Back to the Future III - alternate 88 mph methods

Remember how Doc Brown got the DeLorean to 88 mph by pushing it with a train running on coal and “booster” logs? It makes me wonder what other realistic methods could be used to get a car’s wheels to spin that fast, considering the limitations of the 1700’s (pretty sure it was the 1700’s…).

How about using that big laboratory/barn he had to set up some kind of roller system that the DeLorean could sit on? The rollers (made of wood, I suppose) could be powered by some sort of pulley system, using some other force for power (like a coal-powered crank shaft). Wouldn’t the right kind of power transfer make this method successful? What other ways could it have been done?

Hmm… How high was that one cliff? Might be a little risky, but they could’ve wheeled it to a really tall cliff, got in, and had someone shove it off the edge and let gravity do the work.

Actually it was the 1880’s. There weren’t photographs in the 1700’s, among other things.

They could have attached a small steam engine to the DeLorean itself and aimed it down a long straightaway on a mountain.
Or, they could have built a gunpowder based rocket and attached it to the DeLorean and then used the railroad tracks for control.

It was 1885.

Wasn’t the only problem with the DeLorean that it had run out of gas? If Doc had the chemistry knowledge to make those ‘booster’ logs, couldn’t he have taken some petroleum and refined two or three gallons of gasoline? It wouldn’t have to be very good gas, just enough to get the car to run.

I only saw pt 3 once several years ago so I might misremember the problem.

Yeah, then when they arrived in 1985 they’d still be in free-fall. Unless you mean rolling it down a canyon wall. They mentioned this, but they said they’d never find one tall and smooth enough. Then they thought about waiting for the lake to freeze, but they had to time travel within a few days.

That’s the big constraint. They accidentally blew out the engine using some makeshift gas (some kind of liquor), and Doc said it would take him a month to fix it. So brewing up some petroleum might have been an option if they had more time. He already had the logs ready-made; he said that he used them in his own personal furnace. Remember, he was a blacksmith.

This is all from memory, though, so I could be misremembering something.

Alternatively, he could have hitched it to a team of horses and applied chili-pepper suppositories all around.
Well, maybe not to Marty.

No, on second thought, especially to Marty.

That wouldn’t make the wheels spin, or the speedometer needle rise, which was how the car time-travelled.

Mechanical Engineers: could my roller idea be applicated, or is 88pmh too much to ask for?

After Marty went to 1885, wouldn’t there be two DeLoreans? Doc had the car in 1885 and hid it in the mine. Marty pulled it out in 1955 and drove it back to 1885. So wouldn’t there be two of 'em in 1885 - the one in the mine and the one Marty drove back? Why not use the other one?

I’m assuming that that’s how Doc turned the train into a time machine - by using the parts of the DeLorean in the mine - although its never actually stated.

The required speed of 88 mph leads one to ask, in what reference frame? The only sensible answer consistent with the movie is “the rest frame of the dominant source of local gravitational potential”, i.e., the Earth. Which further suggests (not definitively, just suggestively) that the horizontal component specifically had to be 88 mph. So dropping it off a cliff wouldn’t work, even if you could solve the problem of the sudden stop at the end. You might be able to use a steep hill that rounded off to level at the bottom, but it’d have to be awfully steep to have a terminal speed that high.

If Doc had salvaged parts from the DeLorean in the cave, then it wouldn’t have still been there for Marty to find. But then again, the movies were rather shaky on acausal continuity issues like that. Certainly, though, Doc could have used the hidden parts as models to re-build new parts.

And if it was just a matter of moving the spedometer, then why bother moving the car at all? I think that the spedometer’s only value is as a meter to tell you when it’s about to get to speed, just like the spedometer on a normal car.

And no, I don’t take time off from being a physics nerd. Why do you ask?

