Talk:Time crystal

experimental claim

 * https://www.technologyreview.com/s/602541/physicists-create-worlds-first-time-crystal/
 * https://arxiv.org/abs/1609.08684

Could someone summarize the above in the article if it's relevant? I don't understand it well enough to attempt this. Thanks. 50.0.205.96 (talk) 23:06, 6 October 2016 (UTC)
 * It is relevant, but is really beyond the definition of space-time crystal. I would like to see the study properly published to see if it can get past peer-review. Graeme Bartlett (talk) 09:01, 7 October 2016 (UTC)
 * This is driving up readership, so I have written something. I don't understand this too well either. Graeme Bartlett (talk) 23:29, 9 October 2016 (UTC)

Requested move 12 October 2016

 * The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review. No further edits should be made to this section. 

The result of the move request was: No consensus. Sources are mixed; they use both 'time crystal' and 'space time crystal.' I suggest waiting a reasonable time. Then reconsider the move based on the predominant usage in refereed journals. If we were to go by Wilczek 2012, assuming he is the actual creator of the idea, he called them 'quantum time crystals' in the title of his published paper. EdJohnston (talk) 19:42, 19 October 2016 (UTC)

Space-time crystal → Time crystal – Recent coverage, including coverage of claimed experimental results, seems to have settled on the name "time crystal". Examples:
 * https://www.technologyreview.com/s/602541/physicists-create-worlds-first-time-crystal/
 * http://phys.org/news/2016-09-crystals.html
 * https://www.wired.com/2013/04/time-crystals/
 * http://www.ctc.cam.ac.uk/stephen70/talks/swh70_wilczek.pdf (PDF)

As with the editors above, I don't claim to be an expert on the bleeding-edge science involved here, but these all seem to be covering the same topic as this article does. Given the current attention to this topic, our article title should match what's being used in the press. 64.105.98.115 (talk) 17:42, 12 October 2016 (UTC)
 * oppose It seems every researcher want's to have their own name, but time crystal is just one of several. "space-time crystal" seems to be the longer term name. Because the implementation only has a few atoms it it, it does not yet make a crystal in space, so as to make a space-time crystal in its general sense.  Instead it s a bit of a on-dimensional object, so that would be why they just call it a time crystal. In a way you could call anything that eternally oscillates a time crystal, even a LC circuit. The redirect is already in place to assist. You could include the "time crystal" name in the first sentence though. Graeme Bartlett (talk) 22:41, 12 October 2016 (UTC)


 * The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page or in a move review. No further edits should be made to this section.

second law of thermodynamics?
No clear discussion of 2nd law here. It is needed. — Preceding unsigned comment added by 123.3.154.75 (talk) 05:25, 29 January 2017 (UTC)

Here's a 2021 quote: "The consequence is amazing: You evade the second law of thermodynamics," said Roderich Moessner, director of the Max Planck Institute for the Physics of Complex Systems in Dresden, Germany, and a co-author on the Google paper. That's the law that says disorder always increases.

Source: Eternal Change for No Energy: A Time Crystal Finally Made Real, by Natalie Wolchover, Senior Writer/Editor, July 30, 2021, Quanta magazine. This quote would also seem to contradict the current statement in the Thermodynamics section "Time crystals do not violate the laws of thermodynamics." I'm not an expert in the scientific meanings of the words "evade" and "violate" so I will leave the argument to others.  5Q5 &#124;&#9993; 10:56, 2 August 2021 (UTC)


 * Where exactly was the 2nd law of thermodynamics broken? I think you have a common misconception of what was actually discovered and what's been done, thanks to pop-sci articles. Take a read here and you'll know why the 2nd law of thermodynamics absolutely wasn't broken:

https://bigthink.com/starts-with-a-bang/time-crystal/

--AloisIrlmaier (talk) 05:56, 14 October 2021 (UTC)
 * With "you", you must mean Moessner. He is the one who said it. But I fear you will not reach him via a Wikipedia Talk page. --Hob Gadling (talk) 07:15, 14 October 2021 (UTC)

