#418: From Cosmic Drag to Holographic Hype: Unraveling the Mysteries of Space Travel

Hi there, thanks for joining us on the Q and A edition of Space Nuts. My name is Andrew Dunkley, your host on this episode where you're going to be answering questions about light. It's an interesting question about how far away light has to travel before it's undetectable. And he even gives you a measurement of how strong that light is, so we'll talk about that. Are we living in a holographic universe? I think we've had that question in several forms over several years, so we will tackle that one again. And how fast is fast enough to create drag when traveling through space? And relative relative trouble with this word relativistic speed. That's all coming up on this edition of Space Nuts Q and A fifteen second channel ten nine ignition Space Nuts or three two space and I record it real good and he's back again for more. Don't ask me why, Professor fred what's an astronomer at large? Cello fred Illo, Andrew, It's good to be back, whatever the reason is. Yes, indeed, everything good, Yeah, all good. Well, it's all firing on two cylinders as usual, so that's yes, trouble as we're driving a V eight anyways, shall we get on with it and go straight to our first question. This one comes from Allan. Hi. This is Alan Scahill from Medicine Canada. My question is if an led light one candle power in strength were to be turned on in space, what would be the greatest distance a space tele telescope would be able to detect it? Thank you and love your podcast. Thank you, Allen. Medicine Hat. Do you say medicine hat in Canada? If that's an interesting name, I wonder why it's called that. He might have to tell us. We might want to know what he's got a British accent as well. That happens, I could ask the same about you. That's a really good point. I never thought of that. Yes, medicine Hat. It's a city in southeast Alberta. It's located along the South Saskatchewan River. It's a problem in one hundred and sixty nine kilometers east of Lethbridge, two hundred and ninety five kilometers southeast of Calgary. The city and the adjacent town of Redcliffe to the northwest are within Cypress County. There is don't know why it's called medicine Hat, though it's a great name. It might have something to do with a nearby mountain, I suspect. Yeah, yeah, it's the nearest we got to it during our expedition last month was to Calgary. We flew out of Calgary when we left Calgary a lovely place. The bits I saw of it looked very nice. Yes, that's right, but it was only the airport. Really we were. We were traveling down from Lake Louise that day, and Lake Louise is stunning. So I can answer for that. I think you've been I was wrong. It's got nothing to do with a mountain. Apparently, it's derived from the Blackfoot Indian words samus, meaning the headdress of the medicine man. There you go, There you go. If I'm looking at the right place, I just did get quickly. I stand to be corrected. Alan so police. If I'm wrong, let me know. Led light? Yeah, one one candlepower? How far out before we can't see it? Or something to that. I've no idea. Look, it's it's it's all about. This is the interesting thing about light. It's yes, we regard it as a stream of photons, but it's also a wave motion and light is something that basically has infinite travel possibility, and so that one the photons that that one candle power is emitting, or the the light waves that the LEDs emitting essentially gone forever. But what limits your ability to detect them is the equipment that you've got to do that. And you know if you've got and that's the key thing about telescopes. The bigger your telescope, the bigger the light gathering area of your telescope, the faint of the objects you can see, and therefore the further away you be able to see your one candle power LED. I like, take it on notice, Andrew, and see if I can do a calculation for that, because I do this sort of thing, or I used to when I was thinking about star magnitudes and things like that. So one kind of power LED and how far away could for example, the Hubble space telescope. See I did have a quick look myself, and I I just found this on the physicsforums dot com website and it says, and you said this earlier, there is no known limit to how far light can travel. Yes, that's right, but we're talking about the detectability of it indeed, and it depends on the instrument. And I think Allen mentioned the hubble, Yeah, or just a space telescope. Anyway, it doesn't matter that. We'll try and do some calculations on that. Okay, Well that was easy, No, it wasn't. Well it was easy in the sense that you know. The answer is that light goes on forever. Basically, it's just whether you can detect it or not. That's the tricky bit, that's the hard part. Yeah, for sure. Okay, Alan, we'll get back to you shortly. Now let's move on to our next question. This is a text question that came in from Charles. What do you think of the theory that we live in a holographic universe? Now we better qualify that by explaining what a holographic universe actually is or is supposed to be. Let's just say that. So, let's quote Leonard Suskind, who was one of the great proponents of the holographic universe. The quote is the three dimensional world of ordinary experience, the universe, filled with galaxies, stars, planets, houses, boulders, and people, is a hologram, an image of reality coded on a distant two dimensional surface. There you go. What's when does that date from that quote? It's probably about twenty five years ago, because that's how long this