- "This is what makes time travel possible."
- —Doc Brown
The flux capacitor was the core component of Doctor Emmett Brown's time traveling DeLorean time machine and the following Jules Verne Train. Brown stated that the flux capacitor "is what makes time travel possible."
How it "worked"
- Doc: "It works! Ha ha, IT WORKS! I FINALLY invent something that works!"
- Marty: "You bet your ass it works"
- — The conversation between Doc Brown and Marty McFly after the latter shows him the completed flux capacitor in the DeLorean time machine
It is not made clear exactly how the flux capacitor worked. It consisted of a box with three small, flashing incandescent lamps arranged as a "Y", located above and behind the passenger's seat of the time machine. As the car neared 88 miles per hour, the light of the flux capacitor pulsed faster until it had a steady stream of light, which one was not supposed to look at as indicated by the Dymo warning label placed across the glass panel. The stainless steel body of the DeLorean also had a beneficial effect on the "flux dispersal" as the capacitor activated, although Doc was interrupted before he could finish explaining it fully. Accessing the flux capacitor safely required disconnection of the capacitor drive, as the Dymo warning label at the top of the unit pointed out.
On November 5, 1955, Emmett Brown came up with the idea of the flux capacitor after slipping and bumping his head while standing on his toilet to hang a clock. The idea came to him in a vision he had after being knocked out. He drew an inverted Y-shape with wires and stated "flux compression". He also performed some mild calculations on the paper.
In order to travel through time, the vehicle integrated with the flux capacitor needed to be traveling at 88 mph (140.8 km/h), and required 1.21 gigawatts of power (1,210,000,000 watts), originally supplied by a plutonium-powered nuclear reactor. However, for the time machine's return trip (from 1955 back to 1985), plutonium was not available, so a lightning rod was connected directly into the flux capacitor and was used while the vehicle sustained 88 mph. Plutonium was used once again for a trip forward in time at least 30 years, and at some point thereafter the plutonium reactor was replaced by a "Mr. Fusion" home energy generator from the future that was fueled by extracting hydrogen atoms from garbage.
The DeLorean once again came back to 1985 and proceeded to travel to 2015, where it was stolen and taken back to 1955 and returned back to 2015 without the Doc's knowledge. When they returned in 1985, they found it was a different present, so they traveled back to 1955 to fix the time-space continuum. The DeLorean was again struck by lightning in the year 1955, this time by accident. The lightning created an overload and caused a malfunction in the time circuits. Earlier, the 1885 date was already displayed before the lightning hit, after the LED read-outs flashed. 
It was then hidden in the Delgado mine for 70 years because suitable replacement parts were not invented until 1947. . It was recovered from the mine in 1955 and repaired by Doc Brown's 1955 counterpart, thus restoring it to working order. Since both gasoline and garbage were available, the next trip back to 1885 was performed under the car's own power.
Due to a broken fuel line, the De Lorean's final trip from 1885 to 1985 was partially powered by a steam locomotive pushing the vehicle up to 88 mph while using Mr. Fusion to generate the 1.21 gigawatts required to activate the flux capacitor and break the time barrier. Doc returns to 1985 in a time machine made from a locomotive. This used a flux capacitor that Doc was able to power using steam (at least with the propulsion requirement for time travel), located on the front of the train, in place of the lamp.
Behind the scenes
In the movie, the power required is pronounced "one point twenty-one jigowatts". Although this pronunciation of "gigawatt" was once considered the correct one, it is no longer the most common. (In addition, since Robert Zemeckis and Bob Gale were unfamiliar with the term, they misspelled it in the script.) Because of this, a "jigowatt" will sometimes be referred to on Internet forums as a fictional unit or to make fun of someone's electrical knowledge. The spelling "jigowatt" is used in the novelizations of the second and third films. However, the book of the original film uses the correct spelling "gigawatt".
The phrase "flux capacitor" has appeared in more serious contexts. U.S. Patent 6,084,285 describes a "lateral flux capacitor having fractal-shaped perimeters", the idea being to make a capacitor in an integrated circuit, some of whose capacitance exists between two conductors on a single layer (hence, "lateral"). The device is not a lateral flux-capacitor but a lateral-flux capacitor.
Flux is commonly used in electronics and electromagnetic theory and application, but rarely in the context of a capacitor. In general terms, flux simply means the rate at which some quantity (such as electric charge) passes through a surface (e.g. charge flux). It is speculated that the movie terminology is used fictitiously to represent a new and unknown type of flux.
- The Spanish dubbing of the film mistranslated flux as the nonexistent fluzo instead of flujo, adding to the exoticity of a condensador de fluzo.
- The Italian dubbing of the film mistranslated the name as "flusso canalizzatore", which roughly means "channeling flux"; however, when Marty reads the letter from Doc in the third movie, it talks about the broken "condensatore di flusso", which is an exact translation of "flux capacitor", but at this point appears to be totally unrelated to the rest of the movies (at least for only-Italian-speaking people).
- In the German-dubbed version, the device was once again mistranslated and called the "fluxkompensator" ("flux compensator"). The correct German translation for the word capacitor, however, would be "Kondensator".
- In the French version, the DeLorean needs 2.21 gigawatts instead of 1.21.
- The original flux capacitor props used high pressure gas relays as the active components which while operating created the steady pulsing which is seen when the time circuits are turned on.
- In the fourth draft of Back to the Future, the flux capacitor was called the temporal field capacitor.
For references to the flux capacitor in popular culture, see List of references to Back to the Future
- Back to the Future
- Back to the Future Part II
- Back to the Future Part III
- Back to the Future: The Animated Series
- Back to the Future: The Game
- Jack and the Beanstalk (Non-canonical appearance)
Notes and references
- ↑ This is a reference to earlier in the film when Doc exclaims that he needs to fix them (they also flash a random date before he hits it and they are corrected), contrary to popular belief the 1885 date was not caused by the lightning hitting the DeLorean.
- ↑ This is presumably a reference to the invention of the transistor.