# Back to the Future Question

Discussion in 'Science Fiction & Fantasy' started by Trekker4747, Nov 10, 2013.

1. ### Trekker4747Boldly going...Premium Member

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I've a question on Back to the Future, namely in how the time machine works. Dialogue tells us 1.21 gigawatts of electricity is needed to power the Flux Capacitor in order to allow for time travel. (And then there's 88 miles an hour or something in there.)

Anyway, in the first movie Doc uses nuclear fission in order to obtain this incredible level of power which for the purposes of this discussion we'll assume that a single Plutonium pellet and the reactor in the DeLorean is enough to generate this power. (We'll also assume that a handful of garbage and some really incredible cold fusion does this in the other movies.)

So Marty is trapped in 1955, no Plutonium (although, surprisingly enough, Plutonium is pretty easy to get a hold of in 1955) and him and Doc concoct a plan to channel a bolt of lightning into the time machine to provide the 1.21 GW of electricity to allow for the time travel.

My question is... Is a bolt of lightning the same power as power from a nuclear reaction? I mean even going to AC vs. DC, what about amps, volts, all of the other properties and such of electricity. Electricity is a bit more complex than watts meeting watts isn't it?

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According to Wikipedia, the peak output of an average lightning strike is more on the order of a terawatt, however a rare positive bolt is upwards of hundreds of terawatts. A Terawatt is a thousand gigawatts.

It should really have ripped apart the flux capacitor.

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You want a fantasy to make scientific sense?

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Why? Doc said it needed 1.21 gigawatts, he didn't say that was the maximum it could handle.

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what the hell is a gigawatt?

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Nuclear reactors generate heat from radioactive decay, and the heat is converted to electricity. Atomic batteries would generally use thermocouples, photovoltaic cells, or the like, but whatever method is used, the electricity that comes out the other end is the same kind of electricity you'd get from any other source, since it's all just made of electrons.

Still, I imagine it would've taken a lot of work to refit the car from a power system that used atomic batteries to convert decay heat to electricity to a power system that was fed electricity directly by a lightning strike. And yeah, there'd probably have to be some really heavy-duty circuit breakers to keep the lightning from blowing every circuit in the car.

8. ### Trekker4747Boldly going...Premium Member

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Well, not to mention the wires on the Clock Tower had to be pretty good to handle that much power without melting or catching instantly on fire or something.

But, like I said in the OP, we hear gigawatt (jigawatt) sossed around a lot but never any mention of volts, amps, etc. I'd think that'd make a difference, no?

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I think the interesting part is that we would have had the Delorean at the nuclear test site if they had the budget. I believe that's the problem with many of today's movies. Producers and Directors are now not as often forced to be creative and find new ideas that fit a budget; instead CGI is usually cheap enough to just create whatever their first idea was (no matter how bad it may be).

It's kind of like that How I Met Your Mother episode where Ted goes to high society party with the intellectuals; there are no friends there to make the fart noise so the Director knows he's acting like a douche.

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^I thought they did exactly that. *checks the youtubes* OK, maybe not instantly, but they did catch fire.

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That is one of the things why I think the films in the 80s are so good. They had just the right amount of possibilities to realize their visions. Because quite frankly, their first visions really sucked. I read the script of Indiana Jones and the Monkey King, the film George Lucas would have done had visual effects allowed him to, and what was eventually replaced by The Last Crusade.

People think he "lost" is with the Star Wars Prequels and Indy Crystal Skull. But the true story is that the Prequels and Indy 4 are exactly what he would have done 20-30 years ago had the technology been there.

Spielberg recycled the nuke the fridge scene (and later nuke the Delorean, there's a storyboard sequence on the bluray disc) from the early BttF drafts in Indy 4 because that is also what he always wanted to do but could not do because technology wasn't ready.

That HIMYM comparison is actually brilliant!

13. ### Trekker4747Boldly going...Premium Member

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Well, considering they absorbed gigawatts upon gigawatts of electricity they seemed to fare pretty good all things considered.

14. ### Robert Maxwellso far this is a dumb futurePremium Member

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One could safely assume the Doc calculated just how much energy from that bolt of lightning would end up down in the wire crossing the street, passing into the DeLorean. Going from a rough estimate of how much energy would be infused into the clock tower, and then how much would be lost along the way (since he controlled the type of wiring used and could factor in losses to grounding, light, heat, etc.) he could come up with a reasonably good idea of how to get enough power into the flux capacitor without it being too much. There's just no reason to bore the audience with the math.

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Well just to expand on your great post, the heat generated by the radioactive decay is simply used to boil water to steam, and in turn, spin a generator to create electricity, which comes out the generator as AC current.

The evidence for this process is seen when the Delorean jumps back a minute ahead, and it blows all the steam out from the Cooling Vents strapped to the top of the trunk. Presumably, the steam spun the turbines of the generators, the power was created, and then released via those vents.

So the first question that arises is: Is there even a capable way to create 1.21 gigawatts of electricity from an AC generator that could fit into the engine bay of a Delorean? (considering the internal combustion engine is still there even)

From what I understand, lighting bolts can carry anywhere from gigawatt to terawatts of DC voltage in them.

Assuming Doc Brown understood this, he would have had to connect the lightning rod to some type of massively strong thermistor, to control the rate at which the energy was being fed into the Flux Capacitor, and he would bypass the generator and nuclear reactor completely.

If the lightning bolt was in the terawatt range, it probably would have overloaded the Flux Capacitor, either making it explode (possibly killing Marty McFly), or perhaps react in some strange way to throw Marty way off into some unknown time period, with the likelihood that it was fried, and he'd be stuck there for good.

So they probably got lucky with a bolt that was in the gigawatt range.

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Heh. I like when he invented the skateboard.

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I think that when a movie uses an oxymoronic term like "flux capacitor" (flux means flow or change, while a capacitor stores an unmoving charge), one can't expect it to make much sense from a technological standpoint. It's not as if the temporal physics make any sense either.

18. ### Trekker4747Boldly going...Premium Member

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Well, maybe that's why the device was so revolutionary and "made time-travel possible" was that Doc was able to build a seemingly impossible device and make it work. Or Doc, being a bit out of his mind, just named it something stupid.