Barbara: Do you mean... a sort of... "Time television"?
The Doctor: Yes, that's exactly what this is.
A chronoscope or time viewer is a device that uses images that show past or future events like a television. They can sometimes also cause time travel. They are common in sci-fi, and often take different forms.
Some act like cameras recording past and future events and showing what an object would look like in a different time period. Others are more like TVs and show videos and visions of the past and future. Chronoscopes are often used as plot devices, as they can often reveal various details that are necessary for the plot.
- A lottery commercial shows an old man watching his younger self on a television like device; yelling at him to get a ticket while he instead messes around with a toy sculpture that goes limp when the base is pressed. When he finally does get a ticket, the old man sighs and comments "I scared me", and potters off in his levitating chair.
- A second commercial has an equally old lady watching herself on the same device get a ticket because someone grabbed the last of the candy bars she wanted. She comments to her robot butler she never thanked him properly, to which the butler replies "I'll-send-him-a-chocolate-bar. Ha-ha-ha."
- Pokémon: Lucario and the Mystery of Mew: When activated, the Time Flower shows visions of the history of a place.
- In a Superboy comic story (based on a script from the Superboy live-action TV series that wasn't, apparently) Superboy flies out into space in order to make a home movie to show his friend that the friend's father was a hero during the war. Superboy goes faster than light so he can film the light coming from Earth, which shows what happened in the past.
- Supergirl uses her cousin's Chronoscope in Action Comics issue #309 to see her father's past and discover what happened to her parents after she left their hometown.
Supergirl: This chronoscope can overtake light rays which left Krypton years ago! By watching the screen we can view the past!
- In Krypton No More, Supergirl uses one to show her cousin Superman visions of their fathers' lives before both cousins were born.
- Krona uses one to see the beginning of the universe (unknowingly altering it in the process) in the Green Lantern comics.
- One such device kickstarts the plot of an Italian Disney Ducks saga, the Paperolimpiadi written in occasion of the 1988 Olympics. Scrooge comes in possession of a camera that can shows the near future (a few days). He realizes the camera's potential for making money, but of course so do plenty of other parties that try to take possession of it. The story's climax has Scrooge offer worldwide coverage of the Olympics days before they happen, but a minor character destroys the camera, realizing its potential for abuse.
- In The Supergirl Saga, Pocket Universe Lex Luthor discovers this device in Superboy's secret lab, which he uses to try viewing the future in search of Superboy. However, in his search, he ends up encountering the Phantom Zone criminals who communicate to him through the device.
- The scroll in Tim Burton's Alice in Wonderland (2010) that showed the history of Underland and then prophesied Alice's return and her slaying the Jabberwocky.
- In the Denzel Washington movie Déjà Vu, it's claimed that the "Snow White" technology is just an incredible complicated surveillance system. Turns out that its actually a chronoscope. And when pushed, it even works as a limited time machine.
- In The Invisible Ray, Janos Rukh has invented a telescope that can photograph light rays that will show the Earth's past. He uses it to watch a meteorite fall on Africa, thus starting the plot.
- In Paycheck, the mysterious device employs the curvature of the universe and special lenses to look a short distance into the future, allowing the protagonist to build his escape plan before the beginning of the main action.
- Older Than Television: The Martians in Kurd Laßwitz' Auf zwei Planeten ("On Two Planets", 1897) have a device called the Retrospektiv which allows them to determine what actually caused an armed incident between a British warship and a Martian vessel. It sends out gravitation rays to retrieve light rays sent off into space from the event in question.
- Isaac Asimov's "The Dead Past": This story has a Chronoscope that was developed fifty years ago. The world government has been suppressing use of the device because "the past" can be as recent as one-hundredth of a second ago. Unfortunately, our protagonists invented a cheap and simple way to duplicate the technology, and shared it with others.
- Arthur C. Clarke's The Light Of Other Days: The chronoscope, a machine to create and look through wormholes in this setting, immediately becomes public and the novel explores how society would change as a result of the complete lack of privacy and ability to know the real events that modern myths and religions are based on.
- The first half of Pastwatch: The Redemption of Christopher Columbus is about two such devices. The first one was of limited use and wasn't precise enough to show people (they were seen as fast-moving shadows), but it did allow the researchers to see architecture and the like. Later, a more focused device was created, allowing very detailed images and sound to be shown. Fashions of the past became all the rage throughout the recovering world. Researchers had to learn ancient languages in order to understand what the people on the screen were saying. One case even had a Poke in the Third Eye moment. When viewing the life of a long-dead tribal woman, the researcher is startled to hear a description of a dream she had about people from afar watching her. The researcher shows it to several colleagues, "rewinding" the event twice before continuing. The tribal woman continues that they watched her three times and even gives the correct number of researchers. The researchers are a little freaked out. While the government has told everyone that the machines can't see anything as recent as 100 years ago, in reality it can see as recently as 15 minutes ago.
- The Time Machine stories by Donald and Keith Monroe. The eponymous time machine had a viewing device that allows its users to see scenes of the future and past before traveling to them.
