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So, we all know that the special speed at which the DeLorean will travel through time is 88 miles per hour (if you didn't already, now you do). Yet, you will only travel through time if the time circuits are already activated. So, the thought occurred to me: what would happen if we had the time circuits turned off, accelerated to 89 miles per hour, then activated the time circuits?

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    I'd say if Doc Brown doesn't have the answer, no one else will :) – psubsee2003 Oct 19 '15 at 0:49
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    It's also interesting to note that the flux capacitator seems to be fluxing in the lead up to 88 miles per hour (remember the bars that we see behind Marty's seat that go from green to yellow to red) – Often Right Oct 19 '15 at 0:52
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    You get a speeding ticket? :P – Au101 Oct 19 '15 at 0:53
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    SPOILER ALERT NEEDED! – DVK-on-Ahch-To Oct 19 '15 at 15:16
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    Only a couple days until we know exactly when and where the time machine will be left unattended. Someone intercept it and run a test. – Karl Bielefeldt Oct 19 '15 at 22:00
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No official information.

First of all, there seems to be no official in-universe explanation, as writer Bob Gale essentially picked the number with no in-universe reasoning in mind:

The fact that everybody says, "Why 88 miles an hour? What's so special about that?" It's easy to remember. That's all. There's no special significance to that.

(See @Hypnosif's answer to another question, where I found this quote.)

Gale doesn't seem to have revisited the "88" since making that statement, nor has director Robert Zemeckis.

Also, we don't see the effects of faster-than-88-mph time circuit activation in the films.

Unfortunately, we may never know until they make a Back to the Future IV. ;-)

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    The sad thing is that it's really only a matter of time until they do make another. – PointlessSpike Oct 19 '15 at 9:42
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    Which leads to the question: what would happen if it hit 88 Mph on a rolling road? – SeanR Oct 19 '15 at 9:48
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    @SeanR So true. Would the DeLorean be able to travel through time on a treadmill? – Daniel Oct 19 '15 at 12:53
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    @DanielCook That has already been discussed – Zommuter Oct 19 '15 at 13:24
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    @PointlessSpike Fortunately, the last time I checked a sequel is very unlikely, because the rights holders have said the series is complete and they don't want a sequel. – user11521 Oct 19 '15 at 16:58
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Somewhat speculatively, because as said already - there is no canonical answer.

I'd backtrack a bit and ask - "Why does my time machine need to be in motion anyway?".

The most obvious would be that it's not really a time machine as such, as a hole punch - it makes a hole in spacetime that is a certain size. One of the limits is how long the 'hole' lasts.

We have the dimensions of the delorean as:

https://en.wikipedia.org/wiki/DeLorean_DMC-12

  • 1.8m tall
  • 1.1m wide
  • 4.2m long

At 88mph, you cover 39m/sec - so in 0.1s it will cover 3.9m. Or - very nearly the length of the car. Let's give us a bit of a safety margin and give the 'hole' a length (or maybe your time is slightly longer than 0.1s)

So I'd suggest your 'time jump' aperture only opens for that sort of time span, due to some metaphysical constraint, and therefore if you're not moving fast enough you'll get cut in half or otherwise mangled by the jump.

Logically therefore - what would happen if you were moving faster than 88mph and then activated the circuit - nothing much. You're moving more than fast enough to make it through the "hole".

Which leads to the question: what would happen if it hit 88 Mph on a rolling road?

Depends how close to the front of the vehicle the "aperture" opens. Would suggest it has to be in front, so it might actually not be too bad - it'll open, close, and you'll have burned up some expensive black market fissionables. Of course, if you've somehow 'gimmicked' the speedo so you're moving slower - but still forwards - then you'd be part way through a collapsing temporal rift. I cannot help but think 'That Would Be Bad'.

