# Navigating the Cosmic Questions: Gravity Assists, Neutrinos, and Time Dilation Explained

An episode of [Space Nuts: Astronomy Insights & Cosmic Discoveries](https://invisiblenetwork.ai/podcast/1080090608), 21 Sep 2026, 31 min.

Audio: https://dts.podtrac.com/redirect.mp3/pscrb.fm/rss/p/op3.dev/e/api.spreaker.com/download/episode/75254643/navigating_the_cosmic_questions_gravity_assists_neutrinos_and_time_dilation_explained.mp3

Space Nuts: Q&A on BepiColombo, Neutrinos, and Time Dilation In this Q&A edition of Space Nuts, hosts Andrew Dunkley and Professor Fred Watson dive into a series of intriguing listener questions that span topics from the nuances of orbital velocity to the enigmatic world of neutrinos and the complexities of time dilation. Join them as they unravel these cosmic queries with their signature blend of insight and humour. Key topics - Larry from Nebraska asks about the BepiColombo mission and the relationship between gravitational assists and orbital velocity, prompting a discussion on how spacecraft navigate the solar system. - Eduardo explores the nature of neutrinos, questioning whether they are affected by gravity and whether they can be trapped by black holes. - Shumo presents a thought-provoking idea about using high-energy gamma rays or neutrinos as interstellar beacons, leading to a discussion on the potential for advanced civilisations to communicate through unconventional means. - Colin from Adelaide raises questions about time dilation effects as depicted in the science fiction movie "Project Hail Mary," specifically the implications of travelling close to the speed of light and the resulting age differences upon return to Earth. Timestamps 00:00 - Introduction to the Q&A format and listener interactions 01:20 - Larry's question about BepiColombo and gravitational assists 10:30 - Eduardo's inquiry on neutrinos and black holes 18:45 - Shumo's question about interstellar beacons using gamma rays or neutrinos 26:00 - Colin's confusion about time dilation in "Project Hail Mary" 32:15 - Discussion on the implications of time dilation and relativity Become a supporter of this podcast: https://www.spreaker.com/podcast/space-nuts-astronomy-insights-cosmic-discoveries--2631155/support.

## Transcript

[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] You've been listening to the Space Nuts
[30:34] podcast, available at
[30:37] Apple Podcasts, Spot, Spotify,
[30:39] iheartradio or your favourite podcast
[30:42] player. You can also stream on
[30:43] demand@bytes.com. this has been another
[30:46] quality podcast production from
[30:48] bytes.com.

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