Max Tegmark has provided a four part taxonomy of multiverse theories (http://arxiv.org/abs/astro-ph/0302131). The first type can be labeled the "bubble universe" multiverse, in which universes like ours are scattered throughout an infinite space in every direction. Going the other direction, we have in the last century developed a good idea about the nature of the lowest level of reality - the realm of the quantum. There is of course much more to be learned, and much controversy exists over string theory and other theories that attempt to provide a reconciliation of quantum mechanics and GR, but we do seem to have reached in our theorizing and our experimentation the realm where the continuity we see all around us dissolves into discontinuity at the level of the very very small. A related and very interesting outstanding problem in physics concerns the discrepancy in strength between gravity and the other forces - a difference of about 25-38 orders of magnitude. As of now, it seems no one has a clue why there is such a huge discrepancy. If we live in a bubble universe, however, it seems we may speculate fruitfully about some of these problems. For example, might not our universe constitute a single quantum for a much larger universe? If this is the case, the strong and weak forces would be invisible from this level, as would EM, and only gravity would play a role. What would a universe look like if only gravity was operative? Further, could it be the case that other forces are hidden from our detection because we can't access the appropriate scale - whether above or below us in the grand chain of being?