For a long time, Back to the Future, Part II was my favorite movie of the trilogy. It was only with time and multiple viewings that I realized how bad it is, and how good the first one was--even Part III was more internally consistent. Here's why:

[NOTE: I'm assuming everyone in here has seen the movie. If you haven't, and wish to, read no further.]

When the Biff of 2015 steals the time machine, not only does he figure out how to use it with apparent ease, but he comes back to 2015 without a hitch (well, until he presumably dies after getting out). Yet, when Marty and the Doc go back to the "altered" 1985, and Marty suggests going back to 2015 to stop Biff from getting the book, Doc tells him that they can only go forward to the future of the alternate 1985. If so, Biff should have been *equally* unable to return to Marty and Doc's "good" 2015; indeed, they would have never gotten the time machine back at all.

Just some before-work nitpicking.

__________________
"Call me old-fashioned, but I think fire is magic. And it scares me a lot."

--The State

As fun as they are, the Back to the Future movies only work by repeated application of the Mystery Science Theatre 3000 mantra.

"If you're wondering how he eats and breathes and other science facts
(Lalala)
Then repeat to yourself 'It's just a show, I should really just relax'"

__________________
Carl Matherly

Offical Battlestar Galactica Apologist

Named Time Magazine's 2006 "Person of the Year"

It is easy to work that particular time machine - I mean the controls are all labled and everything. The only tricky part might be getting up to 88, but even someone like Biff could figure out "go faster until it works".

The timeline in the Back to the Future movies takes time to adjust to changes. Marty doesn't immediately disappear when he takes his dad's place in meeting his mom in part I - it takes most of the movie for that to happen.
Presumably the changes Biff put in place in 1955 took time to "filter" down through the timeline to 2015, allowing Marty and Doc to go back to 1985 before everything changed completely.
Hey, it's time travel. Nobody knows how it would really work.

__________________
"You miss 100% of the shots you don't take" - Wayne Gretzky

Hey, it's time travel. Nobody knows how it would really work.


Oh! Oooh! I do I do I do!!! :waves hand excitedly:


...it wouldn't. But that's boring, and nobody would want to see a time-travel movie about how they can't really time travel.

__________________
I'm like one of those idiot savants...well, except for the savant part.

Theory of Zombie Relativity:
1) Everyone Else is a Zombie relative to You
2) Whether or not it matters is related to the inverse square of the distance between their teeth and your brain
(Quoted from Demigrog)

Doc: "If my theory's correct, when this baby hits 88 miles per hour, you're going to see some serious s@!#."
The radio-controlled DeLorean accelerates straight towards the Doc and Marty, with Einstein visible in the windshield.
Marty starts to edge away. Doc looks at him and he steps back.
The car is getting closer and going faster. The flux capacitor lights up behind Einstein.
Marty again steps away from the Doc. The Doc grabs his arm and pulls him back.
Doc: "Wait for it!"
Suddenly the DeLorean smashes into Doc and Marty, throwing them up into the air and hurling them to the pavement of the Twin Pines parking lot. The DeLorean continues on to crash over the concrete barrier and then flip over. It's fuel tank explodes, rupturing the nuclear plant and showering the area with fall out.
As Doc Brown lies dying from his injuries and radiation exposure, he looks over at Marty's twisted form.
Doc: "Well. I guess time travel isn't possible after all."

The End

__________________
"You miss 100% of the shots you don't take" - Wayne Gretzky

@ Jason, Hahahaha, I LOVE it! ...Though I have no gripes with the original, I think this way is just a good.

__________________
I'm like one of those idiot savants...well, except for the savant part.

Theory of Zombie Relativity:
1) Everyone Else is a Zombie relative to You
2) Whether or not it matters is related to the inverse square of the distance between their teeth and your brain
(Quoted from Demigrog)

I think you're looking too hard for nits; there are many other much more fundamental problems--if you even get past the idea of time travel itself.

Just start with the whole 88mph thing; in south California, the Earth's rotation alone means the Delorean would be going 800mph all the time--to say nothing of Earth's movement around the sun, the sun's movement in the galaxy, the galaxy's movement, etc. Which brings us to fundamental problem #2: if you went back in time, Earth would be in a totally different place, yet the Delorean somehow winds up in the same geographical location.

__________________
Do try not to take me too seriously.

Never mind the fact that Marty and Jennifer instantly travel 30 years into the future, but are still apparently somehow living their lives, so that Marty can meet his future son and Jennifer can meet her future self. How does that work? i.e. In the initial DeLorean test, Einstein didn't jump 1 minute into his future and meet his future self... but then Doc didn't send him back, either.

If the future Marty/Jennifer are the same Marty/Jennifer that had already experienced the subsequent events of the alternate '85 and trip back to 1885 (well, Marty, anyway, since Jennifer was out cold for all of that), then wouldn't at least Jennifer expect to meet her younger self on that day, or Marty Sr. know not to fall into Needles' ill-defined corporate scam (assuming Jennifer passed on what few details she learnd of it to Marty)? That, in and of itself, would seem to make the timeline inviolable, by virtue of the fact that any time-travel events were already, and always will be, part of the timeline. This would then invalidate the central premise of the series: altering the past to one's detriment (Marty) or benefit (Biff).

