#355: Find Out About the Universe: Space Science Questions Answered

AI Transcript

ANDREW DUNKLEY: Hello again. Thanks for joining us on Space Nuts. My, I'm your host, Andrew Dunley. This is episode 355. And as we tend to do every fifth episode, we dedicate it all to audience questions, which we'll be doing today. We'll be looking at the expansion of the universe. What it's like to actually stand on an another planet. How will your eyes work?

ANDREW DUNKLEY: Will you see what is actually there? Will they work properly? We're going to talk about causation, we're gonna run one really fascinating question is does a planet need a moon to bear life and a few other things like tumbling in space? What happens there and a bunch of other stuff all coming up on this episode of Space Nuts.

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ANDREW DUNKLEY: And joining me to answer all is Professor Fred Watson astronomer at large. Hello, Fred.

FRED WATSON: Good day. Is that the correct term?

ANDREW DUNKLEY: Good day. Depends if you're talking, if you're talking English or Australian. Good day, Andrew.

FRED WATSON: Good day.

ANDREW DUNKLEY: Good day. Soft on the G.

FRED WATSON: Yeah. So on the.

ANDREW DUNKLEY: That's right. Yeah. It's amazing though when you're Overseas, particularly Canada and the US, how many people try to say it to you because they know you're an Aussie, please. Please don't.

FRED WATSON: Well, I do too good.

ANDREW DUNKLEY: I, no, it's, it's just, just a thing, isn't it? We're known for saying it. So, and we do, it's just a part of our natural vernacular, isn't it?

FRED WATSON: Exactly.

ANDREW DUNKLEY: So, anyway, we've got a heck of a lot to cover. Did you have some homework from last week that you wanted to do? Deal with? I don't know. Ok. Well, let's knock that over first.

FRED WATSON: Do you want to hear that? Sure. Ok. We had a question.

FRED WATSON: I think it was, where are we? Yes, it was Rusty.

ANDREW DUNKLEY: He's got, he's got another one for us. This is he.

FRED WATSON: And he was talking about, I think he'd read about a white dwarf star that was 10 billion years old.

FRED WATSON: But that contradicts all the, the problem with white dwarf stars is that they are the end product of normal stars like the sun. So you only get a white dwarf when the star runs out of its energy and it is by then about 10 billion years old. So, the star is about 10 billion years old. Yeah.

FRED WATSON: But the universe is only, he's only 13 years old. That's right. So, if, if you've got a white dwarf that's 10 billion years old. And I think that was the number, then you can't have, you know, a star that's gone through its life and then formed a white dwarf and that was 10 billion years ago because that makes 20 billion years and the universe isn't that old.

FRED WATSON: And I, I think that, it may well be that what? Rusty read, I don't know because I'm not in Rusty's head. But what he read was that maybe the age of the star is 10 billion years before it forms a white dwarf.

ANDREW DUNKLEY: Maybe that would make more sense, the.

FRED WATSON: The record breaker for a white dwarf. In other words, a star that is, that has become a white dwarf at the end of its long life, it's turned into a white dwarf. That record is an object whose name I had in front of me a minute ago. I wonder if I can find it again. Because it's not, it's not the kind of name that you come across every day.

FRED WATSON: It is called L S PM J 0207 plus 3331, that's the oldest white dwarf star and it is thought to be three billion years old. So, that means, you know, if it's progenitor star did last 10 billion years, then it, it turned into a white dwarf having shed its outer envelope, then you've, you've got three billion years and it still means it's within the age of the universe.

ANDREW DUNKLEY: So, at that age it whinges about everything, blames the government for everything and thinks young people have no idea.

FRED WATSON: Yeah. Yeah. Just, just like me.

ANDREW DUNKLEY: The young stars have no idea today.

FRED WATSON: Don't do any of those things.

ANDREW DUNKLEY: All right. Was it, was there another one?

FRED WATSON: Yes, there was about, what you would see inside a black hole and that if you were trying to look out. Yes. But you wouldn't be in the black hole because the black hole is a singularity. And once you're in there, you've had it.

FRED WATSON: But you would be within the event horizon and it turns out that the gravitational distortion is so much that the singularity itself which is black fills your entire field of view because of the gravitational distortion. So it's dark you see inside the event horizon. That's right.

ANDREW DUNKLEY: Ok. Very good. Alright, I like this homework situation.

FRED WATSON: Well, it means you get a better answer than the one that I pull off the top of my head, which is the usual scenario he had very tough on based of course on the nearly 60 years of astronomical experience, but that as against four billion years of which is coming next.

ANDREW DUNKLEY: Alright. Let's get stuck into our questions. And the very first one comes from, in fact, these first two are related, but they're different questions. The first one comes from Gary.

