For an experiment designed to reverse time, the equipment was surprisingly easy: little greater than a tank of water. With a puff of air to disturb the floor, Emmanuel Fort created a set of ripples transferring outwards in concentric circles. Then, because the waves unfold, he gave the tank a practised jolt – at which level they out of the blue began travelling inward, refocusing on the level of origin.

Fort’s work in 2016 was the primary of what has change into a deluge of experiments by which waves are manipulated, managed and even reversed with unprecedented precision. And nowadays, we’re now not simply enjoying with water. Researchers have found out how one can create a variety of “temporal metamaterials” that may manipulate and rewind electromagnetic waves, together with seen gentle itself, with ever better precision.

The important thing to those weird supplies isn’t a lot the cautious engineering of their spatial association of atoms, however how they work within the fourth dimension, time. Just like the speedy jolting of the water tank, temporal metamaterials can transform their properties within the blink of an eye fixed. This creates a form of boundary that acts like a mirror in time – and it’s this that exerts such refined energy over waves.

Not solely are these supplies a mind-bending invention, they’ve additionally change into an unexpectedly wealthy playground by which physicists can take a look at a raft of basic concepts at their limits. What occurs once you ship quantum particles via a slit in time? Does friction actually exist within the quantum world? And might we…