Overly complex referencing
The article has been changed to have an extremely complex referencing format. This is now so complex that readers will likely not bother to use it. Readers click through to a note that can have 4 clickable links in it. These links then can go to a citations section. Then they have to click on a Harvard format reference to get to an entry in one of three following sections. This is non standard for Wikipedia and is very complex for readers or editors. Few editors will be able to maintain this. This is not a textbook but an encyclopedia article mostly read on online devices. I propose this should be much simplified. The Notes section should only be for textual notes: currently q, ae, ag, ah. The other entries prefixed with "see" become regular references. For the other references, clicking on their footnote should go directly to a references section with entries as in the academic papers section. The section labelled "citations" should be scrapped. Entries in academic, Papers, and Books that are not used as references in-line can become entries in an "Extra reading" (or External links) section


 * Yeah I agree the referencing is kinda obtuse, and will take a while to fix... for now the priority should be on the news and interviews coming out of the Nature publications this month.--Sparkyscience (talk) 11:34, 13 March 2017 (UTC)
 * But this is definitely on the to-do list! Editors should just add references for the time being however they want and I'll do my best to swoop in and tidy things up, and get round to reformatting at some point --Sparkyscience (talk) 11:41, 13 March 2017 (UTC)

Simple English
Need someone to write the "Simple English" article ASAP. SammyMajed (talk) 09:00, 10 March 2017 (UTC)
 * see https://en.wikipedia.org/w/index.php?title=Space-time_crystal&oldid=764370454 -- should we revert back to that version? The current one explains a lot more background, but at too advanced a level to be useful for the average reader here. Graeme Bartlett (talk) 13:09, 10 March 2017 (UTC)
 * Articles should have background, I vote for the "https://en.wikipedia.org/w/index.php?title=Space-time_crystal&oldid=764370454" version to be simplified a notch and put up for the Simple English Wikipedia while keeping the English Wikipedia version as it is SammyMajed (talk) 14:53, 10 March 2017 (UTC)
 * I think its best to outline areas that need a simplification/further explanation then to revert to a version which is now out of date and misses a lot of key scientific points. If you had to pick a few, what areas are most difficult to understand? Worth noting that I don't think any scientist fully understands the implications of time-crystals, it is frontier of science stuff so is likely to remain a complicated subject however we cut it.--Sparkyscience (talk) 11:39, 13 March 2017 (UTC)
 * Yea, at the very least, the opening paragraph needs to be in lay-man terms. Body sections of the article can go more into detail. KyuuA4 (Talk:キュウ) 20:24, 15 March 2017 (UTC)

In plain English the opening paragraph could be made quite simple: For example: A time crystal refers to a crystal who's structure is not rigid but rather in perpetual motion. The perpetual motion is achieved by continuously imparting energy into the crystal from an external source to get it out of its zero energy ground state. The perpetual motion moves in a specific pattern that repeats itself over and over again. The movement is thought to cause a phenomenon called quantum entanglement between the particles of the crystal. This entanglement makes the crystal impervious over time to outside forces that would normally breakdown a rigid crystal structure. This breakdown by outside forces is called quantum decoherence by physicists. Essentially the crystal remains forever young and will not lose any information encoded within it. This is a property highly sought after by engineers who are designing quantum computers. Gaurus (talk) 19:22, 3 May 2017 (UTC)

Request renaming 13 March 2017
With this request I would like to reopen the so-called "Requested move 12 October 2016" issue. With the latest scientific issues published, the scientific community starts to use the term Time-Crystal more and more exclusively, henceforth this article should follow suit and refect the census of the scientific community.