GARY: Hi guys. It's Gary from Sale in Manchester in England. I love the podcast. I love this. It's one of my favorites I listen to all week and I look forward to listening to it, but I do have a question. And I was hoping you may help or maybe it's just a theory or just a bit of moment of madness. So the, the universe is expanding or the edge of the universe is expanding faster than the speed of light.

GARY: What I was wondering could this be caused by the fact that space itself between here and that point actually has, is not, it is a vacuum obviously, but is there a density to it which is created by dark matter? And obviously, as there isn't anything to which is therefore restricting light or anything to travel beyond the speed of light.

GARY: But at the end of the universe, there is no, there's nothing there restricting it, no dark matter or energy or anything. And his space is space therefore being having the to expand. I was also wondering if that could be influenced by heat. So at the end of the universe, I would assume that it's on the, on the premise of the universe it's free or a bit more, you know, below to the point where there is no measurement on heat.

GARY: And therefore, does that give it the ability to expand? And as soon as you put any, anything, anything above minus 273 into the equation, does that therefore force it to be, some form of restriction on the, on the ability for that matter is, is influenced by something else anyway. Bit Bonkers. But hopefully you can, give something about and, and, and let us know what you think.

ANDREW DUNKLEY: Do you? Ok, thank you, Gary. Bit Bonkers. He thinks these questions a bit Bonkers. It's a big one. It's a big question.

FRED WATSON: It's got lots to it. But lovely to hear that. That northern England, the, the flat, flat vowels that, I've had all my life and, I'm just gonna do a quick aside, harking back to something that we were talking about a few minutes ago. The Australian Way is good. Yep. Where I grew up in Bradford, in the north of England that the greeting was then.

FRED WATSON: Oh, really?

ANDREW DUNKLEY: Then I thought you were gonna say that that's Liverpool, isn't it?

FRED WATSON: Well, it's, it's a different, that's a, that, that's, that's a, that's an alert signal a up whereas, hello translates to nothing now then. Yeah, that was it. Usually that's all you got. Nothing. Wow. And I'm sure Gary, listening to this from Sale in Manchester, I think it's probably very similar in Manchester. It is across the, across the border. Of course, the Lancashire Yorkshire border.

FRED WATSON: But yeah, nothing. So, I should, I should use that when we start the show. Should, should the trouble is people where I grew up, they don't say much and quite often now you got, so let's move on to the question indeed about the edge of the universe. Well, yeah, so the, I mean, the horizon that really stops us from seeing any further into the universe is the cosmic microwave background radiation.

FRED WATSON: And in a sense that tallies with what Gary's saying because that horizon is actually receding from us at the speed of light. It's all the time. It is moving away from us at the speed of light, which sounds crazy. But it's currently 13.8 billion light years away in the sort of in the reference frame that we're, we're, you know, that, that, that we can understand.

FRED WATSON: It's so there is a point beyond which we cannot see and it is, it is flooded with radiation now that radiation permeates the whole universe and probably the universe beyond the horizon as well because it's the same thing.

FRED WATSON: It's, it's a radiation that comes from the Big Bang that you're wherever you are in the universe, you're looking back so far in time that you're seeing that sphere of radiation surrounding you, you're in a bubble and I call the cosmic microwave background radiation, the cosmic wallpaper because it's behind everything that we can see all the galaxy stars planet everything is in front of that.

FRED WATSON: So that's a horizon. And the idea of because it's a radiation. It, it, it's got a temperature. And the temperature is 2.7 degrees above absolute zero. That's the temperature of space and it's the same everywhere.

FRED WATSON: And so, you know, Gary's point, our idea about the, the warm universe being, or, or the, the, the outer, this sort of beyond, beyond the horizon being colder than, than what we are, doesn't really hold up because in fact, beyond that horizon, it's, it's hotter than what we are because you're looking back at the Big Bang itself. And so, but, but, but the temperature in our areas 2.7 degrees above absolute zero.

FRED WATSON: So I think you know that there is a, the, the, the, the pressure that that Gary speaks of is, is essentially the radiation, the dark energy that we don't really know too much about dark matter behaves like normal matter does as far as gravity is concerned and it pulls back on the acceleration of the the universe.

FRED WATSON: It tries to slow it down. But the dark energy, the energy of the space itself that springing us of space is fighting against that and wins easily because it's about 75% of the mass energy budget of the universe. So some interesting ideas there, Gary and I'm glad you you, you said sent that to us because you formulated things in a, in a, in a different way.

FRED WATSON: But the bottom line is. I think we're still baffled about what dark energy and dark matter are and we still have a universe whose edge we've never seen and which may not have any kind of limit. It's, it may be infinite. And we don't know the answer to that if.

ANDREW DUNKLEY: There is an edge and it's moving out at the speed of light. If we knew the actual size of the universe, it would be just unthinkable as to how much bigger it's getting every split second. Yeah.

FRED WATSON: And in fact, that's sort of that it, you can say that about the cosmic microwave background radiation, the way that is receding from us at the speed of light.

