Formally speaking, the multiverse is a “hypothetical set of infinite or finite possible universes that together comprise everything that exists and can exist” (Wikipedia). The premise of this theory is that in an infinite space, such as our universe, even the most unlikely and unimaginable events must occur somewhere, no matter how hard it might be to imagine conceptually. In fact, Tegmark remarks that it “is not whether the multiverse exists but rather how many levels it has” (Tegmark).
In addition, Tegmark has actually created a ranking system that consists of four different levels of the multiverse.
The framework for the first one is fairly simple, and accepted by most of the cosmological community. The level one multiverse is essentially one huge universe, and if you go far enough away from Earth in the level one multiverse, you should be able to find your twin.
The level two multiverse is a little bit more complicated than level one, granted that it should be. The idea behind it is that our level one multiverse is surrounded and enclosed by some sort of bubble volume. Now, try to conceptualize that there are an infinite amount of these bubble volumes, or level one multiverses, enclosed within another volume. That is our level two multiverse. This level two multiverse is so far away that even if you could travel at the speed of light, you would never get there, because the space between our bubble and its neighbors is expanding faster than the speed of light.
The level three multiverse is extremely multifaceted, even more so than level two. This level however does not add any qualitative multiverses. Instead, it is merely superimpositions of the same universes. One explanation in support of this relies on the natural outgrowth of the Many-Worlds interpretation in relation to quantum mechanics. Essentially, the level three multiverse explains that we only experience one out of an infinite amount of possible outcomes that could happen in our own universe. Thus, the level three multiverse explains that whatever can happen, will happen somewhere. However, quantum mechanics explains that each scenario is unique and will only happen once.
The fourth level of the multiverse changes everything. It says that universes can not only change location, properties, or quantum state, but the level four multiverse can also change the laws of physics that operate within them. This level four multiverse includes any conceivable universe.
To summarize, level one consists of different initial conditions, level two of different physical constants, level three, which adds the concept of quantum probabilities, and level four, which introduces new physical laws.
Just remember, that somewhere out there, you have a twin, who is reading this blog just like you, but rather, likes to be called Mr. President. Oh how I love the amazing possibilities of the multiverse.
For more information, see:
"Max Tegmark." Wikipedia. Wikimedia Foundation, 19 Feb. 2014.
"Multiverse." Wikipedia. Wikimedia Foundation, 20 Feb. 2014.
Tegmark, Max. "Parallel Universes."
"The Universes of Max Tegmark." The Universes of Max Tegmark. 20 Feb. 2014.