Quantum decoherence

Quantum decoherence is the loss of quantum coherence. 

The Many-worlds interpretation of quantum mechanics can be understood further by using a fundamental of the quantum theory known as "decoherence". Quantum decoherence was discovered in 1970 by H. Dieter Zeh. According to quantum decoherence, the alternate universes created in the MWI will never be accessible to us. This is because:

• once their is a measurement done, the measured system is entangled with both the observer and with a large number of other particles.

• some of these other particles are photons moving at the speed of light.

• to prove that the wave-function did not collapse, one would have to bring all of these particles back and measure them again.

In quantum mechanics, an electron can be described by it's wavefunction as having different probabilities of being measured to be in different locations. There even exists a probability that the electron can exist in more than one state at once. Decoherence can explain why these superpositions are not measured in observation. Quantum decoherence can be understood as the loss of a system's information into it's environment. A quantum system can become too entangled to it's surroundings and some of it's quantum properties can leak out of the system. A quantum system will lose relevant quantum properties through this decay of coherence. For example, when an electron interacts with other particles, or is observed, the probability of it existing in more than place disappears.