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Time Travel, Saturn's Rings, and Favourite Planets In this engaging Q&A edition of Space Nuts, hosts Andrew Dunkley and Professor Jonti Horner dive into a series of thought-provoking questions from listeners. From the complexities of moving through time to the intriguing origins of Saturn's rings, this episode is packed with cosmic insights.
Episode Highlights:
- Understanding Time Travel: Rennie from California poses a fascinating question about the nature of time and whether one's lifespan could differ based on their movement through time. Jonty unpacks the concept of time as a dimension, exploring relativity and time dilation.
- The Mystery of Saturn's Rings: Paul from Brisbane asks about the potential for debris from a collision between Saturn’s moons to have impacted Earth 65 million years ago. The discussion delves into the origins of Saturn's rings and the dynamics of celestial collisions.
- Favourite Planets: Dan from the Gold Coast wonders about the hosts' favourite planets in the solar system. Andrew shares his admiration for Mars and its geological wonders, while Jonty contemplates the complexity of Earth and the awe of Jupiter.
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Stay curious, keep looking up, and join us next time for more stellar insights and cosmic wonders. Until then, clear skies and happy stargazing.
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- Introduction to Time Travel
- The Nature of Time and Relativity
- Saturn's Rings and Cosmic Collisions
- The Search for Debris and Impacts
- Favourite Planets: Mars vs. Earth vs. Jupiter
00:00:00 --> 00:00:01 Andrew Dunkley: Hi there. Thanks again for joining us. This
00:00:01 --> 00:00:04 is a Q and A edition of Space Nuts where
00:00:04 --> 00:00:07 we talk astronomy and space science. And in a
00:00:07 --> 00:00:09 Q and A edition, uh, UQ and we
00:00:09 --> 00:00:12 A, uh. Which means we'll answer audience
00:00:12 --> 00:00:14 questions. Uh, today we're going to talk
00:00:14 --> 00:00:17 about, uh, moving through time. What does
00:00:17 --> 00:00:20 that mean? Uh, also some stuff from
00:00:20 --> 00:00:23 Saturn's rings and a sort, uh, of
00:00:23 --> 00:00:25 hypothetical. Not a hypothetical, but a, you
00:00:25 --> 00:00:28 know, uh, not even a what if question. It's
00:00:28 --> 00:00:30 just a question asking our favourite
00:00:30 --> 00:00:33 planets and why. Well, you know, um, that's
00:00:33 --> 00:00:36 Jonty's thing. So we will talk about all of
00:00:36 --> 00:00:38 that on this episode of space nuts.
00:00:38 --> 00:00:41 15 seconds. Guidance is internal.
00:00:41 --> 00:00:44 10, 9, ignition.
00:00:44 --> 00:00:47 Sequence time. Space nuts. 5, 4, 3,
00:00:47 --> 00:00:50 2. 1, 2, 3, 4, 5, 5, 4,
00:00:50 --> 00:00:53 3, 2, 1. Space nuts. Astronauts
00:00:53 --> 00:00:56 report it feels good. And while
00:00:56 --> 00:00:58 Fred Watson's away, Jonty is here to play
00:00:58 --> 00:01:01 and answer your questions. He is Professor
00:01:01 --> 00:01:04 Jonty Horner, professor of Astrophysics at
00:01:04 --> 00:01:06 the University of Southern Queensland. Hello,
00:01:06 --> 00:01:06 Jonny.
00:01:07 --> 00:01:08 Jonti Horner: Hey, how are you going?
00:01:08 --> 00:01:10 Andrew Dunkley: I'm very well. Good to see you again.
00:01:10 --> 00:01:12 Jonti Horner: Well, it's good, yeah. Now, I've got
00:01:12 --> 00:01:13 interesting questions today.
00:01:13 --> 00:01:16 Andrew Dunkley: Yeah, we've got some beauties. Um, we
00:01:16 --> 00:01:18 might get straight into it.
00:01:18 --> 00:01:20 Our first question comes from Rennie, uh, in
00:01:20 --> 00:01:22 sunny West Hills, California. Hi, Rennie.
00:01:22 --> 00:01:24 Rennie's a regular contributor, so we hear
00:01:24 --> 00:01:27 from Ren regularly.
00:01:27 --> 00:01:30 Uh, can you please explain what it means to
00:01:30 --> 00:01:33 be moving through time? If I
00:01:33 --> 00:01:36 theoretically could sit in a chair from birth
00:01:36 --> 00:01:38 to death, will I die on a faster
00:01:38 --> 00:01:41 timeline than someone who lived a regular,
00:01:41 --> 00:01:44 normal life? Uh, is
00:01:44 --> 00:01:47 what's ageing me about the movement of the
00:01:47 --> 00:01:49 Earth around the sun, combined with the sun
00:01:49 --> 00:01:51 moving around the galaxy, combined with the
00:01:51 --> 00:01:53 galaxies moving around each other, and my own
00:01:53 --> 00:01:55 physical movement,
00:01:56 --> 00:01:58 really, that. That's kind of a what if
00:01:58 --> 00:02:00 question. We love what if questions. Thanks.
00:02:00 --> 00:02:03 Uh, Rennie, um, let's open that one up to,
00:02:03 --> 00:02:05 uh, a little bit of, um, investigation.
00:02:06 --> 00:02:08 Jonti Horner: Absolutely. And I think the first thing I'd
00:02:08 --> 00:02:10 say here is, this is such a fun question. It
00:02:10 --> 00:02:13 may be. Well, give it a couple of months and
00:02:13 --> 00:02:15 ask it again and see whether Fred Watson
00:02:15 --> 00:02:17 gives a similar answer to me or not. Um,
00:02:18 --> 00:02:20 it's a really interesting one.
00:02:21 --> 00:02:24 So the idea of time being a
00:02:24 --> 00:02:26 dimension is something that I think makes all
00:02:26 --> 00:02:28 of our heads hurt a little bit when we first
00:02:28 --> 00:02:31 encounter it, and for most of us, continues
00:02:31 --> 00:02:34 to do so forevermore. It's one of
00:02:34 --> 00:02:37 the fundamentals of the idea of what I guess
00:02:37 --> 00:02:38 is often described as space time. Physics
00:02:39 --> 00:02:42 comes out of the work that people like Albert
00:02:42 --> 00:02:44 Einstein did with Relativity
00:02:46 --> 00:02:49 we used to the three physical
00:02:49 --> 00:02:51 three spatial dimensions, up,
00:02:51 --> 00:02:53 down, left, right and forward and back.
00:02:54 --> 00:02:56 Although I, I'm realising more and more that
00:02:56 --> 00:02:59 we actually live in a two, two plus one kind
00:02:59 --> 00:03:02 of existence really, because we don't
00:03:02 --> 00:03:05 look up very often. Part of our common sense
00:03:05 --> 00:03:07 is about two dimensional movement, not three
00:03:07 --> 00:03:08 dimensional, because we think about moving
00:03:08 --> 00:03:10 around on the surface of the Earth. And um,
00:03:10 --> 00:03:12 there's all sorts of weird and fundamental
00:03:12 --> 00:03:15 things with that. Now the idea that time is
00:03:15 --> 00:03:18 also a dimension is part of
00:03:18 --> 00:03:20 that whole thing of space time physics built
00:03:20 --> 00:03:22 into the relativity twins, you know, special
00:03:22 --> 00:03:25 in general. And it's a very weird one because
00:03:25 --> 00:03:28 with the other dimensions we choose
00:03:28 --> 00:03:31 where to move or we're carried along where
00:03:31 --> 00:03:33 we're aware of motion. Motion in a way that
00:03:33 --> 00:03:35 is changing direction, we can change speed,
00:03:35 --> 00:03:38 we feel urgency. But with
00:03:38 --> 00:03:40 time, when you get told that time's a
00:03:40 --> 00:03:42 dimension, you think, but I can't move, I
00:03:42 --> 00:03:45 can't choose my motion in it. Were all
00:03:45 --> 00:03:47 carried through time at 1 second per
00:03:47 --> 00:03:50 second. And um, so it's like a
00:03:50 --> 00:03:52 dimension without agency. It's all a little
00:03:52 --> 00:03:55 bit weird. Now it does
00:03:55 --> 00:03:58 lead to that concept of time as a dimension
00:03:58 --> 00:04:00 is one of the things that's part of the
00:04:00 --> 00:04:02 underpinning of all this stuff, like with
00:04:02 --> 00:04:05 special and general relativity, things like
00:04:05 --> 00:04:08 time dilation, stuff like this. It's
00:04:08 --> 00:04:09 also tied into,
00:04:11 --> 00:04:13 um, events and consequences, See
00:04:13 --> 00:04:16 logical order of things. You know, a cause
00:04:16 --> 00:04:18 has to cause an effect. You don't get the
00:04:18 --> 00:04:20 effect before the cause. Things like this.
00:04:20 --> 00:04:22 Now this
00:04:23 --> 00:04:25 rapidly gets very complicated. And I know at
00:04:25 --> 00:04:27 university, when you study physics as a
00:04:27 --> 00:04:29 partner to astronomy or you study, um,
00:04:29 --> 00:04:32 relative relativity as part of an astronomy
00:04:32 --> 00:04:35 thing, I'll know. A lot of people find it
00:04:35 --> 00:04:36 hugely challenging to get their head around
00:04:36 --> 00:04:39 it. And I will openly admit that when I did
00:04:39 --> 00:04:42 my relativity courses as an undergrad, my
00:04:42 --> 00:04:43 head hurt was really, really hard. And
00:04:43 --> 00:04:45 particularly in first year, special
00:04:45 --> 00:04:48 relativity didn't work for me. And it's
00:04:48 --> 00:04:50 something I always say to my students,
00:04:50 --> 00:04:51 something I'm very aware of and something
00:04:51 --> 00:04:54 I've said to listeners is that no one
00:04:54 --> 00:04:57 explanation will work for everybody. We
00:04:57 --> 00:04:59 all learn in different ways and one source
00:04:59 --> 00:05:00 that is brilliant for me might not be
00:05:00 --> 00:05:02 brilliant for you. So if my explanation
00:05:02 --> 00:05:04 doesn't work, please go out and seek another
00:05:04 --> 00:05:06 one. That's no slight on me. It just means
00:05:06 --> 00:05:07 that your way of learning and my way of
00:05:07 --> 00:05:09 explaining didn't m match in that case and
00:05:09 --> 00:05:12 another explanation is needed. And when it
00:05:12 --> 00:05:14 came to relativity, I was very much in that
00:05:14 --> 00:05:17 boat. I was sat in These lectures and this is
00:05:17 --> 00:05:19 all style education 30 years ago. And it
00:05:19 --> 00:05:22 actually is that 29 and a half years ago that
00:05:22 --> 00:05:23 I was in these lectures because it was late
00:05:23 --> 00:05:26 1996, sat there taking notes on
00:05:26 --> 00:05:28 paper while somebody's talking at you and
00:05:28 --> 00:05:29 writing on a board. So a lot of the
00:05:29 --> 00:05:31 information was going from my eyes to the
00:05:31 --> 00:05:33 page without going through my brain I
00:05:33 --> 00:05:35 suspect, you know, that autonomous writing
00:05:35 --> 00:05:38 thing. But it just wasn't gelling for me. The
00:05:38 --> 00:05:41 whole the equations are ah, written down
00:05:41 --> 00:05:43 so you can use them, but it wasn't making
00:05:43 --> 00:05:45 sense. And the course textbook we had was
00:05:45 --> 00:05:47 incredibly mathematical because
00:05:48 --> 00:05:51 the person who wrote the textbook understood
00:05:51 --> 00:05:53 it through the maths, so they explained it
00:05:53 --> 00:05:54 through the maths. And that's not the way
00:05:54 --> 00:05:56 that I learned. Some people learn brilliantly
00:05:56 --> 00:05:59 from maths. I don't. I'm much more of a
00:05:59 --> 00:06:02 visual form of pitch form, a metaphor type
00:06:02 --> 00:06:04 thinker than an equation is a be all and end
00:06:04 --> 00:06:06 all sorts of. About the only
00:06:06 --> 00:06:09 textbook I ever used in my undergrad days. I
00:06:09 --> 00:06:11 was terrible. I'd buy the textbooks, not open
00:06:11 --> 00:06:13 them and I'd sell them on at the end of the
00:06:13 --> 00:06:15 trimester, end of the term for someone else
00:06:15 --> 00:06:16 to take off me and probably do the same
00:06:16 --> 00:06:19 thing. But I found a textbook in the library
00:06:19 --> 00:06:21 that worked for me and ended up buying it.
00:06:21 --> 00:06:22 Now I was going to recommend it because it
00:06:22 --> 00:06:25 was so foundational in helping me to
00:06:25 --> 00:06:28 overcome something I couldn't understand.
00:06:28 --> 00:06:29 That I always think when people are
00:06:29 --> 00:06:31 struggling with the relativity stuff. Worth
00:06:31 --> 00:06:33 recommending it. It's a big book called Space
00:06:33 --> 00:06:36 Time Physics by Edwin F. Taylor and ah,
00:06:36 --> 00:06:39 John Archibald Wheeler. And to my shock I
00:06:39 --> 00:06:41 looked it up just before this podcast. Um,
00:06:41 --> 00:06:43 the first edition was published in 1965.
00:06:44 --> 00:06:47 So the first edition was born, was
00:06:47 --> 00:06:50 launched closer to the publishing of the
00:06:50 --> 00:06:52 theory of general relativity and the theory
00:06:52 --> 00:06:54 of Special relativity than my reading it.
