Quantum Entanglement between 2 observers

[NEXT]

Ok I have a question, If you have 2 quantum entangled particles at a distance N away from each other and at each location you have 2 different measurement systems. One is named Alice and the other Bob. If Alice measures one of these 2 quantum entangled particles, causing a wave function collapse, will Bob measure that the particle has collapsed on an defined state or will he just see observe nothing but a random state.

[elfmotat]

If he observes/measures it then he is also causing wave-function collapse!

[Strange]

He will measure the value (of whatever property it is). He will not be able to tell if Alice has previously made her measurement or not. The only difference that entanglement makes is that when they compare their measurements later, they will find there is a correlation between them.

[NEXT]

Yes, however what if both Alice and Bob have previously confirmed with one another that they would measure there own particle respectively ( Alice has particle A Bob has particle anti-A, anti just meaning the entangled particle and not meaning the actual anti-particle ) at the "same time." Meaning that at any distance, whether it be defined or undefined, both Alice and Bob would have measured these two entangled particles at the same instance in time regardless of relativistic properties.

[elfmotat]

Yes, however what if both Alice and Bob have previously confirmed with one another that they would measure there own particle respectively ( Alice has particle A Bob has particle anti-A, anti just meaning the entangled particle and not meaning the actual anti-particle ) at the "same time." Meaning that at any distance, whether it be defined or undefined, both Alice and Bob would have measured these two entangled particles at the same instance in time regardless of relativistic properties.

 

1) Why do you think this would make a difference?

 

2) If they measure at "the same time" in their rest frame, they won't measure at the same time in a frame moving w.r.t. them.

[swansont]

Yes, however what if both Alice and Bob have previously confirmed with one another that they would measure there own particle respectively ( Alice has particle A Bob has particle anti-A, anti just meaning the entangled particle and not meaning the actual anti-particle ) at the "same time." Meaning that at any distance, whether it be defined or undefined, both Alice and Bob would have measured these two entangled particles at the same instance in time regardless of relativistic properties.

 

 

 

Let's say they are possibly entangled in their spin. If they are not entangled, Alice or Bob will measure spin up or spin down. If they are entangled, Alice or Bob will measure spin up or spin down.

 

It's only after the measurement and they compare (which is limited to happening no faster than t = d/c) will they notice that the spin measurements are correlated.

[NEXT]

I believe that this thread should belong inside of the speculation page and I am sorry for adding inside of the physics forum page. This is supposed to be a question that leads toward an invention idea using speculative ideas.

 

That being said to answer Organisms 2 questions:

 

1) By looking at 2 locations and pre-informing both Alice and Bob while by removing relativistic properties it becomes easier to go into moving along with the design stages of the idea. Taking a bottom up approach if you will. I am not dis-counting there importance, the opposite in fact. I am maintaining relativistic properties in there extremes and uses them as a comparison check, however again I am currently designing upward so I need to consider the most perfect conditions.

 

2) I am assuming that both inertial frames S' are moving at the same velocity in respect to an observer S( Please correct me if I am incorrect ).

 

To answer swansont

 

I am assuming that both Alice and Bob are pre-informed that a measurement is going to occur at a certain period of time.

When this time is reached first Alice will measure there entangled particle,and Bob will measure there's.

 

Under these circumstances I believe that once Alice measures the entangled particle, the wave function will collapse for each pair, therefore causing Bob's particles wave function to already be collapsed before even being measured. ( Please Correct if Wrong )

 

That way they would not need to compare with one another because they know when they are measuring and what they are looking for. So if Alice measures the first entangled particle to be say (spin up) then the particle will have collapsed and the entangled particle with Bob will be (spin down) even before Bob measures it.

 

So there is no need to check for a comparison because they both know that Alice will measure first causing the entangled pair to decay and that Bob will measure second. So whatever Bob measures they will know that it is the opposite spin value as the Alice's.

[Strange]

I see nothing new here. It makes no difference who measures first (or if the measure at the same time). They both know that they will measure opposite spins.

[elfmotat]

1) By looking at 2 locations and pre-informing both Alice and Bob while by removing relativistic properties it becomes easier to go into moving along with the design stages of the idea. Taking a bottom up approach if you will. I am not dis-counting there importance, the opposite in fact. I am maintaining relativistic properties in there extremes and uses them as a comparison check, however again I am currently designing upward so I need to consider the most perfect conditions.

 

I'm still not sure why it matters if they make their measurements simultaneously or not. Could you explain why this would impact the experiment?

 

2) I am assuming that both inertial frames S' are moving at the same velocity in respect to an observer S( Please correct me if I am incorrect ).

