Time viewer
[7]: 158–159 A common explanation involves the finite speed of light and astronomical distances; this method appears in the 1935 short story "The Space Lens" by Donald A. Wollheim, among others.
[2]: 100 [8] The earliest known example of a fully fledged time viewer in fiction appears in the 1883 short story "L'historioscope" by Eugène Mouton in the form of an electrical telescope, though it was prefigured by a couple of proto-variations on the concept;[3][8][9] in the 1872 work Recits de l'infini (which later turned into the 1887 novel Lumen) by Camille Flammarion a spirit accomplishes the same effect by travelling faster than light, and the titular device in the 1873 short story "The Automaton Ear" by Florence McLandburgh enables listening to the past.
The most basic premise is of the time viewer as simply a "neat gadget", with a common variation being something going wrong, typically the past being unintentionally altered.
According to Baxter, the wider implications of the existence of time viewers are sometimes explored in hard science fiction by performing what's known as a PEST (Political, Economic, Social, and Technical) analysis.
Science fiction author Damien Broderick says that "using a time viewer is in essence no more absurd than watching a movie made 50 years ago" since the past cannot be affected by it.
[2]: 103 [5]: 127 Revealing the truth about historical events also appears in the 1953 novel Childhood's End by Arthur C. Clarke, where alien invaders show humanity that our religions are false.
[3] Scientists in the 2000 novel The Light of Other Days by Stephen Baxter and Arthur C. Clarke use time viewer technology to study the entire history of life on Earth.
[3][15] The 1926 novel The Vicarion by Gardner Hunting is an early example of time viewers being used for entertainment;[3] in the story, moments from history are shown in movie theaters to great public interest.
Baxter compares the in-story effects on society, where "mass addiction to this vibrant spectacle quickly overtakes the public", to the later real-world advent of the television.
[2]: 104–105 [5]: 127 In the 1972 fix-up novel Other Days, Other Eyes by Bob Shaw, particles of the slow glass that captures images are spread all over to enable mass surveillance.
[3] The 1976 short story "I See You" by Damon Knight posits that the complete loss of privacy resulting from universal access to a time viewer would usher in a utopia free from deceit and embarrassment.
[2]: 99 In the satirical 1948 short story "The Brooklyn Project" by William Tenn, the scientists in charge insist that the past is immutable even as they and their surroundings undergo drastic changes, because from their new perspective those alterations have always been in place.
[2]: 99 Humorous depictions include the 1972 short story "The Greatest Television Show on Earth" by J. G. Ballard, where a TV company hires additional people as soldiers to make the Battle of Waterloo live up to viewers' expectations, and the 1967 novel The Technicolor Time Machine by Harry Harrison, which implies that the Viking settlement of Vinland only happened because Hollywood wanted to make a movie about it.
[3][5]: 128 Another is the instantaneous "Dirac communicator" introduced in the 1954 short story "Beep" by James Blish which due to the lack of a speed-of-light delay can send messages to the past.
