Further thoughts on mixing science and fiction: Back to the Future · 10:58pm Oct 21st, 2015
Yesterday I wrote about the impressive attention to scientific accuracy in the film The Martian. Today is the day to celebrate the other end of the science-themed cinema spectrum, being Back to the Future Day – 21 October 2015, the date visited by time travellers Marty McFly and Doc Brown in the second instalment of that series.
According to theoretical physicist Sean Carrol, Back to the Future might be “The least realistic time-travel movie of all time” (He can’t have watched the entire Doctor Who franchise).
The films make use of multiple timelines (21 in one interpretation), like the many-worlds interpretation of quantum mechanics (which Twilight mentions in Temporal Irregu-Rarity). But bizarrely, we see events in the past changing photos taken in the future, and then taken back in time, which doesn't fit any sensible theory. Applying scientific accuracy to time travel is not a great tactic for film making. As I explained in my old post: Time travel in Equestria and other universes, it is most likely impossible.
But that’s not the point of BTTF. It’s got flying cars, hoverboards, steam trains, humour, adventure, cross-generational drama. What more do you need? And even if the physics doesn't make sense, it is totally respectful of senior eccentric scientists with crazy hair—so no complaints. There wasn’t a great deal of educational benefit from the trilogy. But it did introduce millions to the word gigawatt. These days, thanks to Moore’s Law, everyone is familiar with the 1,000,000,000 prefix, but back in the days when having a VCR recorder at home made you one of the cool kids, everyone just assumed this was technobabble.
Works for me. I thought the time circuits just scanned for a nanowormhole that was connected back to the time in question, as in you dont move spacially, so any energetic length measurement will be in the temporal direction, then used the charge store, charge as motion in 4th spacial dimention and massless, to hold the wormhole mouth open as the cars minimum momentum was used to ram it down the throat like a pig down a reluctant python.
Then again, I beleive that because you travel slower than the wormhole speed of light through a wormhole but faster than light relative to the universe, the two effects combine to give negative gravity, which in normal spacetime is only given by exotic matter etc.
Somthing has to give, if a Plank mass is the quanta of self sustaining gravity fields, a black hole, wormhole, what stops spacetime foam from condensing into a single particle but the inversion effect?
I think the movie with the best time machine was Idiocracy.
Sadly, it didn't introduce them to the pronunciation of gigawatt...
Still, that 21-timeline article was fascinating. Thanks for sharing it.
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In fairness, Doc Brown is kinda nuts.
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I always thought Doc's pronunciation was correct, but archaic, like the original ways of saying quark and Linux.
More discussion: You Say Gigawatt, I Say Jigowatt
If it only require power-output 1.21 GW, just discharge 1.21 Joules in 1 nanosecond. It seems to me that a minimum Jouleage should be required too.
Yeah, BTTF makes no Celestia-damned sense, but it is a fun movie regardless.
Strangely, the most accurate time travel movie, in terms of logic, I have scene has to be X-Men Days of Future's Past. There is only one timeline, and that timeline is temporarily split into two when, whoever her name is, keeps applying the energy into Logan and keeping both timelines isolated, but then when she stops applying the energy the past events overwrite the future instantly. That is the key here; instant. Now, scientifically it is bogus, but that is because time travel into the past in any way is most likely never going to happen. So, in-canon logic and scientifically accurate are not the same thing. It can be logical, but not scientific, but it can't be illogical and be scientific, does that make sense?
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We can impose that by positing that the time machine works quickly, but not instantanously, so it needs to be supplied with 1.21 GW for a certain period of time (much like how my computer, which draws 300 watts, will not do anything useful if supplied with 0.3 J for a single millisecond). Unfortunately, the nature of lightning puts upper bounds on the duration. A typical stroke lasts 30 μs, and there are four strokes in a typical lightning bolt. Depending on how continuous the supply needs to be, we can assume that the time machine needs to be powered for 30-120 μs (really it should be faster so that there's a safety margin, so this would seem to be a decent upper bound).
Sadly, as impressive as a gigawatt is, this only adds up to 36.3-145 kJ. This is not very much energy at all. You can get it by burning a few grams of coal. So, we must assume that, while flux capacitors have been invented in the world of BTTF, regular capacitors have not.
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Maybe Doc Brown could use Leyden-Jars.
Seriously, overthinking silly fiction is fun.
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A typical pint-sized Leyden jar has a capacitance on the order of a nanofarad. At 20 kV (a reasonable voltage for a Leyden jar), that only stores a fifth of a joule, so fitting the required pile of jars into the DeLorean would be difficult. Unless you get this guy to give you a hand, but he'd probably find it easier to just give you a lift.
My time-travel head-canon is some combination of:
- you can't travel to any spot whose light cone you are in
- you can't travel to any time and timeline from which your present is still accessible
Might need some probabilistic and/or informational-theoretic refinement on that last one. Like, you can change your present by a number of bits of information equivalent to the energy you spend travelling back in time, so that the change can be accounted for by that expenditure of energy. Or, you must spend energy equivalent to the information distance between time T in your past, and time T in the alternate past that you travel to, where that distance must be large enough that you can't re-access your starting point by moving forward in time.
There is some mapping between information and energy, but I don't understand it.
Or say some sort of exchange is possible, like, you can increase the... um, Everett flux, I'm making up that term, but I mean the probability of a person starting at <state Y, time T0> getting to <state X, time T1>, provided you decrease the Everett flux from all other <Z,T0>, Z <> Y, to <X,T1>, by the same amount. E.g., you can travel into the past to increase the probability of avoiding some event in the near future only by increasing the probability of other versions of the present time arriving at that future.