Talk:Cosmological constant

message: The previous changes look good to me, DAGwyn. I am trying to understand this better and I notice that on the Friedmann equation page there is an equation with c and G in it, (the first Friedmann equation, written in what they call Hubble constant form). This equation which appears to me to be missing a factor of  c^2. The LHS is \dot{a}^2/a^2 which has dimensions of T^{-2} (unless everything is non-dimensional). This has to match the dimensions of G\rho on the RHS. It seems to me it should be G\rho/c^2 which has the required dimensions T^{-2}. I am not a big fan of units which make c=1 in this context; it seems very difficult for a beginner (someone reading wikipedia trying to learn) and has confused me somewhat, for example. If one is going to write non-dimensional terms, which is fine, I think there needs to be a clear statement about it; i.e. a = r/r0 where r is a distance and r0 is a reference length; v = u/c where u is a speed and so on. It could be just as easy to re-insert all the symbols for c, and anything elsewhere `missing', becasue of non-dimensionalization? Maybe someone can look at it? Thanks. E4mmacro 04:37, 7 April 2007 (UTC)
replies: text: I see that if \rho is mass-density (not energy density as I originally thought and as it is on the cosmological constant page), G\rho has units of T^{-2} as requried. E4mmacro 22:05, 9 April 2007 (UTC)
replies: text: There is a discussion of that above ("What are the units of Λ?").  Units are problematic when various differently defined quantities are being related to each other.  I excised the statement of units from the article, which seems just fine without it. —  DAGwyn 19:14, 10 April 2007 (UTC)

text: The edit summary of the revert is worth reading: I'm not against introducing c and G, but then the rest of the sentence should be kept consistent with that. That is, we shouldn't explain why we omit something we don't actually omit. Btw: why did you re-introduce only G, but not c? — HHHIPPO 20:23, 27 April 2013 (UTC)
thread_title: Reinstating c?

message: I find it dishonest to speak about fine-tuning without qualifying the statements, but I don't know how to add this properly. I am watching "What we still don't know" documentary right now and they go out of their way to express how unlikely coincidence would that be to have the cosmological constant fine-tuned to 10^120th. But what we must note is that our understanding of this area of physics is still not final. It's not like we are already sure about the way expansion works. Even more important is that there may be no fine-tuning involved at all - we are just looking at the problem in the wrong way.
For example, I can claim that there is a remarkable finetuning of a certain variable for each couple - if that variable wasn't correctly set to 1 part in 10 million, there would be no conception or the mother would die. What that variable is? It's the number of dead sperms. If the difference between that number and the number of total produced sperms is more than, say, 10, the mother would explode, as its womb tries to produce 10 babies. :) If the difference is 0, no child will be born.
 That BS, because the limiting factor to the number of babies conceived is the number of ova ready to be
 fertilized, not the number of sperms. In fact there are millions of live sperms in each ejaculation, but since
 only one sperm can fertilize each ovum, and usually only one (rarely two, and more than that usually only due
 to hormonal treatment) ova are available in each period, only one (rarely two or more) sperm succeeds. No danger
 of explosions here at all! 142.3.164.195 23:12, 6 March 2006 (UTC)
thread_title:  Fine-tuning 

message: There's some interesting news out today  that Paul Steinhardt at Princeton University, and Neil Turok at Cambridge University are hypothesizing the age of the universe to be about a trillion years (after it's been through a series of big bangs and crunches), allowing for the cosmological constant to decrease over time.  Of course, I'm not sure how to work the theory into the article ;-)  -- ke4roh 20:40, 5 May 2006 (UTC)
thread_title:  Decreasing for a trillion years? 

message: Is Steinhardt's idea notable enough to be included here? With some effort, it should be possible find any number of ideas why the CC is that small, but none of them gathered a sizable followship so far. --Pjacobi 14:16, 24 November 2006 (UTC)
replies: text: In "cosmological units" the constant is 1, which puts a different slant on the question.  Eddington thought that it related the (inverse of the) radius of the universe to our laboratory units of length. — DAGwyn 23:41, 26 November 2006 (UTC)
thread_title:  Steinhardt 

message: I am not an astrophysicist or cosmologist.  A point that the article, in my opinion does not clarify is, what is the cosmological constant? What does it measure?  Why is it constant? 
* It's a constant of integration in the solution to the metric in general relativity.  So if GR is exactly right (which it isn't) then the Cosmological constant is physically constant.  What it is physically?  Nobody knows (although there are lots of ideas...) WilyD 22:40, 21 December 2006 (UTC)
replies: text: re "what is it?", there is now an early link to the Einstein field equations where the cosmological can be viewed in context.  --Michael C. Price talk 23:19, 21 December 2006 (UTC)
replies: text: I think what the original editor was getting at, is that the lead section fails to answer the question.  It needs to be rewritten. —Viriditas | Talk 05:31, 24 February 2007 (UTC)

text: Note that this was done recently. — DAGwyn 22:40, 5 April 2007 (UTC)
thread_title:  What is it?

