View source for Talk:Retrocausality

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==Main Article==

Reverse Causation redirects here - this is an epidemiological concept that is not the same as the physics concept retrocausality. I am happy to delete the redirect, or to create a disambiguation page. Any views?  <small class="autosigned">— Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/128.240.82.163|128.240.82.163]] ([[User talk:128.240.82.163|talk]]) 14:33, 7 November 2014 (UTC)</small><!-- Template:Unsigned IP --> <!--Autosigned by SineBot-->

Okay, so this article obviously needs a lot of work. I'm glad that somebody started it though, since it didn't exist until recently. The general summary, even, is inaccurate though. Retrocausality doesn't ignore cause and effect, it suggests that there may be waves capable of traveling in any temporal direction. Particularly, a particle could emit a wave that moves both forward and backward in time, and as the wave moves back, the 'signal' connects with the waves of another particle, thus linking two otherwise unrelated particles in the present (and potentially explaining why two particles at any distance from each other can appear to be 'coupled').

At any rate, I am not a scientist and do not have a whole lot of spare time and energy on my hands, which is why I hadn't started the article myself. Anyone else out there keeping track of this?

Additionally, while to my knowledge no experiments have been done to test this yet, there is at least one experiment that has been proposed and may be tested sometime next year. Heading the experiment is [http://faculty.washington.edu/jcramer/ Professor John G. Cramer] from University of Washington, Seattle, who was recently featured [http://www.newscientist.com/channel/fundamentals/mg19125710.900-whats-done-is-done-or-is-it.html in this New Scientist article]. Professor Cramer's daughter, Kathryn Cramer, [http://www.kathryncramer.com/kathryn_cramer/2006/09/retrocausality.html responded to the article] and posted a note she says he wished to pass along:<blockquote>As implied in the article, I have recruited an atomic physics experimentalist (Warren Nagourney) and we have decided to do at least the first stage of the experiment. I now have a LiIO3 non-linear crystal on order that will be needed to do this. We will begin the experiment in a couple of months when the argon-ion laser owned by the UW Atomic Physics group becomes available (sometime around December to February).</blockquote>

All this information would probably be helpful in the main article, but I've never actually started an article myself before, so anyone have any suggestions or things to add? --[[User:Kasha.re|&#39;Kash]] 18:21, 20 October 2006 (UTC)

:Okay, I updated the article from it's original incarnation, to include what might make a decent introduction. I mentioned just enough to not get into detail, and also lightly address the common arguments I've seen about it. I might try getting back to it sometime in the near future if others don't tackle it first, but I think that's all for today. --[[User:Kasha.re|&#39;Kash]] 00:09, 21 October 2006 (UTC)

==Discussions and editing==
Someone recently edited the main article to add "(not true but cant be assed to explain but read Newscientist What's done is done… or is it? * 28 September 2006* Patrick Barry* Magazine issue 2571)." A notation like this belongs in the discussion page, not in the main article, so I have removed it.

Additionally, I have a subscription to New Scientist, have read that article, and no emperical observations of retrocausality have yet been made. The article discusses an experiment designed by Professor John G. Cramer, as mentioned above, and this experiment has not yet been performed. --[[User:Kasha.re|&#39;Kash]] 22:41, 27 October 2006 (UTC)

There indeed has been recent published research in a peer-reviewed journal showing observed evidence of retrocausality, see Xiao-song Ma et al,"Experimental delayed=choice entanglement swapping,: Nature Physics 8, 479–484, (2012)
doi:10.1038/nphys2294 or http://www.nature.com/nphys/journal/v8/n6/full/nphys2294.html
It is an area of active experimental physics research.  <small><span class="autosigned">— Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[User:Afross22|Afross22]] ([[User talk:Afross22|talk]] • [[Special:Contributions/Afross22|contribs]]) 18:57, 25 July 2013 (UTC)</span></small><!-- Template:Unsigned --> <!--Autosigned by SineBot-->

I started ro edit the Feynman diagram caption as I thought it misleading (or I misunderstanding) though I think I understand where the writer was coming from. Two separate concepts that include time reversal: antiparticles can be interpreted as a regular one traveling back in time (positron is electron going back in time) and separately Feynman diagrams can be rotated 90° to produce another valid solution for the same interaction. So a 180° rotation, or going backwards in time, is also valid, i.e. the  antiquark/quark pair annihilate to create photon which then decays into an electron positron pair. [[User:Quasispecies|Quasispecies]] ([[User talk:Quasispecies|talk]]) 05:33, 16 March 2022 (UTC)

==Proper sources==

Per [[Wikipedia:Requests_for_arbitration/Pseudoscience]], ''Acceptable sources'', none of the sources given here are reliable for the purposes of an article on a scientific topic. The article either needs to be deleted, changed to address the topic from a mass media perspective, or supported by proper references for a scientific article per ArbCom, such as textbooks or articles in reputable peer-reviewed journals in the appropriate field. With the current sources, it is not possible to write a verifiable ([[WP:V]]) article on the topic as a scientific or philisophical concept. --[[User:Philosophus|Philosophus]] <sup>[[User talk:Philosophus|T]]</sup> 06:59, 19 December 2006 (UTC)

==Original Research==
Original research does not belong on Wikipedia. Furthermore, the notion of retrocausality is proved false in most modern physics textbooks. This is never mentioned in the article. Also, if retrocausation were possible, we would have memories of the future. Clearly that is not the case.


Retro-causation could indeed be possible.  The past while appearing solid, may in fact be fluid and subject to change all the time.  Our past would be part of that change so we would not be aware of this motion. Perhaps this is the root of Einstiens hidden variable. -AMO  <span style="font-size: smaller;" class="autosigned">—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/63.95.64.254|63.95.64.254]] ([[User talk:63.95.64.254|talk]]) 17:22, 28 August 2009 (UTC)</span><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->

==Things to do==
Assuming this survives AFD in its current form...
*On the philosophy side:
**A citation for Hume's definition of causality would be nice.
**Some discussion on how retrocausality related to predestination/free will would be great, but will need a source.  I didn't find one.
**Should there be any discussion of "hard" time travel here, rather than just the wikilink to the article?  Should we have include a <nowiki>{{main|time travel}}</nowiki> with a quick summary, as currently done with tachyons in science?
*On the science side:
**The blurb on Feynman's positron model badly needs expansion.
**Should any more tachyon information be included, given that tachyons are generally interpreted not to induce causal violations in time-like systems?
**Did I miss anything that is/was actually legitimate science?
--[[User:Serpent's Choice|Serpent&#39;s Choice]] 14:57, 25 December 2006 (UTC)
:I would also work on the introduction. Right now, it seems to imply that such phenomena actually exist. --[[User:Philosophus|Philosophus]] <sup>[[User talk:Philosophus|T]]</sup> 20:15, 26 December 2006 (UTC)
::Agreed, and altered.  The [[WP:HEY|mid-AFD article quick-fix]] is rarely the final draft, and I'll admit to having written a fairly slipshod lede at first.  However, I do want to discuss the ''wording'' of the denial-of-reality.  "Generally discounted" is a weaker denial than I might give similar concepts, but there are enough open questions regarding CTCs in heavily deformed space that I'm reticent to drop the bar on it any harder in the lede.  I'm ambivalent about my current "no observation ... has been confirmed" wording versus a similar "has never been observed" -- is the Crough/Clay superluminal "cosmic ray" significant (and directly applicable) enough to contraindicate the simpler phrasing? [[User:Serpent's Choice|Serpent&#39;s Choice]] 06:11, 27 December 2006 (UTC)