It is no longer a question if 'every researcher want's to have their own name', it has become common treatment, and thus is no longer a moot question iof personal preference. Asragin 2A02:8071:2388:8300:E1E9:62E:7173:1426 (talk) 08:45, 13 March 2017 (UTC)


 * I completely agree. The vast majority of all literature now uses the word "time crystal" to describe the phenomena and the article should be renamed. I think I've seen references to a "phase space crystal" here and there in the literature to describe something similar, but I have not seen "space-time crystal", maybe one of the earlier editors has a RS for the term?--Sparkyscience (talk) 11:29, 13 March 2017 (UTC)
 * I won't oppose a name change now, as what has happened is that a genuine Space-time crystal cannot be made, and what has been made is related but does not have physical extent in space in the same way so most use now in writings is Time crystal. Not many people are entering our article from the time crystal redirect though, only 493 compared to Space-time crystal with over 53000 page views in the last month. Graeme Bartlett (talk) 12:05, 13 March 2017 (UTC)|Time_Crystal
 * I'm pretty sure you can't read anything into the redirects: If I search "time crystal" in Google I will then click on the "space-time crystal" link and this will show up as a "space-time crystal" statistic rather then "time crystal" redirect. You can see comparison of search terms in google here: --Sparkyscience (talk) 13:47, 13 March 2017 (UTC)
 * That is not a big number. This query https://trends.google.com/trends/explore?date=all&q=time%20crystal,space-time%20crystal,time-crystal,space%20time%20crystal shows more, but may not be what we think. Graeme Bartlett (talk) 01:25, 14 March 2017 (UTC)

Yeah the peak in April 2009 from the above seems to be from "Final Fantasy Crystal Chronicles: Echoes of Time" I don't think a query without quotes is going give you any indication of the proportion true volume on the topic of time crystals vs space-time crystal. I've changed the name of the article since no-one seems to oppose.--Sparkyscience (talk) 09:37, 14 March 2017 (UTC)

There is an undefined abbreviation in the first graphic.
At no place I can find the abbreviation "MBL" defined either in the graphic or the article, nor is it listed as anything relevant in Wikipedia in the disambiguation pages. J with a B (talk) 06:27, 14 March 2017 (UTC)


 * It stands for "Many body localization" a big topic at the forefront of condensed matter physics but unfortunately isn't really covered by Wikipedia properly . I can squeeze the term in under the picture caption but unsure how much insight will be gained by the reader as i can't see any obvious article to link to for the term? What are your thoughts?--Sparkyscience (talk) 08:43, 14 March 2017 (UTC)
 * I have created a tentative redirect of many-body localization and put an entry for this at MBL. Note that we also have many body problem but that seems too general for this specific case.  Andrew D. (talk) 15:09, 15 March 2017 (UTC)

Introduction opaque to me
Please define: time translation nonlocal correlation fault tolerance Quantum correlated state

Thanks — Preceding unsigned comment added by 24.224.248.82 (talk) 14:33, 14 March 2017 (UTC)

Clarification
Can the lead-in explain things for 'non-physicists/crystallographers'? 86.146.99.55 (talk) 13:50, 15 March 2017 (UTC)

Perpetual motion?
The article states "The crystal's pattern repeats not in space, but in time, which allows for the crystal to be in PERPETUAL MOTION"

But Wikipedia's own article on 'perpetual motion' states: "Perpetual motion is motion of bodies that continues indefinitely. This is IMPOSSIBLE because of friction and other energy-dissipating processes."

79.76.99.103 (talk) 19:20, 15 March 2017 (UTC)

A quote from a member of the team who made one states “It’s not a perpetual motion machine,” Jiehang Zhang, a member of the University of Maryland team, tells Gizmodo. “We’re driving it!" unquote, so to summarize, your correct it not in perpetual motion.
 * Indeed. All experimenters and theoreticians make clear that time crystals are not in perpetual motion.  –  SJ  +  07:17, 1 July 2017 (UTC)

Semi-protected edit request on 16 March 2017
The link to "Perpetuum mobile" links to a music reference instead of to the physics perpetual motion page: https://en.wikipedia.org/wiki/Perpetual_motion Samuel Thornkey (talk) 00:41, 16 March 2017 (UTC)
 * Yes check.svg Done DRAGON BOOSTER   ★  04:16, 16 March 2017 (UTC)

