Talk:Dark energy/Archive 4

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Unmeasureable energy

There are forms of energy that we know that exist but do not know their nature and amount, since we can not measure them. Like ultra short wave gamma rays and ultra long wave radio waves. --Nevit (talk) 19:20, 28 March 2010 (UTC)

First, we can detect and measure both of those types of EM radiation. Second, we don't "know something exists" unless we have either detected it directly or found strong circumstantial evidence for it. Third, this article is about "dark energy", a substance with negative pressure whose presence is inferred both by its mass and by its effects on the expansion of space. The types of electromagnetic radiation you mention do not have negative pressure, so I'm having trouble seeing how they relate to the topic of the article ("dark energy" as used in cosmological models). --Christopher Thomas (talk) 22:51, 28 March 2010 (UTC)

Additional evidence for dark energy

The section Dark energy#Evidence for dark energy currently discusses Supernovae, Cosmic Microwave Background, Large-Scale Structure, and Late-time Integrated Sachs-Wolfe Effect. I just happened to run across this paper, hot off the presses: Evidence for the accelerated expansion of the Universe from weak lensing tomography with COSMO. It is interesting for two reasons. First, it claims "we find a negative deceleration parameter q0 at 94.3% confidence from the tomographic lensing analysis, providing independent evidence for the accelerated expansion of the Universe", so a section on this technique could be added to the article. Second, in the intro it quickly lists "several independent cosmological probes" providing "strong evidence for an accelerated expansion of the Universe". These include (with references, naturally) type Ia supernovae, cosmic microwave background, galaxy clusters, baryon acoustic oscillations, integrated Sachs-Wolfe effect, and strong gravitational lensing. We should probably add BAO and strong gravitational lensing to the article. I started to do it myself, but I'm a bit too far away from the subject matter to be confident I'll get it right without spending a good deal of time. Is anyone game to take on the task? --Art Carlson (talk) 13:57, 29 April 2010 (UTC)

Ok, so...

There's this sentence in the intro section:

Measuring the equation of state of dark energy is one of the biggest efforts in observational cosmology today.

I'm not sure if this is poorly written or just some techno-jargon. As it stands, this sentence is not comprehensible to me, nor any layperson that I can imagine. Vranak (talk) 03:08, 15 May 2010 (UTC)

Could you be more specific? Is it the term "equation of state," or the prepositional pile-up "equation of state of dark energy," or something else? When I read the sentence you have quoted, the part that strikes me as not very well written is "one of the biggest efforts," but that may not be the same part that you're objecting to. --Amble (talk) 03:37, 15 May 2010 (UTC)

'Equation of state of dark energy'. This makes absolutely no sense to me whatsoever. Would balance of dark energy be a correct and meaningful substitute? Vranak (talk) 05:01, 15 May 2010 (UTC)

No, "equation of state" has a very specific meaning. We know how much dark energy there is, but we don't know very well how it behaves. I would rewrite the paragraph as "The properties of dark energy are described by an equation of state, which determines how and whether the expansion rate of the Universe changes over time. One of the major goals of observational cosmology is to measure the expansion history of the Universe precisely enough to determine the equation of state, and thereby test ideas about the nature of the dark energy." Any better? Thanks for the feedback. --Amble (talk) 06:35, 15 May 2010 (UTC)

Quite frankly, equation of state has no meaning either from a familial understanding of those words, or from having a look at the article on that subject. I have to wonder, in the end, what this business is all about. But nevermind that. If I don't understand, that doesn't matter to those who do. I'm sure that whoever first coined the phrase knew what they were talking about, even if it remains as barren and inaccessible as the putative matter that it describes. Vranak (talk) 08:09, 15 May 2010 (UTC)

Per the linked article, which User:Amble pointed you to, "equation of state" refers to the relation between the energy density of a volume of space (rest mass and thermal energy of matter within it, plus vacuum energy) and the pressure within that region of space. The term "equation of state" is used in other branches of physics to define the relation between density, temperature, and pressure of various types of matter (from common to exotic), so this is not an uncommon use of it. Different properties given to dark energy result in different equations of state for the universe's substance. This in turn affects the equations describing how the universe evolves over time in any given model of it.

I've tweaked the article text to make this clearer. --Christopher Thomas (talk) 08:39, 15 May 2010 (UTC)

Epicycles

Heh? Heh??  :-D MrBook (talk) 20:34, 1 September 2010 (UTC)

The article does not mention epicycles. What exactly is your point or question ? Gandalf61 (talk) 08:08, 2 September 2010 (UTC)

I believe he's suggesting that dark energy is just a big fudge factor to salvage the standard cosmological model, much like epicycles did for the Ptolemaic theory. We're postulating that the universe must be composed mainly of undetectable energy of unknown nature, when it is equally plausible that our model is inaccurate.

The introductory paragraph refers to dark energy as a hypothetical form of energy and as a theory. I think both these descriptions are misleading. The first suggests that dark energy is a well-defined hypothesis, when in fact it is a catchall term applied to the missing energy needed to sustain the standard cosmological model, for which numerous hypotheses have been advanced, proposing different forms for dark energy. The second claim, that dark energy is a theory, makes even less sense. At best, various cosmological theories may incorporate one or another hypothetical form of dark energy. JoeFink (talk) 20:12, 19 May 2011 (UTC)

Edit Request In Our Time broadcast

BBC Radio 4's In Our Time is a 45 minute discussion programme with three eminent academics, hosted by Melvyn Bragg. Each edition deals with one subject from one of the following fields: philosophy, science, religion, culture and historical events. It is akin to a seminar. The entire archive going back to 1998 is now available online in perpetuity.

An edition about Dark Energy was broadcast with Sir Martin Rees, Astronomer Royal and Professor of Cosmology and Astrophysics, Cambridge University; Carolin Crawford, Royal Society University Research Fellow at the Institute of Astronomy, University of Cambridge; Sir Roger Penrose, Emeritus Rouse Ball Professor of Maths at Oxford University.

You can listen to the programme on this link: http://www.bbc.co.uk/programmes/p003k9g5. Request to editor: would you be able to include this as an external link?--Herk1955 (talk) 14:39, 21 September 2010 (UTC)

Orphaned references in Dark energy

I check pages listed in Category:Pages with incorrect ref formatting to try to fix reference errors. One of the things I do is look for content for orphaned references in wikilinked articles. I have found content for some of Dark energy's orphans, the problem is that I found more than one version. I can't determine which (if any) is correct for this article, so I am asking for a sentient editor to look it over and copy the correct ref content into this article.

