Warning: This article includes MAJOR SPOILERS for Doctor Who season 15, episode 1, "The Robot Revolution."

ending of Doctor Who season 14, so the Doctor is taking on a new companion named Belinda Chandra.

Classic Who. Unfortunately, by going this route, they created a plot hole in an episode that came out 15 years ago.

Belinda Sets Off The Blinovitch Limitation Effect In The Doctor Who Season 15 Premiere

The Blinovitch Limitation Effect Goes All The Way Back To The Third Doctor

Early in the premiere, Belinda and the Doctor discuss the Blinovitch Limitation Effect, a rule first introduced by the Third Doctor, without stating its name. Belinda says, “I’ve seen films. When you get two versions of the same thing crossing over in time, don’t they explode?” The Doctor responds, “Yes, yes. If you get the same atoms in the same space twice, the Laws of Time say no.” The principle of time specifically says that when two things made of the same atoms come into close proximity or directly touch, they will “short out the time differential” or “go zap.”

Later in the episode, she and the Doctor intentionally decide to set it off, using the star certificate that the robots had obtained and the one Belinda owned, to prevent Alan from continuing to hurt the people on the planet MissBelindaChandra 1 that orbits the star MissBelindaChandra. When the certificates touched, the Blinovitch Limitation Effect went into effect, causing a boom. Luckily, the Doctor was able to save Belinda because Time Lords can sometimes dampen the effect. Though, as shown in “The Robot Revolution,” the Blinovitch Limitation Effect can still cause pain for them.

The Same Thing Happened In "A Christmas Carol" Without Any Consequences

The Plot Hole In "A Christmas Carol" Is More Noticable After "The Robot Revolution"

Although it was nice to see the show enacting the Blinovitch Limitation Effect again, it unfortunately creates a major plot hole for the Matt Smith Doctor Who Christmas special “A Christmas Carol,” which came out 15 years ago. Episodes where the Doctor comes into with other versions of themselves can possibly be written off by the fact that they’re all Time Lords. The same goes for Missy and the Saxon Master coming into in “The Doctor Falls.” However, in “A Christmas Carol,” the Doctor tries to teach Kazran Sardick a lesson by showing him his past, present, and future.

At the end of the episode, Young Kazran and Old Kazran come into direct with each other, rather than just existing in close proximity. Old Kazran nearly hits Young Kazran, like his father did to him, but he stops himself. He then embraces his younger self while crying. Oddly, all of this happens without any boom. They've never explained why this episode had zero explosions or time paradoxes.

While this was already on the minds of some Whovians, like myself, the Doctor Who season 15 premiere brings the Blinovitch Limitation Effect to the forefront of conversations again. Unless he’s secretly a Time Lord, which seems highly unlikely, Kazran shouldn’t have been able to hug himself without significant consequences, like an explosion. It can’t really get overlooked anymore that “A Christmas Carol” has a a glaring plot hole.

The Inconsistency Is A Reminder That Doctor Who Plays Fast And Loose With The Rules Of Time Travel

The Rules Of Time Travel Are Pretty Flexible In Doctor Who

The fact that direct of the same object or person causes a boom in “The Robot Revolution” but not “A Christmas Carol” is just the most recent reminder that Doctor Who doesn’t apply the rules of time travel equally, and they frequently rewrite the rules altogether. The First Doctor said in “The Aztecs” that you can’t rewrite history, yet the Doctor and their companions constantly rewrite the past. One of the most hilarious examples is “mavity,” but it also happens in episodes like “The Pyramids of Mars.” Sometimes, when events change, time travelers keep their memories, while at other times, they lose them.

It’s best not to focus on the rules of time travel in Doctor Who because they’re maddeningly inconsistent. That's bound to happen on a show that has lasted 60 years.

The Third Doctor introduced the Blinovitch Limitation Effect in "Day of the Daleks," and the Fifth Doctor defined it in “Mawdryn Undead.” Meanwhile, the show picks and chooses which situations cause it. Time Lords can sometimes dampen the effects of time paradoxes and the Blinovitch Limitation Effect, but then those things are used as an excuse as to why the Doctor doesn’t go back in time to change things. Doctor Who introduced fixed points to help the issue, but there aren't any rules that viewers can follow to figure out what's a fixed point and what's malleable.

If RTD’s comments about bigeneration in Doctor Who are true, that has the potential to write the rules of time travel because it might have created multiverse. Numerous questions come up about how time travel works across different timelines. Though, to be fair, bigeneration hasn’t actually been fully explained on the actual show – only through interviews, so many fans write it off as a headcanon. Most recently, the show expanded the rules of time travel by introducing the Time Hotel, which connects all times at once.

Ultimately, it’s best not to focus on the rules of time travel in Doctor Who because they’re maddeningly inconsistent. That's bound to happen on a show that has lasted 60 years. Instead, Whovians can find solace at the confusion by focusing on this quotation from the Tenth Doctor: “People assume that time is a strict progression of cause to effect, but actually, from a nonlinear, non-subjective viewpoint, it's more like a big ball of wibbly-wobbly, timey-wimey... stuff.”