Latest / Space Nuts: Astronomy Insights & Cosmic Discoveries / Navigating the Cosmic Questions: Gravity Assists, Neutrinos, and Time Dilation Explained

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Navigating the Cosmic Questions: Gravity Assists, Neutrinos, and Time Dilation Explained · Space Nuts: Astronomy Insights & Cosmic Discoveries

• 0:00
  Professor Fred Watson: Hi there.
• 0:00
  Andrew Dunkley: Thanks for joining us. This is Space Nuts, a
• 0:02
  Q and A edition, and we've got a bunch of
• 0:04
  questions to get through. Uh, Larry wants to
• 0:07
  know about orbital velocity and his question
• 0:10
  is quite timely because he brings up the
• 0:12
  BepiColombo mission. And we have an update
• 0:15
  on that. Uh, Eduardo is
• 0:18
  asking us about neutrinos. In fact, these
• 0:20
  last three questions dovetail into each
• 0:23
  other. So Eduardo about neutrinos. Uh,
• 0:25
  Shumo is asking about interstellar beacons
• 0:28
  that might be powered by neutrinos.
• 0:32
  And, uh, Colin is asking about time
• 0:34
  dilation. So plenty to talk about on this Q
• 0:37
  and A edition of Space nuts. Stick
• 0:40
  around.
• 0:40
  Professor Fred Watson: 15 seconds. Guidance is internal.
• 0:43
  10, 9.
• 0:45
  Ignition sequence start.
• 0:47
  Professor Fred Watson: Space nuts.
• 0:48
  Professor Fred Watson: 5, 4, 3. 2. 1, 2, 3, 4,
• 0:51
  5, 5, 4, 3, 2, 1.
• 0:53
  Andrew Dunkley: Space nuts.
• 0:54
  Professor Fred Watson: Astronauts report it feels good.
• 0:56
  Andrew Dunkley: And he's back again to, uh, solve all those
• 0:59
  riddles for us. It's Professor Fred Watson
• 1:01
  Watson, astronomer at large. Hello, Fre.
• 1:04
  Professor Fred Watson: How are you doing, Andrew?
• 1:05
  Andrew Dunkley: I'm doing well. You looking rather, um,
• 1:08
  um.
• 1:09
  Professor Fred Watson: Cold.
• 1:10
  Andrew Dunkley: Yes. Maybe. Yeah, we had
• 1:13
  a really good warm spell there for a while
• 1:15
  and then it just petered out and we're back
• 1:17
  to some quite chilly weather. By
• 1:20
  the time this podcast comes out, it could be
• 1:22
  back to warm again. It's
• 1:25
  that time of year where we've got the tug of
• 1:27
  war between winter trying to hang on and
• 1:30
  spring trying to take over. And so,
• 1:33
  uh, you get a little warm snap and then it's
• 1:34
  cold again and then you another warm snap and
• 1:36
  then one day it just stays warm and then it
• 1:38
  gets hot, hot, hot. And then the opposite
• 1:40
  happens going into autumn or fall or
• 1:43
  whatever, wherever you're from. And however
• 1:45
  you say it. But, um, yeah, right now we're
• 1:47
  into spring, uh, very windy
• 1:50
  weather this time of year out our way.
• 1:52
  Nothing to do with actual wind. It's just so
• 1:54
  many people sneezing. You just, you know,
• 1:57
  volatile environment.
• 1:59
  Professor Fred Watson: Yeah.
• 1:59
  Professor Fred Watson: Ah, did you, um, you were going to try and
• 2:01
  get some shots of, uh, pollen?
• 2:04
  Andrew Dunkley: I did try and so far I've failed.
• 2:06
  Professor Fred Watson: Okay.
• 2:07
  Andrew Dunkley: I haven't been, uh, but see, last time I got
• 2:09
  the pollen, uh, corona photo, I was
• 2:12
  using an older model phone and I've got
• 2:15
  a feeling that the new phone
• 2:17
  compensates and actually stops me from
• 2:19
  getting the shot.
• 2:21
  Professor Fred Watson: Yeah.
• 2:22
  Andrew Dunkley: Ah, but I'll give it another try. Uh, I might
• 2:24
  have been too early. Cause the best time is
• 2:26
  mid afternoon, isn't it?
• 2:27
  Professor Fred Watson: Probably, yeah. Uh, you should be able to see
• 2:29
  it with the naked eye and that should tell
• 2:30
  you what your, um, phone is likely
• 2:33
  to pick up.
• 2:34
  Andrew Dunkley: A good friend of mine once told me, though,
• 2:36
  never to look at the sun.
• 2:38
  Professor Fred Watson: Uh, indeed, I tell people that all the time.
