How to Time Travel

Mass is one thing, reality is a different one. What would be the impact of a wormhole near Saturn? When people talk about time travel, we tend to think about jumping further into the future. Hello, welcome to the Supermassive podcast from the Royal Astronomical Society with me, science journalist Izzy Clark and astrophysicist Dr Becky Smethurst. we're doing it we are traveling through time this episode i feel like the doctor who like theme should have come in there that's the twilight zone get your science fiction references right izzy they're going to be right all the way through this episode um yeah we did our time special earlier in the year but that brought up so many questions about time travel we're going back again yes i mean there was too many things to pick up that We're just like, let's put those in a little box, shut the lid, and we'll address those later in the year. That time has come. Yes. Once Becky had finally rewatched Back to the Future as a cozy sort of Christmassy time film, we could finally do this. Very, very important research, I think. And Dr. Robert Massey from the Royal Astronomical Society is here too. Now, we've had this question a lot of where would you go in time if you could travel to the past or to the future? So I'm going to change that for this episode. and I want to know if you could go back in time would you meddle with anything yeah it's just so tempting isn't it I mean there's so many things that come to mind and some are far too political for this podcast so I'm keeping my mouth sealed on those but I'll leave people to guess I don't know I think I'd sort of want to be there to stop the kind of outrageous misfortune that hits people from time to time you know I'm thinking of Becky actually if we could do something I think we'd definitely want to help with that but you know just enough to stop people getting sick or stopping the worst accidents or atrocities which then i said you don't know that i'm ill that sounds like you're gonna stop me being born no no not my intention okay that wasn't for those who don't know yes yes exactly oh god yes okay well there we go right yes well anyway i'm fine yes i promise you there's got the best of intentions but is yet another example of yeah not thinking you through you're gonna travel back in time and stop yourself saying that robert yeah anyway it starts to sound like a perhaps a slightly flawed superhero character so other than that i thought you know really simple things like if i've screwed up cooking then just being able to go back 10 minutes would be perfect just to add the ingredient at the right time i don't think that's too much to ask is it you know if you're gonna have minor godlike powers then a few minutes here and there would be really really helpful i love that you're like irreversible reactions oh no yeah i have time travel exactly exactly you get that eggs i burnt the roast chicken hang on back exactly just dial back the dial 10 minutes and it's perfect how about you becky um i'm gonna have to stick with the physics here that says you know you don't you do not mess with anything for fear of creating like any sort of ripple effects butterfly effects that you do not know how it's going to create any sort of, I mean, there's so many different theories around time that we just don't know if they're, you know, and there's so many different stories around the multiverse and things like that. It comes back to our episode on multiverses as well. If we go back in time and change something, do you create a parallel universe that you then can't return back to where you came from almost? Oh, it's so confusing. Yes, and there will be a lot of that sort of confusingness throughout this entire episode. I mean, the bad thing for me is like, I just want to go back a medal and maybe if I could time travel, just pull some pranks. But you're like, no, that is an irresponsible use of the power of time travel. Because Robert's responsible use of irreversible reaction. My mind may create some serious ripple effects in kitchen. What would happen if I hadn't burned that chicken 10 years ago? This is so crazy that I'm the responsible one. I'm usually the one that I'm like, don't maybe even astronaut, I'd press all the buttons And now I'm like, no, but don't mess with time. Let's not mess with time. Whereas I'm just sitting there thinking how convenient it will be. There's two parts to me. Theoretically, I would. If physically, no, would not. The fear of, yeah, as you say, the possibility of butterfly effects. Are we starting new timelines in different universes? It all gets a little bit complicated. And we are about to get into all of that right now, because I think the big question that everyone wants to know is, can we travel through time? So buckle up. Apart from forward, since we are all already time journeying forward. Well, it's an excellent point that you make there, Becky, because this is where I started with Dr Emma Osborne. She's a theoretical physicist from the University of York. And I just wanted to know, can we travel through time? Well, yes, we time travel all the time. We're moving forwards in time as we speak. But when people talk about time travel, we tend to think about jumping further into the future or more perhaps excitingly the possibility of traveling backwards in time. Well future time travel and jumping forwards in time has been experimentally verified and so that is absolutely possible but traveling backwards in time well that's a little bit trickier. Okay okay so let's start with going forwards in time. How do you travel into the future? well there's two ways the first is to move really really quickly if I have a clock and you have a clock and we synchronize our clocks and what I'm going to do is I'm going to travel around at close to the speed of light I'm going to move at 96% the speed of light and I'm going to do that for one minute and when I stop after I've been doing it by one minute by my clock when we compare our clocks even though mine clock would have measured one minute yours would have measured nearly four minutes of time passing so essentially the faster you move the slower time passes relative to somebody who is stationary or moving slower than you yeah okay so let's unpack that a bit why does that happen what's going on there this has just come straight from einstein's theory of relativity the thing is we don't