If interaction with a human, under the conditions normally present in a laboratory, are sufficient to prevent interference, then I see no sensible interpretation where two worlds full of human observers are not prevented from interfering. Perhaps I should have been more clear—by larger, I meant a scale which includes human observers, such as the entire earth, not just one which is much larger than a human.
I don’t understand your first sentence, and even can’t specifically say why. What do you mean by an interpretation where human observers are prevented from interfering?
On the other hand, I would agree that if the collapse is objective, then we should be able to detect collapse induced by observers other than ourselves and experimentally tell apart observers from non-observers. But the standard use of “Copenhagen” doesn’t imply objective collapse, see e.g. Wikipedia.
Suppose a scientist measures some qbit’s state to be 0. My understanding is that, whatever version of Copenhagen you adhere to, you no longer believe that there is another version of the scientist somewhere who has measured 1. Maybe this is wrong because of the distinction between objective and subjective collapse, but then I have absolutely no idea what distinguishes Copenhagen from many worlds. In particular, I assume that Copenhagen implies that there aren’t many worlds.
Now, assume that after observing this 0, the scientist told the entire world and influenced the course of world events, having a significant effect on billions of human observers. According to my understanding, Copenhagen says there is only a single version of earth which actually exists—the one in which the scientist observed 0 and told everyone about it.
According to many worlds, there are multiple versions of earth—one in which the scientist observed 0, and one in which the scientist observed 1. Many worlds says that it is possible for these different versions of earth to interfere with each other, in exactly the same way that the worlds where the electron went through the left slit and where the electron went through the right slit can interfere. However, because the earth is chock full of physical observers to measure which state the earth is in, Copenhagen seems to say that there is only one version of the earth and so there certainly can’t be any interference.
My understanding is that, whatever version of Copenhagen you adhere to, you no longer believe that there is another version of the scientist somewhere who has measured 1.
Depends. From the outside observer’s point of view, he can be in a superposition of [has measured 0] and [has measured 1]. From the scientist’s point of view, the collapse has happened.
...but then I have absolutely no idea what distinguishes Copenhagen from many worlds.
That’s why it’s called “interpretation”. It’s the way how we speak about it, and some untestable statements about consciousness perhaps with some philosophical implications, which make the whole difference. Of course, an objective collapse is a different thing, but I don’t believe much Copenhagenists today believe in an objective collapse.
According to many worlds, there are multiple versions of earth—one in which the scientist observed 0, and one in which the scientist observed 1.
Such statement can be misleading. There is one version of Earth, but the individual observers see only certain projections. The difference between MWI and single-world interpretations is that MWI says that all projections are experienced.
If interaction with a human, under the conditions normally present in a laboratory, are sufficient to prevent interference, then I see no sensible interpretation where two worlds full of human observers are not prevented from interfering. Perhaps I should have been more clear—by larger, I meant a scale which includes human observers, such as the entire earth, not just one which is much larger than a human.
I don’t understand your first sentence, and even can’t specifically say why. What do you mean by an interpretation where human observers are prevented from interfering?
On the other hand, I would agree that if the collapse is objective, then we should be able to detect collapse induced by observers other than ourselves and experimentally tell apart observers from non-observers. But the standard use of “Copenhagen” doesn’t imply objective collapse, see e.g. Wikipedia.
Suppose a scientist measures some qbit’s state to be 0. My understanding is that, whatever version of Copenhagen you adhere to, you no longer believe that there is another version of the scientist somewhere who has measured 1. Maybe this is wrong because of the distinction between objective and subjective collapse, but then I have absolutely no idea what distinguishes Copenhagen from many worlds. In particular, I assume that Copenhagen implies that there aren’t many worlds.
Now, assume that after observing this 0, the scientist told the entire world and influenced the course of world events, having a significant effect on billions of human observers. According to my understanding, Copenhagen says there is only a single version of earth which actually exists—the one in which the scientist observed 0 and told everyone about it.
According to many worlds, there are multiple versions of earth—one in which the scientist observed 0, and one in which the scientist observed 1. Many worlds says that it is possible for these different versions of earth to interfere with each other, in exactly the same way that the worlds where the electron went through the left slit and where the electron went through the right slit can interfere. However, because the earth is chock full of physical observers to measure which state the earth is in, Copenhagen seems to say that there is only one version of the earth and so there certainly can’t be any interference.
Depends. From the outside observer’s point of view, he can be in a superposition of [has measured 0] and [has measured 1]. From the scientist’s point of view, the collapse has happened.
That’s why it’s called “interpretation”. It’s the way how we speak about it, and some untestable statements about consciousness perhaps with some philosophical implications, which make the whole difference. Of course, an objective collapse is a different thing, but I don’t believe much Copenhagenists today believe in an objective collapse.
Such statement can be misleading. There is one version of Earth, but the individual observers see only certain projections. The difference between MWI and single-world interpretations is that MWI says that all projections are experienced.