Reference named "ly93":

• From Universe: Lineweaver, Charles (2005). "Misconceptions about the Big Bang". Scientific American. Retrieved 2008-11-06. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
• From Redshift: Lineweaver, Charles (2005). "Misconceptions about the Big Bang". Scientific American. Retrieved 2008-11-06. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

I apologize if any of the above are effectively identical; I am just a simple computer program, so I can't determine whether minor differences are significant or not. AnomieBOT⚡ 02:03, 28 November 2010 (UTC)

Thanks to whomever coded you, I've fixed it. --Falcorian ^(talk) 04:29, 28 November 2010 (UTC)

Confusing Paragraph

The second to last paragraph of the "Cosmological constant" section ("Another problem arises...") is rather confusing (at least, to someone with fairly basic physics knowledge like myself). It seems to be just a collection of experimental/observational results thrown together without any real purpose, other than that all those results seem to contradict the cosmological constant explanation of dark energy.

For example: "the appearance of solutions with regions of discontinuities"... solutions to what, exactly? Another: "not overwhelming evidence for an accelerating Universe expansion which may be simply gliding"... I assume the word "gliding" refers to an expansion at a constant rate, but that's not explained there, nor does the word appear in the article being referenced.

Most of that paragraph has remained untouched for over 2.5 years, so maybe it's just me, but perhaps it should be rewritten?

Incidentally, "supernovae data" is just silly... 167.24.104.150 (talk) 19:48, 27 December 2010 (UTC)

Negative pressure

Need a little more clarification for laymen: why does dark energy have to have negative pressure to be repulsive? Doesn't zero/positive pressure produce the same effect?Mastertek (talk) 14:05, 23 October 2011 (UTC)

Dark energy measurement

Need a little more clarification for laymen: was dark energy "measured" or just deduced from various observations of CMB radiation done by WMAP? Can dark energy be just an epiphenomenon to something like wavefunction collapse is to decoherence?Mastertek (talk) 14:05, 23 October 2011 (UTC)

The 4% Universe

Added Richard Panek's recent book to the bibliography. Serves as a secondary source to much of the material in the History section, although I have not attempted to cite specific points, or add information from the book that might be relevant. What more is required before removing the "citations missing" flag? Tunborough (talk) 15:05, 4 September 2011 (UTC)

Technically, no one's preventing anyone from removing the tag, but roughly, the article should have an inline citation in each paragraph on which source was used to write it. Since all theories put forth are the imaginations of single individuals, verifiability and reliability is crucially important to distinguish mainstream science from fringe science, idle speculation and outright mysticism. Personally, I'd prefer if the scientists that proposed each theory are explicitly named. --vuo (talk) 22:10, 4 September 2011 (UTC)

I would prefer to read the experimental evidence upon which the scientific conclusions are based rather than an "authority" telling me his new theory based on "new matter" forming 73% of the universe.Larry R. Holmgren (talk) 06:03, 29 February 2012 (UTC)

Quantum entanglement at the big bang productive of "dark energy"

This paper claims that 'dark energy' can be explained by quantum entanglement. It occurred to me also, since entanglement would imply all particles are entangled from at the singularity at the beginning of the universe, and if their "entanglement" means the movement of one 'moves' the other, a volition would be presumed responsible for exponential expansion. Nagelfar (talk) 19:33, 23 September 2011 (UTC)

Proposed delete

"A possible resolution of this difference has been provided in a work by Marco Spaans, a cosmologist at the University of Groningen (Netherlands). He argues that the cosmological constant, in the form of dark energy, is proportional to the number of macroscopic black holes in our universe. This result follows from a space-time that takes the form of a lattice of three-tori in four-dimensional space, onto which black holes are attached. The quantum properties of this space-time allow black holes to squeeze out vacuum energy."

This idea does not seem to be shared by the main cosmology community. The relevant work has a small number of citations, mostly by the author himself (who also seems to be responsible for adding this paragraph in the first place). I propose to deleted it. 93.145.171.108 (talk) 06:00, 27 December 2011 (UTC)

I agree with your concerns. Another problem: the one cited paper was submitted in 1996. It doesn't attempt to explain dark energy, since it was written before anyone knew of the existence of dark energy! I have deleted the paragraph. If anyone disagrees, feel free to revert this edit and explain your reasoning here on the talk page. --Amble (talk) 02:50, 3 January 2012 (UTC)

Removed claims of priority based on periodic redshift

Since October, the article has contained claims that György Paál first detected the presence of dark energy and determined that omega-lambda = 2/3. These claims were problematic in several ways. From the point of view of Wikipedia policy: they cited only primary sources, the papers by Paál et al. themselves; they depend on original synthesis to connect these papers with dark energy as we know it; and they give undue weight to Paál's work. From the point of view of physics: although Paál may have gotten the right value for omega-lambda, he did not derive it from anything that mainstream cosmology would consider valid evidence for dark energy. Instead, he based his calculations about claims of periodic quasar redshifts that are essentially a fringe topic today and not supported by modern data sets. --Amble (talk) 02:10, 11 June 2012 (UTC)

Good catch. Yes, that section should have been removed some time ago. - Parejkoj (talk) 14:36, 11 June 2012 (UTC)

OK, let's have a discussion. My English is not good, so please forgive me if I am not clear. Firsty, that you write here is correct. However, if you read the three papers of Paal you can realize the periodicity idea does not change anything. One can call this background philosophy. The mathematics does not change if you change the background thinking. Think about BAO if you like. Before continuing answer this question please: Have you read the papers? Kozmokonstans (talk) 07:02, 28 June 2012 (UTC)

First off, re-adding the connection to Perlmutter et al. and Riess et al. is pure WP:SYNTH. The ideas of Paal have nothing much to do with the work showing accelerating expansion from supernova standard candles; those papers make no mention of Paal or his work; so you can't put them next to each other in the article and imply a connection that's not supported by reliable sources.

Second: You have provided no support for the claim at György Paál that in 1992 Paal et al. was the first who suggested non zero cosmological constant. That's obviously false. Forget about 1992, Einstein suggested this in 1917 when he invented the idea of the cosmological constant. The source you cite doesn't make any such claim. So where are you getting it from?

Third: I have looked through the papers, not read them in detail, but it doesn't much matter. These papers have not been accepted by cosmologists as an earlier detection of dark energy. You can tell that by the lack of secondary sources saying that Gyorgi Paal was the first to detect dark energy. So you're trying to draw conclusions based on your own interpretation of WP:PRIMARY sources. That's not altogether forbidden, but primary sources can only be used for information that's uncontroversial, completely straightforward, and (essentially) blindingly obvious. The fact that multiple people have disputed your use of primary sources means that you need secondary sources.

(By the way, your English is very clear.) --Amble (talk) 15:13, 28 June 2012 (UTC)

Thanks for your answer. This is going to be a long discussion. I am a scientist so as (I assume) you. My request is, please discuss the topic from a scientific POV. When we reach conclusions, some statements which we agree, we can decide how can we put into the wiki articles. I do not want to arguing as some wikipedians do.

I probably will not answer your sentences which I agree. If you need that I will do. For now I ask you to consider two things.

