Order of observations in Bell experiments

In summary: If the measurements are done in different reference frames, the results will still be symmetrical.In summary, Bell's inequality is a result of how different observers can see different aspects of the same event. Even if the events happen at different times, the outcome is still the same for all observers.
  • #1
Android Neox
23
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I've been trying to find information on how Bell's experiment works on the macroscopic scale. I think that the scale of current measurements is meters, for the most part. I've been curious about how Bell's Inequality is supposed to work, Relativistically. Haven't found quite what I'm looking for. Non-simultaneity means that different frames can see different observers collapse the wavefunction. What happens if two observers see themselves as making the first observation but of different entangled quantities? Attached, below, is what I've been messing with. If someone could direct me to existing work on Bell with different reference frames, I'd be grateful.

It has been explained to me that you don't do science here but I've not been able to find anything on this topic and thought someone here might be able to direct me to something.

Thanks in advance
Extended Bell Experiment.jpg
 
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  • #2
Android Neox said:
. I've been curious about how Bell's Inequality is supposed to work, Relativistically. Haven't found quite what I'm looking for. Non-simultaneity means that different frames can see different observers collapse the wavefunction. What happens if two observers see themselves as making the first observation but of different entangled quantities?

Alice and Bob both make measurements and get results. Depending on their relative speeds, some observers will say that Alice's measurement came first, others will say that Bob's measurement came first, and observers at rest relative to Chris will say that both measurements happened at the same time. At some later time - all observers will agree that this happens after both of the measurements - we compare Alice's and Bob's notes to see how their measurements are correlated. (To actually prove the correlation and that we're dealing with entangled pairs we'd need to repeat this process many times with many pairs. If Bob and Alice measure on the same axis and get oppoiste results once, that's just happenstance, happens half the time even if the particles are not entangled. But if they try hundreds of pairs, and it turns out that way every single time... then we know that something is going on).

It makes no difference which observation we say came first. Let's say, for definiteness that Bob measured spin-up and Alice measured spin-down. We could say that Bob went first and his "up" measurement collapsed the wave function to "Bob-up, Alice-down" so that Alice was fated to measure "down"; or we could say that Alice went first and her "down" measurement collapsed the wave function to "Bob-up, Alice-down" so that Bob was fated to measure "up". Both descriptions lead to exactly the same physical result: Bob measures spin-up, Alice measures spin-down. Thus, relativity of simultaneity is not a problem here - the outcome is the same whether we describe it using a frame in which Alice's measurement was first, Bob's measurement was first, or both happened at the same time.
Android Neox said:
If someone could direct me to existing work on Bell with different reference frames...
This question suggests that you are the victim of a (very common) misconception about reference frames. Events don't happen in reference frames - they happen and then (optionally) we choose some reference frame and use it to assign x, y, z, and t coordinates to them. Thus everything is always in every imaginable reference frame already, and that includes the labs where in which Bell experiments are being done.
(If this is not clear to you, you may find some helpful threads over in the Relativity subforum).
 
  • #3
There is a strange sort of symmetry here, that I can illustrate if we take an entangled photon pair fired at polarization filters instead of an electron pair: Suppose filter A is at angle α and filter B at angle β. If we assume that photon A arrives first at filter A, it collapses to polarization direction α. Now, photon B has probability amplitude cos(β-α) to pass filter B. Conversely, if photon B arrives first at filter B, it collapses to polarization direction β, leaving A a probability amplitude of cos(α-β) of passing filter A. When the information of the two is combined we obtain probability cos(β-α)*cos(α-β) of correlation. This is symmetrical. The same holds for measuring entangled particle spins at some angle.
 
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1. What is the "order of observations" in Bell experiments?

The "order of observations" refers to the sequence in which measurements or observations are made in a Bell experiment. In other words, it is the specific order in which the properties of particles are measured or observed in order to test the principles of quantum mechanics and the existence of hidden variables.

2. Why is the order of observations important in Bell experiments?

The order of observations is important in Bell experiments because it can affect the outcome of the experiment and subsequently impact our understanding of quantum mechanics. The sequence of measurements can reveal hidden correlations between particles and provide evidence for the non-local nature of quantum entanglement.

3. How is the order of observations determined in Bell experiments?

The order of observations in Bell experiments is determined by the experimental setup and the specific properties being measured. Scientists carefully design the experiment and control the sequence of measurements to ensure that the results are reliable and free from any potential biases.

4. Can the order of observations be changed in a Bell experiment?

Yes, the order of observations can be changed in a Bell experiment. In fact, scientists often vary the order of measurements to test the robustness of their results and to explore different aspects of quantum mechanics. However, changing the order of observations must be done carefully to avoid introducing any unintended biases into the experiment.

5. How does the order of observations in Bell experiments relate to the concept of causality?

The order of observations in Bell experiments challenges the traditional concept of causality in physics. In quantum mechanics, certain events can appear to happen simultaneously or have a non-causal relationship, which goes against our classical understanding of cause and effect. The order of observations plays a crucial role in revealing these non-local correlations and expanding our understanding of the fundamental nature of reality.

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