Observers in Consistent Histories

[jms5631]

I was reading about the Consistent Histories interpretation, or Super Copenhagen as it is called(though I see more similarity to Everett) when the question of reality in such a scheme was addressed. The answer, I believe by Hartle, was along the lines of this: "The agreement among human observers about what is happening and has happened...this agreement is explained in quantum mechanics by the fact that the great majority of us are using various coarse grainings of a single set of histories consituting the quasiclassical realm."

My question, which may reflect just an ignorance(I'm still just an undergrad) is if observers were using various coarse grainings in a set, wouldn't they be perceiving various histories instead of one which they can agree upon? I don't see how agreement emerges. Just a peculiarity I noticed that's been bothering me, thanks in advance for any responses showing where I go wrong.

 

[wawenspop]

I would say that the coarse grain is a quantum-sized coarse grain. ie very very small - about 10 to the minus 35 meters and similar small times.
So histories at the macro size would show no contradiction.
For example, the orbit of Jupiter is consistent as would be its histories whereas the orbit of an electron is not because its in the quantum realm.

 

[WaveJumper]

I was reading about the Consistent Histories interpretation, or Super Copenhagen as it is called(though I see more similarity to Everett) when the question of reality in such a scheme was addressed. The answer, I believe by Hartle, was along the lines of this: "The agreement among human observers about what is happening and has happened...this agreement is explained in quantum mechanics by the fact that the great majority of us are using various coarse grainings of a single set of histories consituting the quasiclassical realm."

My question, which may reflect just an ignorance(I'm still just an undergrad) is if observers were using various coarse grainings in a set, wouldn't they be perceiving various histories instead of one which they can agree upon? I don't see how agreement emerges. Just a peculiarity I noticed that's been bothering me, thanks in advance for any responses showing where I go wrong.

Particles become entangled with the environment and decohere in a single state out of the probability amplitude calculated with the Schroedinger equation. This causes the relative agreement between observers. If you are thinking quantum mechanically about the classical realm, you will fail. This also holds true vice-versa. However, the classical phenomena governed by the Newtonean laws, when viewed quantum mechanically, are essentially deterministic.