originally posted in:Secular Sevens
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I just picked up a book by Brian Greene and one portion of it mildly stumped me. I figured that a few of you here could lend a helping hand and provide insight on it. I was reading and the book began delving into quantum uncertainty and I completely understood it up to one point and that point was when he began talking about observing the spin of an electron. Maybe he didn't word it properly or I just blew past it without much thought (probably the latter), but he broke down how electrons spin and how if you observe it the electron will "choose" between spinning clockwise or counterclockwise on the axis you picked to observe it from (at least from I gathered, correct me if I am wrong). Now, I'm not very well informed on the tools used in modern day labs and my question is, what happens if you observe the same electron from two different locations at once? Is this possible or with modern day equipment are we only limited to one direction? Would the electron spin clockwise or counter-clockwise from each observation point no matter how many angles we observe it from?
Thanks.
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"Observation" in physics usually basically refers to any interaction with the particle. When the electron isn't being observed, it's in a superposition of its quantum spin states. That means its spin is both up and down, "undefined" for all practical purposes. But when the electron comes into a situation where it has to "choose", where it is observed, it will fall down to either spin up or spin down. If the electron is in a magnetic field, it will more likely "choose" spin down because spin down is a lower energy state. On the other hand, shooting it with a photon and giving it just enough energy can transfer it into the higher energy spin up state. We can never observe it having both spins at the same time. It's a natural limitation of quantum mechanics. Unless the particle has a preferred spin, its spin is impossible to predict before observation. When it's observed, it will only have one spin and one spin only.