calculations about this. I think
00:20:58 --> 00:21:01 time dilation falls directly within the
00:21:01 --> 00:21:03 province of cosmologists who understand it
00:21:03 --> 00:21:05 obviously a lot better than, than I do. Um,
00:21:05 --> 00:21:07 but, yeah, that's the bottom line.
00:21:07 --> 00:21:10 Heidi Campo: Yeah. And the time dilation is always, uh,
00:21:10 --> 00:21:12 it's always so hard to wrap your head around,
00:21:12 --> 00:21:14 but you do a great job of explaining it to
00:21:14 --> 00:21:14 us.
00:21:16 --> 00:21:19 Professor Fred Watson: Um, I just try and put it into terms that
00:21:19 --> 00:21:21 I can understand myself, which is not always
00:21:21 --> 00:21:23 the cleverest way to do it, but that's all
00:21:23 --> 00:21:23 right.
00:21:25 --> 00:21:28 Heidi Campo: Well, that, that wraps up all of
00:21:28 --> 00:21:31 our questions for today. Um, Fred,
00:21:31 --> 00:21:33 thank you so much for always being available
00:21:34 --> 00:21:36 to help us out with all of our questions. And
00:21:36 --> 00:21:39 to you, the listeners, please keep sending in
00:21:39 --> 00:21:41 your awesome, well thought out questions. You
00:21:41 --> 00:21:43 guys are really so smart. Every time I read
00:21:43 --> 00:21:45 your questions, I'm like, how are you guys
00:21:45 --> 00:21:47 even thinking of this stuff? Uh, you guys are
00:21:47 --> 00:21:50 brilliant. So keep sending in your
00:21:50 --> 00:21:52 questions. Um, you only have, like I said,
00:21:52 --> 00:21:54 you only have a few more weeks with me before
00:21:54 --> 00:21:57 Andrew is back, and so take advantage
00:21:57 --> 00:21:58 of that.
00:21:58 --> 00:22:01 And I guess without further ado,
00:22:01 --> 00:22:03 Fred, do you want to sign us off? Do you have
00:22:03 --> 00:22:04 anything else you want to say?
00:22:05 --> 00:22:07 Professor Fred Watson: No, just keep the questions coming exactly as
00:22:07 --> 00:22:09 you've said, Heidi. And, uh, thanks again to
00:22:09 --> 00:22:12 all of our great listeners who sent in
00:22:12 --> 00:22:14 questions. Thanks to you, Heidi, for keeping
00:22:14 --> 00:22:17 the show going and we'll, uh, see you next
00:22:17 --> 00:22:20 time. You'll be listening to the
00:22:20 --> 00:22:21 SpaceNuts podcast.
00:22:23 --> 00:22:25 Andrew Dunkley: Available at Apple Podcasts, Spotify,
00:22:25 --> 00:22:28 iHeartRadio, or your favorite podcast
00:22:28 --> 00:22:29 player.
00:22:29 --> 00:22:31 Professor Fred Watson: You can also stream on demand at Bytes.
00:22:31 --> 00:22:34 Com. This has been another quality podcast
00:22:34 --> 00:22:36 production from Bytes. Com.
00:22:36 --> 00:22:37 Heidi Campo: Um.