notice it on our daily lives even though it is technically happening but that's just because we don't move fast enough when you start getting close to the speed of light that's where it really where we see it so we see it when we accelerate particles at sun and get them moving close to the speed of light and if space travel like distant space travel was possible we would want to move at those speeds so it starts becoming relevant in those circumstances yeah But the big thing is here we have to go so close to the speed of light, which is pretty tricky. So what's our second option that's potentially on the table? OK, so the second option comes again from the theory of relativity. And just as we saw that time passes slower the faster you move relative to something moving slower than you, we get a similar effect arising from gravity. so essentially time passes slower or clocks tick slower in strong gravitational fields compared to weaker ones this is a really cool one and it comes from einstein's picture of gravity of no longer being a force but rather the geometry of space-time which i don't know about you is like well space-time has a shape uh yep it's curved it can be stretched and that's what we're having space and time are unified things that have mass like you me planets we stretch that kind of fabric of space time and with that time becomes stretched so the heavier something is the more it stretches space time the stronger the gravitational field the slower time starts passing okay can you put that into a some sort of context can you give me like a scenario how would it work okay so let's say we had a local black hole we've got our clocks we've re-synchronized them and i'm going to be an intrepid explorer and i'm going to go and travel close to this black hole and kind of slingshot around it and come back to earth and we'll compare our clocks okay and but what we've got because we've got this really good technology in my spaceship you can actually see the clock in my spaceship and what you'll see is as I travel and I start getting very close to the black hole you will see my clock ticking slower in comparison to your clock. If I was to get almost to the event horizon you would think that my clock has stopped because it's ticking infinitely slowly but actually when I look at my clock whilst I'm in my spaceship it just looks normal to me so as I slingshot round and I start moving away from the black hole as I make my return journey to earth you would see my clock start ticking at a rate more in line with yours. Okay so how much time would have changed? Well that literally depends on how close you get to the black hole. How close are you planning to get to this black hole than ever hopefully not too close maybe well if I got too close right I could be there for a couple of minutes but hundreds of years could pass on earth so I really don't want to get so close that you know I come back and everybody I know has moved on and we're a few centuries into the future so I'd want to probably keep my distance to a certain amount but get close enough that I can see this change happen yeah and so this is obviously this is all kind of theoretical physics but the really important part of all of this is that we are comparing to what we say frames of references it has to involve me staying on earth with my clock and you traveling off into the deep depths of space near a black hole to some extent and that's how we're measuring that change of time, right? Yeah, absolutely. It's all relative. It has to be relative from one clock to another. And that's why it's called the theory of relativity. Okay, so that's us whizzing through going into the future. What about travelling into the past? Can we do it? Okay, good question. So let's look at the faster we move, the slower time passes. well that's really good but so technically if we could travel so fast that we traveled faster than the speed of light we would actually be able to go back in time but the universe has a speed limit which happens to be the speed of light traveling in a vacuum which prevents us from doing that and you know that equation e equals mc squared that equation tells us that the faster we move the more energy we will require to then move even faster. So that means I would need an infinite amount of energy just to travel at the speed limit of the universe. So the reason light can travel at the speed of the limit of the universe is because light doesn't have a rest mass. It doesn't weigh anything if you were able to stop it. Whereas we do indeed have mass. So that's what stops us. So if we wanted to travel faster than the speed of light, we would need more than an infinite amount of energy. And I don't know how that's going to work. OK, OK. So kind of, is there anything that we could do to break that limit? Ah, so we can't break the laws of physics, but we can bend them and we can bend them with gravity. So this is where it starts getting pretty cool. So what you can do is you can put perhaps stretch space time so much that you could almost stop time, which we saw close to a black hole. So essentially, I mean, if you want to build a time machine, you would need to combine the special relativistic effects. They're moving very quickly with the gravity. So what we could do is combine them to bend the laws of physics to then make a time machine. Okay, Emma, so how are we going to build this time machine? What is the best way to build a time machine? I recommend you do it by creating a wormhole. We get questions about wormholes a lot. Do they actually exist? What is a wormhole? A wormhole is technically two black holes whose, if you think of like a 2D picture of a black hole, they have these tails and you can join them together. So they form a tunnel through space-time, okay? The problem with wormholes is because they have such strong gravity, like black holes, their tails, when they join, they are not stable. So they collapse really quickly and break off. They could be constantly joining and collapsing and so on. Or they could join for a very short period of time and break and not reconnect again. So do they exist We don know We haven been able to observe such a thing yet Okay so can we break it down a little bit more How is it that wormholes are our best option? Theoretically speaking what's going on there? Talk me through the physics of it. Okay so a wormhole if we could create one and we were