- On the Discworld, there are the Omni-scopes which have the power to do this, although true to form the wizards spend a great deal of time and effort trying to eliminate that capacity, treating it as a bug instead of a feature. It seems all they wanted was an expensive version of a webcam.
- Also from The Science of Discworld books, Hex is able to treat our entire universe as one of these. Fast fowarding, or rewinding to see specific spots in human history (our universe canonically exists in a snowglobe on a shelf in the Unseen University, a wobbly shelf).
- Such a device is invented in Noon: 22nd Century, but it can only look into the past. The pictures it shows... aren't pretty.
- In the science fiction novella E for Effort, a man invents a time viewer which can see any past occurrence. It doesn't have audio, so they employ lipreaders to find out exactly what people are saying. Initially they use it to make films about the past.
- The Fellowship of the Ring. The Mirror of Galadriel can show visions of the past and the future. Sam sees events that will occur in The Two Towers during his and Frodo's entry into Mordor, as well as events in the Shire after Saruman takes over. Frodo sees the fall of Númenor and the founding of Gondor, which occurred in the distant past.
- Robert A. Heinlein's short story "By His Bootstraps". The Time Gate can be used to look backward and forward in time as well as to travel to the time shown.
- The Pensieve from the Harry Potter novels, which records and plays back memories, is a version of this. (Powerful wizards like Voldemort can falsify memories, but other powerful wizards like Dumbledore can usually tell.)
- Mirrors that work like this are mentioned in Septimus Heap.
- In L. Ron Hubbard's Battlefield Earth, the heroes want to find out what happened to a planet they bombed a year earlier, and so teleport a probe a light year away from the target to effectively look into the past with a ridiculously powerful telescope. They're also somehow able to manipulate the images and zoom in on particular cities after the probe has returned and they're watching the recording.
- In Mission Earth, also by Hubbard, the Voltarian Confederation uses "time-sights" to peer into the future in order to avoid oncoming obstacles when aboard spaceships using time-based "Will-be Was" engines (don't even ask). A character later has the bright idea to make millions on the stock market by looking at tomorrow's figures and investing accordingly.
- Phillip K. Dick's short story, Paycheck, employs one of these as a centerpiece of the conflict.
- Doctor Who:
- "The Chase" (with the first Doctor William Hartnell, and only the third Dalek story ever) features a Time-Space Visualiser which can view any event in history.
- "The Girl Who Waited": The Two Streams medical facility has a time glass that can be used by people in the Green Anchor section watching their loved ones in the Red Waterfall section. The Doctor steals it and makes some adjustments so he and Rory can find Amy, who's stuck in the Red Waterfall section.
- The Atavachron from Star Trek: The Original Series.
- In Star Trek: Enterprise, the time traveller Daniels uses a device like this, while he is congratulating Captain Archer for successfully fixing the time stream.
- The Twilight Zone episode "A Most Unusual Camera" has a camera that can see into the future.
- The Time Tunnel. In addition to sending items and living beings through time, the scientists controlling the eponymous device could also use it as a time viewer to see the past and the future.
- GURPS Ultra-tech describes the "timescanner". It has very limited abilities: it can only display things in a two-yard radius, it needs days to focus on the specified moment in time, and it is only available in soft sci-fi settings anyway. And until a portable version is invented, the timescanner machinery occupies an entire room.
- In The Golden Apple, Mother Hare gives Ulysses and Penelope a glimpse of a verdant valley turned into future wasteland, and presents them with a kaleidoscopic vision, projected in the form of woodcuts and lithographs, of the spectacular scientific achievements forthcoming in the twentieth century.
- The clouds on Skaia in Homestuck are natural versions of this.
- It's heavily implied that a device like this will show up in Girl Genius at some point... though so far we've only seen it from the "other side", as it were. At several points in the comic, strange "windows" suddenly appear hovering in mid-air, with doubles of some of the comic's characters standing on the other side, seemingly discussing what they're seeing as if they were watching events happening in their past.
- In Kakos Industries Corin Deeth III's grandfather Corin Deeth I uses a Predict-O-Vision device to see glimpses of what his successor is up to, being Crazy-Prepared for the day he'd be succeeded as CEO of the company. He's increasingly been sending letters from around the mid 1960s to offer advice, or sometimes just to send an immature joke. Most notably, he's unable to accurately see what Belladonica is and urges Corin to give up on trying to open the contraption.
- One of the villains in The Impossibles is shown using this to observe 20th-century events from the 40th century.
- The various time-windows in Clockwork's lair in Danny Phantom.
- In Ben 10, one of Ben's alien forms, Clockwork, can do this on a massive scale.
- The chrono-arch in The Adventures of Jimmy Neutron is this.
- A Pinky and the Brain episode sees Brain invent one of these. He sees an image of himself as a very old mouse still trying and failing to take over the world and has a bit of a breakdown, until he realizes that what he's seeing is only one possible future rather than a guarantee.
- Wormholes in theory could be used as this, you could move one exit of a wormhole near to a strong gravitational field, like a black hole, the gravitational effect will cause time to go slower in said wormhole exit than in the other; then when moving the wormhole's exit away from the gravitational field it will retain the "time delay" and effectively become a window/portal to the past, the only caveat being that it cannot show anything before the wormhole's creation.