- #36
bhobba
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durant35 said:Bill said it isn't correct.
Just to be clear what I am saying. When objects are entangled with other objects and you observe one of those objects and not the other it is found to be in a mixed state. If the system as a whole is isolated they evolve by unitary evolution.
Suppose you have system 1 that can be in state |a> or |b> and system 2 can be in state |a> or |b>. If system 1 is in state |a> and system 2 is in state |b> that is written as |a>|b> and similarly if system 1 is in state |b> and system 2 in state |a> that is written as state |b>|a>. Now according to the principle of superposition you can have a superposition of these ie c1|a>|b> +c2|b>|a>. The systems are entangled. Each system is no longer in a pure state - they have lost their individuality. The interesting thing however is if you observe system 1 it acts as though its now in a mixed state. The entanglement has broken the unitary evolution. The two systems as a whole evolve unitarily - but the systems when observed behave differently. This is the origin of decoherence and since everything here in the macro world is entangled why we have classical properties.
Thanks
Bill