message: First, im I'm fairly inexperienced when it comes to wikipedia modifactions. Last time i deleted an innaccuracy i was told it should be reported why first. Everyone can click on the "inverse gamblers fallacy" link and see that anthropic explanations do not commit it (which some user added in to the original statement which notes that a multiverse in response to fine-tuning does commit the fallacy. So im going to fix it back to how it was before. —The preceding unsigned comment was added by Gnarlyocelot (talk • contribs) 19:03, 6 April 2007 (UTC)
thread_title:  Inverse Gamblers Fallacy 

message: This article should explain empirical evidence for or against this hypothesis, or clearly point to other article(s) that do. -- Beland (talk) 15:51, 26 February 2008 (UTC)
thread_title:  Empirical evidence 

message: I just came across this article. I split the section titled `general relativity' into two sections; one which seems to be logically the history of the cosmological constant and the other which deals with the measured positive cosmological constant. 
I felt that the second issue -- that of a measured positive cc (according to the most popular cosmological models at least) -- definitely deserved a separate section. Moreover, `general relativity' was not very descriptive. 
I also elaborated the explanation of the cc problem, explaining that we expect to get a cc of the order of M_{\rm pl}^4 and get one that is 10^{-120} orders smaller.
btw I think the numbers on this page should be checked. For example, the value of the cc is given in different units and while everything is consistent to a couple of magnitude, its not quite right. For example, 10^{-47} Gev^4 ~ 10^{-123} M_{pl}^2. This can be a source of some confusion. I didnt want to change this without checking through all the units, but if someone else has this on the tips of their fingers they should do this. cheers, Perusnarpk (talk) 20:04, 30 July 2008 (UTC)
thread_title:  Changed section headings, created new section, expanded description of cc problem 

message: Could I just take a second here to point out that the first sentence of the lede in this article does not actually say what the cosmological constant is?
It would be sort of nice if we could kinda shoehorn that in somewhere...  (I see a bit on the talk page, above, suggesting that this was once corrected; it appears broken again.--Baylink (talk) 18:47, 10 September 2008 (UTC)
thread_title:  Bad lede 

message: Corrected missing negative sign in second sentence of second paragraph of "Cosmological constant problem" (10^-120 was incorrectly written 10^120).
Also changed:
Critics note that these theories, when used as an explanation for fine-tuning, commit the inverse gambler's fallacy.
To:
Critics claim that these theories, when used as an explanation for fine-tuning, commit the inverse gambler's fallacy.
As whether the fallacy is committed is a matter of debate (and, for the most part, has been refuted).
Does this line even need to be included? I have not heard any application of the "inverse gambler's fallacy" not addressed by the Leslie rebuttal. I.e. it is only possible to observe a fine tuned universe. Given that you know you cannot observe non-tuned systems, it is reasonable to assume that likely variations exist unobserved. Hacking's math is sound given his assumptions, but his application is flawed, even at a glance. The "inverse gambler's fallacy" is only committed if one tries to use the "fine-tuned" universe as evidence for multiple universes, not vice versa.  —Preceding unsigned comment added by 24.233.77.207 (talk) 15:04, 30 October 2009 (UTC)
thread_title:  Corrected Missing Sign, Incorrectly Definitive Statement 

message: 1.	What is the actual figure of the Cosmological constant?
2.	Do we have tangible evidences of existence of other universe / multiverses?
Cheers
89.211.115.190 (talk) 13:42, 10 November 2009 (UTC)
thread_title:  Multiverses 

