This is an archive of past discussions with User:Quondum. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.
I was tempted to open a discussion on the talk page first, but then thought that you might see it from my perspective, and that discussing it only if you objected would likely be the more efficient process. We probably differ on how "extraneous" material is to an article (me towards the side of "keep it directly relevant to the topic" and you towards "include related interesting information"). I lean towards the latter perspective if there is no better place to put some useful information. In this instance, TU (time unit) and Unit of time are sufficiently obvious and give the necessary information (admittedly, I only found these when expressing my thoughts here). However, here I respect the feelings of others such as yourself, and if you have any strong feelings on the matter, they are likely stronger than mine :) —Quondum18:29, 7 October 2024 (UTC)
I think you made the right choice (Trust me. My feelings are no stronger than yours). Happy to let the consensus be determined by what others think. Dondervogel 2 (talk) 19:02, 7 October 2024 (UTC)
Template editor
Regarding our discussion at Template talk:Val#A teragram is not a tonne (permalink), I would be happy to assign you the right if wanted. First, please examine WP:TPE and my comment in this ANI report. Template editing means bold does not apply. Even if no one ever responds, a template editor should announce what they plan to do, allow a day or two, then do it, then check for problems. Module:Val/units is unlikely to give errors but it is useful to check the current script errors before making a change live, and after, and a couple of days after that (it takes time for changes to have an effect in articles). That link currently shows a stuff-up which can be found by picking a representative article, then looking at its "related changes" in the left sidebar. Then select Namespace (Article) and check (tick) "invert selection" and click Show. It's likely that some of the recent infobox edits broke some articles. That might be a bug in the new code, or it might be broken wikitext in the articles. Either way, someone should look for it and fix it. Module:Val is not used on very many articles but it is nevertheless a good idea to first copy the current module to Module:Val/units/sandbox, then make changes, then test them. Think about it, then update the main module in one edit. If the right is wanted, reply here and say you have absorbed all that. Johnuniq (talk) 01:11, 11 October 2024 (UTC)
I am really in two minds about this, so let's hold off. Though I have reviewed and understood all that you have said and linked above (especially the measured systematic approach), there are too many personally specific factors to list here. I cleaned up all but one of the script errors at the script errors link above for familiarization; they were predominantly malformatted geographic coordinates in the wikitext. I'll think about it a while, and ping you if I would like to proceed with something. —Quondum17:12, 12 October 2024 (UTC)
Whenever you like. Don't sweat about it. There is just a need to understand that template editing is different. For example, a revert should only happen if there is a fairly urgent problem. A full discussion should occur before reverting or making significant changes. Thanks for cleaning up the problems. Johnuniq (talk) 23:33, 12 October 2024 (UTC)
Notice of Dispute resolution noticeboard discussion
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Thanks for the consideration. I have been watching Double-slit experiment so am aware of this anyway, and have not been encouraged by the continued obstinacy. Maybe there is a lesson for me in this: that grumpiness can make one blind to social cues that would lead to better outcomes. —Quondum13:21, 4 November 2024 (UTC)
ANI comment
I didn't get a chance to reply to you at ANI as the discussion was closed, I hope you don't mind if I reply here. Decoherence of a system AB is entanglement with an environment E. It does break entanglement between A and B. This is not dependent on interpretation, and has nothing to do with collapse. The simplest model for that lets AB start in the maximally entangled state , and then get maximally entangled with the environment, ending up in the GHZ state. Now this state has no entanglement between A and B alone, it only has tripartite entanglement.
I apologize (about the intensity of my tone there): I'm very reactive to tone and antagonism. Coming in at the tail end of an interaction, that was about all I saw.
It seems that I was jumping unduly to conclusions: you use terms that I assume to be foreign to a many-worlder ("collapse", "breaking entanglement").
Anyhow, before it seems that I think that I really know what I'm talking about, I'm on shaky ground here.
It would be good to find descriptions that are directly understandable to the normal reader and unobjectionable under any of the mainstream interpretations of QM (which may need thoughtful choice of terminology), and to reduce the temperature of the interaction (for which patience and focus on content rather than on people will be needed). —Quondum23:45, 23 November 2024 (UTC)
Yes, there is still correlation between A and B, but no entanglement. Quoting from the article:
Another important property of the GHZ state is that taking the partial trace over one of the three systems yields
Incidentally, the "first" in your quotation is incorrect: one can make the measurements with spacelike separation, so there is no "first" one to determine the results of the other two.
As for "collapse", I use that because that's what textbook quantum mechanics use. It's the closest thing we have to interpretation-neutral language. All interpretations must handle the fact that there is an apparent collapse going on. Now why there appears to be a collapse will be interpretation-dependent, so we don't go into that. Many-Worlds explains collapse via branching and relative states, but if I start inserting this everywhere it will be clearly a violation of NPOV. The edit I reverted was particularly unhelpful because it was still using the mathematics of wavefunction collapse, it just removed the word "collapse". Tercer (talk) 08:28, 24 November 2024 (UTC)
It seems that the article that we are referencing could be improved. It seems to be incorrectly referring to operators/observables (which linearly transform kets) as states (which are kets), at least in my understanding. This does not tell me how to derive a ket that describes the result of a "measurement" on one particle (perhaps equivalent to extracting one eigenstate of a mixed state). I am dubious of the claim is an unentangledmixed state from your quote. It goes on to say It has certain two-particle (qubit) correlations, but these are of a classical nature, which makes sense if we assume that objective collapse has occurred, and only a pure state remains, or if we define entanglement from the perspective of an observer in one of the branches in MWI. However, the mixed state (actually still a GHZ state) remains in MWI, and appears to squarely fit the description Quantum entanglement is the phenomenon [where] the quantum state of each particle [...] cannot be described independently of the state of the others.
