The Doctor's TARDIS is a technologically advanced time machine from the planet Gallifrey. While it isn't in the best shape after several centuries of space and time travel, it still has some impressive features that help with the Doctor's adventures. One of the most notable features is the TARDIS translation circuit. Introduced in the 1976 Doctor Who episode "The Masque of Mandragora," the TARDIS translation circuit has been used to translate different languages from alien planets and dead languages from planet Earth, but it does have some limits.

A fan theory on Reddit suggests that this translation circuit may not be able to translate complex Gallifreyan teachings to humans, as humanity is canonically a less advanced race than the Time Lords. This is exemplified in Season 2, Episode 3 "School Reunion," in the scene where David Tennant's Doctor teaches a physics class. The students heard the Doctor say, "Physics. Physics, physics, physics," but the theorist posits that he was actually explaining some incredibly advanced Gallifreyan concepts. Unable to put them into terms that humans could understand, the TARDIS simply translated this as "physics."

RELATED: Doctor Who: How The Thirteenth Doctor Saved Christmas from Krampus

The theory implies that the Doctor started his physics lesson with an incomprehensible opening line of scientific teachings, which is very in character for the Time Lord. There have been many instances in Doctor Who where the Doctor has shared incredibly complex scientific theories with his companions, who often have no idea what's going on and also have a limited understanding of advanced science. The Doctor is known for being the smartest person in the room, as well as a leader who often bounces complicated theories and solutions to dangerous situations off of their companions, who usually play the role of the everyman or a proxy for the audience.

The TARDIS translate function has been used in many Doctor Who episodes since its introduction in 1976. One such episode is Season 4, Episode 2, "The Fires of Pompeii," where the Doctor tells Donna that she can understand all the merchants speaking Latin because the TARDIS is translating their speech into English for her. Similarly, in Season 7, Episode 8, "Cold War," Clara also discovers that she is speaking perfect Russian thanks to the TARDIS' translation circuit, although more modern words and phrases like "karaoke" and "hen night" cannot be translated. There are also several other Doctor Who episodes where the Doctor and their companions travel to other countries and planets where the residents most likely don't speak English, but the companions hear them speaking in English because of the translation circuit.

RELATED: Why 'A Christmas Carol' Is the Best Doctor Who Christmas Special

David Tennant as the Tenth Doctor in Doctor Who

Interestingly, the Doctor is a part of the TARDIS' translation circuit, and it does not work without the Doctor's presence. This is shown in "The Christmas Invasion," when Rose cannot understand the Sycorax because the Doctor is incapacitated after his regeneration. The translation circuit also does not always work for TARDIS passengers at different points in time -- this happens in the audio drama 1963: Fanfare for the Common Men, when the Doctor's companion, Nyssa, cannot understand German signs because she's stuck in 1957 while the Doctor and the TARDIS are in 1963.

While the validity of this fan theory is questionable, as there is no canonical proof of the TARDIS translation circuit failing to translate Gallifreyan speech or teachings to humans, it does line up well with the Doctor's character and the nature of Doctor Who. While Season 6, Episode 7, "A Good Man Goes to War" showed that the TARDIS translation circuit doesn't translate Gallifreyan script, this does not support the theory in question, as it does not account for spoken Gallifreyan or Gallifreyan teachings. However, this fan theory captures the character of the Doctor perfectly and provides some interesting questions about the extent of the TARDIS' abilities.

KEEP READING: The 13th Doctor Hints at Her Sexuality in Doctor Who: Flux Finale