Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Jimbee on 25/08/2023 09:52:44
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Einstein called quantum entanglement "spooky action at a distance". I certainly don't understand it. Maybe people like Einstein really didn't either.
Anyways, it basically says one particle can affect another particle no matter how far away. One particle twists to the left, so does the other one, and vice versa. Instantaneously. My question is, could it be used to things like interstellar communication? Using just one pair of particles, you could have something like Morse code going. Or if you have enough particles working at the same time, you could have thousands, maybe millions of messages sent. Maybe they could all form pixels on a computer screen, or something like that.
But is it possible?
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Bottom line is "you cannot transmit information faster than light". Don't ask me to explain, I can't, but I have seen arguments that are rock-solid and I am convinced. Not a very helpful answer, I realise. Halc or Origin would give you a rigorous answer.
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Einstein called quantum entanglement "spooky action at a distance". I certainly don't understand it. Maybe people like Einstein really didn't either.
Einstein, Podolsky and Rosen came up with the thought experiment in which they proposed quantum entanglement, the purpose was to show that quantum mechanics must be wrong or incomplete. What they actually did was to add more support to the theory of quantum mechanics.
My question is, could it be used to things like interstellar communication?
No, you cannot send any useful information using entangled particles.
Let's say I have an entangled particle and I am on a space ship 10 ly away from earth and back on earth you have the other entangled particle. Neither particle has a defined orientation, they are both in a superposition state. If I measure the particle as being 'up' then I immediately know the other particle is 'down'. Since I had no idea what the orientation was before I measured the particle there cannot be any information other than the other particle is in the opposite direction. In other words when I measure the particle the orientation is completely random and when the person back on earth measures the particle the results will be completely random. The only thing I can know is the random results I got means the other particle will have an opposite orientation. Each person will only see a random result, even though there is correlation between the 2 particles.
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It is impossible, but so was the splitting of the atom, flight, etc.
If you have 2 particles and you give one to your accomplice to go on their light speed ship, if they conveyed information to you from 1LY, it would only be at the speed of light, you could have garnered the information yourself if you went on their ship at the speed of light. I do not see you knowing information that you could have discovered yourself at lights peed a problem
If precisely 1 year after your accomplice departed, another conspiritor from 1LY the opposite direction to that of your accomplice arrives bringing an entangled particle, you and likewise your explorer accompice would know what was going on in either direction but you would know the information if you had travelled to the lication and so could your accomplice. I do not know whether this is a problem or not.
The conspiritor and their particles would however would be privvy to information that would take another year to reach them. They could not have travelled 2 light years from their start point in 1 year. This would suggest it is impossible.
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If you have 2 particles and you give one to your accomplice to go on their light speed ship,
It is not possible for a ship to go light speed but we can assume it is possible. Let's call this accomplice Jim.
if they conveyed information to you from 1LY, it would only be at the speed of light, you could have garnered the information yourself if you went on their ship at the speed of light.
Ok so Jim who is one ly away sends a signal, I can:
1. Wait a year for the signal.
2. Fly to the Jim at light speed and ask what was in the signal, which would take a year.
3. Fly in my ship towards Jim at light speed and intercept the signal in 6 months.
Where do the entangled particles come in?
If precisely 1 year after your accomplice departed, another conspiritor from 1LY the opposite direction to that of your accomplice arrives bringing an entangled particle,
Let's call the new conspirator Bob.
So when Jim is one light year away, Bob shows up having flown one ly from the opposite direction. He has an entangled particle. I have no idea what this new entangled particle has to do with anything.
you and likewise your explorer accompice would know what was going on in either direction
Who is the explorer accomplice (Jim I assume)? What is it that we would know 'is going on'?
but you would know the information if you had travelled to the lication and so could your accomplice.
What information? The signal? So after 1 year both Bob and I would know the contents of the signal sent by Jim. That is correct if that is what you are saying.
I don't see how this has anything to do with entanglement.