FRED WATSON: And you can, you can't, you can't see anything beyond that. And, but if you were in a different part of the universe, you'd still see it receding from us at the speed of light. And it looks as though it's 13.8 billion light years away. But, but because the universe is so big, we really don't know what's beyond it and how far long it goes.

ANDREW DUNKLEY: It's a big question and thank you, Gary for sending it in to us, which leads to another question from Rod on large scales. The universe is expanding by increasing the amount of space where whatever force is causing the universe to expand, that force is greater than gravity. Hope that makes sense.

ANDREW DUNKLEY: However, if space itself is expanding and time is bound up with space to be space time? Does this mean that on those large cosmic scales, time is also being created along with space? In other words, the very fabric of space is being created or is the existing fabric of space being stretched?

ANDREW DUNKLEY: And what does that mean for time or the time part of space that is being stretched, would time run slower in that stretched space? Thank you very much Rod and thanks for signing up. He's become a patron. We really appreciate that kind of support. So, thank you very much. Indeed, Rod. And that too is a very interesting way of thinking about the expansion of the universe.

FRED WATSON: Yeah, so time is bound up with space in this thing we call space time. But what's interesting is that to talk about an expansion, you're talking about a rate, something happening at a rate and a ray always tells you that time is in the, in the denominator. So it's something divided by time is gives you a rate. And so time kind of in there twice, which is a bit odd. Maybe it cancels out.

FRED WATSON: So, but, you know, we think in in cosmology, we do think more in terms of the expansion of space itself. That Rod's right. I didn't pick up where the rods from. Actually, I didn't say he didn't tell us, I don't think it came up on the email, maybe not, not that, that makes him the answer to the question could be different if you're in Lancashire though.

FRED WATSON: The, the, the, the idea is that, the, the, the universe, yes, what, what, what I was gonna say was if you, if you think about, rest frames, that's what you've got to get your head around in terms of the relativistic ideas. So, we are in a rest frame that is kind of sitting there quite at peace with the universe. Well, most of it and, and sort of watching, watching all this motion take place.

FRED WATSON: But if you think about the, the fact that when you look back in, in time, which we are doing with our telescopes, then you're looking at a different rest frame and, and even if time was behaving in the same way, then it would look slightly different to us.

FRED WATSON: And we see that we see that effect in the way Galaxies evolve and the way they behave, you have to put in a sort of relativistic correction because of the different the, the, the different reference frame that we're in.

FRED WATSON: And I'm kind of making a bit of a hash of this because it's quite a complicated question. But the bottom line is, you know, it's probably easiest to think in terms of just space when we think of the expansion of the universe and time will change. But by amounts less than what you might think.

FRED WATSON: In terms of, you know, the time dilation, that the gravitational time dilation and things of that sort, I suppose the best instance of it is when you look at, and I think this is going the right way when you look at the, the, the, the, the, the, the, the steps in the earliest phase of the universe's life, we talk about all these things happening, but they happen within 10 to the minus 33 of a second or something like that.

FRED WATSON: So everything is really squashed up. And I think should check this, but probably part of that is because of the relish, relativistic effects.

ANDREW DUNKLEY: Ok. I hope Rod understood what you just said because I wish I completely bamboozled.

FRED WATSON: There you go. Can we get tune in next week listeners? They'll be baffled again.

ANDREW DUNKLEY: Yeah, that's part of the job. Thank you, Rod.

ANDREW DUNKLEY: I appreciate it and we, we appreciate you becoming a patron. So that's terrific.

FRED WATSON: Cancel his membership after that.

ANDREW DUNKLEY: Next question comes from Yanis.

YANIS: Hello. Space Nuts. I'm Jens from Sweden.

YANIS: I think the most evocative data from space exploration or the image is invious from the landings of foreign planets of unknowns like Vine and Dina, the Mars Rovers and Hogans and Titan.

YANIS: They make me imagine that I stand there at these places and look at the surroundings.

YANIS: But what would I actually be able to see in those places.

YANIS: Venus has a very thick atmosphere that probably blocks much light. Mars is farther from the sun than Earth and tiling us even further. How bright would an unaided eye perceive these places to be?

YANIS: Would it be too dark to see anything? We can assume that I stand in each of these places at the equator at noon. How well would I see?

YANIS: Thank you for a good show.

ANDREW DUNKLEY: Thank you, Janis. It's interesting question and eyes come up in astronomy and space science a lot because when you're off the planet, it's one of the things that's at risk, eyesight or your eyes in general physically can be affected by zero gravity in orbit.

ANDREW DUNKLEY: And there have been documented problems with that and I imagine if you're on another planet and the gravity is different, you'd face the same perils. But how would your eyes work properly in a different environment?

FRED WATSON: Yeah. So putting that to one side slightly, you, you're absolutely right grav. You know, we, we know from what's happened on the International Space station that zero gravity actually affects eyesight. And all the objects that Janis mentioned except Venus has a different gravitational pull from ours. So, but that, that's the kind of thing that is a long term effect.

