what tests do quantum physicists do to know, say, the spin of two entangled have not been decided at the moment of their creation as entangled particles?

I have been having trouble with this for some time. how do you know it is ambiguous if you can't measure it without making it definite?

My understanding is this.

You can alter the spin (up/down) by passing one of the entangled pair through a magnetic field. You can't know what the spin is, but you can flip it from whatever it was. When you do this, the final detected spin of the other partner, is always opposite so it must change instantaneously at the time of "flipping". You can't send information this way because you have no control over the actual spin state of the partner you are messing with. To do this would require manipulating the spin to a known state (a measurement) and will destroy the entanglement.

Anyone else have thoughts on this?

(Hey look! Two threads that have nothing to do with relativity!)

Hum,
My take on it would be that all we know about the two particles, when they are created, is that they have, say, opposite spins…
They are just probabilities.

The actual confirmation of that property (wither it is up or down), by measuring one particle will instantly collapse the probability wave function of the other particle.
This is a collapse of a probability function; and since I would regard the two particles as actually being <b>same</b> extended particle and share the same wave function, it would explain why they react instantaneously. Though, what seems to be action at a distance may also be an interaction between the two particles through the temporal dimension.
Either way, `information` had not been transmitted faster than the speed of light and upset special relativity…

blobrana:

and since I would regard the two particles as actually being same extended particle

Not sure I agree with this. Are they not considered two particles that share a quantum state? I have always understood entanglement to involve real and seperate particles.

I have always understood entanglement to involve real and seperate particles.

Yes.
That would be a simpler explanation.
Er, i was also thinking about the Classic Two-Slit Experiment, where the probability wave of a particle is basically split 50/50.

Please disregard that radical thought.

Radical? On this forum? Never!

Does any one know for sure if particles of all the same spin can be generated? Or is it like nuclear decay - inherently unpredictable?

I think I know what the answer has to be...

Ask W. Pauli - he has an "exclusive" take on this!

Yeah, figured as much. Can't have fermions with the same quantum numbers.

Yay! That was quick. It's called the exclusion principle. So, how many quantum numbers are there (it's a test, a tease).

Quarkhead:

Principal Quantum Number: n

Azimuthal Quantum Number: L

Magnetic Quantum Number: mL

Spin Quantum Number: ms

I may not have the stuff off the top of my head, but an educated mind with google is a powerful thing!

cato, I suggest looking up "Bell's theorem".

Seems to still be much ongoing theorizing and experimenting to decide if there are hidden local variables (QM is not "complete"), or non-local "spooky action at a distance"

Bell's theorem (+experiments) rules out local hidden variable theories, doesn't it?

Yes, but I find many apparently valid references to experiments being questioned (Alain, et al) and other papers interpreting QM and nonlocality differently.

If this has been resolved, I'd like to know about it. Maybe I'm just not looking hard enough...