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    If you're going to try to give a physical explanation: 88 mph relative to what? – Rhymoid Oct 19 '15 at 12:42
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    The current inertial frame of reference. – Sobrique Oct 19 '15 at 12:51
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    That raises more questions than answers. What is the significance of the "current frame"? Which frame do you pick if the DeLorean is on a vehicle that moves relative to the earth, and what difference will it make? – Rhymoid Oct 19 '15 at 13:15
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    @Rhymoid We're talking about time travel, and you want to know what frame of reference we are looking at? If you are time travelling, relativity is already so bent out of shape, I'm not sure we have the knowledge of physics to answer the question - or to even makes sense of the question. – Shane Oct 19 '15 at 13:41
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    @Rhymoid - The writers of BTTF seem to implicitly assume the Earth is at rest, since the DeLorean always ends up at the same point on Earth. But if you want to come up with an explanation that jibes with relativity, we can imagine Doc used some kind of Earth-centered coordinate system (like what the GPS satellite computers use) to control the time jumps, and perhaps intentionally designed the tachyon field generator so it would create a wormhole (or other type of "hole in spacetime") that was at rest in this coordinate system. – Hypnosifl Oct 19 '15 at 18:20
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On a largely speculative basis, I would imagine that it depends on whether the time circuits are activated.

Time Circuits Not Activated:

You drive at speeds higher than 88 miles per hour, just like you would in any other car. According to a report by Road & Track magazine, the top speed of the DeLorean was a measly 109 miles per hour, and reaching this speed required a staggering 40 seconds of driving on a perfectly straight highway. Even hitting 60 miles per hour took 10.5 seconds, which is truly pathetic for a vehicle marketed as a sports car. The movie was surprisingly close to reality, as it takes the DeLorean a full 19 seconds to reach 88 miles per hour in the test run.

Time Circuits Activated:

The first part is obvious, as we see it happen more than once in the series. When you hit 88 miles per hour, you travel through time. However, as far as I can recall, every time the DeLorean arrives in a new time, the driver (whether that happens to be Marty, the Doc, or Biff) hits the brakes. I would imagine that, if the driver were to keep his foot on the gas pedal after arriving in the destination time, the DeLorean would simply continue to accelerate until it reached its maximum speed.

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    DMC-12's 0-60 was 8.8 to 10.5 seconds depending on the test and the transmission used (manual was 1 to 1.5 seconds faster). But 10 seconds isn't exactly "truly pathetic" for the first car the company made, in 1981. The base '84 MR2 did 9-ish seconds, the Fiero was 10-11, the '80 Trans Am was at 9-ish. By modern standards, those times are crap, but in 1981 that was pretty decent for a base-model vehicle. Certainly there were faster cars even then (late 70's Corvettes could do 7-8), but the DMC-12 wasn't that bad. The $25k purchase price, on the other hand... – MichaelS Oct 19 '15 at 7:39
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    @MichaelS wasn't it made of steel too, very heavy compared to many sports models – user46509 Oct 19 '15 at 10:12
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    Hmm, I'd think if you didn't slow down upon arrival, the time circuits would keep bouncing you back to the time you set your arrival to, so you'd essentially be "frozen" in time until you let off the gas. But you'd have to have nerves of steel and good reflexes to not slow down even a little when your entire surroundings changed in an instant. – Darrel Hoffman Oct 19 '15 at 14:52
  • @CarlSixsmith Stainless steel panels, although the doc specifically mentions how it would be no match against Biff's apparently heavier, more steel car. – user11521 Oct 19 '15 at 17:01
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    @MichaelS - Also, you're talking about a normal, out-of-the-factory unmodified Delorean, which might be relatively durable. But when you add all those timey-wimey things onto the outside, it's likely to be a good deal more fragile. – Darrel Hoffman Oct 20 '15 at 14:34
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Speedometer uses two digital 7-segment displays to indicate current speed. When all segments light up… well, that could be an electronic trigger to start the time machine parts!

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    I don't see how this answers the question asked – Jason Baker Oct 20 '15 at 15:59
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    Let me rephrase: when the car exceeds 88mph the indicator rolls over the value where all segments are lit. – user1306322 Oct 20 '15 at 17:13

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