00:06:55 --> 00:06:58 Um, certainly than we are today, should I
00:06:58 --> 00:07:00 say? Absolutely than we are today. Um, it is
00:07:00 --> 00:07:03 still in print and what worked for me was ah,
00:07:03 --> 00:07:05 it didn't go straight to the maths. Instead
00:07:05 --> 00:07:07 it used drawings and figures and thought
00:07:07 --> 00:07:10 experiments. And I read it voraciously.
00:07:10 --> 00:07:12 It was very readable. I remember it from 30
00:07:12 --> 00:07:13 years ago and it had an impact. So I'd really
00:07:13 --> 00:07:15 recommend that if you're struggling with the
00:07:15 --> 00:07:17 relativity stuff, um, go to your local
00:07:17 --> 00:07:19 library. The textbooks are punishingly
00:07:19 --> 00:07:22 expensive and um, therefore I'd always
00:07:22 --> 00:07:24 recommend people get them from library first
00:07:24 --> 00:07:27 and make absolutely sure. But if you're at
00:07:27 --> 00:07:29 all interested in those foundations of how
00:07:30 --> 00:07:33 relativity and everything works. I found that
00:07:33 --> 00:07:35 book Astonishing. Okay, that's all getting a
00:07:35 --> 00:07:38 bit off the topic though, but that explains a
00:07:38 --> 00:07:40 lot better than I could do. The concepts
00:07:40 --> 00:07:43 behind relativity that include time as a
00:07:43 --> 00:07:46 dimension include space time diagrams, which
00:07:46 --> 00:07:48 are these weird cone shaped figures where
00:07:49 --> 00:07:51 if you're travelling at the speed of light,
00:07:51 --> 00:07:54 you move the same distance in X, which is
00:07:54 --> 00:07:56 distance, as you do in time Y. So you get a
00:07:56 --> 00:07:58 cone opened out like this and everything
00:07:58 --> 00:08:00 inside that cone is moving slower than the
00:08:00 --> 00:08:02 speed of light because it's going up the Y
00:08:02 --> 00:08:04 axis quicker than it goes on the X axis.
00:08:05 --> 00:08:08 Anything that is nearer to the X axis of
00:08:08 --> 00:08:11 that line is further away from the observer
00:08:11 --> 00:08:13 than they could observe it yet. So any light
00:08:13 --> 00:08:15 that left that would not have reached you yet
00:08:16 --> 00:08:18 now hard to visualise. But if you look into
00:08:18 --> 00:08:21 the book, that is what it means.
00:08:21 --> 00:08:23 Now, moving in time is
00:08:24 --> 00:08:26 talking about our motion on the Y axis of
00:08:26 --> 00:08:29 that graph, where we move up it by one second
00:08:29 --> 00:08:32 every second. That is something
00:08:32 --> 00:08:34 over which we do not really have control.
00:08:35 --> 00:08:38 Um, I suspect some people would argue that
00:08:38 --> 00:08:40 certain substances that can be ingested
00:08:40 --> 00:08:42 change your perception of how time loads. So
00:08:42 --> 00:08:43 you might be able to control the speed you
00:08:43 --> 00:08:46 fly through it there. But that's what we mean
00:08:46 --> 00:08:49 by moving in time. It's perceiving time
00:08:50 --> 00:08:53 moving forward so that from one second to
00:08:53 --> 00:08:56 the next, change happens. You know,
00:08:56 --> 00:08:58 yesterday is a time in the past that's
00:08:58 --> 00:09:00 already happened. That's a cause you'll see
00:09:00 --> 00:09:02 the effects today. Tomorrow hasn't happened
00:09:02 --> 00:09:05 yet. You can't see what is there tomorrow.
00:09:05 --> 00:09:07 That's what it means by moving in time. And
00:09:07 --> 00:09:10 it. There's all sorts of wonderful ways
00:09:10 --> 00:09:12 people have described it or played with this
00:09:12 --> 00:09:13 again. You know, I often come back to the
00:09:13 --> 00:09:15 Terry Pratchett stuff and I was just looking
00:09:15 --> 00:09:16 at a thread the other day of people talking
00:09:16 --> 00:09:18 about their favourite Terry Pratchett quotes.
00:09:18 --> 00:09:20 I'll just try and pull this one up.
00:09:20 --> 00:09:23 Um, it's from when the eternal
00:09:23 --> 00:09:26 is surprised. Uh, who was the founder of the
00:09:26 --> 00:09:29 History Monks, um, basically
00:09:29 --> 00:09:31 talking about his perception of time. So I'm,
00:09:31 --> 00:09:33 you know. MAN LOOKS AT KEYBOARD Because I
00:09:33 --> 00:09:35 didn't think of doing this. But yeah, this is
00:09:36 --> 00:09:38 from Thief of Time, I think it was. Yes.
00:09:39 --> 00:09:41 Um, talking about how when
00:09:41 --> 00:09:43 viewed the universe and viewed moving through
00:09:43 --> 00:09:46 time as this ancient philosopher who set
00:09:46 --> 00:09:49 up the Monks of History, who are the people
00:09:49 --> 00:09:51 who run around unseen in the background,
00:09:51 --> 00:09:53 fixing things when they go wrong. Because in
00:09:53 --> 00:09:55 the Discworld they go wrong all the time. But
00:09:55 --> 00:09:58 says when considered the nature of time
00:09:59 --> 00:10:01 and understood that the universe is instant
00:10:01 --> 00:10:04 by instant, Recreated anew. Therefore, he
00:10:04 --> 00:10:06 understood there is, in truth, no past, only
00:10:06 --> 00:10:09 a memory of the past. Blink your eyes and the
00:10:09 --> 00:10:10 world you see next did not exist when you
00:10:10 --> 00:10:13 closed them. Therefore, he said, the only
00:10:13 --> 00:10:15 appropriate state of the mind is surprise.
00:10:16 --> 00:10:17 The only appropriate state of the heart is
00:10:17 --> 00:10:20 joy. The sky you see now you have never
00:10:20 --> 00:10:21 seen before.
00:10:21 --> 00:10:24 The perfect moment is now. Be glad of it.
00:10:25 --> 00:10:25 Andrew Dunkley: That's good.
00:10:25 --> 00:10:27 Jonti Horner: I talk about Pratchett a lot, but I always
00:10:27 --> 00:10:29 think that's really beautiful. And it fits in
00:10:29 --> 00:10:31 with this concept of time
00:10:32 --> 00:10:34 moving irrevocably forward. You can never
00:10:34 --> 00:10:36 return to the past and change things. What
00:10:36 --> 00:10:39 you can change is the future. When you
00:10:39 --> 00:10:42 wake up every morning, it says, though you're
00:10:42 --> 00:10:44 newborn into the universe effectively,
00:10:45 --> 00:10:47 because who is to say that you ever lived
00:10:47 --> 00:10:49 before? You know, it may well be that all of
00:10:49 --> 00:10:51 your memories were just implanted in you when
00:10:51 --> 00:10:53 you woke up this very instant. We don't know.
00:10:53 --> 00:10:56 Obviously, the Occam's Razor
00:10:56 --> 00:10:58 argument is, yes, you existed yesterday and
00:10:58 --> 00:11:01 we did do the record the other day. But it's
00:11:01 --> 00:11:03 interesting to think of that and it's the way
00:11:03 --> 00:11:04 that people perceive time.
00:11:06 --> 00:11:07 Now, moving on to the motion side of it,
00:11:07 --> 00:11:10 Renny M. Um, the idea of sitting in a chair
00:11:10 --> 00:11:13 from birth to death and how that would affect
00:11:13 --> 00:11:15 your life. I'm not a medic, but I suspect if
00:11:15 --> 00:11:17 you ask your doctor that question, they will
00:11:17 --> 00:11:20 probably tell you that indeed, if you sat in
00:11:20 --> 00:11:22 a chair from birth to death, your life would
00:11:22 --> 00:11:23 be shorter than if you lived a normal life as
00:11:23 --> 00:11:26 a person because of health reasons. I mean,
00:11:26 --> 00:11:27 if nothing else, if there's no one around to
00:11:27 --> 00:11:29 feed you, it might lead to a relatively short
00:11:29 --> 00:11:32 existence. So there is that aspect of
00:11:32 --> 00:11:35 it as well. We can't see the
00:11:35 --> 00:11:37 future, so we can't predict what our choices
00:11:37 --> 00:11:39 are going to do in terms of lengthening or
00:11:39 --> 00:11:41 shortening our lives. But there is one way in
00:11:41 --> 00:11:44 which your motion can lead to you having a
00:11:44 --> 00:11:46 slightly different timeline.
00:11:47 --> 00:11:49 So from the point of view of your life, or
00:11:49 --> 00:11:50 the number of beats of your heart, or your
00:11:50 --> 00:11:53 perceived time, you'll live the time that you
00:11:53 --> 00:11:55 live. The faster you're moving though. Ah,
00:11:56 --> 00:11:58 and this is an outcome of general relativity.
00:11:59 --> 00:12:01 Motion causes time dilation,
00:12:02 --> 00:12:04 particularly motion with acceleration. You
00:12:04 --> 00:12:06 know, there's loads and loads of complexity
00:12:06 --> 00:12:09 to this. If you were moving
00:12:09 --> 00:12:12 faster, the time you
00:12:12 --> 00:12:14 perceive is very slightly slower. Now
00:12:15 --> 00:12:17 you then get into rest frames and all that
00:12:17 --> 00:12:19 stuff makes my head hurt. So the only place
00:12:19 --> 00:12:21 this actually really becomes relevant,
00:12:21 --> 00:12:24 particularly in our day to day lives, in
00:12:24 --> 00:12:27 our lived experience, is when you've got a
00:12:27 --> 00:12:28 moving platform that's changing direction so
00:12:28 --> 00:12:31 it's undergoing acceleration. Think about
00:12:32 --> 00:12:35 satellites circling the Earth. They uh, are
00:12:35 --> 00:12:36 circling the Earth, they are moving at uh, a
00:12:36 --> 00:12:39 faster speed than we are here on the surface
00:12:39 --> 00:12:42 of the Earth. We however are slightly nearer
00:12:42 --> 00:12:43 the centre of the Earth. So we get a little
00:12:43 --> 00:12:46 bit of gravitational time dilation. As I
00:12:46 --> 00:12:48 understand it, our clock runs slightly
00:12:48 --> 00:12:50 slower because we're at the bottom of a
00:12:50 --> 00:12:52 gravity well. But that is hugely overcome by
00:12:52 --> 00:12:54 the fact of the high speed things are moving
00:12:54 --> 00:12:56 in orbit. You're talking several kilometres
00:12:56 --> 00:12:59 per second. Now under
00:13:00 --> 00:13:03 general and special relativity you can work
00:13:03 --> 00:13:05 out the number of seconds you experience per
00:13:05 --> 00:13:08 second that ticks in a certain rest frame
00:13:08 --> 00:13:10 using these equations to get the time
00:13:10 --> 00:13:13 dilation. And typically that is a
00:13:13 --> 00:13:15 vanishingly, vanishingly small effect unless
00:13:15 --> 00:13:17 you get very near the speed of light, then it
00:13:17 --> 00:13:20 ramps up. But it is a large enough effect
00:13:20 --> 00:13:23 that both we need to understand
00:13:23 --> 00:13:24 it and we can measure it
00:13:26 --> 00:13:28 now to illustrate the level of this. It's not
00:13:28 --> 00:13:30 a huge effect. There's a fabulous stat
00:13:31 --> 00:13:33 that there are people who spent time on the
00:13:33 --> 00:13:35 International Space Station who therefore
00:13:35 --> 00:13:37 technically have experienced less time
00:13:37 --> 00:13:39 passing while they were up there than we did
00:13:39 --> 00:13:41 on the ground watching them because of time
00:13:41 --> 00:13:43 dilation, because of their fast movement and
00:13:43 --> 00:13:45 their acceleration and all the rest of it.
00:13:45 --> 00:13:47 Space stations go around the Earth, what,
00:13:47 --> 00:13:50 nearly eight kilometres per second, roughly.
00:13:50 --> 00:13:52 A couple of Russian guys were up there for
00:13:52 --> 00:13:54 six months, Sergei Krikalev and
00:13:54 --> 00:13:57 Sergey Avdeev. They did six months
00:13:57 --> 00:14:00 up there and as a result of time
00:14:00 --> 00:14:03 dilation, when they returned to the surface
00:14:03 --> 00:14:05 of the Earth, they would have experienced
00:14:05 --> 00:14:07 less time passing than the people on the
00:14:07 --> 00:14:09 ground did while they were up there. Yeah,
00:14:09 --> 00:14:11 but not enough for them to perceive. It would
00:14:11 --> 00:14:14 have been 20 milliseconds. Right. Uh, so
00:14:14 --> 00:14:16 that's 0.02 seconds, um,
00:14:16 --> 00:14:19 21th of a second. It's not very much,
00:14:19 --> 00:14:22 but it has a huge impact on our day to day
00:14:22 --> 00:14:25 life. And this means that that
00:14:25 --> 00:14:27 part of the theories of relativity
00:14:28 --> 00:14:31 are among the most tested theories ever
00:14:31 --> 00:14:32 to have been developed by humans. And the
00:14:32 --> 00:14:35 reason I say that is that every time you use
00:14:35 --> 00:14:37 your generic fruit based device to
00:14:37 --> 00:14:40 navigate, anytime you use a sat nav, you're
00:14:40 --> 00:14:42 using GPS satellites.