FRED WATSON: It's something that, you know, affects your eyesight over time. It doesn't affect the perception at the time because your eyes still work pretty well. In those conditions. But he's right that all of these worlds would probably be dimmer than what we see on a bright sunny day here on Earth. Certainly Venus has these thick clouds. Venus isn't some way you want to hang around anyway.

FRED WATSON: But the, the Vera spacecraft all used visible light as their, you know, to, to take the images that they took and you can see details on the surface pretty well as, as as you would with the camera here on Earth Mars again, further away from the sun, clear skies, but further away from the sun. So the radiation is lower and Titan with the Hogans probe landing on Titan further away still and pretty gloomy really.

FRED WATSON: But having said all that if you were transported there, I'm pretty sure that you would see pretty clearly during the day. And the reason I say that is the our eye has an incredible range of sensitivity can cope with the brightness of a summer day, it can cope with Starlight, which is millions of times fainter and our eyes so adaptable to these different light levels.

FRED WATSON: That you would, you know, you would see, you would see, you would still see things pretty well during the day on those worlds. I, I I was reminded of this actually a couple of months ago, nearly on the, when I was watching the solar eclipse, the total eclipse of the sun on the 20th of April.

FRED WATSON: And that you're seeing more and more of the sun's disk being covered by the moon as the, as it progresses, it's about an hour and a half for the moon to cover the entire disc of the sun. And during that period, you don't, you really do not notice the drop in illumination towards the end. You do, you start seeing a kind of grayness about the landscape?

FRED WATSON: It's different in color, but your eye is kind of keeping up with the changes in brightness. And you know that, you know, 95% of the sun's disk is obscured and you can still see perfectly well and your surroundings. So, the eye is really astonishing in the way it adapts to different different environments and I'm sure it would in all these worlds.

ANDREW DUNKLEY: Yeah. Didn't you? I think you told me not so long ago that the eye is so powerful that it could see as little as one photon.

FRED WATSON: There has been experiments, yes, we did talk about it probably a year or so ago that some physiology experiment demonstrated that the eye responded to one photo, which is incredible. Amazing. It is incredible. That's why I've forgotten that. Andrew. Thank you for that.

ANDREW DUNKLEY: All right. That's what I'm here for. Yes, occasionally useful. Thank you f really love that question. It's a, it's a good one. This is Space Nuts. Andrew Dunkley here with Professor Fred Watson.

ANDREW DUNKLEY: Now, Fred, we, we, we'll just sort of continue on because we've got so many questions to get through and we mentioned Rusty earlier, Rusty sends in questions semi regularly.

ANDREW DUNKLEY: And again, throwing us a Curveball is Rusty.

RUSTY: It's Rusty in Donnybrook looking at a perfectly clear night sky here. And I've been noticing that the plane of the ecliptic seems to intercept due east and west, about midway between summer solstice and the equinox here.

RUSTY: And probably the reverse happens between the Vernal equinox, the spring equinox and the summer solstice again. So I was just wondering if you could enlighten us a bit more on that.

RUSTY: And, yeah, I still haven't been able to work out why Fred hasn't got a knighthood for being the most influential practical astronomer alive today. And Andrew probably should get some sort of award for creating this podcast about the best podcast ever. See you guys.

ANDREW DUNKLEY: Thanks Rusty. Oh, he's so nice.

ANDREW DUNKLEY: The plane of the elliptic, ecliptic, ecliptic. Yeah. Oh, that's what I said. Please explain.

FRED WATSON: So, so Rusty is commenting on when it lies, I think he's commenting on when it lies due east west, which is when it crosses the equator. So the equator of the sky, which is just an extension of Earth equator out into space that crosses the horizon anywhere on Earth due east and due west because it's the equator.

FRED WATSON: So the celestial equator, the equator of the sky goes directly over your head when you're on the equator of the Earth because as I said, it's just an extension of the Earth's equator into space.

FRED WATSON: Now, the Ecliptic, the path of which the sun takes throughout the year is inclined at that to the equator at 23 a half degrees. So as the year progresses, the ecliptic is going to cross the east and west point.

FRED WATSON: In fact, he says the day progresses because it happens every 24 hours. You, you'll get this, this, this this point where the Ecliptic crosses the equator, which rejoices in the name of the ascending and descending nodes of the ecliptic.

FRED WATSON: No, is node is a word that means it's short for no displacement. And so that what that means is it's not displaced from the, from the equator at those points, it's crossing them. So, if you've got, I can't remember the details of what Russ's question was, but you can kind of work it all out from there.

FRED WATSON: Because if you have this, you know, if you imagine sunset and you imagine it's at the equinoxes, then the sun is actually crossing the equator. So the sun sets due due west, it means that on the other side of the sky, the ecliptic is also crossing due east. And so, you know, and vice versa.