You are right. It is not true that in 1992 Paal et al. was the first who suggested non zero cosmological constant. However the original sentence was From the observed galaxy distribution in 1992 Paal et al. was the first who suggested non zero cosmological constant. So the statement is: Paal et al. was the first who suggested non zero cosmological constant from observed data. Still it can be not true. But as far as I know from real data Paal et al. was the first. Einstein idea did not come from observations. If you know earlier publications which used observed data and calculated non zero Lambda, please write here.

You can find more detail in this article, which was written by one of Paal's coauthor.

Finally, I believe they did not said/suggested anything about dark energy. They wrote about non zero cosmological constant. Therefore may be not the Talk:Dark_energy page is a good place to discuss this ;-). Kozmokonstans (talk) 05:35, 29 June 2012 (UTC)

It would be better to use the relevant talk page. At Talk:György Paál I have explained my edits to that article. In general, you're going to have a difficult time because you're trying to build the article out of your own interpretation of and extrapolation from primary sources. You can't write that someone was the first to do something on the basis that you don't personally know of anyone who did it earlier. You need a source. As it happens, even if you modify the claim to "first to suggest a nonzero cosmological constant from observed data", it's incorrect. See, for example, Petrosian, Salpeter, and Szekeres from 1966 [1]. I mention that only as a side comment. My reading of the journal article by Petrosian et al., a primary source, is also not a valid basis for writing Wikipedia articles. --Amble (talk) 06:23, 29 June 2012 (UTC)

Good idea. Let's continue the discussion at Talk:György Paál. Kozmokonstans (talk) 08:51, 29 June 2012 (UTC)

Alternative ideas

This section needs a great deal of fleshing out and citation. I'm not an expert, but I was under the impression that some modified gravity theories were being taken seriously. Discussion of this is lacking in the article. — Preceding unsigned comment added by 24.13.86.160 (talk) 02:25, 6 December 2011 (UTC)

I added information about the new discovery by Tsagas that the universe's accelerated expansion may be an illusion. It is in a peer-reviewed journal. However, it'd be great if someone could replace the reference to a common magazine with the bibliography information for the journal article itself. Netdragon (talk) 20:50, 28 September 2011 (UTC) http://www.msnbc.msn.com/id/44690771/ns/technology_and_science-science/#.ToNr_6h4Cdd

You are looking for http://www.astro.auth.gr/~tsagas/Publications/Journals/PRD/PRD14.pdf and dark flow. Dualus (talk) 04:08, 9 October 2011 (UTC)

Possible New Mechanism for the Cosmological-Redshift: In the volume-III of Progress in Physics, July 2012, possible new mechanism for the cosmological-redshift has been proposed by Hasmukh K. Tank. This mechanism can account for a large percentage of the redshift; reducing the requirement of 'dark-energy', may be, to the observable 5% mass of baryonic-matter. [Ref. Tank H. K. "Cumulative-Phase-Alteration of Galactic-Light Passing Through the Cosmic-Microwave-Background: A New Mechanism for Some Observed Spectral-Shifts" Progress in Physics, Vol 3, July 2012, pp 39-42]122.102.126.92 (talk) 17:17, 8 August 2012 (UTC)

shame on the nobel institute for rewarding junk science like this

why does society pay scientist big money to sit around and dream up ideas so far fetched that they are laughable? This is only a hypothesis and yet the nobel institute has had the gall to award them the nobel prize for this hypothesis?they havnt even been able to clearly define what they think dark energy actually is yet, so why are they winning nobel prizes, for having an active imagination? These scientists get big bucks to sit around and try to relate the physics of the universe to the physics of earth, as if they both have to be the exact same thing somehow. what if the explination for the acceleration of the expansion of the universe is as simple as this: the "big bang" that took place 14 billionish years ago is actually still taking place right now and is really just getting started. I'll do what other scientists do and make up theory, except mine is free of charge,and if i'm proven right later somehow maybe I can still win the nobel prize money that was wasted on the dark energy imagineers. The explination for the "proven" acceleration in the expansion of the universe could simply be similar to this:Just like if you took a grenade on earth and it exploded;in the first few nano seconds of elapsed time, the matter accelerating would reach a certain velocity.And then a few nano seconds later, that matter would in fact continue to increase in its acceleration. So that could very well be whats going on right now in the universe. even if 14 billion years have already passed,so what, thats nothing in the time scale of the universe.Scientists are just arrogantly assuming that after 14billion years things should slow, because thats a long time to THEM. This 14 billion years of elapsed time could just be the equivilent of the first 14 nano seconds of a grenade explosion.. the fasest acceleration of matter is yet to come at that point in time.Just like would be true in the first 14 nanoseconds of an explosion on earth.The matter in the explosion will in fact slow down eventually due to gravity and other forces,just like the expansion of the universe will slow eventually too, just on a time scale beyond our comphrehension.Inertia from the big bang will last alot longer and be alot more powerful in the vacuum of space too,naturally. I'll bet that the scientists that exist in another billion years from now(if humans endure) will surely laugh out loud and mock all the ignorant fools that invented dark energy, and got awarded a nobel prize for it on top of it being completely wrong. (pbs and other channels continue to make big budget programs about unproven infant theories like this, well ok pbs, begin work on a show about the theory I have just proposed here then too.) — Preceding unsigned comment added by Gawdsmak (talk • contribs) 06:40, July 12, 2012

The 2011 Nobel Prize in Physics was actually awarded for "the discovery of the accelerating expansion of the Universe through observations of distant supernovae" i.e. for the discovery of the accelerating universe, and not for any theoretical explanation. Nobel prizes in the sciences are generally awarded for ground-breaking inventions or discoveries, and not for purely theoretical work, precisely to avoid the possibility of awarding a prize for a plausible theory that turns out to be incorrect. Dark energy is one possible explanation of the accelerating universe phenomena, but there are other possibilities (as our article says), and there are several different versions of the dark energy theory. Gandalf61 (talk) 08:58, 12 July 2012 (UTC)

What experimental work is ongoing?

I added The Dark Energy Survey to the "See also" section, but it would be interesting to have a general overview of current research empirical projects in this area. -- Beland (talk) 00:37, 20 September 2012 (UTC)

Agreed. Here are some projects I found using Google:

(http://hetdex.org/other_projects/)

BOSS: Baryon Oscillation Spectroscopic Survey. A consortium of astronomers will use the 2.5-meter (100-inch) Sloan Digital Sky Survey telescope at Apache Point, New Mexico, to measure the imprint of sound waves from the Big Bang at distances of up to 10 billion light-years. An earlier Sloan study found some evidence of these waves in the distribution of galaxies.

DES: Dark Energy Survey. A new 500-megapixel camera and related instrumentation for the 4-meter (158-inch) Blanco telescope in South America will measure the distances to remote galaxies and supernovae and use weak gravitational lensing to probe the universe's expansion history.