message: Mechanism-Revealed Physics (36/40) 
   Solving the problem of cosmological constant by proving that the concept of cosmological constant in itself turns out to be mechanistically thus essentially wrong.  The problem of cosmological constant has been widely recognized as one of the most fundamentally important unsolved problems in physics; as a matter of fact, the problem of cosmological constant actually becomes an inescapable fundamental puzzle in physics. 
    The long-term perplexing problem of cosmological constant has been completely solved by proving that the so-called problem in itself is mechanistically thus essentially invalid (P. 788 ~ 789, 7.7.2, Ch.7B, reference #2).  Why? All in all, the concept of cosmological constant has been proven to be mechanistically thus essentially wrong, because the cosmological constant is literally the aftermath of the mechanistically thus essentially wrong postulate of ‘invariant scales of space (length) and time’ embedded in Einstein’s postulate-based general relativity (EPBGR).   [*Note, EPBGR’s postulate of ‘invariant scales of space (length) and time’ has been proven to be mechanistically thus essentially wrong (P. 420 ~ 423, 4.5.2, Ch.4A, reference #1)]. 
   The key to understanding of this solving the problem of cosmological constant: (1) the well-known and undeniable fact, which is that Einstein’s postulate-based general relativity (EPBGR) does not and cannot solve the problem of why space and time are variable thus relative in gravitational field. (2) The so-called cosmological constant turns out (proven) to be literally the consequence of EPBGR does not and cannot know why time and space are variable thus relative in gravitational field (i.e., the root of the cosmological constant is that EPBGR does not and cannot know why space and time are variable thus relative in gravitational field). (3) The cosmological constant is embedded in EPBGR, whereas EPBGR has been proven to be mechanistically thus essentially wrong literally due to it utterly skipping over the mechanism thus essence behind its describing phenomena via the “help” of a series of postulates and assumptions (P. 399 ~ 444, Ch.4A, reference #1).   (4) The cosmological constant is connected to ‘expanding Universe’ (i.e., the zero value of cosmological constant corresponds to ‘expanding Universe’), whereas the ‘expanding Universe’ has been proven to be mechanistically thus essentially wrong (P. 761 ~ 765, 7.2, Ch.7A, reference #2).  (5) The cosmological constant is connected to the hypothesized dark energy that has been proven not existing at all (P. 784, 7.6.3, Ch.7B, reference #2).  (6) Knowing of why time and space are variable thus relative in the Universe (P. 445 ~ 514, Ch.4B; P. 541 ~ 548, 5.5, Ch.5B, reference #1). (7) Knowing of the newly revealed mechanism of universal gravitational constant G – the value of G is and represents the reduction in the scales of space and time occurring in gravitational field (P. 505 ~ 509, 4.16, Ch.4B, reference #1). 
Reference #1: 2009, Bingcheng Zhao, From Postulate-Based Modern Physics to Mechanism-Revealed Physics [Vol. 1(1/2)], ISBN: 978-1-4357-4913-9. 
Reference #2: 2009, Bingcheng Zhao, From Postulate-Based Modern Physics to Mechanism-Revealed Physics [Vol. 2(2/2)], ISBN: 978-1-4357-5033-3. 
Ph.D., Bingcheng Zhao,  
The author of “From Postulate-Based Modern Physics to Mechanism-Revealed Physics” 
1401 NE Merman Dr. Apt. 703, Pullman, WA 99163   USA.
Email: bczhao12@gmail.com   or   bzhao34@yahoo.com   or   bingcheng.zhao@gmail.com  —Preceding unsigned comment added by 204.52.246.120 (talk) 19:17, 18 March 2010 (UTC)
replies: text: Wikipedia is not the place to try to publish or popularize your own ideas. See WP:NOR and WP:RS. --Christopher Thomas (talk) 19:21, 18 March 2010 (UTC)
thread_title:  The problem of cosmological constant has been completely solved  

message: I would hope to find when Einstein added and removed the cosmological constant. Was it in the 1916 paper? That sort of thing. The History section has no dates at all. Ronstew (talk) 19:25, 6 December 2010 (UTC)
replies: text: I think it was always there in his work - his "mistake" was that he didn't remove it. -- cheers, Michael C. Price talk 15:53, 25 August 2011 (UTC)
thread_title:  History has no dates 

message: I removed the " or even 10−120 in reduced Planck units." because "reduced Planck units" is not a unit. It is like saying the CC has the value of 10^-35 in SI units. And it causes confusion with the next paragraph which states "As noted above, the measured cosmological constant is smaller than this by a factor of 10−120." But it is NOT mentioned above.  — Preceding unsigned comment added by 217.225.77.88 (talk) 03:15, 25 August 2011 (UTC)
thread_title:  Positive value 

