Hey. So. My name is Fran. I'm a Ph.D. student here at Oxford, and I work in a department who quantum materials. So we work with very special materials, not just you normal word or, you know, metal. And they can only be described using quantum mechanics. And so I want to start off with a question. Has anyone ever been on a train and wished it was going a little bit faster?
Yeah. No, I feel you. So I grew up in London, so I spent a lot of time waiting for the tube to just kind of slowly drive along. And does anyone know why trains can't go any faster? Does anyone know what limits the speed of a train? Any ideas? Yeah. So so that that's a good speed limit that trains by some can go a little bit faster but you know why is 60. Why can't trains go any faster? Yeah. They could be really dangerous if they hit something. Any other ideas? Yeah. Um, if it has to stop.
Because there might be a fire. In the as well. Yeah that so imagine kind of you in kind of the perfect safe situation where you just have a truck and there wouldn't be any fires, you wouldn't have to hit something. What would limit the speed of a train then? What would kind of give it maximum possible speed? Yeah. If it went in Berkeley, it come off, right. Yeah.
It might come off the rails. That's right. But the reason trains can't go extremely, extremely fast is because of friction between the train and the tracks and also because the engine has kind of only a small amount of or a limited thrust they can use to power the train forward. So there is a way we could actually make trains go a little bit faster. Does anyone have any idea how you might be able to get rid of one of these things to be able to make the train go faster? Any ideas? Yes. Vacuums.
One idea. Another idea. Imagine, right? If there was no friction between the train and the track and the train would just go up and levitate above the track, that'd be pretty cool, right? Then I think it would be cool. This is my hope. HD To be too high. You get you could get a ladder or something to get onto the train. Trust me, it works. It works. So imagine that we're all very enthused about Levitating Train.
And does anyone have any idea how we might be able to get a train to levitate in the first place? Yes. So we actually. Yeah, that's exactly right. If we're going to use magnets to try and levitate things, I've got t ball magnets here. And so if you have a North Pole, South Pole comes together, right? They attract they really like that sort of thing. But if I put you North Poles together or two South Poles together, they're not going to like it.
They're going to repel. So imagine you kind of use this repelling force, right, to make them levitate. So I've got North Pole, South Pole here and then North Pole, South Pole here. Who thinks that they're going to levitate when I drop one onto the other? Yeah. Yeah. Okay. Well, moment of truth. Three, two, one. Oh. Oh, well, that's that. And the reason why it doesn't work is because these levitating. So these are just regular ball magnets and they're actually metastable.
So they're not very stable. If you have them perfectly one on top of the other, it'll be stable. But as soon as it slips a tiny amount, then they're just going to kind of snap together and fall over, just like you saw there. So that's quite a big problem because obviously you want your train to be moving. So as soon as the train moves a little bit, that's going to stop being stable and then it just going to flip around and fall over.
Does anyone know how we might be able to overcome this problem? Yeah. There is one against one. I think we still got the same problem here because this is one magnet and this is one and then we still have one without the. So that's a very interesting idea to use. Just a North Pole on its own, just the South Pole. And we think in physics they should exist. But actually physicists haven't even been able to find them yet.
So we're going to have to try and work with things at the moment that we've already discovered. Anyone have any other idea? Well, how about using a different kind of Mac now? Has anyone ever heard of a superconductor before? Yes. Someone has heard of a superconductor. Now, superconductors are really interesting because they are a quantum magnet.
So you cannot describe these magnets with normal classical mechanics that kind of describe both rolling down hills and kind of normal trains moving along. You have to use quantum mechanics. And they've got some very interesting properties. So superconductors have no electrical resistance. So who's ever touched a wire when it's part of a circuit and it's got a little bit warm?
So anyone felt that. Yeah. So actually that's because the wire has resistance and superconductors, they have no resistance. So if you put a current through a superconducting wire, the current will keep going round and round and it won't lose any energy to heats and it would just keep going. And so there have been experiments where this kind of this current has been going for tens of years.
So that's pretty neat. But the thing that's really important for us today is that it acts like a magnetic mirror. So if you get a superconductor so I've got I have got a superconductor here and you put it in as a magnets.
I've got some magnets here. If you put one on top of the other, the electrons from the atoms, they're going to rearrange themselves inside the superconductor in such a way that it will become a magnet, but it will be a magnet that perfectly repels these magnets, which is pretty neat. So I've got some magnets for some nice magnets here. I've got a superconductor who thinks this is going to levitate when I put one on top of the other. Okay. Well, you got big expectations, so. Three, two, one.
Oh, well, this is just a talk full of disappointment. So does anyone know why that didn't work? Any ideas why it didn't work? Yes, that's reflected. It's kind of perfected. The opposites do it. Not quite. No. So it is kind of. It's. It's reflective so that it perfectly repels so. Actually, the reason is because this is at room temperature. So this is this is a superconductor.
