Einstein and "spooky actions"

[AdityaMookerjee]

About Albert Einstein and the 'Theory of Relativity', ancient civilizations speak of humans being very ancient, in measurement of time. Western civilization measures the existence of, for instance, the Hindu Civilization, in time, from about 2500 B. C.. The Indians believe, civilization is many, many, if I may use the term, 'eons' old. The term 'eon' is metaphorical, because I don't know the measurement.
Why so? The watch measures time, but in relation to it's own ticking. There are twenty four hours, and sixty minutes. But, the idea that this is in relation to it's own ticking, is worth the idea, that the watch can only measure it's own tick. The civilizations like in the East, measured time, differently, as compared to after the watch was invented.

 

[zaybu]

Great. So before Alice does a measurement, Bob's particle is in the singlet state. After Alice does a measurement, Bob's particle is no longer in the singlet state. It's now in the down (or up) spin state. Right?

You need to be a little more clear in your question. You need to specify from whose point of view you are considering: Alice's POV or Bob's POV. These are not the same.

When Alice makes her measurement and finds that her particle is spin up, knowing that this particle is entangled with the particle that Bob will get, she can conclude that Bob will measure a spin down.

From Bob's POV, he hasn't measured yet, doesn't know what Alice has measured, and so the only thing he can say is that his particle in the singlet. It would be wrong for him to say it is no longer in a singlet - how would he know that?

 

[zaybu]

About Albert Einstein and the 'Theory of Relativity', ancient civilizations speak of humans being very ancient, in measurement of time. Western civilization measures the existence of, for instance, the Hindu Civilization, in time, from about 2500 B. C.. The Indians believe, civilization is many, many, if I may use the term, 'eons' old. The term 'eon' is metaphorical, because I don't know the measurement.
Why so? The watch measures time, but in relation to it's own ticking. There are twenty four hours, and sixty minutes. But, the idea that this is in relation to it's own ticking, is worth the idea, that the watch can only measure it's own tick. The civilizations like in the East, measured time, differently, as compared to after the watch was invented.

Your post is off-topic. But to clarify some points:

1) Different cultures used different units to measure time. We can always find a correspondence between.

2) Einstein's ideas are of a different kind. What he showed was that the ticking of your clock, irrespective of the units it uses, would be different if a) two observers move with respect to each other; b) two observers are in different gravitational fields.

 

[PolyHedral]

If Alice knows what the state of Bob's particle is, ( which will be a down-spin for Bob), then that's what it is, a down-spin state. From Bob's POV, who hasn't measured yet, and doesn't know what Alice has measured, then as far as he's concerned, the particle is still in its initial state, the singlet - 50% chance that it will be up, and 50% down.

We are repeating ourselves. There's not much else to add to this scenario. What's your point?

The point is that what you've just said means quantum states are observer-dependent, which isn't supposed to happen. (At least, not in collapse interpretations. How can the state be collapsed for one person but not for another?)

 

[zaybu]

The point is that what you've just said means quantum states are observer-dependent, which isn't supposed to happen. (At least, not in collapse interpretations. How can the state be collapsed for one person but not for another?)

The state of a particle is not only unknown until a measurement is done, but the measurement itself will affect the state of the particle. That's the whole point about QM. In classical physics, the observation of an object ( be it a car, a tree, etc.) does not affect the state of that object. But in QM, the observation does. So it's important to know in the scenario under discussion who has made the measurement. So when Alice makes her measurement, the state of her particle will be revealed. But for Bob, it's a different particle, and until its state is measured, it remains in what it started out, in this case, the singlet.

If what you suggest is right, then measuring the state of one single particle, I would know the state of every particle in the universe, as they are all entangled since the Big Bang!!!

 

[PolyHedral]

The state of a particle is not only unknown until a measurement is done, but the measurement itself will affect the state of the particle. That's the whole point about QM. In classical physics, the observation of an object ( be it a car, a tree, etc.) does not affect the state of that object. But in QM, the observation does. So it's important to know in the scenario under discussion who has made the measurement. So when Alice makes her measurement, the state of her particle will be revealed. But for Bob, it's a different particle, and until its state is measured, it remains in what it started out, in this case, the singlet.

If what you suggest is right, then measuring the state of one single particle, I would know the state of every particle in the universe, as they are all entangled since the Big Bang!!!