FRED WATSON: So it's just a question of being able to imagine how the, how the tilt of the of the ecliptic works its way around the sky. I'd suggest the best, one of the best ways to visualize all this and get your head around it is to use a plano sphere.

FRED WATSON: You know, the little star wheels that you've got because they usually have the ecliptic marked on them. And they certainly have the equator marked on them. Well, if it's a good one, it does. So you can see, you know, you can see what times of year you're gonna have it crossing, crossing the the, the, the horizon.

FRED WATSON: No matter whether it's crossing the, the, whether it's the ascending or descending node or not, you can see when the ecliptic crosses the horizon.

ANDREW DUNKLEY: Is, is there a visual effect when you witness this or is it just, it's just like every other day?

FRED WATSON: Just geometry? Yeah, it's just like every other day you wouldn't notice unless you were watching carefully what the sun was doing throughout the year. It's why, you know, what, what we're talking about is why the sun's rising and setting points shift along the horizon. So, you know, in, in our summer time, the sun shifts towards the north on the, on the horizon. And our winter time it shifts towards towards the south.

ANDREW DUNKLEY: Yeah, some ancient civilizations have built calendars on that basis, haven't they? With the, you know, put rocks on the, on the hills to pinpoint where the sun is at certain times of the year.

ANDREW DUNKLEY: Very good. Alright, thank you, Rusty. Another headache creating question. Now, this is a big one. We've this one's been doing the rounds on our social media platforms and a lot of people chatting about this. It is Matt and he's asking about causation.

ANDREW DUNKLEY: Hi, Frank and Andrew. This is Matthew from Adelaide, South Australia. I'd like to ask the question is, what is the connection between the speed of light and causation? I've been thinking about this now for a couple of days and it's been really been sort of been doing my head in. So I'm hoping you guys can help me out. Thank you. Ok, thanks Matt. Take it away, Frank.

FRED WATSON: Ok, Martin. Well, in answer to your question, there's a technical term that I want to use that. I'm gonna have to look up. Oh, ok.

ANDREW DUNKLEY: It's another easy one.

FRED WATSON: Well, yes, it's, it, look the, the, the bottom line and the best way to, to think of this is to think about diagrams. But and that's what I was just looking for there and time to find it. So why, what's the speed of light have to do with causation?

FRED WATSON: And it's all about the fact that the speed of light is the speed of information. So, you, so if you, if you think of an event taking place within our range of visibility, let me put it that way.

FRED WATSON: So supposing, let's say something, something happens to the, to the son.

FRED WATSON: Now, if something happened to the sun, now, we wouldn't know about it for eight minutes because of the length of time it takes the light to get to us. And so, if you, but if you put the sun further away than eight light minutes, I'm not gonna be able to explain this very well without looking at the diagram, there are regions where you can put the sun and it can't talk to us.

FRED WATSON: And so there's no causality. You know that, that it's, it's to do with the it's basically to do with space and time. And the, the, the diagram I'm thinking of is a plot which has time going on one axis, usually the vertical axis and space going the horizontal axis. And if you've got a a, a region within which you can see which is getting bigger as you go up the time axis.

FRED WATSON: So you've got something you can think of it as a line at 45 degrees. And everything on one side of that line can have a causal influence on you because it's within the the time that light will get to travel to you. But everything outside it won't. Because because it, it, it's not connected to you by the speed of light.

FRED WATSON: I really am explaining this very, very badly, Andrew, but it's, I wouldn't know it's worth going to the web just to have a look at the, the reason why I was looking was because these diagrams have a name and that's what's eluded me at the moment. But before the end of the show, I'll find it and we'll work out what it's called. Ok. Probably, probably called a space time diagram. That will be the easiest way possibly is.

ANDREW DUNKLEY: Ok. So that, yeah, that, that's yeah, it's a very, another confusing one, I suppose from my standpoint.

ANDREW DUNKLEY: But yeah, it's certainly got people talking about it online.

FRED WATSON: I think it's called the Minkowski diagram. Minkowski who is the mathematician who proposed it. But we will see. Yes, that's it. That's it. That is it all right. Go on, go and look it up or space time diagram. Does it? Actually that tells you and that gives you really the insights into what can cause things because the information can get to you and what can't because the information can't get to you. Ok.

ANDREW DUNKLEY: Fascinating. Alright. There you go, Matt. Thanks for such an easy question too. Now, let's move on to a question, a text question from Miranda.

ANDREW DUNKLEY: Is there an assumption that an Earth like planet or habitable water world would require a moon to help create tides like we have on Earth to enable life in the ocean? Or does it not matter if a planet has tides to have life? In other words, does a planet need a moon to have life particularly in its oceans?

FRED WATSON: Yeah. Great question Miranda and one that's certainly thought about long and hard by astrobiologists.

FRED WATSON: So it's not the tides that are the issue here.

