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Post by Progenitor A on Sept 7, 2010 14:24:55 GMT 1
Sorry this is exactly totally wrong! If we could do that (I change spin here, spin changes four light years away) I would have an instantaneous message transmission system, so beloved of science fiction writers. Whjat actually happens is that before you measure, the spin of a single particle is undetermined -- not just we haven't measured it so don't know what it is, but that the statement that it has a single value is not true. It has all possible values at once. When we measure, we now find it has one particular value, the one we measured. And hence so does its connected twin, even though before we measured, they both had all possible values, just linked, so that values always cancelled. Think of it like spining a coin -- before I catch it, it could be either heads or tails, 50% chance of each. Once I have caught it, then if heads, I know the other side must be tails. Same with photons, except the other side is the other photon, which might be a very long way away. OK if you say so, I have no real knowledge, but I recall reading a book (not science fiction) that talked of the spin axis of linked particles being dependent and if one axis is changed the other immediately changes to keep the initial relationship the same. It is impossibel to have all possible values of spin - are you sure you are phrasing that correctly
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Post by speakertoanimals on Sept 7, 2010 15:04:08 GMT 1
All possible values is what I meant.
So, if we have a spin-1/2 particle, it can be spin up or spin down, once you have defined an axis.
If we have two such particles, linked so that if one spin up other is spin down and so on.
If I measure the spin of my particle, then I find that it is either up or down. If up, then I know that if I now go and measure the spin of the other (or someone else does) it will be found in a state corresponding to spin down (assuming we are measuring with respect to same axis, but that is another complication!).
The point, I can't make mine be spin up -- I just measure it find that it is spin up, but it could also have been spin down, in which case the other particle would be found to be spin up if that one was now measured.
But before I make a measurements, or before anyone does, the state of any one particle is completely undetermined, it really does possess all possible spin states, although looked at as a pair, the spin state of one is linked with the spin state of the other.
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Post by Progenitor A on Sept 7, 2010 21:07:10 GMT 1
All possible values is what I meant. So, if we have a spin-1/2 particle, it can be spin up or spin down, once you have defined an axis. If we have two such particles, linked so that if one spin up other is spin down and so on. If I measure the spin of my particle, then I find that it is either up or down. If up, then I know that if I now go and measure the spin of the other (or someone else does) it will be found in a state corresponding to spin down (assuming we are measuring with respect to same axis, but that is another complication!). The point, I can't make mine be spin up -- I just measure it find that it is spin up, but it could also have been spin down, in which case the other particle would be found to be spin up if that one was now measured. But before I make a measurements, or before anyone does, the state of any one particle is completely undetermined, it really does possess all possible spin states, although looked at as a pair, the spin state of one is linked with the spin state of the other. And if we change the axis of spin of one particle from UP to DOWN(using an em field) then the partner particle changes it axis so the original relationship of spin is maintained? Does this change in the spin axis of the second particle happen instantaneously? Or am I misreading you?
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Post by speakertoanimals on Sept 8, 2010 13:12:24 GMT 1
We can't change the spin axis from up to down, because before we do so, the state of a single particle cannot be said to be just up or just down, but a combination of all possible spin states.
Off the top of my head, turning on some em field is more likely to destroy the entanglement between the particles, but I'm not totally sure on that one.
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Post by abacus9900 on Sept 8, 2010 19:14:11 GMT 1
We can't change the spin axis from up to down, because before we do so, the state of a single particle cannot be said to be just up or just down, but a combination of all possible spin states. Off the top of my head, turning on some em field is more likely to destroy the entanglement between the particles, but I'm not totally sure on that one. How are they going to achieve teleportation via entanglement?
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Post by speakertoanimals on Sept 9, 2010 14:00:09 GMT 1
Who said anything about teleportation?
Entanglement is just the name for the state when two particles are entangled like this. Tends to be delicate and easily destroyed, which is why quantum computers haven't got up to many qubits yet -- difficult to maintain the entangled state of the the constituents.
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Post by abacus9900 on Sept 9, 2010 14:46:29 GMT 1
Who said anything about teleportation? Entanglement is just the name for the state when two particles are entangled like this. Tends to be delicate and easily destroyed, which is why quantum computers haven't got up to many qubits yet -- difficult to maintain the entangled state of the the constituents. en.wikipedia.org/wiki/Quantum_teleportation
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Post by speakertoanimals on Sept 9, 2010 18:06:42 GMT 1
And that article agree with what I said, entangled states are delicate!
Let's get ordinary entanglement sorted, before worrying about more complicated things like quantum teleportation.............
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Post by abacus9900 on Sept 9, 2010 18:41:47 GMT 1
Then please explain it to us all.
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Post by speakertoanimals on Sept 10, 2010 13:48:20 GMT 1
What do you think I've been trying to do?
If you want an explanation, then just google and find one of the many popular science websites that will give you a simple explanation. You can't really expect me to do the whole thing on here from scratch.
If you have specific questions, that is a different matter.
mind you, probably best not to attempt it until you have got your head around the basics of quantum theory, such as the fact that and electron can be in two places at once............
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Post by Progenitor A on Sept 10, 2010 14:01:53 GMT 1
Sorry this is exactly totally wrong! Whjat actually happens is that before you measure, the spin of a single particle is undetermined -- not just we haven't measured it so don't know what it is, but that the statement that it has a single value is not true. It has all possible values at once. Perhaps you can explain how a particle can spin both clockwise and anti-clockwise at the same time? I expect that you cannot.
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Post by abacus9900 on Sept 10, 2010 14:25:02 GMT 1
What do you think I've been trying to do? If you want an explanation, then just google and find one of the many popular science websites that will give you a simple explanation. You can't really expect me to do the whole thing on here from scratch. If you have specific questions, that is a different matter. mind you, probably best not to attempt it until you have got your head around the basics of quantum theory, such as the fact that and electron can be in two places at once............ In other words there is little point in trying to ask questions here since I can find out more by 'googling'. Why bother to have a science MB at all?
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Post by abacus9900 on Sept 10, 2010 14:27:27 GMT 1
Apparently you must not ask Speaker a direct question unless you already know the answer. How silly is that?
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Post by visitor on Sept 10, 2010 14:55:22 GMT 1
In other words there is little point in trying to ask questions here since I can find out more by 'googling'. Why bother to have a science MB at all? A science board is for discussion of science - not to teach people who make no attempt to find out simple things for themselves. Try asking informed questions rather than stupid ones.
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Post by Progenitor A on Sept 10, 2010 15:00:22 GMT 1
In other words there is little point in trying to ask questions here since I can find out more by 'googling'. Why bother to have a science MB at all? A science board is for discussion of science - not to teach people who make no attempt to find out simple things for themselves. Try asking informed questions rather than stupid ones. Clown! Why do people discuss? To learn, to sharpen their brains There is no such thing as a 'stupid' scientific question, but stupid answers based on ego and abuse are commonplace. There is also the factor of when, trying to explain a concept to someone else, your own perceptions may be challeged and you may learn something in the process
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