English is not my native language and I only watched the dubbed version of Back to the Future and there the "flux capacitor" was translated to mean something like "flux storage" - literally a unit that accumulates and stores "flux". Given how the thing looks like - three glass tubes pulsating - that sounded just okay.

Now turns out it's "flux capacitor" which is often interpreted as a flavor of a capacitor. So now if anyone asks which capacitor he could use to capture lightning energy he invariably gets a comment that he has to use a flux capacitor.

Is the device called a flux capacitor in Back to the Future indeed a capacitor?

  • 3
    The word "capacitor" or "condenser" refers to a device that can accumulate energy. A capacitor as we know them, is a device that stores energy in an electric field, this is not what a flux capacitor is. ...but in this case the term capacitor can, and does, mean "condenser". Jul 13, 2012 at 11:38
  • Flux is also an ambiguous word: en.wikipedia.org/wiki/Flux - basically, the writer(s) just called the thing something that would sound cool
    – HorusKol
    Jul 13, 2012 at 14:27
  • 2
    Not necessarily. Flux is normally used to describe the flow of something through a given surface area. Although nobody ever mentions it's a flow of what specifically, could we, perhaps, assume the "flux" described in the movies could refer to the flow of time?
    – Dungarth
    Jul 13, 2012 at 14:49
  • in the 1933 movie FEMALE actor George Brent used the term Flux Capacitor in descrbing the macanics of his new invention the automatic transmission
    – user40865
    Jan 21, 2015 at 16:16

6 Answers 6


In the film's official novelisation, it's made explicitly clear that the flux capacitor is aptly named. It's a capacitor that's needed to first create, and then manage the build-up of flux energy.

Moving his head next to it so that he could be on camera and describe its workings at the same time, Doc Brown continued in his professional tone. “This is what makes time travel possible—the flux capacitor.”
“Flux capacitor, huh?” Marty repeated. “Is that its real title or something you made up?”
“It’s a logical title applied by me when I decided to describe its function in one or two words. Any brilliant scientist would have arrived at approximately the same title if given the chance.”


Doc Brown smiled modestly. “The way I figure it,” he replied, “if you’re gonna build a time machine, why not do it with some style and imagination? Besides, there’s a practical aspect. The stainless steel construction of the DeLorean made the flux dispersal—”


Plutonium? You mean this sucker’s nuclear?”
“Electrical, basically,” Doc Brown replied. “But I need a nuclear reaction to generate the 1.21 gigawatts of electricity I need. The flux capacitor stores it, then discharges it all at once, like a gigantic bolt of lightning. It’s really quite efficient.”

So yes, it's a capacitor.


In physics, flux is defined as the flow rate of something (water, electromagnetic fields, etc.) through a given surface area. As Donald.McLean said, a capacitor is normally used to store electrical energy.

If we allow ourselves to enter the realm of movie physics, the term "flux capacitor" could be interpreted as something that accumulates and stores the flow of something for further use. Although this seems weird, knowing that we are talking about time travel, it could be that the flux capacitor stores the flow of time relative to the DeLorean and uses it to travel through time.

Donald.McLean has another great theory in that the accumulation of such flux (or flow of time) can be used to punch through some sort of time travel barrier. I believe this is at least partially correct (if not totally correct). In fact, the first movie itself seems to point this way. Although we don't see in the movie how the flux capacitor works exactly, Doc explains to Marty that the stainless steel body of the DeLorean has a direct influence on the "flux dispersal". Sadly, he is interrupted before he can finish his explanation.

Given how cages made of conductive material works (the steel frame of a car acts as a Faraday Cage, essentially), one could assume that the flux capacitor accumulates a certain amount "time flow" which it then releases through the body of the DeLorean as a means to counteract the effects of time travelling. And since the travellers are inside a protected area, they are immune to the adverse effects of such travel.

Without any word from the creators of the franchise, however, this explanation will remain pure conjecture on my part, although I feel it is faithful to the movies' general feel.

As for the point on lightning, Donald.McLean is also right in saying it is only used as a power source. The amount of energy needed to operate time travel in the BTTF universe is astronomical. In fact, 1.21gW (Watts being a unit of power, as in joules per second) is about the same power output of a normal nuclear reactor inside a nuclear power plant. In the future, Mr.Fusion household reactors have replaced the need for centralized powerplants and Doc mounts one on the car to replace the old plutonium reactor.


In electric circuits, capacitor is often used to accumulate a large charge of electricity to perform some task that requires a burst of energy which is larger than can typically be provided by the available power source, such as a photographic flash.

