A new material created by researchers can refocus sound around certain objects and effectively render them sonically invisible to sonar. No natural material can do this, so man-made “metamaterials” must be created in order to toy with the laws of physics to essentially bend sound back on itself. Mind blown yet?
The "Ruben's Tube" demonstration shown in the video gives a dramatic and visual representation of sound waves creating standing waves in a pipe. Whether or not you light the gas, once the speaker is on, there are sound waves traveling back and forth along the tube. Sound waves consist of alternating regions of high and low pressure. But by igniting the gas in the tube and allowing it to escape out of the holes cut into the top, we can see where the pressure is high and where it is low.