Add third name
chronocrystal (χρόνος + κρύσταλλο[ς]) — Preceding unsigned comment added by 2A02:587:4100:9F00:71BD:A55E:8466:CC77 (talk) 07:22, 16 March 2017 (UTC)
 * I cannot see this in use for this concept. Its current use is for a game item. Graeme Bartlett (talk) 22:38, 16 March 2017 (UTC)

Lede and begining of subsections
It feels as if the sentence and ensuing paragraphs, which begin: "In 2016, Norman Yao and his colleagues from the University of California, Berkeley, put forward a concrete proposal that", belongs in the article and not in the Lede. Suggest moving or condensing those paragraphs into the history section and using the Lede for a more pedestrian explanation of the subject so as to remove the "too technical" tag. Edaham (talk) 09:22, 16 March 2017 (UTC)

Hamiltonian and the need to make it understandable
The History section currently reads: "..misunderstanding the orginal Wilczek paper or, requiring the true ground state i.e. the lowest energy eigenstate of the Hamiltonian to have the perpetual motion that trivially, is impossible because the motion must mean the superposition."

"Hamiltonian" needs further clarification - maybe just a link (presumably to Hamiltonian (quantum mechanics)?) will do. Oh!, and "orginal" should be "original". 199.200.27.9 (talk) 19:36, 16 March 2017 (UTC)

I'm a layperson, albeit one that enjoys reading about and exploring complex scientific topics, such as this. However, this article fails to convey to me a coherent sense of what the topic is. A starting point might be a comparison with ordinary crystals and how these are different. Informata ob Iniquitatum (talk) 02:00, 19 April 2017 (UTC)

I've rewritten the lede to hopeful clarify a few things. I will remove the too technical tag, but please reapply if the lede still is not clear. If there is a specific section in the article which needs more work, apply the too technical tag there as well.--Sparkyscience (talk) 11:59, 4 May 2017 (UTC)

Rewrite needed: currently misleading
Time crystals are fascinating, but this article does not describe them well. I remember reading this article years ago when it gave a pretty concise summary of the topic; it has come far afield since then. (Was this in response to the recent experiments? Something else?)

The current article is full of misleading statements (perpetual motion), gives undue weight to tangents that are barely related to the concept (digressions on every symmetry, topological order, zero-point energy, casimir effect), and uses a confusing non-standard footnote+note scheme. Some important aspects, like the series of no-go arguments, are presented in a confusing way and without context.

I'm not sure how to improve the current state: it seems to be crafting an elaborate narrative with the topic as a starting point, which is not what an article is generally for. I'll start with the most glaring issues:


 * Lede
 * "This allows for the crystal to be in perpetual motion." - untrue, the cited source doesn't say this, indeed no experimenter says this.
 * "Time crystals are closely related to the concepts of zero-point energy and the dynamical Casimir effect." - repeated elsewhere in the article. Misleading, partly original synth.
 * - ZPE isn't related, though you can set up thought experiments where a time crystal is affected by ZPE (as in Chernodub).
 * - Mendonca writes d. Casimir effect is a 'special case of a time crystal' and 'closely related', but their paper (journal IF: 0.6) only shows that, given a time crystal in an ultra-cold gas, if one varies the density of gas atoms just so, one can create a variation of the d. Casimir effect with phonons. That's not normally what "closely related" means. The fact that one can come up w/ a thought-experiment relating two things does not make them closely related, and time crystals are well defined without either of those other concepts.


 * "Time crystals are thought to exhibit topological order" - misleading, a minor speculation, should not be in lede. Possibly a misreading of the source: some think that time crystals, like many other materials, can exhibit topological order, which might allow for more stable crystals [the experiments so far observed crystals that were very unstable]

This section looks fine.
 * History
 * Confusing use of "no-go"; there were no-go arguments & theorems for a variety of assumptions.