== Rewritten article is much better than the previous stub ==

I'd argue that the new version by [[User:Serpent's Choice | Serpent's Choice]] is a big improvement!
I'm concerned about one particular sentence:
:"However, no observation of retrocausality has never been confirmed, and the concept is generally discounted by both modern philosophy and mainstream science"
I'd argue for dropping that sentence, even though I agree with it. We should make clear that retrocausality is not scientifically confirmed, but a sentence like that is hard to give direct citation for. The fact that retrocausality is *not* mainstream should be evident to any reader who reads the whole article carefully. The alternative, which might be very laborious, is for the editor to find another published commentator who actually states 'No observation of retrocausality has ever been confirmed..', and then cite that comment. [[User:EdJohnston|EdJohnston]] 05:43, 28 December 2006 (UTC)

::I actually added that sentence in response to the concerns of [[User:Philosophus|Philosophus]], above, who felt that the lede at the time (which is as it is now, minus that line) came too close to implying that retrocausality was an observed or recognized phenomenon.    I know what a morass the fringe/pseudoscience/speculative/etc. material has been of late, so I've tried to tread lightly around the wordings -- although I'm not really any happier with that phrasing.  Any suggestions for more compelling prose that resolves Philosophus's admittedly legitimate concern?  [[User:Serpent's Choice|Serpent&#39;s Choice]] 05:55, 28 December 2006 (UTC)
:::Perhaps you could go through the list of authors in the AAAS symposium, and check whether any of *them* reported actual experiments on retrocausality, by themselves or others. If not, then you could summarize the drift of what they said. Like: 'No author at the recent symposium.. knew of any actual experiments..'  The phrase 'generally discounted', while very likely true, is hard to cite adequately for WP:V. Also, trying to generalize about modern philosophy is like trying to bottle a cloud. [[User:EdJohnston|EdJohnston]] 17:07, 28 December 2006 (UTC)
::::Made another shot at fixing the lede into something acceptable that doesn't seem to give excessive implication of plausibility.  [[User:Serpent's Choice|Serpent&#39;s Choice]] 07:43, 2 January 2007 (UTC)

== Positrons ==

<blockquote>
Feynman later employed retrocausality to provide a proposed model of the [[positron]].  In this model, [[electrons]] moving backward in time would appear to possess negative [[electric charge]].  Further understanding of [[antimatter]] has rendered this model largely obsolete.
</blockquote>
Electrons moving ''forward'' in time have negative electric charge, don't they? Should the above sentence say "positive" or was the suggestion that electrons ''are'' moving backward in time? --[[User:Hitchhiker89|Hitchhiker89]]<small><sup>[[User_talk:Hitchhiker89|talk]]</sup></small> 19:35, 31 December 2006 (UTC)

::Indeed, and now fixed.  Somehow the claim that I "missed a sign change" in my math seems weak in a text article.  =)  [[User:Serpent's Choice|Serpent&#39;s Choice]] 04:08, 2 January 2007 (UTC)

== Top-down Cosmology ==

Although I've run across a few web references to Hawking's "top-down cosmology" as retrocausality, I'm inclined to consider them in error and not include them here.  Hawking's proposal is clearly a revised [[anthropic principle]], but nothing inherent in that concept actually alters the past.  [[User:Serpent's Choice|Serpent&#39;s Choice]] 07:42, 2 January 2007 (UTC)

:You are conflating the anthropic principle with Hawking top-down thesis, it seems to me. Those are two different subjects. The anthropic principle simply states that theories about the universe must comply with the requirement of being favorable to the development of sentient life. Hawking's top-down theory presumes to show how "constraints" defined by the present state of the universe "selected" initial conditions at the beginning of the universe. It is a quantum mechanical model in which "no boundary" conditions at the beginning of the universe (conditions in which time didn't exist) dissolved the separation between past, present and future. Retrocausality isn't the best word to describe that state of affairs. It is not as if one thing is causing the other, or that one thing happens before the other. [[User:James725496|James725496]] ([[User talk:James725496|talk]]) 18:39, 12 April 2022 (UTC)

== Addressing pseudoscience ==

To what extent is it appropriate or necessary to include coverage of pseudoscientific theories on this topic (as described at [[WP:FRINGE]]), such as those presented in ''[[Journal of Scientific Exploration]]''?  [[User:Serpent's Choice|Serpent&#39;s Choice]] 09:38, 21 January 2007 (UTC)
:I think there would have to be a lot of discussion of the pseudoscientific topic in mainstream circles, as described in [[WP:FRINGE#Examples]]. ("including but not limited to scientists, scientific journals, educational institutions, political institutions, and even the United States Supreme Court"). This mainstream discussion would need to be documented in mainstream references. [[User:EdJohnston|EdJohnston]] 21:46, 21 January 2007 (UTC)
::Well, I took a shot at it.  Other than one reference to the ''Journal of Scientific Exploration'', my journal sourcing was exclusively from ''[[BMJ]]'' and ''[[Foundations of Physics]]''.  It could probably do with at least one more pair of eyes for quality concerns, nevertheless.  [[User:Serpent's Choice|Serpent&#39;s Choice]] 06:10, 22 January 2007 (UTC)

==Progress evaluation for GA==

{| style="border: 1px solid #a2a9b1; border-spacing: 3px; background-color: #f8f9fa; margin: 0.5em 0 0.5em 1em; padding: 0.2em; float: right; clear: right; font-size: 88%; line-height: 1.5em; width: 22em;"
|-
| colspan=6 style="text-align:center;" width=240| <big>'''[[Retrocausality]]'''</big><hr>SCORES IN KEY AREAS
|-
| Legality
|width="40" style="background-color: #66ffff"|'''A'''
|width="40"  style="background-color: #66ffff"|'''A'''
|width="40"  style="background-color: #66ffff"|'''A'''
|width="40"  style="background-color: #66ffff"|'''A'''

|-
| Neutrality
| style="background-color: #66ffff"|'''A'''
| style="background-color: #66ffff"|'''A'''
| style="background-color: #66ffff"|'''A'''
| style="background-color: #66ffff"|'''A'''

|-
| Writing
| style="background-color: #66ffff"|'''A'''
| style="background-color: #66ffff"|'''A'''
| style="background-color: #66ffff"|'''A'''
| style="background-color: #66ffff"|'''A'''

|-
| Sources
| style="background-color: #66ffff"|'''A'''
| style="background-color: #66ffff"|'''A'''
| style="background-color: #66ffff"| '''A'''
| style="background-color: #66ffff"|'''A'''

|-
| Citations
| style="background-color: #"|
| style="background-color: #ffff66"|'''B'''
| style="background-color: #ffff66"|'''B'''
| style="background-color: #ffff66"|'''B'''

|- style="font-size: 90%"
| colspan=6 style="text-align:center;" | ''' '''
|}

The only problem I see in this article is that some paragraphs are missing citations.  The writing is no doubt readable, and it flows very nicely.  For a subject that doesn't attract an organized countermovement, you would expect that much in the GA, on top of neutrality, which I believe has been achieved here.  The sources are no problem.  Overall this is a good article.  However, let someone else have the final say.◙◙◙ '''[[User:Kmarinas86| I M Kmarinas86 ]][[User talk:Kmarinas86| U O 2¢ ]]''' ◙◙◙ 03:59, 11 June 2007 (UTC)

