And from one of the posts we learned that when you blow air through a nozzle at a water surface, you can see a circular wave propagating outwards.
BUT when a vibrational excitation is given to this propagating wave, that wave is split into two traveling waves moving in opposite directions – One towards the source ( called time-reversed waves ) and one away from it.
Now this paper by Bacot ,et.al takes this to the next level by positioning these nozzles in the shape of an Eiffel tower.
Now when one changes the effective gravity through a vibration, the time-reversed waves refocus at the center giving us back the Eiffel tower structure.
The group was also successful in refocusing a smiley face using the same principles which is equally mind blowing. (You can watch the video here)