Although Doctor Who primarily concerns the adventures of the Doctor zipping through time and space in his quirky TARDIS — a box that allows travel through Time And Relative Dimension In Space — there are, in fact other forms of time travel within the canon of the Whoniverse. And oddly, some of the most paradoxical timey-wimey adventures in all of Doctor Who occur when the characters are not using the TARDIS. In the days of the 10th, 11th, and 12th Doctor, the most common alternative to the TARDIS was a wrist device known as a vortex manipulator, commonly described as “cheap and nasty time travel” and used by everyone from Captain Jack Harkness to Missy.
But hiding in plain sight is another Who time travel method, one which makes a sneaky comeback in the penultimate new Season 1 episode “The Legend of Ruby Sunday.” In order to see into the past, back to 2004, the Doctor asks UNIT to use a “time window,” which ends up causing all sorts of problems. But what is a time window? Here’s the cheap and nasty history of this alt-time travel tech.
Spoilers ahead for Doctor Who’s “The Legend of Ruby Sunday.”
Time windows, explained
In “The Legend of Ruby Sunday,” the Doctor is amused by the huge amounts of power that UNIT has to expend to open a time window into the past. This is because by his very nature, the Doctor views time travel, and the ability to perceive time non-linearly as second nature. But, in this case, the time window has a specific purpose. Because the Doctor repaired an alternate universe on Christmas Eve 2004, he can’t cross his own time stream and take the TARDIS there a second time. So he needs another form of time travel to view this moment in the past.
Previously, time windows have appeared in contemporary episodes like “The Girl in the Fireplace” (2006), “The Doctor, the Widow and the Wardrobe” (2011), and “The Day of the Doctor” (2013). In all those cases, physical travel between points in time was possible, but only temporarily. Here, in ‘The Legend of Ruby Sunday,” the time window is treated more like a literal window in which participants can only observe rather than physically travel to this location. (A time window also appeared in an episode of the spinoff show The Sarah Jane Adventures, “Lost in Time.” The Trickster, a villain first introduced in that series is name-checked in this newest episode.)
In all cases, the rules of time windows are limited, and less stable than something like the TARDIS. And, because UNIT seems to have cobbled this together themselves, this time window is perhaps the most rudimentary one we’ve seen in all of Who so far.
UNIT’s time travel ban
When the Doctor asks Kate Stewart if UNIT has a time window on the premises, Kate balks noting that: “You told us in the 1970s that UNIT was expressly forbidden to experiment with time technology.” This refers to the era in which the 2nd, 3rd, and 4th Doctors worked closely with UNIT, beginning with the events of the 1968 serial called “The Invasion.” Throughout the majority of the 3rd Doctor’s era, he was stranded on Earth after the Time Lords purposely disabled the TARDIS.
During that exile, one the Doctor’s most famous time travel jaunts was accomplished via a very rudimentary time machine that had properties similar to a time window. In “The Day of the Daleks” (1972), the 3rd Doctor and Jo encounter a version of themselves from the near future in a way that feels much like the time window in “The Legend of Ruby Sunday.” Throughout “The Day of the Daleks,” the Doctor is involved in a complicated paradox involving time-traveling freedom fighters from the future and the Daleks from an alternate timeline. (Writer John Byrne has said that this storyline inspired the X-Men comic book storyline “Days of Future Past.”)
Because the Doctor himself was unable to time travel through much of his time working as UNIT’s scientific advisor, it makes a certain amount of sense that he would encourage UNIT not to try and duplicate his own technology. In the origin episode of Sutekh, “The Pyramids of Mars,” the 4th Doctor and Sarah Jane learn that the site of the original UNIT HQ exists because of a time paradox they caused, which even further explains the Doctor’s wariness about UNIT creating their own form of time travel. If they did, members of UNIT might accidentally erase their own existence.
That said, in the alternate universe of the Season 4 episode “Turn Left,” created when the Doctor perished in 2006, UNIT did create a time machine in order to send Donna to back in time to prevent herself from causing that universe to exist in the first place. So, when UNIT does create its own time travel, timelines do tend to collapse.
