Flux capacitor

In the ''Back to the Future'' franchise, the DeLorean time machine is a time travel device made by retrofitting a DMC DeLorean vehicle with a flux capacitor. The car requires 1.21 gigawatts ("jigawatts/jigowatts") of power and needs to travel 88 miles per hour (142 km/h) to initiate time travel.

Operation

The control of the time machine is the same in all three films. The operator is seated inside the DeLorean (except the first time, when the remote control is used), and turns on the time circuits by turning a handle near the gear lever, activating a unit containing multiple fourteen- and seven-segment displays that show the destination (red), present (green), and last departed (yellow) dates and times. After entering a target date with the keypad inside the DeLorean, the operator accelerates the car to 88mph (142km/h), which activates the flux capacitor. As it accelerates, several coils around the body glow blue/white while a burst of light appears in front of it. Surrounded by an electrical current similar to a Tesla coil, the whole car vanishes in a flash of white/blue light seconds later, leaving a pair of fiery tire tracks. A digital speedometer is attached to the dashboard so that the operator can accurately gauge the car's speed. Various proposals have been brought forth in the past by fans of the movie franchise for why the car has to be moving at 88 mph to achieve temporal displacement,''Back to the Future: 13 things you may not know''
The Telegraph, October 30, 2016, but actually the production crew chose the velocity simply because they liked how it looked on the speedometer, modified for the movie. The actual speedometer on the production DeLorean's dashboard only goes up to 85 mph, and the car itself was criticized for being underpowered.

Observers outside the vehicle see an implosion of plasma as the vehicle disappears, leaving behind a trail of fire aligned with the DeLorean's tires (which can also appear in midair), while occupants within the vehicle see a quick flash of light and instantaneously arrive at the target time in the same spatial location (relative to the Earth) as when it departed. In the destination time, immediately before the car's arrival, three large and loud flashes occur at the point from which the car emerges from its time travel. After the trip, the exterior of the DeLorean is extremely cold, and frost forms from atmospheric moisture all over the car's body. Vents on the back heat the vehicle after time travel.

The DeLorean suffers assorted malfunctions and damage over the course of the trilogy. In the first film, the car has starter problems and has a hard time restarting once stopped, much to Marty's repeated frustration. In the second film, the destination time display malfunctions and begins to show a series of random dates, causing Doc to be sent back to 1885 when the DeLorean is struck by lightning with him inside. In the third film, a note left by Doc's 1885 self reveals that the DeLorean's flying circuits (added by him in 2015) were destroyed by the strike. After Marty travels back to 1885, the fuel line and fuel injection manifold both suffer damage, leaving the car unable to move under its own power.

The time machine is electric and requires a power input of to operate, originally provided by a plutonium-fueled nuclear reactor. In the first movie, following Marty's accidental trip from 1985 to 1955, Doc has no access to plutonium in 1955, so he outfits the car with a large pole and hook in order to channel the power of a lightning bolt into the flux capacitor and send Marty back to 1985. During Doc's first visit to 2015, he has the machine refitted to fly in addition to standard road driving, and he replaces the nuclear reactor with a ''Mr. Fusion'' generator that uses garbage as fuel.

Although the Mr. Fusion unit provides the required power for the time machine, the DeLorean is still powered by an internal combustion engine for propulsion. The fuel line is damaged during Marty's trip to 1885 in ''Back to the Future Part III''; after he and Doc patch it, they attempt to use whiskey as a replacement fuel since commercial gasoline is not yet available. The test fails, damaging the car's fuel injection manifold and leaving it unable to travel under its own power.

Doc and Marty consider options to reach the required 88 mph (such as pulling it with horses, which fails because the car barely breaks 30 mph) and ultimately settle on pushing the car with a steam locomotive. They replace the DeLorean's standard wheels with a set designed to mate with train rails. For the extra power needed to push it up to speed, Doc adds his own version of " Presto Logs" (a chemically treated mixture of pressed wood and anthracite) to the locomotive's boiler and chooses a location with a straight section of track long enough to achieve 88 mph.