Psh. Doc could have rebuilt the Dolorean from memory if he had the parts. I think you underestimate his knowhow. Recall that he was able, in 1885, over the course of eight months, to assess the damage done to the time circuits by the lightning bolt, and design a vacuum-tube-based repair system using parts that wouldn’t be invented until 1947. This is no two-bit scientist you’re talking about. :slight_smile:

Best bet would probably to locate a long downhill railroad line, haul the DeLorean up to the top on a horse-drawn wagon, put the car on the tracks, get the horses to pull it at full gallop to build up some speed, release the horses, continue rolling downward and hope it’s steep and smooth enough to let you get 88 mph.

And also hope this rail-line still exists in 1985, or it’s gonna be one unpleasant arrival. Safer bet would be to skip ahead only 30 years or so to 1915, when gasoline and basic combustion engine parts were available, but probably before the area would be built up enough for this rail line to be torn down and replaced with something else. Once the DeLorean’s fuel system is fixed, you can finish the trip to 1985.

That was originally the case. However, in attempting to run the car on alcohol Doc broke some part that he said he couldn’t replace, for whatever reason (maybe something in the fuel injection system, or did DeLorean’s have carbeurators?)

But yeah, I thought the same thing. But frankly I don’t know what the heck is involved in refining oil to make gasoline, it might require very large batches to get the necessary energy to start a reaction, or some other such obstacle to just whipping up a few gallons in the barn. He also would have had to find some way to defuse the impending situation with Mad Dog Tannen, who was going to kill him on Monday, long before he probably could have arranged such a feat.

I understand the speedometer is only an informational device, I was just saying that it wouldn’t change (I suppose it was unnecesscary to mention)

Is it just for the sake of saving an explanation that time-travel laws in entertainment don’t account for the likeliness of, if a person were to travel through time, appearing millions of miles away from the earth? I’d say your position when you start and end your time-travelling would be dependent on your position in space rather than on the earth.

Of course, at the end of BTTF2, the DeLorean travels from 1955 to 1885 while hovering, relatively stationary; the impetus provided by a lightning strike instead of 88mph travel in any direction.

Go figure.

How exactly would you plot your locations before and after in an expanding universe? According to your position in the stretch, or where you were from the beginning, on a sub-level from the following position?

Why couldn’t Doc just write another letter to Marty saying “Forget my last letter, come me back and rescue me, and be sure to bring a spare tank of gas!”? It might end up in an alternate timeline, but surely there’s a Marty with a time machine in that timeline too.

But it left a sort of curly fire trail in the sky. According to the DVD commentary, when the DeLorean was hit by lightning it spun around in mid-air, parts of it reaching 88 mph. :rolleyes:

Nope. Obviously, you did not listen to the director’s commentary. Tsk tsk. The impact of the lightning strike caused the DeLorean to spin about its longitudinal axis, achieving a circumferance velocity of 88mph. That’s why the fire trails in the sky go in a spiral.


If they dug up the DeLorean that Doc hid, then Marty would not have found it in 1955, and would have never gone back to 1885 to star in BTTF 3.

Time travel paradoxes are fun.

Oh, and on a less paradoxical note, there was also the fact that some parts of the DeLorean in the mine were destroyed by the lightning strike when it went back to 1885, and could only be fixed by 1955-Doc, who had access to 1950’s technology.

Wait wait wait. Refresh my memory please. At the end of 2, doc is hovering in the DeLorean in 1955. It gets struck by lightning and goes back to 1855. Then Marty receives a telegram that is a hundred years old. Where did Marty find the DeLorean in 1955? I honestly don’t remember.

If he found it in a place that Doc had hidden it, and went back to 1855, sure there would be two DeLoreans there at the same time. There would have to be, because otherwise it wouldn’t be there for Marty to find it in 1955.

But since by that point it hovered and ran off of garbage (Mr. Fusion) I don’t see the need for gas at all. That was just kind of gleaned over in the movie.

I posed the gravity question to a friend, but was immediately shot down. Sure, you would reach 88 mph and time travel, but on the other side you would still be falling and would still crash into the ground.

I always thought that the car had to go 88 mph, not just the wheels or the speedometer.