able to make it stable and I'll come back to that in just a moment how we would do that. What a wormhole does is it creates us a passage through space and time so we can connect two different parts of the universe together using a wormhole well that's going to be really helpful for us because as you know we travel in space as well as time so we can't really separate the two so this is where we start bending the laws of physics to make our wormhole stable we would need some kind of negative energy or something that we could put in place that kind of counteracts the gravitational attraction and therefore stabilizes our wormhole. It's maybe theoretically possible but it's a long way off from our technological abilities and we don't know if it is truly experimentally verifiable at the moment. But that doesn't mean all is lost. If we've created our stable passage through space and time how do we turn it into a time machine is the next question so what we need to do is we need to take this moving quickly slowing time down aspect and put combine that into our wormholes what we'll do is we'll create a wormhole today and we'll keep one end static it's not moving and the other end we're going to jiggle and we're gonna we're gonna jiggle it as quickly as we possibly can close to the speed of light the closer we can jiggle it to the speed of light the better because what we can do is we set that up and we leave it running okay so the reason we do that is the static end time will tick at the rate that we experience but the jiggling end time's going to move really really slowly on that part compared to the static end and so when you talk about these ends we're talking about these two different black holes right it's not like you're just talking about one you've got one black hole and it's the the end of that one black hole it's like you've got one black hole that is static with a tail and at the other end is kind of like the tunnel of the other black hole and that's the one that we're kind of moving jiggling right yes absolutely okay so what's going on why what then happens if we're able to keep one static we're able to wiggle one that's really close to the speed of light why is that changing time so what we've got the clocks if we have a clock at each of our wormhole mouths the jiggle inside the clock will be ticking much slower than the static mouth okay so what we can do is we can leave that running let's say we so we've created a tunnel through space time and each end is creating a difference in time so let's say we leave it running for 10 years and then I think wow I really enjoyed uh that podcast interview I want to go back and chat to Izzy again so what I'll do is I'll go in the static end and then hopefully when I come out the other end because time would have passed significantly slower that would take me back to today. We're going to go into this even more deeper if we've gone through our wormhole we've ended up however many years ago what happens if you then start playing around with things that have happened in the past? Yeah brilliant question so this is a common problem that arises when looking at time travel and it's got its own name it's called the grandfather paradox okay and it's essentially the idea that let me i build a time machine i go back in time what if i kill my grandmother and therefore prevent myself from being born which means i wouldn't be able to create a time machine in the first place to go back and kill my grandmother so something's gone wrong we've kind of we've broken timelines so there are kind of like three resolves to this using the wormhole example where we built our time machine the way that it resolves that issue is that I could only ever go back as far in time as to when the wormhole was created so therefore I cannot go back further and prevent my own birth from happening by killing my grandmother obviously which I don't want to do a very violent choice of time travel yeah Yes. So the other case is what if I was able to build a time machine that I was able to go back further in time than when the time machine itself was initially created and tried to kill my grandmother then? Well, this is more a deterministic universe kind of perspective, which I find personally quite unsettling. And the idea is, is that each time I tried to kill my grandmother, something would happen that prevents her death. So it could be that the gun jams if I'm using a gun or that she steps out the way or a vehicle passes or something like that. And I don't like it because it's almost implies that the universe may have a consciousness and be aware of what we're doing. And I just don't think the universe cares about us. I think we just happen to live in it. So I'm not so keen on that one. But that is one possible way of resolving the paradox. and the third interpretation of how we can resolve the paradox is a bit more exotic and it uses the many worlds theory which comes in from quantum mechanics and this is the idea that there are multiple universes that and they're all in parallel so all these parallel universes and what would happen is is that when I go back in time I don't go back in time on the timeline of my universe. I enter into a parallel universe. So if I was to go and then kill my grandmother on this different timeline, it doesn't stop me from being born. And you could argue that that was always going to be what was meant to happen in the timeline of that universe that I've stepped into via time travel and therefore resolving the grandfather paradox. I see. So it's not only have we've travelled in time, we've crossed into a parallel universe and then that plays out as another hypothetical, another what we've called like a bubble universe. It's just a different timeline and scenario. Gosh, we started in one place and we've ended in another. Thank you to Emma Osborne from the University of York. I had so much fun speaking with her, but there's just a moment though where you're like, you know, asking questions like, how do you wiggle a wormhole? I'm like, what is my job? what actually is my job yeah you really sounded like you you really enjoyed that in a few years like it was so so good I think it's funny because like I don't know like I often take for granted the fact that time travel to the future the black hole is just possible and accepted amongst physicists and it's like yeah whatever fine yeah uh and I think you know if if