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Origin, while I agree 100% with the thrust of your argument I offer one small correction: If YOU travelled to jim at light speed, surely it would take zero time while jim would see it as taking I year?
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Neither particle has a defined orientation, they are both in a superposition state. If I measure the particle as being 'up' then I immediately know the other particle is 'down'. Since I had no idea what the orientation was before I measured the particle there cannot be any information other than the other particle is in the opposite direction.
Now force your particle into an up state: you therefore know mine is down, and I can measure it.
If you want to tell me something, flip your particle. Mine will "suddenly" (the question is how suddenly) flip, so you have sent me information.
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Don't think so, Alan, but I am not good enough( not good at all! ) on quantum phenomena to counter your scenario. Offhand I reckon you would break the entanglement by forcing a state on your particle. If one could do that the other particle would follow instantly.
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Origin, while I agree 100% with the thrust of your argument I offer one small correction: If YOU travelled to jim at light speed, surely it would take zero time while jim would see it as taking I year?
You could be right, his example was rather hard to follow. My take is that when Jim sends his signal Bob had just arrived and he and I are at the same place so we would get the signal at the same time.
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Now force your particle into an up state: you therefore know mine is down, and I can measure it.
It is impossible to force a superposition particle to be measured in the up (or down) position. The position is always random. If it were possible to force the position, you could communicate information but that is not possible.
If you want to tell me something, flip your particle. Mine will "suddenly" (the question is how suddenly) flip, so you have sent me information.
Once either particle is measured they are no longer entangled so flipping one of the particles after the initial measurement has no effect on the other particle.
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Don't think so, Alan, but I am not good enough( not good at all!
No, you very much are good enough, and you are correct here.
Now force your particle into an up state: you therefore know mine is down, and I can measure it.
This is very much wrong. Entanglement does not mean that 'what is done to one particle affects the other'. Yes, a message could be sent if that were true, but it isn't. Spooky action at a distance (as it is called) has never been demonstrated. If it was, all the local interpretations that forbid it would have been falsified.
Spin entanglement says (in short) that if you measure both things in the same way, the results will be correlated. If you force one of the particle spins, that is the same as declining to take one of the two measurements, leaving nothing to compare.
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Thank you, Halc. I had always assumed, mistakenly, that "spooky action at a distance" was a real phenomenon. This is a problem that arises when one has not had proper tuition in a subject-it's 50 years since I attended college and the only quantum theory covered was in connection with semiconductors, apart from the basic stuff ie failure of classical theory to deal with black body, photoelectric and orbitals.
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Jim
If you have 2 particles and you give one to your accomplice to go on their light speed ship,
It is not possible for a ship to go light speed but we can assume it is possible. Let's call this accomplice Jim.
if they conveyed information to you from 1LY, it would only be at the speed of light, you could have garnered the information yourself if you went on their ship at the speed of light.
Ok so Jim who is one ly away sends a signal, I can:
1. Wait a year for the signal.
2. Fly to the Jim at light speed and ask what was in the signal, which would take a year.
3. Fly in my ship towards Jim at light speed and intercept the signal in 6 months.
Where do the entangled particles come in?
If precisely 1 year after your accomplice departed, another conspiritor from 1LY the opposite direction to that of your accomplice arrives bringing an entangled particle,
Let's call the new conspirator Bob.
So when Jim is one light year away, Bob shows up having flown one ly from the opposite direction. He has an entangled particle. I have no idea what this new entangled particle has to do with anything.
you and likewise your explorer accompice would know what was going on in either direction
Who is the explorer accomplice (Jim I assume)? What is it that we would know 'is going on'?
but you would know the information if you had travelled to the lication and so could your accomplice.
What information? The signal? So after 1 year both Bob and I would know the contents of the signal sent by Jim. That is correct if that is what you are saying.
I don't see how this has anything to do with entanglement.
It was written in context to the op considering the instantaneous transmission of information utilising the quantum entanglement of particles. The gist being you would need to transport the particle, light speed or any other. Any information that is aquirable at the speed of light is OK, but if particles could be read it would lead to a situation where you can infact get information faster than light.
