Summary

• Doctor Who's ongoing "mavity" joke highlights the show's commitment to a rewritten history and a shift in time travel rules.
• The "mavity" gag is a clever way of illustrating the larger lore changes introduced in the 60th anniversary special, including the increased flexibility of the show's timeline.

The fact that Doctor Who is still running with its "mavity" joke is hilarious, but, to paraphrase the great Donna Noble herself, this obscures the true gravity of the situation. Doctor Who's second 60th anniversary special, "Wild Blue Yonder," began with a cold open where the Fourteenth Doctor and Donna Noble crashed into Isaac Newton's garden just as the scientist was about to crack gravity. Since Donna couldn't resist uttering the g-word in his presence, Newton ultimately picked the name "mavity" instead. After the episode returned to present-day, Donna then spoke of "mavity" as if the Earth's downward force had always been known by that name.

Doctor Who seamlessly continues that gag into 2023 Christmas special "The Church on Ruby Road." Ncuti Gatwa's Fifteenth Doctor reveals a fancy new toy - mass-defying gloves - and, while explaining their purpose to Ruby Sunday, points out, "all the mass and density and mavity exists in the glove." The Doctor's casual use of "mavity" confirms he is now accustomed to the word, despite knowing it should be "gravity," while Ruby's lack of reaction proves she, like Donna, has only ever known "mavity." Doctor Who season 14 is sticking to this quirky historical rewrite, and while Russell T Davies' dedication to the joke makes it even funnier, there is a serious purpose behind it.

"Mavity" Changes How Time Travel Works In Doctor Who

The rules of time travel within fiction are famously nonsensical, but broadly boil down to three different systems. One is the "whatever happened, happened" format, whereby history is set in stone and any attempt to change it via time travel will only result in bringing about whatever future the time-traveler came from. The second system is where time can be rewritten, à la Marty McFly accidentally erasing himself from existence in Back To The Future. The third basic system of fictional time travel is branch timelines, where changing the past results in two different histories existing separately. "Mavity" shows Doctor Who is now subscribed firmly to the second system.

Doctor Who has previously flitted between the first and second versions of time travel at its convenience. The Doctor regularly warns companions against influencing major events during their adventures, which tacitly suggests time can be changed. Indeed, the entire premise of "Genesis of the Daleks" proves time can be rewritten. On other occasions, Doctor Who has leaned more toward the "what happened, happened" model. "The Shakespeare Code," for example, showed Shakespeare getting his iconic line "all the world's a stage" from the Doctor.

The implication was that an existing part of Earth's history - a Shakespeare quote in this case - was caused by the Doctor all along. The Doctor went to the past, tried not to meddle, but inadvertently caused the future he knew. This is very different from Doctor Who's gravity situation. Here, the Fourteenth Doctor changes the future he knows - the word "gravity" gets replaced by "mavity." If "The Shakespeare Code" followed the mavity example, the Doctor would never have heard of "all the world's a stage" before saying it himself in front of Shakespeare. Upon returning to Earth's future, he then would have found the quote had retroactively become famous throughout history.

Doctor Who hitting audiences repeatedly around the head with "mavity" serves as a constant reminder that the rules have shifted, and the Doctor's actions will have visible consequences moving forward. "The Church on Ruby Road" doubles down on this when the Goblins remove Ruby from history in the episode's final act. Just like the switch from gravity to mavity, reality changes in an instant. One moment Ruby is there, the next she isn't, and a ripple effect rewrites the past to make her adoptive mother cynical, miserable, and desperately lonely. Mavity sets a more definitive precedent for time travel in Doctor Who - one where time is far more malleable.

Doctor Who's "Mavity" Joke Shows How The 60th Anniversary's Lore Changes Work

Amusing it may be, but Doctor Who's mavity gag is actually a clever way of encapsulating how the Doctor's timeline works following the sweeping lore changes made by the final 60th anniversary special, "The Giggle." The episode included a key scene in which the Toymaker boasted "I made a jigsaw out of your history" before going on to suggest he was responsible for the Timeless Child. Speaking on the BBC's official episode commentary, RTD elaborated, describing this line as a "loosening of the rules" that can be used to for prior inconsistencies such as the Timeless Child and the Eighth Doctor being half-human.

RTD also offered more insight into the Doctor's bi-generation, revealing, "The whole timeline bi-generated then... they [the past Doctors] all did." This retroactively means all previous Doctors went on to have further adventures after supposedly regenerating. Both the bi-generation and the Toymaker's jigsaw-making had massive consequences for the entire timeline of Doctor Who, which is a huge paradox for viewers to wrap their heads around.

The mavity joke is a simplified demonstration of how these bigger changes work. Just as one word from Donna retroactively altered every past and future use of "gravity" to "mavity," one swish of the Toymaker's hand rewrote the Doctor's backstory, and one bi-generation added countless chapters to the Doctor's lifetime. All three of these things may have been deviations from what the viewer - and the Doctor, since Doctor Who is told from the Time Lord's own perspective - previously knew, but all three changes are now deeply intertwined into the fabric of Doctor Who, and not going anywhere.

Doctor Who returns in spring 2024.