One explanation that is popular in today's information age is the idea that the universe is like a big computer simulation game where people like ourselves as the players. Under such a model there might be two sets of timelines: the order of interactions of the choices being made by the players and game designers; and the made up history which might have a basic outline written into the game code but with extra historical events being added during the course of the game. Under such a model the imaginary values might relate to probabilities of possible events within the game.
Another assumption we might make is that the universe is real and complete with all parts fitting together but we we need to use imaginary numbers and probability theory to model the extent of our ignorance. Thus the models used by us show our knowledge of the universe but the actual universe could (with complete knowledge) be modeled completely with definite precise real values.
However, there is some evidence that models (even mathematical ones) can only ever approximate reality.
The topic of "indetermination" studies the extent to which mathematical models (or the understandings of human observers) can represent the complexities of real-world situations.
The verdict seems to be that no matter how closely we try to make our measurements we will always encounter limitations which prevent us from getting total assurance or100% accuracy in our measurements or a totally complete description of the thing we want to describe. Even our choice of lexicon can determine what can and can't be said about a situation.