WFMOS: Wide-Field Multi-Object Spectrograph. Another project that will measure the imprint of sound waves, it is a new instrument planned for the Gemini North telescope in Hawaii or another large telescope.

LSST: Large Synoptic Survey Telescope. Scheduled for first light in 2014, this 8.4-meter (27.7-foot) telescope will photograph the entire sky every three nights. Its images and other data will reveal supernovae and plot the distribution of galaxies over the last few billion years.

JDEM: Joint Dark Energy Mission. NASA and the Department of Energy are collaborating to develop a satellite to probe dark energy from space. The agencies are considering three proposed missions, with launch for the winning design no earlier than 2017.

Euclid. A European satellite will use weak gravitational lensing and baryon acoustic oscillations to probe the distribution of dark matter, which will help determine the nature of dark energy. Mission scientists also hope to expand the mission to measure the distances to supernovae. If approved, the mission will launch no earlier than 2017.

There are other list here: http://ned.ipac.caltech.edu/level5/March08/Frieman/Frieman8.html

--Cesarakg (talk) 20:13, 24 September 2012 (UTC)

Minor complaint about Einstein's "blunder"

I have always been annoyed by the "famous" quote where Einstein supposedly said that his "cosmological term was his biggest blunder". As far as I know (and according to http://en.wikiquote.org/wiki/Albert_Einstein ) the ONLY source for this "quote" is the George Gamow autobiography:

Much later, when I was discussing cosmological problems with Einstein, he remarked that the introduction of the cosmological term was the biggest blunder he ever made in his life.

George Gamow, in his autobiography My World Line: An Informal Autobiography (1970), p. 44. Here the "cosmological term" refers to the cosmological constant in the equations of general relativity, whose value Einstein initially picked to ensure that his model of the universe would neither expand nor contract; if he hadn't done this he might have theoretically predicted the universal expansion that was first observed by Edwin Hubble.

This was published in 1970, long after Einstein's death and only depends on one man's memory. Does this meet Wikipedia's standard of a verified citation? At the very least could the word "famously" be changed to "supposedly" as in:

Einstein supposedly referred to his failure to predict the idea of a dynamic universe, in contrast to a static universe, as his greatest blunder.

Shouldn't this have a [citation needed] note at least?

Maybe I am being picky about this but I really dislike having quotes attributed to Einstein posthumously based only on one person's memory. If you say I am being too picky, I will give it up. If anyone agrees with me, I would be happy to make an edit along these lines:

use the word "supposedly" and have a footnote that says this supposed quote came from Gamow's autobiography?

What do you think? FrankH 05:04, 14 October 2012 (UTC) — Preceding unsigned comment added by FrankH (talk • contribs)

Agreed that the source of the statement should be given, but how about "reportedly" instead of "supposedly", which sounds like there is good reason to believe it is not correct? Art Carlson (talk) 08:49, 14 October 2012 (UTC)

Thanks Art Carlson, I made the change with "reportedly" as you suggested - that was the right word, thanks. I added the citation, hopefully in a reasonable format. — Preceding unsigned comment added by FrankH (talk • contribs) 05:57, 15 October 2012 (UTC)

Expansion speed

At what speed does it accelerate actually, and how long to wait before it reaches the speed of light. As maybe thats a limiter for this i wondered. — Preceding unsigned comment added by 84.107.183.36 (talk) 01:02, 16 November 2012 (UTC)

It's proven, not hypothetical

The recipients to the 2011 Nobel Prize in Physics proved its existence

http://www.geek.com/articles/geek-cetera/dark-energy-physicists-nab-nobel-prize-for-physics-2011105/

68.84.158.248 (talk) 22:50, 25 October 2012 (UTC)

If you look at the award citation, the Nobel Prize was given for proving that the expansion of the universe is accelerating. Dark energy is the most likely explanation for the accelerating universe, but dark energy itself is still mostly hypothetical since we have no direct way to measure its properties or distinguish between competing theories of its behavior (e.g. quintessence, cosmological constant). Dragons flight (talk) 23:41, 25 October 2012 (UTC)

Dark Energy is not the Vacuum Energy of Quantum Theory

Half way down, the article confuses the reader by throwing in a discussion of the vacuum energy of quantum theory and makes it sound like the same thing as dark energy. They can not be the same thing because they come from two different unreconciled theories. Dark energy is the vacuum energy of general relativity and tiny vacuum fluctuations are the vacuum energy of quantum theory. Saying they are the same is pure speculation. We will not now how they relate to each other until a successful theory of quantum gravity has been developed that merges general relativity and quantum theory. There are many types of vacuum energy (QED vacuum, QCD vacuum, Higgs vacuum) and we should be careful to distinguish them. 74.104.20.137 (talk) 00:02, 20 January 2013 (UTC)

Inconsistency with Percentages

The lead section states that dark energy accounts for 73% of the mass-energy in the universe, however, the graph in the "Evidence" section changes this number to 74%. Which of these numbers is correct? FrigidNinja (talk) 01:00, 9 January 2013 (UTC)

M. Villata's hypothesis

I've reverted Wellsmax's edits a second time. I note that in a post at User_talk:Wellsmax/Whole_Earth_Blazar_Telescope, Wellsmax claims to be M. Villata. This would be a WP:COI regarding his recent changes here, as it looks like self-promotion. In addition, someone should take a second look at Gravitational_interaction_of_antimatter, as it also has a section promoting Villata's work, also written by Wellsmax.

Note that I am not making any judgement on whether Villata's hypothesis is correct or not, just that these edits appear to violate Wikipedia policy. However, it does appear that Villata's work has received little attention in the field: of the 10 non-self citations that the 2011 paper received, 6 are by a single author, and one is a harsh critique. Though it did get some attention in the popular press a couple years ago, whether it is notable scientifically remains to be seen. - Parejkoj (talk) 19:44, 4 April 2013 (UTC)

The insertion of Villata's work into "Dark energy" (then removed by Parejkoj) cannot be considered as "self-promotion", being highly relevant to the subject and having a wide consolidated basis both in the scientific literature and on tens of web sites (in my opinion no conflict of interest can be claimed when dealing with objective scientific results). Regarding the "little attention in the field" mentioned by Parejkoj, she/he seems not to consider a couple of recent invited talks, and that all four papers illustrating the theory have been published as Letters, i.e. the highest degree of scientific publication, the first of them having collected more than 4000 downloads and being still at the top of the "most read in the last 30 days" list two years after publication (see http://iopscience.iop.org/0295-5075).

Moreover, Parejkoj's suggestion to "take a second look at Gravitational interaction of antimatter" led Aldebaran66 to remove several previous versions in the article history, including also revisions done before the Wellsmax contribution, already reporting on Villata's work.