00:14:43 --> 00:14:45 GPS satellites orbiting the ah, Earth
00:14:46 --> 00:14:48 allow you to work out your position on a
00:14:48 --> 00:14:50 basic level. Because at any time your device
00:14:51 --> 00:14:54 can, can see signals from a number of those
00:14:54 --> 00:14:56 satellites and
00:14:57 --> 00:14:59 figure out where they are. There are clocks
00:14:59 --> 00:15:01 on board all of them. You know, it can figure
00:15:01 --> 00:15:03 out the light travel time to get to it by
00:15:03 --> 00:15:05 seeing the time that they're broadcasting,
00:15:05 --> 00:15:08 knowing what your local time is, figuring out
00:15:08 --> 00:15:09 the difference between the two, you know, how
00:15:09 --> 00:15:11 far away the satellite is from one of them
00:15:11 --> 00:15:13 that places you at any point on a sphere
00:15:13 --> 00:15:14 around that satellite that is, uh, that
00:15:14 --> 00:15:17 distance away. From a second satellite,
00:15:17 --> 00:15:18 you've got another sphere on your way, they
00:15:18 --> 00:15:21 intersect, which gives you a line, and then
00:15:21 --> 00:15:23 a third one brings it down to a point. And
00:15:23 --> 00:15:25 the more you have, the more accurate you get.
00:15:26 --> 00:15:28 So this is all based on measurement of time,
00:15:29 --> 00:15:32 allowing you to measure distance for things
00:15:32 --> 00:15:35 that are a known distance away. This only
00:15:35 --> 00:15:37 works. So, uh, if you can take into account
00:15:37 --> 00:15:39 the way that the clocks are ticking at
00:15:39 --> 00:15:41 different speeds because the satellites are
00:15:41 --> 00:15:43 moving in orbit around the Earth, the
00:15:43 --> 00:15:45 difference, uh, including
00:15:46 --> 00:15:49 relativistic effects and time dilation into
00:15:49 --> 00:15:52 the calculations for GPS has, my
00:15:52 --> 00:15:54 understanding, is it's between a factor of 10
00:15:54 --> 00:15:56 and a factor of 100 on the precision with
00:15:56 --> 00:15:59 which your location can be calculated.
00:15:59 --> 00:16:01 And your GPS is usually good to probably
00:16:01 --> 00:16:03 about a metre. I think some of the modern
00:16:03 --> 00:16:05 ones are even more accurate than that. So if
00:16:05 --> 00:16:07 you imagine that, let's take the really
00:16:07 --> 00:16:09 optimistic case that you're only getting a
00:16:09 --> 00:16:11 factor of 10 improvement by including
00:16:11 --> 00:16:13 relativity at the minute, you've got an
00:16:13 --> 00:16:15 accuracy of one metre and that's good enough
00:16:15 --> 00:16:16 for you to navigate. With 10 metres, it
00:16:16 --> 00:16:19 probably wouldn't be. With 100 metres, it
00:16:19 --> 00:16:21 certainly wouldn't be. So our GPS
00:16:21 --> 00:16:24 systems only work
00:16:25 --> 00:16:27 because of our level of understanding of
00:16:27 --> 00:16:30 relativistic motion and of time dilation.
00:16:30 --> 00:16:33 So those satellites moving very, very quickly
00:16:33 --> 00:16:36 around the Earth are
00:16:36 --> 00:16:37 experiencing an M infinitesimally small
00:16:37 --> 00:16:39 amount of time dilation compared to the
00:16:39 --> 00:16:40 things they're broadcasting to on the
00:16:40 --> 00:16:43 surface. And we have to factor that in into
00:16:43 --> 00:16:45 our calculations to navigate. So your SAT nav
00:16:45 --> 00:16:48 wouldn't work without the theorems that
00:16:48 --> 00:16:50 Albert Einstein put together more than a
00:16:50 --> 00:16:53 century ago that are all about how things
00:16:53 --> 00:16:54 move through time.
00:16:54 --> 00:16:54 Andrew Dunkley: Yeah.
00:16:54 --> 00:16:57 Jonti Horner: So hopefully that has answered that question.
00:16:57 --> 00:16:59 I think. Rennie, I would be very tempted to
00:16:59 --> 00:17:01 suggest that at some point you try and get
00:17:01 --> 00:17:03 Friend to answer that as well, just to see
00:17:03 --> 00:17:06 where he took it. Um, but hopefully that at
00:17:06 --> 00:17:07 least is helpful. And like I say, if the
00:17:07 --> 00:17:09 relativistic stuff really interests you,
00:17:10 --> 00:17:11 space time physics, even though it's a book
00:17:11 --> 00:17:14 that was first published 60 years ago, I
00:17:14 --> 00:17:16 found invaluable in getting me through the
00:17:16 --> 00:17:18 exams and actually allowing me to get out of
00:17:18 --> 00:17:20 my first year and pass rather than being
00:17:20 --> 00:17:21 kicked out of uni. So it was a great book.
00:17:22 --> 00:17:25 Andrew Dunkley: Uh, Rennie might also like to Go on
00:17:25 --> 00:17:27 Wikipedia or any number of platforms and look
00:17:27 --> 00:17:30 up the twin paradox. That's a fun one. That's
00:17:30 --> 00:17:32 a great thought experiment. And I think there
00:17:32 --> 00:17:35 were twin astronauts that have,
00:17:35 --> 00:17:37 uh, had a little bit of a separation in age
00:17:37 --> 00:17:40 because one of them spent much more time in
00:17:40 --> 00:17:43 space than his bro. So um, their
00:17:43 --> 00:17:46 age difference uh, increased by
00:17:46 --> 00:17:48 8.6 milliseconds or something.
00:17:48 --> 00:17:51 Jonti Horner: Something like that I've seen. Really
00:17:51 --> 00:17:54 interesting. There are a couple of. Well,
00:17:54 --> 00:17:55 there are many science fiction books that
00:17:56 --> 00:17:58 play around this. I've spoken before about
00:17:58 --> 00:17:59 this series of science fiction books called
00:17:59 --> 00:18:02 the Mass Works of Science Fiction, which was
00:18:02 --> 00:18:03 an attempt by a publisher to make money
00:18:03 --> 00:18:06 obviously, but also to bring back some
00:18:06 --> 00:18:08 classic science fiction that is regarded as
00:18:08 --> 00:18:11 being very good. And you know, some of the
00:18:11 --> 00:18:12 things I read are very fun, but they're not
00:18:12 --> 00:18:14 necessarily very good. You know, there's
00:18:14 --> 00:18:16 always that side of things. And I'd say the
00:18:16 --> 00:18:18 Chrysalis books I'm reading at the minute the
00:18:18 --> 00:18:20 guy incarnated into the body of an ant,
00:18:20 --> 00:18:22 that's very good fun. I'm really loving it.
00:18:22 --> 00:18:24 But I wouldn't necessarily say they're high
00:18:24 --> 00:18:26 literature, they're fun. The um, Pratchett
00:18:26 --> 00:18:28 stuff is a bit of both. But these mass works
00:18:28 --> 00:18:31 of science fiction are often fascinating
00:18:31 --> 00:18:32 because they are
00:18:34 --> 00:18:36 quite often hard sci fi. So in other words,
00:18:36 --> 00:18:37 they're science fiction that is grounded in
00:18:37 --> 00:18:39 our understanding of science at the time they
00:18:39 --> 00:18:42 were written and tried to use uh, the
00:18:42 --> 00:18:45 laws of physics to help build the narrative
00:18:45 --> 00:18:47 rather than waving the laws of physics to
00:18:47 --> 00:18:48 allow the narrative. You know, there's a
00:18:48 --> 00:18:50 fundamental difference between the soft and
00:18:50 --> 00:18:53 woolly type I and the hard scientific sci fi.
00:18:53 --> 00:18:56 And two books in particular that leap to mind
00:18:56 --> 00:18:57 when we're talking about time dilation and
00:18:57 --> 00:19:00 relativity and things like that are uh, the
00:19:00 --> 00:19:02 Forever War by Joe Haberman, I think his name
00:19:02 --> 00:19:05 was. I'll just put that name up. The Forever
00:19:05 --> 00:19:07 War, um, was basically,
00:19:08 --> 00:19:11 yeah, Joe Halderman. Um, the idea that
00:19:11 --> 00:19:13 there is, um, written in
00:19:13 --> 00:19:16 1974, it's called Military science fiction.
00:19:16 --> 00:19:18 And um, the idea is humans are fighting an
00:19:18 --> 00:19:20 interstellar war against these alien
00:19:20 --> 00:19:22 civilization and they're sent off on
00:19:22 --> 00:19:24 missions, on spacecraft that travel at
00:19:24 --> 00:19:25 relativistic speed because it takes a hell of
00:19:25 --> 00:19:27 a long time to get anywhere. And it's not
00:19:27 --> 00:19:29 really about what they do when they get
00:19:29 --> 00:19:30 there, it's about what they do when they come
00:19:30 --> 00:19:32 back. Because the time you've gone there and
00:19:32 --> 00:19:35 come back, the Earth has moved on hugely. You
00:19:35 --> 00:19:37 know, you've been away for five years, but
00:19:37 --> 00:19:40 uh, Earth has skipped forward 100 years. Can
00:19:40 --> 00:19:43 you reintegrate how a society changed? And
00:19:43 --> 00:19:45 I think it's fair to say that without a
00:19:45 --> 00:19:48 spoiler, the motivation is, uh, you've more
00:19:48 --> 00:19:49 in common with the people you've lived that
00:19:49 --> 00:19:51 experience with than you do with everybody
00:19:51 --> 00:19:53 else. And it's all about
00:19:54 --> 00:19:57 that, grounded in this knowledge of
00:19:57 --> 00:20:00 time delay. Have travelled there and back
00:20:00 --> 00:20:01 again and come back to a world that has
00:20:01 --> 00:20:04 changed. The other one that really stuck in
00:20:04 --> 00:20:07 my mind as a interesting way to get
00:20:07 --> 00:20:08 your head around time dilation is a book
00:20:08 --> 00:20:11 called Tal's Era by Poole Anderson. And I
00:20:11 --> 00:20:12 think that was published even longer ago. I
00:20:12 --> 00:20:15 think it was probably in the 1950s. And, um,
00:20:15 --> 00:20:16 part of the reason I can say that is that
00:20:16 --> 00:20:19 that book, I believe, predates the
00:20:19 --> 00:20:22 Big Bang Theory, um, or, uh, it's around the
00:20:22 --> 00:20:25 time of the Big Bang Theory. It's, um, based
00:20:25 --> 00:20:27 on a short storey, published in 1967. The
00:20:27 --> 00:20:30 book itself was published in 1970. So it's
00:20:30 --> 00:20:32 a fabulous exploration
00:20:32 --> 00:20:35 of. It was actually post Big Bang, but it's
00:20:35 --> 00:20:38 a fabulous exploration of relativity in an
00:20:38 --> 00:20:40 unusual circumstance. In this case, it was
00:20:40 --> 00:20:43 people being the first humans to travel to
00:20:43 --> 00:20:45 the stars on a spaceship that was meant to go
00:20:45 --> 00:20:48 to a star and then come back and
00:20:48 --> 00:20:51 report, um, they were aiming to reach Beta
00:20:51 --> 00:20:54 Virginis. It says, crew of 50, 25 men,
00:20:54 --> 00:20:56 25 women, using something called a Bussad
00:20:56 --> 00:20:59 ramjet. So you have basically a rocket that
00:20:59 --> 00:21:01 scoops up fuel and burns it to go faster and
00:21:01 --> 00:21:04 faster. Right. Um, but there's a
00:21:04 --> 00:21:06 problem. They get up to high speed and then
00:21:06 --> 00:21:07 something breaks. But they're going so quick
00:21:07 --> 00:21:09 that they can't get outside of the spacecraft
00:21:09 --> 00:21:12 to fix it. And so they just have to go
00:21:12 --> 00:21:14 quicker and quicker. And so it
00:21:14 --> 00:21:17 explores this captive group of 50 people
00:21:18 --> 00:21:20 on an island in the universe that cannot
00:21:20 --> 00:21:23 stop, can only go quicker and quicker as the
00:21:23 --> 00:21:25 universe moves around them. And of course, by
00:21:25 --> 00:21:27 continually accelerating, they get closer and
00:21:27 --> 00:21:29 closer to the speed of light and time
00:21:29 --> 00:21:31 dilation impacts them more and more. So they
00:21:31 --> 00:21:34 see the universe to the end of the
00:21:34 --> 00:21:36 universe and beyond within a
00:21:36 --> 00:21:39 human lifetime. And, you know, the cosmology
00:21:39 --> 00:21:41 in it has changed. It was at a time where the
00:21:41 --> 00:21:43 Big Bang, a lot of people thought would end
00:21:43 --> 00:21:44 up in a Big Crunch. Everything will stop
00:21:44 --> 00:21:47 expanding, fall back together. But it's
00:21:47 --> 00:21:50 again, this awesome way of
00:21:50 --> 00:21:52 demonstrating how
00:21:53 --> 00:21:56 relativistic terms work. And the crew on the
00:21:56 --> 00:21:57 mission, before anything went wrong, were
00:21:57 --> 00:21:59 aware that when they returned to earth,
00:22:00 --> 00:22:02 something like 33 years would have passed
00:22:02 --> 00:22:04 before they get to their destination. They
00:22:04 --> 00:22:06 star but for them, only five years would have
00:22:06 --> 00:22:08 passed. So when they turn around and come
00:22:08 --> 00:22:10 home, they'll have aged 10 years, but 66
00:22:10 --> 00:22:11 years would have passed on Earth, give or
00:22:11 --> 00:22:12 take. Yeah.