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Even if one could dictate the state of a remote entangled particle by manipulating the local one, which cannot be done, one still would have to transport one of the entangled pair to the remote location: it would be simpler to just transport the relevant information that's required.
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but if particles could be read it would lead to a situation where you can infact get information faster than light.
Got ya. If information could be transferred by entangled particle pairs you could send information faster than light, in fact it just might be instantaneous. But you can't transfer information by entangled particle pairs so... it's all academic.
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could
That is what they said about the alchemists too! Even if one could dictate the state of a remote entangled particle by manipulating the local one, which cannot be done, one still would have to transport one of the entangled pair to the remote location: it would be simpler to just transport the relevant information that's required.
I wonder what relitavistic effects have on quantum entanglement.
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It is impossible, but so was the splitting of the atom, flight, etc.
The difference is that there are no laws of physics preventing nuclear fission or flight.
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Laws of physics neither permit nor prevent: they describe.
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What they describe prevents us from making things like perpetual motion machines.
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Or explains why they don't work. We observe conservation of energy and momentum, and increasing entropy, all of which conspire against an "overunity" or even a "unity" machine.
Problem is that if we apply said laws retrospectively, we can't explain the status quo because they give us a date for a Big Bang but don't tell us what happened beforehand.
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It is impossible, but so was the splitting of the atom, flight, etc.
The difference is that there are no laws of physics preventing nuclear fission or flight.
Yes but the law is an ass. I believe the way this is got round in siency circles is an "addition". It would be quite easily to add an addition.
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I believe the way this is got round in siency circles is an "addition". It would be quite easily to add an addition.
Don't you know that every rational scientist over the past 3 or 4 hundred years knew that heavier than air flight was possible.
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Yes but the law is an ass.
Can you elaborate?
I believe the way this is got round in siency circles is an "addition". It would be quite easily to add an addition.
I'm not sure what you mean by this.
To be clear, faster-than-light communication technically isn't forbidden by relativity. It just has troublesome consequences if it happens (causality violation). In either case, you can't do it with quantum entanglement because quantum entanglement doesn't work that way.
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An addition, Petro?. I say no, you are in error. What you really need is a subtraction. Subtract all these irritating laws like COE and COM, thermodynamics etc and you are good to go.
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I believe the way this is got round in siency circles is an "addition". It would be quite easily to add an addition.
Don't you know that every rational scientist over the past 3 or 4 hundred years knew that heavier than air flight was possible.
Do you mean 'correct'?
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Yes but the law is an ass.
Can you elaborate?
I believe the way this is got round in siency circles is an "addition". It would be quite easily to add an addition.
I'm not sure what you mean by this.
To be clear, faster-than-light communication technically isn't forbidden by relativity. It just has troublesome consequences if it happens (causality violation). In either case, you can't do it with quantum entanglement because quantum entanglement doesn't work that way.
https://www.phrases.org.uk/meanings/the-law-is-an-ass.html
And yes. Here comes string theory.
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Do you mean 'correct'?
No.
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What does any of this have to do with string theory?
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No, it's not possible
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No, it's not possible
Not as yet.
(MayBee)
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Not as yet.
If you have been following the conversation you'll see that because of the inherent random nature of entanglement it is not possible to use it to send information.
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Let's say you know that I have two socks, one green and one red. I send you a box with one of the socks in it. You don't know which one it is until you open it. As soon as you do, you see that it is the red sock. You can then deduce, instantly, I must have the green sock. Although you acquired this knowledge without delay, you can't use a system of sending red and green socks by mail to communicate faster than light. Quantum entanglement is similar.
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The conspiritor and their particles would however would be privvy to information that would take another year to reach them. They could not have travelled 2 light years from their start point in 1 year. This would suggest it is impossible.
However if you count the communication with transported particles to be allowed under the light speed limit, this would indeed let you communicate over the entirety of the universe(s) instantaneously, you would just need to meet another entangled particle carrier.
