When you create the two opposite-spin particles They are not opposite spin, they are entangled! Their spin is undefined until measured even though they are per

When you create the two opposite-spin particles They are not opposite spin, they are entangled! Their spin is undefined until measured even though they are perfectly anticorrelated, as you mention. Here's another way to frame this: Composite systems can exhibit entanglement. The Hilbert space such systems live in (H) is the tensor product of the individual component Hilbert spaces (H1, H2). Now the most general state in H is a linear combination ∑ c_ij |i>_1 ⊗ |j>_2 where the subscripts 1 and 2 refer to the component Hilbert spaces. Some of these superpositions are not separable into tensor products of states from each component space H1 and H2. One such superposition is (omitting c_ij) |00> + |11>, as you can see it is not separable. The state |01> + |11> on the other hand can be separated as (|0> + |1>)⊗|1>. An entangled state is an inseparable state. So the point is that classical analogies are not to be used when dealing with quantum mechanics. Unless someone proves local realism or something replaces QM, that's how it's got to be!