Well, the old 'balloon analogy' has done an excellent job of giving us some grasp of the basics of an expanding universe, so why not see if it could give us some degree of grasp of the basics of 'branes' and 'bounce' cosmology' as well. Here is an elementary graphic that I will try to utilize for such a daunting task. ;-)

Imagine that what you see above is the surface of a double-skinned hollow sphere with a gap between the two skins. The skins are two membranes (this is where the sci-jargon "brane" comes from) that are expanding like a blown double-skinned balloon with some air trapped in the gap between the two skins.

Also imagine that the outer surface of the inner skin is a 2-D rendering of the total 3-D space of our universe, with the observable portions indicated by a dark blue circle on that surface, with a radius equal to the Hubble radius R

_{H}.

The purple radius R is labeled Hyperradius, because it is the radius of a 3-D rendering of a 4-D spatial sphere (note, not 4-D spacetime). R is indeterminate is size, but from modern observations it is at least 10 times larger than the Hubble radius R

_{H}. Confusing? Yes, but don't despair, there is more confusion to come, but possibly with more clarity (hopeful, wishful thinking?) at a later cosmic time.

Radius R increases with time at a rate dR/dt where dt is a small increment in cosmic time. The rate of expansion is proportional to the Hubble constant, the latter given by H = dR/(R dt) in normalized cosmological units, i.e. per billion year.

The outer skin (Brane B) represents another 4-D (spatial) universe, very close to and parallel to our own, that also expands, but possibly at a different rate than ours. Note that '4-D spatial' here means 5-D spacetime, 4 spatial and one time dimensions.

Being 3-D spatial creatures, we cannot directly observe anything in the parallel universe, but indirectly we may just have the possibility of observing its effects on our own universe. If it exists at all! Interesting, isn't it?

Being already such a cosmologically large chunk to chew, let's break it here for today. Please don't ask very deep questions (if any), because I probably won't be able to answer them.

PS. This is not a personal theory, just a personal effort to try and wrap my own brain around branes - if you would excuse the irresistible pun.