Doctor Who Reveals Why The 60th Anniversary's "Mavity" Change REALLY Happened

Warning: Spoilers ahead for Doctor Who season 14, episode 1, "Space Babies."

Summary Davies' "Mavity" gag alters the Doctor Who timeline but is rectified by Gatwa's Fifteenth Doctor.

Mavity as a running gag has deep implications for Doctor Who canon.

The Butterfly Compensation Switch largely prevents further timeline alterations in Doctor Who Season 14.

Russell T Davies' "Mavity" gag during the Doctor Who 60th-anniversary specials is as funny as it is impactful, changing the timeline on a seemingly permanent basis, but the returning showrunner has already installed a way to prevent similar occurrences from happening again. The fix comes very early in Doctor Who season 14, episode 1, "Space Babies," with Ncuti Gatwa rectifying a major timeline-changing event almost immediately after it occurs. While it's a good way of stopping the show's time travel logic from getting even more confusing, it also explains how David Tennant's Fourteenth Doctor allowed the Mavity mistake to happen.

Isaac Newton misnaming his discovery as "Mavity" after mishearing Donna and the Fourteenth Doctor seemed at first like just a comical sequence for the cold open of "Wild Blue Yonder." However, the Fourteenth and Fifteenth Doctors have continued to get gravity's true title wrong ever since. As a running gag, it's funny, but when the larger implications are considered, it's a game-changer for Doctor Who canon. Permanent changes to the timeline don't come all that often in Doctor Who, and Davies has taken steps to make sure Mavity belongs to a rare group.

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Ruby Stepping On The Butterfly Is Just Like Doctor Who's "Mavity" Joke

Fifteen manages to correct Ruby's mistake

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When Millie Gibson's Ruby Sunday voices her concerns in "Space Babies" about accidentally changing the timeline by stepping on a butterfly in the past, the Doctor is confident that it's not something she needs to worry about. However, the fact that Ruby does just that, changing the evolutionary history of her entire species, is proof that the timeline isn't untouchable. This is very reflective of David Tennant's Fourteenth Doctor and Donna inadvertently causing Isaac Newton to misname gravity.

The biggest difference is that the Fourteenth Doctor is blissfully unaware that anything has changed, as he and Donna exit the scene before Isaac Newton declares, "Mavity!"

Granted, Ruby's mistake leads to much more severe consequences than that of Fourteen and Donna, but the underlying concept is pretty much the same. The biggest difference is that the Fourteenth Doctor is blissfully unaware that anything has changed, as he and Donna exit the scene before Isaac Newton declares, "Mavity!" Fifteen witnesses Ruby change into a new species before his eyes after she crushes the butterfly, so he knows he has to take action to reverse the alterations to the timeline.

Mavity Happened Because The Fourteenth Doctor Wasn't Used To His New TARDIS Controls

The "Butterfly Compensation Switch" wasn't turned on

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The ease with which Fifteen rectifies the situation makes it confusing as to how Fourteen didn't fix his mistake with Isaac Newton. However, not only did Fourteen not witness the fallout of his poorly-timed joke, but he also wasn't yet accustomed to his newly-redecorated TARDIS. Gatwa's Doctor refers to a conveniently-named "Butterfly Compensation Switch." Presumably, the switch in question does far more than rectify the specific scenario involving Ruby and the unfortunate insect. So, Fifteen's admission that he'd neglected to flip the switch yet after the TARDIS' transformation would explain why the Mavity change went unfixed.

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It's also possible that the switch was knocked off when Donna spilled coffee on the TARDIS console in "The Star Beast." This would account for her encounter with Isaac Newton changing the course of history, albeit in a fairly minor way. Having said that, it's still entirely plausible that the switch needs to be manually activated each time the TARDIS changes, and the Fourteenth Doctor either forgot to do so or hadn't gotten around to it yet. Either way, the switch being in the off position in "Space Babies" could have made human history unrecognizable after Ruby killed the butterfly.

Mavity Is Still A Thing In Doctor Who's "Space Babies" Episode

Russell T Davies is sticking by his change

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The Mavity gag didn't finish by the end of the Doctor Who 60th-anniversary specials, nor did it go away in the 2023 Christmas special, "The Church on Ruby Road." As a result, the word "Mavity" still shows up in Doctor Who season 14, episode 1, "Space Babies" - even if it isn't spoken out loud. On a screen on the space station, there's a Mavity reading. It's a subtle addition to the shot, but one that reinforces the fact that Russell T Davies intends to continue the trend, and possibly suggests a bigger payoff relating to Mavity down the line.

Now that the Butterfly Compensation Switch has been activated and Ruby's error has been corrected, the continued presence of Mavity is arguably a worrying sign.

Now that the Butterfly Compensation Switch has been activated and Ruby's error has been corrected, the continued presence of Mavity is arguably a worrying sign. The change to the timeline appears to now be entrenched, and it's unclear if the Doctor will ever notice that something isn't right. If Mavity is the only causality of the switch not being turned on, the Doctor may have gotten lucky, as it could have been much worse.

Don't Expect Any More Changes Like "Mavity" In Doctor Who Season 14

The Butterfly Compensation Switch should prevent any further unwanted alterations

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The Mavity change risked the floodgates being opened in terms of alterations up and down the Doctor Who timeline. Thankfully, Russell T Davies has patched that hole with the introduction of the Butterly Compensation Switch in "Space Babies." As well as being a clever addition to the show's canon, the switch is also a helpful writing device that once again allows the Doctor to travel into the past without worrying about small accidents that could result in big changes to all corners of Doctor Who lore.

It's also an inspired way to wrap up any loose ends from the specials ahead of Doctor Who's main Disney era beginning. Gatwa's first full season is being marketed as season 1 on Disney+, likely in part due to an attempt to entice a new audience. While certain accommodations have been made to make the early moments of Doctor Who season 14 more accessible to newcomers, Davies made sure the show's continuity has remained intact. Proving that time can indeed be changed and then fixed is a great way of helping establish the show's premise for the uninitiated.

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The butterfly scene could be interpreted as the Doctor Who writer/showrunner subtly tying up the unusual cause of Newton's mistake, causing ripples through time. Without Ruby's error being fixed by the Fifteenth Doctor figuring out his new TARDIS controls, the show was in danger of suddenly having to walk on eggshells whenever the Doctor travels anywhere in time and space. A big part of the joy of Doctor Who comes from the sheer scope and freedom of the show's universe, and to limit that because of one joke would have been a huge waste.

Episode Disney+ Release Date "Space Babies" & "The Devil's Chord" May 10 "Boom" May 17 "73 Yards" May 24 "Dot & Bubble" May 31 "Rogue" June 7 "The Legend of Ruby Sunday" June 14 "Empire of Death" June 21