The explanation of spatial reflections – light or sound – is quite intuitive. Electromagnetic radiation in the form of light or sound waves hits a mirror or a wall, respectively, and changes direction. This allows our eyes to see the reflection or echo of the original input. However, for over 50 years scientists theorized In quantum mechanics, there is another type of reflection known as time reflection.

The term may conjure up images of a nuclear-powered DeLorean or a specific police booth (it’s larger on the inside), but that’s not quite what scientists mean by the term. Instead, time reflections occur when the entire medium in which the electromagnetic wave is traveling suddenly changes direction. This causes part of that wave to change and it changes to a different wave in frequency.

Because these time reflections require a uniform change across the electromagnetic field, the scientists assumed that it would take a lot of energy to actually observe the time reflections in motion. But scientists at the CUNY Graduate Research Center (CUNY ASRC) in New York have successfully observed the reflection of time by sending broadband signals onto a metal strip filled with electronic switches connected to reservoir capacitors.

This allowed the researchers to trigger the switches at will by doubling the impedance across the strip. This sudden change caused the signals to carry a successful reverse copy.

“It’s very difficult to change the properties of the medium fast enough, uniformly, and with enough contrast to reflect electromagnetic signals, because they oscillate so fast,” said co-author and CUNY ASRC graduate student Gengu Xu. in a press release. “Our idea was to avoid changing the properties of the base material and instead create a metamaterial where additional elements could be significantly added or removed with quick transitions.”

This temporal mapping also behaves differently from spatial mapping. This time, if you look in the mirror, researchers look at the echo, as the echo first reflects the last part of the signal. timeYou see your back instead of your face. Translating this experience acoustically would be like listening to a tape upside down, fast and at high pitch.

If the frequency shift were perceptible to our eyes, it would appear as if the colors of the light had suddenly changed to another color, like a red to green. This strange, counterintuitive nature of time mapping is part of what makes this concept difficult to learn.