Yet when it comes to simply turning back the clock--akin to stirring a scrambled raw egg and seeing the yolk and white reseparate--a rich and growing subfield of wave physics shows that such time reversal is possible.
The trick is to create a certain kind of reflection. First, imagine a regular spatial reflection, like one you see in a silver-backed glass mirror. Here reflection occurs because for a ray of light, silver is a very different transmission medium than air; the sudden change in optical properties causes the light to bounce back, like a Ping-Pong ball hitting a wall.
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