Quantum Entanglement on two particles

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Discussion Overview

The discussion revolves around the concept of quantum entanglement, specifically focusing on the implications of measurement and changes to entangled particles. Participants explore whether changes to one particle affect the other and the potential for communication using entangled particles.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions whether a change to particle A will also affect particle B, suggesting a need for clarification on the nature of entanglement and its relation to measurements.
  • Another participant explains that entanglement persists unless disturbed, indicating that external interactions can affect the polarization states of entangled photons.
  • Several participants discuss the possibility of using entangled particles to send messages, with one asserting that while measurements yield correlated results, there is no way to control the outcome to send a message effectively.
  • It is noted that the measurement results are random and cannot be predetermined, likening the situation to random chance rather than a reliable communication method.

Areas of Agreement / Disagreement

Participants express differing views on the implications of measurement and the potential for communication through entangled particles. There is no consensus on whether changes to one particle affect the other or on the feasibility of using entangled particles for messaging.

Contextual Notes

Participants reference the randomness of measurement outcomes and the necessity of external conditions for entanglement to persist, highlighting the complexity of the topic without resolving these nuances.

Jalo
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Hi.

Imagine a system of two particles, A and B, where they are entangled.
I've been studying a little bit of quantum entanglement and I understand how measurement of one property of a particle A leads us to find indirectly the value of that property to the particle B. My question is: if I act on one of the particles, let it be A, so that the particle changes in some way, will the particle B also suffer that same change? Or is quantum entanglement strictly related to measurements?

Thanks.
D.
 
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If a pair of photons are prepared with entangled polarization states entanglement persists as long as there is nothing in the way of either photon which disturbs the polarization state. Such a disturbance might be a collision of either of the photons with another particle or absorption by a measuring device.
 
And is there anyway to send a message via morse code with a pair of entangled particles? Let's imagine we're dealing with two particles of symmetric spins separated by a large distance. If I manage to change the spin of one of the particles will the other one's spin also change?
 
Jalo said:
And is there anyway to send a message via morse code with a pair of entangled particles? Let's imagine we're dealing with two particles of symmetric spins separated by a large distance. If I manage to change the spin of one of the particles will the other one's spin also change?

There is no way of sending a message.

You measure the spin, you get a spin-up result, you know the other guy's measurement will yield the opposite result. But when he gets spin-down, for all he knows he's made the first measurement, you haven't made a measurement yet, and when you do you'll get spin-up. Likewise, when you get your spin-up result, you have no way of knowing whether he's sending you a message ("I just got a spin-down result") or whether you're making the first measurement.
 
Nugatory said:
You measure the spin, you get a spin-up result, [...]

And there's no way to control in advance whether you get spin-up or spin-down, and thereby originate a signal, any more than you could with a monkey pounding randomly at the key of a Morse-code telegraph machine.
 
And there's no way to control in advance whether you get spin-up or spin-down

yes, the first measure is pure chance, 50/50 you'll get either one. But the entangled measurements ALWAYS correlates to the first measure...

See the first two sections here for some introductory insights...and some of the controversies surrounding this phenomena:

http://en.wikipedia.org/wiki/Quantum_entanglement
 

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