Back to the Future 2 made many predictions about what the world would be like in 2015, from flying cars to a holographic 19th Jaws movie. While many of these predictions seem outlandish now, there are several technologies that the movie did get right, at least partially. While fingerprint technology is not generally used to secure people’s homes, it is used as a security feature in one way or another on most smart devices that we use almost every day. This, however, is not the most outlandish prediction that the movie got right, that honor goes to the hoverboard that Marty McFly uses throughout the movie, at least in theory.

Many attempts have been made to create a functional hoverboard, including using the same designs as hoverboats by placing fans on the bottom of the board, but the design that most resembles the hoverboard in the movie uses something called quantum locking. While the word quantum preceding anything is enough to make some people apprehensive, in practice this term simply refers to how a superconductor will hover in place above a source of magnetic field.

A superconductor is a material that allows an electric current to pass through it with no electrical resistance whatsoever. Resistance in a conductor such as a metal arises from the collision of electrons in the metal. If the temperature of this conductor is lowered, these collsions happen less frequently, and the resistance of the conductor also lowers. At a certain temperature, these collisions will stop altogether, and the electrons can carry the current through the material without any resistance. This temperature is called the critical temperature, when the material changes from a conductor to a superconductor.

Superconductors display several interesting properties, but the one most relevant here is something called the Meissner effect. When a superconductor is placed in a magnetic field, it will repel all of the magnetic field from within it, so that it effectively bends around the superconductor. Due to this repulsion, the superconductor will float above the magnet at an exact height, as the repulsion has to work against gravity. The levitation is not very stable, however, as the superconductor will repel the magnetic field no matter which orientation it is in. This is where quantum locking comes into play.

When a superconductor becomes thin enough, the magnetic field will be able to go through the superconductor at certain points, called flux tubes. The superconductor will still repel the magnetic field through these tubes, trapping the magnetic field in these areas. This causes the superconductor to be locked in place, as it will oppose the movement of these field lines. The superconductor will then hover in place above the magnet in whatever orientation it was placed in the magnetic field. It will also hold this orientation if it is moved along a magnetic track.

The main problems with using this type of levitation in hoverboards or even flying cars is that, firstly, the superconductor has to be above a magnet to levitate. To make this a viable way to travel anywhere, first magnetic tracks would have to be built, which would be costly and time-consuming. The second problem is that the critical temperature of most known superconducting materials is very low, close to absolute zero in some cases. Work is being done to make materials whose critical temperature is relatively high. Until such a material is discovered, attaching a cooling system capable of maintaining these low temperatures to a hoverboard would be extremely difficult to do efficiently. Unfortunately this means that it is highly unlikely that we will see hoverboards in public anytime soon, but it is a possibilty in the future.



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