Simultaneously Measuring Entangled Particles

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Discussion Overview

The discussion revolves around the measurement of entangled particles, specifically focusing on the implications of measuring their spins simultaneously in relation to the reference frame of the source. Participants explore theoretical aspects of quantum mechanics, including interpretations of entanglement and the nature of measurement, while considering the implications of distance and timing in these measurements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants assert that measuring the spins of entangled particles will yield opposite spins, as suggested by quantum theory, but express uncertainty about the feasibility of simultaneous measurement.
  • Others question whether spins are definite prior to measurement, suggesting that there may be a probability of measuring the same spin.
  • One participant proposes that the connection between entangled particles over distances could involve unknown energies or higher dimensions, while another counters that this depends on the interpretation of quantum mechanics.
  • Several interpretations of quantum mechanics are discussed, including the Copenhagen interpretation and Many Worlds, with participants debating the implications of measurement timing and frame of reference.
  • Some participants express skepticism about the Copenhagen interpretation, noting the lack of equations to describe wave function collapse.
  • A suggestion is made that the first measurement might send a signal backwards in time, ensuring that spins remain opposite, though this raises further questions about causality and testing such ideas experimentally.
  • Participants discuss the concept of Time Symmetric Quantum Mechanics, noting its implications for locality and causality, while acknowledging that it remains an interpretation without experimental validation.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of measurement and entanglement, with multiple competing views and interpretations presented throughout the discussion. Uncertainty remains regarding the implications of measurement timing and the underlying mechanisms of entanglement.

Contextual Notes

Limitations include unresolved questions about the nature of wave function collapse, the role of measurement timing, and the implications of various interpretations of quantum mechanics. The discussion highlights the complexity and ongoing debates within the field.

  • #31
Joncon said:
I've also heard a suggestion that the "first" measurement may send a backwards in time to when the entangled particles were first produced, ensuring that the spins are always opposite.

This seems to solve the issue about the ordering of the measurements, and removes a bit of the "spookiness" involved with the particles being spatially separated.
I'm not sure what other issues this might create though. And I can't think of an experiment which could for this.

Interesting though ...

retrocausality from the
Two State Vector Formalism.
the_pulp said:
Time Symmetric . . it through the Forum. In some threads you will to very interesting papers. It preserves locality but ruins causality.
I really like not only the preservation of locality but also causality aside because it makes you think as time being much more similar to space than what one usually does (in this the arrow of time problem sort of does not occur in microscopic world and arises in the macroscopic human world -by the way my thought about it is that it is a human illusion which arises as a consequence of the fact that we, human beings, are consumers of ordered energy and producers of entropy, and, because of this, we order our life from situation of low entropy -past- to situations of high entropy -future--)

Ps: Remember that all that I said is just an which probably will never be tested! (Nevertheless I have that someone much more intelligent than me will do it!)

Physical Review A 79, 052110
Multiple-time states and multiple-time measurements in quantum mechanics
Yakir Aharonov, Sandu Popescu, Jeff Tollaksen, and Lev Vaidman

... Finally we discuss the implications of our approach to quantum mechanics for the problem of the flow of time...
Maui said:
There is no movement(and hence no causality) in spacetime, according to GR.

the block universe, recently i opened a thread about, but it was deleted.

JPBenowitz said:
If you could construct a closed timelike curve where entropy always increases and Novikov's Self Consistency Principle is satisfied I don't see any problem with this.

from CTCs

Perfect State Distinguishability and Computational Speedups with Postselected Closed Timelike Curves
Foundations of Physics March 2012, Volume 42, Issue 3, pp 341-361

...an entangled state efectively creates a noiseless quantum channel into the past...
 
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Physics news on Phys.org
  • #32
and there are Timlike Entanglement , i.e. entanglements in time.Physical Review A 85, 012306 (2012)
...entangled between timelike separated regions of spacetime...
...non-separability across time...----
and an experiment proposed:

Physical Review Letters 109, 033602 (2012)
...We propose a realistic circuit QED experiment to test the extraction of past-future vacuum entanglement to a pair of superconducting qubits...
...We show that this experiment can be realized with current technology and discuss its utility as a possible implementation of a quantum memory...

i have the complete papers if somebody wish it.
 
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  • #34
mfb said:
arXiv has them, too:

Extraction of timelike entanglement from the vacuum (your link there seems broken)
Extracting past- vacuum correlations using circuit QED
yes, i know, but... mod`s do not like to much, that forums users put arxiv papers.
you know...
 
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  • #35
They are just different links to the same thing - the publications were accepted (and therefore passed peer review), so they shouldn't be completely crap.

Rules said:
References that appear only on http://www.arxiv.org/ (which is not peer-reviewed) are subject to review by the Mentors. We recognize that in some fields this is the accepted means of professional communication, but in other fields we prefer to wait until formal publication elsewhere.
I did not highlight "only", this is already done in the rules.
 
  • #36
Joncon said:
I've also heard a suggestion that the "first" measurement may send a signal backwards in time to when the entangled particles were first produced, ensuring that the spins are always opposite.

This seems to solve the issue about the ordering of the , and removes a bit of the "spookiness" involved with the particles being spatially separated.
I'm not sure what other issues this might create though. And I can't think of an which could test for this.

Interesting though ...

The Conference...

http://www.chapman.edu/research-and-institutions/quantum-studies/speakers-schedule.aspx

Aharonov, Hartle, Gross, Unruh, Pearle, Leggett, Turok, Gisin, Carroll, Vaidman, Steinberg......!


talks on video

.
 
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  • #37
mfb said:
No. In every frame, there is a description which does not involve any propagation backwards in time. And all frames give the same measurements.

Could you please elaborate? From one reference point, A collapses the system and as a result B has a defined spin. From another reference point, the measurement of B seems to happen first and collapses the system. As a result, A takes a defined spin. I don't see how the instantaneous action does not violate causality. I'm probably misunderstanding something.

As a side question, has it been proven empirically (somehow) that the spins are actually undefined before measurement? I'm guessing this is impossible. btw, I'm an engineer not a physicist so I'm sorry if the answers are obvious. Thanks.
 
  • #38
myshadow said:
Could you please elaborate? From one reference point, A collapses the system and as a result B has a defined spin. From another reference point, the measurement of B seems to happen first and collapses the system. As a result, A takes a defined spin.
Both reference frames have their own time-order of the events - you cannot transmit information with those measurements, so you do not need a unique ordering of those events.

As a side question, has it been proven empirically (somehow) that the spins are actually undefined before measurement? I'm guessing this is impossible. btw, I'm an engineer not a physicist so I'm sorry if the answers are obvious. Thanks.
Look up Bell's theorem. It has, and it is a very interesting experiment.
 

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