Despite the fact that the speed of light is an absolute upper limit, faster-than-light space travel is deeply embedded in science fiction. Einstein showed that any object with mass cannot reach, let alone exceed, the speed of light. But science fiction tends to overlook this very inconvenient truth simply because the universe is so big. To reach Alpha Centauri, the nearest star after our own Sun, would take more than four years for a spaceship moving at the speed of light, and a jaunt across the full diameter of our galaxy would take 100,000 years. Knowing this, script writers imagine solutions like Star Trek’s “warp drive” that allow the Enterprise to travel around the galaxy at multiples of light speed, or “worm holes” that provide cosmic short cuts.
Bob Shaw wrote a story in the 60s called “Light of Other Days” which dealt with glass that slowed down the passage of light. Thus, light falling on the glass could take years to make it through. When looking at the glass, then, the scenes one saw could be from years past.
The value of a particular piece of slow glass was dependent on how many years from the past it could ‘hold.’ It was a particularly poignant story and one I remember from the first time I saw it.
I would not expect this correct work to produce something quite so interesting but you never know.