thinking has been going on about the holography. Actually that goes back only to two thousand and eight, and it's from his book The Black Hole War, My battle with Stephen Hawking to make the world safe for quantum mechanics. I love the title. I've read that. So what you've got is the idea and it comes from so think about what a hologram is. It is a way of encoding lights. It's actually we would call it an interferogram in the world of physics. You've got a film, in fact, a two dimensional surface which is transparent, that has a pattern on it, which when you illuminate it with what we call coherent light, that's light from a laser where all the waves are in step, all the light waves are in step with each other, then it will basically that light will be diffracted. It will break up to form a three dimensional image. One of the best holograms I know of is at Macquarie University in the physics department. I haven't honor appointment there, so I go there quite a lot. And what they've got is it's actually it's a conference room, just a small conference room with the table and chairs in it. But one wall of it is lined with windows, and on the other side of the windows is a corridor where you can walk, and that window. The windows have a hologround on them, and so when you look through the hologround through the window at what is in fact just a room full of chairs, what you see is a succession of images of a bar as the night wears on, and the bottles are full to start with, and everybody's everything's neat and tidy. By the time you get to the other end of it, there's empty bottles all over the place. It really not in good shape. So that is what we normally think of as a hologram. It's something that gives us a three dimensional representation of a two dimensional from a two dimensional So so this idea that the unit the universe is like that I've always had trouble with because you know, a direct analog with that with a hologram is that you illuminate it with something and the illumination forms that three dimensional image. And so where does the illumination come from in the you know, the holographic universe. So I think you've really got to look at the details of this, and well, if I if I can read from the Wikipedia entry on holographic principle, which is what it's all about. The holographic principle is a property of string theories and a supposed property of quantum gravity that states that the description of a volume of space can be thought of as encoded on a lower dimensional boundary to the region, such as a lightli like boundary like a gravitational horizon. There you go. So that's that's that's what you're supposed to imagine with a holographic universe. So it's, as I said, it goes back twenty five years, probably more than that. I've never been that keen on it because it seems highly contrived to me, but it does have a theoretical basis for people to think it might be the case. I'd like to see more evidence that there is, you know, there is a holographic event horizon, if I can put it that way, because I think that's the idea that the you know, if we're a black hole, the event horizon is actually where the hologram lies. And there's a whole lot of gobbledygood on the Wikipedia page that if Charles wants to plow through he might be even more illuminated on it than I. I find the theory very confusing. It doesn't sort of gleane with traditional thinking, And no, it's not intuitive. I find it hard argue against traditional thinking. Yes, I understand that. I think by traditional thinking, I think you might mean something that makes sense. Yes, the way we generally understand things the moment. Yeah, traditional thinking. That's my perception of it. And who you are really doesn't it. It's a thinking Yeah, well that's it. I mean, we should be open to all possibilities, because the mystery of our existence at all is one we can't answer. We don't know why it happened. We don't know what caused it to happen. We don't know how things developed to create what has been created. The more we look, the more questions that are raised, the more we know, we get confused about things that shouldn't have been able to happen, that happened, And it just goes on and on and on. So you can't write off anything, I suppose No, and I wouldn't write off the holographic principle either. I think it's a really interesting idea. I don't fully understand it as you've probably realized by now, I don't understand it that much, and that's so we So yeah, So the answer to Charles's question is, yeah, I think it's it's interesting. As I said, I've never been a big fan. That's because I perhaps I'm a traditional thinker, as you would put it. I'd like to think about the universe as being made of atoms and things that really owe their existence not to a hologram, but to to being where we are, to being within a universe that was created in a big bang and has all these other particles generated from that. That makes more sense to me. Now, the next question that's going to come up is, hang on a minute, what if the hologram is made of dark matter? Ah? Yes, I think you've put your finger on something. Then you reckon probably just stirred the pot even more and made it murky. But you know, the holographic universe theory is fantastic in science fiction, really is. Yes. Yeah, I am actually watching a TV series at the moment which I'm thoroughly enjoying. It's called Dark Matter, and it centers around multiple universe theory. And I was going to take a little bit of a break, but we might as well throw straight into this. This is about a bloke who gets abducted