Timeline for Practically, how does an 'observer' collapse a wave function?
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| Nov 4, 2019 at 20:21 | history | edited | A_P | CC BY-SA 4.0 |
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| Nov 4, 2019 at 16:08 | history | edited | A_P | CC BY-SA 4.0 |
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| Oct 29, 2019 at 0:17 | comment | added | A_P | Cavepeople couldn't detect even a single-particle superposition, and every particle is in such a superposition when looked at in some basis. Does this mean every particle was in "two worlds" back then? Of course not. Besides, many people make the mistake of thinking that when the worlds branch, there is a single result. This isn't true. All possibilities are still there, even if they don't interfere. It's only when the whole thing entangles with you that something distinct happens (from your perspective). Then again, I'm just a nobody, so probably better to read "the experts." | |
| Oct 29, 2019 at 0:15 | comment | added | A_P | @JackR.Woods We call a superposition decoherent when it grows beyond our ability to manage (or detect). Because the branches of the superposition are exceedingly unlikely to interfere beyond that point, some people like to say that we should call them "different worlds." But there's no special event that happens that could demarcate a clear boundary, so I feel this is a bit silly. Why should "nearly impossible for modern humans to reverse" be the boundary for world creation? (cont'd) | |
| Oct 28, 2019 at 13:35 | comment | added | Jack R. Woods | @A_P I'm afraid I also need simplistic explanation, but I do watch a lot of science lectures. How does your answer agree/conflict with a "many worlds" interpretation of quantum mechanics? | |
| Oct 27, 2019 at 4:42 | comment | added | A_P | If we let $D_+$ mean detector states where there was detection and $D_-$ where there wasn't, then $|\psi\rangle$ evolves to $|D_+\rangle\otimes|\psi_1\rangle + |D_-\rangle\otimes|\psi_2\rangle$, where $|\psi_2\rangle$ is a superposition of position eigenstates. Those can still interfere with each other; they just couldn't interfere with any $|\psi_1\rangle$ states (ignoring that the particle has been absorbed on that branch anyway). | |
| Oct 27, 2019 at 4:03 | comment | added | A_P | @JPattarini Another question is a good idea. I'm not a physicist. But why do you think we would see a Quantum Zeno effect? There's only one detector, at a fixed distance, that's responsible for the partial collapse. Also, the state still evolves; it just doesn't do so as a coherent superposition. | |
| Oct 27, 2019 at 3:27 | comment | added | JPattarini | @A_P I think I’ll have to post a dedicated question on this, but it seems that if a negative result from a detector is enough to update the wavefunction, then we should see Quantum Zeno effects in any Renninger-like setup. Basically if detection and non-detection are both measurements on equal footing, it feels like state evolution should hardly be able to occur at all | |
| Oct 27, 2019 at 3:21 | comment | added | A_P | @JPattarini Thanks for mentioning this. The lack of a detection event can be just as telling as the presence of one. In the Renninger gedankenexperiment, the wave function isn't reduced to a point, but to the hemisphere of trajectories where it wasn't detected. The simple way to understand this all is that whenever information is gained about a state, this constitutes an entanglement. And clearly information can sometimes come via negative means. Rather than being "forced to disturb it," here we tried and failed to disturb it, in a sense. But trying was enough. | |
| Oct 26, 2019 at 23:59 | comment | added | JPattarini | @A_P It would be great if you could speak to why negative or interaction free results like Renninger’s are equally effective in reducing the wave function to classical values. | |
| Oct 25, 2019 at 4:14 | history | edited | A_P | CC BY-SA 4.0 |
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| Oct 24, 2019 at 22:15 | history | edited | A_P | CC BY-SA 4.0 |
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| Oct 24, 2019 at 16:16 | history | edited | A_P | CC BY-SA 4.0 |
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| S Oct 24, 2019 at 15:58 | history | edited | A_P | CC BY-SA 4.0 |
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| S Oct 24, 2019 at 15:58 | history | suggested | user137661 | CC BY-SA 4.0 |
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| Oct 24, 2019 at 15:53 | review | Suggested edits | |||
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| Oct 24, 2019 at 15:39 | comment | added | Vilx- | In the macro world we can observe things without (noticeably) affecting them because there are tiny things (photons) that can bounce off of big things without significantly affecting them. But when we enter the quantum realm, there is nothing smaller still, because the quantum particles are already (by definition) the smallest things in existence. | |
| Oct 24, 2019 at 15:37 | comment | added | Vilx- | The way I understand it: there's no way to "telepathically" measure something about the electron. We either need to bounce another electron (or proton, or whatever) off of it, or perhaps we can get something to be affected by its electrical field - but the electron will be equally affected by the measuring device's field. In other words, in order to measure the electron, we are forced to disturb it. And that's when the "collapse" happens. That is "observing". | |
| Oct 24, 2019 at 15:34 | history | edited | A_P | CC BY-SA 4.0 |
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| Oct 24, 2019 at 13:54 | history | edited | A_P | CC BY-SA 4.0 |
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| Oct 24, 2019 at 13:45 | vote | accept | Runeaway3 | ||
| Oct 23, 2019 at 23:05 | history | answered | A_P | CC BY-SA 4.0 |