00:22:12 --> 00:22:12 Andrew Dunkley: That's.
00:22:12 --> 00:22:14 Jonti Horner: In fact, that doesn't happen. Wonderful book.
00:22:14 --> 00:22:17 Andrew Dunkley: Yeah, I love those sorts of
00:22:17 --> 00:22:20 storeys. I love time travel, sci fi
00:22:20 --> 00:22:22 and uh, um, all those
00:22:23 --> 00:22:26 relativistic concepts. Uh, I,
00:22:26 --> 00:22:28 Yeah, I'm actually just finished writing a
00:22:28 --> 00:22:30 trilogy and I'm just getting it proofread at
00:22:30 --> 00:22:31 the moment. Um.
00:22:31 --> 00:22:32 Jonti Horner: Oh, fabulous.
00:22:32 --> 00:22:34 Andrew Dunkley: There's a little bit of that in it, but I'm
00:22:34 --> 00:22:35 not giving anything away.
00:22:35 --> 00:22:38 Jonti Horner: So maybe without, without any spoilers at
00:22:38 --> 00:22:40 all, that in a few years time maybe I'll be
00:22:40 --> 00:22:41 picking up your books as part of the
00:22:41 --> 00:22:43 masterworks of science fiction.
00:22:43 --> 00:22:45 Andrew Dunkley: You might. That'd be nice, wouldn't it?
00:22:45 --> 00:22:46 Jonti Horner: No pressure.
00:22:46 --> 00:22:48 Andrew Dunkley: No. Well, okay.
00:22:49 --> 00:22:52 Thanks, Rennie. Um, enjoyed that question.
00:22:52 --> 00:22:54 It's a, it's a fun one to talk about. This is
00:22:54 --> 00:22:56 Space Nuts with Andrew Dunkley and Professor
00:22:56 --> 00:22:56 Johnty H.
00:22:59 --> 00:23:01 I think we need to do a little more all
00:23:01 --> 00:23:03 weather testing. Amen, Space
00:23:03 --> 00:23:04 Nuts.
00:23:05 --> 00:23:07 Our next question, Jonty, comes from Paul in
00:23:07 --> 00:23:09 Brisbane. Although he, uh, doesn't call it
00:23:09 --> 00:23:11 Brisbane. You've probably heard this term
00:23:11 --> 00:23:14 because you live so close to Brisbane, but
00:23:14 --> 00:23:17 overseas people might think, what on earth is
00:23:17 --> 00:23:19 he talking about? G', day, Space Nuts. Paul,
00:23:19 --> 00:23:22 uh, from sunny Bris Vegas, uh, here.
00:23:23 --> 00:23:25 And he's thrown a challenge at me. Before I
00:23:25 --> 00:23:28 ask my question, could you read it in a
00:23:28 --> 00:23:30 Queensland accent to make it sound
00:23:30 --> 00:23:32 authentic? Andrew Tar.
00:23:33 --> 00:23:35 I'll give it a go, Paul, but you know, it's
00:23:35 --> 00:23:37 been a long time since I lived in Queensland.
00:23:38 --> 00:23:40 I was thinking, just listening in
00:23:40 --> 00:23:43 episode 681, when you and
00:23:43 --> 00:23:46 Fred Watson started talking, uh, about the
00:23:46 --> 00:23:48 possibility of Titan and Hypernian,
00:23:49 --> 00:23:52 uh, Hyperion collide and uh, thus creating
00:23:52 --> 00:23:54 Saturn's rings 100 million years ago.
00:23:55 --> 00:23:58 What do you reckon the odds are of
00:23:58 --> 00:24:01 some of the bigger blocks of the collision
00:24:01 --> 00:24:03 spinning off into space, uh, getting
00:24:03 --> 00:24:06 closer to the sun, I don't know, colliding
00:24:06 --> 00:24:09 with the Earth, say, 65 million years
00:24:09 --> 00:24:11 ago? Is that a possibility?
00:24:11 --> 00:24:14 Or does the chemical residue from
00:24:14 --> 00:24:17 on here on Earth, uh, suggest there's more
00:24:17 --> 00:24:19 likely to have been a comet?
00:24:19 --> 00:24:22 Curious to get your thoughts on this, eh? Uh,
00:24:22 --> 00:24:25 as always, keep up the great work and
00:24:25 --> 00:24:28 thank you. Was that
00:24:28 --> 00:24:29 Queenslandish enough?
00:24:30 --> 00:24:31 Jonti Horner: Uh, see, I struggled. So the accent thing.
00:24:31 --> 00:24:33 And again, we're very good at getting off
00:24:33 --> 00:24:33 topic.
00:24:33 --> 00:24:35 Andrew Dunkley: Or I am, it depends what part of Queensland
00:24:35 --> 00:24:36 though, because it's a big
00:24:36 --> 00:24:39 Jonti Horner: state for people listening and you've got to
00:24:39 --> 00:24:40 See, you've got to chuck in
00:24:40 --> 00:24:42 Andrew Dunkley: an A on the end of every sentence.
00:24:42 --> 00:24:44 Jonti Horner: One of the things that's always
00:24:45 --> 00:24:47 made my head hurt a little bit since I moved
00:24:47 --> 00:24:48 to Australia in 2010 and I'm officially
00:24:48 --> 00:24:51 Australian, you know. Yeah. Is a lack of
00:24:51 --> 00:24:53 diversity in the accents. I grew up in the
00:24:53 --> 00:24:56 uk, where accents are
00:24:56 --> 00:24:58 very, very varied to the extent that you
00:24:58 --> 00:24:59 could tell within my school which estate
00:24:59 --> 00:25:01 people grew up in because of subtleties in
00:25:01 --> 00:25:04 their accent locally. And the
00:25:04 --> 00:25:06 variation on a larger scale is astonishing.
00:25:06 --> 00:25:09 It's part of why I think British actors
00:25:09 --> 00:25:12 have so much success, partly because they
00:25:12 --> 00:25:14 get very good training, of course. But if
00:25:14 --> 00:25:16 you're an actor in the uk, you have to have a
00:25:16 --> 00:25:18 fluidity with accents because there's such a
00:25:18 --> 00:25:21 diversity just within the uk. Yeah. I came to
00:25:21 --> 00:25:23 Australia and I do not. I've
00:25:23 --> 00:25:26 lost some of my ear for the UK accents. I
00:25:26 --> 00:25:27 used to be really good, because you grow up
00:25:27 --> 00:25:29 there, it's a natural thing. I've lost a bit
00:25:29 --> 00:25:31 of that. But over here, it seems to be
00:25:32 --> 00:25:35 there isn't a very strong regional diversity.
00:25:35 --> 00:25:37 There's just a little bit of town versus
00:25:37 --> 00:25:39 country and a very little bit of north.
00:25:39 --> 00:25:39 South.
00:25:39 --> 00:25:40 Andrew Dunkley: Yes.
00:25:40 --> 00:25:42 Jonti Horner: But it's very smooth,
00:25:42 --> 00:25:44 although very little variety.
00:25:44 --> 00:25:47 Andrew Dunkley: I'll tell you. When I got into radio, I, um,
00:25:47 --> 00:25:50 did a demo tape and I had a friend listen to
00:25:50 --> 00:25:52 it who'd been in radio a very long time, and
00:25:52 --> 00:25:54 I was only just starting out, and he listened
00:25:54 --> 00:25:56 to it and he said, you know, you've got to
00:25:56 --> 00:25:58 get rid of. Rid of your Newcastle twang.
00:25:58 --> 00:26:00 Because I grew up in the Hunter Valley, um,
00:26:00 --> 00:26:03 in that Newcastle district. And I said, what?
00:26:03 --> 00:26:05 He said, you've got a Newcastle twang.
00:26:05 --> 00:26:08 There's a certain sound that comes
00:26:08 --> 00:26:10 out of the mouths of navocastrians.
00:26:11 --> 00:26:13 And I had to get. I had to train that out of
00:26:13 --> 00:26:15 myself. And. And it. It
00:26:15 --> 00:26:18 can be no disrespect, but it can be a bit
00:26:18 --> 00:26:20 grating. Um, but
00:26:22 --> 00:26:25 there are diversities in accent, uh,
00:26:25 --> 00:26:28 across Australia. When I worked for the abc,
00:26:28 --> 00:26:30 they actually published a map of accents,
00:26:31 --> 00:26:34 and I think the most prominent variation is
00:26:34 --> 00:26:36 South Australia, particularly Adelaide. Much
00:26:36 --> 00:26:38 more posh.
00:26:39 --> 00:26:42 Jonti Horner: But it's also, to me, it's much more evidence
00:26:42 --> 00:26:43 because I just don't quite have the ear for
00:26:43 --> 00:26:45 it, because in the uk, the accents are very
00:26:45 --> 00:26:47 much more valid. So Newcastle accent, to me,
00:26:47 --> 00:26:49 is very different to what you think of a
00:26:49 --> 00:26:51 Newcastle accent, but where I see it is in
00:26:51 --> 00:26:54 language. So there's the perennial
00:26:54 --> 00:26:56 argument among Australians of whether it's a
00:26:56 --> 00:26:58 potato cap or a potato scholar. Is A good
00:26:58 --> 00:27:00 example. You've got regional things like
00:27:00 --> 00:27:03 that. And from my side of things, I worked
00:27:03 --> 00:27:06 in Switzerland for three years and shared an
00:27:06 --> 00:27:08 office with Hagar, who was this
00:27:08 --> 00:27:11 young woman from, I think, Iran or somewhere
00:27:11 --> 00:27:13 Persian, I'm not sure exactly where. But we
00:27:13 --> 00:27:16 communicated in English, which was her sixth
00:27:16 --> 00:27:17 language.
00:27:17 --> 00:27:17 Andrew Dunkley: Wow.
00:27:17 --> 00:27:20 Jonti Horner: Which was astonishing to me. But there
00:27:20 --> 00:27:21 was one time I've been on the phone to my
00:27:21 --> 00:27:23 parents and I finished and she said, so,
00:27:23 --> 00:27:25 Jonty, what does A up mean? And
00:27:26 --> 00:27:28 yeah, ay up. Um, it
00:27:28 --> 00:27:30 reminds me of the wonderful.
00:27:30 --> 00:27:31 Andrew Dunkley: Isn't that Liverpudlian, that.
00:27:31 --> 00:27:34 Jonti Horner: No, AUP's. Yorkshire as well. M not far.
00:27:34 --> 00:27:37 If you want to see the accent of roughly
00:27:37 --> 00:27:39 where I grew up, incidentally, it's worth
00:27:39 --> 00:27:42 people looking up the fabulous song Ilklim al
00:27:42 --> 00:27:44 bar Tat, which is a cultural treasure from my
00:27:44 --> 00:27:45 part of the world. And we all learned, um,
00:27:45 --> 00:27:47 when we were in scouts and at school. And
00:27:47 --> 00:27:50 it's, um, basically a group of. Group of
00:27:50 --> 00:27:52 fellows at the pub saying, where have you
00:27:52 --> 00:27:53 been since I saw you last? You've been.
00:27:53 --> 00:27:55 You've been caught in Mary Jane. And it goes
00:27:55 --> 00:27:57 on about how he's not being dressed
00:27:57 --> 00:27:59 appropriately, he's going to die and they'll
00:27:59 --> 00:27:59 have to bury him.
00:27:59 --> 00:28:00 Andrew Dunkley: And.
00:28:00 --> 00:28:02 Jonti Horner: But it's all in very strong dialect, so you
00:28:02 --> 00:28:04 can see that. But what that resulted in is
00:28:04 --> 00:28:07 everybody in Bern communicated in
00:28:07 --> 00:28:09 English. At, uh, the Physicalisches
00:28:09 --> 00:28:11 Institute, I had to speak German when I was
00:28:11 --> 00:28:14 out in the town. But English has
00:28:14 --> 00:28:16 become this kind of lingua franca. Lingua,
00:28:16 --> 00:28:18 Lingua franca there. Because
00:28:18 --> 00:28:20 Switzerland's country with four different
00:28:20 --> 00:28:22 languages, it's got French, German, Italian
00:28:22 --> 00:28:24 and Romansh, but everybody's proud of their
00:28:24 --> 00:28:27 language. The French speakers will not sully
00:28:27 --> 00:28:29 themselves by speaking German to the German
00:28:29 --> 00:28:31 speakers. The German speakers, therefore,
00:28:31 --> 00:28:33 will not sully themselves by speaking the
00:28:33 --> 00:28:36 foul French to the French speakers. So they
00:28:36 --> 00:28:38 speak English. Um,
00:28:39 --> 00:28:41 but that means people have very good English,
00:28:41 --> 00:28:42 but they've learned a lot of their English
00:28:42 --> 00:28:44 from watching American TV rather than British
00:28:44 --> 00:28:47 tv. But even the British TV is a little bit
00:28:47 --> 00:28:49 denuded in terms of accent
00:28:50 --> 00:28:52 and, um, in terms
00:28:52 --> 00:28:54 particularly of dialect terms.
00:28:56 --> 00:28:57 And it was to an extent we were talking about
00:28:57 --> 00:28:59 the accents. The news presenters, until about
00:28:59 --> 00:29:02 20 or 30 years ago on the BBC had to use
00:29:02 --> 00:29:04 received pronunciation, which is a Queen's
00:29:04 --> 00:29:06 English, and you have to speak very properly.