you're gonna ask me like would you go forward or backward in time like I think I'd always choose the forward option because I'm like we we know what happens in history I'm not curious about that you know a good point it's a good point like I just want to do all the little hops forward in time like I'm always talking about um yeah the wiggling wormholes right what a treat like theoretical physicists are just another breed you know like I don't know how they do it yeah it's one of those interviews where you I just found myself being like just accept it and move on don't keep asking why accept it move on the physics says this we've got to go with it fine I think there is you do have to just accept that at some point right it's just like the physics says this like the math says this and no matter how much you try and visualize this you're not going to be able to yes so listeners it happens to the best of us now we obviously could not do an episode like this without a nod to the tv series and the films that are much loved that play around with time travel. Izzy spoke with the wonderful Dr. Alfredo Carpinetti, astrophysicist and science journalist for IFL Science to discuss Doctor Who, Back to the Future and Interstellar. And side note, you will hear Alfredo talking about the Tesseract here. Tesseract is not the glowing blue cube from the Marvel Cinematic Universe, but actually is a five dimensional construct in the film Interstellar, which is built by future humans. It's what makes time travel possible. I think when it comes to time in Interstellar, we are actually dealing with a lot of really, really, really good science. OK. Before we jump into the black hole, things get a little bit more creative, let's say. all the stuff about Miller's planet that you lovely listener don't remember is the planet that is orbiting that massive black hole and is experiencing enormous time dilation, which is one hour on the planet is equivalent to seven years away from it. That is done very accurately. Sure, there are some cinematographic license of maybe it's unlikely that such a planet would exist, that it would have a shallow ocean with a massive wave, etc, etc. But the calculations are there, and it is possible to have massive time dilation due to gravitational objects. Okay, so tick for that side of things. Tick for that side of things. And I think, crucially, Kip Thorne, who's an astrophysicist, was heavily involved in this, right? Yeah, it's quite common for scientists to consult on this kind of projects. And also the visualization of Gargantuan, the Supermassive Black Hole, it's fantastic. It's probably one of the best looking and more accurate looking black hole in visual fiction. So that is great. And I think it's Kip Thorne's suggestion of work were taken very seriously. And this is why it is so realistic. Okay, so that's the good part. that that's sort of the ticks where does it get a bit unstuck well when you jump inside a black hole and suddenly you can travel to time so okay i am not going to be like this is not how it works i'm not going to be that negative but it is not how it works if you were to jump into a black hole there's this wonderful word for the process that happens if you get close to a black hole. It's called spaghettification. Which sounds even better in an Italian accent. Thank you. But it is so much fun because the idea is that you're getting stretched so much and that if you're jumping feet first, your feet are experiencing such a higher gravity compared to your head that you're just becoming long and thin like a spaghetto. It's fascinating because based on the laws of physics, actually going for a supermassive black hole, like Gargantua in Interstellar, is much more likely for you to survive that process, or at least to survive for longer, than if you're going for a smaller black hole because of the gravitational potential there, the gravitational differences there from just the distance between your feet and your head. But we do not think that anything solid in the universe can survive the gravitational pull of a black hole. You're turning into plasma. Okay, that's good to know. And let's also talk about a fifth dimension, the Tesseract. Yes. What are your thoughts on that? And can you break that down for me a bit more? We don't have to have always realism when it comes to movies. And I found that a very beautiful way to understand time as a real dimension in our universe, because we experience time as something else with respect to space. But as far as we can tell from the laws of general relativity, space and time work in the same way, or mostly work in the same way. So I feel in a very artistic way that Fifth and Ancient, the Tesseract, make it really clear of what it would be like to moving through time. Is that real? No, most likely not. So let's be a little bit more skeptical of my own skepticism, but I think it was absolutely stunning to see. It not exactly by that everything is about love but everything is about physics Yeah yeah fair enough Okay so then I think another series that we have to talk about is Doctor Who So much time travel so much meddling on timelines so I think let's start with more generally how well does Doctor Who cope with portraying physics and some of the science, how accurate can it be? What are your thoughts? Well, I think I need to admit that I am a huge fan of Doctor Who and at the same time I can admit that it doesn't really do a good job in portraying anything in a physical way. What I would say though is that all the producers throughout the many, many series have an appreciation in science because there are a lot of scientific concepts and words that are being used throughout but they're also going like oh this sounds really cool but yeah I'll just do my own thing to make it work. A bit more creative with the physics on that front. I would say a lot more creative. okay i have to know how likely is a tardis okay surprisingly there is some general activity thing that could make a tardis sort of work so technically thinking of an object that is bigger on the inside is not too absurd when it comes to the mathematics of general relativity if any of that is possible that is very much remains to be seen as we said maths is one thing reality is a different one now i think we have to address the fact that doctor who is quite a meddler of timelines Yes. There's a lot of potential challenges with