@jojo @Edgemo A small explanation on multiverse theory within Quantum Mechanics:
Wave/particle dualism is NOT the source of many-universe theory within Quantum Mechanics.
TL;DR: “Many universes” arise from the concept of “measurement” in Quantum Mechanics, in which every possible outcome of an experiment is realized in its own universe. Different universes created in this way have no way of contacting each other. multiverse-75.com is suggesting a way to “break the laws of physics” and maybe have these different universes “talk” to each other. echo-64.com seem to add a time aspect to this, in which different universes happening at different times communicate with each other.
@doctordevice You may move the below text to your physics thread if you want, but the issue arose in this thread so I’m writing it here to begin with 
Dualism in philosophy:
First a definition of what a “Dualism” actually means (Dualism (Stanford Encyclopedia of Philosophy)):
In general, the idea is that, for some particular domain, there are two fundamental kinds or categories of things or principles. In theology, for example a ‘dualist’ is someone who believes that Good and Evil—or God and the Devil—are independent and more or less equal forces in the world. Dualism contrasts with monism, which is the theory that there is only one fundamental kind, category of thing or principle; and, rather less commonly, with pluralism, which is the view that there are many kinds or categories.
Dualism in Quantum Mechanics:
When first devised, people observed electrons - classically taken to be particles (i.e. a tiny sphere with a radius) - to exhibit wave-like behaviour in diffraction experiments. People were very confused as to how a particle could exhibit wave-like behaviour. In other experiments, people observed light - classically taken to be waves (i.e. with a wavelength and a frequency) - to exhibit particle-like behaviour, leading to the concept of a photon which is a “unity of light” with zero mass travelling at the speed of light (duh). The duality arises when BOTH descriptions lead to a full and complete understanding of physical phenomena. Sometimes it seems down to the whim of the actual scientist which language to use in order to explain what she/he is doing.
Multiverse theory (in Quantum Mechanics referred to as “Many Worlds interpretation”):
The following from Many-worlds interpretation - Wikipedia :
_The many-worlds interpretation is an interpretation of quantum mechanics that asserts the objective reality of the universal wavefunction and denies the actuality of wavefunction collapse. Many-worlds implies that all possible alternate histories and futures are real, each representing an actual “world” (or “universe”). In layman’s terms, the hypothesis states there is a very large—perhaps infinite[2]—number of universes, and everything that could possibly have happened in our past, but did not, has occurred in the past of some other universe or universes.
Short explanation: In Quantum Mechanics, particles are represented by the wave-function, which is a mathematical construct with the property that when evaluated at a certain position or momentum (or at a certain energy or time, for example) gives you the PROBABILITY of the actual particle having the property that you are measuring (for example, the probability of the electron being at a certain position in space). In original Quantum Mechanics, it was thought that the wave-function “collapses” at the time of measurement, and the particle falls into a certain state due to the influence of the measuring apparatus. The many-worlds interpretation, however, proposes that each and every possible outcome actually manifests in a physical world at the time of measurement.