 * Symmetry
 * Broken symmetry (2 sections) repeats what's in the detailed article. Only a sentence is needed, not 2 sections.
 * Quasienergy: neologism, remove entirely.
 * "In either case the apparent non-conservation is in reality a transfer to the vacuum field (i.e. zero-point field)." OR, not remotely in source.
 * "The term quasienergy has been coined to explain some of the predicted properties of time crystals." neologism, OR


 * Topological order
 * Not relevant to time crystals (any more than any other matter), should be left out. To the extent that it is accurate, it repeats content from the topological order article, with selective examples.
 * The original speculation about Floquet theory gets pretty wild. Not related to the topic, and not supported by sources.
 * The original speculation about violating the 2d law of thermodynamics is wild and deceptive. The source says the opposite: that the law is never violated.


 * Thermodynamics
 * The first section is fine, but could be clearer.
 * The statement about the no-go theorems is fine to repeat here.
 * The section on zero-point energy should be left out. (Is there some sort of ZPE conspiracy that inserts it into any small-scale physics concept?  It really isn't related to the definition or exploration of  time crystals.)


 * Related concepts
 * Dynamic Casimir effect: better to leave out, for reasons noted above. Not particularly related; needs a better source than Mendonca to suggest it is.

Regards, – SJ  +  07:17, 1 July 2017 (UTC)
 * Changes applied: in particular, the lede was cleaned up, a cleanup notice re-added, and notes were converted to refs (still a bit clunky, since you have to click through from the ref to the biblio entry and then to the original source). Sections on dynamic casimir effect, zero-point energy and topological order left to their dedicated articles. Overall the article is again focused on the topic and reads better, but could still use a pass from someone deeply familier with the field. – SJ  +  22:11, 22 July 2017 (UTC)
 * Great cleanup! That was desperately needed; the article had become a "christmas tree" with all kinds of unrelated topics added. --ChetvornoTALK 21:36, 1 September 2018 (UTC)

A time crystal is a "driven" system?
I applaud all the good work done by SJ mentioned above. However I still have a problem with one sentence:
 * "Because a time crystal is a driven (i.e., open) quantum system that is in perpetual motion, it does not violate the laws of thermodynamics."

This seems to be unsourced: the cited source (Chernodub) is not about time crystals but about a zero-point energy system; the term "open system" does not appear in it; and the word "driven" only appears in the phrase "zero-point energy driven"; this does not refer to an external driving force. I feel this sentence is a very misleading WP:SYNTHESIS. In thermodynamics an "open system" is one that exchanges energy with its surroundings, and a "driven" system is one whose motion is caused by an external force. I agree, time crystals are not "perpetual motion machines", and do not violate the laws of thermodynamics. But the reason for this is not that they are "open" systems which are "driven" by an external energy source. The reason is that they are in their minimum energy quantum "ground state", so no energy can be extracted from them. Their "motion" does not really represent conventional kinetic energy ; they possess "motion without energy". I think this sentence should be rewritten. -- Chetvorno TALK 00:16, 20 September 2017 (UTC)
 * Changed. Please correct or improve as needed.  –  SJ  +  14:41, 21 September 2017 (UTC)

Reference section needs reducing
Now that SJ has done such a great job cleaning up the article, I think the "References" section should be cleaned up. The section has 116 sources, of which only 19 are referenced by inline citations. Without knowing which parts of the article they refer to, the rest are pretty useless. Many of them supported trivial or off-topic content such as Casimir effect which has been deleted. A few of the sources most relevant to the subject could be moved to a "Further reading" section, but the rest should be deleted. --ChetvornoTALK 05:39, 2 September 2018 (UTC)

I agree. I will try to clean up the reference section by first omitting all the off topic ones. CA2MI (talk) 18:01, 5 April 2021 (UTC)

Problematic changes to article
A new SPA has made started making edits, first at Frank Wilczek and then here, representing a 2015 paper by Oshikawa and Watanabe as "scientific consensus as of 2019." The same editor removed (from FW article) the citation of a 2018 article in Physics World written by Philip Ball (which discusses the 2015 paper at some length) as "The prior edits cite popular science articles that do not reflect academic consensus." 

The time crystal article has been in a consensus state, so I think other editors should take a look at the changes I reverted before the article displays them.

