So I’m running through the Quantum Mechanics sequence, and am about 2⁄3 of the way through. Wanted to check in here to ask a few questions, and see if there aren’t some hidden gotchas from people knowledgeable about the subject who have also read the sequence.
My biggest hangup so far has been understanding when it is that different quantum configurations sum, versus when they don’t. All of the experiments from the earlier posts (such as distinct configurations) seem to indicate that configurations sum when they are in the “same” time and place. Eliezer indicates at some point that this is “smeared” in some sense, perhaps due to the fact that all particles are smeared in space in time; therefore if two “particles” in different worlds don’t arrive at the same place at exactly the same time, the smearing will cause the tail end of their amplitude distributions to still interact, resulting in a less perfect collision with somewhat partial results to what would have happened in the perfect experiment.
The hangup becomes an issue, barring any of my own misunderstanding (which is of course likely), when he starts talking about macroscopic other worlds. He goes so far as to say that when a quantum event is “observed,” what really happens is that different versions of the experimenter become decohered with the various potential states of the particle.
Several things don’t seem quite right here. First, Eliezer seems to imply here that brains only work (to the extent that they can have beliefs capable of being acted on) when they work digitally, with at least some neurons having definite on or off states. What happens to the conservation of probability volume due to Liouville’s Theorem described in Classical Configuration Spaces? Or maybe I misunderstand here, and the probability volumes actually do become sharply concentrated in two positions. But then why is it not possible for probability volumes to become usually or always sharply concentrated in one position, giving us, for all practical purposes, a single world?
Backing up a bit though. What keeps different worlds from interacting? Eliezer implies in Decoherence that one important reason that decohered particles are such is a separation in space. What I fail to understand, if there is not some specified other axis, is why the claim stands that different but similar worlds (different only along that axis) fail to interact! According to his interpretation (or my interpretation of his interpretation) of quantum entanglement, your observation of a polarized particle at one end of a light-year limits the versions of your friend (who observed the tangled particle) that you are capable of meeting when you compare notes in the middle. But why do you just as easily not meet any other version of your friend? What is the invisible axis besides space and time that decoheres worlds, if we meet at the same place and time no matter what we observe?
More importantly, what keeps neurons which are at the same space and time from interacting with their other-world counterparts, as if they were as real as their this-world self?
Unless I’m completely off here, couldn’t there be many fewer possible worlds than Eliezer suggests? In extremely controlled experiments, we observe decoherence on rather macroscopic levels, but isn’t “controlled” precisely the point? In most normal quantum interactions, isn’t there always going to be interference between worlds? And what if that interference by the nature of the fundamental laws just so happens to have some property (maybe a sort of race condition) that causes, usually, microscopic other worlds to merge? On average, if possible worlds become macroscopic enough, still-real interactions between the worlds become increasingly likely, and they are no longer “other worlds” but actually-interacting same-world, to the point where no two differently configured sets of neurons could ever observe differently.
I should stop here before I carry on any early-introduced fallacy to increasingly absurd conclusions. Would be very interested in how to resolve my confusion here.
First, Eliezer seems to imply here that brains only work (to the extent that they can have beliefs capable of being acted on) when they work digitally, with at least some neurons having definite on or off states.
I assume you mean this section:
Your world does not split into exactly two new subprocesses on the exact occasion when you see “ABSORBED” or “TRANSMITTED” on the LCD screen of a photon sensor. We are constantly being superposed and decohered, all the time, sometimes along continuous dimensions—though brains are digital and involve whole neurons firing, and fire/not-fire would be an extremely decoherent state even of a single neuron… There would seem to be room for something unexpected to account for the Born statistics—a better understanding of the anthropic weight of observers, or a better understanding of the brain’s superpositions—without new fundamentals.
He’s not exactly saying that brains only work digitally—they don’t; neuron activation isn’t only about electrical impulses—he’s just talking about one particular process that happens in the brain. At least, as far as I can tell.
They certainly don’t work only digitally, but the suggestion seems to be that for most brain states at the level of “belief” it is required that at least some neurons have definite states, if only in the sense of “neuron A is firing at some definite analog value.”
So I’m running through the Quantum Mechanics sequence, and am about 2⁄3 of the way through. Wanted to check in here to ask a few questions, and see if there aren’t some hidden gotchas from people knowledgeable about the subject who have also read the sequence.
My biggest hangup so far has been understanding when it is that different quantum configurations sum, versus when they don’t. All of the experiments from the earlier posts (such as distinct configurations) seem to indicate that configurations sum when they are in the “same” time and place. Eliezer indicates at some point that this is “smeared” in some sense, perhaps due to the fact that all particles are smeared in space in time; therefore if two “particles” in different worlds don’t arrive at the same place at exactly the same time, the smearing will cause the tail end of their amplitude distributions to still interact, resulting in a less perfect collision with somewhat partial results to what would have happened in the perfect experiment.
The hangup becomes an issue, barring any of my own misunderstanding (which is of course likely), when he starts talking about macroscopic other worlds. He goes so far as to say that when a quantum event is “observed,” what really happens is that different versions of the experimenter become decohered with the various potential states of the particle.
Several things don’t seem quite right here. First, Eliezer seems to imply here that brains only work (to the extent that they can have beliefs capable of being acted on) when they work digitally, with at least some neurons having definite on or off states. What happens to the conservation of probability volume due to Liouville’s Theorem described in Classical Configuration Spaces? Or maybe I misunderstand here, and the probability volumes actually do become sharply concentrated in two positions. But then why is it not possible for probability volumes to become usually or always sharply concentrated in one position, giving us, for all practical purposes, a single world?
Backing up a bit though. What keeps different worlds from interacting? Eliezer implies in Decoherence that one important reason that decohered particles are such is a separation in space. What I fail to understand, if there is not some specified other axis, is why the claim stands that different but similar worlds (different only along that axis) fail to interact! According to his interpretation (or my interpretation of his interpretation) of quantum entanglement, your observation of a polarized particle at one end of a light-year limits the versions of your friend (who observed the tangled particle) that you are capable of meeting when you compare notes in the middle. But why do you just as easily not meet any other version of your friend? What is the invisible axis besides space and time that decoheres worlds, if we meet at the same place and time no matter what we observe?
More importantly, what keeps neurons which are at the same space and time from interacting with their other-world counterparts, as if they were as real as their this-world self?
Unless I’m completely off here, couldn’t there be many fewer possible worlds than Eliezer suggests? In extremely controlled experiments, we observe decoherence on rather macroscopic levels, but isn’t “controlled” precisely the point? In most normal quantum interactions, isn’t there always going to be interference between worlds? And what if that interference by the nature of the fundamental laws just so happens to have some property (maybe a sort of race condition) that causes, usually, microscopic other worlds to merge? On average, if possible worlds become macroscopic enough, still-real interactions between the worlds become increasingly likely, and they are no longer “other worlds” but actually-interacting same-world, to the point where no two differently configured sets of neurons could ever observe differently.
I should stop here before I carry on any early-introduced fallacy to increasingly absurd conclusions. Would be very interested in how to resolve my confusion here.
I assume you mean this section:
He’s not exactly saying that brains only work digitally—they don’t; neuron activation isn’t only about electrical impulses—he’s just talking about one particular process that happens in the brain. At least, as far as I can tell.
They certainly don’t work only digitally, but the suggestion seems to be that for most brain states at the level of “belief” it is required that at least some neurons have definite states, if only in the sense of “neuron A is firing at some definite analog value.”