When answering fan questions via an exclusive IMDb interview video, the Fifteenth Doctor and Ruby Sunday actors Ncuti Gatwa and Millie Gibson discussed what happened behind the scenes involving the word, “mavity”.

Unsurprisingly, they had no idea what it meant whilst filming The Church on Ruby Road and Season 1/Series 14, up until the second 60th anniversary special Wild Blue Yonder aired on 9th December 2023.

“Oh!” Ncuti and Millie exclaimed upon realising the context, after showrunner Russell T Davies and executive producer Phil Collinson kept them in the dark. Frankly, I’m not surprised at all by their hilarious reactions, even with us viewers knowing nothing about the retcon prior to broadcast.

So far, there have been a total of two* mavity references in the Fifteenth Doctor era. The first in The Church on Ruby Road, where the Doctor explains to Ruby about the “mass and density and mavity” existing in the intelligent gloves. The second in Space Babies with a mavity reading, displayed visually (in English and Cantonese) instead of having spoken dialogue.

* Although Dot and Bubble doesn’t really count, the Doctor says “antigrav” to Lindy Pepper-Bean (Callie Cooke), like how he previously said “gravity field” before correcting himself to “mavity field”.

What’s also funny about the mavity gag is that it actually debuted in the Torchwood Big Finish audio story Oodunnit, in which Zachary Cross Flane (Shaun Parkes), from the Series 2 Ood two-parter The Impossible Planet/The Satan Pit, notes a “mavitational anomaly”. Since it was released less than a month before Wild Blue Yonder, and recorded back in October 2022, everybody (including myself) missed the reference until someone later pointed it out on the TARDIS Wiki (which now has its own dedicated page). And furthermore, I was pleasantly surprised when my tweet featuring the sound clip from Oodunnit was quoted in Den of Geek‘s article on the subject.

With the two-part finale The Legend of Ruby Sunday/Empire of Death on the horizon, we hope the mavity gag is brought up once again (and possibly be resolved). I would say that it all links with Susan Twist’s recurring cameos as multiple characters across the RTD2 era, beginning with her debut as Mrs Merridew in Wild Blue Yonder. If it’s the case that Susan Triad, her character in the finale, has been taking on various identities across time and space, she may very well be responsible for messing history with the gag; therefore making her the mavity of the situation. That’s just my theory.

So, to give a word of advice, don’t blame the Fourteenth Doctor (David Tennant) and Donna Noble (Catherine Tate) for joking about appreciating “the gravity of the situation.” Don’t blame Isaac Newton (Nathaniel Curtis) for mishearing it as “mavity.” Blame Mrs Merridew for keeping the roots of gravitas hidden from Mr Newton.

And if you need a recap of mavity, I made a compilation with all the references from 2023.