My husband is watching YouTube and there’s a man discussing quantum entanglement.
His description: There are two particles. They can be either green or red, but they are both colors until they’re measured. Once you measure one, though, it automatically determines that the other is the same. No matter how many times you measured, or how far you separated the particles, the two would always be the same color.
Why does one being one color guarantee that the other one would be? How do they “know” to always be that color? And what sort of implication does that have for science/real world, other than being really cool?
In: Physics
Because all physical interactions follow conservation laws. If you have a good enough understanding of how two particles interact, you can predict the outcomes following an actual experimental interaction. For example, if you shoot a photon into a fancy crystal (a bean splitter), and it is split into two lower energy photons, you know that the total spin of the system must be conserved. For such a pair of photons in this example, the total spin must be zero. Therefore, if you measure the spin of one of the photons, and get a spin of 1/2, you then “instantaneously” know the spin of the other particle must be -1/2.
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