On 18/11/2017 4:05 pm, Brent Meeker wrote:
On 11/17/2017 8:35 PM, [email protected] wrote:
On Friday, November 17, 2017 at 7:18:23 PM UTC-7, Brent wrote:
No, Bruce was thinking of what /*local */operator could be
implemented. In theory any pure state can be an element of a
basis. So if the superposition is pure it will an eigenstate of
some operator....although in general it will often be one that is
impractical to implement.
Brent
*
*
*If you can remove the superposition from any pure state by a change
of basis, *
Just because one exists doesn't mean you can determine what it is.
The no-cloning theorem says there is no measurement by which you can
determine the state of an arbitrary system.
*why not do it for the cat and maybe the problem will go away? AG
*
Because the cat, being macroscopic, doesn't have a pure state. The cat
/plus everything the cat is entangled with/ has a pure state, but that
is an impossibly complex and growing system. Even for a small system
for which we might be able to calculate its orthonormal basis states
(e.g. all the excited modes of a water molecule) it will generally be
impossible to construct an apparatus that will measure in that basis.
The basis we can actually measure in will generally include averaging
over some of the excitations.
I think that this is actually what einselection is all about. As you
say, the pure state is the cat plus everything it is entangled with,
but the basis (|dead> +/- |alive>)/sqrt(2) is not stable against further
entanglement. It is only the basis |dead> or |alive> that is stable
against further interactions with the environment. That is why we see
only dead or alive cats, not arbitrary superpositions of the two.
Bruce
--
You received this message because you are subscribed to the Google Groups
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at https://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