• 2:41
  But that's why what you do is you get the sun
• 2:43
  behind a wall or a building or something,
• 2:45
  just enough that you can see the immediate
• 2:48
  sky around it and that's where you might see
• 2:50
  these colour bands. And just in case any of
• 2:52
  our listeners wonder what we're talking
• 2:54
  about, um, pollen, uh,
• 2:56
  particles in the atmosphere. Because there
• 2:58
  are many, many millions of them and they're
• 3:00
  all of a uniform size, they have an effect on
• 3:03
  light called diffraction, uh, and that
• 3:06
  you can get coloured rings around the sun
• 3:08
  caused by the diffracting effect of these
• 3:11
  pollen, uh, uh, particles. And that's
• 3:14
  what Andrew's looked for. I've seen them in
• 3:15
  Coonabarabran on occasion when I used to live
• 3:18
  out there. We tend not to see them in Sydney
• 3:20
  because the air is probably not
• 3:22
  Andrew Dunkley: clear enough because there's more pollution
• 3:24
  in
• 3:24
  Professor Fred Watson: the air than pollens. Yes, there is. Pollen
• 3:27
  pollination.
• 3:28
  Andrew Dunkley: Yeah, yeah. It's quite
• 3:31
  spectacular though. Yes, I think
• 3:34
  we talked about it on an episode and I said,
• 3:36
  okay, um, challenge acceptance, and went
• 3:38
  outside, took one photo and got it.
• 3:40
  Professor Fred Watson: Yes, yes, that's right.
• 3:42
  Andrew Dunkley: Proving more difficult this time. Let's get
• 3:45
  into our questions.
• 3:46
  Uh, this first one comes from Larry.
• 3:49
  Professor Fred Watson: Hello, Fred Watson and Andrew.
• 3:53
  This is Larry from, um, York,
• 3:56
  Nebraska, that is.
• 3:59
  I've been listening to your podcast
• 4:03
  almost continually for months.
• 4:07
  Heard an old edition
• 4:10
  talking about
• 4:14
  Speaker D: using,
• 4:14
  Professor Fred Watson: uh, the gravitational boost
• 4:17
  around planets,
• 4:20
  particularly Pepe
• 4:22
  Colombo. Fred Watson
• 4:25
  said that, uh, had to
• 4:28
  use, uh, nine booths to get
• 4:31
  the BP Columbo spacecraft to
• 4:35
  speed up to the speed of
• 4:37
  Mercury. However, from
• 4:40
  previous podcasts it seems
• 4:43
  the more you speed up the orbital
• 4:46
  velocity, the further away from the
• 4:49
  sun you get. So don't you have to
• 4:51
  use the
• 4:54
  gravitational wells to slow down
• 4:58
  to get to Mercury? Because Mercury's
• 5:00
  orbital velocity should be a whole lot less
• 5:02
  than Earth's. Thank you.
• 5:06
  Andrew Dunkley: Thank you, Larry. And, uh, hope all is well
• 5:09
  in wonderful Nebraska. Um,
• 5:12
  yeah, he brings up an interesting point. Uh,
• 5:15
  maybe we can discuss that after we break the
• 5:17
  news about BepiColombo. The
• 5:20
  BepiColombo mission to Mercury. And
• 5:23
  we did talk about how it had to do,
• 5:26
  um, quite a bit of manoeuvring, um, to,
• 5:29
  to achieve the velocity it required. You
• 5:32
  might remind us about that, Fred Watson, and
• 5:33
  then tell us, um, what's happening now.
• 5:36
  Professor Fred Watson: Uh, yes, so, uh, BepiColombo,
• 5:39
  a joint, um, ESA,
• 5:42
  uh, JAXA mission, I think. Japanese
• 5:45
  Aerospace Exploration Agency.
• 5:48
  Um, eight years it's been on
• 5:51
  its way so far and ah,
• 5:54
  there have been nine, I think I'm right, nine
• 5:57
  gravity assists, one of Earth, two of
• 6:00
  Venus and six of Mercury itself.
• 6:03
  Uh, and the reason why it's in the news at
• 6:05
  the moment is because um, the
• 6:08
  spacecraft has separated
• 6:11
  from its um, something called
• 6:14
  the MTM M M which
• 6:17
  is the uh,
• 6:21
  Mercury Transfer Module. In other
• 6:24
  words it's almost like a service module
• 6:26
  that's been uh, attached to the spacecraft.
• 6:28
  It's got solar panels, it's got you know,
• 6:31
  various uh, um, uh,
• 6:33
  feeds uh, on board for
• 6:36
  the requisites of the spacecraft itself
• 6:39
  that has now basically been jettisoned.
• 6:42
  Uh, and so BepiColombo is on its
• 6:45
  own as it spirals
• 6:47
  down towards the planet
• 6:50
  Mercury to eventually go into orbit
• 6:53
  around Mercury.
