we have introduced imaginary things like magnetic field as something real in the past, in order to find a missing link to explain interactions.

I'd very much like to know when this happened. As far as I know, the magnetic field was pretty much the first field to be understood as such, and a quick search only turns up papers about measuring and modelling complex (imaginary) magnetic fields. Is this something like virtual particles?

"threads of fate" or more provokingly "world lines"

I have mixed feeling about these. In fiction where you can actually go back and try again or see the future with some level of accuracy, there could be some compelling stories about following the causal chain and finding the lynchpin of something, or the far reaching implications of a decision, or even recursive causal chain building rapidly switching between making minute changes and massive paradigm shifts. There are definitely stories that do this, where a fate is defined and then fought against or worked around, but particularly when causality and worldlines get mentioned I see a different idea called "cannon events" that I really don't like. Where no matter what else happens this one person will die on a specific day, or the evil organization must be allowed to exist. It's a big cop out that says "the status quo is already the best it can be, don't go trying to change it". Sometimes that's just trying to justify why fictional Earth with time machines still has dictators and not a huge past interventionist problem, but other times it feels very arbitrary, like groundhog day but it's just accepting death by banana peel into train. It's less like a causality that can't be changed and more like being noticed by a vengeful trickster god.

I think a world defined perpendicularly to our understanding of time would either have any changes fully integrated into the past and future (which could be a huge writing load in fiction) or have massive seams where one causal chain encounters another. The boundary between these areas might even be fraught with sudden energetic bursts, like solar magnetic field reconnection.

In everyday life though, I don't think strong causal chains vs chaos means much. Both mean there's something out of our control, and if we can't change that it doesn't matter why. Maybe there are great causal chains fixing the future in place, maybe the future is chaos becoming what it may, either way what happens still happened. A universe on rails or on dice doesn't change how we live, how we struggle, or the choices we make, it's our limits and eachother that define the space in which we cause change. Where that chain of causes started doesn't change that we're in it.

That's so many ungrounded thoughts and opinions though! The topic of this comment thread has changed like 7 times, I'm just having fun at this point. =D