Not necessarily. The standard theory is that there is one expanding universe and that space and time as well as energy all began with the Big Bang. Under that strict cosmology any multiverse would not fit. But the Inflationary Theory of Guth that accounts for the superluminal inflation of space at the first instant after the Big Bang has opened the door for theoretical twists. Guth discusses bubble universes and the similar Eternal Inflation with patches of space inflating faster or slower than others that form due to perturbations in the energy density of the early instants of expansion are both multiverses. In String Theory there are an almost infinite number of possible universes that Susskind refers to as the Cosmic Landscape. So my answer is not necessarily.
The Many Worlds interpretation of Quantum Mechanics is a perfectly viable metaphysical theory that can be used to conceptualize why QM works (or appears to work from our perspective) in the way it does, and that requires many universes to constantly be springing into existence. In fact it would not even make sense to call them "other" universes in every case, since you and I and everything we know are there already in many of them. Unfortunately there is no was to "cross over" into the other universes under that theory since the various universes spring into existence not "parallel" to exch other (in which case moving into a new universe can be likened to lanes on a roadway, and crossing over akin to changing from one lane t the next), but rather they are orthogonal to one another. To continue the roadway analogy, the universe comes to a dividing point, splits in two and one universe goes left, and the other goes right. You can't get into the "left" universe from the "right" one because the two parted completely back at that intersection.
Well I have a LOT to learn first. I need to get a Ph.D mathematics, then physics, quatum physics, and possibly astoronomy and right now I'm only a senior in high school.
