3 ms·

I also was interested in the same quote. In what sense did quantum mechanics break this principle?

• Tor3 8y ago
  That depends a bit on how we look at it, I suppose.. usually we talk about about e.g. an electron that spins up and down at the same time, whereas in classical physics it could only do one of those things at the time. So it does two things that (classically) contradict each other. So when you look at it with a classical view it seems like the electron belongs to the group that spins up, thus it can't belong to the group that spins the opposite way.. but it does.
  • naasking 8y ago
    > usually we talk about about e.g. an electron that spins up and down at the same time, whereas in classical physics it could only do one of those things at the time. So it does two things that (classically) contradict each other. That's because you're conflating "spin" for "angular motion" in classical physics. They just aren't the same thing, as particle spin clearly has different properties.
    • Tor3 8y ago
      I'm not conflating it - I'm fully aware that it isn't angular spin. It's still called 'spin' simply because it's hard to find a term that explains what it really is. But as far as I know it's still considered separate states, in the same way that two locations are considered separate. In the quantum world it's still possible to be in both states or places at once - and that's where the quantum weirdness is. Nobody would care or talk about it if being in two spin states at the same time wasn't more strange than wearing a shoe and a tie at the same time.
      • naasking 8y ago
        > It's still called 'spin' simply because it's hard to find a term that explains what it really is. No, it's called spin because it's a quantum mechanical form of angular momentum that simply has no analog in classical physics, and some physicists at the time suggested a physical interpretation that was consistent with an older form of quantum theory. > In the quantum world it's still possible to be in both states or places at once - and that's where the quantum weirdness is. Nobody would care or talk about it if being in two spin states at the same time wasn't more strange than wearing a shoe and a tie at the same time. Again, because they are conflating it with classical notions. Superposition has classical, deterministic interpretations which feature none of this apparent "weirdness".