Also, is the IP correct to remove the entire section on Thermodynamics? They disagree with a statement sourced to Science Alert, but other material removed was sourced to Scientific American and academic papers. Thermodynamics seems a worthwhile topic to cover, and blanking the section seems extreme.

Also we should be careful that we rely on secondary sources and RS to evaluate which concepts are of critical importance to the field. Quite a lot has happened since 2015. Perhaps published RS exist that assert the Oshikawa/Watanabe paper from 2015 represents "scientific consensus as of 2019," but until/unless we can cite such RS, the article should not be making such claims. HouseOfChange (talk) 17:22, 26 March 2019 (UTC)

Two independent experiments in 2016
I have found a citation for the uncited assertion (which I reverted because it was uncited) that two experiments in 2016 were independent work. Similarly, Philip Ball writing in Physics World emphasizes that the two experiments should be treated on an even-handed basis.

IMO, the article should talk about these two experiments with a similar level of detail, and based what independent RS have said about them, not so much on the original primary sources. HouseOfChange (talk) 16:03, 19 June 2021 (UTC)

Definition in the lead
Partially quoting a paper from 2012 that described time crystals as "systems with time-periodic ground states that break translational time symmetry" can hardly be our best possible choice. There have now been lots of articles about time crystals, and we should search them for good ways to explain what a time crystal is. Here are some other possibilities.


 * IOP 2017, by the same author, "Time crystals are time-periodic self-organized structures postulated by Frank Wilczek in 2012."
 * Lodi Valley News 2021, "First, we need to understand what a crystal is for physics: an object with atoms arranged to create a repeating pattern...Now think of a crystal whose pattern does not repeat itself at every specified distance, but at every specified time. That will crystallize time...Motion is not generated by stored energy, but rather by symmetry breaks in the fluid."
 * Quanta 2021, "...a time crystal is an object whose parts move in a regular, repeating cycle, sustaining this constant change without burning any energy."
 * Science Alert Explainer, post-2019, "Time crystals are similar to regular crystals in that they are based on structures of atoms that repeat. Rather than forming repeating across three dimensions of space, these ones change in a set pattern over time."

I think a good clear definition will explain the analogy to crystals and say something informative about the role of symmetry breaking in their realization. What do other editors think? HouseOfChange (talk) 01:21, 4 August 2021 (UTC)


 * I don't think any definition that includes the crystal analogy and symmetry breaking is going to be clear for general readers,  although it's going to have to be in the introduction since it is the official definition.  I also think the sentence "A discrete time crystal never reaches thermal equilibrium..." is also too confusing for general readers and should be explained in the introduction.   The current definition, "....a system or subsystem whose lowest-energy states evolve periodically." is better, but still vague; what does 'evolve' mean?


 * The def in the third bullet point above is adequately user friendly, but it omits the crucial point that the crystal's quantum nature is the reason it moves perpetually. I would suggest:
 * "A time crystal is a quantum system of particles whose lowest-energy state is one in which the particles are in repetitive motion."
 * The system cannot lose energy to the environment and come to rest because it is already in it's quantum ground state. Because of this the motion of the particles does not really represent kinetic energy like other motion, it has "motion without energy".
 * --ChetvornoTALK 05:59, 4 August 2021 (UTC)
 * Thanks, HouseOfChange, for all the great work looking up those possible definitions. The intro looks much improved to me.  I didn't know I'd be the only editor expressing an opinion; I'm no expert.   Also, just want to make clear, I have nothing against defining the time crystal in the introduction as a system that breaks time symmetry; or stating that it is a "nonequilibrium" system.  I just meant there should be clarifying sentences in the intro explaining to nontechnical readers what these statements mean.

WP:NOTNEWS problem
There is a lot of recent news about time crystals but... Is there some rule of thumb we could use to decide when "this group made a 2021 discovery (link to primary research paper and to the home institution news article)" does or doesn't require a separate paragraph? When independent RS cover somebody's new experiment, we get better context of how it relates to time crystals.

