The Time Travel Paradoxes of Back To the Future

brumgrunt sent in a fun little piece to get your brain going on a cloudy monday morning. Despite countless viewings of BTTF I still never thought of a few of these. "Throughout Back To The Future Part III, there has to be two Deloreans in 1885. Also, why don't George and Lorraine recognize their son? Why doesn't the time machine disappear in the alternative 1985? These and more Back To The Future paradoxes explored..."

Comments

The one they always overlook

[elrous0]

If you travel back in time to the exact same spot, just in a different time, then (unless you're REALLY precise on the exact time of day and year), you'll most likely end up floating in space. People who make time travel movies don't seem to realize that the earth moves around its axis and around the sun. The spot I'm standing on right now will be vaccum in just a few minutes.

If Marty had went back to a different time of year without a space suit, Biff would have been the least of his worries.

Re:The one they always overlook

[simcop2387]

Even if you're precise on the exact time of day and year you'll still be in space. the solar system moves too!

Re:The one they always overlook

[mea37]

Well, according to Einstein's description of gravity this may not be such an issue as you think. The Earth's movements are, after all, governed by gravity. Now gravity doesn't so much "curve" an object's course, as it bends spacetime around the object's path (which is a straight line).

And you're here on the Earth's surface, so you're moving along the same line. You hop in your car, start deviating from the straight-line path by 88mph, and then... what, exactly?

Your post (and many people's intuition) assumes that you suddenly change velocity in all dimensions, so that you move in time but stay at a fixed position in space. The problem is, the concept of a "fixed point in space" is a figment of human imagination; there's no such thing. A fixed point in space implies a prefered frame of reference, and there simply is no such thing.

So what spacial trajectory does the time machine follow? Well, why would it not continue moving at 88mph deviation from the straight-line path through curved spacetime that it's already following - that being the same line being followed by the Earth?

Gravity would cause the time machine to "follow" the Earth as it moved through time. Not the Earth's gravity, as many other posters have suggested, but rather the Sun's gravity and the other various forces that move the Earth.

There are many, many, many problems with time-travel fiction, but the idea that you would be lost in space just isn't one of them.

Of course there are two DeLoreans

[rarel]

Of course there are two Deloreans. Doc's and Marty's. It's not a plot hole at all, the whole point is that they can't gut Doc's DeLorean for parts since it would create a paradox and prevent Marty from going back in time to 1885.

The cool thing is that at one point there are FOUR DeLoreans for a few hours in 1955, Marty I, Cowboy Doc, Marty 2 (with Doc) and Biff's.

Frame of Reference Problem

[eldavojohn]

I picture a lone Delorean, forever floating through empty space at 88 miles per hour.

I don't understand why you post first about a frame of reference problem and then joke about 88 miles per hour ... in reference to what? In the movies the DeLorean is traveling at 88 miles per hour as would be seen by an observer standing on Earth's surface. But to someone standing perfectly still in reference to the absolute center of the solar system -- as you seem to imply time machines are initially calibrated to -- then the velocity of the DeLorean would change with the velocity of the Earth around the Sun. Why are you only referencing the solar system and not galaxy or nebula or universe? So ... yeah, 88 miles per hour for those of us still on Earth many miles away. But your own post suffers the same problem that the movie suffers which is a frame of reference to the velocity and position.

Basically for new writers who write a science fiction time travel story you gotta make sure you mention briefly that you solved the orbit/rotation/surface problem and have calibrated your time machine to account for the ever changing topography of the Earth as well as its orbit and rotation ... Or maybe claim that you machine is anchored to Earth's gravity well to simplify things a bit more?

They were fun movies and nothing more. It might be fun to dissect them but if this is news, stand back in awe for my dissection of about a hundred other movies ...

Re:Frame of Reference Problem

[fat4eyes]

I don't even understand why this needs explanation. We all travel forward through time, and no-one needs an explanation of why we don't phase through the planet as time moves forward. Yet somehow traveling through time in a different direction (or at a different speed) will somehow cause you to end up in space. What needs asking is what does a time machine look like to the people in "normal" time when it is traveling backwards through time.

Re:Frame of Reference Problem

[maxwell demon]

I don't even understand why this needs explanation. We all travel forward through time, and no-one needs an explanation of why we don't phase through the planet as time moves forward.

Of course we need an explanation. Fortunately we have it: Because the matter below us causes a force on us (combined gravitational, elastic and friction), keeping us at "the same" place relative to the ground. For the very same reason there's no problem with H. G. Wells' time machine, because it's at its place all the time (he constantly sees the surrounding, just in another pace; of course that sort of time travel has its own set of problems, but that's another story), so it also should be subject to this force. However the time machine in BTTF (as well as the time machines in most stories/movies/series today) basically makes a jump in time, i.e. it simply isn't there in the intermediate times, thus there's no force which would keep it in place.

Of course one could argue that since "the same place at another time" isn't exactly defined anyway, the inventor of the time machine must have built in some calculation of the relative position of earth at the destination, and manages to move the time machine to exactly that place. However, that should enable you to not only choose the time, but also the place where you appear (possibly restricted to the future/past light cone, but that covers all of the earth for any reasonable time travel; of course if you only travel a microsecond, your choices of reentry are severely limited). There's absolutely no reason then to restrict the time machine to enter at the "same" place.

The universal answer to these questions

[FranTaylor]

Can be found in a "Rocky and Bullwinkle" episode from long ago.

Boris Badenof has just cut the rope on a large treasure chest that dangles over a cliff. Of course he is standing on the treasure chest at the time so they both fall together. In typical comic form the treasure chest inverts as it falls, so Boris is underneath it as it crashes to the ground.

Natasha cries out, "Oh Boris are you okay?"

Boris says in response: "Don't worry, tis only cartoon".

Remembering 'Calvin Klein'

[j-beda]

The article states: "Even appreciating that they didn't know 'Calvin Klein' for long, his impact upon them was such that they'd still have an idea what he looks like, many years later."

I think the author overestimates how much visual memory is likely to fade after 30 years. I just saw some high school classmates after 25 years and looked over some old HS photos. I could barely recall the linking between HS photos and names of the people I saw daily for over three years - including some I lusted after with all the strength of a stereotypical adolescent. Without photographic backup (did Marty get in any photos at the dance?) I doubt they could remember his look very well after only knowing him for a week or so. Combining this with later knowing Marty's face since birth and gradual growth, I do not find it at all implausible that they wouldn't recognize his as a teenager as looking like "Calvin".