  The multiverse is a hierarchy in the number of universes, increasing stepwise
towards infinity. It is an evolutionary system, in which universes survive only
near critical mass. That mass is actually a factor of 1.94 less than the
critical mass, and this is found to be consistent with the baryon density
inferred from nucleosynthesis in our universe; it is also precisely verified as
a cosmological effect. That factor seems to have originated in the multiverse
for causing intersecting expansions of its universes, such that mixing occurs
of debris from aging galaxies (over proton-decaying time scales). It follows
that there is an inter-universal medium (IUM), probably having the demand of
new universes in balance with the supply of dark radiation and sub-atomic
particles from the decaying galaxies. The mixing causes the universes to have
the same quantum, relativity, gravity, and particle physics as our universe.
The making of a universe from the radiation and sub-atomic particles occurs
through re-vitalizing the protons, and other particles as well, by
gravitational energy obtained in accretion of the IUM. This process therefore
begins wherever the IUM space density reaches proton density, near 10 E18 kg m
E-3. The process continues quietly as the sweeping-up and gravitational
accretion proceeds, until the near-critical mass is reached. Some of the IUM
debris must also be pervading our present universe, steadily or in partially
accreted lumps. The model therefore predicts that the IUM sub-atomic particles
appear as our dark matter, and its radiation component as our dark energy, both
near 0 K temperatures. The dark energy may cause expansion phenomena, in
addition to the above non-flatness expansion, from an accretion lump that
arrived at our universe at age near 9 x 10 E9 y.