:I have added a few more references throughout and cleaned up some wording.  The only paragraphs without citations at this time are brief passages that serve as organizational introductions to fully-cited subsections.  [[User:Serpent's Choice|Serpent&#39;s Choice]] 21:10, 12 June 2007 (UTC)
===GA review===
Hi!
OK, no big objections here after the first read. There are some things that need clarification I believe, or could be elaborated upon to make the article more accessible. In detail:
<blockquote>In the 1950s, Michael Dummett wrote in opposition to such definitions, stating that there was no philosophical objection to effects preceding their causes.[6] This argument was rebutted by fellow philosopher Anthony Flew[7] and, later, by Max Black's "bilking argument".[8] A more complex discussion of how free will relates to the issues Black raised is summarized by Newcomb's paradox.</blockquote>
To better understand how sentences 2 and 3 relate: what is the bilking argument? (which issues raised black?)
<blockquote>Jan Faye</blockquote>
There's no wiki link, maybe it would help to say s.th. Jan Fay, a philosopher of the University of Ulm, Germany, or something
<blockquote>CTC arise from some exact solutions to the Einstein field equation. </blockquote>
I'd quickly explain what CTCs would imply. I know that's at the CTC article, but for a better understanding of the following sentences, it seems necessary. I'd propose to add s.th. like "A CTC is a [[world line]] of an object returning to origin, which would seem to imply at least the theoretical possibility of retrocausality and timetravel."
<blockquote>proposed an alternative theory.[25] University of Washington physicist John Cramer presented the design for an experiment to test this theory at an American Association for the Advancement of Science symposium, subsequently receiving some attention from the popular media,[26][27] although the experiment has never been performed as of 2006.</blockquote>
please clarify. the idea proposed relates to the tachyon idea, I think? add the basic idea of the proposal (taken from the src: "Cramer's approach to explaining entanglement is based on the proposition that particles at the quantum level can interact using signals that go both forward and backward in time") to better connect this proposal with the following paragraph regarding tachyons.
<blockquote>In popular culture</blockquote>
Can you elaborate on the example given? if you cite example, why not explain how retrocausality (or time-travel) works in Hogan's novel.<br/>
I haven't really looked at the other GA criteria yet ([[WP:MoS]], images, sources), at a first glance everything seems fine, that's why I decided to focus on the prose. Good work by the way :) I will return shortly to check the other criteria, but as of now, I'd probably just put it on hold to because of the minor issues raised above. Well, read you soon I hope! [[User:Johnnyw|<span style="color:#454545;">Johnny</span><span style="color:#999999;">w</span>]] [[User talk:Johnnyw|<span style="color:black;">''talk''</span>]] 11:25, 18 June 2007 (UTC)
After reading it a second time, the only things that spring to mind are 
* "prayer healing" should probably not link to "prayer" but to "Faith healing", right? 
* maybe mentioning in the lead that the concept is used in popular culture is justified?
Well, all in all, I'll put in on hold for now (image, sources seem OK). Hope to hear from you soon :) [[User:Johnnyw|<span style="color:#454545;">Johnny</span><span style="color:#999999;">w</span>]] [[User talk:Johnnyw|<span style="color:black;">''talk''</span>]] 15:50, 20 June 2007 (UTC)

:I have defined the bilking argument, identified Faye more clearly, added a gloss for CTCs, and provided more substantial revision of the section on Cramer, including a discussion of another experiment in the field.  I've also improved or expanded wikilink targeting throughout.  How's it looking? [[User:Serpent's Choice|Serpent&#39;s Choice]] 17:09, 21 June 2007 (UTC)

::Very nice, good work. Could you take another look at the "in popular culture" proposal I made above to see if my remark is justified? And on a side note: I am receiving visitors until the beginning of next week and probably won't be able to take another look until Tuesday. So don't worry if I am not responding to any changes until then &mdash; if you worry about what else to do, you could compare if you missed out on any other proposals I made above, as I said, I don't have time to double-check right now myself, sorry for that! And: thanks for your work on this topic! Best wishes, [[User:Johnnyw|<span style="color:#454545;">Johnny</span><span style="color:#999999;">w</span>]] [[User talk:Johnnyw|<span style="color:black;">''talk''</span>]] 17:29, 21 June 2007 (UTC)
===GA pass===
Fair enough, looking good, thanks for addressing the issues I mentioned above. The article passes of course. I'd wish to see a bit more of info in the popular culture section, since it only covers literature right now: A short mentioning of other forms of media and a quick explanation of the idea used in the Hogan's novel would be desirable. Well, that's it: congratulations and thanks for your work. --[[User:Johnnyw|<span style="color:#454545;">Johnny</span><span style="color:#999999;">w</span>]] [[User talk:Johnnyw|<span style="color:black;">''talk''</span>]] 11:33, 25 June 2007 (UTC)

== Tag removal ==

I removed the current-events tag from this article.  Although there is some ongoing research into the topic (Cramer, et al.), that is true of all topics in science.  There is no "current event" in this field in the typical sense: no sudden breakthrough (or expectation of one), no major event that would lead researchers or readers to expect that in a day's, week's, or month's time the content of this page would be different.  The alternative would be to tag nearly all pages about science topics with the current-events tag, but I am reasonably certain that does not follow from current practice and procedure.  [[User:Serpent's Choice|Serpent&#39;s Choice]] 03:36, 16 June 2007 (UTC)

==GA Sweeps (Pass)==
This article has been reviewed as part of [[Wikipedia:WikiProject Good articles/Project quality task force]]. I believe the article currently meets the criteria and should remain listed as a [[WP:GA|Good article]]. The article history has been updated to reflect this review. 

Some minor suggestions for improvement, outside the GA review process:
*I thought this sentence in the "As physics" section intro encroached on NPOV: "In general, models that appear to permit retrocausality or time travel are often thought to possess mathematical artifacts or to simply be conceptually flawed."  It should be sufficient to discuss the theories and let the weight of evidence for each side speak for itself.
*There's a brief allusion to Costa de Beauregard's alternative theory of quantum entanglement—it would be nice if a brief explanation of this theory was included.



