Wow. There's a lot to respond to in this one.
First of all, yes, it is a quiet forum at times. But please keep posting your thoughts and questions and you will certainly help to raise the energy level.
Second, when you ask for "clarity", all anyone can provide is speculation. There are no existing experiments that can determine the validity of any of these theories.
When it comes to parallel universes and multiverses, these concepts can mean many different things and, unfortunately, some people use these terms to mean something completely different than how other people use them, despite both sets of people being reputable physicists, mathematicians, philosophers, etc. Look up Max Tegmark's definition of different levels of Multiverse for more information. However, he actually misses out on some forms that are possible. I would also refer you to Chapter 2 of my book, in the section on metaverses and multiverses.
Here are some examples:
1. The Everett interpretation of Quantum Mechanics says that every time a quantum mechanical decision is made, the universe forks into two different universes - one with one result of that decision and one with the other. This was an alternative to the "Copenhagen interpretation" that invokes the concept of a collapsing wave function in order to explain how probabilities become events. However, given that quantum mechanical decisions are made on every sub-atomic particle continuously on a frequency of the order of magnitude of 10E43 Hz (inverse of the Planck time), and that the number of universes spawned is not simply linearly proportional to those factors, but exponentially proportional to those factors (e.g. over 10 Planck intervals, there would be not 10 but 2^^10 or 1000 different sequences of states of a particular subatomic particle), the number of existing universes in this "many worlds interpretation" (MWI) is astounding!
BUT NOT INFINITE! (As should be clear from the mathematics. The concept of infinity in mathematics is actually quite complex. For example, there are such concepts as "countably infinite", "infinite", "potential infinity", "actual infinity", and "the limit as a number approaches infinity." But anything that has a starting point and grows exponentially is theoretically finite.)
In any case, these universes exist in a theoretical space called the Hilbert Space, and it is theoretically impossible to travel or communicate between any two universes in this space. You can search the web for estimates of the number of universes in Hilbert space and may find widely different ones. One such estimate is 10E296460 which can be found here:
http://www.thefoggiestnotion.com/how_many_universes.htm. In comparison, by some estimates there are 10E79 atoms of hydrogen in the universe, a number that would be 10E296381 times smaller than this estimate of the number of MWI universes.
2. There is also the idea that if space is truly infinite or even sufficiently large but finite, then there are an uncountable set of configurations of atoms, which means that every (infinite case) or most every (finite case) conceivable universe must exist somewhere. This is the kind of multiverse that you seem to be referring to, which Max Tegmark refers to as the Level 1 Multiverse. Again, according to current theories, even if the metaverse is infinite, you can't travel between these "local" universes due to limitations of relativity. I refer you to the "Hubble volume" of space described in my book, which is generally accepted to be about 42 billion light years in diameter. The problem here is that the idea of space being either infinite or sufficiently large to have near duplicates of yourself is a BIG assumption, by no means true or even supported by any existing cosmological theory.
3. The idea of fractal universes comes from Stanford physicist Andre Linde, who postulated that the universe expands in a fractal manner, with bubbles of inflation sprouting other bubbles of inflation, each one being a new “big bang". See page 61 of my book for a more detailed explanation. In terms of traveling or communicating between any of these universes, the problem here is the same as the issue in multiverse type 2 above - that because of the speed of light and Hubble volumes, we can never communicate between universes.
Having said that, if the speed of light is not a true physical limit, it might be possible to communicate between universes in Metaverses types 2 and 3 above.
4. What if there are parallel universes in different dimensions, a concept described mathematically, but not based on any known ideas in science? Imagine the concept of sheets of paper, collectively comprising a 3-dimensional structure, where each sheet of paper is a universe in a 2-dimensional space. The content or objects written on the paper would be the inhabitants of that universe. But those objects could not communicate between different sheets of paper, or other 2-dimensional universes. Perhaps we live in a universe that is parallel to others in this sense. There may even be some as yet unknown physical process that allows inhabitants of one universe to "tunnel" in to another one. See type 5 below for just such a model (but I am using type 4 here to consider non-programmed reality types of models.)
Don't confuse what string theorists say about our reality consisting of 10 or 11 dimensions as being these kinds of dimensions that hold parallel universes. What string theorists are talking about is the idea that these additional spatial dimensions are tiny "curled up" ones within the existing universe.
5. I don't for even a minute imagine that the concept of a "server" described below is remotely close to the computational mechanism that might generate our reality, but consider the following scenario:
Think of our reality as a video game, running on some server. Our bodies are our avatars. Our consciousness is elsewhere, but controlling our avatar's every action, as other consciousnesses control the other avatars with which we interact in this "apparent" reality. This is very similar to the model of the many MMORPGs (massively multi-player role-playing games) that people play today. Now imagine that there are other servers, containing other sets of avatars which other consciousnesses control in separate realities. These realities, also called universes, exists in parallel, in what we might call "server space". It doesn't even have to be physical servers, as "instances" of realities could all run in parallel on the same physical server. Whatever the case, these universes may be forced to be completely inaccessible to each other. On the other hand, the "Programmer" may very well provide mechanisms that allow a player in one universe to travel to another, or even to experience some aspect of another universe. In today's computer systems, such mechanisms are well defined and easy to program. Consider methods called IPC (inter process communication), such as shared memory, messaging, or semaphores, that make it possible to interact with other universes. It would be like have a World of Warcraft player whose universe of users is on server ABC having the ability to "tunnel" into server XYZ to interact with XYZ's users instead. All completely possible today, all completely possible in a Programmed Reality model.
The rules of interacting between universes may be set in stone or continuously variable by the Programmer. It is up to us to push the envelope in terms of implementing reality experiments, in order to determine if any of these multiverse concepts hold water.
My bets are on #5.
If God is defined as the "Programmer," I would postulate that the multiverse would have to be finite. To me, infinite means no creator and really makes little sense. It is maybe just a concept to capture the frustration of humans in attempting to imagine sufficiently large numbers.
A finite universe neither implies a creator nor a lack of one. However, for many of the reasons outlined in my book, it only makes sense that there is a creator, and that its creation is finite.
Hope this makes some sense! :)