FRED WATSON: So you could certainly envisage a planet that doesn't have tides that could form life. We do think in the case of the Earth that it was the tides that actually allowed life to migrate from being ocean dwelling to being on land because what the tides do is they give you this zone where sometimes it's wet and sometimes it's dry and it's kind of intermediate zone between the ocean and the land.

FRED WATSON: So, for, for us on Earth, it may be that we're land dwellers because of the tides because our very, very distant ancestors crawled out the sea. And had an environment that was kind of benign because it was, it was wet and it was going to be wet again a lot wetter soon. The high tide every 12 hours.

FRED WATSON: And so the the, the, the thinking is that yes, perhaps tides played an important role in the evolution of life from being ocean dwelling to land dwelling. However, that there is a bit more to the question than that because we think that the moon has helped to stabilize the Earth's axis of rotation.

FRED WATSON: Yeah, a little while ago that the Earth equator is tilted to the ecliptic, the plane of the, of the Earth orbit by 23 a half degrees. And that's actually the tilt of the Earth's poles with respect to the plane of its orbit or perpendicular to the plane of its orbit if you want the, the the the full thing. So the Earth tilted over at 23 a half degrees is what gives us seasons.

FRED WATSON: But the, the moon is thought to have stabilized that tilt. Because on the planet Mars where there are two tiny tiny moons that have no effect whatsoever on the planet's rotation. Mars has actually changed its tilt over relatively short periods, probably tens to hundreds of thousands of years. It's tilt has moved.

FRED WATSON: And that would be a very bad thing for any evolving species because you've suddenly got this whole new regime of seasons. And not the kind of stability that, that you need. So, a big moon like ours, our moon is 1/80 of the mass of the Earth. It's a quarter of its diameter. It's, it is a substantially large object. That is thought to have acted almost like a fly wheel as it rotates, sorry, revolves around the Earth.

FRED WATSON: And, and kept our axial tilt stable. So maybe a big moon is something that will be very desirable for the evolution of life, but it might not be essential. We simply don't know because we've got a, an example of one ourselves. But yeah, it's, it's a great question and certainly one that's in the minds of astrobiologists.

ANDREW DUNKLEY: Yeah, I suppose it is circumstantial. Like if life developed on a planet that didn't have a substantial moon, it would adapt to that environment and perhaps thrive under whatever circumstances, but it might evolve in a very different way because it you know, if the tides are the reason we ended up on land that might not happen there.

ANDREW DUNKLEY: Yeah, it's a, it's a really interesting conundrum. It is.

ANDREW DUNKLEY: Thank you, Miranda. And, I think that wraps up segment two. I think it does. Yes, it does. Gosh, I'm, I'm losing my place. We've been all over the place today. There's been a lot to talk about. This is Space Nuts with Andrew Dunkley and Professor Fred Watson.

ANDREW DUNKLEY: Oh, we will continue with our questions and we are going to the next one. Oh Shock horror. It's about black holes. This is, this is from Staffan.

STEFAN: Hi guys, Stefan here from the north coast of Ireland. Big fan.

STEFAN: I've just got like a quick question. It's a, just an a as an impossible thought. Experiment. Nothing can escape from a black hole. Ok. This is what we say. So what if you had two super massive black holes passing each other at quite a close distance, but with the enough escape velocity that they weren't going to get sucked into each other's gravity.

STEFAN: So two new super massive black holes passing each other really fast and then imagine you had like one small, like maybe 11 sun sized black ball in the middle.

STEFAN: Would the gravity of the two super massive black balls not be able to rip apart one small, relatively small Michael and they send its contents like rip apart its contents and send it flying out if you get what I'm trying to say, I don't know if you want to talk about it or what you think. Thanks guys, love you.

ANDREW DUNKLEY: I love you too. We don't want to talk about it.

ANDREW DUNKLEY: Yeah.

ANDREW DUNKLEY: Well, ok, we've got three black holes by the sound of it. You've got two super massive black holes that are sort of passing each other and the poor little one in the middle. And he's wondering if the power of the two which would be equal, would counter any impact on the one in the middle. Is that what he's saying?

FRED WATSON: Yeah, that's right.

ANDREW DUNKLEY: So I reckon they all rip each other to, that's, that's what I reckon.

FRED WATSON: Yeah. So I mean, you know, the, the the, the passing so near to each other that they, they, they are not gonna are so fast that they're not going to merge. So yeah, there, there's even in extreme gravity, there will be a gravitational null point, which is akin to all the gran points that we have to talk about, I guess the same sort of thing.

FRED WATSON: There's a little a null point between the Earth and the sun. And if you put something there, it, it's, it basically feels no gravity. But it's, it's something that is not particularly stable.

FRED WATSON: You can't put something there and just leave it there because it'll tend to move back to the drift, drifting out, which is why the James Webb telescope, which is at the second Lagrange point on the other side of the Earth from the sun has to have thrusters to keep it, you know, keep it on an even keel. So that's all that's what happens with things that are black holes.