Jigowatts

The power required is pronounced in the film as "one point twenty-one ''jigo''watts", with a jigowatt referring to "one billion watts." The spelling of jigowatts is used in the script and was also the spelling used in the closed-captioning in earlier home video versions of the film. However, the correct spelling is " ''giga''watts". Although rarely used, the "j" sound at the beginning of the SI prefix "giga-" is an acceptable pronunciation. Later versions of closed captioning, such as in the 2020 DVD Trilogy release have corrected the spelling to gigawatts. In the DVD commentary for ''Back to the Future,'' Bob Gale states that he had thought it was pronounced this way because it was how a scientific adviser for the film pronounced it.

Equipment

Flux capacitor

The ''flux capacitor'', which consists of a rectangular-shaped compartment with three flashing Geissler-style tubes arranged in a "Y" configuration, is described by Doc as "what makes time travel possible." The device is the core component of the time machine.

As the time machine nears 88 mph, light coming from the flux capacitor begins pulsing more rapidly until it becomes a steady stream. Doctor Emmet Brown originally conceived the idea for the flux capacitor on November 5, 1955, when he slipped on the edge of his toilet while hanging a clock in his bathroom and hit his head on the sink. In 1955 “Doc” had named the flux capacitor the “Flux Compresser” as shown on 1955 “Doc’s” diagram A similar, but possibly steam-powered, flux capacitor is also seen in the chimney headlamp of Doc's second time machine, the Time Machine Locomotive, at the end of ''Back to the Future Part III.''

Although the films do not describe exactly how the flux capacitor works, Doc mentions at one point that the stainless steel body of the DeLorean has a direct and influential effect on the "flux dispersal", but he is interrupted before he can finish the explanation. The flux capacitor requires 1.21 gigawatts of electrical power to operate, which is roughly equivalent to the power produced by 15 typical commercial airplane jet engines.

The instruction manual for the AMT/ERTL DeLorean model kit says: "Because the car's stainless steel body improves the flux dispersal generated by the flux capacitor, and this in turn allows the vehicle smooth passage through the space-time continuum."

Time circuits

The time circuits are an integral part of the DeLorean time machine. They were built with an input device and a display. The display was divided into three sections: destination time (shown in red), present time (shown in green), and last time departed (shown in yellow), all annotated with Dymo labels. Each display includes a month, a day, a year, and the hour and minutes in that point in time. The years on the time circuits were limited to four digits and there were no possible negative years that could be reached, i.e. years before "0 A.D." (1 B.C.). This means the DeLorean could travel to any time from 12:00 am on January 1, 1 B.C. to 11:59 p.m. on December 31, A.D. 9999. It is unknown what would happen if one were to travel to the latter date since, after only one minute, it would be the year A.D. 10000 and the time circuits would no longer be able to show the present time.

The destination time display shows the date that the operator wants the DeLorean to go to (when the operator types in a date using the keypad in the DeLorean, it will be shown in the destination time display), the present time display shows the DeLorean's current location in time, and the last time departed display shows what point in time the DeLorean originally was after making a journey through time. Doc demonstrated its capabilities to Marty after its first test, giving three well-known but erroneous dates as examples: the signing of the Declaration of Independence, July 4, 1776; the birth of Christ, December 25, 0000; and the day that he invented time travel, November 5, 1955.

During the second film, because of Biff Tannen's fiddling after he steals the DeLorean, the time circuits began malfunctioning, displaying January 1, 1885 in the destination time display. A bolt of lightning triggered the malfunction to send the DeLorean from 1955 to 1885. Though the vehicle was in mid-air, the spin created by the lightning bolt allowed it to reach 88 mph. Doc was trapped in 1885 and repairs were impossible because the time circuit control microchip, which powered the time circuits, was destroyed by the lightning bolt, and suitable replacement parts would not be invented until at least 1947. Doc placed repair instructions and a schematic diagram in the time machine to enable his 1955 counterpart to repair it using components from that era — which included vacuum tubes — before boarding it up within
a silver mine. He then wrote Marty a letter explaining the situation and handed it over to Western Union