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
A key property of quantum mechanics is superposition. For example, a particle that we know can only be spinning clockwise or counterclockwise can simultaneously be doing both because of superposition. When we measure it, it will land in one of the two options – CW or CCW – randomly. This isn’t because it was secretly in one the whole time, before we measured it the particle was literally doing both.
What if that particle, however, were two particles? And maybe all we know is that they are spinning opposite of each other. And so the state is no longer CW or CCW but (CW & CCW) OR (CCW & CW). In this way both of the particles are in superposition, not just with another “version” of themselves, but in superposition with each other. If I just measure the first particle and find it to be CCW then because the only way to measure this was if it was (CCW & CW) then I know that the second particle must be CW. Because they are in superposition with each other, by measuring one of them I have forced them both to collapse their states. If the options had been (CW & CCW) OR (CCW & CCW), then measuring the first to be CW would have done nothing and so they wouldn’t be entangled. But that’s all entanglement is: The property of superposition applied to more than one particle.
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