FRED WATSON: So, it, to be honest, I don't know what the answer will be, you know, you've got a gravitational low point. But you've also got with black holes. They're not. Yes, it's a singularity, but it's got all this other baggage that it carries around with it. It's a swirling round and all of that.

ANDREW DUNKLEY: They're just huge bag ladies, aren't they?

FRED WATSON: That would affect the location of the, the null point which may be blurred out completely. And, you know, you, you, you poor sun size black hole in the middle there. Almost certainly would move one way or the other and get sucked into one of them or ripped apart. But it's a nice, a nice thought experiment and it is and, and, and I do quite like thinking about things like that. Yeah.

ANDREW DUNKLEY: I, I love the way people come up with ideas for questions. Like there, there's been some real pearls today. It's it's great.

FRED WATSON: That's right. Keep me going. Yeah.

ANDREW DUNKLEY: Well, he did. He didn't get to rehearse them. This is all, this is all blind.

ANDREW DUNKLEY: Ok. We'll move on to, oh, well, no introduction needed.

MARTIN: Hello. Space Nuts. Martin Berman Gor Vine here, writer extraordinaire in many genres including science fiction. And today's question is a relatively straightforward one for my current science fiction novel in which my heroine just destroyed a, a an interstellar spacecraft that was powered by a fusion motor.

MARTIN: So she caused a thermonuclear explosion and the shock wave hit her spacecraft and sent it into a tumble. I am going to presume that she was far enough away not to get killed by the radiation. So my question is about the tumbling. I have read that there is no dizziness when you tumble in space because your inner ear and what you see are not in conflict. So I wanted to check on this.

MARTIN: My research, the one solid thing I found was about the Gemini eight incident in which Neil Armstrong saved the day. So can't wait for the answer. Berman Gor Vine over and out.

ANDREW DUNKLEY: Thank you, Martin. I love his questions. He's, he's for his thinking outside the box. My first command as the, the captain of that spaceship would be to engage inertial dampeners.

FRED WATSON: That that would be it.

ANDREW DUNKLEY: That would be, that would be, that would be the first thing. Yeah. But yeah, yeah, what happens when you tumble in space? Do you not really feel the effect like you would tumbling on Earth chasing cheese down the hills near Gloucester in the UK, for example, what on Earth brought that time because that happened last week and a woman won her championship unconscious because she knocked herself out.

FRED WATSON: Dear me, still cross the line. I didn't see that.

ANDREW DUNKLEY: I didn't hear about that. That, that's tumbling to the nth degree but tumbling in space.

FRED WATSON: But in space. That's right. So Martin, I don't know the answer to this because it's kind of physiology rather than astrophysics. But I, I take your point about the disconnect between the gravity vector because there isn't one and your, which your inner ear responds to and your, your vision.

FRED WATSON: But my guess is you'd still feel, feel pretty sick and, you know, people experiencing the, the those zero G para parabolic flights that are often used to give people an idea what weightlessness is.

FRED WATSON: Weightlessness is like the, the, the aircraft is called the Vomit Comet. And that's because, you know, even though you're not feeling gravity, your insides are, you know, so, so confused by what's going on. That. Yeah, you throw up and I bet your heroine throws up as well.

ANDREW DUNKLEY: You know, you better write that into the story. We want space, we want space.

FRED WATSON: With a an acknowledgement to the the the the the the chief space vomit him and me.

FRED WATSON: Yeah.

ANDREW DUNKLEY: I I think you'd get tossed around a lot too, wouldn't you if, if there's if the things to tumbling?

ANDREW DUNKLEY: Yeah and and you're inside it, you're gonna get bounced around, you're gonna hit things, things are gonna hit you. It wouldn't be pretty.

FRED WATSON: No, it wouldn't, it would not be pretty. What's right?

ANDREW DUNKLEY: Yeah, indeed. You would, you would probably have to have magnetic boots or something.

ANDREW DUNKLEY: Yes. Alright, thank you, Martin. Not sure we helped but yeah, I I I the inertial dampen it definitely the way to go there. And finally we have a text question from Robert who is in Vienna, Austria and he says what aspects of our universe determine the speed of light in a vacuum?

ANDREW DUNKLEY: Are we lucky that the number is almost exactly 300,000 kilometers per second and easy to remember or have units been chosen to make this a nice number. And do we have do we have to feel sorry for people in a multiverse where the speed of light is probably something nasty, like 215,000, 335 kilometers per second. Love your show. Cheerio Robert from Vienna.

FRED WATSON: Where I not a few months ago. Yeah, it was a lovely, lovely city. In fact, my colleagues with whom I spent time in Vienna in February at the science and technical subcommittee. They're there at the moment on the main committee on the Peaceful Uses Of Outer Space. So it's a nice reminder to have the thinking, thinking about about the you know, the, the the lovely surroundings in Vienna.

