It is called 'entanglement' and it would be true to say that nobody really understands it. Atoms and the particles that comprise them, as well as light and energy, behave in strange ways, none more so than the phenomenon of entanglement. An intriguing demonstration has been carried out at the California Institute of Technology and Aarhus University in Denmark. In the quantum world normal rules about matter and energy do not apply. Everything, including space and time itself, comes in lumps or quanta.
Entanglement occurs when two photons of light have related properties even when they are far apart.
Do something to one photon and instantaneously the other will change. In a sense this appears to violate one of the golden rules of physics - that no information can be transmitted faster than the speed of light. In reality most scientists believe that entanglement may not allow super-light information transfer. Nonetheless it is something that has mystified researchers for decades. The scientists used two entangled beams to carry information about the state of a third beam.