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.

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Goldsmiths diversity officer Bahar Mustafa receives court summons in wake of “#KillAllWhiteMen” outcry

Mustafa will answer charges of "threatening" and "offensive/ indecent/ obscene/ menacing" communications.

In May this year, Bahar Mustafa, then diversity officer at Goldsmiths, University of London, posted a Facebook message requesting that men and white people not attend a BME Women and non-binary event. There was an immediate backlash from those also enraged by the fact that Mustafa allegedly used the hashtag #KillAllWhiteMen on social media. 

Today, Mustafa received a court summons from the Metropolitan Police to answer two charges, both of which come under the Communications Act 2003. The first is for sending a "letter/communication/article conveying a threatening message"; the second for "sending by public communication network an offensive/ indecent/ obsecene/ menacing message/ matter".

It isn't clear what communciation either charge relates to - one seems to refer to something sent in private, while the use of "public communication network" in the second implies that it took place on social media. The Met's press release states that both communciations took place between 10 November 2014 and 31 May 2015, a very broad timescale considering the uproar around Mustafa's social media posts took place in May. 

We approached the Met to ask which communications the summons refers to, but a spokesperson said that no more information could be released at this time. Mustafa will appear at Bromley Magistrates' Court on 5 November. 

Barbara Speed is a technology and digital culture writer at the New Statesman and a staff writer at CityMetric.