-- [[User:Jwanders|jwanders]]<sup>[[User_talk:Jwanders|Talk]]</sup> 23:58, 27 February 2008 (UTC)
[edit]

== New editor has removed mention of pseudoscience ==

With [http://en.wikipedia.org/enwiki/w/index.php?title=Retrocausality&curid=7506128&diff=238453205&oldid=217560773 this edit], [[User:RudolfBerger]] has removed all mention of pseudoscience from the article. Since this wording has been in place for a long time, and has some justification, I proposed that any removal should have discussion here. [[User:EdJohnston|EdJohnston]] ([[User talk:EdJohnston|talk]]) 23:59, 14 September 2008 (UTC)
*I've gone ahead and reverted the change that removed the pseudoscience section.  Some significant, cited material was removed by that change and replaced with an unreferenced discussion of a topic in part already included elsewhere in the article.  That said, we probably might say a little more about that AAAS symposium.  I'll see if I can't scrape up a useful citation.  [[User:Serpent&#39;s Choice|Serpent&#39;s Choice]] ([[User talk:Serpent&#39;s Choice|talk]]) 14:08, 16 September 2008 (UTC)

Sorry, I am fairly new to Wikipedia, at least actively. I mixed things up and apologize. The reason why I chose to remove the word "pseudoscience" is that I believe that it does no justice to Helmut Schmidt's work. True, his work is controversial, and rightly so; but is it pseudoscientific? In which sense? As far as I can see, even declared skeptics like Randy and Hyman acknowledge that Schmidt's experiments are just that - controversial; but they still adhere to scientific standards. Why not settle on the term "controversial"? The designator "Pseudoscience" gives the impression that the controversy is already "solved"; yet it isn't. Therefore, I plead for "Controversial Findings", or something similar. I believe in this section, findings on the presentiment effect, Bem's precognitive habituation protocol, etc. would fit, too. I am certainly open to be corrected if anyone knows more about Schmidt's experiments and why they are, indeed, pseudo-, rather than science. Sorry for the confusion I may have caused; unintentionally, though.  <span style="font-size: smaller;" class="autosigned">—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[User:RudolfBerger|RudolfBerger]] ([[User talk:RudolfBerger|talk]] • [[Special:Contributions/RudolfBerger|contribs]]) 23:17, 18 September 2008 (UTC)</span><!-- Template:Unsigned --> <!--Autosigned by SineBot-->

== In literature -- really examples of retrocausation? ==

The [[retrocausality#In literature|In literature]] section of the article cites multiple examples of [[self-fulfilling prophecy]] as examples of retrocausation. This seems to me to be a miscategorization, since the prophecies that cause their own predicted outcome exist prior to the outcome that they cause, and therefore are not examples of retrocausation. One might argue that, at least within the fiction, it is the future event that causes the prophecy, making it retrocausation, but the same can be said of <em>all</em> prophecies about the future, thus making self-fulfilling prophecies <em>not</em> a specific example of retrocausation. Unless someone weighs in on this subject, I'm just going to go ahead and completely change, replace, or simply remove the section. (How exactly, I haven't decided yet, but I promise to try to be minimalist, since the appearance of retrocausality in fiction doesn't seem to be a very important aspect of the concept.)
[[User:Alweth|Alweth]] ([[User talk:Alweth|talk]]) 18:48, 16 October 2009 (UTC)

== In theology ==

I understand that a recent book discusses the possibility of retrocausation from a theological point of view: That prayer can have an effect on the past, that the Redemption of Christ can redeem people who were dead long before the birth of Christ, and that death in the world can precede the cause of that death, namely the Fall of Adam and Eve. I do not have access to the book, but perhaps it deserves mention:

William Dembski
The End of Christianity: Finding a Good God in an Evil World
Nashville: B & H Publishing Group, 2009
ISBN: 978-0-8054-2743-1
[[User:TomS TDotO|TomS TDotO]] ([[User talk:TomS TDotO|talk]]) 16:00, 19 January 2010 (UTC)

:A friend has suggested to me that the Roman Catholic doctrine of [[Immaculate Conception]] provides an example of retrocausation from two points of view: (1) Mary's exemption from [[Original Sin]] at the time of her conception predates the cause, namely the [[Redemption]] (2) it was also dependent upon her free choice to accept the offer to be the mother of the Redeemer. I do not feel qualified at all to write much about this. And, to repeat myself, I haven't even seen Dembski's book. I know, be bold, but this seems a little too much for me. [[User:TomS TDotO|TomS TDotO]] ([[User talk:TomS TDotO|talk]]) 14:44, 21 January 2010 (UTC)

::Don't forget [http://biblehub.com/john/9-2.htm John 9:2]. The Apostles seemed to regard backward-causality as a perfectly reasonable explanation for a man's blindness. The Church Fathers likewise did not hold to a strictly linear view of time, and Eastern Christians still don't. It was only around the time of the Reformation and Enlightenment that western Christians (especially Protestants) adopted a more linear, rationalistic, and "modern" view of time. Retrocausality is not a novel idea; belief in forms of it was and is the ''norm'', rather than the exception, among most non-[[Psychology#Systemic bias|WEIRD]] cultures and societies.  [[User:FiredanceThroughTheNight|FiredanceThroughTheNight]] ([[User talk:FiredanceThroughTheNight|talk]]) 20:33, 6 July 2014 (UTC)

== Earman and Antimatter ==

I removed the following nonsense: Although further understanding of antimatter has rendered this model largely obsolete,<ref>{{cite journal |last=Earman |first=John |title=On Going Backward in Time |journal=Philosophy of Science |issue=34 |year=1967 |doi=10.1086/288153 |volume=34 |pages=211}}</ref> it is still employed for conceptual purposes, such as in [[Feynman diagrams]].
<references/>

Which is talking about the standard idea that antiparticles are particles going backwards in time. This point of view is known to be mathematically equivalent to other descriptions, which describe time as only going forward. It is not made obsolete by anything at all. Earman is a ''philosopher''.

Further, the notion of "cause" and "effect" are not violated by the description of antimatter as going backwards in time. The notion of cause and effect are macroscopic, involving intentional actions and their consequences, and other highly entropy-loaded words. The microscopic laws of physics simply tell you what happens without using terms like "cause" or "effect" (except for illustrative purposes--- to communicate the idea). So even if you interpret antiparticles as backwards-in-time moving particles, they still "cause" things into the future.[[User:Likebox|Likebox]] ([[User talk:Likebox|talk]]) 17:50, 22 January 2010 (UTC)

== Tachyons don't move back in time ==

A better term is to say that they move "sideways in time" I suppose. But tachyons are fully compatible with causality, but the article already says that.[[User:Likebox|Likebox]] ([[User talk:Likebox|talk]]) 17:53, 22 January 2010 (UTC)

== specific sentence ==

"This is not considered part of science, since the distinction between cause and effect in physics is not made at the most fundamental level."