Perhaps though the velocity you transport a particle at affects it and it may slow down or affect other parties in some way.
What does any of this have to do with string theory?
It's a theory on a theory, just as newton was before Einstein or people who believed that atom could not be split, as I said the alchemists showed them, or that a nuclear bomb would require several tonnes on uranium. Do you mean 'correct'?
No.
Oh.
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However if you count the communication with transported particles to be allowed under the light speed limit, this would indeed let you communicate over the entirety of the universe(s) instantaneously, you would just need to meet another entangled particle carrier.
No you couldn't. There is no way to communicate information with 2 entangled particles. This has been explained in the thread.
Perhaps though the velocity you transport a particle at affects it and it may slow down or affect other parties in some way.
No that makes no difference.
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@Anybody interested in discussing this Topic further?
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@Anybody interested in discussing this Topic further?
Sure.
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@Anybody interested in discussing this Topic further?
Sure.
Great!
: )
Well, let's first Establish a Factual point...
Quantum Entanglement can NOT transfer Information Faster than the Speed of Light in a Vacuum.
Agreed?
& then can we Please discuss Q.E. further by choosing the Left/Right socks Analogy?
That way, it will be Alot easier for me to grasp the Concept in depth & details.
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Well, let's first Establish a Factual point...
Quantum Entanglement can NOT transfer Information Faster than the Speed of Light in a Vacuum.
Agreed?
I would be more comfortable saying "entanglement does not allow for faster than light communication."
& then can we Please discuss Q.E. further by choosing the Left/Right socks Analogy?
That way, it will be Alot easier for me to grasp the Concept in depth & details.
Sure.
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Quantum Entanglement can NOT transfer Information Faster than the Speed of Light in a Vacuum.
Agreed?
Origin gave a better wording of this statement. There are non-local interpretations that posit faster than light causation in entanglement situations, but none of them suggest that this can be used to transfer information faster than c.
then can we Please discuss Q.E. further by choosing the Left/Right socks Analogy?
Socks tend to not come in left and right, but gloves do. So entanglement is a little like wrapping a pair of gloves in two packages and one goes to Mars. Once there, either person can open the package he has and instantly know the contents of the other no matter how far away. Nothing physical changes, and the mechanism cannot be used to send a message.
The analogy ends there. A glove in a box is a classical object in a classical state of being left or right, and the package only serves to prevent knowledge of this classical state until opened. In quantum mechanics, the particle-pair is not classical, but in superposition of being in either state (let's say spin up/down). One can perform an experiment on either particle to demonstrate this superposition state, all without actually measuring its spin. That can't be done with the gloves.
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That's interesting, Halc. How would one go about demonstrating that such a particle is in a state of superposition?
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That's interesting, Halc. How would one go about demonstrating that such a particle is in a state of superposition?
I do not know the exact procedure to detect superposition of spin state, but I do know that it is a statistical thing, that it can be demonstrated only by doing the experiment repeatedly. So for instance, the photon might be in superposition of having gone through one slit and the other, but the measurement is the dot it creates on the screen which doesn't tell you anything, but 1000 dots creates an interference pattern (superposition) and 1000 dots creates a simple bell curve (not in superposition). The spin state is similar, so you'd need to have a lot of them.
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How would one go about demonstrating that such a particle is in a state of superposition?
Here is a Youtube video that does a good job of simply explaining superposition IMO.
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Hi Origin, I understand the concept of superposition but was curious how one could demonstrate such a scenario without incurring the measurement that would "break" the superposition. I rarely if ever look at videos and prefer a document I can read. Thank you anyway.
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I would be more comfortable saying " entanglement does not allow for faster than light communication. "
Carved on a Rock & Set in Stone.
Totally Agreed!
& Thanks for the Wording, coz it Matters.
& HiYa Halc!
Two Teachers are Better than One.
Hope Mr Cotter would join in too, Three is Definitely not a crowd.