00:29:06 --> 00:29:07 And they got rid of that because people
00:29:07 --> 00:29:09 realised that actually diversity in accents
00:29:09 --> 00:29:11 represents a diversity of people. And that's
00:29:11 --> 00:29:13 great. What that meant, though, was,
00:29:13 --> 00:29:16 uh, my accent, I've reliably been told, is
00:29:16 --> 00:29:19 relatively Strong. But I don't really use
00:29:19 --> 00:29:21 any dialect terms anymore other than the old
00:29:21 --> 00:29:23 bit of Aussie stuff I've picked up. Because
00:29:23 --> 00:29:24 what was really throwing people in
00:29:24 --> 00:29:27 Switzerland was the dialect terms, not
00:29:27 --> 00:29:30 the accents. Things like A up. And, um. So my
00:29:30 --> 00:29:32 language has shifted. I've lost a bit of an A
00:29:32 --> 00:29:34 for the UK stuff, but I don't hear much
00:29:35 --> 00:29:37 variety in the Australian accent. Now. Part
00:29:37 --> 00:29:39 of that is because I'm not from here,
00:29:40 --> 00:29:42 but I, I always find that kind of stuff
00:29:42 --> 00:29:44 really, really interesting. So, I mean, I
00:29:44 --> 00:29:45 could tell you were getting a stronger
00:29:45 --> 00:29:48 Australian accent. Um, but it wasn't
00:29:48 --> 00:29:50 necessarily. I couldn't have told you where
00:29:50 --> 00:29:53 it was from. Um, other thing is, again,
00:29:53 --> 00:29:55 saw an interesting discussion online about
00:29:55 --> 00:29:56 the Australia accent changing over time,
00:29:57 --> 00:30:00 asking why, when you watch Aussie films and
00:30:00 --> 00:30:02 TVs from 30, 40, 50 years ago,
00:30:02 --> 00:30:04 everybody almost sounds like they're a
00:30:04 --> 00:30:06 pastiche of the Australian accent. It's so
00:30:06 --> 00:30:09 full on and there's so many terms and
00:30:09 --> 00:30:10 insults and stuff that aren't, um, used
00:30:10 --> 00:30:13 today. Yeah. And, um, apparently part of it
00:30:13 --> 00:30:15 is language evolves. We've got all these
00:30:15 --> 00:30:17 multicultural influence, we've got all that
00:30:17 --> 00:30:20 stuff. But also apparently the actors were
00:30:20 --> 00:30:22 trained to ham it up.
00:30:22 --> 00:30:25 Andrew Dunkley: Oh, absolutely. That's exactly what it was.
00:30:25 --> 00:30:27 And, uh. See what you started, Paul. But,
00:30:27 --> 00:30:30 uh, I understand because I did some research
00:30:30 --> 00:30:32 on it. The Australian accent came about
00:30:32 --> 00:30:34 because we were, uh,
00:30:35 --> 00:30:38 a colony of convicts brought over from the
00:30:38 --> 00:30:41 uk. But the convicts were all from
00:30:41 --> 00:30:43 different walks of life, but they were
00:30:43 --> 00:30:46 conglomerated into a new community and
00:30:46 --> 00:30:48 all their accents merged into what is now the
00:30:48 --> 00:30:49 Australian accent.
00:30:49 --> 00:30:52 So, you know, you
00:30:52 --> 00:30:55 had Welsh, you had Irish, you had Scottish,
00:30:55 --> 00:30:57 you had English, of. With all their
00:30:57 --> 00:31:00 variations all coming together and
00:31:00 --> 00:31:02 creating the Australian accent. So that's why
00:31:02 --> 00:31:03 it is what it is.
00:31:03 --> 00:31:04 Jonti Horner: Yes.
00:31:04 --> 00:31:05 Andrew Dunkley: But it's ever evolving too.
00:31:05 --> 00:31:07 Jonti Horner: It is a wonderful thing that does change over
00:31:07 --> 00:31:09 time. Yes. Which I found interesting. Anyway,
00:31:09 --> 00:31:10 sorry about that.
00:31:10 --> 00:31:12 We get off topic. Wonderfully, wonderfully.
00:31:12 --> 00:31:13 Well, Saturn.
00:31:13 --> 00:31:14 Andrew Dunkley: Good at that. So Fred Watson started talking
00:31:14 --> 00:31:17 about the possibility of Titan and Hyperion
00:31:17 --> 00:31:19 colliding and what happened to the stuff.
00:31:19 --> 00:31:22 Could a big rock from that event have hit
00:31:22 --> 00:31:24 Earth 65 million years ago? And you know what
00:31:24 --> 00:31:26 he's talking about there? Or did it all just
00:31:26 --> 00:31:28 go flying off into space or did it do
00:31:28 --> 00:31:30 something, something else, etc. Etc.
00:31:30 --> 00:31:33 Jonti Horner: All sorts of ways we can go with this. So
00:31:34 --> 00:31:36 the origin of Saturn's rings, first and
00:31:36 --> 00:31:39 foremost is not yet definitively known.
00:31:39 --> 00:31:41 We know that the ruin systems around Jupiter,
00:31:41 --> 00:31:44 Uranus and Neptune as well. We suspect
00:31:44 --> 00:31:45 strongly that in the past and in the future
00:31:46 --> 00:31:49 Mars has had and will have ring
00:31:49 --> 00:31:52 rings. I think red dwarfy has, will have,
00:31:52 --> 00:31:54 possibly going to have whatever it is, it may
00:31:54 --> 00:31:56 have had episodic rings. In the past we found
00:31:56 --> 00:31:58 rings around a few of the solar system
00:31:58 --> 00:32:00 smaller objects like um, the Centaurs, Chiron
00:32:00 --> 00:32:03 and Curricula, um, rings are a thing.
00:32:03 --> 00:32:05 We've also found potentially rings around
00:32:05 --> 00:32:08 exoplanets. Some debate about that. We find
00:32:08 --> 00:32:10 rings around stars in the form of debris
00:32:10 --> 00:32:13 discs and all the rest of it. Ever
00:32:13 --> 00:32:16 since Saturn's rings were known there's been
00:32:16 --> 00:32:19 ongoing how did they get there? And there is
00:32:19 --> 00:32:21 an ongoing not only how did they get there,
00:32:21 --> 00:32:23 but are they transient or permanent? And
00:32:24 --> 00:32:27 there are a wide variety of opinions on this
00:32:27 --> 00:32:29 and modelling has not yet come down strongly
00:32:29 --> 00:32:32 one way or the other. Currently the best
00:32:32 --> 00:32:33 thinking about Saturn's rings is that they
00:32:33 --> 00:32:36 are more likely to be new than old.
00:32:37 --> 00:32:40 So we're probably seeing a ring system that
00:32:40 --> 00:32:43 has in bulk not existed since the birth of
00:32:43 --> 00:32:45 the Sol system. And estimates of the age
00:32:45 --> 00:32:48 range from 10 to 100 to
00:32:49 --> 00:32:52 300 million years. These estimates on the
00:32:52 --> 00:32:54 which the rings are being depleted
00:32:54 --> 00:32:57 suggest that they may well return to the
00:32:57 --> 00:32:59 level of Neptune, Uranus, Jupiter type rings
00:33:00 --> 00:33:02 within about 300 million years from now.
00:33:03 --> 00:33:06 Those theories, those arguments
00:33:07 --> 00:33:09 would suggest that if the ring system is
00:33:09 --> 00:33:10 younger than the edge of the solar system,
00:33:10 --> 00:33:12 there had to be an event to bring it into
00:33:12 --> 00:33:14 being. Obviously and there have been
00:33:14 --> 00:33:17 a number of different suggestions to
00:33:17 --> 00:33:19 cause this. One is that, and this was
00:33:19 --> 00:33:21 commonly argued when I was a kid learning
00:33:21 --> 00:33:23 about it, that Saturn had a commodore
00:33:23 --> 00:33:25 asteroid that got too close was Taunus under
00:33:25 --> 00:33:28 creating the rings. Now this invokes
00:33:28 --> 00:33:30 a part of planetary science knowledge and
00:33:30 --> 00:33:33 physics called the Roche limit, which is
00:33:33 --> 00:33:35 essentially if you have two massive objects
00:33:36 --> 00:33:37 and you bring them close enough together,
00:33:38 --> 00:33:41 tidal effects will disrupt the smaller of
00:33:41 --> 00:33:43 them due to the gravity of the bigger of
00:33:43 --> 00:33:45 them. And the point there is if you think
00:33:45 --> 00:33:47 that the strength of the gravitational pull
00:33:47 --> 00:33:49 falls off as the square of the distance and
00:33:49 --> 00:33:51 you've got an object that's 100 kilometres
00:33:51 --> 00:33:54 across, the side that is nearer a planet will
00:33:54 --> 00:33:55 be feeling a stronger pull than the side
00:33:55 --> 00:33:58 that's further away. Now depending on the
00:33:58 --> 00:34:01 strength of the object that distance will
00:34:01 --> 00:34:02 vary. The stronger the object is, the closer
00:34:02 --> 00:34:05 it can get to a planet before disruption. But
00:34:05 --> 00:34:07 we have this concept of the Roche limit and
00:34:07 --> 00:34:09 Saturn's rings are within the Roche limit
00:34:09 --> 00:34:11 which is why they've been disrupted. And the
00:34:11 --> 00:34:14 largest objects in them are uh, probably to
00:34:14 --> 00:34:16 be honest the shepherd moons that are
00:34:16 --> 00:34:19 kilometre scale objects which are probably
00:34:19 --> 00:34:21 due to the nature of the Roche limit and
00:34:21 --> 00:34:24 stuff. They're probably fairly robust
00:34:24 --> 00:34:25 rather than rubble piles. Because if they're
00:34:25 --> 00:34:27 rubble piles, they get disintegrated.
00:34:27 --> 00:34:27 Andrew Dunkley: Yeah. Um.
00:34:28 --> 00:34:30 Jonti Horner: So they're probably at a distance where they
00:34:30 --> 00:34:33 are within the Roche limit. For a fluid
00:34:33 --> 00:34:34 object that has no strength, but they are
00:34:34 --> 00:34:36 strong enough that the Roche limit for them
00:34:36 --> 00:34:37 will be closer in Anyway. A bit off topic
00:34:37 --> 00:34:40 there, but that's the physics behind it. And
00:34:40 --> 00:34:42 you can work out that Roche limit either as a
00:34:42 --> 00:34:44 ratio of the mass of the object and the mass
00:34:44 --> 00:34:46 of the thing it's the bigger thing that it's
00:34:46 --> 00:34:48 coming near, or as a ratio of the densities.
00:34:48 --> 00:34:50 It works either way, which is kind of cool.
00:34:51 --> 00:34:53 Um, that's
00:34:54 --> 00:34:57 what the physics is behind why
00:34:57 --> 00:34:58 you don't have a single object there. It
00:34:58 --> 00:35:00 can't form single object. It's got to be
00:35:00 --> 00:35:03 broken up into debris. The rings are
00:35:03 --> 00:35:06 decaying, dust is lost to Saturn all the
00:35:06 --> 00:35:08 time. They're also being slightly replenished
00:35:08 --> 00:35:10 by the activity, particularly of Enceladus,
00:35:10 --> 00:35:13 um, which is repopulating the earring. So
00:35:13 --> 00:35:16 there are system influx and it's not
00:35:16 --> 00:35:18 clear exactly where they're formed. There was
00:35:18 --> 00:35:20 the idea when I was a kid that it was a
00:35:20 --> 00:35:22 commodore asteroid that was disrupted to make
00:35:22 --> 00:35:25 that much material. I think that has gone
00:35:25 --> 00:35:28 probably by the wayside because you
00:35:28 --> 00:35:30 need a way to dissipate the energy for an
00:35:30 --> 00:35:33 object to be captured. So if you have a comet
00:35:33 --> 00:35:35 or an asteroid get close enough to Saturn to
00:35:35 --> 00:35:38 be torn apart, that material is still
00:35:38 --> 00:35:40 moving faster than Saturn's escape velocity.
00:35:40 --> 00:35:42 So we'll just fly away, albeit torn apart.
00:35:42 --> 00:35:42 Andrew Dunkley: Right.
00:35:42 --> 00:35:44 Jonti Horner: If you have something that is temporarily
00:35:44 --> 00:35:47 captured as a satellite, it'll be on a fairly
00:35:47 --> 00:35:49 elongated orbit. If it's going to get close
00:35:49 --> 00:35:51 enough to be disrupted and it will continue
00:35:51 --> 00:35:53 to follow that. So if you look at Comet
00:35:53 --> 00:35:55 Schumacher, Levy 9 back in the
00:35:55 --> 00:35:58 1990s, it came very close to Jupiter in 1992,
00:35:58 --> 00:36:00 I think was torn apart so that we had many
00:36:00 --> 00:36:03 smaller comets that all followed essentially
00:36:03 --> 00:36:05 the same art orbit. Ah. In a lengthy chain
00:36:05 --> 00:36:08 and fell apart, crashed into Jupiter one
00:36:08 --> 00:36:10 after the other over the space of a couple of
00:36:10 --> 00:36:11 weeks in 1994.
00:36:11 --> 00:36:11 Andrew Dunkley: That's right.
00:36:12 --> 00:36:13 Jonti Horner: They didn't form a ring system.
00:36:14 --> 00:36:14 Andrew Dunkley: No.