that. So what are the implications of that and how well does that fare in the grand scheme of science and timelines? What I can appreciate in Doctor Who is it has its own inbuilt mythos of how you can get around the grandfather paradox. And it's the fact that there are things that you can change in the past and things that you cannot change. And this is very interesting because on one hand it gives you freedom to meddle and change things and improve things or mess with things etc. But also it gives you like oh this historical thing is always going to happen etc. and I find fascinating because if you had the ability to travel through time like that and you knew that oh this event is always going to happen you can go on and mess it up and do something fun with it because you know that it's always going to happen yeah make it make it even more ridiculous and would you rather travel through time by TARDIS or by car because we have to talk about back to the future absolutely i need to say obviously i would choose the tardis the tardis is so much fun but we cannot argue that the lauren is pretty cool yeah so i was going to say how much does it get right but perhaps we're back to the future i think we need to look at how creative does this show get with the idea of time travel it gets nothing right it gets extremely creative I absolutely adore Back to the Future, but it is very much actually the bubbles idea. It's probably closer to how Back to the Future works, because going into the past and into the future, you have all these things that change and have a massive effect. And it is not perfectly clear if those changes at the end of the first movie seems permanent. We do not travel through time or at least to the past. We only go forward into the future. But I'm afraid that there is not any physical explanation that I can come up with for a realistic interpretation of Back to the Future. Okay, so we've started with Interseller, does it fairly well and progressively got more and more, I want to say wrong, let's say creative with that theory. we've covered quite a lot there but I just have to know are there any series or films that you also want to mention that either get something really right or get something really wrong not exactly getting things really right but I always enjoy the time travel aspect in Star Trek especially in the movies and it's the fact that they use big gravitational objects at high speed so it feels relativity at least they're putting some thought on how it works and you need to put some effort I think the worst come on it needs to be Superman flying the other way round around the earth to go backwards that is absolutely the worst I'm afraid that winner hands down thank you to Alfredo Carpinetti his first book Invisible Rainbows will be out next year I can't wait to read that one yeah I look forward to it now Becky I know you wanted to talk about time travel in Harry Potter yes so what does what does physics say about Hermione's time turner honestly I wanted to talk about this so badly because I think of like all the you know the sci-fi things that go into like time travel stories I honestly think the time travel aspect of Prisoner of Azkaban is one of the most logical time travel stories out there because I mean for those who aren't familiar with the part but for those who are need reminding right they travel to the past Harry and Hermione only by a few hours but cannot change the events because it's already happened when both like present Harry and Hermione were there and future Harry and Hermione were there in what was then their past right the time traveling Harry and Hermione Harry and Hermione and so it's what's known as a closed loop scenario when you sort of think about like the time traveling aspect of it and it means almost there's there's no use going back and trying to change events because the events have already happened so there's nothing you do about it and it and it's a really sort of like logical way of thinking about it and i also think you know one of the sort of plot holes that people poke in this is like why would the adults give 14 year old to my name a time turner like why would they give her the ability to go back into time and i think the reason is why is because if you think about it in this closed loop scenario like you know they would figure well she can't have screwed up that bad otherwise we already know about it yes okay so it'd be safe to give it to her she's just going to use it for to get to her classes and yes she's going to be really tired all the time because basically she's just adding extra hours to her day without getting any extra sleep so um i really actually think this is like the answer to robert's wish from before right it's ability to go back only a few hours only it's just that mundane everyday thing right to rescue your failed cookery attempts and i think that's why it so beautifully fits in with the magical world of harry potter and not necessarily sci-fi because it's kind of like you know in harry potter there's spells for like cleaning up your house you know it's just like those mundane everyday things of like what an actual wizard living you know today would would want and it's one of those weird wishes that's like i had one that really weird things people just go back an hour and fix the fact that I burnt my chicken you could do that with a time turner you know and I just remember watching that film feeling the stress of what if what if they're seen and what if all of that happens because it's so key in all of that and yeah to be fair like Hermione is warned against that because I think you know physically speaking in that whole setup there is a possibility of you meeting your past self and going mad and changing events and the butterfly effects and all of that but as long as you don't mess with time and this is what's impressed upon a mind and then you have a closed loop and it's absolutely fine yeah so good okay and i actually have one more interstellar question because obviously there's so much going on in that film don't talk to me about interstellar yes the black hole visualization was a work of science art we can all appreciate that but everything else i'm still annoyed at years later okay okay fine but what would be the impact of a wormhole near saturn i love that that's what's keeping you up at night That's what I would like to know, please. Very