Why Marty McFly will never truly ever be able to go "Home" again
There's been a lot of Back To The Future chatter amongst several of my FBBFFs lately, which got me thinking about the reality of Marty McFly's experience with time travel. You may have noticed that I'm a bit obsessed with higher order spacial dimensions and the quantum mechanics that govern them. I'm not going to pretend to understand the math that's used to define them, but I think I understand the basic concepts from a theoretical perspective. Based on this rudimentary understanding, I'm pretty sure that once Marty went back in time, he was, by influence of observation, continually entering into alternate 4th dimensional spaces that exist simultaneously within alternate 5D space. Furthermore, I think it's impossible for Marty to ever return to the original 4th dimensional space in which he existed before he started fucking about with time travel.
To start off, I don't actually believe that the 4th dimension is "time", at least not in the conventional sense. It was easier for me to conceptualize the 4th dimension when it was explained to me as infinitely adjacent and contiguous "freeze frames" of 3D spaces. When 3D objects move through the 3rd dimension we use time. But this is the same for 4D objects moving through the 4th dimension. Movement through any spacial dimension requires "time". So it's improper to assume that 5D objects would require leverage from a lower order dimension to move through their own space. This is similar to saying that 3D objects require the leverage of 2D space to move about. It doesn't make sense. This is why time is relevant. It's the imposition required for objects to move within their spacial dimensions, and extends relevantly across all higher order spacial dimensions. So when I refer to time, I'm referring to movement of objects through their spacial dimension, not the 4th dimension specifically.
So Marty McFly is a 3D object. His reality is based on his 3D perspective of his particular 3D space within a 4D space. A 4D object could observe Marty's entire 4th dimensional reality by using time to move around it, just as we can use time to move around 3D space to experience the realities of other 3D objects. The Delorean artificially mimics the abilities of 4D objects by allowing Marty to move to ajcacent 3D spaces. The problem is that Marty isn't actually capable of observing these adjacencies the way 4D objects can. He can only experience a single 3D space at any given time. The biggest disadvantage that Marty has against actual 4D observation is the ability to compare and contrast multiple 3D spaces within the 4th dimension. The implications make for great movies, but this is precisely why Mary can never go home again.
Let's identify Hill Valley, 1985 as a 3D space call 3D30 and Hill Valley, 1955 is 3D1, with continually adjacent 3D spaces in between. When Marty travels to 3D1, he didn't move adjacently, he skipped over several 3D spaces. Unlike actual 4D objects, who can see these adjacencies, Marty has no way to observe 3D spaces 2 through 29 as he moved from 3D30. Furthermore, the original version of 3D1 did not include Marty. Marty's existence in 3D1, by default, has corrupted the reality of 3D1, and by function of observation, Marty has moved in a 5th dimensional direction to an alternate 4D space, where it's possible for Marty to have existed in 3D1. Doc Brown explains this concept later in the BTTF2. But in my opinion, he makes two mistakes. First, he implies their influence on a particular 4D space could have been avoided despite having observed it, or that it doesn't already exist to begin with. And second, he implies that simply by going back and "fixing" a mistake, they can return to their original 4D space.
So what has Marty actually done? Well, instead of actually moving through a single 4th dimensional space, Marty is clumsily behaving like a 5D object. The biggest difference being that when he synthetically moves through 4D space, the influence of his observation creates alternate 4D spaces for his 3D perspective. A 5th dimensional object has the ability to look at 4D objects and see all 4 dimensions instantaneously, the way we're able to see length and width instantaneously. In other words, rather than moving through the 4th dimension to see the adjacency of 3D spaces, a 5th dimensional object sees the entirety of a 4th dimensional object without having to utilize time. A 5th dimensional object is capable of moving through 5th dimension spaces, comprised of adjacent 4D spaces. This is what Marty is actually doing. It's literally impossible for Marty to actually enter a 3D space that previously existed without him, without moving to an alternate 4D space for this new 3D space to exist with him.
In other words, Marty isn't just moving along various points on a line that starts with A and ends with B. Every time, Marty travels through "time", what he's literally doing is branching off to entirely different 5th dimensional realites. And it's impossible for him to return to the original 5D reality in which he existed for at least two reasons. First, he's not a true 5D object. Marty's movement to various 5D spaces is incidentally imposed on him, not a function of his ability to navigate higher order spacial dimensions. Second, his influence on every 4D space that he enters, permanently influences it. But in the end, this actually works to Marty's benefit. So hooray for Marty!
The End
