“It is very difficult to change the properties of a medium quick enough, uniformly, and with enough contrast to time reflect electromagnetic signals because they oscillate very fast,” Gengyu Xu, a co-author and post-doc student at CUNY ASRC. “Our idea was to avoid changing the properties of the host material, and instead create a metamaterial in which additional elements can be abruptly added or subtracted through fast switches.”
This time reflection also behaves differently than spatial reflections. Because this time echo reflects the last part of the signal first, the researchers say that if you looked in a time mirror, you would see your back instead of your face. To translate the experience acoustically, it would be like listening to a tape on rewind, probably fast and high-pitched.
The shift in frequency, if perceived by our eyes/ears, would seem like colours of light suddenly changing to another colour, such as red to green. This strange counter-intuitive nature of time reflection is part of what has made studying the concept so difficult so far.
Corresponding author Andrea Alù, physics professor and director of CUNY ASRC’s Photonics Initiative, said, “This has been really exciting to see, because of how long ago this counterintuitive phenomenon was predicted, and how different time-reflected waves behave compared to space-reflected ones”.
A big question: Why have scientists worked creating theoretical time reflections in a laboratory? Well, more minute control of electromagnetic waves can significantly improve wireless communications and even lead to advancements in low energy, wave-based computers - a significant step forward in understanding how time lays down its temporal tracks.
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