# Is Decoherence essentially a measurement? Then what?

1. Aug 20, 2015

### rasp

2 basic questions from a non-physicist (sigh!). Is decoherence essentially a measurement? And if so is the system of quantum particles set into the classical world forever? Or is there a mechanism by which it will evolve again into a superimposed state? Secondly, if the particle (as in the 2 slit experiment) is essentially everywhere possible at a given time, then what sense can be given to assessing the probability that the particle can be found in a specific place?

2. Aug 20, 2015

### rasp

Clarification: 2 basic questions from a non-physicist (sigh!). Is decoherence essentially a measurement? And if so is the system of quantum particles that has experienced decoherence set into the classical world forever? Or is there a mechanism by which it will return into a superimposed state? Secondly, if the particle (as in the 2 slit experiment) is essentially everywhere possible at a given time, then what sense can be given to assessing the probability that the particle can be found in a specific place?

3. Aug 20, 2015

### StevieTNZ

Decoherence is merely the entanglement of the quantum system with the quantum (assuming everything is quantum) environment. It remains in a pure, superposition, state, evolving according to the fundamental Schrodinger equation.

4. Aug 21, 2015

### Demystifier

Essentially, yes.

The latter.

It is not correct to say that the particle itself is everywhere. Instead, it is a non-vanishing probability of finding the particle which is everywhere.

For example, I don't know where do you live on Earth right now. Perhaps New York? Or London? Or a small village in India? I have no idea, so I can say that you can be "everywhere". But of course, I know that you are not at all those places at once. If I find you, I know I will find you at only one of those places.

Last edited: Aug 26, 2015