# Scientists can levitate stuff and make it fly around using sound

Japanese scientists have made hundreds of tiny plastic balls float around like miniature spaceships.

Today’s news from the world of Awesome Science comes from the University of Tokyo, where a team has been levitating and controlling objects using sound. Here’s the video:

As the video points out at the beginning, levitation of objects using sound has been around for a few years. If you’ve ever stood in front of a large speaker you’ll know that they can pump out what feels like quite a forceful blast of air as they vibrate - but, somewhat deceptively, that’s not quite the whole story.

Rather than physically push air out from the speaker, what you’re experiencing is a wave of compression moving through the air. The speaker compresses a packet of air, which then “rolls” through the room, with the size of the compressed air corresponding the wavelength of the sound wave. And, just like sound waves, waves that overlap each other create new waves.

To levitate something just requires creating a standing wave. Think of it like this - if you’re watching a sound wave plotted out on a graph, it’ll be rolling along, going up and down as it oscillates. A standing wave occurs when two or more waves combine to create a new wave where, as the wave oscillates, there are points where there’s no movement. They’re called nodes.

Here’s a gif to illustrate how that works. The blue and green waves are combining to create the red wave, which has those points on the central axis that aren’t moving:

(Image: Wikimedia Commons)

If a speaker outputs a standing wave, in the most basic sense it means that it won’t feel like the areas of compression - those blasts of air - are moving. The gaps between those blasts of air will be positions of neutral force, with air pressure pushing in on it from both directions. If you stick an object in there that’s light enough, and smaller that the size the gap (which will be the sound’s wavelength), the force of the air should keep it floating in a stable position.

What the Tokyo University team has done is build upon that idea, by combining sound waves in three dimensions. The video shows not just tiny little plastic balls being levitated and controlled, but also resistors, LEDs, screws, bolts, and other small items. Rhett Allain at Wired worked out that you could levitate anything both smaller than 8mm and less dense than 1,000kg/m3, which is tiny - but it does have practical applications, particularly when people are working with sterile things they want to move but can't touch, like spaceship parts or medicines.

Ian Steadman is a staff science and technology writer at the New Statesman. He is on Twitter as @iansteadman.

Photo: Getty
Show Hide image

# The internet dictionary: what is astroturfing?

Yes, like the fake grass.

Thanks to the internet, there are a lot of new words. You’re most likely up to speed with your LOLs and OMGs, which became Oxford English Dictionary-worthy in 2011 (LOL OMG if you’re not). But words emerge constantly, and it can be hard to keep track of them. This is what this column is for. Every week, I’ll define a word that is crucial to understanding the internet, starting with “astroturfing” – like the fake grass.

To astroturf is to mask the author of a message to make it appear to have come from the grass roots. Messages created by brands, politicians and even the military are disguised as comments made by the public. The practice existed before the web – the term is thought to have been coined in 1985 by a US senator who received a “mountain” of letters from insurance companies posing as the public – but the internet has propelled it to new, disturbing heights.

“GIRLS U NEED TO READ THIS,” reads a tweet by a handsome teenage boy named Ashton, who tweets the same words day after day, followed by crying and heart emojis. Ashton lives to promote the book of a 19-year-old self-published author from Sheffield – or, at least, he would, if he lived at all. Ashton is fake, a profile designed to make the book seem popular. Many teenage girls have been duped by this. One told me: “I felt very cheated out of my money and my time.”

It has been estimated that a third of all consumer reviews online are fake. But it doesn’t end with bad books. In China, the “50 Cent Army” are astroturfers who are allegedly paid a small fee for each positive post they write about the Chinese Communist Party. And in 2011, it emerged that the US military was developing an “online persona management service” to spread pro-American messages, allowing one person to manage multiple online identities.

We would be foolish to assume that our own democracy is immune. Much was written about how the Tories used targeted social media adverts at the last election, and it is easy to see how astroturfing could transform our political landscape for ever.

Amelia Tait is a technology and digital culture writer at the New Statesman.

This article first appeared in the 10 August 2017 issue of the New Statesman, France’s new Napoleon