# How long, after dis-entanglement, does the photon retain its newly created spin/state

## Main Question or Discussion Point

how long, after dis-entanglement, on average, does an event occur that causes the photon to loose its newly created spin/state?

To illustrate the above, lets say:

Alice measures her entangled photon at 10 am. She gets spin up. We all know if Bob measures at 10:000000000001 am he will get spin down.

However lets assume Bob was having beer and was a bit slow and measured his photon at say, 10:15 am.....

## Answers and Replies

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If nothing further happens to Bob's photon (i.e. interacts etc.), then it will remain spin down.

(Technically, though, when Alice measures her photon, the photon at Bob's side is still entangled with Alice's (i.e. in no definite state, according to standard QM). This is a consequence of the linearity of the Schrodinger equation.)

and if bob after see his spin down change it to up, alice it will see then her spin down ?......

and if bob after see his spin down change it to up, alice it will see then her spin down ?......
Nope.

(Technically, though, when Alice measures her photon, the photon at Bob's side is still entangled with Alice's (i.e. in no definite state, according to standard QM). This is a consequence of the linearity of the Schrodinger equation.)

What do you mean by "in no definite state"? 'Collapse' is instantaneous as far as we can tell at this point(>10^4 C), and we are talking about one system.

What do you mean by "in no definite state"? 'Collapse' is instantaneous as far as we can tell at this point(>10^4 C), and we are talking about one system.
right.

What do you mean by "in no definite state"? 'Collapse' is instantaneous as far as we can tell at this point(>10^4 C), and we are talking about one system.
By "in no definite state", I mean in a superposition of spin up and down.

By "in no definite state", I mean in a superposition of spin up and down.

Indefiniteness is broken once a measurement is made on the system. Bob's photon cannot remain in an indefinite state(up and down).

As I stated earlier, according to standard QM no measurement occurs.