• 6:53
  Andrew Dunkley: And seeing they've now separated, uh, the
• 6:55
  lawyers will be deciding who gets what
• 6:57
  Professor Fred Watson: assets, who gets what. Yeah,
• 7:00
  indeed, that's right. Um, but let's just
• 7:03
  go to um, Larry's question. Uh,
• 7:06
  Larry's. You're
• 7:08
  absolutely right. This is something
• 7:11
  I think it does all our heads in that
• 7:17
  ah, if you've got a spacecraft in orbit
• 7:19
  around something and you speed it up,
• 7:22
  what happens is it goes to a higher orbit but
• 7:25
  it slows down that um,
• 7:28
  speed the bottom line. And the
• 7:30
  reverse is true with BepiColombo
• 7:33
  going to Mercury. So um,
• 7:37
  remembering that the Earth's orbital velocity
• 7:40
  around the sun
• 7:42
  is 30 kilometres per second,
• 7:45
  uh Mercury has an orbital
• 7:48
  velocity which is in the
• 7:51
  region of 50 kilometres per second.
• 7:54
  M uh because it's nearer the sun it
• 7:57
  needs a higher velocity to stop it from
• 7:59
  falling into the so 50
• 8:02
  kilometres per second is its speed. So in
• 8:04
  that respect BepiColombo
• 8:07
  is catching up uh in terms of
• 8:10
  speed uh with Mercury.
• 8:13
  But to do that you slow it
• 8:16
  down, you have to shed the Earth's
• 8:19
  uh, orbital velocity to push the
• 8:22
  spacecraft in towards the sun which
• 8:24
  speeds it up uh, so that it would be
• 8:27
  travelling faster than the Earth. If I can
• 8:29
  put it that way. It's all about the balance
• 8:31
  between gravity and velocity.
• 8:34
  Uh, I'm probably not making this sound very
• 8:36
  clear but the bottom line is that it's taken
• 8:38
  those uh, nine gravity assists to get
• 8:41
  from 30 kilometres per second going around
• 8:44
  the Earth to roughly 50
• 8:47
  kilometres per second average speed of
• 8:49
  Mercury. I think it gets significantly higher
• 8:52
  and lower because Mercury's got quite an
• 8:53
  elliptical orbit. Um, believe Its maximum
• 8:56
  is 59 kilometres per second when it's closest
• 8:59
  to the sun. So you're talking about a
• 9:01
  significant increase in velocity which
• 9:04
  achieved by slowing the spacecraft down so it
• 9:07
  falls in towards the Inner solar system. Does
• 9:10
  that make sense?
• 9:11
  Andrew Dunkley: Yeah, I think we talked about, uh, when this
• 9:14
  first came up, we talked about how much more
• 9:16
  difficult it is to go towards the
• 9:18
  centre of our solar system than it is to go
• 9:21
  Professor Fred Watson: outwards in that regard. It is, that's
• 9:24
  correct, yes.
• 9:24
  Professor Fred Watson: Yeah.
• 9:25
  Andrew Dunkley: So there's a lot of mathematicians, um,
• 9:28
  at work trying to figure this one out.
• 9:31
  Um, um, you know, taking into account
• 9:33
  orbital mechanics, M and the, uh,
• 9:36
  everything that goes into it, uh, it's quite
• 9:38
  an amazing feat, to be honest, to uh, to
• 9:41
  come up with this. And yet you think a jump
• 9:43
  of only 20 kilometres per second, 30 to 50,
• 9:46
  wouldn't. It doesn't sound all that
• 9:48
  difficult. But when you look at what they've
• 9:50
  actually had to do to achieve it.
• 9:52
  Professor Fred Watson: That's right.
• 9:52
  Andrew Dunkley: Quite extraordinary.
• 9:53
  Professor Fred Watson: It is, it's, it's, it is a significant amount
• 9:57
  when you think about it. You know, you're
• 9:59
  like that 20 kilometres per second, uh,
• 10:03
  is, it's. I think it was about the
• 10:06
  same orbital speed that, um, New Horizons
• 10:09
  was launched at when it was one of the
• 10:10
  fastest spacecraft ever launched. I think it
• 10:12
  was 23 kilometres per second it had. So
• 10:14
  it's a not insignificant jump in velocity.
• 10:18
  Andrew Dunkley: It just takes a lot of manoeuvring to make it
• 10:21
  happen.
• 10:21
  Professor Fred Watson: Indeed, yeah, that's right.
• 10:23
  Andrew Dunkley: There you go. Larry explained and still, um,
• 10:26
  scratching my head.
• 10:29
  Thanks for the question. Um, this is Space
• 10:32
  Nuts with Andrew Dunkley and Professor
• 10:34
  Fred Watson Watson. It's a Q and A edition.
• 10:37
  Professor Fred Watson: I believe that this nation should commit
• 10:39
  Andrew Dunkley: itself to achieving the goal,
• 10:42
  before this
• 10:43
  Professor Fred Watson: decade is out, of landing a man
• 10:45
  Professor Fred Watson: on the moon and returning him safely to the
• 10:48
  Earth.
• 10:48
  Andrew Dunkley: These nuts. Now, next question comes from
• 10:51
  Eduardo. I hope I'm pronouncing that
• 10:54
  correctly. Um, he says, given
• 10:57
  that neutrinos are the second most abundant
• 11:00
  subatopic particle, just after photons.
