Levitation, ultra-powerful servers, and gyroscopes so sensitive that they can directly measure the curvature of spacetime around the Earth. Each one is an application of a truly amazing type of material called a superconductor.
To see how they work, we have to quickly explain electricity.
Electricity is the movement of electrons through a material. Electrons moving through copper cables power your home, your car pulls them from a battery and moves them through your engine to start your car, and your computer controls their flow through its circuit boards to perform calculations.
But when electrons flow they create heat. When they travel through a wire or circuit board, some of them smack into the atoms of the circuit board which makes them vibrate. This vibration is heat, and the material gets hotter as more electrons flow through it.
To get powerful computers, you have to cool them down, which is why they have fans or liquid cooling.
Our ability to cool things down is a limiting factor that impedes the development of many more advanced technologies, like smaller and more powerful computers.
But an alternative option is to use special materials, like superconductors. They are a special class of material that possess a strange property that comes from quantum mechanics.
As a quick overview, there are two categories of particles in quantum mechanics:
- Fermions, which include quarks and electrons, and
- Bosons, like gluons, which carry the fundamental forces.
These particles spin all the time like mini gyroscopes. The type of spin is what makes a particle a fermion or a boson.
Bosons spin in ‘whole’ amounts, like a regular gyroscope. They spin 360° degrees to get back to their starting position.
Fermions spin in ‘half’ amounts. There is no real analogy for this in our normal world. They spin 720° to get back to their starting position. Fermions are like strange mathematical objects that should only exist in the mind of a deranged mathematician, but are actually a fundamental part of reality.
The spin has a bunch of effects, but the most important one for superconductors is called it’s ‘state’, which is like its position and momentum. Multiple bosons can occupy the same state at the same time and not interfere with each other, like multiple radio waves travelling through the air simultaneously.
Multiple fermions can’t occupy the same state at the same time, like two tennis balls can’t sit on the same spot on ground at the same time. This is called the ‘Pauli exclusion principle’, and it won a physicist called Pauli a Nobel prize.
Ok, time for what a superconductor actually is.
In some special kinds of materials, and at very low temperatures, two electrons (which are half-spinning fermions) can join up together, forming a pair, and act like a whole spinning boson. Suddenly, like bosons, they can occupy the same state at the same time as other electron pairs.
This is actually incredible. The fundamental nature of electrons change, and they get zero resistance from the material they’re flowing through, or from each other (this is called ‘BCS theory’). The material is transformed into the perfect, heatless conductor of electricity.
These materials are called superconductors.
You could make a wire, a circuitboard, or anything out of a superconducter and pass electricity through it without creating waste heat.
That is very useful so far, but they can also levitate magnets.
Because all of the electrons inside the superconductor can move around inside it completely unimpeded, they create a magnetic field. But if you place a magnet on top of the superconductor, the flow of electrons will shift to accommodate the magnet, and the field they create will repel and attract the magnet at exactly the right about to suspend the magnet above it. What you end up with, is levitation.
The easiest superconductor to use is called Yttrium-barium-copper oxide. To get it to the right temperature, you have to pour liquid nitrogen on to cool it to -200oC.
The problem is that it is too brittle to make into a wire or circuit board, and most of the other superconductors need way colder temperatures which makes them impractical. One of the holy grails of materials research is a superconductor that is malleable and can operate at room temperature.
This is called a ‘high temperature superconductor’, and it would change the world. Some practical uses could be:
- Replacing all copper wires with the superconducter. This would mean:
- Computers that give off very little heat allowing us to build them much smaller and much, much more powerful.
- Move electricity much more efficiently in a city’s central power grid.
- Replacing a city’s extensive electrical wires with a small, thin underground strip.
- Moving electricity across longer distances, making renewable sources of energy more viable.
- Batteries that do not degrade over time.
- Making a ‘qubit’, the fundamental component of quantum computers.
- High precision gyroscopes that will be able to measure the exact curvature of spacetime around the Earth.
- New types of high-speed magrail trains that will move with far less friction.
A superconductor on a special magnetised track, like a prototype super magrail train