CAN SCIENTISTS EVER DEMONSTRATE WINGARDIUM LEVIOSA?

There is that jaw dropping moment in every muggle’s life when they see something levitated without any obvious explanation of how, except for the possibility that the person causing it has some special, magical ability.

Muggle magicians and spiritualists have been amazing people with these impossible feats for centuries. Increasingly, though, the people who have been providing the most public awe have been scientists, whose exploits are equally as mesmerizing. These talented men and women perform their feats by enhancing their knowledge of nature and developing techniques to exploit it.

In Harry Potter, levitation is considered one of the wizard’s most rudimentary skills. It can be achieved a number of ways, like with Wingardium Leviosa or the Locomotor spells, which can lift a target a few inches off the ground and move it in any given direction. In the real world, though, what methods have muggles mustered to achieve levitation?

The Gravity of the Situation

Levitation is all about somehow supporting the weight of an object in midair. When we typically talk about weight, we’re used to saying that something weighs, say, 100 pounds, but when we say this, we are really talking about the mass of the object. The mass of an object doesn’t change from place to place and is a measure of how much matter is contained within it.

All objects have a gravitational field associated with them that attracts other objects that have mass or energy. The bigger an object’s mass, the larger the associated gravitational field and the more it attracts other objects. As the Earth has a very large mass compared to objects on it, it’s gravitational field is the one that dominates objects on or near Earth. The force of attraction within Earth’s gravitational field is proportional to the mass of the object being attracted to the Earth. This attractive force is what scientists refer to as the weight of the object.

To levitate an object on Earth, it’s necessary to find a mechanism that can overcome the object’s gravitational pull toward the Earth i.e. its weight. Either that, or somehow find a way to negate the effect of Earth’s gravity, like H. G. Wells’s fictional substance called cavorite from his 1901 novel, The First Men in the Moon. Unfortunately, in our non-fictional magic-absent world, such a substance or quality is deemed impossible, although it didn’t stop some engineers and scientists from giving it a good go.

From the mid-1990s there was a BAE Systems supported research program called Project Greenglow, which was set up with the sole purpose of developing antigravity technology. The man behind the project, Ronald Evans, was inspired by the thought of gravity control and gravitational propulsion. Despite all the enthusiastic work throughout the following two decades, the project officially closed in 2005, with no real viable antigravity technologies on the horizon. Antigravity attempts aside, there are a few existing technologies that can overcome an object’s gravitational pull toward Earth i.e. its weight. A relatively obvious one is through the use of air.

Aerodynamic levitation

If we needed to get a feather to stay aloft, we could simply blow it with puffs of air from underneath. Generally, the bigger and heavier the feather, the larger the puff of air needs to be to support it. However, its shape and orientation are important, too. This isn’t very impressive, though.

A more impressive trick is to suspend a ping pong ball in a current of air from a bent straw or hair dryer. The ping pong ball sits on a cushion of air pressure provided by the upward air current, though the ball doesn’t fall off of this stream of air like a feather eventually would. As the airflow moves around the ping pong, it creates regions of high and low pressure, which provides a restoring force that keeps the ball in the stream of air and balanced against its weight. It will even work with the airflow tilted a little to the side. If tilted too much, though, the weight overcomes the pressure and the ball drops.

By using a larger stream of air, it’s possible to suspend a beach ball, but the application doesn’t stop at completely spherical objects. Using more powerful streams of air, it’s possible to suspend a screwdriver, egg, light bulb, test tube, and a small bottle, among many other things. It’s even possible to keep a human aloft with air, although it involves a slightly different process.

When skydivers jump out of planes, they are falling past the air. As they fall faster, the air resistance (drag) on them increases until it balances the weight forces pulling them down. With the upward and downward forces in balance, the skydivers don’t gain any extra speed and are said to have reached their terminal velocity.

If enough air is pushed upward at a speed equal to a skydiver’s terminal velocity, then the downward force of their weight will be balanced by the upward drag caused by the moving air. This can cause the skydiver to be suspended in midair, which is how indoor skydiving centers work.

Although large and small objects can be levitated using aerodynamic forces, it probably wouldn’t be very practical to blast objects with strong gusts of wind to keep them airborne. There would likely be too much noise and/or collateral damage. So, maybe this next levitation technique is better?