Bob's measurement acts as an operator on the particle's state, yes, but what state is the particle in when he does the measurement? One part of the pair can't be entangled while the other isn't, so if Alice has already made her measurement, then it should act on the state Alice already infers Bob's particle's in, whereas if she hasn't, it would act on the superpositional state.

But whether or not Alice has performed a measurement before Bob depends on where you are in relation to the two of them. This would be fine if we were describing epistomological results, but we're not - there should be one quantum state that the particle is in that shouldn't vary depending on where you are. (at least, says Copenhagen, I think. You don't subscribe to MWI, do you?)

 

[zaybu]

Bob's measurement acts as an operator on the particle's state, yes, but what state is the particle in when he does the measurement?

According the scenario we have established: the state is singlet, prior to the measurement. When he makes the measurement, it will be in the down state. There's no ambiguity.

One part of the pair can't be entangled while the other isn't, so if Alice has already made her measurement, then it should act on the state Alice already infers Bob's particle's in, whereas if she hasn't, it would act on the superpositional state.

Her measurement is totally independent of Bob's. Whether she measures now, or in a hundred years from now, Bob is free to do as he pleases, that is, measures whenever he wants to. And her act of measurement has no bearing on Bob' particle.

there should be one quantum state that the particle is in that shouldn't vary depending on where you are. (at least, says Copenhagen, I think. You don't subscribe to MWI, do you?)

Right about the state, it shouldn`t depend on where you are. But don't confuse that with ''describe what is happening from whose POV''. We need that description as we have two observers doing things not exactly the same or not exactly at the same time.

 

[Mr Spinkles]

You need to be a little more clear in your question. You need to specify from whose point of view you are considering: Alice's POV or Bob's POV. These are not the same.

When Alice makes her measurement and finds that her particle is spin up, knowing that this particle is entangled with the particle that Bob will get, she can conclude that Bob will measure a spin down.

From Bob's POV, he hasn't measured yet, doesn't know what Alice has measured, and so the only thing he can say is that his particle in the singlet. It would be wrong for him to say it is no longer in a singlet - how would he know that?

Yes Bob wouldn't know. But Alice knows after her measurement that the state of the other particle, the thing we represent as Psi or a ket vector, has changed, from singlet to spin-down (or up). Right? In other words, as you said: "the measurement itself will affect the state of the particle." Right?

Just to clarify, you said in full: "The state of a particle is not only unknown until a measurement is done, but the measurement itself will affect the state of the particle." When I say "state" I am talking about the full quantum state of the particle, the thing we represent as Psi or a ket vector. This is known before a measurement is done, in our case. It is known with 100% certainty to be the singlet state. What is not known is what spin you will measure (up or down) and therefore which eigenstate (up/down or down/up) the singlet state will collapse into after a spin measurement.

 

[zaybu]

Yes Bob wouldn't know. But Alice knows after her measurement that the state of the other particle, the thing we represent as Psi or a ket vector, has changed, from singlet to spin-down (or up). Right? In other words, as you said: "the measurement itself will affect the state of the particle." Right?

Just to clarify, you said in full: "The state of a particle is not only unknown until a measurement is done, but the measurement itself will affect the state of the particle." When I say "state" I am talking about the full quantum state of the particle, the thing we represent as Psi or a ket vector. This is known before a measurement is done, in our case. It is known with 100% certainty to be the singlet state. What is not known is what spin you will measure (up or down) and therefore which eigenstate (up/down or down/up) the singlet state will collapse into after a spin measurement.

Yes, we've established all that, though you've put more technical language in your post. Now, going back to the topic of this debate, do you agree with what was established with Reptillian in post #173?

http://www.religiousforums.com/forum/3325467-post173.html

 

[Mr Spinkles]

Yes Bob wouldn't know. But Alice knows after her measurement that the state of the other particle, the thing we represent as Psi or a ket vector, has changed, from singlet to spin-down (or up). Right? In other words, as you said: "the measurement itself will affect the state of the particle." Right?

Just to clarify, you said in full: "The state of a particle is not only unknown until a measurement is done, but the measurement itself will affect the state of the particle." When I say "state" I am talking about the full quantum state of the particle, the thing we represent as Psi or a ket vector. This is known before a measurement is done, in our case. It is known with 100% certainty to be the singlet state. What is not known is what spin you will measure (up or down) and therefore which eigenstate (up/down or down/up) the singlet state will collapse into after a spin measurement.

Yes, we've established all that, though you've put more technical language in your post. Now, going back to the topic of this debate, do you agree with what was established with Reptillian in post #173?