Due to these reasons, I consider these two actions as vandalism, and ask for the restoration of the two articles.--Massimozanardi (talk) 17:08, 5 April 2013 (UTC)

Please read WP:vandalism before making such accusations. Otherwise you might be accused of trolling. — kwami (talk) 19:41, 5 April 2013 (UTC)

Delete an entire article, as your policy, may be considered an act of vandalism, although I have often received in the Italian edition of Wikipedia, similar accusations for much less. I do not see how you can accuse me of being a troll, because it is the first time that I am talk on wikipedia in English.However, I'm an old contributor since 2007 of the Italian edition of Wikipedia, where I wrote hundreds of articles, and I've never been accused of being a troll, nor a Sockpuppet or otherwise.--Massimozanardi (talk) 10:13, 8 April 2013 (UTC)

Massimo Zanardi is a comic book character, and these comments by User:Massimozanardi are his first edits outside of his own userspace. What are the chances that User:Massimozanardi is the same person as Massimo Villata / Max Wells / User:Wellsmax? --Amble (talk) 21:20, 5 April 2013 (UTC)

User:Massimozanardi is not me. As you know, I've never made ​​any secret of my identity, and, since I was accused of possible self-promotion, this is my last speech on this matter. I wrote in Wikipedia articles only after I saw that other people was mentioning my work (see Gravitational_interaction_of_antimatter), and just because I felt that those additions were useful to the knowledge that Wikipedia wants to spread (My theory is actually the only complete theory of antigravity, and not a "minor hypothesis" as stated by Aldebaran66). The motivations for your first removal were inconsistent, so I reverted it. Then you found a different motivation, which suggests that either you do not like my research or that you like to delete in general. In any case, all this does not concern me: I do not like wars, and I have other things to do. The worst thing, which seems to reveal your intentions, is that you have deleted any trace of my work in Gravitational_interaction_of_antimatter, even what was written by other users before and after me (I think this is the reason why someone spoke of "vandalism", since these actions are not justifiable). The first citation to my paper was made on 19 April 2011, while my addition was of December 2011. After that, various users intervened on it, thus showing interest and no intention of removing. Nevertheless, now you feel entitled to cancel everything, but the arbitrariness of this choice (i.e. the intention of obscuring important and relevant scientific results) should be evident to every reader. As already said, I will not answer more. Good luck. Wellsmax. — Preceding unsigned comment added by Wellsmax (talk • contribs) 08:58, 8 April 2013 (UTC)

@Amble, i'm not a Wellsmax's sockpuppet, but i'm a active contributor, since 2007, of the Italian edition of Wikipedia, where I wrote hundreds of articles on various topics. I'm also working with the portal of astronomy of the same edition of wikipedia in Italian, as you can control yourself from my page. --Massimozanardi (talk) 09:58, 8 April 2013 (UTC)

Confusing/incorrect paragraph

The paragraph starting "Another problem arises... these terms should be considered shortcomings of the standard model, ... included." is misleading.

Problems (e.g. a past change from contraction to expansion) may appear for values of the cosmological constant much larger than observed, but there are no "discontinuities" as claimed for the c.c. value similar to the standard model of cosmology. So, this paragraph is largely irrelevant to the real universe, and per WP:Due_weight I suggest to delete it, unless someone suggests a good reason to keep it.

Wjs64 (talk) 20:36, 10 May 2013 (UTC)

Possible candidate of dark energy section shouldn't be removed

Dear Administrator,

The section of possible candidate of dark energy should not be removed. The person who removed it is biased. Please help to do {{Edit Protected}} Thanks

MiceEater — Preceding unsigned comment added by MiceEater (talk • contribs) 02:03, 11 March 2013‎

I've deactivated this {{Edit Protected}} because it's not clear what should be done. Also please note that the article is not protected. --Redrose64 (talk) 20:50, 10 May 2013 (UTC)

Dark energy should be renamed to Universe expansion Factor or Energy.

--Jangirke (talk) 01:46, 19 October 2013 (UTC)

This is not a forum on physics. This is a forum on how to improve the article. Changing terminology to go against the general convention is not done here. --vuo (talk) 19:55, 19 October 2013 (UTC)

for me the whole dark matter- dark energy hypothesis never computes well, however in the article it is stated that such is required for a flat model of the universe. well in that case it appears rubbish so much more, since negative pressure would only explain a non-directional factor of expansion. so in any case it seems that the theories get it wrong and perhaps the external (outside the "flat" universe) structure produces a energy residue we call dark (unseen) energy/mass (among with what I perceive as more "unlit" mass and local variation of cosmological vectors). don't be mad just trying to be helpfull62.163.114.47 (talk) 00:07, 28 December 2013 (UTC)

That's a large extra dimensions theory. It's a valid guess, but not very likely. But, this is the reason it's called "dark"; very little is known about it. --vuo (talk) 16:51, 28 December 2013 (UTC)

Virgo supercluster survives cosmological constant?

The article claims that the Virgo supercluster would remain after all other galaxies vanish over the cosmological horizon. But the galaxy cluster claims that these are the largest bound structures, implying that a supercluster is not gravitationally bound. So how would it remain? --192.75.48.150 (talk) 18:17, 25 August 2014 (UTC)

Mass of dark energy within pluto's orbit

I think there is an error in the fact quoted that "in the solar system, it is estimated only 6 tons of dark energy would be found within the radius of Pluto's orbit"

I attempted to do the calculation with the energy density quoted within the article of 6.91 × 10−27 kg/m3 and an orbital radius of 5.874*10^12 m (the semi major axis) which gives a mass within the orbit of 5.87*10^12kg , significantly higher than 6 tons.

Looking at the source for the quote (http://hyperphysics.phy-astr.gsu.edu/hbase/astro/dareng.html) I believe the mistake is due to the author using a radius of 5.9*10^9 m (possibly a mistake between km and m) which does give an answer of rougly 6 tons.

I just wanted to make sure I haven't made a mistake and didn't want to do a bad edit leaving the page looking sloppy

Quogle (talk) 03:15, 4 January 2015 (UTC)

That's an interesting argument. I hope someone else can confirm whether you're right Tetra quark (talk) 03:32, 4 January 2015 (UTC)

This concern looks right to me. Using the correct semimajor axis of Pluto's orbit, I get 6×10⁹ tons of dark energy within a sphere of that radius. The only bit I can't immediately confirm is that 6.91 × 10⁻²⁷ kg/m³ is the right number; that also comes from the suspicious hyperphysics source. —Alex (ASHill | talk | contribs) 03:56, 4 January 2015 (UTC)

Using the data from this paper (http://arxiv.org/pdf/1212.5225v3.pdf) which gives the Hubble constant and the dark energy density relative to the critical density (the table of data is on page 129) I calculate a dark energy density of 6.44x10^-27kg m^-3 which is roughly the same as 6.91 × 10⁻²⁷ kg/m³ Quogle (talk) 17:02, 4 January 2015 (UTC)

Good enough for me; I was just too lazy to do that calculation. :) Thanks. I'll remove the statement. —Alex (ASHill | talk | contribs) 17:32, 4 January 2015 (UTC)