Acoustic Levitation

Acoustic levitation is a process that makes it possible to lift and move objects using sound waves alone. A sound wave consists of areas of alternating high and low pressure, where molecules have been pushed together (compression) or drawn apart (rarefaction) respectively. The distance between successive compressions or between successive rarefactions is called the wavelength, and however many pass a point every second indicates the frequency of the sound wave.

Sound waves can exert a pressure on surfaces they come into contact with. It’s called the acoustic radiation pressure or acoustic radiation force. If the amplitude (volume) of the ultrasonic sound wave is large enough, it can carry sufficient energy to suspend things.

Acoustic levitation uses a loudspeaker or transducer to produce sound waves with frequencies higher than 20,000 hertz, known as ultrasound, because it’s beyond the limit of human hearing. Like any sound waves, if these sound waves encounter other sound waves, they can interact and produce a resulting wave pattern that is a combination of the waves. If identical sound waves are traveling in opposite directions when they meet, this interaction or interference can result in a standing wave.

In standing waves, there are points which vary between maximum and minimum pressures, called antinodes. Then there are points that lie between the antinodes in which the pressure doesn’t vary at all, called nodes. The nodes represent stable areas within the standing waves, in which objects can be levitated, providing they are small and light enough. Objects are usually limited to a size of a quarter to a half of the wavelength of the sound waves, which can be about 17mm or less. So, objects larger than about 4mm generally can’t be supported in this type of ultrasound standing wave.

Using this system, polystyrene balls and droplets of water have been levitated, as well as ants, ladybugs, and tiny fish. Other systems use multiple loudspeaker sound sources to manipulate objects like small screws, matchsticks, and LEDs. By controlling the sound output from each individual loudspeaker, the objects can be levitated in stable regions as well as moved around; similar to the locomotor spell.

So, what about levitating a feather like Hermione did in Harry Potter and the Sorcerer’s Stone? Well, we put the question to Asier Marzo, who researches acoustic levitation at University of Bristol, UK. He’d never tried it before but within weeks of our request, he sent a link to a video in which, yes, a feather is successfully levitated. The feather was only about a centimeter or so across, but it proved that acoustic levitation could be used to produce effects similar to those seen with the levitation charm.

Diamagnetic Levitation

You may be familiar with the effect that magnetism has on materials that contain iron. Iron is known as a ferromagnetic material and is strongly attracted to magnetic fields. Cobalt and nickel are also ferromagnetic.

Ferromagnetism is the most familiar form of magnetism, but there are also others, such as paramagnetism and diamagnetism. Paramagnetic materials are weakly attracted to an external magnetic field, whereas materials with diamagnetic properties tend to be repelled by an external magnetic field.

Diamagnetism acts on all materials (rather than just metals), causing them to feel a relatively weak repulsion when in a strong enough magnetic field. This can cause objects to levitate when they are within a strong enough vertical magnetic field, as demonstrated with small frogs, crickets and mice.

When levitating a frog, it’s not just a case of applying the strongest magnetic fields. Although this would provide lift to the frog, it wouldn’t allow the frog to remain hovering, as instabilities can quickly set in. This is because there is a stable zone on the vertical axis within which diamagnetic objects can be levitated. To achieve levitation, the magnetic fields need to be adjusted to an accuracy of a few percent. The theory underpinning the flying frogs was developed in the 1990s by British professor Michael Berry, a leading theorist in mathematical quantum physics.

It is still a problem to create a stable zone big enough to accommodate a human being, though. You would need a magnet that uses about 100 megawatts of power and it would need to have a central space of 2 feet in diameter to levitate a human. For comparison, the experimental levitating space (at the center of the superconducting magnet) used to levitate the mouse had a diameter of 60 mm.

So, Can Scientists Ever Demonstrate Wingardium Leviosa?

The answer is most definitely yes. On a smaller scale, acoustic levitation can be used to levitate and manipulate objects, but it requires an array of transducers to send the waves and is limited to roughly 4mm objects. Diamagnetic levitation has improved on that by levitating bigger objects, including small animals; but only within particular stable regions and not yet for larger objects. It also requires a huge and powerful magnet to work. For larger objects, aerodynamic levitation is the most capable option. but it relies on a strong blast of air, so rather inconvenient again. In any case, levitation is a real thing and a very active area of research.