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I'm not sure your description of the difference between classical and quantum contradicts what I said. In fact I think they are compatible I didn't use any n

by platz 10y ago

I'm not sure your description of the difference between classical and quantum contradicts what I said. In fact I think they are compatible I didn't use any notion of "predetermination" when describing the quantum mechanical version. I said that "there could be several different degrees of freedom to measure on" I meant this to exactly correspond to "the exact outcome is only established when one looks in the first box". The only notion of "predetermination" I ascribe to is that of the whole system, which is completely described by the quantum states before observation, but as i said this tells us nothing of the parts it's composed of. (I am choosing in my description to put less emphasis on the particles/parts (which normally get all the attention), and more on the quantum system)

danbruc 10y ago
I was especially responding to this part. This (intuitively) makes more sense to me than saying "information traveled" and "action at a distance" You can not get away from non-locality in quantum mechanics. Because the outcome is only determined when a measurement is performed, this »information« has to travel to the entangled partner when the measurement is made. And this must happen instantaneously. In the classical example you can avoid this because the outcome is already determined during the setup. I said that "there could be several different degrees of freedom to measure on" I meant this to exactly correspond to "the exact outcome is only established when one looks in the first box". This are three different things. You can of course decide to measure the spin along any axis you like, that is you can choose the observable. When you do this, then you are not measuring different degrees of freedom, you are measuring the same degree of freedom, the spin, in different bases. But, and that is what I meant, even if you always measure the spin along the same axis, say along the positive x axis, then the spin of an electron in a superposition of spin either +1 or -1 along this axis is only determined at the time of the measurement. Before that measurement the electron had no definite spin along this axis.
- platz 10y ago
  > You can not get away from non-locality in quantum mechanics. I didn't/am not claiming that the effects are local. > only determined at the time of the measurement... Before that measurement the electron had no definite spin along this axis. That is what I'm saying as well. I didn't claim otherwise.
  - danbruc 10y ago
    Well, then I just misunderstood you. I should probably better have quoted this sentence in my last comment. So to me, that doesn't suggest that something "traveled" to the other box, just like in the Classical version. I read this as you saying nothing travels from the measurement to the entangled partner. But this is what happens, »Someone just looked inside me and saw heads, please show tails when someone looks inside you!« travels from the measurement to the entangled partner. And if that happens instantaneously, then this is a non-local effect. That is why I thought you wanted to say nothing travels, neither slowly nor instantaneously and therefore non-locally.

by platz 10y ago

danbruc 10y ago

I was especially responding to this part. This (intuitively) makes more sense to me than saying "information traveled" and "action at a distance" You can not get away from non-locality in quantum mechanics. Because the outcome is only determined when a measurement is performed, this »information« has to travel to the entangled partner when the measurement is made. And this must happen instantaneously. In the classical example you can avoid this because the outcome is already determined during the setup. I said that "there could be several different degrees of freedom to measure on" I meant this to exactly correspond to "the exact outcome is only established when one looks in the first box". This are three different things. You can of course decide to measure the spin along any axis you like, that is you can choose the observable. When you do this, then you are not measuring different degrees of freedom, you are measuring the same degree of freedom, the spin, in different bases. But, and that is what I meant, even if you always measure the spin along the same axis, say along the positive x axis, then the spin of an electron in a superposition of spin either +1 or -1 along this axis is only determined at the time of the measurement. Before that measurement the electron had no definite spin along this axis.

platz 10y ago
> You can not get away from non-locality in quantum mechanics. I didn't/am not claiming that the effects are local. > only determined at the time of the measurement... Before that measurement the electron had no definite spin along this axis. That is what I'm saying as well. I didn't claim otherwise.
- danbruc 10y ago
  Well, then I just misunderstood you. I should probably better have quoted this sentence in my last comment. So to me, that doesn't suggest that something "traveled" to the other box, just like in the Classical version. I read this as you saying nothing travels from the measurement to the entangled partner. But this is what happens, »Someone just looked inside me and saw heads, please show tails when someone looks inside you!« travels from the measurement to the entangled partner. And if that happens instantaneously, then this is a non-local effect. That is why I thought you wanted to say nothing travels, neither slowly nor instantaneously and therefore non-locally.