message: The section was of negligible relevance to the main subject of this article.
The short text also contained a factually wrong statement, even contradicting the main article on de Sitter relativity. 
It did not even contain any references for its claims.
Const.S (talk) 20:28, 8 December 2011 (UTC)
replies: text: Agreed WP:Undue D. Flassig (talk) 21:27, 8 December 2011 (UTC)
thread_title:  Removal of section on [[de Sitter relativity]] 

message: It's said "measured cosmological constant is smaller than this by a factor of 10^−120." Does this means "1"???Mastertek (talk) 14:23, 19 March 2012 (UTC)
thread_title:  CC value based on quantum field theory 

message: This "explanation" lacks an explanation of what the cosmo constant is in the opening paragraph. That paragraph notes its historical significance but fails to provide a useable definition. Please add a definition of what the cosmo constant is. And please don't fall back on some tired cliche about how it's all in the math. Lets have a comprehendible definition, preferably one which can be maintained in the mind after the page is exited.  — Preceding unsigned comment added by 70.112.237.119 (talk) 02:46, 19 April 2012 (UTC)
replies: text: I agree; this page doesn't actually give any values for the constant, or even an expression!  So frustrating when trying to work on Cosmology HW.
Popa910 (talk) 03:38, 19 October 2015 (UTC)
thread_title: Lacks definition in opening paragraph

message: The Arxiv paper Spontaneous creation of the universe from nothing has received some press reports and links the cosmological constant with the quantum potential and maybe with the initial exponential expansion of the baby universe (if I understand what it says). How do we decide whether the paper should be mentioned in the article? Absinthia Stacy (talk) 15:37, 15 April 2014 (UTC)
thread_title:  Cosmological constant linked to the quantum potential 

message: From the introduction to the article, "...the main required properties of dark energy are that it dilutes much more slowly than matter as the Universe expands, and that it clusters much more weakly than matter, or perhaps not at all." Does this leave out it's main required property? Shouldn't this read: "...the main required properties of dark energy are that *it functions as a type of anti-gravity,* that it dilutes much more slowly than matter as the Universe expands, and that it clusters much more weakly than matter, or perhaps not at all." Bob Enyart, Denver KGOV radio host  (talk) 17:08, 3 March 2015 (UTC)
replies: text: Any objection to incorporating this into the main article? Bob Enyart, Denver KGOV radio host  (talk) 22:59, 17 April 2015 (UTC)
thread_title:  Dark energy primary requirements 

message: So "ΩΛ is estimated to be 0.692 ± 0.010 ..."  0.692 what?
Please someone knowledgeable express this in units so that people reading this can understand what the scale of ΩΛ is. 166.184.170.35 (talk) 21:13, 20 March 2015 (UTC)
replies: text: Like, make something up just to please you?  The constant is a dimensionless value, which the article clearly specifies. The lack of units is appropriate. Owen× ☎ 23:23, 20 March 2015 (UTC)
thread_title:  Can someone '''please''' put appropriate units on this thing? 

message: Substituted at 12:19, 29 April 2016 (UTC)
thread_title: Assessment comment

message: "Instead, the cosmological constant gradually diminishes over many cycles to the small value observed today."
Then that's some other model of "dark energy". The point of the cosmological constant model of dark energy is that it's ... constant ... right?
I looked at the arXiv link in the primary source cited, it seems to use a scalar field, and not use the term "cosmological constant". That seems right.
Perhaps this should be moved to a "dark energy" article. --174.116.141.16 (talk) 19:11, 5 July 2016 (UTC)
replies: text: Done. --174.116.141.16 (talk) 23:38, 28 August 2016 (UTC)
thread_title:  Cyclic model: what? 

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thread_title:  External links modified 

message: I feel that in
The cosmological constant has the same effect as an intrinsic energy density of the vacuum, ρvac (and an associated pressure). In this context, it is commonly moved onto the right-hand side of the equation, and defined with a proportionality factor of 8π: , where unit conventions of general relativity are used (otherwise factors of G and c would also appear, i.e. , where κ is Einstein's constant). It is common to quote values of energy density directly, though still using the name "cosmological constant", with convention . The true dimension of Λ is a length−2.
should appear
 , 
because otherwise this rho is dimensionally a matter density. I note that
* this misprint seems related to the fact that some authors use lambda for lambda*c^2 -- it might be useful to warn the reader of this occurrenc
* in the section positive value the energy density of vacuum appears explicitly as a mass density (there are also problems with MKSA and cgs values).
I would also enjoy something like
 (and an associated pressure) -> (and associated pressure P=constant*rho)
with a guess of the constant (that I suppose to depend on the details of the theory, a fact that makes this addition difficult)
If you are expert in this, I suggest to give in the proper article a clear definition of the Gibbons-Hawking temperature. This because I have found in many places the definition T=H/2pi in natural units, from which I have deduced T=hbar*H/2pi*k.
Unfortunately, the value 10(-29) comes out with T=hbar*H/k.
pietro (by the way, I  wrote talk 29 and if you feel that some consideration I made there may be useful, I may revise for an insertion)
151.29.203.130 (talk) 08:30, 21 February 2018 (UTC)
thread_title:  please check 