and when he wakes up, he's in a different universe and he's trying to figure out what the hell happened because it's the world, but not as he knows it. Same people, different situations, different relationships, different career path situations. It's all out of whack and he thinks he's going mad. There's only been three episodes so far, but g it's good. It is really good. But the reason I bring it up and thanks for your question, Charles, but this question popped into mind and I'm giving it to you without notice from Rennie, who is a regular contributor. Could it be possible that our universe is in a universe cluster as our Milky Way is in a galaxy cluster. If all universes are expanding, would they eventually overlap each other at some point? I think the sort of standard multiverse idea is exactly that, that you've got multiple universes which may be clustered together or not necessarily. One way of looking at this is the M theory universe and M nobody's ever a short M stands for mystery membrane is probably where it comes from, because the idea is that we are all on a living in a three dimensional membrane which is right next to other three dimensional membranes that contain other universes, and when membranes collide, you get a big bang. Yeah, that theory. I remember checking it out once in quite some detail. And you know, we think of these membranes as being well membranes with a universe somehow imprinted on it. But it turned out in the theory it's actually when I think about it, it's called the act pyotic theory of the origin of the universe, and it turns out that these membranes are only separated by something like zero point five of a millimeters. When nic collide, you get a big bang, and you're thinking, oh, that's a bit close. You know, something went wrong. I'm not sure where m theory is at the moment in terms of its acceptance by the cosmological community, but I think the answer terraneous question is yes, that's possible. And if they keep expanding, which ours is, would they eventually overlap at some point? I'm sure overlap would be I mean, what if two universes that are expanding ump into each other. I think bump would be an understate. Yeah, but they might be expanding in a higher dimensional space, which might preclude that. Well, there's a thought too. And here's another thought. If you've got two universes expanding towards it, towards each other, and let's just say ours is one of them, Ours is expanding at an accelerating rate. What if the one that's near us is expanding at an accelerating rate, but their acceleration is faster than ours. Now, it doesn't stand a reason that we're all going to hit at exactly the same speed. No, I think. I think you've got to ensure that your other universe is in a different bit of the higher dimensional space than you are, and then it can expand as much as it likes. And it doesn't doesn't it ours unless it's a membrane. And that if it's a membrane and it collides with us, you've got a big bang. Yeah, it's just like watching child's balloons burst or rum or bubbles bubbles, they go boom. Yes, they could be mini universe versus that live for a fleeting moment and the people go, oh, look at don it's all. It's really interesting to talk about that. It's fascinating theory, and this dark matter series sort of leans on that particular multiverse theory very very well, and they travel around in a box just like Doctor whod Yeah. Thanks Rennie. This is Space Nuts with Andrew Dunkley and Professor Fred Watson. Okay, we've tacked all space nuts. One more question, Fred, and this one comes from Craig. Professors. I'm Craig Miller calling from sunny Umbula in New South Wales. I have a confession. I have a solitary habit n't usually mentioned in public. I write science fiction, so that's this question is a little what if the vacuum of space is, as we know, not exactly empty. The density is low, but gas and dust fill the vac human space. So I'm wondering how fast you would have to be traveling before that gas and dust began to produce drag. Surely, if you went fast enough, you'd have to consider aerodynamic principles for the profile of your spaceship. As a secondary question, wouldn't a ship traveling at relativistic speed smash into that aforementioned gas and dust like a mobile particle collider. If there were lots of spaceships traveling at light speed, you'd see the trails all over the sky. Maybe. Anyway, thanks for answering my question. Keep up with the great work. I love your show. Thanks very much, Chow, thank you very much. Craig, lovely to hear from you. You'll have to send us some book titles. I'd like to take a look at those, if you don't mind. I'd love to see what your what your angle is and science fiction and steal your ideas. Now I'm kidding now my thoughts on his first question. You know, how much speed to create the drag in the vacuum of space would be dependent on the concentration of particles, would it not? Because some parts of space only have one speck of stuff per gazillion miles. Now I'm exaggerating slightly. Well, you're not exaggerating that much. Maybe the gazillion is a bit some Yes, you're at the level of a handful of particles per cubic meter. And it's a really interesting question actually, that Craig, that he poses because even at those low densities, so we've got a sort of a bit of an example of this around the Earth. When you get to heights of one hundred, two hundred and three hundred kilometers, there's still enough of the atmosphere that you're going to get drag on your spacecraft if it's in orbit, and that's what brings them down. So