I'm not finished with my line of questioning. I have two more very simple questions, if you answer them directly then we will be finished soon and then I would be happy to answer your questions. I know you're impatient but we would have reached this point faster if you had not dodged the question at the beginning.

So we have established that Alice, by measuring one particle in the singlet state, knows she has changed the state of the other particle.

The next question is, how much time does it take after Alice's measurement for the other particle to change its state (from singlet to spin-down [or up])? As usual let's stick to Alice's POV for convenience.

 

[zaybu]

So we have established that Alice, by measuring one particle in the singlet state, knows she has changed the state of the other particle.

Sorry, but I disagree here. I've never said that she has changed the state of the other particle. Only her particle has gone from the singlet to the up-spin when she has made her measurement. Her measurement has no bearing on the other particle.

The next question is, how much time does it take after Alice's measurement for the other particle to change its state (from singlet to spin-down [or up])? As usual let's stick to Alice's POV for convenience.

Time has no bearing in this case.

 

[PolyHedral]

Sorry, but I disagree here. I've never said that she has changed the state of the other particle. Only her particle has gone from the singlet to the up-spin when she has made her measurement. Her measurement has no bearing on the other particle.

Bob's particle can't be in a superposition if Alice's isn't. Either that, or it sounds like you've got a hidden variable that says that Alice's particle "knows" it should be up before she measures it.

 

[zaybu]

Bob's particle can't be in a superposition if Alice's isn't. Either that, or it sounds like you've got a hidden variable that says that Alice's particle "knows" it should be up before she measures it.

No, what we said is, "If Alice measures an up-spin". It's a given in the problem. In the real world, she doesn't know what she will measure until she makes the measurement. But here in our discussion, we simplify the problem by making Alice measuring an up-spin. So we are not assuming she "knows" before she measures it.

The particle is in superposition before the measurement, not afterward.

 

[PolyHedral]

The particle is in superposition before the measurement, not afterward.

Meaning that whether or not Bob's particle is in a superposition is frame-dependent, which is the part I'm objecting to.

 

[zaybu]

Meaning that whether or not Bob's particle is in a superposition is frame-dependent, which is the part I'm objecting to.

No, it has nothing to do with frame-dependency. Bob's particle remain in superposition until he makes a measurement. That's at the core of QM. Deny that, and you deny QM.

 

[Mr Spinkles]

Sorry, but I disagree here. I've never said that she has changed the state of the other particle. Only her particle has gone from the singlet to the up-spin when she has made her measurement. Her measurement has no bearing on the other particle.

You're wrong. Think carefully now, because you are contradicting yourself. You said earlier, correctly: "When Alice makes her measurement and finds that her particle is spin up, knowing that this particle is entangled with the particle that Bob will get, she can conclude that Bob will measure a spin down."

Alice cannot conclude this if according to her the particle by Bob remains in the singlet state.

Let's go back to the previous question. You say, correctly, that after Alice's measurement obtaining spin-up, she knows with 100% certainty that if Bob does a measurement on the other particle, he will get spin-down. Therefore, according to Alice, what state is the other particle in, after her measurement but before Bob's measurement? (Hint: what is the quantum state that guarantees an outcome of spin-down if someone measures it? It's not the singlet state.)

I'm avoiding math here because I assume that will only confuse you even more, but let me know if you prefer to see the math.

 

[Kilgore Trout]

Watching this conversation is like watching two football coaches arguing over whether the home team's quarterback just hit a home run or not.

 

[zaybu]

You're wrong. Think carefully now, because you are contradicting yourself. You said earlier, correctly: "When Alice makes her measurement and finds that her particle is spin up, knowing that this particle is entangled with the particle that Bob will get, she can conclude that Bob will measure a spin down."

Alice cannot conclude this if the particle by Bob remains in the singlet state.

Yes she can know from two factors: her own measurement and conservation of angular momentum. So she knows that WHEN Bob will make his measurement what his observation will be. But knowing that doesn't affect Bob's particle, no more that my knowledge of the sun rising tomorrow in the East will affect that event.

Note: Bob's particle is in the singlet only until he makes the measurement, after that, it is no longer in that state, but the down spin.

 

[PolyHedral]

Note: Bob's particle is in the singlet only until he makes the measurement, after that, it is no longer in that state, but the down spin.

This is incompatible with Alice's observation.

 

[zaybu]

This is incompatible with Alice's observation.

Alice's observation is that her particle has an up spin. How's that incompatible?