Maybe there should be a separate article about time crystal experiments? Hoping for guidance from more experienced editors. HouseOfChange (talk) 00:24, 9 August 2021 (UTC)

Removed incomprehensible material, let us fix it before re-inserting
Wikipedia is an encyclopedia, whose articles are aimed at informing a general audience about notable topics. We rarely cite primary research papers, because topics of general interest should have been treated in an accessible way by secondary or even tertiary sources. If this article should have a section on "Condensed matter in crystalline structures in time", it needs to be a lot clearer why this improves the encyclopedia project, as opposed to why it matters to people who have published scholarly papers to see their work mentioned in Wikipedia.

"Time crystalline structures can also be created externally like photonic crystals. The latter do not emerge spontaneously because periodic modulation of the refractive index in space is imposed externally. Resonant periodic driving of a single or many-body systems can reveal condensed matter-like behavior . For example, Anderson and many-body localization in time, topological time crystals, superfluid-Mott insulator phase transition in the time domain can be realized in resonantly driven systems, see also."

Here is the section I removed. If others feel it belongs in the article, how can it be improved and where should it go? HouseOfChange (talk) 13:51, 30 August 2021 (UTC)
 * Working to understand this piece of the puzzle: Kryzsztov Sacha (pub. 2015) proposed a model of time crystals based on "an ultracold atomic cloud bouncing on an oscillating mirror." Lingzhen Guo in 2013 proposed another time-crystal analog called "phase space crystals."


 * Much of the Wikipedia article, however, reflects secondary sources writing about a different model of time crystals involving periodically driven spin systems. Meanwhile, both Guo and Sacha have written review articles, citing each other's work as examples of "condensed matter physics in time crystals." Unfortunately, there seem to be no independent secondary sources that give a clear explanation of "condensed matter physics in time crystals" -- neither about what it means or about why it is important to understanding time crystals. The article already gives KS credit for an important and early piece of work. Again, I welcome input from other, more experienced editors or people with deeper knowledge of physics. HouseOfChange (talk) 17:56, 31 August 2021 (UTC)

Inconsistency in the "Thermodynamics" section
Time crystals do not violate the laws of thermodynamics [....] Time crystals do evade the Second Law of Thermodynamics

?

IncompleteBits (talk) 16:57, 6 November 2021 (UTC)

Google experiment
I reverted an extensive edit talking up the Google experiment, not least because it replaced the accurate description of Google's many collaborators coming from "multiple universities" with the inaccurate claim that all came from "Standford University" [sic]. Could other editors take a look? HouseOfChange (talk) 20:10, 27 December 2021 (UTC)


 * Hi, the reverted edit was done by me I think I deleted that part to write it again as in the first paragraph of the quanta magazine article "Google in collaboration with physicists at Stanford, Princeton and other universities" which seemed better and left it midway with some distraction, the article mentions how the group of Stanford proposed the experiment to Google but it doesn't say anything about the others universities so I had probably Stanford more on my mind and didn't notice but I was aware that it wasn't only Google and Stanford as the edit which included the paragraph about the google experiment with the line "Google and physicists from multiple universities" as currently stands was also done by me so it was really just a mistake.
 * I was trying to improve what I had edited previously so if there are others problems with the changes I had intended please let me know. Dabed (talk) 21:58, 27 December 2021 (UTC)


 * Concerning your edit, which cites the rather unbalanced Quanta article four times: My concerns included removing credit from universities other than "Standford" as well as WP:RECENT and WP:WEIGHT. The Google experiment is currently covered in both the Thermodynamics section and the Experiment section. Before adding more highly-technical material about this experiment, I suggest you review the material already in the article about it, as well as the level of detail given for other experiments mentioned in the article. It would be more interesting to hear more about other experiments. HouseOfChange (talk) 03:08, 28 December 2021 (UTC)