Well, back to Q.E.
Socks got no left/right...lol true that...let's not use them.
Gloves got Pre-Determined left/right...hmm let's not use them too.
Ummm...can We Plz use a Coin.
(())
Two sides...head/tails.
We toss it up n it's spinning as an independent system.
While it's spinning, We slice n dice it in half.
(( // ))
Both halves have a head side & a tail end.
Still spinning.
Both (2) parts of the same (1) system now in a Singlet state.
Head/Tails Undetermined.
Then we separate Them, while they are still Spinning, across a linear perpendicular path so as to avoid Decoherence.
(( - - - - - - - ))
Now we check one of Them.
Observation thru Instrumentation breaks Coherence and it Stops spinning and We see a Head.
(H(
Okay...if Everything above seems Sensible then Please lemme know & Only then shall i move ahead.
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Hi Zero, there is not much I could contribute, I am just a lowly retired electrical engineer, not a physicist and my knowledge of quantum phenomena is primitive. I have always had an interest in all areas of science but my knowledge is very patchy on this subject.
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Hi Zero, there is not much I could contribute, I am just a lowly retired electrical engineer, not a physicist and my knowledge of quantum is phenomena is primitive. I have always had an interest in all areas of science but my knowledge is very patchy on this subject.
If this is your Personal outlook of your Ownself, then you most certainly do Not Know Thy Self.
I have Observed you providing Corrections on posts & being Thanked for doing so.
Anyways, to continue or not is your decision & i shall Respect that.
ps - Problem with the World is, Fools are full of Confidence & Wise full of Doubts.
(Bertrand)
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True enough, Zero. But the more you know the more you realise how little you know. Honestly if I could contribute more, I would without hesitation.
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Ummm...can We Plz use a Coin.
(())
Two sides...head/tails.
We toss it up n it's spinning as an independent system.
While it's spinning, We slice n dice it in half.
(( // ))
Both halves have a head side & a tail end.
Still spinning.
Both (2) parts of the same (1) system now in a Singlet state.
Head/Tails Undetermined.
Then we separate Them, while they are still Spinning, across a linear perpendicular path so as to avoid Decoherence.
(( - - - - - - - ))
Now we check one of Them.
Observation thru Instrumentation breaks Coherence and it Stops spinning and We see a Head.
(H(
This seems like an overly complicated analogy that can't reflect what is really going on since you are trying to use a classical system to describe a quantum system.
What question are you wishing to have answered about entanglement and communication?
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See if this helps.
Let's look at 2 entangled particles. We will assume that the property we are going to look at is the spin of the particles.
The 2 particles are separated by 10 million miles. Each location has a detector that will measure the particles spin direction (up or down).
Here are the rules about the entangled particles:
1. When an initial measurement of one of the particles is measured there is a 50-50 chance the direction will be up and a 50-50 chance the particle will be down.
2. There is no way to predict what direction the spin will be it is completely random.
3. When measured the particle can only be up or down.
4. There is no way to force the particle to a certain orientation.
5. Once either particle is measured they are no longer entangled.
6. Once you measure the orientation of your particle you instantly know the orientation of the other particle.
7. When either location measures their particle the result is completely random. So if I measure my particle as up I will know that your particle will measure down, however you don't know that. Your measurement will be completely random as far as you can tell, but once you measure our particle, you will know that my particle will be up.
Since both locations can only get a random result there is no way to use these random result to communicate.
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A couple of clarifications, based on my limited knowledge of the issue.
We will assume that the property we are going to look at is the spin of the particles.
The 2 particles are separated by 10 million miles. Each location has a detector that will measure the particles spin direction (up or down).
We are measuring the spin relative to some particular axis. Only if both measurements use the same axis will the measurements be fully correlated. If perpendicular axes are used, there will be no correlation. If something between is used (45 degrees say), there will be partial correlation.
