Our observable universe consists of a calculable sphere with the earth precisely in the center. This is also called the Hubble volume. This sphere extends out to the surface of last scattering, which is the furthest observable surface that is causally connected to our point in the universe.
Anything about the multiverse beyond the surface of last scattering is conjecture. However, we *can* prove that our region of space is relatively homogeneous and flat (i.e. space-time around us largely conforms to a euclidean manifold).
Since geocentrism has proved a fallacy in the past, there is no reason to assume our observable universe is any different from any other reference frame. It is realistic to assume that the principle of general covariance applies to the Multiverse as a whole. What this means is that every observable Hubble volume of the multi verse should be equivalent.
Since we have all but discounted a closed universe, that means the Multiverse has to be infinite to preserve the principle of covariance. The real kicker is that this means that there have to be an infinite number of non-overlapping Hubble volumes in the Multiverse (infinity does crazy stuff). Since the state of our Hubble volume can likely be described in finite terms (there is only so much energy/mass contained in the volume), that means there are an infinite number of other Hubble volumes in the Multiverse that are in *exactly* the same state as our own. Every past, current and future state of our observable universe has already occurred elsewhere in the Multiverse.
Considering our latest study of the CMB we have all but proven the universe is open (probably flat) and homogeneous. That means one only has to apply Occam's Razor to the principle of covariance in order to arrive at the conclusion that there are an infinite number of instances of you reading this email in the Multiverse!