It's kind of at the moment a bit like a ceramic, like something you get in a fancy bathroom or fancy place and it's pretty boring. So we need to cool it down. We need it to be really, really, really, really, really cold. And we need it to be below its critical temperature. And when the temperatures below the critical temperature, then it's superconducting. And so this one has a critical temperature of, I don't know, like -150 degrees.
So then, you know, how are we going to get down to that sort of low temperature? Yeah. Bingo. And there is. But so has everybody heard of liquid nitrogen before? Yeah. Liquid nitrogen is a wicked is you basically you take nitrogen from the air and that means is actually pretty cheap. It's about the same price per litre as milk, but it's a lot less weird to throw around. And so I just take a little bit. It never gets old is very, very cool.
And so you get nitrogen, you take it from the earth. So that means if I put a balloon full of air in here, the air inside will also liquefy. Right. So these are balloons I blew up earlier. And so who thinks they're going to explode? They're only going to explode if they're low quality balloons. I think they work fine earlier. It's just stuck together. That's fine, because I blew them up with a certain amount of air.
I put them in here and then the air condensed down and became a liquid and the balloon shrank. But now the air is going to evaporate, hopefully, and then hope they all go back to being the same size. I think it's okay. I think it's okay. So, yeah, so that's very cool. And the main point of that is that liquid nitrogen, when you turn it from a gas to a liquid, it actually condenses down quite a lot. So I've got a a little what is the tiniest amount of nitrogen in there?
And I'm going to stick a balloon over it and I'm going to try and work out how much. Yes. That's going to produce. So give a little shake. So you see there that tiny amount of nitrogen is blowing up that entire balloon. And in fact, the nitrogen, when it goes from being a liquid to being a gas, it increases by 700 times in volume. So it's actually a little bit dangerous and you've got to be a little bit careful. Okay. I'm just going to intervene. Okay.
I'm glad that's the highlight of the talk. So yes, I increases by 700 times in volume when it goes from being a liquid to being gas. So it's a little bit dangerous. You might have heard a story a few years ago now. So it became very fashionable for a while to pour liquid nitrogen inside drinks because I mean, it's really neat to look at. It is really cool. And you can put it in drinks and it freezes things really quickly and it is really interesting.
But obviously if you have a drink which has got something which is like -200 degrees and then you generally wait for the -200 degrees bit to evaporate outright. I mean, it's not just me, but someone in the news a few years ago drank a cocktail which still had the liquid nitrogen in it, and then the liquid nitrogen went down her throat, expanded 700 times, and her stomach blew off her stomach. She had to have an operation to have a stomach for me. She's still alive, so it's okay.
But the point is, don't drink. This is what I'm trying to say here. And so I've got some nitrogen and I've got my superconductor here and I'm going to try cooling it down, see what happens. And so now the little superconductor, the little puck in there is cooling down. And what happens when it goes through the critical temperature? It goes through something called a phase transition. A phase transition is basically when you get something and it changes its properties after a certain temperature.
And there are lots of different examples when you have water boiling 100 degrees, that's an example of a phase transition. When you have water freezing at zero degrees, that's an example of a phase transition. And so I'm going to show you another phase transition. So I've got this rubber rod. And can you tell me, how does it feel? Does it feel brittle or so? Yes, I soft and bendy. And if I hit this with a hammer, I mean, no, particularly exciting, but whatever.
And so I'm going to put in the nitrogen. What happens up in the nitrogen is that it heats up the nitrogen that's immediately around it because the rod is about 200 degrees hotter than the liquid nitrogen. And so when he's set up, it turns into a gas and then that pushes more liquid nitrogen through the rod and now it's stopped, which means it's at -200 degrees. And the rod is going through a phase transition which changes material properties and now it's like grass cool.
And so it's not just that, it's not just your rod. You can also do with flowers. So flowers, they're made from from plant cells which are mainly water. And so obviously water's going to be frozen at -200 degrees. So just give a little moment. So we are a shadow like lost. So this is really good if you're having a really bad Valentine's Day friend told me that.
So that's pretty neat. I mean, you can smash a lot of things, but let's try and be a little bit constructive now with our phase transitions and see how it goes for our superconductor. So I'm hoping I superconductor is pretty cool now and I'm going to put it on here. We see that is levitating. That's pretty neat. And so it's going to be heating up now because it's obviously in the air, which is much hotter than the superconductor.
And once it goes above the critical temperature, goes through the phase transition and then stop, superconducting becomes boring again. So that's pretty neat I think anyway. So this is what it acts like, a magnetic mare. So you get a superconductor, you cool it down, it starts superconducting. And then what happens is arranges the electrons inside itself so that it pushes all the magnetic field out and it perfectly repels it.