 

You can assume whatever you'd like. Relativity tells us that if two events happen simultaneously in one frame, they do not and cannot happen simultaneously in any other frames. So you can set up the experiment so that Bob and Alice are at rest w.r.t. each other, and so that they make their measurements simultaneously in their rest frame. The fact that they made their measurements simultaneously in this frame is physically irrelevant, because there are an infinite number of equally valid frames in which they don't make their measurements simultaneously.

 

I am assuming that both Alice and Bob are pre-informed that a measurement is going to occur at a certain period of time.

When this time is reached first Alice will measure there entangled particle,and Bob will measure there's.

 

Under these circumstances I believe that once Alice measures the entangled particle, the wave function will collapse for each pair, therefore causing Bob's particles wave function to already be collapsed before even being measured. ( Please Correct if Wrong )

 

That way they would not need to compare with one another because they know when they are measuring and what they are looking for. So if Alice measures the first entangled particle to be say (spin up) then the particle will have collapsed and the entangled particle with Bob will be (spin down) even before Bob measures it.

 

So there is no need to check for a comparison because they both know that Alice will measure first causing the entangled pair to decay and that Bob will measure second. So whatever Bob measures they will know that it is the opposite spin value as the Alice's.

 

The point is that there's no way for Bob to tell if the wave-function has collapsed until he makes his measurement. And once Bob makes his measurement, he is also causing wave-function collapse.

Edited May 22, 2016 by elfmotat

[NEXT]

So if they both know that they will measure opposite spins, then when Bob makes the final measurement to be say (spin up) then they would know that Alice must have gotten say (spin down) ?

 

Also thank you for the response Strange

[elfmotat]

So if they both know that they will measure opposite spins, then when Bob makes the final measurement to be say (spin up) then they would know that Alice must have gotten say (spin down) ?

 

Also thank you for the response Strange

 

Yes!

[NEXT]

Thank you for all of your responses, it has allowed me to obtain more clarity toward my designing.

 

Have a wonderful day

 

Scientifically N≡XT

[swansont]

So if they both know that they will measure opposite spins, then when Bob makes the final measurement to be say (spin up) then they would know that Alice must have gotten say (spin down) ?

 

 

 

Yes. But Bob getting spin up does not tell him that Alice has also made the measurement. She did not know she was going to measure spin down.

[NEXT]

All Alice in Bob know is the following

- Alice has Entangled Particle A

- Bob has Entangled Particle ~A

- When Either Alice or Bob Measures there own respective particle it causes either particles wave function to collapse to a certain spin state ( spin up vs. spin down )

- When either Entangled Particle ( A or ~A) are observed the measured spin stated is completely Random ( Cannot be predicted )

 

So Alice and Bob come up with an experiment

 

1) Alice and Bob go to a location that has separate rooms room A and room B

2) In each room there are machines that allows Alice/Bob to "measure" each particles spin state (spin up and spin down )

 

Note: before the "experiment" 2 particles ( A and ~A ) are entangled and one is put into each room.

Note: Before the experiment Alice and Bob decide that Alice will measure her/his particle first at t = 0, then Bob will measure her/his particle at t = 1;

Note: Alice and Bob both have agreed that they would up hold the previous statement and if they do not then they will both lose the credential in the scientific community have have there PhD's Revoked ( Note: I am not sure this is how it works, I am only using this so that each party will trust each other)

 

3) At t = 0 Alice measures there particle (A), at t = 1 Bob measures there particle (~A)

 

4) At t = 0 Alice measures there particle (A) to be at a random spin state ( spin up/ spin down )

5) At t = 1 Bob measures there particle (~A) to be at the opposite random spin state as Alice's particle (A) ( spin up/ spin down )

 

Now my question is this, because Alice has measured there particle first, causing both particles wave function to collapse. Would

Bob's entangled particles (~A) spin state at t = 0 , after wavelength collapse, be the same as Bob's entangled particle (~A) spin state at t = 1?

 

Thank you for your responses

 

Scientifically NEXT

[Markus Hanke]

Would Bob's entangled particles (~A) spin state at t = 0 , after wavelength collapse, be the same as Bob's entangled particle (~A) spin state at t = 1?

 

 

You seem to be asking whether or not the spin state of the particle, which is definite after the measurement, changes over time. The answer is that this depends on whether or not the particle interacts with other particles, but this information isn't given in your setup. You also need to bear in mind that after the initial measurement at t=0, the particle pair is no longer entangled, since wave function collapse always destroys entanglement. The other subtle issue I see here is the question of simultaneity, since t=0 may not necessarily mean the same thing to Alice and Bob, depending on the spatial and temporal relationships between the rooms.

[swansont]

The answer is yes. The correlations have been made at various time intervals between the two measurements. All consistent with what entanglement predicts. If Bob measured spin up at t=1, he would have measured spin up at any t ≥ 0