One of the great head spinners of quantum theory is the principle of Entanglement. The fact that two particles once entwined will always know what the other is doing........even if they are separated by a million light years.

When a electron is fired through a double slit, you would expect two neat bands to form on the other side. But no......they actually form a wave pattern, as if they were going through both slits simultaneously. If you try to observe what the hell is going on.....then the electron behaves like a particle......forming a nice band as you would expect, Welcome to the quantum world.

The strange phenomena causing this is called - superposition.....the ability of a subatomic particle to exist in a number of states all at once. The  Double Slit experiment was the first to highlight this dual nature of matter. Showing that existence at the subatomic level became more a subject of probabilities than of any fixed reality.

The very act of observing, or measuring sub atomic particles pulls them out of their superpositional state (the potential of being a wave or a particle and indeed multiple states) into a fixed position.

An electron as it comes out of superposition, the wave form collapsing into a fixed point in space.

Decoherence is the term used to describe the collapse of the quantum wave world of "many states" - superposition, into the normal world.

The ability of particles to communicate beyond the speed of light defies Einsteins relativity laws. As of yet there has been no satisfactory explanation or a unifying theory that would link these two fundamental laws of the universe.