A: They all are—partially. Each one sees only part of the truth, and not the whole of it. Each has grasped onto a portion of reality and called it true, but none have seen the whole picture. Unfortunately, none of them can [see the whole picture] as long as they remain corporeal (in the physical world).
For to measure time (truly measure it), do you need to be outside of it, and to be outside of it, do you need to be outside of the physical world. To see the reality of physical space, again, do you need to transcend physical space, which you cannot do while occupying physical space.
Membranes (branes), big bangs, sine waves, singularities, black holes, expansions and contractions of the universes, these are only partial understandings of how your physical world works. Each is true inasmuch as it describes the perceptions of those doing the exploring; however, when combined it would show a more comprehensive, though still incomplete picture of your reality.
Are there multiple realities (multiverses), yes. Are there strings and particles, yes. Are there membranes, in a fashion, for each universe, each reality floats in its own frequency range or membrane. Is time and space flexible, of course, because time, space, and all of reality are whatever you (all of you) want it to be.
If you want particles, you see particles. If you want waves, you’ll see waves.
Q: What about the contracting and expanding of the universe that they have measured and observed?
A: The Tao, the All, created a reality based on a thought. In your minds, that reality appears to flow outward, expanding like a fan from a single source. This is your perception, it is neither right nor wrong, it is merely how you try to explain your world.
At moments of choice, alternates are created (existing within different frequencies or “branes”), and that is the expansion that you see; that is the expansion that you experience. As those choices conclude; as those paths finish, will they collapse back into the one from which they originally branched. When all the choices but the one with which it all started have finished, will it appear as if the universe has contracted. And once that one path, that primary path created by the thought of the Tao is no longer needed, wanted, or viable, then it, too, will return to the Tao and there will be no paths, no reality, no universe.
Will this happen in a time soon to you? No, for the Tao is still growing; you (all of you) are still growing; and the paths and choices are still infinite.