Does Doc Brown sabotage himself in Back to the Future 2?

Question

Back in 1955, Doc Emmet Brown is spotted by his past self as he is working on the cable in the park, at which point, the latter asks the unrecognizable white-haired man to "be a pal and hand my five-eighths wrench" out of a toolbox, to which future Doc Brown replies "Five-eighths? Don't you mean three-quarters?", with his past self realizing the mistake, Why, you're right.

The whole scene seems to imply (to me at least) that future Doc, realizing that was the reason why the cable snapped 'back then', tried to be indeed a good pal and helped past Doc by giving him the proper wrench.

Now after rewatching the movie I realize, that the wrench was used to adjust a bolt that could arguably have no impact on the outcome of what is to come, so which one is right?

1. The whole interaction is indeed harmless and will have no effect.
2. He gave himself the right wrench, but that was indeed the reason why the cable snapped.
3. He deliberately gave himself the wrong wrench passing it as good so that the cable would snap.
4. Is this just a plot hole?

PS: I do realize the movies never claimed to be hard bend on getting things right or being proper Sci-Fy, but given how well thought of a lot of the stuff is (in terms of continuity) I'd like to know if there is something to the scene considering how the Doc was so adamant in avoiding interactions.

Answer 1

Maybe I am missing a point to your question, but the wrench is a wrench, it either is good for the nut/bolt you use, or it is not. Ie. if the future Doc gave the past Doc the five-eighths wrench the conversation would probably look like:

Yes, be a pal and hand my five-eighths wrench out of that toolbox. {Fiddles with a wrench} Ugh, wrong size of course, would you please pass me three-quarters

In this sense

Yes, be a pal and hand my five-eighths wrench out of that toolbox.

Is just a sentence of someone who mistook the nut/bolt size.

Five-eighths? Don't you mean three-quarters?

Is a sentence of someone who remembers the actual nut/bolt size.

It is just a funny poke at the time travel.

Answer 2

Of the options you presented, I'd go with...

A) The whole interaction is indeed harmless and will have no effect.

In regard to your second option...

B) He gave himself the right wrench, but that was indeed the reason why the cable snapped.

... neither the wrench, nor the bolt it was being used to tighten, were obviously responsible for the cable disconnecting. The cable disconnected due to a tree branch that fell on it (as shown near the end of the first film), and that would've happened regardless of which wrench Doc handed to his younger self.

Also, why would using the right wrench -- as opposed to the wrong one -- cause the cable to disconnect? I don't follow your logic there, unless you meant that the cable was going to disconnect anyway, regardless of which wrench was used, in which case, I agree; it was.

In regard to your third option...

C) He deliberately gave himself the wrong wrench passing it as good so that the cable would snap.

... again, neither the wrench, nor the bolt it was being used to tighten, were obviously responsible for the cable disconnecting, so I don't see why Doc would think that handing himself the wrong wrench would cause that to happen.

It also doesn't seem likely that he did in fact hand his younger self the wrong wrench, because his younger self double-checked the bolt he was about to use the wrench on, and agreed that the three-quarters wrench was the correct one to use.

1955 DOC: Excuse me, sir. Yes, you with the hat.

1985 DOC: Who me?

1955 DOC: Yes, be a pal and hand my five-eighths wrench out of that toolbox.

1985 DOC: Five-eighths? Don't you mean three-quarters?

1955 DOC: Why, you're right.

In regard to your last option...

D) Is this just a plot hole?

... no, I don't see how this scene constitutes a plot hole, provided you interpret it the same way I do.

The way the scene reads to me, the whole interaction was entirely unplanned on Doc's part; he never intended to be spotted by his younger self, and simply forgot that his younger self was so close by. When he realised he'd been spotted though, he was forced to play along as best he could in order to avoid raising suspicion, until the opportunity to leave presented itself.

I don't think he wanted to change anything, in regard to the cable disconnecting or otherwise. And the likely reason he suggested using the three-quarters wrench, rather than the five-eighths one, is because that's what he remembered using in the same situation, and he wanted to keep everything the same as before, insofar as that was possible, in order to minimise the risk of a temporal paradox.

Answer 3

There was no "snap"

If you rewatch the original movie, you'll see that in both cases (up on the clock tower and down at the street post) the cable uplugged. Nothing was broken, it just came undone because the wire was taut from the branch falling on it.

Here is a movie prop showing the junction box that was used.

Back to the wrench...

A wrench is a wrench. Had Doc handed the 5/8 wrench, it would have been too small and not worked. It could not contribute to the "snapping of cable", as the diameter of a 5/8 wrench would not fit around a 3/4 bolt. All Doc-B did was save Doc-A a couple of seconds by giving the correct wrench the first time. Seconds which really didn't matter as there was no time-crunch this early in the process.

On the other hand...

Had the scene gone the other way, where the bolt was a 5/8 and Doc-B handed Doc-A a 3/4 it might have caused a problem. The 3/4 would fit loosely around the 5/8, and if Doc-A didn't go back to get the correct wrench, he could have possibly not correctly tightened the connector and stripped the bolt, thus allowing a wire that pops out from its connector.

But as shown in the movies, it was never a wire snapping/breaking. It was a junction where the two ends disconnected. Nothing to do with the wires themselves.

In the end, it was all just for comedy