5. Once either particle is measured they are no longer entangled.
Sort of. The measuring system is effectively entangled with the unmeasured particle, which is why you can know what the measurement will be if it ever gets done. I think if you measure a particle along the same axis twice in a row, you'd get the same result, so in that way of looking at it, the two particles remain entangled, but the entanglement is now restricted to the axis that has been chosen, so a subsequent measurement along a perpendicular axis isn't going to be correlated with the unmeasured particle.
6. Once you measure the orientation of your particle you instantly know the orientation of the other particle.
You instantly know the outcome of a measurement of the other particle along the same axis, regardless of if it has already been done or will be done (a frame dependent distinction). The far guy of course knows none of this, so from his point of view, the outcome is still totally random.
Anyway, your wording implies that the unmeasured particle actually has a spin orientation, which most interpretations deny.
All that said, the glove analogy (a classical example) still satisfies pretty much all of the above points. I separate the gloves in envelopes unopened, When one is opened, that person instantly knows the contents of the other envelope. It's a epistemological thing, not a metaphysical one. The glove system is classical, so metaphysically, there is in fact a left glove in this envelope and a right in the other. No superposition. We just don't know which is which.
Quantum systems go further than that. The EPR paradox showed that quantum entanglement cannot be classical like the gloves. I'm not going to attempt to explain that since I'd get it wrong. Look up the paradox or Bell's theorem if you want the detail. They are probably well beyond what Zero want's to know. They are beyond my capability to convey correctly without just copying text from a website.
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We are measuring the spin relative to some particular axis. Only if both measurements use the same axis will the measurements be fully correlated. If perpendicular axes are used, there will be no correlation. If something between is used (45 degrees say), there will be partial correlation.
The particle is measured by applying a magnetic field. The measurement will detect if the spin is up, aligned with the direction of the field or if it is down, aligned opposite of the field direction. Therefore the orientation of the lab frame is not important.
I think if you measure a particle along the same axis twice in a row, you'd get the same result,
That is not an aspect of entanglement. For instance if you measure the spin of any quantum particle as up and then measure it again it will measure up again 100% of the time.
so in that way of looking at it, the two particles remain entangled, but the entanglement is now restricted to the axis that has been chosen, so a subsequent measurement along a perpendicular axis isn't going to be correlated with the unmeasured particle.
This is not correct. The particles are no longer entangled. When 2 particles are entangled they have the same wave equation. When one of the particles is measured the wave function collapses and now the particles are no longer described by a single wave equation, now both of the particles are described by different wave equations.
All that said, the glove analogy (a classical example) still satisfies pretty much all of the above points.
Agreed.
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The particle is measured by applying a magnetic field. The measurement will detect if the spin is up, aligned with the direction of the field or if it is down, aligned opposite of the field direction. Therefore the orientation of the lab frame is not important.
It is the orientation of the field that is important. That defines the axis of measurement. It has nothing to do with choice of abstract coordinate system (lab frame).
This is not correct. The particles are no longer entangled. When 2 particles are entangled they have the same wave equation.
Good point. The wave functions (at least that concerning their spin) are different now. Other parts (wave function of position say) were never the same, even though they were spin-entangled. You can't say that two entangled particles millions of miles apart are equally likely to be found at a given location.
When one of the particles is measured the wave function collapses and now the particles are no longer described by a single wave equation, now both of the particles are described by different wave equations.
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This is Exactly what i was Wishin for...a Detailed discussion.
Thank You both & Please continue.
ps - I'm all set, switched on potato mode, crashed on bean bag, pack of crispy chips in one hand & a slurpy cola in the other.
( I'm Lovin it! )
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Hmm...shows over eh?
Bummer!
Well, i think I'll have to ditch my simple coin analogy & step into your socks to get some Answers...
Okay.
How do We know or how can We confirm 2 particles obtained from 1 system have reached or are in a Singlet State?
w.r.t. Electrons being paired, is it an Assumption?
Or is it that a Million Q.E. measurements made shall Always provide a 100% deterministic result bcoz of Conservation of Angular Momentum?