• 11:03
  Uh, but contrary to photons, they don't seem,
• 11:06
  seem to interact that much with matter. Do
• 11:09
  black holes swallow neutrinos
• 11:12
  or do they just pass through them? Are
• 11:14
  neutrinos affected by gravity at all?
• 11:18
  Professor Fred Watson: Um, so yes, they are. Uh, and
• 11:21
  I mean in the, you know, light is as. Well,
• 11:24
  of course, light, that's the thing about a
• 11:25
  black hole, um, uh, won't even
• 11:28
  allow the release of light beyond the event
• 11:31
  horizon. Uh, and the same is true
• 11:34
  with neutrinos. So neutrinos,
• 11:37
  they can't pass through a black hole. Uh, if
• 11:39
  they cross the event horizon, they're
• 11:41
  trapped, uh, just like particles of
• 11:44
  light. Uh, um,
• 11:47
  uh, it is a bit weird with
• 11:50
  neutrinos because they Exactly. Um, as
• 11:53
  Eduardo says, they pass through normal matter
• 11:56
  very easily. They don't interact much with
• 11:58
  normal matter. Uh, but nevertheless
• 12:01
  gravity and the curvature of space time,
• 12:03
  which is really what we're talking about with
• 12:05
  a black. Black hole, uh, they affect them
• 12:07
  just the same as everything else.
• 12:09
  Speaker D: Hmm.
• 12:10
  Andrew Dunkley: Simple as that. It wouldn't be too much. That
• 12:12
  would not be affected by gravity.
• 12:15
  Professor Fred Watson: Yes, that's right. Uh, we think dark
• 12:18
  matter is too. Well, we know dark matter is.
• 12:20
  That's the only way we know it exists. So.
• 12:21
  Andrew Dunkley: Yes, well, it seems to clump in higher
• 12:24
  gravitational fields, doesn't it?
• 12:26
  Professor Fred Watson: That's correct, yes.
• 12:27
  Andrew Dunkley: Um, even though we don't really understand
• 12:29
  it, although we do think they may have
• 12:32
  identified it recently. Uh, I think we talked
• 12:34
  about that last episode. So, um,
• 12:37
  yeah, we're slowly chipping away at the
• 12:39
  mystery of dark matter, hopefully. So
• 12:42
  he said that, um, neutrinos are the second
• 12:44
  most abundant subatopic particle. Is that
• 12:47
  right?
• 12:48
  Professor Fred Watson: Um, I'd need to cheque that, but I think it's
• 12:50
  probably right. Yes. Uh,
• 12:53
  I think that's ah, a correct statement.
• 12:56
  Andrew Dunkley: Do we know what they're supposed to do?
• 12:58
  What's their function?
• 13:00
  Professor Fred Watson: Well, yeah, they're um, byproduct
• 13:03
  of, uh, nuclear reactions.
• 13:06
  And they are prolific, as
• 13:09
  Eduardo suggested. So, um,
• 13:11
  with um, for example, the nuclear reactions
• 13:14
  that power the sun, uh, the
• 13:17
  um, what's it called, the fusion
• 13:20
  reactions, uh, it's got a name.
• 13:23
  Proton. Proton reaction. There's several
• 13:24
  different ones anyway. They not only
• 13:27
  produce, uh, helium from hydrogen,
• 13:30
  uh, but the energy that they produce, uh, is
• 13:32
  in gamma rays and in neutrinos as well.
• 13:36
  Professor Fred Watson: There you, um, go.
• 13:37
  Andrew Dunkley: Fascinating.
• 13:39
  Um, Eduardo, that's um, about all we can tell
• 13:41
  you about that, but thanks for the question.
• 13:43
  Lovely to hear from you. We're whipping m
• 13:45
  through them, Fred Watson. We are.
• 13:48
  Uh, this is Space Nuts, a Q and A edition
• 13:50
  with Andrew Nunkley and Professor Fred Watson
• 13:52
  Watson.
• 13:56
  Professor Fred Watson: Three, two, one.
• 13:59
  Andrew Dunkley: Space Nuts. Uh, our next question
• 14:02
  comes from Shumo, who says. Hi, Fred Watson
• 14:04
  and Andrew. Another alien communication
• 14:07
  question. SETI understandably concentrates on
• 14:10
  radio and optical signals, but are we being
• 14:13
  too anthropo. I can't
• 14:15
  say it. Anthropocentric
• 14:19
  about the carrier. Couldn't, uh, advanced
• 14:21
  civilization use high energy gamma rays or
• 14:24
  even neutrinos as an interstellar beacon,
• 14:27
  encoding information in the timing or energy
• 14:30
  of individual event. Example, repeated gamma
• 14:33
  ray or neutrino events from the same point
• 14:36
  in the sky following the prime numbers would
• 14:38
  be very difficult to explain. Naturally,
• 14:41
  given that, uh, uh, we
• 14:44
  already have gamma ray and neutrino
• 14:46
  observatories watching the sky. Has anyone
• 14:48
  systematically searched their data for
• 14:50
  mathematically structured patterns that might
• 14:53
  be artificial? That comes from Shumo in
• 14:56
  Oxford in the uk. That's a really good
• 14:58
  question. Like that's out of the box. Isn't.