 * I think I explained the best I could the matter about the universities so not sure what more can I say to make it clear so that bad faith isn't assumed. In the paragraph I cited the quanta magazine article once and in this edit I cited it two more times as I added two others experiments mentioned in the article so that is 3 concerning my edits which I agree it wasn't ideal nevertheless all in all I don't understand why it has to be assumed I didn't read the material already present. The google experiment is mentioned once more in the thermodynamics section and in this case the editor probably didn't read the experiment section because he/she duplicated the reference but even then it is not the more cited reference which is reference 38 with 5 citations. I also want to hear about about more experiments and that is why I included the one from google, the one made using magnons and wanted to add two more experiments one using carbon-13 nitrogen-vacancy centres and another using trapped ions qubits. I think these issues are things that could have been edited rather than reverted and I don't agree WP:RECENT and WP:WEIGHT either but this is not the first or last contribution that will amount to nothing for one reason or another and as one can only keep track of a handful of things I will rather move on I try to contribute on other articles. Thank for your work and best regards.Dabed (talk) 06:03, 28 December 2021 (UTC)

Are the 2017 experiment results actually time crystals? [I am asking, not answering, *in case* revision is needed.]
Hello, people who know more than I do. I just watched the video at https://m.youtube.com/watch?v=ieDIpgso4no. That was my very first exposure to the term and concept covered by this article, time crystals.

In that video, the speaker says that the 2017 time crystals were not true time crystals. My impression was that they failed to fit the definition in some technical or crucial way. The speaker goes on to say that in 2021, the Google experiment produced true time crystals, and others have as well. I can't say anything about the speaker's source of information or understanding of the material (except of course that they both probably exceed my own, very greatly).

It's also worth noting that the video was posted only about 11 hours ago, so this could be new information, or relatively new, whatever. Yay for bleeding edge science!

So, I've posted this only so that better and more concerned minds can consider whether any of the article needs updating, or not. Should the description of the 2017 results be adjusted? I am not especially invested in the answer, other than the general desire to help Wikipedia be accurate. I won't be checking back, and don't have anything more to contribute to the conversation.

Thanks for all you do, people!

Signed,

Just a casual passer-by, hoping to be helpful. — Preceding unsigned comment added by 24.56.77.201 (talk) 08:26, 16 June 2022 (UTC)
 * A real time crystal would not need the input of any energy. But has minimum energy in its time crystal state. Graeme Bartlett (talk) 08:44, 16 June 2022 (UTC)

An isoenthalpic process?
It would probably be worth including in the article, in light of the fact that our chief interest in time crystals is their apparent (though faux) violation of second law of thermodynamics, by way of perpetual motion. (I say faux because the term 'motion' is questionable in this context, given that the oscillations are trapped in the system and shouldn't be treated as 'free' energy. Actually, if we could quantify the energy that it takes to set up a time crystal, which is then converted into unavailable energy, it would have to be identical to the 'change in entropy', right? But because you're necessarily setting up a system that doesn't have any free energy, it's non-enthalpic, and therefore the net change in entropy is... zero. Augh! It breaks my understanding of thermodynamics. This could use attention from an expert). Atomic putty? Rien! 14:31, 14 September 2022 (UTC)

Time crystals and thermal equilibrium
Currently, the article includes this paragraph: "An earlier 'proof' that a time crystal cannot exist in thermal equilibrium was shown to have a subtle error that renders it invalid (See Appendix A of Khemani, Moessner, and Sondhi (2019). ). Recent experimental advances in probing discrete time crystals in their periodically driven nonequilibrium states have led to the beginning exploration of novel phases of nonequilibrium matter."

I have disputed this proposed edit, because it references primary research by involved authors rather than secondary source confirming it:

"However, the proof was completed shortly after and now is thought to hold."

I agree that Wikivoice shouldn't say the proof was wrong if its error has since been corrected. But the primary source cited is dated 2020, plenty of time for secondary source to weigh in on one side of the other. Perhaps the entire paragraph should just be eliminated. What do others think? HouseOfChange (talk) 23:16, 10 November 2022 (UTC) HouseOfChange (talk) 23:16, 10 November 2022 (UTC)
 * We should remove the paragraph. We should also avoid using the term "thermal equilibrium" unless the source itself uses such a broad term, and WO 2015 does not use that term. Rolf H Nelson (talk) 03:17, 13 November 2022 (UTC)