FRED WATSON: Ok. And while we've been talking, I've just brought up the speed of light in kilometers per 2nd, 299,792 0.458 kilometers per second. So it, it's not really a round number. And it's, it, it's yes, it's comfortably close to 300,000, but it certainly wasn't chosen to be that because the, the meter is defined in terms of the circumference of the Earth.

FRED WATSON: That's how you work out what a meter is. You take the planet and you divide it up into, well, it will be 40,000, I think for, for kilometers. Is that right? Anyway, it, so you know, it comes from a different, completely different, fundamental quantity if I can put it that way. And it just turns out actually.

ANDREW DUNKLEY: Fred can, sorry, can I interrupt you? I need you to go back because I dropped out and start from. It certainly wasn't chosen as in this, the 300. Yeah, because I've, I had a drop out. I thought we were going to get through it today, but we didn't.

FRED WATSON: I didn't notice it. Yeah, I did.

FRED WATSON: It certainly wasn't chosen to be 300,000. Exactly. Because the, you know, in this is determined in terms of kilometers and meters which were themselves, originated as a fraction of the circumference of the Earth. So that, you know, they, they themselves come from a completely different physical quantity.

FRED WATSON: You take the Earth and divide it up into small enough chunks and you've got a unit of length and that becomes a standard meter, which I think is in Paris still. So, so it's not chosen to be a round number. In fact, I grew up thinking it was 100 and 86,000 kg, sorry, 100 and 8600 and 86,000 miles per second.

FRED WATSON: That's, that was the number that was ingrained in my mind until quite late in my life because we've worked in miles. So it's, and, and it's the speed of light measured by, you know, very accurate means these days. It was first measured back in the 16 hundreds by a Danish astronomer whose name was doctor.

FRED WATSON: He looked at the moons of Jupiter and said they're doing some funny stuff here and he figured out that that was because he was not allowing for the travel time of the light from one side of the Jupiter orbit to the other for these moons. Very clever. Yeah. He made the first measurement which actually it wasn't, wasn't too bad. So, yes. So nice question, Robert.

ANDREW DUNKLEY: And it is what it is and I suppose a another culture in another universe or another part of this universe would have their own way of measuring things and their number would be whatever the number is. Exactly. And it would be the same speed.

FRED WATSON: Yeah, there is one nice aspect of the speed of light though. And it kind of mixes up the kilometers and and imperial units in one billionth of a second light travels one ft.

ANDREW DUNKLEY: Oh, there you go. Exactly.

FRED WATSON: That's because it's, well, it's, it's, it's, you know, 30 centimeters roughly is a foot. So that's, that's how it all works in a building to the second light travels one ft. All right.

ANDREW DUNKLEY: Very good. So, yeah, not very helpful but very.

FRED WATSON: Good at times useful.

ANDREW DUNKLEY: Yes, maybe. All right. Thank you, Robert. Really appreciate it. Thanks for all the questions, that came in today. We've, really enjoyed ourselves. There's a bit of homework to do. I'm sure Fred's written down notes so we can chase them up for next week. But, great to get your questions and please keep them coming in.

ANDREW DUNKLEY: You can send them to us via our website Space Nuts podcast dot com or Space Nuts dot I O and you can send us text or audio questions through the A MA tab or through the button on the right hand side of the home screen that says, send us your audio question or comment or whatever it says, I can't remember.

ANDREW DUNKLEY: And one more thing if you're a social media user, particularly on linkedin dot com, linkedin, we're on there as well and we need a minimum of 100 and 50 followers so that we can do our recordings live to linkedin. We already go live via YouTube and through Patreon and through Facebook. But we want to add linkedin, but we need to get to 100 and 50 users.

ANDREW DUNKLEY: So if you're a linkedin user, just use their search engine and look for bites dot com. B I T E S Z dot com. That's the easiest way. The other way is link dot com slash company slash bites, I think. Yeah, something like that.

ANDREW DUNKLEY: But just do bites dot com in your search engine for linkedin and and follow us there and when we get to 1 50 we'll be able to offer, live studio recordings, as we, as we record them is what I'm trying to say, which we tried to do today except for the internet dropouts. Still haven't solved that one. Fred. Thank you. As always. You are fantastic. We really appreciate it.

FRED WATSON: It's very kind of you to say so. Andrew wish I knew more answers than I do, but never mind. That's right.

ANDREW DUNKLEY: Or if we knew all the answers, we wouldn't have to be here.

ANDREW DUNKLEY: Exactly. All right. Thanks, Fred. We'll catch you next time. Yes, looking forward to it, Fred Watson astronomer at large part of the team here at Space Nuts. And thanks to Hugh in the studio because, and for me, Andrew Dunkley, thanks Phil. Thanks for listening. Thanks for watching and we'll catch you on the very next episode of Space Nuts.

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