Set up a two-slit configuration and put a detector at one slit, and you see it firing half the time.
No, I see it firing both ways every time. In one world, I see it going left, and in another I see it going right. But because these very different states of my brain involve a great many particles in different places, the interactions between them are vanishingly nonexistent and my two otherworld brains don’t share the same thought. I am not aware of my other self who has seen the particle go the other way.
You may say that the electron goes both ways every time, but we still only have the detector firing half the time.
We have both detectors firing every time in the world which corresponds to the particle’s path. And since that creates a macroscopic divergence, the one detector doesn’t send an interference signal to the other world.
We also cannot predict which half of the trials will have the detector firing and which won’t.
We can predict it will go both ways each time, and divide the world in twain along its amplitude thickness, and that in each world we will observe the way it went in that world. If we are clever about it, we can arrange to have all particles end in the same place when we are done, and merge those worlds back together, creating an interference pattern which we can detect to demonstrate that the particle went both ways. This is problematic because entanglement is contagious, and as soon as something macroscopic becomes affected putting Humpty Dumpty back together again becomes prohibitive. Then the interference pattern vanishes and we’re left with divergent worlds, each seeing only the way it went on their side, and an other side which always saw it go the other way, with neither of them communicating to each other.
And everything we understand about particle physics indicates that both the 1⁄2 and the trial-by-trial unpredictability is NOT coming from ignorance of hidden properties or variables but from the fundamental way the universe works.
Correct. There are no hidden variables. It goes both ways every time. The dice are not invisible as they roll. There are instead no dice.
Five years ago I sat in a lab with a beam-spitter and a single-photon multiplier tube. I watched as the SPMT clicked half the time and didn’t click half the time, with no way to predict which I would observe. You’re claiming that the tube clicked every time, and the the part of me that noticed one half is very disconnected from the part of me that noticed the other half. The problem is that this still doesn’t allow me to postdict which of the two halves the part of me that is typing this should have in his memory right now.
Take the me sitting here right now, with the memory of the specific half of the clicks he has right now. As far as we understand physics, he can’t postdict which memory that should have been. Even in your model, he can postdict that there will be many branches of him with each possible memory, but he can’t postdict which of those branches he’ll be—only the probability of him being any one of the branches.
Moving the problem down one step puts it at the bottom.
The problem is that this still doesn’t allow me to postdict which of the two halves the part of me that is typing this should have in his memory right now.
One half of you should have one, and the other half should have the other. You should be aware intellectually that it is only the disconnect between your two halves’ brains not superimposing which prevents you from having both experiences in a singular person, and know that it is your physical entanglement with the fired particle which went both ways that is the cause. There’s nothing to post-dict. The phenomenon is not merely explained, but explained away. The particle split, on one side there is a you that saw it split right, on one side there is a you that saw it split left, and both of you are aware of this fact, and aware that the other you exists on the other side seeing the other result, because the particle always goes both ways and always makes each of you. There is no more to explain. You are in all branches, and it is not mysterious that each of you in each branch sees its branch and not the others. And unless some particularly striking consequence happened, all of them are writing messages similar to this, and getting replies similar to this.
The issue is not want of an explanation for the phenomenon, away or otherwise. We have an explanation of the phenomenon, in fact we have several. That’s not the issue. What I’m talking about here is the inherent, not-a-result-of-my-limited-knowledge probabilities that are a part of all explanations of the phenomenon.
Past me apparently insisted on trying to explain this in terminology that works well in collapse or pilot-wave models, but not in many-worlds models. Sorry about that. To try and clear this up, let me go through a “guess the beam-splitter result” game in many-worlds terminology and compare that to a “guess the trillionth digit of pi” game in the same terminology.
Aside: Technically it’s the amplitudes that split in many-worlds models, and somehow these amplitudes are multiplied by their complex conjugates to get you answers to questions about guessing games (no model has an explanation for that part). As is common around these parts, I’m going to ignore this and talk as if it’s the probabilities themselves that split. I guess nobody likes writing “square root” all the time.
Set up a 50⁄50 beam-splitter. Put a detector in one path and block the other. Write your choice of “Detected” or “Not Detected” on a piece of paper. Now fire a single photon. In Everett-speak, half of the yous end up in branches where the photon’s path matches your guess while half of the yous don’t. The 50⁄50 nature of this split remains even if you know the exact quantum state of the photon beforehand. Furthermore, the branching of yous that try to use all your physics knowledge to predict their observations have no larger a proportion of success than the branching of yous that make their predictions by just flipping a coin, always guessing Fire, or employing literally any other strategy that generates valid guesses. The 50⁄50 value of this branching process is completely decoupled from your predictions, no matter what information you use to make those predictions.
Compare this to the process of guessing the trillionth digit of pi. If you make your guess by rolling a quantum die, then 1 out of 10 yous will end up in a branch where your guess matches the actual trillionth digit of pi. If you instead use those algorithms you know to calculate a guess, and you code/run them correctly, then basically all of the yous end up in a branch where your guess is correct.
We now see the fundamental difference. Changing your guessing strategy results in different correct/incorrect branching ratios for the “guess the trillionth digit of pi” game but not for the “guess the beam-splitter result” game. This is the Everett-speak version of saying that the beam-splitter’s 50⁄50 odds is a property of the universe while the trillionth digit of pi’s 1⁄10 odds is a function of our (current) ignorance. You can opt to replace “odds” with “branching ratios” and declare that there is no probability of any kind, but that just seems like semantics to me. In particular the example of the ten trillionth digit of pi should not be what prompts this decision. Even in the many-worlds model there’s still a fundamental difference between that and the quantum processes that physicists cite as intrinsically random.
