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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?

Often Right
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4 Answers4

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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'.

Sobrique
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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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    @Shane If it works the way Sobrique suggests, then general relativity can handle it just fine; read up on Einstein-Rosen bridges. As I understand it, the only reasons E-R bridges are thought to be impossible in Real Life are (a) the requirement for negative energy density (a plausible thing for the flux capacitor to be doing), and (b) most physicists take global causality as an axiom (i.e. "if this theory appears to permit time travel then there must be something wrong with it".) – zwol Oct 19 '15 at 15:39
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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
  • @zwol - That's almost right, but a minor nitpick--what you're talking about is a traversable wormhole, which is actually different from an Einstein-Rosen bridge. An Einstein-Rosen bridge doesn't have any negative energy to hold it open, and it turns from a wormhole to two black holes so quickly that nothing can actually make it through (though objects from either side can meet inside before being destroyed by the black hole singularity). See the "impossible to pass through" section here. – Hypnosifl Oct 19 '15 at 18:24
  • @Hypnosifl Huh, I thought "Einstein-Rosen bridge" was an umbrella term for GR metrics which are not simply connected. I never did actually learn GR, though, so I could easily be wrong. – zwol Oct 19 '15 at 19:09
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    @zwol - I believe "wormhole" is the umbrella term, while "Einstein-Rosen bridge" refers to the specific solution found by Einstein and Rosen--that's how the two terms seem to be used here, for example (note the comment 'The Einstein-Rosen bridge, however, is not traversable'). – Hypnosifl Oct 19 '15 at 19:28
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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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Praxis
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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 09:42
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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 09:48
  • I would continue to speculate - you'd waste some energy, but not have too much a problem, because your 'wormhole' would be a few inches in front of the car. Now, if you gimmicked it so your speedo reported wrongly and you were moving, but not at 88mph... that would be Bad. – Sobrique Oct 19 '15 at 12:11
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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. –  Oct 19 '15 at 16:58
  • @Michael Until time travel is really discovered, and the sequel is a documentary movie where they go to the past and change the rights holders.. errm I've said too much already. – DoubleDouble Oct 19 '15 at 19:12
  • @Michael- The rights holders will not always hold the rights. It could take fifty years or more, but I think another will be created. – PointlessSpike Oct 20 '15 at 07:50
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    @PointlessSpike: "...it's really only a matter of time until they do make another" - pun intended? :-) – Bob Jarvis - Слава Україні Oct 20 '15 at 16:41
  • Just speculation, but "88" makes all of the segments on a 7-segment numeric LED display light up (the type used in the time circuits display panel). The speed may have been chosen in part for this reason. – JYelton Oct 22 '15 at 03:33
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    @JYelton : Sure, but Bob Gale himself (the writer of the film), said he had no reason in mind, it was just an easy-to-remember number. – Praxis Oct 22 '15 at 05:30
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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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Wad Cheber
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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 07:39
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    @MichaelS wasn't it made of steel too, very heavy compared to many sports models –  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. –  Oct 19 '15 at 17:01
  • Steel isn't particularly heavy. Stamped steel panels can be as light as fiberglass or aluminum for the same material strength. Either way, the DMC-12 was around 2700 lbs, which is certainly heavier than the 2300 lb MR2, but on par with the 2600 lb Fiero and quite light compared to the 3300-3600 lb '81 Camaro or 3300 to 3500 lb Corvettes. The '46 Ford, around 3100 lbs, was heavier, but may have been built more solidly, so direct impacts would be more likely to disable the DeLorean than the Ford. – MichaelS Oct 19 '15 at 21:09
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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!

user1306322
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