I don't think it should be removed. The raw density is a number which is very difficult to conceptualize. The dark energy hypothesis claims, after all, an entity with material existence and a real density. The density is 1.6 kg inside a sphere of lunar orbital radius, so that could be another way of putting it. --vuo (talk) 18:18, 4 January 2015 (UTC)

I'm not sure I agree, I think that it gives a deceptive impression of knowing what the density is, trying to think about it without doing calculation it is quite difficult to tell how much the difference in density is between 6 tons in a sphere of Pluto's orbital radius and 1.6kg within a sphere of lunar orbital radius. It is obviously large but I'm not sure if I would have guessed at a 10⁹ difference. I am sure there must be a better way of trying to demonstrate the low density, perhaps as I have seen used somewhere else in terms of numbers of hydrogen atoms per cubic metre which I think is a little under 4. Quogle (talk) 19:30, 4 January 2015 (UTC)

Note that Dark energy is not Black Energy

Not sure if this needs clarifying as Black energy is not a widely used term, but it might be good to note that Dark energy is not at all related to Black Energy. Dark energy is a mostly unknown forum of energy, while black energy comes from the term Black Gold (illegally traded gold). Black energy is a broad term to describe any not sustainable energy. Energy from an energy grid were the energy is produced by coal would be considered black energy. Solar energy would not be black energy. — Preceding unsigned comment added by Jooe15 (talk • contribs) 10:48, 8 January 2015 (UTC)

I don't think it is necessary to note that in the article because they are two wildly different things Tetra quark (talk) 13:28, 8 January 2015 (UTC)

Alternative ideas/Theories

May DDHB theory be consider a suitable alternative for Accelerating Expansion of the Universe? The thesis is the following: The accelerated expansion of the universe is caused by a Decreasing Density of the Higgs Boson (DDHB) across the known universe. Probably radial. Consequently, the very same element in different parts of the universe would have different mass. Particles that would typically interact with the Higgs Boson would not do it in certain parts of the universe. Simply because there are not so many Boson Higgs particles to interact with. Thus having less mass, thus accelerating more and more as they move into areas with less density of Higgs Boson particles.

— User talk:ES DFG Yebra 27th /Aug /2013

Source? Without a reliable source, this is obviously not suitable for inclusion. —Alex (ASHill | talk | contribs) 22:26, 27 August 2013 (UTC)

Has anyone here taken a look at timescape cosmology [2]or(http://www.nottingham.ac.uk/physics/documents/talesoflambda/wiltshire.pdf) ? It seems to me to be a very viable alternative and very well cited alternative theories out there. Armchairphysicist (talk) 18:08, 5 March 2014 (UTC)

One thing that doesn't appear to be explained well in the article is that taking dark energy as a property of space alone outside the space time continuum strips it of its fourth dimension and any subsequent dimensionality making it essentially three dimensional.

That means that it may be Real but can't exist. Everything which exists in a spacetime continuum is constantly changing if simply by growing older. While relativity allows Space to have Energy as a property it is a potential or kinetic energy which requires the addition of a dimension of time for it to act.

If we conceive of a spacetime continuum as like a sponge with pockets of three dimensional space containing Dark Energy as a potential energy and emitting Dark Energy in the presence of gravity as a sponge emits water when it is squeezed, then that explains the structure the article talks about with voids of three dimensional space surrounded by Galaxies which have gravity that can squeeze the three dimensional space as an event bringing it and its energy into existence.142.0.102.87 (talk) 12:35, 25 November 2014 (UTC)

Please consider, though I am no physicist, it seems "dark energy"'s increasing expansion speed is a completely logical process demonstrated by the clingy-fibrous cosmic web matter as universally decaying orbits in the zero-G zero-friction environments of 3D+gravity (3D+time) spinning faster and farther as the cosmos consolidates itself. Decaying orbits "fuels" the expansion. I'd show you with math if I could. Rather imagine a slow spinning ice skater pulling arms closer to spin center increasing spin speed and focusing gravity (and harder to disrupt). Add a second concept - lean forward to walk/run, fall and catch yourself. Drop the ground away and you are falling, as in orbit, faster and faster leaning into the fall that you cannot unlean out of (you cannot catch yourself, slow or stop), increasingly away from the post-big bang's diffuse cosmic mist, sliding into condensed cosmic matter fibers spread across the cosmic gravitational-thermodynamic "bubble" or sphere of existence which may only seem to be expanding relatively by stretch+consolidation. The spinning skater is leaning into the fall. Without purchase on ground or some kind of quantum dimensional friction I just don't know how orbit decay exactly translates/fuels/stretches into faster expansion. Perhaps, once decayed orbit matter reaches a planet, sun, or black hole singularity the collision propels the "off-balance" trajectory accordingly, converting gravitationally kinetic potential energy into this dark energy. The denser matter consolidation gets the more it stretches the fabric of space-time like a giant waterbed stretched by carbon dust coagulating into lead ball-bearings into gold pearls into plutonium pellets, heavier and heavier. Sorry for posting this here like this, I had a fundamental logic insight. The dark energy isn't energy so much as redirected momentum propelled by gravitational kinetic energy on all matter as the big bang's energy is inverted into the cosmic web structures. I only hope it might be useful. ~MJasonCarswell — Preceding unsigned comment added by JasonCarswell (talk • contribs) 03:53, 29 April 2015 (UTC) A further illustrative idea - Do our collective elliptical orbits ultimately affect our solar system's course direction? In several billion years before it shrinks our bloated sun may consume Earth or Earth will collide with the sun much later, both resulting in an extremely slight Sun course change. Assuming galactic collisions don't dislodge Jupiter and Saturn, they will collide with the Sun to tighten up course with less wobbling. Aerodynamics in dark matter? Our orbits may be so round that it may be difficult to determine how they might collide, but it's clear to see that when Halley's comet eventually collides with the Sun it will affect it with a certain directional displacement. Average all these propulsions out and you might get the drift of our solar system's course, perhaps in a galactic flow, or cosmic current that is propelled by dust to solar systems engulfed by ultimately black holes strung out across the cosmic web. It may be extremely difficult to simulate decaying orbital vector normal flows and galactic currents increasing cosmic expansion speeds without first starting with simpler dynamic models and reverse engineer, building up from this hypothesis. Might someone try this? ~MJasonCarswell — Preceding unsigned comment added by JasonCarswell (talk • contribs) 20:09, 30 April 2015 (UTC) Cosmic gyroscopic precession? ~MJasonCarswell — Preceding unsigned comment added by JasonCarswell (talk • contribs) 07:49, 9 May 2015 (UTC)

0% ordinary energy

According to the current lead, there's no ordinary energy in the observable universe at all. That can't possibly be correct; I'm observing energy in the form of light this very second. -- Kendrick7^talk 08:47, 12 July 2015 (UTC)