I would guess that time travel requires a burst of "flux" and so the flux capacitor is used to accumulate the necessary flux until there is a sufficient quantity, and the proper conditions have been achieved, to do the time travel thing. I'm guessing there's some sort of "time travel barrier" and the flux is used to "punch" through this barrier.

Note that the lightning is used strictly as a source of electricity. The electric power almost certainly is used, in part, to generate the flux accumulated in the flux capacitor, but any other electric power source that generates the necessary amount of electricity would work equally well.

  • Since they use a train in the last one, I assume that it's a hybrid electric/gasoline vehicle (Marty mentions him being out of gas in one of the movies), and that flux is generated by the speed of the vehicle.
    – Chris
    Jul 13, 2012 at 14:12
  • It is possible that flux could be generated as a byproduct of movement, but I don't think so. 1.21 gigawatts is a heck of a lot of power. It's something like a million hair dryers. Jul 13, 2012 at 14:16
  • A standard nuclear reactor produces between 0.9 and 1.6 gW of power. In fact, 1.21 gW is a bit higher than 1.6 million horsepower.
    – Dungarth
    Jul 13, 2012 at 14:46

The term "Flux Capacitor" is a sort of oxymoron, describing two phenomena which are distinctly different and cannot be combined as they are in a sense orthogonal, and therefore is an appropriate device to describe a phenomena (time travel) which outside the realm of proven scientific fact or experience.

More specifically, it contains both the word "flux" which refers to property of an inductor where by the electric current through the conductor creates a magnetic flux, and the word "capacitor" which refers to the device in which a voltage causes the accumulation of charges on two separated plates. The nature of an inductor is that changes in current are resisted (essentially) by a magnetic effect, e.g. the building or collapsing of the magnetic field, whereas the nature of a capacitor is that changes in voltage are resisted by (essentially) an electric effect.

It doesn't make sense for a device to be both a capacitor and an inductor simultaneously, at least not without breaking it down into separate capacitor and inductor devices which must be placed in some combination of series and parallel within the circuit. When you do that, you (often) effectively have an oscillator, where energy stored in on component will be transfered to the other back and forth at a diminishing amplitude as the resistance in the circuit turns it into heat. However, as oscillation of one sort or another is essentially the means by which we measure time this deeper meaning suggests that the successful combining of both of these types of devices (the three tubes combining in the center suggesting how this is possible) results in an effective in-story explanation for how it works - by combing the two devices there is effectively oscillation of such a high frequency that the speed of light is not a barrier and time travel is effectively achieved.


The De Lorean needs 1.21 gigawatts of continuous electricity to work and this is not possible even now unless with a large nuclear plant. But you CAN generate 1.2 GW pulses off of a much lower power supply.

It's clear from the fact that a lightning can be used to activate time travel o nthe DeLorean that it need high power, but not for a very short moment.

For example, if the 1.2 GW is only needed for 1 microsecond, you could store a charge from a 1.21 MW source 1000 times in a capacitor and get a 1,21 GW pulse once per millisecond.

That would need a capacitor that does not exists, but that is the point of the story, Doc had a vision of this capacitor and he was able to build it.

So the flux capacitor is the most awesome capacitor ever invented.

  • While this is an interesting answer, it's not an answer to THIS question.
    – Monty129
    Jul 3, 2013 at 11:40
  • 1
    "it need high power, but not for a very short moment." -- Not that odd; think of Florescent lights; they require a significant amount of power to get them to where they can work, but then only a trickle to run. Under that analogy, the Flux Capacitor would simply be holding the charge until it is released by time travel.
    – K-H-W
    Nov 9, 2013 at 3:08

Maybe feasible to think of it in terms of a regulator: that wormhole generator is quite interesting. I've done some calculations here and as it turns out time travel is actually possible and occurs in nature as what we know to be ball lightning. In this case the natural CTC forms in the future and sends a small amount of energy back in time in the form of a coherence field formed by the interaction of storm-generated antimatter and gravity that causes ambient electrical energy already present to coalesce as a ball of plasma. As it turns out the explanation of magnetic skyrmions isn't that far off. As the energy dissipates it causes atmospheric instability that causes the storm to migrate to a location where the BL "will be" at some point in the future. The flux capacitor harnesses this effect, so essentially allowing a specific point in time to be selected by altering the destination point of the wormhole, which happens to be stable at a speed of 88mph relative. As it only lasts 0.16 seconds the energy requirements aren't as high as you might expect and as the vehicle goes through its extra mass reacts with the exotic matter of the wormhole and "seals" the rift thus prevents unnecessary contamination of the surrounding space-time. Any exces energy is seen as acoustic bangs and flashes of light.

  • This seems like gobbledegook.
    – Valorum
    Mar 4, 2018 at 7:53

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