little, surprisingly. Like, you've got to remember, wormholes are not black holes, right? So, yes, okay, you bend space to punch through to somewhere else in this sort of hypothetical wormhole scenario. But you don't bend space in such an extreme because you've got like a massive object there, like a black hole that's incredibly dense that's then going to warp space around it and, you know, have an incredibly strong gravitational field. if you've got this sort of like stable wormhole then as long as the thing that you're near is in a stable orbit saturn's in a stable orbit around the sun the moons around saturn are in a stable orbit around it like the the forces between its moons are probably going to be stronger right than the wormhole fairly close by so i think if anything you just want to be on the surface of saturn because you'd have a really cool light show every time the wormhole or you know like pass by and bend like the starlight from behind it so very very cool okay well i'll probably go watch interstellar over christmas and then come back in the new year with even more questions i would do however if people are really interested in this like time travel in sci-fi movies i have to give a shout out to one of the classic youtube videos out there which is a minute physics video love minute physics i think oh so good but they have a video called time travel in fiction rundown which basically like considers a load of different films and thinks about like you You know, did they have a closed loop or did they, you know, by going back in time, you know, like in Back to the Future, then produce a whole new different, you know, future timeline that branched off the other one and everything like that? And or is it a multiverse? And it's really, really well done and really well visualized as well, because it's a minute for this video. So, of course, it is. They're so good. I'll put that in the show notes as well. this is the supermassive podcast from the royal astronomical society with me science journalist izzy clark and astrophysicist dr becky smithurst now if we travel back to last month's topic robert can you tell us about the recent work that you've been doing on dark skies because you've been traveling somewhere you've been a busy bee i have i have far too much far too much i know so last week at the time of recording the podcast I was at this big meeting in Vienna at the United Nations you know go me that was really exciting actually going in there it was it's it's a fairly you know it looks like you think 1960s architecture not the most exciting bit of Vienna at all except for the fact the UN is there so UN pass which I've kept as a souvenir and all those things and it was a couple hundred people coming together more people online to talk about dark and quiet skies and in the specific context of what satellites are doing and might do to the sky and how we can work to to prevent it so it was interesting it was companies were there um there were some diplomats there you know including ambassadors and so on and the uh and a lot of astronomers as you would expect a lot of people working on this stuff so we had three days of quite i guess quite intense discussions quite you know good presentations quite a lot of questions about what we might do about this and it was everything from companies saying we can't possibly meet the standards you're setting you're completely unreasonable if they weren't able to through to companies saying oh these are fine because our satellites meet them already. Or people like me saying, well, do we need, you know, a new outer space treaty to govern all this stuff? And then another guy, Aaron Bolley from Canada, talking about the idea of a cap and trade system for satellite light pollution, like the one you have for carbon emissions. And that was quite a radical thought, you know, people were chewing over that one. And we are then, alongside that, writing a paper for, and this is a mouthful, the science and technical subcommittee of the united nations committee on the peaceful uses of outer space which we'll meet in february so that's our next bit of work the stsc unc p uo s yeah the stsc of un copious yeah which means nothing unless or still means nothing to those people but it was it was quite cool to meet the people who are involved with that and all those sort of things a lot of people i've interacted with online many many years and actually getting seen face to face so so that's that was that was great and i i came out of it quite optimistic and at the same time thinking there's you know so much to do to move things along because satellites launch all the time in large numbers and mostly from space eggs but and uh you know this trying to get the world to catch up with it is quite a challenge but we're working on it thanks robert for all you doing our best that's oh keeping everything crossed like it's clearly so needed yeah well I think not just thank you to Robert thank you to everyone who is putting in the time and the effort to sort this out because I think it's something that a lot of people care about yeah and we had actually some lovely messages on that Dark Skies episode as well from listeners So thank you to everyone that enjoyed that as well Now questions We've had a lot of questions on time travel. I don't know how easy or hard they are. So over to you guys. So Becky, listener Dave has emailed and says, I've just listened to the bonus episode of the 13th of December 2024. explaining why things with mass cannot reach the speed of light. The explanation was clear and I believe I have a good understanding of the underlying reason. It made me wonder, however, if a thing with mass could theoretically always have a speed equal to or greater than the speed of light instead of being accelerated to or beyond it. Perhaps some big bang leftovers could theoretically still be travelling at or faster than the speed of light. either way provided it was somehow actually possible what would be the implications that is a great question dave because theoretical physicists have wondered just that you know if superluminal which is the sort of fancy physics term for saying faster than light speed if superluminal motion is possible and what would be the consequences and they've even given a hypothetical name two things capable of faster than light travel and that is tachyons which is a fun fun word to say t-a-c-h-y-o-n-s because they