Watch scientists knock down Lego minifigs with “time reversal”

Lego plays a starring role in demonstrations of new “time reversal” research out of Brigham Young University.

Honestly, it sounds like a riddle:

"A crowd of 29 stands still, positioned as lookouts in various directions. A chirp punctuates the silence before being replaced by a distinct buzz. The buzzing grows louder, then abruptly drops back into silence. Twenty-eight [figures] shift slightly — they survive. But one unlucky companion lies on his back, toppled by an invisible force."

What happened?

The answer is something called time reversal. (Disappointingly, time reversal has nothing to do with time travel – the field was previously known as “matched signal processing.”) Brigham Young University physics professor Brian Anderson describes time reversal, also known as targeted sound vibrations, as like ventriloquism. Instead of throwing voices, they’re throwing vibrations.

A speaker releases vibrations that are picked up by a sensor at the other end of the table. The sensor’s recording is processed by a software the scientists developed that alters the timing. When the speaker plays the new recording, it’s timed to be one big vibration that knocks over the target.

The BYU scientists used Lego minifigs to demonstrate how the process works. Meaning that one Lego knocked down in the scene? That was a targeted takedown.

The whole thing looks extremely nuts. See for yourself in the demo below. If you watch closely, you can even see the minifigs bounce a bit.

While the power to bounce and target Lego minifigs looks like a lot of fun – it would certainly step up the level of Star Wars battle recreations – the BYU scientists have something more in mind. They hope to use this technology to destroy kidney stones or find underwater objects. Anderson even sees uses in private communications and noise cancellation.

For now, the Lego demonstrations serve the not insignificant purpose of making presentations – particularly at elementary schools – more engaging than a powerpoint. Which is to say, more simulations featuring Lego minifigs, please.