00:36:14 --> 00:36:17 Jonti Horner: When that had its first approach to Jupiter,
00:36:17 --> 00:36:19 it was torn apart, but it didn't make a new
00:36:19 --> 00:36:22 ring system. So you need somewhere to
00:36:22 --> 00:36:23 dissipate the energy to trap all the debris
00:36:23 --> 00:36:26 onto a circular orbit near the planet. And
00:36:26 --> 00:36:27 it's very hard to visualise how you do that
00:36:27 --> 00:36:30 from an asteroid or comet passing through. So
00:36:30 --> 00:36:33 that's led to uh, instead the idea of
00:36:33 --> 00:36:35 the collision between two moons. Now the most
00:36:35 --> 00:36:38 recent version I've seen discussed of this
00:36:39 --> 00:36:41 is that uh, there was a moon
00:36:42 --> 00:36:44 that was possibly as large as Hyperion or
00:36:44 --> 00:36:47 even bigger, that collided
00:36:48 --> 00:36:51 sorry whose orbit spiralled inwards to the
00:36:51 --> 00:36:54 point it crossed the Roche limit. Now we're
00:36:54 --> 00:36:56 seeing this happen with Phoebe, the innermost
00:36:56 --> 00:36:59 of Mars 2 moons. Phoebe is closer to Mars
00:36:59 --> 00:37:02 than what we call the CO rotation altitude,
00:37:02 --> 00:37:05 which means its orbit around Mars takes less
00:37:05 --> 00:37:07 time than Mars takes to spin. And when you're
00:37:07 --> 00:37:09 closer than that corrotation place, tidal
00:37:09 --> 00:37:11 forces will make you spiral inwards rather
00:37:11 --> 00:37:13 than spiralling outwards. Our moons further
00:37:13 --> 00:37:15 out, it takes longer to orbit the Earth than
00:37:15 --> 00:37:17 the Earth takes to spin. So it moves away.
00:37:17 --> 00:37:18 Andrew Dunkley: Yeah.
00:37:19 --> 00:37:21 Jonti Horner: Imagine then that you had a moon
00:37:22 --> 00:37:24 few hundred kilometres across, 200, 300, 400
00:37:24 --> 00:37:27 kilometres across, close end that
00:37:27 --> 00:37:29 spiralled inwards and crossed the Roche
00:37:29 --> 00:37:31 limit. It will be disrupted from a ring
00:37:31 --> 00:37:33 system. That's one theory. Another is that
00:37:33 --> 00:37:36 you had a moon that was pretty close in that
00:37:36 --> 00:37:39 was then struck by an object large enough to
00:37:39 --> 00:37:41 shatter and disrupt it.
00:37:42 --> 00:37:44 But collisions of that size would
00:37:44 --> 00:37:46 be relatively rare these days because
00:37:46 --> 00:37:48 projectiles big enough to shatter a moon of
00:37:48 --> 00:37:51 that size are relatively scarce.
00:37:52 --> 00:37:54 Um, a more, more recent version that's been
00:37:54 --> 00:37:56 proposed is that you had a much larger
00:37:56 --> 00:37:59 object, something more like the size of Titan
00:37:59 --> 00:38:01 and that was stripped off during the
00:38:01 --> 00:38:03 formation period of time. There's all sorts
00:38:03 --> 00:38:06 of theories here but like I said, we're not
00:38:06 --> 00:38:07 fully there yet. We're still exploring.
00:38:08 --> 00:38:10 That's where future missions to Saturn are
00:38:10 --> 00:38:13 going to teach us a lot more. Um, we've got
00:38:13 --> 00:38:16 an edge here. Um, observations based on the
00:38:16 --> 00:38:18 Keck telescope suggest that the rings
00:38:18 --> 00:38:21 will be gone in 292
00:38:21 --> 00:38:24 plus 818 minus 124 million
00:38:24 --> 00:38:26 years. Which illustrates that as astronomers
00:38:26 --> 00:38:29 we are terrible at, ah, choosing significant
00:38:29 --> 00:38:30 figures. And I tell my students this all the
00:38:30 --> 00:38:32 time because if you talk to a physicist
00:38:32 --> 00:38:34 they'd see those numbers and weep because
00:38:34 --> 00:38:36 they'd say, well that should just be 300 plus
00:38:36 --> 00:38:39 800 minus 1 because the other numbers are
00:38:39 --> 00:38:41 meaningless anyway. Um, but it's
00:38:41 --> 00:38:44 a very large uncertainty on how long they
00:38:44 --> 00:38:46 will take till they're gone. We don't know
00:38:46 --> 00:38:49 how massive they were initially and how
00:38:49 --> 00:38:52 massive they are initially will be part
00:38:52 --> 00:38:54 of what determines how long they've
00:38:54 --> 00:38:57 been around anyway. So that's why
00:38:57 --> 00:38:59 there's still a lot of misunderstanding and a
00:38:59 --> 00:39:01 lot of confusion there. And it may well be
00:39:01 --> 00:39:04 that rings of the scale of the rings of
00:39:04 --> 00:39:05 Saturn around the giant planets are an
00:39:05 --> 00:39:08 episodic thing. It may well be the
00:39:08 --> 00:39:10 planets like Saturn, Jupiter, uh, Uranus and
00:39:10 --> 00:39:13 Neptune have minor ring systems all the time,
00:39:13 --> 00:39:15 but occasionally will get a really good one.
00:39:15 --> 00:39:17 And it could be that in the past Jupiter had
00:39:17 --> 00:39:19 a massive ring system like this and in the
00:39:19 --> 00:39:21 future Uranus back, for example,
00:39:22 --> 00:39:24 Mars will probably get a ring system when um,
00:39:24 --> 00:39:26 Phobos gets close enough and is disrupted.
00:39:27 --> 00:39:29 All that now to aside, the next part was
00:39:30 --> 00:39:32 about debris reaching us from
00:39:33 --> 00:39:36 the collision and reaching the Earth.
00:39:36 --> 00:39:38 Yeah, um, two parts to this. The first is
00:39:38 --> 00:39:41 that some
00:39:41 --> 00:39:43 material from that collision could
00:39:43 --> 00:39:45 potentially have reached Earth. I don't doubt
00:39:45 --> 00:39:47 that. I did work while I was at the
00:39:47 --> 00:39:49 University of Bern, which we talked about
00:39:49 --> 00:39:52 earlier with a PhD student at the time called
00:39:52 --> 00:39:55 Augustine Anich, who was doing simulations
00:39:55 --> 00:39:58 of the giant collision that made Mercury
00:39:58 --> 00:40:00 the planet we know it is today. Mercury is
00:40:00 --> 00:40:03 over dense, it has an oversized core. And the
00:40:03 --> 00:40:05 thinking is it was probably once a planet
00:40:05 --> 00:40:08 twice the diameter of the current Mercury.
00:40:08 --> 00:40:10 And it had this massive collision that
00:40:10 --> 00:40:12 stripped it of its mantle and crust, leaving
00:40:12 --> 00:40:13 behind a core with a little bit of rubble on
00:40:13 --> 00:40:16 top. And he was doing simulations of that
00:40:16 --> 00:40:19 impact. And my contribution
00:40:19 --> 00:40:21 was I ran orbital mechanics simulations. This
00:40:21 --> 00:40:23 is kind of core to my day to day work. This
00:40:23 --> 00:40:26 is what I've done all through my career. And
00:40:26 --> 00:40:29 I said where would the ejector go? If you
00:40:29 --> 00:40:30 have a collision like that, some of the
00:40:30 --> 00:40:33 material ejected will be travelling at less
00:40:33 --> 00:40:34 than the escape velocity for all of the
00:40:34 --> 00:40:36 masses around. So that material won't be
00:40:36 --> 00:40:39 lost. And it would either in the case of the
00:40:39 --> 00:40:40 Earth Moon collision, form a satellite like
00:40:40 --> 00:40:43 the Moon or fall back and contribute to the
00:40:43 --> 00:40:46 re accretion. Material travelling
00:40:46 --> 00:40:49 above the escape velocity will escape and
00:40:49 --> 00:40:51 go into orbit around the Sun. And at that
00:40:51 --> 00:40:53 point it is subject to all of the dynamics
00:40:53 --> 00:40:54 that goes on, the gravity, gravitational
00:40:54 --> 00:40:57 interactions with all the other planets. And
00:40:57 --> 00:40:59 I run simulations of the ejector to see what
00:40:59 --> 00:41:01 their eventual fates would be, where they
00:41:01 --> 00:41:04 would wind up. The majority of the ejector
00:41:04 --> 00:41:06 from the Mercury forming collision hit the
00:41:06 --> 00:41:09 sun or was flung from the solar system, never
00:41:09 --> 00:41:11 to return as a final fate. That's where it
00:41:11 --> 00:41:13 ended up. But about 2% of the material
00:41:13 --> 00:41:16 ejected from Mercury would have landed on
00:41:16 --> 00:41:18 Earth. So we will have been polluted by the
00:41:18 --> 00:41:21 Mercury forming impact by what you
00:41:21 --> 00:41:23 describe as Hermian material. If, if we were
00:41:23 --> 00:41:26 talking about Venus being venereal
00:41:27 --> 00:41:29 material which then became Venusian material,
00:41:29 --> 00:41:32 Mars being Martian, Jupiter being Jovian
00:41:32 --> 00:41:35 for Mercury, Mercurian never quite worked So
00:41:35 --> 00:41:37 a lot of people used to call it Hermione, um,
00:41:37 --> 00:41:39 so the traditional name. But anyway, the
00:41:39 --> 00:41:41 material from Mercury, about 2% of it, would
00:41:41 --> 00:41:42 have rained down on the Earth.
00:41:42 --> 00:41:45 Now this ties into the
00:41:45 --> 00:41:47 work that I've talked about before about
00:41:47 --> 00:41:50 panspermia as well. Material ejected from one
00:41:50 --> 00:41:52 planet becomes objects moving
00:41:52 --> 00:41:55 freely within the solar system, subject to
00:41:55 --> 00:41:58 the gravitational pinball that goes on.
00:41:59 --> 00:42:01 If you have a collision in orbit around
00:42:01 --> 00:42:04 Saturn, if it is a collision between two of
00:42:04 --> 00:42:07 Saturn's moons, the overwhelmingly vast
00:42:07 --> 00:42:09 majority of ejecta will stay bound in the
00:42:09 --> 00:42:11 Saturn system because the moons are both
00:42:11 --> 00:42:13 themselves very deep in Saturn's gravity
00:42:13 --> 00:42:16 while very tightly held. So
00:42:16 --> 00:42:18 the vast majority of ejector from two moons
00:42:18 --> 00:42:20 colliding with each other will be kept in
00:42:20 --> 00:42:23 house. But that's not all of it.
00:42:24 --> 00:42:26 Also some of that ejector, uh, that ejector
00:42:26 --> 00:42:28 in the Saturn system will be like ejector in
00:42:28 --> 00:42:30 the solar system. It'll be bounced around and
00:42:30 --> 00:42:32 moved around by the gravity of the moons. So
00:42:32 --> 00:42:34 a small tiny fraction of it could eventually
00:42:34 --> 00:42:36 be ejected that way as well. If you have a
00:42:36 --> 00:42:39 collision that instead involves or
00:42:39 --> 00:42:41 invokes an object that is not currently
00:42:41 --> 00:42:43 orbiting Saturn, but is a comet or an
00:42:43 --> 00:42:45 asteroid passing through, that object itself
00:42:45 --> 00:42:47 is moving faster than the escape velocity of
00:42:47 --> 00:42:49 Saturn. So a significant amount of the
00:42:49 --> 00:42:52 ejector also will be that case. You'll get
00:42:52 --> 00:42:54 more material put into orbit around the sun.
00:42:55 --> 00:42:57 Once the material has escaped from Saturn,
00:42:57 --> 00:43:00 it is moving on an orbit that makes it one of
00:43:00 --> 00:43:02 the Centaurs. And the Centaurs are one of my
00:43:02 --> 00:43:04 favourite populations of objects anyway
00:43:04 --> 00:43:06 because they're what I studied for my PhD and
00:43:06 --> 00:43:08 I did the same dynamic simulations of them.
00:43:08 --> 00:43:09 Where do they come from? Where are they
00:43:09 --> 00:43:11 going? How will they get there? The
00:43:11 --> 00:43:14 Centaurs are uh, the parent population of the
00:43:14 --> 00:43:16 short period comets. The Centaurs themselves
00:43:17 --> 00:43:19 are uh, daughters, sons,
00:43:19 --> 00:43:22 children of the transept union. Objects
00:43:22 --> 00:43:24 moving around in the after solar system being
00:43:24 --> 00:43:27 scattered inwards. In my simulations
00:43:27 --> 00:43:29 of the Centaurs, about one third of
00:43:29 --> 00:43:31 Centaurs, which is about one third of those
00:43:31 --> 00:43:33 objects between the orbits of Jupiter and
00:43:33 --> 00:43:35 Neptune that are on unstable orbits, about
00:43:35 --> 00:43:37 one third of them will eventually become a
00:43:37 --> 00:43:38 Jupiter family comet will be flung into the
00:43:38 --> 00:43:41 inner solar system, usually by Jupiter, uh,
00:43:41 --> 00:43:42 which means it'll be put onto an Earth
00:43:42 --> 00:43:45 crossing orbit, which means that if you eject
00:43:45 --> 00:43:48 enough material from the Saturn
00:43:48 --> 00:43:50 system, some of it will hit the
00:43:50 --> 00:43:53 Earth. It'll be vanishingly small amount.
