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back to the future - Can the Delorean meet its speed requirement without moving?



Everyone knows that to time travel, the Delorean had to "hit 88 MPH".
Watching the movie right now though, got me wondering...


When Doc first demonstrates the time machine to Marty, he holds the brakes and revs up the drive wheels. This got me wondering... does the Delorean have to actually be MOVING at 88 MPH? Or is it somehow tied to the speedometer? What if he had the back wheels up on rollers, like they do when doing the emissions test on cars, and got the wheels (and speedometer) up to 88 while the car itself was still actually stationary?


To clarify, I am not asking why the "magic speed" was 88. There are some pretty good answers to that on the question Izkata linked to in his comment.


Nor am I asking why he needed to use a car. He didn't. He stated that in the first movie.
If you're going to build a time machine into a car, why not do it with style?
He CHOSE to use a car as his platform, and the Delorean for style.


More, I'm asking, regarding the functionality of the time machine AS BUILT into the car, what exactly was it that had to hit the magic speed? I see two possibilities...





  • the car had to be in actual spatial motion. maybe it had to do with the friction of the air over those "flux dispersal" stripes around the car or relativistic motion of the car to the surrounding environment or something.




  • only the speedometer was required to hit the target speed. the car itself could have the drive wheels lifted or on rollers of some sort, that would allow the speedometer to hit the magic speed without the car actually moving.





Answer



I think Back to the Future 3 offers an answer. While in the past and out of gas, Marty and Doc try to get the car up to 88 mph. Two of their attempts suggest that the car needs to be moving at 88 mph, and not just the wheels spinning at the same rate as if the vehicle was moving at that speed. They drag the Delorian behind a bunch of horses, and they push the Delorian in front of a train.


Now, treadmills existed at the time (Wikipedia says they're pretty damn old). Moving a car at such a high speed takes more energy than putting the car on top of a treadmill and just spinning its wheels. Doc possesses the knowledge and skill to have tried this, so I posit that he didn't try it because it wouldn't work.


There's something about moving at 88 mph that enables time travel, it's not just a matter of spinning wheels.



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