From a cosmological and relativistic viewpoint there is no essential difference between mass and energy - they are different ways of measuring the same thing. See mass-energy equivalence. "Ordinary energy" is included in the 4.9% of the total mass/energy of the universe that is labelled "ordinary matter". Gandalf61 (talk) 10:47, 12 July 2015 (UTC)

And I'd just add that there is no corresponding equivalence between dark matter and dark energy. Isambard Kingdom (talk) 11:06, 12 July 2015 (UTC)

The term closest to "ordinary energy" is the energy density in photons, which is primarily the energy density in the CMB. This is very small, something like Ω_CMB = 2.48 × 10^-5 h^-2 [3]. There was an early radiation-dominated era in which this was the largest contribution, but today it's negligible. Of course there are all kinds of things that contribute in principle, like gravitational waves, but that make up a very small portion of the total. The fact that they aren't listed here doesn't mean they don't exist, just that they don't significantly contribute toward critical density. --Amble (talk) 02:58, 13 July 2015 (UTC)

But ordinary energy does exist. Writing off what our readers see when they open their eyes when they wake up in the morning as a mere universal "rounding error" is encylopedically, if not exactly scientifically, negligent. Let's not divide by zero here. -- Kendrick7^talk 09:36, 28 July 2015 (UTC)

There is no difference between ordinary energy and ordinary matter. You're referring specifically to radiation, which is a (now-tiny) subset of the ordinary energy. And the contents of the Universe aren't the subject of this article anyway; I don't think we need to mention negligible amounts of things that aren't dark energy in the article about dark energy. But saying "4.9% ordinary matter and energy" would be ok with me. —Alex (Ashill | talk | contribs) 14:32, 28 July 2015 (UTC)

Sorry, this is too far in the direction of WP:SYNTH. "Ordinary energy" is not an established term and has no definite meaning, and we can't just redefine what it is that accounts for the 4.9%. If we mean photons, we should say so and give some indication of Ω_photons (although I don't think it's necessary). We also haven't included neutrinos, gravitational waves, or free electrons although they exist, or primordial black holes although they probably exist. --Amble (talk) 16:15, 31 July 2015 (UTC)

Assuming that our readers natively understand that matter equals energy, while dark matter and dark energy are entirely different things is just a bridge too far when trying to write a general purpose encyclopedia. Yell E=MC^2 all you want, but all 4 are the subjects are different articles, and must be on some level, fundamentally different concepts. -- Kendrick7^talk 08:21, 3 August 2015 (UTC)

Energy and matter are different concepts, sure, but sources don't treat them as different when talking about the contents of the Universe. Ultimately, we report what sources say, and sources don't itemize "ordinary energy" as one of the constituents of the Universe. —Alex (Ashill | talk | contribs) 15:21, 3 August 2015 (UTC)

And we point out earlier in the sentence you're mentioning that these numbers are on a mass-energy equivalence basis, so we already make the connection between matter and energy (but in a way that is consistent with sources). As mentioned above, if you're arguing that we should itemize radiation, that's a different argument. But it is in fact correct, to two significant figures, that 0.0% of the current mass-energy in the Universe is radiation; as Amble noted, it's 0.005%. And again, no need to mention something that is so negligible and not at all the subject of this article. —Alex (Ashill | talk | contribs) 15:30, 3 August 2015 (UTC)

I have sympathy for the points raised by Kendrick7. While energy and matter have equivalence, in the sense that once can be converted to the other, it still requires a conversion. And, energy and matter have important differences. Mass has a gravitational field, and gravity affects the the universe in a way that mass-less light does not. I see in the article photon epoch that the interaction between energy vs matter has changed over the evolution of the universe. And, as Kendrick7 points out, the human experience, which is affected by the difference between energy and matter, is important for many readers of an encyclopedia. Still, these issues, as interesting as they are, don't seem appropriate for this particular article on dark energy. However, these issues might find a place somewhere else, in some other article, and I would enjoy reading about them. Isambard Kingdom (talk) 02:08, 4 August 2015 (UTC)

You're contrasting matter and energy in a way that reflects a misunderstanding about what matter and energy are. The mass of baryons truly is energy just as much as the energy carried by photons is energy. Not "can be converted to", it simply is energy. In the breakdown of Omega_total some things are matter and some aren't, but it's all 100% energy. You might enjoy this essay that explains further. [4] --Amble (talk) 20:42, 4 August 2015 (UTC)

@Amble, thank you for this very interesting article. Perhaps you can clear something up for me. I have a proton and an antiproton, they both have mass and, therefore, a gravitational field. Put them together, I understand that they can be converted to pure light (just my understanding, and I might be wrong). The light, then, with zero mass, has no gravitational field (again, just my understanding). So, to my perception, a universe with lots of mass-energy in the form of light is a very different universe than a universe with the same amount mass-energy in the form of matter. In the first case, gravity would not have be much of a player in the expansion of such a universe, while in the second case it could be. This is seems like a fundamental distinction. Pointing me to a reasonable article on this, written for the semi-informed layperson, would be appreciated. And, also, forgive me for asking a question that seems kind of forum-y. I won't do it again. Isambard Kingdom (talk) 23:09, 4 August 2015 (UTC)

I can't think of any good article to refer you to, but gravity doesn't work the way you think. Light does create a gravitational field. According to general relativity, all energy bends the shape of spacetime. In fact, since light also exerts a significant positive pressure in comparison to its energy density, the effective gravitational pull of a concentration of photons is twice as great as it would be if that same amount of photon energy existed as a concentration of matter instead. So, after matter and antimatter particles (pure mass) annihilate to become photons (pure light), their effective gravitational pull doubles. You are right that a universe dominated by radiation (photons) behaves differently than a universe dominated by matter; but, the difference in expansion behaviour is subtle (the expansion of the universe decelerates in both situations, but at different rates), and this is due to a difference in pressure, not to a difference in energy density. Meanwhile, dark energy has such a strongly negative pressure that it acts like an anti-gravity which accelerates the expansion rate. Again, though, this is due only to a difference in pressure. Radiation, mass, and (supposedly) dark energy are three forms of energy that each have different relationships between density and pressure, but only the latter two contribute significant amounts to the current contents of the universe as a whole.50.174.178.168 (talk) 07:17, 25 September 2015 (UTC)

(Outdenting) @Isambard Kingdom. Massless particles such as photons do gravitate. The source of gravitation in GR (unlike Newtonian gravity) is the stress–energy_tensor. When you annihilate your proton/antiproton pair to get photons, the gravitational field just before and just after will be the same (because the total stress-energy tensor is the same). Also, a collection of massless particles (such as a "box of light") can have a net mass. Some forum-y posts on talk pages are not such a bad thing... we're talking about a point where readers of the article may get confused, which can hopefully result in a better article. I think part of what's confusing is that once we have dark matter, ordinary matter, and dark energy, a reader expecting sensible semantics might reasonably led to infer that the next thing in the list will be ordinary energy. That's one of the reasons that "dark energy" is not great terminology. Perhaps the article needs to do more to let readers know they shouldn't take the term "dark energy" too seriously. --Amble (talk) 01:10, 5 August 2015 (UTC)

