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## Main Question or Discussion Point

Hello everyone, I hope you are having a nice day,

I was reading [The principles of Quantum Mechanics by P.A.M Dirac], and I was attracted to the definition of size. The book says: "

If I am correct, we can observe the state of one of the entangled particles (in case of 2 particles) by observing the state of the other particle. If this implies that the particle is observed with very little disturbance (maybe no disturbance at all), then

the particle should be really, really big (if not infinite) in "size", right? Does that mean entangled particles can be divided into two halves, a quantum mechanical half (the particle we observe) & a classical mechanical half (the particle we observe by relying on the observation of the other particle)?

Is the problem with our definition of size? or is it that I am missing more information?

I was reading [The principles of Quantum Mechanics by P.A.M Dirac], and I was attracted to the definition of size. The book says: "

*If the object under observation is such that the unavoidable limiting disturbance is negligible, then the object is big in the absolute sense and we may apply classical mechanics to it. If, on the other hand, the limiting disturbance is not negligible, then the object is small in the absolute sense and we require a new theory for dealing with it.*" This definition makes me wonder about the "size" of entangled particles.If I am correct, we can observe the state of one of the entangled particles (in case of 2 particles) by observing the state of the other particle. If this implies that the particle is observed with very little disturbance (maybe no disturbance at all), then

the particle should be really, really big (if not infinite) in "size", right? Does that mean entangled particles can be divided into two halves, a quantum mechanical half (the particle we observe) & a classical mechanical half (the particle we observe by relying on the observation of the other particle)?

Is the problem with our definition of size? or is it that I am missing more information?