No.
First, at this point I am reasonably confident that collapse actually happens. Either it does or it doesn’t, and non-collapse interpretations of QM are those that have unfounded faith that quantum wave states always evolve unitarily. As I argued in this paper, that assumption is a logically invalid inference. So given that we don’t observe quantum superpositions in the macroscopic world, I’d wager very heavily on the conclusion that collapse actually happens.
But what causes it? Since we can’t consciously observe a (collapsed) quantum mechanical outcome without being conscious – duh! – many have argued that conscious observation actually causes collapse. (Others have argued that consciousness and collapse are related in different ways, such as collapse causing consciousness.) In this blog post, I discussed the consciousness-causes-collapse hypothesis (“CCCH”) in quantum mechanics. I pointed out that even though I didn’t think CCCH was correct, it had not yet been falsified, despite an awful paper that claimed to have falsified it (which I refuted in this paper).
Two things have happened since then. First, I showed in this paper that the relativity of quantum superpositions is inconsistent with the preparation of macroscopic quantum superpositions, which itself implies that CCCH is false.
Second, this paper was published a few days ago. Essentially, it’s a Wigner’s-Friend-esque thought experiment in which a poison-containing breaks or does not break at 12pm, per a QM outcome, but the person in the room will be unconscious until 1pm. That’s it. If CCCH is correct, then collapse of the wave function will not occur until the person is conscious at 1pm... but if he is conscious at 1pm, how could the wave state possibly collapse to an outcome in which the person dies at noon? It’s a very simple logical argument (even though it is not explained well in the paper) that is probably valid, given some basic assumptions about CCCH.
So when does collapse actually occur? I’ve been arguing that it happens as soon as an event or new fact (i.e., new information) eliminates possibilities, and the essentially universal entanglement of stuff in the universe (due to transitivity of correlation) makes it so that macroscopically distinct possibilities are eliminated very, very quickly. For example, you might have a large molecule in a superposition of two macroscopically distinct position eigenstates, but almost immediately one of those possible states gets eliminated by some decoherence event, in which new information is produced in the universe that actualizes the molecule’s location in one of those position eigenstates. That is the actual collapse, and it happens long before any quantum superposition could get amplified to a macroscopic superposition.
Is this what is meant by decoherence?
ReplyDeleteNot quite. A decoherence event is just one that destroys the coherence of a quantum superposition, but decoherence is not necessarily (nor usually) associated with collapse or the production of new information. The original creators of decoherence theory are mostly MWI supporters, and they would say that decoherence just results in splitting worlds that are out of phase with each other and will never interfere (although they could "in principle," giving rise to the purported possibility of Wigner's Friend). Obviously I think MWI is silly (and unscientific), so if collapse actually occurs, then the information content of the universe changes.
ReplyDeleteWhy the assumption that consciousness needs to come from the single observer? If the room never opens, the outcome would still be undetermined, and the superposition would remain. The opening or closing of the room, and our consciousness of the situation in the room would only then determine the position.
ReplyDeleteThanks for the comment! You said "If the room never opens, the outcome would still be undetermined, and the superposition would remain." This is incorrect. The only way to keep the objects in a room in a superposition is if there is no interaction between particles/fields in the room and those outside the room, a situation that philosophers of physics often call "isolation." Such isolation is not possible because the universe is bathed in radiation, particles, etc., that constantly decohere superpositions. Long (long, long) before a conscious observer ever looks at a macroscopic system, any detectable superposition has already collapsed. Consciousness does not collapse superpositions.
DeleteThanks for the quick reply! The thought experiment is that the room never opens, that it is already open is irrelevant. That rooms get opened by decoherence, meaning the door slips open or something, makes it possible to watch. When the door is open but no one watches, it is still in superposition. For two different people there can be different states. For astronaut John, who will travel to the far side of space, remaining in isolation, the room can be in superposition, while for Henry, remaining here and watching the position in the room the room is no longer is superposition. They are both right.
DeleteI think that in every experiment done, there is always a conscious observer present as a final checkpoint. So we never can tell that that conscious observer is not the one that causes the collapse. And about time, or causality: John Wheeler's Delayed Choice experiment shows us that the past is not the past as we know it, so we see that timeline can change backwards
Delete