• 15:01
  Professor Fred Watson: Um, is a good question. And
• 15:05
  in a way, um, the answer lies in
• 15:08
  the fact that uh, when gamma ray bursts
• 15:11
  were first detected, uh, which you'll
• 15:14
  remember were detected by spacecraft
• 15:16
  satellites that had been launched
• 15:18
  specifically to look for evidence of breaches
• 15:21
  of the Nuclear Test Ban Treaty, the
• 15:23
  Atmospheric Nuclear Test Ban Treaty. That's
• 15:26
  what they were built for. They didn't see any
• 15:28
  nuclear tests, but uh, they
• 15:31
  saw these things coming from the sky, uh,
• 15:34
  bursts of radiation. So the first thing you
• 15:36
  think of when you see something like that is,
• 15:38
  is this a SETI signal,
• 15:41
  uh, or something artificial now,
• 15:43
  um, with gamma rays and indeed neutrino,
• 15:46
  uh, radiation. I guess
• 15:49
  you would tend to put that,
• 15:52
  to put an artificial origin fairly
• 15:55
  low on the list of, of candidate,
• 15:58
  um, reasons why these things are flying
• 16:01
  through space. Because they're very, very
• 16:04
  high, energetic, high energy, um,
• 16:07
  carriers. Uh, we're talking about a high
• 16:10
  energy universe here. Having um,
• 16:14
  said that, I recently wrote the
• 16:16
  foreword for a book by a group of
• 16:19
  colleagues at the Western Sydney University,
• 16:22
  which is called High Energy
• 16:23
  Astrobiology. Uh, and there you
• 16:26
  have it. The link between high energy
• 16:30
  physics phenomena and the science
• 16:32
  of the origin and evolution of life.
• 16:36
  Uh, and so I can't remember actually the
• 16:38
  details of the chapters. Um, uh, I
• 16:41
  do have a copy of the book which I looked
• 16:43
  through and enjoyed reading. Um,
• 16:46
  but uh, I can't remember the details. But
• 16:49
  um, I wouldn't mind betting that somewhere in
• 16:52
  there somebody is basically
• 16:55
  highlighting essentially the same question
• 16:58
  that Schumach has raised here.
• 17:01
  So.
• 17:01
  Andrew Dunkley: Yeah, I imagine so. But
• 17:04
  surely there'd be easier ways to send a
• 17:06
  message if you were.
• 17:07
  Professor Fred Watson: Yeah.
• 17:07
  Professor Fred Watson: Uh, rather than blowing up a planet or
• 17:09
  something like that, which is, you know, the
• 17:11
  kind of energies that we're talking about
• 17:12
  here. Yes.
• 17:13
  Andrew Dunkley: No, it kind of worked for. Ah, the Empire
• 17:16
  didn't.
• 17:19
  Professor Fred Watson: Depends on whose side you're on really.
• 17:21
  Andrew Dunkley: Yes, but,
• 17:23
  um. Would lasers be feasible over, um,
• 17:26
  parsecs?
• 17:28
  Professor Fred Watson: Yeah, they are. I mean, and so. Yes. But you
• 17:31
  know, in that regard I, uh, guess, um.
• 17:34
  Uh, you know, Shuma's already raised
• 17:38
  the issue that um, we've got,
• 17:41
  uh, the idea of optical communications
• 17:44
  as part and parcel of our
• 17:46
  retinue of researchers,
• 17:50
  uh, when it comes to possible
• 17:52
  SETI signals. Um,
• 17:55
  and exactly as
• 17:58
  Schumacher says, uh, SETI understandably
• 18:00
  concentrates on radio and optical signals.
• 18:02
  And yeah, that's why, because they're going
• 18:04
  to be the easiest to produce. Very much so.
• 18:07
  Optical signals I think have been neglected a
• 18:09
  bit in comparison with radio signals.
• 18:13
  But that is coming to an end because,
• 18:17
  uh, the latest instruments
• 18:20
  that we have, looking at the optical sky,
• 18:22
  optical and near infrared sky, and I'm
• 18:24
  thinking particularly of the Vera C. Rubin
• 18:27
  Observatory. Now it finds transient
• 18:29
  events, uh, millions per
• 18:32
  night. By transient events, I mean things
• 18:35
  that come and go in the dark. And of course
• 18:37
  communication signals would fall into that
• 18:40
  category.
• 18:40
  Speaker D: Yeah.
• 18:41
  Andrew Dunkley: When I was doing the research for my
• 18:45
  new sci fi trilogy, um,
• 18:48
  the first book in the series is called the
• 18:50
  Signal. And I did
• 18:53
  quite um, a bit of research on what
• 18:56
  signal would be likely to be received
• 18:59
  on Earth by an alien intelligence.