When I first read this sentence, I thought it meant that retrocausality was simply pseudoscience, although now I'm thinking it means that science simply cannot address the question of whether there is retrocausality.
If what I'm now thinking is correct, would it be better to change the sentence to:

"This question is not considered part of science, since the distinction between cause and effect in physics is not made at the most fundamental level."

[[User:JumpDiscont|JumpDiscont]] ([[User talk:JumpDiscont|talk]]) 10:26, 2 March 2010 (UTC)
:This sentence confused me too, I'd appreciated it if an expert changed or clarified it.--[[User:Physics is all gnomes|Physics is all gnomes]] ([[User talk:Physics is all gnomes|talk]]) 15:20, 20 January 2011 (UTC)

== Experiments ==

There's an [http://discovermagazine.com/2010/apr/01-back-from-the-future/article_view?b_start:int=0&-C= article] that describes the retrocausality experiments. [[User:GregorB|GregorB]] ([[User talk:GregorB|talk]]) 20:42, 12 December 2010 (UTC)

Forgive my ignorance, but doesn't Wheeler's delayed choice experiment pretty much prove retrocausality on a quantum level?
I'm just asking, I'm no expert.  <span style="font-size: smaller;" class="autosigned">— Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/2.227.66.211|2.227.66.211]] ([[User talk:2.227.66.211|talk]]) 20:45, 25 October 2011 (UTC)</span><!-- Template:Unsigned IP --> <!--Autosigned by SineBot-->

== Out of date article ==

Could someone with knowledge of John Cramer's experiment status please update the following:
:Work on the experiment will continue during 2010.[25][26]
Many thanks. [[User:Savlonn|Savlonn]] ([[User talk:Savlonn|talk]]) 22:53, 1 May 2011 (UTC)


: {{ping|Savlonn}} I've just been trying to update it myself, though I'm not a physicist, just a WP editor. The text line and reference numbers you mention are no longer there, so I can't tell what you're citing. I'm getting pretty confused myself; I wasn't sure if this 2009 quote <ref name=5Decades>Cramer, John, (2009-09-11). [http://www.physics.ohio-state.edu/~lisa/CramerSymposium/talks/Cramer.pdf Five Decades of Physics]. ''[A listing of talks and publications, with titles but no content.]'' "Quantum Optics and Retrocausality: Investigation of the Possibility of Nonlocal Quantum Communication with Momentum-Entangled Photon Pairs (1997-now)". Retrieved 2016-09-19.</ref>{{rp|15}} is describing an ''actual'' result or a ''predicted'' one, especially since '''the same slide is included in his 2007 presentation to a class ("Physics 324A, August 14, 2007")'''<ref name=CramerExperiment>{{cite web |last1=Cramer |first1=John G. |authorlink1=John G. Cramer |title=The UW Nonlocal Quantum Communication Experiment |url= http://faculty.washington.edu/jcramer/PowerPoint/Physics324A_20070814.ppt |website=UW Faculty Web Server: John G. Cramer's Home Page |publisher=[[University of Washington]] |quote=The experiment has been in testing phases since mid-January.... The experiment is presently being rebuilt, using avalanche photodiodes as the primary detectors.  It will continue this Fall.  |accessdate=19 September 2016 |location=Seattle, Washington, USA |format=slide presentation |date=14 August 2007}}</ref>{{rp|30}}.
:: We have 10 km of high quality optical fiber coiled in the corner of the laboratory. We split the V-polarized entangled photon beam with a D-mirror, and pass each of the two paths of entangled photons through 10 km of fiber. The H-polarized entangled photons have no optical delay, and the signal is received as soon as these photons are detected at '''D'''<sub>1,2</sub>, which is about 50ms before the signal is transmitted, when the twin entangled photons arrive at '''D'''<sub>3,4</sub>.
: On looking more closely at the 2009 document, I now see that the slide is part of the final section, beginning on p.7, titled "Status of the UW Test of Nonlocal Quantum Communication with Momentum-Entangled Photon Pairs", so I guess it's presented there as a result. But I'm asking for help at {{slink|Wikipedia talk:WikiProject Physics |Help, please: prediction or result?}}
: Please {{Tn|Ping}} me to discuss. --[[User:Thnidu|Thnidu]] ([[User talk:Thnidu|talk]]) 16:12, 19 September 2016 (UTC)
::First, it's a primary source of an isolated experiment, so it's not a great source. Second, [http://faculty.washington.edu/jcramer/NLS/NL_signal.htm recent papers by Cramer] explore different methods for nonlocal communication and conclude for each method tested, "Our conclusion is that no nonlocal signal can be transmitted from Alice to Bob by varying Alice's configuration in any of the ways discussed here" and "Thus, the Shiekh scheme for nonlocal communication is fatally flawed." [[User:BrightRoundCircle|BrightRoundCircle]] ([[User talk:BrightRoundCircle|talk]]) 11:30, 21 September 2016 (UTC)
{{reflist}}

== Entanglement?==

I have never heard of quantum entanglement allowing sending information back in time and the wikipedia on quantum entanglement article does not mention it. Is anyone else of the opinion that that statement is erroneous? --[[User:Ask a Physicist|Ask a Physicist]] ([[User talk:Ask a Physicist|talk]]) 20:47, 1 August 2011 (UTC)

:Retrocausality is actually quite a hot topic at the moment, see the conference at http://prce.hu/centre_for_time/jtf/retro.html which I've just been to.  There's a link on that page for the programme and from there you can get to the abstracts.  On the basis of the talks there, I added to the article a link to the w'pedia page on the rather technical topic of the two-state formalism which has been around for some time.  Possibly it counts as fringe but some very respectable physicists are involved with it.  As regards the connection with entanglement, the talk by Gisin covered that.  The idea originally came from Costa de Beauregard, who noted that the EPR connection between entangled distant objects could be explained without anything travelling faster than light if a signal could go backwards in time to when the entanglement was set up and then forwards again.  So there is a genuine connection with entanglement, and now that retrocausality is now being considered a useful idea, by some physicists at least (even ones that do not at all subscribe to the paranormal), this makes to that degree retrocausality as an explanation for entanglement and EPR OK.
:The article is clearly out of date as, except for my own addition earlier today, there is no reference to recent developments.  This would require an expert with time to spare! --[[User:Brian Josephson|Brian Josephson]] ([[User talk:Brian Josephson|talk]]) 21:02, 6 July 2014 (UTC)
PS: the conference talks were videoed and will be available online in due course. --[[User:Brian Josephson|Brian Josephson]] ([[User talk:Brian Josephson|talk]]) 21:05, 6 July 2014 (UTC)

==Consequences of antimatter being considered as matter moving backwards in time==
I don't want to start a Forum Debate BUT do want to point out some consequences of what the article states.  
"Wheeler invoked this concept to explain the identical properties shared by all electrons, suggesting that "they are all the same electron" with a complex, self-intersecting worldline."

