Please forgive the following quasi-metaphysical bullshit.
Time is not the 4th dimension. The passage of time, while a dimensional experience, is purely an effect of biological perception. The physical universe incorporates both past and future; the universe, in essence, is a singularity. Within a 10-dimensional orbit of the singularity is the potential for all matter and energy. From a human point of view, all but the narrowest ~3.14 dimensions of space are hidden behind a dimensional horizon. That is why most matter is dark.
Let’s say, at the “beginning” of “time,” the universe is 0-dimensional. The “speed” of light is immediately set. From our point of view, it is the fastest it will ever be, and it will slow down continuously until the end of time. This is why the most distant galaxies are red-shifted; why the universe appears to be expanding ever faster. In fact, the speed of light is slowing down. At the “end” of “time” the speed of light will be zero. This is the boundary of our 10-dimensional universe.
If there is a multiverse in the sense of quantum potential, it is possible that only living awareness collapses it and makes it tangible. Life is a material process that proceeds away from the center of ‘creation.’ Thus in our lives time seems to pass, light slows and the universe seems to expand. Our consciousness “tunnels” through the 10-dimensional sphere of universal potential toward its limit.
It seems that matter and energy may only be the products of consciousness or awareness. In that case the quantum ‘multiverse’ is an immaterial fantasy and thus there is no need to account for duplicated mass or energy. There are no concurrent universes because we have no concurrent selves. Consciousness collapses wavefunctions and is not forked by them.
But there is a finite amount of mass in the universe, and a finite number of dimensions in which it can express matter and energy. The universe is singular. If anything it might seem to repeat itself in endless variations but it can’t run alternate states in parallel.