okay, on the common everyday macroscopic scale, matter and existence could be considered “absolute”… in other words, if we see a ball bouncing along the street, you can turn around and reasonably expect it to continue bouncing behind your back… and conventional Newtonian laws (as well as extended Einsteinian/relativistic laws) of physics would apply without fail…

however, on the subatomic or quantum level, matter and existence are not so absolute… for the simple reason that any attempt to observe them affects the outcome… that is, since the act of observation (where light is made up of photons) is on the same subatomic scale as the bouncing particles you are trying to observe in the first place, those photons would hit/interfere/affect the “certain” outcome of those particles (hence, the “uncertainty principle”)…

using the “bouncing ball” metaphor, if you tried to see the ball, this time, you would only observe an infinite fog of possible bounces and paths, where nothing would be certain… since direct observation is impossible in ascertaining the absolute state of particles, they are described (for lack of a better way) in terms of mathematical “probabilities”… in other words, if one outcome/existence cannot be ascertained, then ALL outcomes/existences must also exist (in terms of probabilities)…

inevitably, such a titanic contradiction between these two contradictory descriptions of the universe (macroscopic vs. quantum) even rattled Einstein and gave birth to his famous anti-quantum exclamation: “God doesn’t play dice with the universe”… consequently in the decades since, one attempt to resolve this seeming contradiction is the “many worlds” or “parallel universe” theory/interpretation…

in a nutshell, it allows for the “certainty” of an outcome on the “observable” macro scale, while simultaneously permitting the “uncertainty” of probabilities on the “unobservable” quantum scale… in other words, while we live in one “ascertainable” universe, ALL other parallel universes must also exist as probabilities…

but one thing that most profoundly emerges from this interpretation, is that the nature of the universe is suddenly and undeniably dependent upon the role of human observation/consciousness/awareness and its power to define an outcome/existence/reality…