1) In this case, the worldline is, in fact, a digraph/directional-graph - with objects moving forward in time and backwards in time having arrows in different directions (associated with the direction in time that they are moving) BUT there is a problem with there being more matter in the observable universe than antimatter.  This would imply that the cosmic digraph has MORE forwards-time arrows on it than backwards-time arrows, and we would have to explain the "directional asymmetry". 

2) It MAY also be clear that the Baryon asymmetry of the universe does not actually exist, as there may be another universe, travelling backwards in time to compensate for the baryon asymmetry or digraph "directional asymmetry".
    
3) We have transferred the problem of Baryon asymmetry to one of forwards-time moving and backwards-time moving asymmetry, and would have to create a mechanism to explain this asymmetry UNLESS we have a "mirror-image" universe moving backwards in time.  See Andrei Sakharov's theory and further points below. 
   
4) These observations motivate natural questions: (i) How does all this tie into Hidden variables theory and General Relativity?, (ii) What is the role of black-holes given that worldlines APPEAR to end there (though with some potential of Hawking radiation)?, (iii) Does gravity affect forwards moving worldlines the same as backwards moving worldlines?  In particular, is antimatter REPULSED by gravity?

5) The digraph could be closed (ie: a completely self-intersecting worldline cycle), in which case each event is its own cause OR

6) The digraph could extend infinitely into the future (for the forwards-time moving matter that is the matter universe) and infinitely far ito the past (for the backwards-time moving matter that is the antimatter universe).  Due to entropy the infinite future will have chaotically branched digraph structure, as will the infinite past BUT they will not interact UNLESS there is a conformal rescaling (as per Penrose's theory), this conformal rescaling MIGHT allow the two universes to annihilate each other.  Alternatively, time MIGHT be conformal/circular by its own very nature (but this is conjectural).  There is the question of whether the electron would remain massive infinitely far into the future (also discussed in Penrose's book) and also infinitely far into the past.  

7) The idea of all electrons being the same electron with a "complex, self-intersecting worldline" is appealing, but in the above we would have the problem of how the forward-time moving digraph components could create a CYCLE with the backward-time moving digraph components.  One resolution to this issue would be to suppose that the electron becomes MASSLESS in the infinite future and the infinite past (I think Penrose banks on this in his theory).  Then the electron digraph just terminates without stretching out to infinity (though I could be wrong*).  Another resolution is that the backwards-moving universe occupies the same spacetime as the forwards-moving universe BUT doesn't interact with it for some reason (matter oscillates with a quantum frequency related to Planck's length - Antimatter might oscillate out of phase) OR that the infinite future of the matter universe corresponds to the bigbang of the antimatter universe (which would imply that antimatter should become more common, but this is also completely conjectural).  

8) IF antimatter is repelled by gravity AND if the Big Bang were gravitationally attractive, then the Big Bang of the Matter universe could correspond to the heat death of the antimatter universe [somehow].  

9) According to Yoichiro Nambu, the Feymann diagram shows that antimatter-matter "annihilation" creates energy, and presumably increases entropy.  DOES antimatter-matter "creation" do the opposite (consume energy and POSSIBLY decrease entropy)? 
How gravity interacts with any of this is not clear, nor is it clear how entropy would behave once gravity is taken into account. 

There MAYBE some connection of these ideas to Roger Penrose's book "Cycles of Time" also, but I cannot comment further.    

Looking at wikipedia, these ideas COULD connect the Wheeler-Feynman theory to Sakharov's theory with potential links to Penrose's theory.  BUT how any of this would be experimentally verified is far from clear.  

[[User:ASavantDude|ASavantDude]] ([[User talk:ASavantDude|talk]]) 13:31, 19 July 2015 (UTC)
:Your post appears to be [[Wikipedia:No_original_research|original research]]. If you want to incorporate this information into the article you will need to cite [[Wikipedia:Identifying reliable sources|reliable sources]]. Regardless, talking about physics without using mathematical equations is like talking about math without using mathematical equations. [[User:IsaacAA|IsaacAA]] ([[User talk:IsaacAA|talk]]) 16:52, 19 July 2015 (UTC)

::I'm not sure about the 'original research' label, but what I state rather constitutes a summary of consequences of what the article states.  It speaks about antimatter being considered, in some sense, as matter travelling backwards in time without necessarily explaining why this might be so.  There is also an interesting article at https://phys.org/news/2011-04-antimatter-gravity-universe-expansion.html which speaks about the possibility that matter and antimatter may be mutually gravitationally repulsive when one considers time and parity (ie: performs a CPT operation, as per Sakharov?).  In terms of Mathematical equations - inclusion of these would be good but (i) A Good deal of physics is non-mathematical in terms of conceptual intuition AND (ii) The article doesn't seem to have much physics.
::The primary reason for this post is to include the website reference as this seems to be potentially important.  [[User:ASavantDude|ASavantDude]] ([[User talk:ASavantDude|talk]])  <!--Template:Undated--><small class="autosigned">—Preceding [[Wikipedia:Signatures|undated]] comment added 22:54, 14 August 2017 (UTC)</small> <!--Autosigned by SineBot-->

==Assessment comment==
{{Substituted comment|length=758|lastedit=20070107063431|comment={{nw=}}{{nw=}} Regarding my assessments {{nw=}}{{nw=}}

Low-importance: Part of a few viable physics concepts, such as CTCs and the modeling of antimatter as retrocausal, but hardly a topic that demands immediate attention by any means.

Start-class: I've done most of what I can ... the absorber theory stuff is a cast-off substub of a section, and I don't know where to look for more.  I'm not sure how much further discussion on CTCs, Roman rings, etc. belongs here and not at their articles.  Another couple sets of eyes from the Project won't hurt.

And, of course, the philosophy/social discussion section its a separate beast, although I'd like to think I've given it the same measure of attention.
--[[User:Serpent's Choice|Serpent&#39;s Choice]] 06:34, 7 January 2007 (UTC)}}
Substituted at 04:13, 30 April 2016 (UTC)

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== Article in New Scientist ==