No, I see it firing both ways every time. In one world, I see it going left, and in another I see it going right. But because these very different states of my brain involve a great many particles in different places, the interactions between them are vanishingly nonexistent and my two otherworld brains don’t share the same thought. I am not aware of my other self who has seen the particle go the other way.
We have both detectors firing every time in the world which corresponds to the particle’s path. And since that creates a macroscopic divergence, the one detector doesn’t send an interference signal to the other world.
We can predict it will go both ways each time, and divide the world in twain along its amplitude thickness, and that in each world we will observe the way it went in that world. If we are clever about it, we can arrange to have all particles end in the same place when we are done, and merge those worlds back together, creating an interference pattern which we can detect to demonstrate that the particle went both ways. This is problematic because entanglement is contagious, and as soon as something macroscopic becomes affected putting Humpty Dumpty back together again becomes prohibitive. Then the interference pattern vanishes and we’re left with divergent worlds, each seeing only the way it went on their side, and an other side which always saw it go the other way, with neither of them communicating to each other.
Correct. There are no hidden variables. It goes both ways every time. The dice are not invisible as they roll. There are instead no dice.
You’ve only moved the problem down one step.
Five years ago I sat in a lab with a beam-spitter and a single-photon multiplier tube. I watched as the SPMT clicked half the time and didn’t click half the time, with no way to predict which I would observe. You’re claiming that the tube clicked every time, and the the part of me that noticed one half is very disconnected from the part of me that noticed the other half. The problem is that this still doesn’t allow me to postdict which of the two halves the part of me that is typing this should have in his memory right now.
Take the me sitting here right now, with the memory of the specific half of the clicks he has right now. As far as we understand physics, he can’t postdict which memory that should have been. Even in your model, he can postdict that there will be many branches of him with each possible memory, but he can’t postdict which of those branches he’ll be—only the probability of him being any one of the branches.
Moving the problem down one step puts it at the bottom.
One half of you should have one, and the other half should have the other. You should be aware intellectually that it is only the disconnect between your two halves’ brains not superimposing which prevents you from having both experiences in a singular person, and know that it is your physical entanglement with the fired particle which went both ways that is the cause. There’s nothing to post-dict. The phenomenon is not merely explained, but explained away. The particle split, on one side there is a you that saw it split right, on one side there is a you that saw it split left, and both of you are aware of this fact, and aware that the other you exists on the other side seeing the other result, because the particle always goes both ways and always makes each of you. There is no more to explain. You are in all branches, and it is not mysterious that each of you in each branch sees its branch and not the others. And unless some particularly striking consequence happened, all of them are writing messages similar to this, and getting replies similar to this.
The issue is not want of an explanation for the phenomenon, away or otherwise. We have an explanation of the phenomenon, in fact we have several. That’s not the issue. What I’m talking about here is the inherent, not-a-result-of-my-limited-knowledge probabilities that are a part of all explanations of the phenomenon.
Past me apparently insisted on trying to explain this in terminology that works well in collapse or pilot-wave models, but not in many-worlds models. Sorry about that. To try and clear this up, let me go through a “guess the beam-splitter result” game in many-worlds terminology and compare that to a “guess the trillionth digit of pi” game in the same terminology.
Aside: Technically it’s the amplitudes that split in many-worlds models, and somehow these amplitudes are multiplied by their complex conjugates to get you answers to questions about guessing games (no model has an explanation for that part). As is common around these parts, I’m going to ignore this and talk as if it’s the probabilities themselves that split. I guess nobody likes writing “square root” all the time.
Set up a 50⁄50 beam-splitter. Put a detector in one path and block the other. Write your choice of “Detected” or “Not Detected” on a piece of paper. Now fire a single photon. In Everett-speak, half of the yous end up in branches where the photon’s path matches your guess while half of the yous don’t. The 50⁄50 nature of this split remains even if you know the exact quantum state of the photon beforehand. Furthermore, the branching of yous that try to use all your physics knowledge to predict their observations have no larger a proportion of success than the branching of yous that make their predictions by just flipping a coin, always guessing Fire, or employing literally any other strategy that generates valid guesses. The 50⁄50 value of this branching process is completely decoupled from your predictions, no matter what information you use to make those predictions.
Compare this to the process of guessing the trillionth digit of pi. If you make your guess by rolling a quantum die, then 1 out of 10 yous will end up in a branch where your guess matches the actual trillionth digit of pi. If you instead use those algorithms you know to calculate a guess, and you code/run them correctly, then basically all of the yous end up in a branch where your guess is correct.
We now see the fundamental difference. Changing your guessing strategy results in different correct/incorrect branching ratios for the “guess the trillionth digit of pi” game but not for the “guess the beam-splitter result” game. This is the Everett-speak version of saying that the beam-splitter’s 50⁄50 odds is a property of the universe while the trillionth digit of pi’s 1⁄10 odds is a function of our (current) ignorance. You can opt to replace “odds” with “branching ratios” and declare that there is no probability of any kind, but that just seems like semantics to me. In particular the example of the ten trillionth digit of pi should not be what prompts this decision. Even in the many-worlds model there’s still a fundamental difference between that and the quantum processes that physicists cite as intrinsically random.