So that's quite good, but it's not particularly stable. It can fall off quite easily. So we need something a little bit better in order to make our superconducting train. But fortunately, we've got science on our side here. So if I actually cooled down the superconductor. Inside the magnetic field, it's going to be something a little bit different. So. There's a more nitrogen. Alex, coach. And now we're superconducting again. But this time it trapped the magnetic field inside itself.
So now you can I superconducting rollercoaster which I basically the reason I'm doing a Ph.D. so I can do a superconducting rollercoaster and now it heats up is through the phase transition and stop superconducting. So that's a different kind of superconductivity and that's called quantum locking.
So what happens there? You get your superconductors at like super boring and then you put it in the magnetic field and then it pretty much holds on to the magnetic field inside the superconductor, and then it's stuck inside. So it's basically the same as kind of, I don't know if I would hold this pocket like this for the, for the first one, the magnetic mirror. But then if I put my arm through the bucket for the quantum locking, it's a little bit more stable.
So that's the sort of thing we want to be using with our train and loop history. Superconductors were discovered by this guy coming on us in Leiden in the Netherlands in 1911, and he discovered Mercury Superconducting at -269 degrees. So that's a little bit colder than liquid nitrogen. Does anyone know how we're going to be able to get to a temperature colder than liquid nitrogen? Yeah, dry ice is actually not going to work in this case, I'm afraid.
I think draw us a little bit warmer than liquid nitrogen. Any other ideas? Yeah, that's true. That's a very good idea. So these days we actually use liquid helium because that's really safe and it doesn't react with things. But back in Camerlengo Onassis day, they did use liquid hydrogen. But as you probably know, if you have hydrogen and then you have a flame, it will set on fire and blow up enormously as soon as it reacts with the oxygen in the air.
And so it's not particularly safe. So there were a few of the early students in in superconductivity did die because they were smoking that. This is all back in the day where people like to wear suits and smoking pipes in the lab and they were smoking that pipe. And then the the flame from that pipe caught on to some of the hydrogen and blew up the lab. But generally, this doesn't happen anymore. I mean, I don't like taking risks.
I don't even go ice skating. So I think I wouldn't do this if this is very dangerous. And so superconductors are really exciting, but they're actually they're actually useful. And so it's very important when you're doing science to think about why why these things will be useful for society, not only to justify it yourself, but also to get funding. So does anyone recognise that thing up in the corner? Has anyone seen that before? Yeah. Do you know what it is? Anyone know what it could be? Yes.
Has anyone heard of the Large Hadron Collider before? That was big in the news of the Higgs boson. Well, in the Large Hadron Collider, they got loads of particles and they got really, really, really fast in circles. And the way you get the particles to go round in circles is by using magnets. And we've got to use the superconducting magnets because they you can make really, really big magnets that are able to push the really fast particles round in circles.
Then you can also use them in telescopes. So you can use superconductors and very special detectors that allow you to see very dim and faraway stars. You can obviously you can use them in trains. So train, train one is really neat. Has anyone ever been to Birmingham Airport before? There is a maglev train between Birmingham International Station and Birmingham Airport, which is pretty neat. So I went on that for the first time recently, was definitely more excited than any of the kids on there.
And so the Birmingham airport doesn't go very fast, but maglev trains can go incredibly fast. They can go up to 600 kilometres an hour, which I think might be the land speed record. So pretty quick you can also use them in quantum computers. So quantum computers are a very special kind of computer that allow you to calculate things really, really, really quickly. So no more waiting for the computer to load. You can use them, obviously, because there's no resistance.
You can use them and wires to transmit enormous amounts of current over long distances without losing any energy. So that would be amazing. Imagine if you could get high transmission lines that don't lose any energy. And finally, MRI scan is need a very big magnet. And if you have a very make, if you want to have a very big magnet, what are you going to use as a superconductor?
So superconductors, they're basically everywhere. And one question I get a lot of free with the train is how does it hold the train off? And that's really interesting because because superconductors can actually hold up to 70, 70,000 times their own weight just with the force of repulsion. So I think that's pretty neat. So I'm going to finish off with one final example of how you can use superconductors, and that's to make a levitating sumo wrestler.
So as you see there, it can even hold up the sumo wrestler. So thank you very much for listening. I have got a little train down here, the front, if any of the kids parents would like to have a go, pushing it around, seeing how stable it is and you want to have a go. Yeah. Just come down to the front. It's fine. And does anyone have any questions? I'm just going to cool this down. Just. You're it. Another moment. Next to the.
The droplets of the liquid nitrogen that. So you see the levitating train. Does anyone to give it a little push? See, they can just go for it. Just be gentle. Yeah. Cool. Well, thank you very much for coming. I think if you don't want to stay for the other talks, please go out of the store. Apart from that, I hope you have a nice rest of your day.