message: In the Equation section, the following statement currently appears without citation "It is common to quote values of energy density directly, though still using the name "cosmological constant", using Planck units so that 8 π G = 1 ."
Is this actually common?  My understanding (per the relevant Wikipedia entry) is that, using Planck units, G = 1, so it would follow that 8 π G = 8 π.  Furthermore, I have not been able to find another instance where this claim is made (let alone justified).
Recommend that a citation for this be provided, if indeed it's true, or that the claim be deleted/clarified if not.  WJTP (talk) 03:17, 2 February 2021 (UTC)
thread_title:  Questionable claim regarding values of energy density 

message: The cosmological constant is not "the energy density of space, or vacuum energy, that arises in Albert Einstein's field equations of general relativity."  There is one theory, part of quantum mechanics, not general relativity, that gives rise to a cosmological constant.  It has nothing to do with Einstein.  The original cosmological constant was an arbitrary term added by Einstein.  It was not generated by vacuum energy.  Many, many years later the idea of vacuum energy combined with the discovery of increasing universal expansion to regenerate interest in the cosmological constant with a currently unproved hypothesis about what might generate it, namely vacuum energy.  The introduction totally fails to convey most of this factual information.  I will rewrite it if someone doesn't do a better job first.  Zaslav (talk) 21:34, 28 August 2021 (UTC)
thread_title:  Inaccuracy in introduction 

message: The lead graphic is a misleading introductory visualisation of universe expansion. Please see my critique here;
https://commons.wikimedia.org/w/index.php?title=File_talk:CMB_Timeline300_no_WMAP.jpg#Graphical_representation_of_the_expansion_of_the_universe
Richardbrucebaxter (talk) 00:56, 7 September 2022 (UTC)
thread_title:  Lead graphic conveys misleading expansion rate 

message: Isn't it the case that the sign of the cosmological constant depends upon the sign convention of the metric tensor?  If so, which convention is this article assuming:  vs.  —Quantling (talk | contribs) 22:54, 10 November 2022 (UTC)
thread_title:  Sign convention 

message: Looks like we might now need an article on the topic of "cosmological coupling". AllGloryToTheHypnotoad (talk) 14:11, 16 February 2023 (UTC)
thread_title:  cosmological coupling? 

message: The article says Friddman worked with the original general relativity equations. But the cosmological constant also appears in Friddman's equations ! Also, you need to explain why Einstein removed the cosmological constant, if Fridmann used it in his equations that gave an epxanding universe. By removing it would simply revert to a contracting universe, and not 'update' his theory to an expanding universe. Marvas85 (talk) 01:49, 8 September 2023 (UTC)
thread_title:  Wtf is this non-sense ? 

message: The final sentence reads: 
It is also possible that the difficulty in detecting dark energy is due to the fact that the cosmological constant describes an existing, known interaction (e.g. electromagnetic field).[37]
Physicists are looking for dark energy. They're not looking for a cosmological constant, which is a number describing the cause and effect dark energy is believed to have. And so far they've been unable to find the dark energy. It's quite possible the cosmological constant is an inaccurate description of the effects caused by dark energy, i.e., we've modeled dark energy incorrectly. In that case the model is wrong. That in itself is no reason for thinking that the model accurately models something other than dark energy. And even if it - which is highly unlikely - then presumably we would have found that other thing which it models and confirmed that it models something other than what we thought it modeled. But even in that highly unlikely scenario, that would not explain why we had not found dark energy. The cosmological constant does not define or constrain the experiments conducted to search for dark energy. So it doesn't explain our failure to find it. The entire last paragraph makes no sense under any possible scenario. Only if the cosmological constant defines the search criteria can it be suggested as a reason for failure of the search to find anything. TopScholarNZHistory1993 (talk) 21:21, 21 October 2023 (UTC)
thread_title:  The final section of the article is a logical fallacy and should be deleted together with its footnote reference articles