Slow Glass is a concept from science-fiction author Bob Shaw from Northern Ireland, introduced in his 1966 short story "Light Of Other Days". Not to be confused with the 2000 science-fiction novel called "The Light Of Other Days", by Stephen Baxter and Arthur C Clarke.
Slow Glass is related to the scientific concept of Slow Light (the fact that light can be slowed down in different mediums):
https://en.wikipedia.org/wiki/Slow_light
In Shaw's story, it is possible to view the past through a special form of glass called Slow Glass.
In Baxter and Clarke's story (which is also excellent), "wormhole cameras" allow anyone to view any moment, anywhere, in history.
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Artwork: Hour Glass by Catharina77, DeviantArt