• 19:02
  And it basically came down to the signals
• 19:05
  we use every day on our own planet. The
• 19:07
  signals in the hydrogen line,
• 19:10
  1.4 to, to 1.66
• 19:13
  gigahertz, um, 14, 20 megahertz
• 19:16
  range that AM radio
• 19:18
  frequencies basically, um, more or less. Uh,
• 19:21
  so that's what I based it on.
• 19:24
  Um, but
• 19:28
  that's more likely to be the kind of
• 19:31
  signal that would be sent by a communicative
• 19:34
  intelligence beyond Earth. And
• 19:36
  that's where the Drake equation comes in.
• 19:39
  Um, I think they're based on an
• 19:41
  intelligence that is capable of
• 19:44
  communication.
• 19:46
  Professor Fred Watson: And you're absolutely right.
• 19:49
  Right from the beginning of what you might
• 19:51
  call the SETI era, looking for
• 19:54
  extraterrestrial intelligence. That
• 19:56
  hydrogen line that you've spoken of, 21
• 19:59
  centimetre line, to put it in wavelengths
• 20:01
  rather than frequency, um,
• 20:04
  is what cold hydrogen emits.
• 20:07
  So it's the most prolific
• 20:10
  Professor Fred Watson: spectral uh,
• 20:11
  Professor Fred Watson: line in the whole universe
• 20:14
  of any uh, frequency band.
• 20:17
  And so um, it is naturally where you would
• 20:20
  start thinking about broadcasting if you are
• 20:22
  trying to send a signal out, uh, to
• 20:25
  another intelligence, which
• 20:28
  that's a whole, I guess the whole um,
• 20:32
  proposition of SETI that uh, the
• 20:35
  intelligent species out there might want to
• 20:37
  communicate. And how they're going to do it.
• 20:39
  Well, they're going to use the spectral line
• 20:41
  that we're looking for anyway because that's
• 20:43
  something we're using to m. Map the universe.
• 20:45
  Speaker D: Yeah.
• 20:46
  Andrew Dunkley: Was the wow. Signal in that frequency range?
• 20:48
  Professor Fred Watson: I think I, uh, think it was, yes. Yeah, I
• 20:50
  think it was.
• 20:51
  Andrew Dunkley: And that, that came from the um,
• 20:54
  Sagittarius constellation region of
• 20:57
  spaces. Because I researched that as well
• 21:01
  off the top of my head. Um, they
• 21:04
  have actually studied that part of the
• 21:06
  universe and they at this moment cannot find
• 21:08
  anything to suggest that it was an artificial
• 21:11
  uh, signal. But
• 21:14
  they still haven't figured that one out, have
• 21:16
  they?
• 21:16
  Professor Fred Watson: No, there have been a few ideas like radio,
• 21:19
  uh, emission from comets. That was one. Uh.
• 21:21
  Cause I think there were comets in the sky at
• 21:23
  the time. But yeah,
• 21:26
  it's still an open question.
• 21:29
  Andrew Dunkley: Yeah, I guess so. All right, um, that's
• 21:32
  a great question. Thanks uh, Shumo, for
• 21:34
  sending it in. Um, but uh, yeah, there's
• 21:37
  probably easier ways to do things and uh, if
• 21:40
  you're going to send a signal to an
• 21:42
  alien civilization, you probably want them to
• 21:45
  be able to figure it out rather
• 21:48
  than send them something complex and they go,
• 21:50
  no, no, I don't know what that was. Um, let's
• 21:53
  go to our final question from Colin.
• 21:56
  Speaker D: Hello, Andrew and Fred Watson.
• 21:58
  Colin from Adelaide. I love the
• 22:00
  science fiction movie project Hail Mary,
• 22:03
  which I've seen twice. But I'm still quite
• 22:06
  confused about the time dilation effects. In
• 22:09
  the movie. RYLAND Grace travels
• 22:11
  12 light years to his destination
• 22:15
  at ah, Tau Ceti in four years
• 22:18
  and eight months. How can this be? The
• 22:20
  Beatles powered by the astrophage
• 22:23
  fuel carrying Tau Moeba, the
• 22:26
  solution to the astrophage problem with
• 22:29
  the sun reach Earth even quicker than.
• 22:32
  Than this. How can that be? And lastly,
• 22:35
  if Ryan Grace had returned
• 22:38
  to Earth, how much younger would he be
• 22:41
  than those he left behind? Very confusing.
• 22:44
  I hope you can help. Thank you. Love the
• 22:46
  podcast.
• 22:48
  Andrew Dunkley: Yeah, thanks, Colin. Um, I've seen the movie
• 22:51
  a couple of times myself and I've got to
• 22:53
  confess that I'm as confused as Colin
• 22:56
  in regard to the distances travelled and how
• 22:59
  fast they achieved it. Even though they came
• 23:02
  up with a new drive concept that
• 23:05
  um, even that I had trouble getting
• 23:08
  my head around, they, they did explain it and
• 23:10
  I just sat there sort of glazed look on
• 23:13
  my, on my face. Um, because it
• 23:16
  was uh, it was very cleverly done.
