### Wave Function Collapse and information

Posted:

**Sun Sep 23, 2018 12:52 pm UTC**So I was reading about wave function collapse and quantum decoherence of separated entangled pairs of photons and a paradox was mentioned. Namely that measuring one of a pair determines the state of the other.

Scenario:

A pair of entangled photons are fired to the left and the right of the source. Of these two photons, one is 0° polarized and the other 90° polarized.

We have two observers on the left and right side of the source.

So let's say the observer on the right side measures the polarity of the photon and it turns out to be 90°. So the other photon is the 0° photon.

Yet, it has been proven that the photons are not determined to be 90° and 0° until the right observer measured it.

Once the right observer knows the photon is 90°, the left photon is now 0° with probability 1.

The two observers now collude beforehand, they set a time at which the measurement is to be taken. The right hand side observer will then measure the photon slightly before or slightly after that time. The left hand side observer will perform their measurement/tests exactly on the dot.

The time difference between the right and left side will be small enough that the two observers are outside each other's light cones.

So my question is:

Is it possible for the left observer to know (over a large number of measurements), if the photon they are looking at has already decohered before their measurement? (ie. did the right side observer already measure it?)

If this is possible, the left side observer could run the test across some large number of photons to determine, faster than light, whether the right side observer measured their photon(s) before or after the agreed time...

Scenario:

A pair of entangled photons are fired to the left and the right of the source. Of these two photons, one is 0° polarized and the other 90° polarized.

We have two observers on the left and right side of the source.

So let's say the observer on the right side measures the polarity of the photon and it turns out to be 90°. So the other photon is the 0° photon.

Yet, it has been proven that the photons are not determined to be 90° and 0° until the right observer measured it.

Once the right observer knows the photon is 90°, the left photon is now 0° with probability 1.

The two observers now collude beforehand, they set a time at which the measurement is to be taken. The right hand side observer will then measure the photon slightly before or slightly after that time. The left hand side observer will perform their measurement/tests exactly on the dot.

The time difference between the right and left side will be small enough that the two observers are outside each other's light cones.

So my question is:

Is it possible for the left observer to know (over a large number of measurements), if the photon they are looking at has already decohered before their measurement? (ie. did the right side observer already measure it?)

If this is possible, the left side observer could run the test across some large number of photons to determine, faster than light, whether the right side observer measured their photon(s) before or after the agreed time...