here's the International Space Station four hundred kilometers high that has to have its orbits boosted periodically every few months, I think, in order to counteract the effects of drag. And there's not that many atoms of atmosphere up at that height. It's certainly well over one per cubic meter. But yes, so the the atmosphere drag on a spacecraft is a real thing, and I think to extrapolate that as Craig is doing, is actually a valid thing to do. Should you think in aerodynamic terms, if you were designing very, very high speed spacecraft, And I think the answer is probably in the second part of Craig's question, because yes, those relativistic velocities where you are approaching the speed of light, then your spacecraft is more like a particle accelerator. It's more like what's going on at the Large Hadron Collider where you might well see you know, atomic scale impacts that would have showers of other particles coming off them. So you know, your occupants of your spacecraft might be being irradiated by highly ionizing radiation from the particle impacts that you're traveling through, which would be not very nice. If you've got dangerous rays coming out of the walls of your spacecraft, no matter how aerodynamic it is, you're not going to be very happy about it. So I don't know that specific answers to the questions, but it's really it's a really interesting one. You know, I can't tell you what velocity you really need to think about designing. And you're absolutely right as well, Andrew in that different bits of space have got different densities. If you're looking at the star formation region, a nebula, as we would see it as the pressure there is unbelievably low. It's lower than the hardest vacuum you can make on the Earth, but there are still enough particles there that you're essentially forming an EBuLa. You're seeing the glow of it, Whereas in regions between the galaxies the density of particles is very low, indeed, but it's still there. They're still there. The particles subatomic particles are still there. So yeah, if you were capable of traveling at the light speed and you wanted to travel any significant distance, you'd have to really be able to calculate your navigation with so many parameters in play. It's not just about I want to go from there to there, because there won't be there you get there, it'll be there somewhere, and you've got to allow for what's in between to make the trip without sort of hitting something, you know, like a giant star or whatever. It's it's it's uh. I think interstellar navigation would be a very tricky little thing, tricky chop. Well, we've got spacecraft that are doing that, you know, basically with with the Voyagers and the Pioneers there in effectively interstellar space. They're still they're still feeling, all of them, but some of them are feeling the magnetic field of the Sun rather than the magnetic field of the galaxy. I think Voyager one feels the magnetic field of the galaxy. So yeah, you're out there in in very deep space. I wonder whether you know we certainly. I'm just trying to think of this the other way around. Particles what they do. When I was building instruments for ground based astronomy. Back in the eighties, nineties, early two thousands, we were often beset by the effect of cosmic rays, which are seatomic particles coming in at a very high speed on our detectors. You'd get you get an image that was supposed to be the spectrum of an object, but it have all these It looks as if somebody had thrown a whole lot of just white bits of sand all over the image, and they were the impacts of cosmic rays which were being recorded by the detector. Wow. So that sort of thing must happen when you've got a spacecraft, you know that's doing science or imaging or whatever. You must have this cosmic ray flocks anyway. But if you've got a significant velocity in a particular direction that might affect the cosmic ray flocks, you might see more than more than you expected or less than you expected. Yeah, it's a really interesting thought. Thank you for bending our minds in that direction, Craig. Indeed, yes, and I mean it when I say send it. Send me some intro about your sci fi books. I'd love just see what you write about and if you do have questions for us, of course, please send them through our website, spacenuts podcast dot com or spacenuts dot io. You can click on the AMA link at the top and send us text and audio questions, or the little purple button on the right hand side to send audio questions only. But as we always say, please remember to tell us who you are and where you're from. You might be from medicine hat in Canada, who knows. And thanks to everyone who contributed, Alan, Charles, Rennie and Craig. Looking forward to some new questions in coming weeks. And that wraps it up for another episode. Fred, thank you very much, Oh thank you. Thanks for having me and thanks for everybody's questions. Is very stimulating, it is, isn't It gets a brain going sometimes he does. Yeah, people dooms a lot. Yeah. Thanks Fred. We'll see you soon and see your light to cheers for the bye. Fred Watson, astronomer at large and here in the studio. Who does what? Who does in the studio? When he's not in the studio, I don't know what he does? And from me Andrew Duncley, thanks for your company. See on the next episode of space Nuts coming to you real soon. Oh Bynuts to The Space Nuts podcast available at Apple Podcasts, Spotify, iHeart Radio, or your favorite podcast player. You can also stream on demand at bites dot com. 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