tachyon to the speed of light i don't know why i have no idea where the name comes from i'm sure someone knows out there um but it is a fun fun word it's one of those physics words that you go where did they pull that from you know yeah yeah But these are hypothetical particles that would essentially increase in their speed, even though their energy was decreasing. Just because of this sort of like weird, like counterintuitive, relativistic things that happen beyond the speed of light. Okay. And you would essentially, instead of requiring infinite energy to accelerate something up to the speed of light, as Dave mentioned in his question, you would instead need infinite energy to slow them down to the speed of light. Right. So they're very, very strange. Exactly. This is why we're hypothetical. We have no evidence that these things like this actually exist. And the big problems with tachyons, though, is is this implications that Dave was asking about is because they break everything. Yeah. Because if it's possible to travel faster than light, you essentially break like cause and effect. Like something happens and then, you know, if it's a message or something like that, it reaches where it's supposed to go and then something happens there. and if you think about okay if you can travel faster than the speed of light then you have you know two reference frames because this is the key idea in physics where you've got you know the earth's reference frame and then your reference frame in a spacecraft or something like that you could send a signal from somewhere that would arrive before it was sent because of the rules of reference frames and even you know if you sent it to a spacecraft and it's arrived before it's sent they could even and then send a signal back that arrives before the original signal was sent. So it completely breaks cause and effect entirely. And this is one of the reasons why tachyons and fast and light travel always comes up when we talk about time travel, because even though there's no physical traveling necessarily, you could send a message to the past if it was possible. Okay. Great question, Dave. I'm going to need to think about that for some more time. Your dreams tonight, you know, wiggling, wormholes, tacky arms. Travel on the fastest speed of light. Have I burnt a chicken? Okay. Robert, I'm sorry. We'll stop taking the mic out of you for that eventually. Okay, Robert. Eric Moir asks, how fast do I need to travel to see the sun die before me? Great question. That was a great question, Eric. Yes, which means had to think. Yes, I did get thinking about this. And you need an incredibly high, what's called a gamma or Lorentz factor, which in this context would be the ratio of the time elapsed for the person moving at that high speed compared with an observer not moving at anything like that kind of speed. say you're sitting on earth and that's calculated from one minus the ratio of squares of the speed of the travel and the speed of light and you can see the equation online. Helpfully there are some online calculators to save time and so I could play around with it. There's one on the Omni website that's pretty good for this. The internet is great for this stuff really and it turns out anyway that if you expect to live say another 30 years without judging you know how old you are you might have longer then you need a Lorentz factor of a bit over 200 million assuming the sun will take 7 billion years from today to become a white dwarf and there's a bit of argument about that a billion years either way that means traveling at 299,792.4579973 kilometers a second or very very very very very close to the speed of light and i did wonder if that meant you know going round and round and round the sun akin to a classic star trek episode where i think they actually went back in time so we can we can sort of link that badly to the to the other discussions here or racing back and forth you know my thought was you just racing because if you if you travel at that speed away from the sun clearly the sun will recede into the distance rather too fast for you to see it die so you need to stay close but anyway if you go that fast that that'll probably do it no challenge there yeah so that's all you have to do eric don't worry about it that's fine and i love how you thought about the logistics like don't speed away from the sun and come back no because the sun will be disappearing don't do that yeah and then i'm like but if you're going back and forth and And what about that turnaround time? Like, anyway. It's going to make it harder. It's going to make it harder. Anyway, it's unravelling. Let's go. Very, very fast is the answer. And you'd have to decelerate to come back as well. Exactly. You'll take you longer, you know. Yeah, it's going to be tricky. Okay. And Becky, here's the final time-related question from Alexander in the Netherlands, who says, Thank you so much for the wonderful podcast you make. One of the very first words my son Victor ever said was man while pointing at the moon. Can I say that again? And his love for space has only grown since. His curiosity even sparked my own interest in astronomy, which is how I found your podcast. Victor, who is six, almost seven, keeps... Happy almost birthday, Victor. Keeps coming up with new questions. I love it when parents message us. It's like, help, a difficult question has come from my child. And so far, I've managed to stay one step ahead. Thanks to you. Today, he asked, why is there no time inside a black hole? And I had absolutely no idea what to say. Is time standing still inside a black hole or is even the concept of time questionable inside a black hole? Could you help me and Victor out? All the best. A dad a bit lost in space. Also, your pronunciation of questionable was questionable. Was also questionable. Yeah, we're just moving on. too many syllables let's go all right i am happy to help you out alexander and victor um so it's not that there's no time inside a black hole it's more that time and space swap if you will um the only place you can go is the very very center that we call the singularity this sort of like you know all the mass is concentrated into one infinitesimally small point. But the thing is that becomes your future. So a point in space sort of becomes where you're going to end up in the future. So this is why I'm sort of saying time and space swap. So it's