*Adam Becker; "Blast from the future", ''New Scientist'', 17 February 2018, pp.28-31.
This article, in a well-established [[WP:RS|reliable source]], gives a popular discussion of some recent work on retrocausality in theoretical physics, and in particular its relation to [[quantum entanglement]]. I am not familiar with the subject, so it would be great if someone could take a look and see if it has anything that can be usefully added to this Wikipedia article. &mdash; Cheers, [[User:Steelpillow|Steelpillow]] ([[User Talk:Steelpillow|Talk]]) 16:40, 16 February 2018 (UTC)
:Thanks. Fundamentally from considerations of the [[no-communication theorem]], quantum retrocausality cannot be tested. Interpretationally, looking at systems instead of isolated particles (see Rubin (2001) in [[retrocausality]]) removes nonlocality (and retrocausality) from quantum interactions. (For example how does a [[particle in a box]] "know" it's a particle in a box without non-locality? Well, if you look at the ''system'', the particle doesn't have to "know" anything. But if you look only at the particle, it appears non-local.)
:This article (I'm assuming [https://www.sott.net/article/377599-Retrocausality-may-explain-how-the-future-can-change-what-happens-now-as-in-a-quantum-time-machine this] is the same article even though the headline is different) is rather sensationalist. In the article's defense, it does cover all the ground and the author does interview actual researchers and quote actual papers, so in that regard it's very good. But obviously it emphasizes the more exciting (yet uncertain) aspects of this research. [[User talk:BrightR|Bright☀]] 13:23, 17 February 2018 (UTC)
::Yes, it is the same article, just in a slightly different wrapper. ''[[New Scientist]]'' is like ''[[Scientific American]]'' in seeking to popularize genuine science, so yes it does tend to emphasize the sensational speculations. But it also often provides a high-level view of the context, which I tend to find useful. &mdash; Cheers, [[User:Steelpillow|Steelpillow]] ([[User Talk:Steelpillow|Talk]]) 16:18, 17 February 2018 (UTC)

== Page needed ==

Citing the exact page of a book is a Wikipedia [[WP:CHALLENGE|policy]] and [[WP:CITETYPE|guideline]]. If you don't like the "aesthetic degration" then open the book in question and provide the page that supports the information which relies on the reference. [[User talk:BrightR|Bright☀]] 07:46, 5 April 2018 (UTC)

== Bias in article ==

I'm very familiar with bias in WP articles on so called 'fringe subjects', but am surprised to find it prominent in this article, with what looks like a preponderance of dismissive comments.  Just a thought — I don't in fact believe in retrocausality myself, but I also believe in articles displaying a '[[Wikipedia:Neutral point of view|neutral point of view]]', which is not much in evidence here. Perhaps this is all a hangover from a time when this was a fringe subject. --[[User:Brian Josephson|Brian Josephson]] ([[User talk:Brian Josephson|talk]]) 22:15, 2 November 2018 (UTC)
: You're going to have to give more details before I can give an informed comment on the issues you see in this article. [[User:power~enwiki|power~enwiki]] ([[User talk:Power~enwiki|<span style="color:#FA0;font-family:courier">π</span>]], [[Special:Contributions/Power~enwiki|<span style="font-family:courier">ν</span>]]) 23:15, 2 November 2018 (UTC)
:As an editor who has tried to update this article with some modern physics, I would agree with the assessment that the lead in particular is too negative and that that is a hangover from the old pre-quantum days. In quantum theory, retrocausality has recently gained attention as a postulate or interpretation, i.e. a theoretical construct, and not a thought experiment, but I have been wary of updating too much too quickly. Maybe it's time I had another go. A century of hard experience has taught us that in quantum theory, if it is in the equations then it is a real effect. Probably the most rational suggestion would be that, as with superluminal entanglement effects, it occurs at the quantum level but there are serious (and controversial) issues when trying to communicate macroscopic information over it. As Wikipedians, the problem we face is finding [[WP:RS]] to support any such editorial stance. Lacking that, the article is forced back onto the long-established and very negative stance of the parapsychology sceptics. &mdash; Cheers, [[User:Steelpillow|Steelpillow]] ([[User Talk:Steelpillow|Talk]]) 08:46, 3 November 2018 (UTC)
::Re the request for details, it's difficult to explain my reaction, but I think [[User:Steelpillow|Steelpillow]] captures the general sense of how I felt about the article (which I just looked at as I wanted to comment about retrocausality in a paper I'm writing and was hoping to get a clear summary, which I did not find) pretty well, so I'll just leave it at that. --[[User:Brian Josephson|Brian Josephson]] ([[User talk:Brian Josephson|talk]]) 09:10, 3 November 2018 (UTC)
:::I have now recast the article to bring the modern scientific usage of the term a bit more to the fore. I have plenty to say about other aspects, especially [[precognition]], but how much time have you got? Maybe an [https://en.wikipedia.org/wiki/Special:EmailUser off-wiki conversation] would be more appropriate? &mdash; Cheers, [[User:Steelpillow|Steelpillow]] ([[User Talk:Steelpillow|Talk]]) 09:34, 3 November 2018 (UTC)
:::Or, check out my essay on [http://www.steelpillow.com/blocki/sci/retrocausality.html Retrocausality: Backwards in Time]. &mdash; Cheers, [[User:Steelpillow|Steelpillow]] ([[User Talk:Steelpillow|Talk]]) 10:34, 3 November 2018 (UTC)
::::I'm pretty busy at the moment, but maybe in a few days' time.  But I wonder how much the wikiguardians will let you keep in about precognition? --[[User:Brian Josephson|Brian Josephson]] ([[User talk:Brian Josephson|talk]]) 10:38, 3 November 2018 (UTC)
:::::See the article on [[precognition]]. &mdash; Cheers, [[User:Steelpillow|Steelpillow]] ([[User Talk:Steelpillow|Talk]]) 11:09, 3 November 2018 (UTC)
::::Proves my point!  Is it worth taking up time ineffectively battling the guerillas? --[[User:Brian Josephson|Brian Josephson]] ([[User talk:Brian Josephson|talk]]) 12:01, 3 November 2018 (UTC)
:::::It does seem to help that a lot of the material can be presented as a narrative of historical significance, so we don't need to get steamed up about its scientific credentials. As long as we can just cite say [[Brian Inglis]] and [[Antony Flew]], we don't have to worry about which of 'em was right. &mdash; Cheers, [[User:Steelpillow|Steelpillow]] ([[User Talk:Steelpillow|Talk]]) 12:08, 3 November 2018 (UTC)

You sound like you want to fill the article with original research ("read my article") and speculation. If you have reliable sources about [[No-communication theorem|quantum superluminal communication]], here's your article and here's your Nobel Prize. If you don't, quit blowing smoke up our asses. [[User talk:BrightR|Bright☀]] 21:19, 6 November 2018 (UTC)
:Which of us are you whingeing at? In what way is that supposed to help improve Wikipedia? &mdash; Cheers, [[User:Steelpillow|Steelpillow]] ([[User Talk:Steelpillow|Talk]]) 22:11, 6 November 2018 (UTC)
::There's no smoke without fire!  In a paper published in IL NUOVO CIMENTO VoL. 51 B, N. 2, 267–279, Costa de Beauregard writes "the Einstein correlation does indeed entail an entirely new causality concept". And incidentally I don't see Brightsun's comment as a wish to fill the article with OR. --[[User:Brian Josephson|Brian Josephson]] ([[User talk:Brian Josephson|talk]]) 09:25, 7 November 2018 (UTC)
:::Beauregard is currently referenced in the section on [[Retrocausality#Quantum_physics|Quantum physics]], No. [25] at the time of writing. However that cites Vol. 42B so may be a different paper. I'd suggest you put any additions in that section. &mdash; Cheers, [[User:Steelpillow|Steelpillow]] ([[User Talk:Steelpillow|Talk]]) 11:24, 7 November 2018 (UTC)
::::I don't have time to do that kind of thing myself at present.  In fact retrocausality is quite a hot topic at the moment, e.g. papers by Huw Price and Roderick Sutherland, and you may find things to quote there. --[[User:Brian Josephson|Brian Josephson]] ([[User talk:Brian Josephson|talk]]) 11:54, 7 November 2018 (UTC)