00:43:54 --> 00:43:56 It is unlikely though that you'll get a
00:43:56 --> 00:43:59 chunk big enough to cause a mass extinction,
00:43:59 --> 00:44:02 making it all that far. The
00:44:02 --> 00:44:04 thing that killed the dinosaurs was about 10
00:44:04 --> 00:44:06 kilometres across, we think, maybe even a
00:44:06 --> 00:44:08 little bit bigger. That's a very, very, very
00:44:08 --> 00:44:11 big bit of stuff. Now, obviously there's a
00:44:11 --> 00:44:12 small chance it could have been the result of
00:44:12 --> 00:44:14 something like that. There are suggestions
00:44:15 --> 00:44:17 that the thing that killed off the dinosaurs
00:44:17 --> 00:44:19 might have been an asteroid that was probably
00:44:19 --> 00:44:21 producing a collision in the asteroid belt.
00:44:21 --> 00:44:23 And being a member of one of the collisional
00:44:23 --> 00:44:24 families that feed material to the inner
00:44:24 --> 00:44:26 solar system, others have suggested it could
00:44:26 --> 00:44:29 be a comet, it could potentially
00:44:29 --> 00:44:32 have been a fragment of a smashed
00:44:32 --> 00:44:34 moon, like Paul is suggesting. It could have
00:44:34 --> 00:44:36 been a very ancient fragment of another
00:44:36 --> 00:44:38 Mercury collision that had managed to survive
00:44:38 --> 00:44:40 4 billion years. But that's vanishingly
00:44:40 --> 00:44:42 unlikely. Cause things are ejected on a m
00:44:42 --> 00:44:43 much shorter time scale. So there'll be
00:44:43 --> 00:44:46 nothing left, effectively. But we don't know
00:44:46 --> 00:44:49 that's a fundamental thing. What drives
00:44:49 --> 00:44:52 the understanding that the impact itself was
00:44:52 --> 00:44:55 extraterrestrial was initially the
00:44:55 --> 00:44:56 iridium layer that was found globally. That
00:44:56 --> 00:44:59 was kind of a bit of a smoking gun. At the
00:44:59 --> 00:45:00 point of the mass extinction in the fossil
00:45:00 --> 00:45:03 record, they found the crater. You
00:45:03 --> 00:45:06 cannot tell from the crater's size alone, um,
00:45:06 --> 00:45:08 what the nature of the impactor was or the
00:45:08 --> 00:45:11 impact speed. Now, for a crater
00:45:11 --> 00:45:13 that old, it's a bit impossible to do.
00:45:13 --> 00:45:16 Anyway, I've been really interested and we've
00:45:16 --> 00:45:18 never got around to doing this as research to
00:45:18 --> 00:45:20 talk with people like the creator, counting
00:45:20 --> 00:45:22 people to see if there is anywhere for bodies
00:45:22 --> 00:45:24 like the Moon or Mars where there's much less
00:45:24 --> 00:45:27 weathering to distinguish between a cometary
00:45:27 --> 00:45:29 or asteroidal impact on the basis of
00:45:31 --> 00:45:33 whether the speed's influence on the
00:45:33 --> 00:45:36 kinetic energy of the impact can modify
00:45:36 --> 00:45:39 the crater formation process. Probably it
00:45:39 --> 00:45:41 can't, because effectively you're dumping X
00:45:41 --> 00:45:43 energy into the surface and that's what makes
00:45:43 --> 00:45:46 the crater. But I've been interested in that.
00:45:46 --> 00:45:47 But what that means from the Earth's point of
00:45:47 --> 00:45:49 view is, uh, from the morphology of the
00:45:49 --> 00:45:52 crater, from what's left from that impact, we
00:45:52 --> 00:45:54 cannot tell what the impact was or how fast
00:45:54 --> 00:45:56 it's travelling. Had to be faster than the
00:45:56 --> 00:45:58 escape velocity of the Earth because it came
00:45:58 --> 00:46:00 from beyond the Earth. So the minimum speed
00:46:00 --> 00:46:03 is 12 kilometres a second. It is almost
00:46:03 --> 00:46:05 guaranteed that it was a solar system object,
00:46:05 --> 00:46:07 not an interstellar comet like Comet Atlas.
00:46:07 --> 00:46:09 Which means that the maximum speed it could
00:46:09 --> 00:46:11 have hit us is 72 kilometres a second.
00:46:12 --> 00:46:15 Which is, you get that number by
00:46:15 --> 00:46:17 combining the orbital speed of the Earth,
00:46:17 --> 00:46:19 which is 30 kilometres a second going forward
00:46:19 --> 00:46:21 with the maximum speed that something could
00:46:21 --> 00:46:23 be travelling at one astronomical unit at our
00:46:23 --> 00:46:25 location and still be bound to the sun,
00:46:25 --> 00:46:28 which, if you work out the velocity, if
00:46:28 --> 00:46:31 you're going at 42 kilometres a second at the
00:46:31 --> 00:46:32 location of the Earth's orbit, you're right
00:46:32 --> 00:46:34 on the boundary between the solar system's
00:46:34 --> 00:46:37 escape velocity and not so anything faster
00:46:37 --> 00:46:39 than that will escape. Take those two numbers
00:46:39 --> 00:46:41 and say, right, you've got an optic, the
00:46:41 --> 00:46:43 object coming head on at, uh, the fastest
00:46:43 --> 00:46:45 speed it could have and stay bound to the
00:46:45 --> 00:46:48 solar system. 42 kilometres a second one
00:46:48 --> 00:46:50 way, 30 kilometres a second the other way
00:46:50 --> 00:46:53 gives you 72 kilometres a second. So we know
00:46:53 --> 00:46:55 the velocity with which this thing was coming
00:46:55 --> 00:46:58 in within a factor of six. Most likely it's
00:46:58 --> 00:46:59 at the lower end because we get more
00:46:59 --> 00:47:02 asteroidal impactors and cometary ones, but
00:47:02 --> 00:47:04 we don't really have much more than that on
00:47:04 --> 00:47:07 the composition of it. There is a lot of
00:47:07 --> 00:47:09 debate over whether it was cometary, whether
00:47:09 --> 00:47:12 it was asteroidal. An object
00:47:12 --> 00:47:15 formed from part of one of the moons of
00:47:15 --> 00:47:18 Saturn would be ice rich and, uh,
00:47:18 --> 00:47:20 so it would look like a cometary impactor. So
00:47:20 --> 00:47:23 I'm not sure for an impact 65 million years
00:47:23 --> 00:47:26 old, whether we would ever be able to
00:47:26 --> 00:47:28 distinguish between a fragment of one of the
00:47:28 --> 00:47:31 moons of Saturn as the impactor and a
00:47:31 --> 00:47:34 comet as the impactor. Um,
00:47:35 --> 00:47:37 I just have no idea how we would do that.
00:47:37 --> 00:47:39 What we would probably be able to do is if we
00:47:39 --> 00:47:42 went to a near Earth object, whether
00:47:42 --> 00:47:44 it's a comet or an asteroid, and took
00:47:44 --> 00:47:47 samples, there is a potential that
00:47:47 --> 00:47:50 then maybe through isotopic analysis we could
00:47:50 --> 00:47:52 tell that something was a fragment of a
00:47:52 --> 00:47:55 Saturnian moon. But we need things to compare
00:47:55 --> 00:47:58 that to. That is very much on the very
00:47:58 --> 00:48:00 fringes of what we can do. But we do that a
00:48:00 --> 00:48:02 little bit with some meteorites. There's a
00:48:02 --> 00:48:04 couple of families of meteorites where we
00:48:04 --> 00:48:06 think we know the parent object. And these
00:48:06 --> 00:48:09 meteorites are compositionally grouped
00:48:09 --> 00:48:11 together with such tightness that they are
00:48:11 --> 00:48:14 distinguishable against the compositions of
00:48:14 --> 00:48:16 everything as a background. It's like if you
00:48:16 --> 00:48:17 measure the composition of everything and
00:48:17 --> 00:48:19 then points on a wall. These ones all group
00:48:19 --> 00:48:21 together so they come from the same parent.
00:48:22 --> 00:48:23 But I don't know how we could
00:48:25 --> 00:48:28 figure out whether it was a fragment of a
00:48:28 --> 00:48:30 Saturnian moon versus a comet.
00:48:31 --> 00:48:32 If we got to the point where we could
00:48:32 --> 00:48:35 distinguish comet versus asteroid, I think
00:48:35 --> 00:48:37 the argument will be it's a cometary body,
00:48:37 --> 00:48:40 probably, um, but we couldn't tell you
00:48:40 --> 00:48:41 whether it's short or a long period comet.
00:48:41 --> 00:48:43 But people will probably come down on the
00:48:43 --> 00:48:46 cometary exclamation rather than the fragment
00:48:46 --> 00:48:48 of a moon explanation because of the Occam's
00:48:48 --> 00:48:49 razor thing. So if you've got two
00:48:50 --> 00:48:52 explanations that are equally good at
00:48:52 --> 00:48:54 explaining the storey, take the one that's
00:48:54 --> 00:48:55 simpler. Yeah, that might not be Occam's
00:48:55 --> 00:48:57 razor, but that's one of those philosophical
00:48:57 --> 00:48:59 constructs that, you know, it's a
00:48:59 --> 00:49:02 more complex and challenging
00:49:02 --> 00:49:04 route to get a fragment of a saturnian
00:49:04 --> 00:49:06 satellite to kill the dinosaurs than it is to
00:49:06 --> 00:49:08 have it just be a normal comet.
00:49:08 --> 00:49:10 Andrew Dunkley: Yeah, fair enough. All right, very good.
00:49:11 --> 00:49:13 Um, thank you, Paul. I think we
00:49:13 --> 00:49:16 covered that topic uh, very, very well and
00:49:16 --> 00:49:18 hope all's well in Queensland.
00:49:18 --> 00:49:21 Hey, uh, we're going to take a breath
00:49:21 --> 00:49:24 and then we'll quickly go into our final
00:49:24 --> 00:49:26 question here on Space Nuts.
00:49:31 --> 00:49:32 Jonti Horner: Space Nuts.
00:49:32 --> 00:49:35 Andrew Dunkley: And we're with Professor Johnty Horner today
00:49:35 --> 00:49:38 with Fred Watson Away, uh, a Q A edition.
00:49:38 --> 00:49:41 One last question. Uh, we'll have to make it
00:49:41 --> 00:49:42 quick because I think we really burnt the
00:49:42 --> 00:49:44 clock today. Too much talking about accents.
00:49:44 --> 00:49:46 I think, uh, I have a question.
00:49:47 --> 00:49:49 Jonti Horner: I was just gonna say talking of accents, get
00:49:49 --> 00:49:52 Fred Watson to sing a Climb or Bata because
00:49:52 --> 00:49:54 he's from my neck of the woods originally.
00:49:54 --> 00:49:56 Andrew Dunkley: Okay. Uh, I have a question
00:49:56 --> 00:49:59 that might come across as lame or childish.
00:49:59 --> 00:50:02 Yes it did. No, no it didn't. Uh, but I'm
00:50:02 --> 00:50:04 hoping that a professor and a genuine
00:50:04 --> 00:50:07 space nut, uh, or I'm
00:50:07 --> 00:50:10 hoping that asking a professor and a genuine
00:50:10 --> 00:50:12 space nut this question, it might prompt
00:50:13 --> 00:50:15 for much more interesting answer than the
00:50:15 --> 00:50:16 average Joe.
00:50:16 --> 00:50:19 What is your favourite planet in our solar
00:50:19 --> 00:50:21 system and why? I wish I could give you an
00:50:21 --> 00:50:23 interesting answer myself. I do find Jupiter
00:50:23 --> 00:50:26 fascinating. And Europa. Okay, yeah, I know
00:50:26 --> 00:50:29 it's a moon, but I'm intrigued by what could
00:50:29 --> 00:50:31 be under all that ice. Hopefully um, we'll
00:50:31 --> 00:50:33 find out in my lifetime. So yeah, childish
00:50:33 --> 00:50:35 question from a 40 year old, but hopefully
00:50:36 --> 00:50:38 you can turn it into a more deep and
00:50:38 --> 00:50:40 meaningful answer. That's Dan from the Gold
00:50:40 --> 00:50:42 coast, also a Queenslander.
00:50:42 --> 00:50:45 Um, I can go first and be very quick. I'm
00:50:45 --> 00:50:48 fascinated by Mars. I just find the
00:50:48 --> 00:50:50 geography um,
00:50:51 --> 00:50:53 outstanding. A smaller planet than Earth
00:50:54 --> 00:50:57 with geographic um,
00:50:57 --> 00:51:00 highlights that are just mind bogglingly
00:51:00 --> 00:51:02 huge. Like the, the Olympus
00:51:02 --> 00:51:05 Mons for example. That, that is a volcano
00:51:05 --> 00:51:07 that is, it's the biggest in the solar
00:51:07 --> 00:51:10 system. And um, I think
00:51:10 --> 00:51:12 it is so high that it's actually sticking out
00:51:12 --> 00:51:14 of Earth's, out of Mars's atmosphere.
00:51:15 --> 00:51:17 Um, the canyons on Mars and
00:51:17 --> 00:51:20 there's more than one, but the biggest
00:51:20 --> 00:51:23 one dwarfs the Grand Canyon. On Earth.
00:51:23 --> 00:51:25 Like I think you can fit the Grand Canyon in
00:51:25 --> 00:51:28 one of its tributaries. Um, and the
00:51:28 --> 00:51:30 list goes on. It is a
00:51:31 --> 00:51:33 fascinating planet. I always like to think of
00:51:33 --> 00:51:35 it as, um, that was God's first attempt and
00:51:35 --> 00:51:38 he stuffed it up and then we came next.
