During his studies on the anomalies of Gravity Falls, Ford Pines theorized that the source of it all was a dimension of weirdness that leaked into the Earth. Deciding to investigate this dimension, Ford eventually hit a dead end. He soon after encountered Bill Cipher, who gave Ford the means to build the Portal alongside his associate Fiddleford McGucket. Ford used technology salvaged from a UFO buried under the town to provide the parts for the Portal. Ford believed the Portal's purpose was to break the boundaries between worlds, but Bill intended for it to merge his realm with Earth. During the initial test run, McGucket was almost sucked in, and after being pulled out by Ford, began to speak in gibberish and says the strange prophecy; "When gravity falls and earth becomes sky, fear the beast with just one eye." Regaining his senses, McGucket realized that the Portal could destroy the world and begged the Author to take it down. When Ford refused, McGucket left to forget what he had seen.
Eventually, Ford realized that he was in over his head and that McGucket's warnings were right. Confronting Bill, he learned the truth and decided to shut down the Portal, and ensure it could never be activated again. Hiding Journals 2 and 3, he called his brother Stan to Gravity Falls to take Journal 1 and hide it somewhere on the other side of the planet. However, Stan was outraged over Ford's apparent indisposition to reconcile with him and the two began to fight. During the struggle, the Portal activated, and pulled Ford in. Stan would spend the next thirty years trying to reactivate it and bring his brother back.
After Dipper and Mabel Pines defeat Gideon Gleeful's giant robot and Stan exposes Gideon for the fraud he is, Stan steals Journal 2 from Gideon. Later, Dipper shares that he owns Journal 3 and Stan takes it on the pretense that fantasy books such as those were making Dipper's imagination run wild.
Stan takes the two books and combines them with Journal 1. He inputs the combined data gathered from them into a large machine. This activates the portal, and Stan sets his computer to run a scan on the other side quadrant by quadrant.
At the end of "Society of the Blind Eye," Stan is shown supplying the portal with more fuel as its gateway grows stronger and starts pulling things into it.
In "Not What He Seems," the portal slowly starts to lose its stability, causing anomalies that result in the Earth losing its gravitational pull. It is then revealed towards the end of the episode that, when fully functional, the portal could result in a universal catastrophe, resulting in the destruction of everything. After Mabel decides to trust Stan's word and let the timer reach zero, the portal explodes with tremendous force, seemingly obliterating everything around it. However, the energy given off from it settles before any damage happens. The explosion results in most of the portal being destroyed, save for the still-functional main centerpiece, where Ford is able to walk out and return back to his own dimension.
In "Dungeons, Dungeons, and More Dungeons," Ford shows Dipper that he dismantled the portal because an inter-dimensional gateway is too dangerous for the world it feeds into. In addition, the instability of the machine created the interdimensional rift, which is extremely dangerous, so he asks Dipper to keep this secret from everyone he knows.
Originally the machine was built to potentially benefit all of mankind, but something went wrong. Dipper gathered from the section of the portal page in Journal #3 that it is some kind of strange, futuristic, super weapon. Gideon believed it would lead to a gateway of unimaginable power. The cryptogram written on the page describes it as a portal that opens a gateway to infinite new worlds.
However, according to calculations by a young McGucket, the more time that passes the more unstable the portal becomes, and the probability of failure increases dramatically. If necessary there is an emergency shutdown switch to the right of the portal.
When all three journals are placed together, the following is written in invisible ink:
The machine was meant to create knowledge but it is too powerful! The device, if fully operational could tear our universe apart! I was wrong the whole time! It must not fall into the wrong hands. If the clock ever reaches zero our universe is doomed! Total global destruction!
Beyond the portal
In "Weirdmageddon 3: Take Back The Falls," Bill Cipher mentions that the dimension beyond the portal was totally flat. Bill also mentions to Ford that he liberated the "2-D" world and he was there to liberate "the real world'.
The main section is a large, inverted metal triangle with lights dotting along its edge. There is a large hole in the center and symbols encircling the hole. The symbols represent the Behenian fixed stars, which are a selection of fifteen stars considered especially useful for magical applications in medieval astrology. The bottom tip of the triangle is connected to a base with many large thick cords.
In the episode "Not What He Seems", the portal was seen many times. In the beginning, it was found out that it is fueled by radioactive waste. Late in the episode, the portal was seen to cause several anomalies that in which case, the world will lose gravity and then drop everything shortly after. In the end, the symbols seen on the outside flash rainbow colors and spin until a dark background appears revealing Stan's brother, The Author.
Most of the portal's infrastructure was destroyed in the blast when its countdown clock reached zero. The only part left intact was the main portal itself. The symbols for Spica and Arcturus stay lit. After this, it was dismantled, leaving only non-functional pieces.
- 120. "Gideon Rises"
- 201. "Scary-oke"
- 204. "Sock Opera" (pictured)
- 207. "Society of the Blind Eye"
- 211. "Not What He Seems"
- 212. "A Tale of Two Stans"
- 213. "Dungeons, Dungeons, and More Dungeons"
- 215. "The Last Mabelcorn" (flashback)
- 217. "Dipper and Mabel vs. the Future" (mentioned)
- 218. "Weirdmageddon Part 1" (mentioned)
- 220. "Weirdmageddon 3: Take Back The Falls"
- Once activated, anomalies occur in close proximity, causing periods of zero gravity and, briefly, even anti-gravity.
- Once unstable enough, it creates rips in the universe.
- Each of the stars have meanings, such as Sirius being the dog star.
- It is used as part of the Shacktron in "Weirdmageddon 3: Take Back The Falls."
- When the pen, coffee cup and notebook fly through the portal in the credits of "Society of the Blind Eye," they reappear in the Rick and Morty episode "Close Rick-counters Of The Rick Kind."