not that there's no time inside a black hole. It's more the fact that it becomes so warped that it doesn't behave like we'd expect it to. And then actually at the singularity, at the center, there we can't really define space or time so i guess that's what we could be talking about when you say why is there no time inside a black hole you could be talking about that very central point that we cannot define at all never mind in space but also in time as well okay thank you mecky and if you want to send in any questions for a future episode or your child has difficult questions that you need some help answering. Are you a parent of a child who asks too many questions? And is very intelligent. She knows what to do. Well exactly do that. You can find us on Instagram at supermassivepod and we have quite a few more questions to tackle so we are doing an extended Q&A for January so just keep sending them in. We love reading them. So shall we finish as usual with some stargazing? Robert, what can we see in the night sky this month? Well, despite the cold, the January stars are really pretty good, though admittedly I realise I say that about every time of year. But it's true, of course. The stars are always nice to look at. We've got the really dominant winter constellations of Orion, Taurus and Gemini are still very much there. It's pretty much the best time of year to look at them. And the dogs in the sky, Canis Major and Canis Minor. And so for stellar targets, I would suggest looking at things like Sirius, actually in canis major the brightest star in the sky after the sun which just really for the sake of it to look at it if you look at it with a good telescope you can if you're very lucky see that it's got a little white dwarf companion thinking about the question earlier on and even without that you get this beautiful twinkling and violent twinkling in different colors which is obviously all down to the atmosphere of the earth rather than the star itself but it is it's quite a special thing to see um below that you can see i mean there are a lot of these things at this time of year but there's a nice open cluster of stars down below Sirius Messier 41 if you move up to Gemini higher up you've got you can look at things like the star Castor which is actually a triple star system well actually it's a six star system but you can only see three of them and each of those is in turn double and the same constellation's got another cluster Messier 35 so really I tend to think this time of year is all about taking the view of some of the brightest stars in the sky together it just happens to be that the way that they are and searching for the objects among them And another one I like is the 37 cluster of stars above Orion. And it really does look like two numbers if you get a small telescope looking at it. And then, of course, there's the nebula and so on, all these perennial things that you should always look at with a pair of binoculars every time you can. In the solar system, this is the best month of the year for Jupiter as it's opposite the sun in the sky on the 10th, so-called opposition. And that means it's highest in the sky at midnight. it's also this year really high in the sky for the UK where it is you know the in the middle of the winter that means that the sun is low and therefore Jupiter is really high up up in the stars of Germany really fantastic view and it's a really great object for small telescopes even with a pair of binoculars you can see the shape of the planet you can see it bulges out a bit because it rotates so fast and you can see the Galilean moons the four ones that funny enough Galileo discovered back in the 17th century. With a telescope you get to see a bit more detail than that, you know, obviously the bigger the better, but even a small telescope you'll see these belts, these atmospheric features that change over time, the great red spot if you're really lucky too. And apart from that there are two nice photo opportunities that I'll mention. One is when they're both involving the moon, one is when the moon appears to be very close to the cluster Prisipi in Cancer on the 5th and it passes in front of some of the Pleiades on the 27th. Now I think these are great you know great photo opportunities we have some amazing astrophotographers out there and but again even with your eye even picking up a pair of binoculars it's always quite special to see the moon moving in front of stars and actually realizing it or seeing for yourself how it moves through space so yeah January great month for looking at the stars don't be afraid of the cold just get yourself a warm coat I have one more thing for the next few weeks as well because I like to give this warning every year to any parents of children out there that the International Space Station, when it passes over, is very bright and very obvious and can look very convincingly like Father Christmas's sleigh is passing overhead. And, you know, I wouldn't want any kids out there to confuse the two. So just a warning to all the parents out there that there is a Passover of the International Space Station at around about six o'clock in the morning on Christmas Day. so if your kids have got you up that early that might be a fun thing to do if it's clear to peek out of the curtains and see if you can spot it there's a great nasa app called spot the station um which can tell you for your location like which direction to look in and how long the space station will be going overhead for and you can get like notifications as well to remind you which are really fun to set up so would totally recommend doing that um even if you don't have children wake up at 6am on christmas day look for the international station and not just Christmas Day either you know it's visible you know most days in the run-up to Christmas as well yes we would hate there to be a terrible mix-up on that front goodness me yeah I would hate for you to do that uh I think that's it for this episode next month is our Q&A special but for our members of the Supermassive Club there will be an extra Q&A coming out next week as a little thank you for supporting the show this year contact us if you try some astronomy at home It's at supermassivepod on Instagram, or you can email your questions to podcast.ras.ac.uk, and we'll try and cover them in a future episode. But until next time, everyone, until next year, happy stargazing.