== Differences with Precognition  ==

First i want to proclaim that i don't have any agenda to support pseudoscience here, but someone did give an example to this and i want to ask about the differences between them, pretty much he did give an example for retrocausality but it clicked like it's a precognition, the example is this: say we gathered 10 different people (different in age, culture and education) who don't know each other in different rooms without them seeing each other in a sunny summer day, and we asked them to write a random word, and they all write lightning, they go home and then they get strike by lightning but survive with heavy injuries.
And then the guy who wrote this proclaimed that it's a retrocausality where they got hit by lightning and because they survived the knowledge returned to their past selves and that's how they wrote it. though the idea of knowledge of events transferring through time is what we usually call precognition or prophecies (like predicting death of someone or a sudden reappearance of someone without previous hints).
So i'm curious if:
1-is this an accurate example to retrocausality or did the guy messes it up?
2-In the case of the example here, will we call this retrocausality or precognition?
3-What are the differences between the two?
4-Does the idea of knowledge transferring through time fit into retrocausality or no?

And sorry for any mistakes, this is my first Talk: and english isn't my native language.  <!-- Template:Unsigned --><small class="autosigned">—&nbsp;Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[User:Gep10000|Gep10000]] ([[User talk:Gep10000#top|talk]] • [[Special:Contributions/Gep10000|contribs]]) 17:27, 11 September 2020 (UTC)</small> <!--Autosigned by SineBot-->
:Wikipedia talk pages are for improving the encyclopedia, they are not a general discussion forum. You might do better looking for a suitable [https://stackexchange.com/sites Stack Exchange site]. &mdash; Cheers, [[User:Steelpillow|Steelpillow]] ([[User Talk:Steelpillow|Talk]]) 17:37, 11 September 2020 (UTC)
::The issues raised are in principle relevant to the subject, and so could help to improve the encyclopedia.--[[User:Brian Josephson|Brian Josephson]] ([[User talk:Brian Josephson|talk]]) 17:45, 11 September 2020 (UTC)
:::Not without reference to a reliable source they aren't. &mdash; Cheers, [[User:Steelpillow|Steelpillow]] ([[User Talk:Steelpillow|Talk]]) 17:57, 11 September 2020 (UTC)
::::Of course!  But a specific reference is not needed in the preliminary review of an important issue in a talk page.--[[User:Brian Josephson|Brian Josephson]] ([[User talk:Brian Josephson|talk]]) 18:45, 11 September 2020 (UTC)

== Split the article: weak retrocausality and strong retrocausality ==

This article mixes two completely different concepts.  In physics these are known as "strong-causality principle" and "weak-causality principle".  See for example 
Cramer, John G. "Generalized absorber theory and the Einstein-Podolsky-Rosen paradox." Physical Review D 22.2 (1980): 362.

The strong version requires macroscopic causality: this is the venue for philosophy and parapsychology. The weak version allows microscopic retrocausality without requiring macroscopic causality. This is the domain of most fundamental physics models. 

One split could be weak/strong, but if that is unacceptable, we should move the physics to [[Retrocausality (physics)]] Strong retrocausality cannot be verified and it is not scientific. [[User:Johnjbarton|Johnjbarton]] ([[User talk:Johnjbarton|talk]]) 02:42, 29 October 2023 (UTC)
:You mischaracterise philosophy. The issue there is to ''understand'' the causality that science and psychology already study, not invent wacky ideas for the sake of it. We must also be careful to distinguish scientific sources on strong/weak causality from sources on strong/weak '''''retro'''''causality. I am seeing precious little of direct relevance to retrocausality in there, which would not require that forbidden bogey of [[WP:OR|original research]] on our part. Also, a parent article explaining the difference between the weak and strong versions would remain essential, and this is clearly the place for that overview. If you can help find relevant sources discussing retrocausality and grow this article accordingly, then maybe one day it can bud off a child. But that time is not yet. &mdash; Cheers, [[User:Steelpillow|Steelpillow]] ([[User Talk:Steelpillow|Talk]]) 15:25, 29 October 2023 (UTC)
::Indeed, as you say there is no such thing as strong retrocausality! 
::Nevertheless, retrocausal physical theories are completely unrelated to parapsychology. Grouping them together here creates the impression that they are related. [[User:Johnjbarton|Johnjbarton]] ([[User talk:Johnjbarton|talk]]) 16:15, 29 October 2023 (UTC)
::I reorganized the physics section in an attempt to separate the microscopic models where retrocausality is a possible part of the model from hypothetical macroscopic retrocausality. [[User:Johnjbarton|Johnjbarton]] ([[User talk:Johnjbarton|talk]]) 17:17, 29 October 2023 (UTC)
:::Thank you, that is definitely an improvement. One concern; the article now states that "''retrocausality at the microscopic level can be part of theory without violating the macroscopic causality of relativity.''" As I recall this has been a key point of argument in the recent past. So I think it needs properly sourcing. On parapsychology, many researchers would disagree that the physics is not connected; quantum retrocausality in particular seems to be reopening old wounds. Either way, I'd like to see that section become less of a pointless mole-whacking demonstration and more of an outline of that literature for its own sake as a social and historical phenomenon. A source does not have to be scientifically reliable in order to verify the prevalence of such claims. &mdash; Cheers, [[User:Steelpillow|Steelpillow]] ([[User Talk:Steelpillow|Talk]]) 21:10, 29 October 2023 (UTC)
::::Thanks, I rephrased the sentence. [[User:Johnjbarton|Johnjbarton]] ([[User talk:Johnjbarton|talk]]) 15:11, 30 October 2023 (UTC)

== When it really happens in Wikipedia articles ==
Since retrocausation is valid, how is there not a single mention of it in any inventions on Wikipedia or in any book about inventions? There should be hundrends of 1990's inventions that date back to 1700's and the origin is not the 1700's or 1900 but rather 1998 or 2024. Are people going to document this or is retrocausation mostly ignored in a history writing fraud.
:As the article makes plain, while the phenomenon exists at the quantum level, like other quantum weirdnesses it does not manifest at the macroscopic or classical level. Relativistic solutions are just speculative mathematical games. There can be no "hundreds of inventions" at the classical level, as you suggest. &mdash; Cheers, [[User:Steelpillow|Steelpillow]] ([[User Talk:Steelpillow|Talk]]) 05:34, 21 February 2024 (UTC)

:Regarding the original post, please see [[WP:Signatures]].
:* "Signing your posts on talk pages, both for the article and non-article namespaces, is required,"
:[[User:Johnjbarton|Johnjbarton]] ([[User talk:Johnjbarton|talk]]) 15:17, 21 February 2024 (UTC)