How maglev trains float and stay stable

HostI was on an old train last week, and you know that classic sound... the rhythmic thumping of the wheels on the rails? It has its charm, but you can really feel every bump and turn in your seat. It got me thinking about those high-speed trains that do away with wheels entirely. How do you actually get a massive train to just hang there in the air without falling?

GuestIt does feel like a bit of a magic trick, but it really comes down to the way magnets behave when they get close to each other. You know how if you try to push two magnets together the wrong way, they fight you? There's this invisible wall that pushes back. Maglev trains use that same force to lift thousands of pounds of metal. Instead of wheels, the train has powerful magnets on the bottom that face magnets on the track. When they have the same charge, they push away from each other, and that push is strong enough to keep the whole train hovering an inch or two off the ground.

HostOkay, but magnets can be a bit... jumpy. If I try to hover one magnet over another with my hands, it always wants to flip over or slide off to the side. What keeps the train from just sliding right off the track and crashing into the dirt?

GuestThat's the big hurdle. It's one thing to lift a train, but it's another thing to keep it steady. Most of these trains use a track that's shaped like a wide U or a cradle. The train actually sits inside this cradle. There are magnets on the sides of the track and on the sides of the train, too. If the train starts to lean a little bit to the left, the magnets on that side push a bit harder to shove it back toward the middle. It's like having invisible hands constantly poking the train from both sides to keep it perfectly centered. It happens thousands of times every second, so you don't even feel the tiny shifts.

HostSo it's a constant dance of pushing and pulling. But what happens if the power goes out? If these are powered magnets and the lights go dark, does the train just drop like a stone while it's going three hundred miles an hour?

GuestThat would be a nightmare, right? But the people who build these thought of that. They use a few different tricks. Some trains have a backup battery system that keeps the magnets humming long enough to slow down and land softly. Others use a special kind of metal called a superconductor. They cool this metal down to a temperature that's way colder than ice. When it gets that cold, the magnetic field gets sort of locked in place. Even if the power cuts out, the train stays floating because the magnetic grip is frozen into the very nature of the metal. It would take a long time for that metal to warm up enough to lose its lift. And for the systems that don't have that, they usually have small sets of wheels that pop out like the landing gear on a plane, just in case they need to roll to a stop.

HostThat makes me feel a bit better. So we have the floating part down. But how does it actually go anywhere? If it's just hovering there, you can't exactly have an engine turning an axle to move it forward.

GuestIt's basically like surfing on a wave, but the wave is made of magnetism. Inside the walls of the track, there are coils of wire. When you run electricity through them, they turn into magnets. The engineers switch the power on and off in those coils in a very specific pattern. They create a magnetic pull just in front of the train to tug it forward, and a magnetic push right behind the train to shove it along. As the train moves, that wave of pulling and pushing moves with it. The faster they flip those magnetic switches, the faster the train "surfs" down the track.

HostWait, I thought the whole point of this was that there's no rubbing or drag because nothing is touching. If there's no friction to slow it down, could these things just keep going faster and faster until they hit the speed of sound?

GuestIn a vacuum they could, but we still have to deal with the air. Even though the train isn't touching the ground, it's still smashing into all the air molecules in front of it. At those high speeds, air starts to act almost like thick syrup. It takes a huge amount of energy to push through it. That's really the only thing holding them back. Some people are even talking about putting these maglev tracks inside giant tubes where they suck all the air out. If you did that, you could potentially travel across a whole country in less than an hour.

HostIt sounds like we have most of the science figured out, then. Is it just a matter of time before we see these everywhere? It seems like a lot of work and money just to avoid having wheels.

GuestThat's exactly the rub. Building a regular train track is already expensive, but a maglev track is a whole different beast. You're basically building a computer-controlled magnet that's hundreds of miles long. Every inch of that track needs power and sensors. It's a massive project that costs way more than just laying down some steel rails. Plus, you can't just run a regular train on a maglev track, or a maglev train on regular rails. You have to build an entire new system from scratch.

HostThe world just might not be ready to swap every old rail for a high-tech cradle.

GuestThe most amazing part is that even with all that power, the ride is so steady that you can balance a coin on its edge on a little table while the train is flying at top speed.

HostThose old steel wheels and their rhythmic thumping might feel like the past, but they're a lot easier to build than a hundred miles of high-tech magnets.