

The researchers also demonstrated that the duration of the time-reflected signals was stretched in time due to broadband frequency conversion. As a result, if the light signals were visible to our eyes, all their colours would be abruptly transformed, such that red would become green, orange would turn to blue, and yellow would appear violet
This sounds like wave propagation through a given medium, that changes state uniformly, having an instant ‘reflection’ where the wave doesn’t bounce off of anything (so not hitting a wall… it just reverses in ‘time’) and then drops two ‘octaves’ due to energy loss.
BRITAN