Scientists have been stunned by seeing “time reflections” in electromagnetic waves – an astonishing phenomenon that was previously only hypothesised to exist.
The effect has been likened to looking in a mirror and seeing the reflection of your own back, or hearing an echo but with the sound reversed as when a tape is played backwards.
Scientists have long hypothesised that such an effect exists. But it was difficult for it to be observed because it requires changing the properties of a material quickly and substantially enough for them to happen.
Now, using a special kind of material, scientists say they have observed it happening. By sending signals through a strip of metal, and quickly triggering a change in the physical properties, researchers saw those signals reverse in time.
“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,” said Andrea Alù, Distinguished Professor of Physics at The City University of New York Graduate Center and an author on the new paper, in a statement. “Using a sophisticated metamaterial design, we were able to realize the conditions to change the material’s properties in time both abruptly and with a large contrast.”
A paper describing the findings, ‘Observation of temporal reflection and broadband frequency translation at photonic time interfaces’, is published in Nature Physics.