__________________
"Earth diameter is 7,900 miles, and Moon diameter is 2,160 miles. It takes on average 90 minutes to complete one Earth orbit, so one Moon orbit should take roughly 25 minutes." - Sam "NasaScam" Colby

Bearer of the highly coveted "I found Venus in nine Apollo photos" sweatsocks.

DataCable^2008 A+

It may just be gravity, so that even when timetraveling the car can't go up the well.

As for the speed needed, perhaps it is important that the speed is somehow relative to the earth... Maybe there is a sort of timelike counterpart to escape velocity, so that there is a minimum rate for effective timetravel(or else you just drop back to the same time), and that when the fluxcap kick in it somehow switches the car's spatial velocity relative to the earth over to time velocity along the propper dimension(s)...

__________________
Game over, you lose, we hope you enjoyed playing the exciting game of Thermodynamics...

Re DataCable:
<<Never mind the fact that Marty and Jennifer instantly travel 30 years into the future, but are still apparently somehow living their lives, so that Marty can meet his future son and Jennifer can meet her future self. How does that work? i>>

Thats bugged me, too.

Re Jason:
That movie is just waiting to be made...

<<The timeline in the Back to the Future movies takes time to adjust to changes. Marty doesn't immediately disappear when he takes his dad's place in meeting his mom in part I - it takes most of the movie for that to happen.>>

That's an idea...it's sort of reminiscent of an old Robert Silverberg story, set in a world where time travel is so easy that people can--and do--travel back constantly to alter the present to their own benefit. The main character is being persecuted by someone who keeps changing his past, and hence his present--his only trump card is that when the universe "switches" he can remember the old one for just a minute or two.

Thanks all for the replies. For the record, I still love the movies (though Part III hasn't grown on me yet); I guess time travel being my favorite SF "sub-genre" makes me pickier than I otherwise would be.

__________________
"Call me old-fashioned, but I think fire is magic. And it scares me a lot."

--The State

Ah, then you're probably familiar with "A Sound of Thunder"...a prime example of how you take something so elegant and beautiful on paper, and turn it into...well, typical Hollywood fare, not fit for 3am sci-fi channel slots (though, that's where it landed anyway).

__________________
I'm like one of those idiot savants...well, except for the savant part.

Theory of Zombie Relativity:
1) Everyone Else is a Zombie relative to You
2) Whether or not it matters is related to the inverse square of the distance between their teeth and your brain
(Quoted from Demigrog)

I am reminded of Arthur C. Clarke's use of "Bradbury's Defense" in "Imperial Earth":

"One dreadful boy ran up to me and said:
'That book of yours, The Martian Chronicles?'
"Yes," I said.
"On page 92, where you have the moons of Mars rising in the east?"
"Yeah," I said.
"Nah," he said.
So I hit him.

The Ray Bradbury Theatre did a much better job, naturally.

There's also the Clancy defense (which he used on Alt.Fan.Tom-Clancy):

"guys, it's *fiction*." (I think the question was something about how Red Rabbit had two real-world events happening the same year when they happened a few years apart).

__________________
-----
Todd (Bowie, MD, US, North America, Earth, Sol System, Vega region, Local Bubble, Orion arm, Milky Way Galaxy, Local Group, Virgo A Cluster, Virgo supercluster, the universe in which spock is clean shaven)

Quidquid latine dictum sit, altum sonatur.

personal page: http://blog.astrosketches.info

I strongly believe that well-thought-out fiction is better fiction than poorly-thought-out fiction. Generally, the more fantastic it is, the more thinking-out it needs.

However, stories about time travellers changing the past cannot make narrative sense*. No matter how hard you try, there will always be a hole somewhere in the plot**. So the art is to cover that hole as well as you can.

Romanus, the fact that you were able to enjoy the film repeatedly before noticing the hole suggests it was hidden well. I must admit I spotted it immediately, but I have read a lot of time travel stories! Certainly the plot holes in BTTF are a lot less distracting than in most time travel films; that, and the fact that the action is done so well, are good reasons to love 'em!

*Stories about time travellers who cannot change history can make narrative sense.

**Offhand I cannot actually remember spotting the holes in the other two films but I'm sure they're there.

"*Stories about time travellers who cannot change history can make narrative sense."

"By his Bootstraps" by Heinlein--fits together like a jigsaw puzzle!

__________________
-----
Todd (Bowie, MD, US, North America, Earth, Sol System, Vega region, Local Bubble, Orion arm, Milky Way Galaxy, Local Group, Virgo A Cluster, Virgo supercluster, the universe in which spock is clean shaven)

Quidquid latine dictum sit, altum sonatur.

personal page: http://blog.astrosketches.info

Actually that sounds like a fantastic setup for a modern day Waiting for Gadot. Two characters are inventors trying to invent time travel, and they never succeed. Even if some might find it boring, at least it hasn't already been done to death.

Primer. I don't know of any time travel related plot holes, though it's hard to say whether it counts as changing the past if you're only repeating the same day.

I have seen that. Can't say I enjoyed it. I found it very hard to follow, but if it was saying what I think it was saying, it was a pretty standard time travel story presented in an obscure manner.