The "Gravity Falls Main Title Theme," composed by Brad Breeck, is the opening theme song played over the title sequence to Gravity Falls. The official theme song is available on iTunes for $0.99. Beginning with "Northwest Mansion Mystery," a shortened version of the theme is used in episodes that are longer than usual. The "Weirdmageddon" episodes use a corrupted version of the song.
A shortened version of the main title —15 seconds long instead of the regular 41— is used in episodes that are longer than usual. These are:
- "Northwest Mansion Mystery"
- "Not What He Seems"
- "The Stanchurian Candidate"
- "The Last Mabelcorn"
- "Dipper and Mabel vs. the Future"
The Weirdmageddon story arc episodes use corrupted versions of the theme song, along with apocalyptic opening sequences showing the destruction and weird changes Gravity Falls suffers during the event, like an up-going waterfall or Paul Bunyan's statue coming alive, and many Bill images and references.
"Weirdmageddon Part 1" uses an opening sequence replacing every single main character with Bill and his friends. In this apocalyptic version, Dipper is the only character normally in the opening screen that still appears: he's seen as a human skeleton wearing the blue and white pine hat that appears instead of the normal horned monster skeleton, even if only as a resemblance. Bill Cipher's page is seen with a hole where Bill's picture should be, nodding to the fact that he has finally entered Gravity Falls' world.
"Weirdmageddon Part 2" uses a shortened version of the corrupted theme song and opening sequence.
"Weirdmageddon Part 3" also uses the corrupted song and sequence, but it has the regular images for introducing Dipper, Mabel and Stan.
Gravity Paws version
Unused and alternate theme songs
A demo reel of music for the show was released in 2011 by Dan Cantrell with singers chanting the title of the show. Neil Cicierega also made two more theme songs.  There were two other themes considered for Gravity Falls: one instrumental and the other lyrical. These were relegated in favor of Breeck's work. Breeck had also composed an alternate theme song which would eventually be used in the 2014 San Diego Comic Con trailer for the then-upcoming season.
"You Made Me Realize" misconceptions
The main theme is often mistaken for the song "You Made Me Realize," due to its strong similarities to the real "You Made Me Realize" song Breeck wrote for MTV's Awkward. "Made Me Realize" is commonly mistaken for the extended version of the Gravity Falls theme song. It is also stated on Breeck's website that the two songs are indeed different, and not related to each other.
- Intro: "Gravity Falls Main Title Theme"
- See also: List of allusions
- There is a quick glimpse of a large, hairy figure that appears to be Bigfoot.
- Towards the end of the song, a whisper plays and sounds like "I'm still here." But if it is played backwards, the whisper is revealed to be "Three letters back." This is how one solves the cryptograms at the end of each episode.
- In "Double Dipper," a new message is whispered: "Switch A with Z." It is an explanation to the "ATBASH" cipher.
- Starting in "Bottomless Pit!," the whisper changes to "26 letters," a reference to the "A1Z26" style substitution cryptogram, which uses numbers to stand for letters of the alphabet.
- In Season 2, starting with "Scary-oke," the whisper is now "Key Vigenère," referring to the fact that the cipher at the end is a Vigenère cipher that requires a keyword hidden in each episode.
- In "Not What He Seems," the whisper is changed to "not what he seems."
- It changes back to "Key Vigenère" the episode after that, "A Tale of Two Stans."
- Towards the end of the theme song when the title shows up, a stamp can be seen near it. The number 618 can be seen on it, which is a reoccurring number in the show.
- In the episode "Little Dipper", right before cutting to the theme song when the Pines are discussing what else to watch on T.V., Mabel states that 'the theme song is [her] favorite part'.
- The cryptogram at the end of the song is "Stan is not what he seems."
- The television version of the song features the whisper and a flashing scene of a journal page of Journal 2 with Bill on it. But the animatic version has no whisper and instead of the journal page, a six-fingered hand with the number 3 and astrological symbols all over it appears.
- As the pictures are thrown down, several of the antagonists in the show can be seen, including a gnome, Gideon Gleeful, Blendin Blandin, the Summerween Trickster, the Pterodactyl.
- Additional pictures portray mythical creatures from North American folklore, including the Fiji Mermaid, the jackalopes, and the Bat Boy.
- The bottom half of Alex Hirsch's face is seen in one of the many photos between the jackalopes and the Hand Witch's hand.
- On some international airings of the show, and on SAP, the whisper at the end isn't heard.
- Dipper's bag has a sticker that says Piedmont on it, referencing the birth city of Alex Hirsch.
- Dipper seems to be inspecting some runes or symbols before he is startled by the skeleton. The symbols look similar to the ones in the game "Mystery Shack Mystery."
- The symbols are (from top to bottom) the Norse runes for U, M, O, and A.
- The runic symbol for "O" (as mentioned above) is from Elder Futhark. It is "odal" and means real estate, or non-movable property. It is the last symbol in the futhark.
- In two different scenes, Dipper appears to have much thicker eyebrows.
- At the end of the theme, Bill Cipher's entry page in Journal 2 flashes, even to the point that the lines of the character seem indented into the screen and fade from the outside in after the screen goes black.
- There are some changes between the animatic and the official theme song:
- In the animatic version, Mabel and Dipper arrive on a "Fast Dog" bus. It is changed to "Speedy Beaver" in the final version.
- One of the photos appears to be a robot, but was replaced with the Summerween Trickster.
- The photo of the gnome has a bite out of it on the right side.
- There is a picture of three spaceships and a monster, but they were replaced with the picture of the pterodactyl and a clawed hand. (The picture of three spaceships is flashed on Bill Cipher's body in 'Dreamscaperers'.)
- The totem pole is on the left hand side of the Mystery Shack in the animatic version, while it is on the right hand side on the final version.
- The matrix in the Opening Ending Image represents a scalar, rotation and translation matrix (also known as a transformation matrix), used to perform linear transformations.
- A clip towards the end of the Gravity Falls theme song shows gravity rising and falling (hence Gravity Falls) with Mabel lying on the ground and Dipper reading the journal. This is an allusion to episode 11 of Season 2 "Not What He Seems," and it even references the theme song directly with a rising black 8-ball in both clips, although the Twins are sleeping in the actual episode.
- Beginning with "A Tale of Two Stans," the full title sequence has the picture of a pterodactyl replaced with a picture of Ford Pines holding Journal #1.
- The title card flickers from "GRAVITY FALLS" to "JUDYLWB IDOOV," which, using the show's Caesar cipher, translates to "GRAVITY FALLS." The water tower's inscription also changes to "JUDYLWB IDOOV."
- Instead of Bigfoot appearing for a frame, there is a walking pine tree. This may be due to the fact that the Pines are the ones hiding now, instead of the paranormal phenomena. It may also be just a switch of the places of Bigfoot and the pine trees in the normal version.
- Where it would normally say "Created by Alex Hirsch," in the apocalypse version it says "Created by Bill Cipher."
- When the first apocalyptic version is played backwards, Bill can be heard saying the words "I'M WATCHING YOU NERDS." The second one has him saying only "I'M WATCHING YOU!" sounding much angrier. The final one says "Good bye Gravity Falls," since it's also the final episode of the series.
- The man at the stamp at the end is replaced with his skeleton.
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