• 23:19
  But I don't know how they did it.
• 23:22
  Someone else might be able to explain uh, it
• 23:25
  to me. Um, I suppose we
• 23:28
  can tackle the question in two ways. My
• 23:31
  answer, Colin, is it's science fiction. You
• 23:33
  can do whatever you damn would like. Um,
• 23:36
  but that's just, that's the, that's a very
• 23:38
  simplistic answer. Um, when I
• 23:41
  write my science fiction novels, I
• 23:44
  want at least some of it to be as
• 23:47
  believable as possible. And so
• 23:50
  I'm, I'm in your boat. I want to know how
• 23:52
  they did it. Um, the
• 23:55
  other, yeah, the other side of it is,
• 23:57
  um, that we should
• 24:00
  explain time dilation and
• 24:03
  see where that falls within the parameters of
• 24:05
  the film. You haven't seen it, Fred Watson,
• 24:08
  have you? Oh, you have? What did you Think.
• 24:10
  Professor Fred Watson: Um, so, uh. Well, I was hoping you'd have the
• 24:12
  answer to this question. Not like, because I
• 24:15
  did watch it. I watched it on a flight from,
• 24:19
  a flight from Sydney to Paris,
• 24:23
  um, which uh, gave
• 24:26
  me enough time to watch the movie uh,
• 24:30
  thoroughly but still,
• 24:33
  I was still vaguely half asleep at the time.
• 24:35
  So um, and look, so I can't,
• 24:38
  I'm, I can't comment on those um, those uh,
• 24:41
  values uh, that um, that uh, Colin's
• 24:44
  given us. But.
• 24:45
  Andrew Dunkley: Well I, I got it. I've just done a quick
• 24:47
  search and. Okay, so the, the destination
• 24:50
  for our hero of the movie uh,
• 24:53
  was the star system Tau Ceti which was,
• 24:56
  is 11.9 light years from
• 24:59
  Earth. To get there.
• 25:02
  Um, the spacecraft was
• 25:04
  powered by a microorganism called
• 25:07
  Astrophage that converts mass into pure
• 25:10
  energy and that enabled
• 25:13
  the constant acceleration of
• 25:15
  1.5 g for the first half of the trip
• 25:18
  and then it flips and decelerates at 1.5 g
• 25:21
  for the second half of the trip. Its peak
• 25:23
  velocity was roughly
• 25:25
  92% the speed of light. Okay.
• 25:29
  If that's the case, travelling
• 25:31
  11.9 light years would take
• 25:34
  longer than 11.9 years and
• 25:37
  he got there in, I think it was
• 25:40
  four years. Uh, uh, that's why
• 25:43
  Colin's confused.
• 25:44
  Professor Fred Watson: Well, I mean time dilation only works.
• 25:47
  Andrew Dunkley: Yes.
• 25:48
  Professor Fred Watson: When you're talking about two separate frames
• 25:51
  of reference.
• 25:52
  Andrew Dunkley: Well, it's 11.9 light years if
• 25:55
  you're staying on Earth.
• 25:56
  Professor Fred Watson: Yes.
• 25:57
  Andrew Dunkley: When you're travelling it's a different
• 25:59
  kettle of fish.
• 26:00
  Professor Fred Watson: Yes, that's correct. Um, and so the
• 26:03
  time dilation, the time basically
• 26:06
  slows down for you as you're travelling
• 26:09
  relative to the person back on Earth.
• 26:12
  Uh, and so that seems to make sense from
• 26:15
  what you were saying that um, the experience
• 26:19
  of the astronaut is one
• 26:22
  of, in terms of Earth, time is a
• 26:24
  shorter time even though as far as the clocks
• 26:26
  are concerned they're still ticking at the
• 26:28
  same speed for the person who's travelling.
• 26:30
  Andrew Dunkley: Yeah. And I uh, must confess that
• 26:33
  in doing my research for the book that's
• 26:35
  um, the target star that
• 26:38
  shall remain nameless in my storey. Otherwise
• 26:41
  it gets too predictable.
• 26:44
  Professor Fred Watson: Um,
• 26:47
  Andrew Dunkley: was a certain distance from Earth
• 26:50
  as the crow flies or as the photons
• 26:53
  fly, but in travelling there
• 26:56
  in a, in a capable vessel,
• 26:59
  um, the, the time to get
• 27:02
  there was cut. Right. Quite dramatically
• 27:05
  but in doing so you didn't age,
• 27:08
  but everybody back on Earth did still age
• 27:11
  the so many light years. Uh,
• 27:14
  and, and that's the quandary, isn't it?
• 27:16
  Professor Fred Watson: It's um.
• 27:17
  Professor Fred Watson: Well, yes, the Twins paradox, basically.
• 27:19
  Andrew Dunkley: Exactly.
• 27:20
  Speaker D: Yeah. Yeah.