On your comment about "first", I am aware of the independence of measurements on timelike/spacelike separation of the interactions/"measurements"; I took that as an artificial choice to present an illustration. Perhaps we should just delete the word "first".
On As for "collapse", I use that because that's what textbook quantum mechanics use, textbooks (and universities) tend to still almost universally teach undergraduates the Copenhagen interpretation, to paraphrase Sean Carroll. You will by now no doubt automatically re-interpret withing MWI even undisguised Copenhagen interpretations and terminology, and hardly notice the strong barrier to interpretation that it presents for those entering the field. Do you think Sean Carroll would agree that "collapse" is an interpretation-neutral term? Textbooks also lag mainstream thinking. We only need to use terminology by established authorities that is more neutral.
I'll be a bit more strident about terminology. I believe that the biggest contribution to the advancement of any field is when the language and representation is shaped to reduce the learning curve and forestall misconceptions so that students get past the learning hurdles and have the best tools to where they are able to work on developing new knowledge. And, by implication, one of the biggest retarding factors is the resistance by those practitioners/teachers who have learned the historical language and refuse to give it up to something that would clearly be better. Energy that new students need to figure out a working interpretation delays their progress, and weight of hundreds of little conventions to be learned can become huge. Learned internal mathematical contradictions often last for life without people even being aware of them – I've seen this often enough, including vehement defences. To give a small example in mathematics: we use the same notation for the (single-valued) complex exponential function and the (multi-valued) power function when . How many people are even aware of the difference? Simply using distinct notation would fix this without any cost, but for the cost of transition, which has now become too large. The "cheapest" and most successful time to improve terminology and representation is as early as possible. Sadly, most students learn by rote, and are not able to think critically about what they have absorbed in their early befuddled state. I'll qualify this by noting that the principle is important in article space where the majority of reader are unfamiliar with the learned conventions; in talk space it can be confusing, but at least its impact is less lasting.
There is nothing wrong with using both matrices and vectors (kets) to describe quantum states, both are valid. We can use matrices for both pure and mixed states, whereas vectors (kets) can only represent pure states. This is standard terminology that you'll see in any textbook. We definitely do not assume that collapse or branching has occurred to describe Alice and Bob's reduced state as the mixed state . We have only taken the partial trace, i.e., ignored the environment. Taking the partial trace gives us an effective state that tells us all that Alice and Bob can achieve without using the environment. Since this reduced state is not entangled, Alice and Bob cannot perform any task that requires entanglement. Therefore we simply say that Alice and Bob are not entangled. This is again standard terminology that you'll find in any textbook, I didn't come up with it. Now this reduced state is explicitly not a full description; the full one is the one that includes the environment. But decoherence is about assuming that you cannot control the environment, and asking what you can do with the system that you do control.
Textbooks definitely do not teach the Copenhagen interpretation. Take the standard textbook used in quantum information, Nielsen & Chuang. It is as interpretation-neutral as it gets. There's no mention of classical/quantum dualism, complementarity, Heisenberg cut, or the quantum state not being real. These are core elements of Copenhagen. What it does have is wavefunction collapse. Now I don't think there's any textbook that doesn't use it; it is after all one of the postulates of quantum mechanics. Even if I were to write a textbook myself I would include collapse (while explaining of course that it's only apparent, and that branching is what is actually going on).
Okay, this shows just how far out of my depth I am. vectors (kets) can only represent pure states – this is a new surprise to me. Matrices being used does not in itself say anything; they can represent vectors in Clifford algebras, for example. But what you are saying is that kets cannot be used for general states, which says that Hilbert space is only the space of pure states.
On the terminology, I guess I'll have to concede: not actually having any quantum mechanics textbooks, I can't familiarize myself with this. I found a short article called "Quantum information – Joining the Foundations of Physics and Computer Science" by Chuang. His single use of "collapse" appears to be somewhat informal, and he then more formally calls it "decoherence", and then sticks to that. Anyhow, I suppose that quantum computing is at least increasing the comfort of the QM community with MWI.
decoherence is about assuming that you cannot control the environment – I imagine that the assumption is stronger than that: that entanglement spreads rapidly in the environment. —Quondum01:27, 25 November 2024 (UTC)
Pure states form a Hilbert space, but the set of general states (pure and mixed) also form a Hilbert space.
In which case the inner product probably looks like Tr(A†B).
You do need indeed decoherence to spread rapidly in the environment. I was talking about the assumption that allows you to take the partial trace over the environment and use only Alice and Bob's reduced state. Tercer (talk) 07:43, 25 November 2024 (UTC)
The I would have put it along the lines that this assumes that you are ignoring the environment and isolating the "particles" of interest. —Quondum16:31, 25 November 2024 (UTC)
thread split
below is in apparent response to initial post in § ANI comment above
BTW, your ping here will not have generated a notification: you need a fresh signature in the same post for this to work. Also, I'm not sure I want to volunteer my talk page for something that does not seem to be focused on resolving the underlying issues. —Quondum12:43, 24 November 2024 (UTC)
![{\displaystyle \operatorname {Tr} _{3}\left[\left({\frac {|000\rangle +|111\rangle }{\sqrt {2}}}\right)\left({\frac {\langle 000|+\langle 111|}{\sqrt {2}}}\right)\right]={\frac {(|00\rangle \langle 00|+|11\rangle \langle 11|)}{2}},}](https://wikimedia.org/api/rest_v1/media/math/render/svg/1f1cc333b846acdabf149eedb46973581b61920c)