00:51:40 --> 00:51:43 Uh, and, and because we've been able
00:51:43 --> 00:51:46 to send so many probes and rovers
00:51:46 --> 00:51:49 and satellites to Mars, we've
00:51:49 --> 00:51:51 been able to document it, get some
00:51:51 --> 00:51:54 incredible high res pictures of
00:51:54 --> 00:51:57 it. I just find it a beautiful, beautiful
00:51:57 --> 00:52:00 world. And I mentioned my sci fi
00:52:00 --> 00:52:02 trilogy earlier. Um,
00:52:03 --> 00:52:05 Mars is in it. I couldn't leave it out.
00:52:06 --> 00:52:09 So Mars for me that was a quick answer.
00:52:09 --> 00:52:11 What's yours? It's got to be in the solar
00:52:11 --> 00:52:11 system.
00:52:12 --> 00:52:14 Jonti Horner: It's a really tough one. And these kind of
00:52:14 --> 00:52:17 questions throw, throw me because it
00:52:17 --> 00:52:19 might be a childish question because it's
00:52:19 --> 00:52:21 kind of questions kids ask, but it's entirely
00:52:21 --> 00:52:24 a good question. I'm um, not as broken
00:52:24 --> 00:52:27 by this. While I was over in Switzerland, um,
00:52:27 --> 00:52:29 met up with an ex of mine whose daughter's
00:52:29 --> 00:52:32 now 9 or 10 years old and her daughter's
00:52:32 --> 00:52:35 doing English in school and all well and good
00:52:35 --> 00:52:38 and she wanted to practise her English and
00:52:38 --> 00:52:40 was talking to us a bit in English. And kids
00:52:40 --> 00:52:41 ask you what's your favourite colour? Things
00:52:41 --> 00:52:43 like that. She asked me what my favourite
00:52:43 --> 00:52:45 fruit was. And um, I was just broken because
00:52:45 --> 00:52:48 I've never really thought of that. And um, it
00:52:48 --> 00:52:49 took me like two or three minutes to kind of.
00:52:49 --> 00:52:52 It just put me into this head jam and um, I
00:52:52 --> 00:52:55 didn't know an answer. This one's a little
00:52:55 --> 00:52:57 bit like this. And to me this question's a
00:52:57 --> 00:53:00 bit like asking somebody with a large family
00:53:00 --> 00:53:02 who their favourite child is or asking
00:53:02 --> 00:53:03 someone who their favourite pet is. Now I
00:53:03 --> 00:53:05 suspect I don't have kids but I think
00:53:06 --> 00:53:07 the favourite kid varies from time to time
00:53:07 --> 00:53:09 with people who've got parents and they'd
00:53:09 --> 00:53:11 never say they have a favourite but there's a
00:53:11 --> 00:53:13 little ranking scale. It's Nanny Ogg and her
00:53:13 --> 00:53:15 extended family in the Discworld series where
00:53:15 --> 00:53:16 you could tell how in favour people were
00:53:16 --> 00:53:18 where, where the trinkets that they bought
00:53:18 --> 00:53:20 her were in the house. And you know, heaven
00:53:20 --> 00:53:21 forfend that the little thing you brought
00:53:21 --> 00:53:23 back from holiday ended up on the coffee
00:53:23 --> 00:53:25 table outside in the hallway because that
00:53:25 --> 00:53:27 meant you were really in the bad books. I
00:53:28 --> 00:53:30 really struggle to answer questions like this
00:53:30 --> 00:53:32 because they're all fascinating in
00:53:33 --> 00:53:35 different ways. You know, there are things
00:53:35 --> 00:53:37 that we can really get from the Mars, from an
00:53:37 --> 00:53:39 astrobiology point of view is really the
00:53:39 --> 00:53:41 obvious answer. Because it's a place that
00:53:41 --> 00:53:43 will look for life elsewhere. Jupiter's the
00:53:43 --> 00:53:45 obvious answer because it's been fundamental
00:53:45 --> 00:53:47 to a lot of the research I've done in terms
00:53:47 --> 00:53:50 of the question of Jupiter, friend or foe. It
00:53:50 --> 00:53:51 throws a lot of comments our way. It's a
00:53:51 --> 00:53:54 source of, therefore, indirectly the
00:53:54 --> 00:53:56 cause of many of the meteor showers and many
00:53:56 --> 00:53:58 of the meteor stones and stuff we see. I
00:53:59 --> 00:54:01 they would be contenders, as would the
00:54:01 --> 00:54:04 others. To a certain degree. Neptune, because
00:54:04 --> 00:54:06 it's a fabulous insight into how
00:54:06 --> 00:54:09 science can change of time and how we can
00:54:09 --> 00:54:11 discover things without seeing them. Neptune
00:54:11 --> 00:54:14 kind of presaged the exoplanet era
00:54:15 --> 00:54:17 because we discovered Neptune not by seeing
00:54:17 --> 00:54:19 Neptune but by observing Uranus, misbehaving
00:54:19 --> 00:54:22 and inferring that Neptune had to be there to
00:54:22 --> 00:54:24 cause that, uh, misbehaviour. Although there
00:54:24 --> 00:54:26 are some suggestions that Galileo actually
00:54:26 --> 00:54:29 saw Neptune in 1610 and should be
00:54:29 --> 00:54:31 credited as the discoverer but didn't realise
00:54:31 --> 00:54:33 what he had. There's a background star marked
00:54:33 --> 00:54:36 on one of his drawings, I think of the
00:54:36 --> 00:54:39 Galilean moons, the moons of Jupiter, where
00:54:39 --> 00:54:40 there is no, uh, star and people think it was
00:54:40 --> 00:54:42 actually Neptune. So there are some
00:54:42 --> 00:54:44 suggestions. Galileo was a discoverer of
00:54:44 --> 00:54:44 Neptune.
00:54:44 --> 00:54:45 Andrew Dunkley: Interesting.
00:54:45 --> 00:54:47 Jonti Horner: But for me, Neptune's fascinating because of
00:54:47 --> 00:54:49 that indirect discovery. But I think for me,
00:54:50 --> 00:54:52 if you really push it, I probably have to say
00:54:52 --> 00:54:54 the Earth. Oh, and a. It's the, uh, Earth
00:54:54 --> 00:54:57 because we is here. But the Earth is a place
00:54:57 --> 00:54:59 that's driven all that complexity in terms of
00:54:59 --> 00:55:01 life. And if you think about Mars being a
00:55:01 --> 00:55:04 complex place, the Earth is even more so
00:55:04 --> 00:55:06 because of the influence of the water and the
00:55:06 --> 00:55:07 atmosphere, the weathering and the plate
00:55:07 --> 00:55:10 tectonics, you know, so it's my favourite
00:55:10 --> 00:55:11 from the point of view of it's the only place
00:55:11 --> 00:55:13 I can sit around comfortably in shorts and T
00:55:13 --> 00:55:16 shirt and chat like this. Also because
00:55:16 --> 00:55:18 it is the window into
00:55:19 --> 00:55:21 the future of our knowledge of life elsewhere
00:55:22 --> 00:55:24 and it's a cradle of everything we know and
00:55:24 --> 00:55:27 everything we've experienced. I do have a
00:55:27 --> 00:55:28 deep and abiding love of the Earth, uh, from
00:55:28 --> 00:55:30 that point of view, but also as a scientist,
00:55:30 --> 00:55:33 the Earth is fascinatingly complex
00:55:33 --> 00:55:36 compared to the other planets. It's the only
00:55:36 --> 00:55:39 planet on which we observe plate
00:55:39 --> 00:55:41 tectonics. Yeah. Therefore it's the only
00:55:41 --> 00:55:44 planet whose surface on long time scales is
00:55:44 --> 00:55:47 that degree of changeable, immutable. You
00:55:47 --> 00:55:50 know, if I brought you back, say we did,
00:55:50 --> 00:55:52 um, play with Rennie's question from the
00:55:52 --> 00:55:54 start a bit more. We built the spacecraft
00:55:54 --> 00:55:57 from Tau Zero, we accelerated, had a problem,
00:55:58 --> 00:56:00 couldn't slow down, eventually managed to fix
00:56:00 --> 00:56:02 it, came back and we came back. In a billion
00:56:02 --> 00:56:04 years time, Mars would still look like it
00:56:04 --> 00:56:07 does today unless humanity terraforms
00:56:07 --> 00:56:09 Mars. Mars would look like it does today.
00:56:09 --> 00:56:11 Venus would look like it does today. All of
00:56:11 --> 00:56:12 the planets would look like they do today.
00:56:13 --> 00:56:15 Saturn's rings may have gone, peripheral
00:56:15 --> 00:56:16 things like that will have gone, but the
00:56:16 --> 00:56:18 Earth will be unrecognisable. With
00:56:18 --> 00:56:20 continental drift, the Earth wouldn't look
00:56:20 --> 00:56:23 like home. And even with a change in the
00:56:23 --> 00:56:24 atmosphere, the Earth may have changed.
00:56:24 --> 00:56:26 I've seen some suggestions that when the
00:56:26 --> 00:56:29 Earth was young, the oceans weren't blue,
00:56:29 --> 00:56:30 they were green. Yeah, I've heard, uh, that's
00:56:30 --> 00:56:33 how much the Earth has changed. The mountain
00:56:33 --> 00:56:34 ranges will have shifted. I always find it
00:56:34 --> 00:56:37 fascinating to wonder what is the biggest
00:56:37 --> 00:56:39 mountain that the Earth has ever had? And you
00:56:39 --> 00:56:41 Google that, that's been asked a lot.
00:56:41 --> 00:56:44 Nobody's really got a strong answer
00:56:44 --> 00:56:46 because a lot of it depends on the elasticity
00:56:46 --> 00:56:48 of the Earth's interior and the energy
00:56:48 --> 00:56:50 available for plate tectonics. Because the
00:56:50 --> 00:56:52 limiting factor on the height of the mountain
00:56:52 --> 00:56:55 on Earth is the sinking that you get as a
00:56:55 --> 00:56:57 result of the m mass of the mountain and the
00:56:57 --> 00:56:59 weathering that we get that wears it away on
00:56:59 --> 00:57:01 Mars, you don't have that. With Olympus Mons,
00:57:01 --> 00:57:03 there's no weathering. So it could just get
00:57:03 --> 00:57:05 bigger and bigger. Even though it will have a
00:57:05 --> 00:57:07 very deep root, it could keep getting bigger
00:57:07 --> 00:57:09 because there was nothing wearing it down
00:57:09 --> 00:57:11 again. So I think for me, because of the
00:57:11 --> 00:57:14 complexity and, um, because it gives me a
00:57:14 --> 00:57:16 place to do my astrophotography and live my
00:57:16 --> 00:57:19 life and all the rest of it, the Earth would
00:57:19 --> 00:57:20 have to be the top of the list. But trying to
00:57:20 --> 00:57:23 pick a planet other than the Earth is a bit
00:57:23 --> 00:57:25 like trying to pick your favourite pet or
00:57:25 --> 00:57:27 your favourite child. And it might be that
00:57:27 --> 00:57:28 you have one internally, but Heaven and you
00:57:28 --> 00:57:29 tell them.
00:57:31 --> 00:57:33 Andrew Dunkley: Very good answer, Very good answer. I love
00:57:33 --> 00:57:35 the question. So, uh, not childish at all
00:57:35 --> 00:57:37 and, uh, appreciate you sending it in. And if
00:57:37 --> 00:57:40 you'd like to send questions into us at Space
00:57:40 --> 00:57:42 Nuts, jump on our website, spacenuts
00:57:42 --> 00:57:44 IO or
00:57:44 --> 00:57:47 spacenutspodcast.com and click on
00:57:47 --> 00:57:49 the Ask me anything button at the top. It's
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00:57:51 --> 00:57:53 have a look around, cheque out the shop, sign
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00:58:00 --> 00:58:02 us and that'll wrap us up for another
00:58:02 --> 00:58:04 episode. Jonty, thank you so much.
00:58:05 --> 00:58:06 Jonti Horner: That's a pleasure. Thank you for having me.
00:58:06 --> 00:58:07 Andrew Dunkley: Always a pleasure.
00:58:07 --> 00:58:09 Professor John T Horner, professor of
00:58:09 --> 00:58:12 Astrophysics at the University of Southern
00:58:12 --> 00:58:15 Queensland. Hey. And, uh, Huw in
00:58:15 --> 00:58:17 the studio, um, couldn't be with us today. He
00:58:17 --> 00:58:19 realised that Earth wasn't his favourite
00:58:19 --> 00:58:22 planet, so he left. And from me, Andrew
00:58:22 --> 00:58:23 Dunkley. Thanks for your company. Catch you
00:58:23 --> 00:58:26 on the next episode of Space Nuts. Bye. Bye.
00:58:27 --> 00:58:30 Jonti Horner: You've been listening to the Space Nuts
00:58:30 --> 00:58:32 podcast, available
00:58:32 --> 00:58:35 at Apple Podcasts, Spotify,
00:58:35 --> 00:58:37 iHeartRadio or your favourite podcast
00:58:37 --> 00:58:40 player. You can also stream on demand at
00:58:40 --> 00:58:41 bytes. Com.
00:58:41 --> 00:58:43 Andrew Dunkley: This has been another quality podcast
00:58:43 --> 00:58:45 production from Bytes.
00:58:45 --> 00:58:47 Jonti Horner: Com. Um.