• 27:21
  Andrew Dunkley: So, um, it is a thing and it.
• 27:25
  Yeah, the. The traveller doesn't,
• 27:28
  um, take that amount of time to get there
• 27:30
  because of the fact that they're
• 27:33
  moving through space at a. At a high
• 27:35
  velocity. And, um.
• 27:39
  Yeah, I really
• 27:42
  struggle to explain this stuff.
• 27:44
  Professor Fred Watson: Well, you should. Yeah. The calculation's
• 27:46
  easy. Uh, for time dilation, I've seen
• 27:49
  it. 1 over the square root of 1 minus
• 27:52
  V squared over C squared. You could do that
• 27:54
  in your head, Andrew.
• 27:55
  Andrew Dunkley: Yeah, I actually had it written down.
• 27:58
  I did have it written down. Yeah. That's the
• 28:01
  one. Um, but, yeah, I don't have to.
• 28:04
  Professor Fred Watson: Nearly everything in special relativity has
• 28:06
  this terminate of 1 over the square root
• 28:09
  of 1 minus V squared over C squared. It pops
• 28:12
  up everywhere. Time dilation, Lorentz
• 28:14
  contraction, all of those things. It's the
• 28:17
  same factor.
• 28:19
  Andrew Dunkley: Suggest to Colin, um, if he wants to read the
• 28:22
  Human Epoch, Part one, uh,
• 28:25
  there is an explanation of it in there.
• 28:27
  Professor Fred Watson: This is your trilogy. Yes, part one
• 28:30
  of the trilogy. I think that's what you
• 28:32
  probably should do, Colin. Uh, and then you
• 28:35
  can bug Andrew about it.
• 28:38
  Andrew Dunkley: Well, I've already had a few people come to
• 28:40
  me and say, hang on a minute, hang on
• 28:43
  a minute. How did you figure that out?
• 28:45
  Professor Fred Watson: As you say, you're a science fiction writer.
• 28:48
  You can say whatever you want.
• 28:50
  Professor Fred Watson: Yeah.
• 28:50
  Andrew Dunkley: But I like. I like to get things right, so.
• 28:52
  Professor Fred Watson: Uh. Yeah, well, you should. That's right.
• 28:55
  Andrew Dunkley: All right. Uh, Colin, that's a fun question.
• 28:58
  And it is a really great film. If.
• 29:00
  If you haven't seen it. It's still one of the
• 29:03
  top picks on some of those, um, streaming
• 29:05
  platforms. Because it's, uh. It's such a.
• 29:07
  It's almost a delightful film in. In some
• 29:10
  ways.
• 29:11
  Professor Fred Watson: Yeah. I thought it was a comedy, actually.
• 29:13
  Andrew Dunkley: Yeah, it bordered on that.
• 29:15
  Speaker D: That.
• 29:15
  Professor Fred Watson: Yeah.
• 29:15
  Speaker D: Yeah.
• 29:16
  Andrew Dunkley: And it sort of. It sort of had a little
• 29:19
  bit of the Muppet show in it at times,
• 29:22
  but. But it really was a great storey. I
• 29:24
  loved it.
• 29:25
  Professor Fred Watson: Yeah.
• 29:25
  Andrew Dunkley: Yeah, yeah. Thanks, Colin. Great to hear from
• 29:27
  you. Thanks to everyone who sent us
• 29:29
  questions. Don't forget you can do the same
• 29:31
  via our website, space nutspodcast.com space
• 29:34
  nuts IO and just click
• 29:37
  on the Ask Me Anything tab at the top. And
• 29:39
  don't forget to tell us who you are and where
• 29:40
  you're from. And have a look around while
• 29:41
  you're there. And don't forget to leave
• 29:43
  reviews wherever you listen or watch us. Um,
• 29:47
  they help. Don't know who they help. I don't
• 29:49
  know why they help, but apparently they help.
• 29:51
  Uh, unless they're not good reviews, then
• 29:53
  they don't help. See,
• 29:56
  that's, you know, that's harder to
• 29:59
  explain than time dilation. Uh, and thank,
• 30:02
  uh, you, Fred Watson, for your help today.
• 30:04
  Couldn't have done it without you.
• 30:05
  Professor Fred Watson: Uh, I don't think I could have done it
• 30:07
  without you either, Andrew. So there you go.
• 30:10
  Just as well we're here. You're welcome. And
• 30:12
  we'll talk again soon.
• 30:13
  Andrew Dunkley: We will. Professor Fred Watson Watson,
• 30:15
  astronomer at large, and thanks to Huw in the
• 30:16
  studio. Couldn't be here due to an issue with
• 30:19
  time dilation, but we're expecting him in the
• 30:21
  year 2154. And from me, Andrew
• 30:24
  Dunkley. Thanks for your company. We'll see
• 30:26
  you on the next episode of Space Nuts. Bye
• 30:28
  Bye. Oh, hang on. Bye Bye.
• 30:32
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• 30:34
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• 30:37
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• 30:42
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• 30:48
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