Here's a blog post that gives some more information [5], although sadly the math doesn't seem to display correctly. --Amble (talk) 01:16, 5 August 2015 (UTC)

Thanks very much! Isambard Kingdom (talk) 01:21, 5 August 2015 (UTC)

How is "Dark energy" bad terminology when the lead of the article begins "dark energy is an unknown form of energy"? Is it not a form of energy, which is equivalent to matter? Give it to me straight doc! Some of you here are obviously experts, and can see why I'm telling you non-experts are confused. -- Kendrick7^talk 05:50, 5 August 2015 (UTC)

Did you read the essay by Matt Strassler? It outlines some of the reasons why the term "dark energy" can be misleading. --Amble (talk) 06:41, 5 August 2015 (UTC)

I would like to see, somewhere in this article, a definition of "ordinary matter" that includes energy, because it's obviously being used this way. It could be a footnote, it could be, you know, an actual *explanation* that the amount of energy, light, radiation, what-have-you is 0.005% and thus not worth mentioning. The article does not mention energy AT ALL, and this is the part that needs fixing.  The Steve  07:32, 7 August 2015 (UTC)

Some succinct elaboration on the definition of mass-energy would be useful. Note that there is a nice article at Mass–energy equivalence, which I only just now discovered. Isambard Kingdom (talk) 13:17, 7 August 2015 (UTC)

@Thesteve: A definition of ordinary matter is right there in the sentence that refers to ordinary matter (emphasis added): "According to the Planck mission team, and based on the standard model of cosmology, on a mass–energy equivalence basis, the observable universe contains 26.8% dark matter, 68.3% dark energy (for a total of 95.1%) and 4.9% ordinary matter." I'm not clear what more we need. It's possible that that sentence has too many qualifiers and thus this important one gets lost; for example, the "According to the Planck mission team" bit could go; that's a detail that can be left to the reference and the body of the article. I'll tweak the sentence to be more clear. —Alex (Ashill | talk | contribs) 23:22, 7 August 2015 (UTC)

Why do you think that "ordinary matter" includes energy? That's true if you mean that ordinary matter possesses energy. It's obviously incorrect if you mean that energy in general is a subset of ordinary (baryonic) matter. Energy is not 0.005%, it's 100.0%, as I have already pointed out several times. It's all energy. The energy of light is about 0.005% of the total energy density. --Amble (talk) 18:08, 7 August 2015 (UTC)

Amble, I think that your insight on "it's all energy" has been very much appreciated. The article you've highlighted by Matt Strassler was written for a purpose, to address some common confusions about matter and energy. I, myself, have had some of those confusions, and, then, I was happy learn. Now, I think that Thesteve is suggesting that the article itself might be changed or augmented slightly so that the typical reader can also better understand and learn about some of these issues. Perhaps you can dive in and make some edits? Thanks again, Isambard Kingdom (talk) 19:11, 7 August 2015 (UTC)

IK is correct. The article should take into account the common (not scientific) definition of matter. Also, you pointed out the *mass*-energy equivalence. Is mass the same as matter? Mass and energy are equivalent, sure, but are they the same? If they are the same, why do you have to convert from one to the other? I'm not saying you have to write a huge paragraph in basic terms, but the universe breakdown as-is is confusing, and the confusion is not helped by reading either the mass-energy equivalence article OR the matter article.  The Steve  04:51, 12 August 2015 (UTC)

There's no way we're going to explain mass-energy equivalence in everyday terms in a few words -- that's too mcuh. As you say, just look at the mass-energy equivalence article. It has several pages to work with, and it's certainly hard to follow. I would like to hope, though, that we can say something that's scientifically correct and (at least) clear enough to be self-contained for someone who isn't terribly familiar with these ideas. That should be attainable. I think something along these lines could work: "dark energy contributes 68.3% of the energy in the observable universe; the mass-energy of dark matter and ordinary matter contribute 26.8% and 4.9%, respectively; and other components such as neutrinos and photons contribute a very small amount." I hope this makes it clearer that the entire total is energy, and mass-energy equivalence comes in because dark matter and ordinary matter have mass, which is equivalent to a certain amount of energy. --Amble (talk) 17:41, 12 August 2015 (UTC)

Yeah, that's really good  The Steve  15:15, 13 August 2015 (UTC)

Thanks! Please continue to make it better. :-) --Amble (talk) 17:27, 13 August 2015 (UTC)

Graph of Dark Energy to Dark Matter

Is it possible to provide an expression or graph of the relationship of Dark Energy to Dark Matter required to account for observations, with error budgets, extrapolated to zero Dark Matter? GilesW (talk) 13:34, 27 November 2015 (UTC)

Would a pie graph suit you? Graeme Bartlett (talk) 02:34, 28 November 2015 (UTC)

No, because I cannot see how that could provide the information I ask for: How much dark energy would be needed if there was more or less dark matter than hypothesised, or none at all? GilesW (talk) 21:31, 5 December 2015 (UTC)

I think you're looking for something like this. You can satisfy some of the experimental constraints with zero dark matter, but you can't satisfy all of them, and certainly not all at once. It's not 100% clear what you mean by "extrapolated to zero dark matter", since that requires throwing out some of the available data. For example, the fit to CMB is not too bad with Ω_DM=0 and Ω_Λ≈1, but you have to throw out BAO and supernovae. Or you can nearly fit the supernova data with Ω_DM=0 and Ω_Λ≈0.25, but it doesn't work at all for CMB and BAO. There's no way to match all the data with Ω_DM=0, so the extrapolation depends on which data you want to keep and which you want to ignore. This type of plot is a common way of showing observational constraints on DM and DE. Hopefully it gives you what you're looking for. The one I linked probably isn't the most recent, so we could try to find the most up-to-date version if you like. --Amble (talk) 22:19, 5 December 2015 (UTC)

Effect of dark energy

Under this heading, in the last sentence, the article says

Dark energy is persistent: its density remains constant (experimentally, within a factor of 1:10), i.e. it does not get diluted when space expands.

This seems to imply that dark energy represents a violation of the second law of thermodynamics, i.e., it implies that the total amount of dark energy increases over time as the volume of space expands over time. Should the article address this issue? 72.35.113.154 (talk) 06:40, 15 January 2016 (UTC)

I don't see any decrease in entropy, so no. --Amble (talk) 17:03, 15 January 2016 (UTC)

If the volume of space increases over time, and the density of dark energy (amount of energy per unit of space) stays the same over time, that seems to imply that the total amount of dark energy increases over time. Why is this not a violation of the second law of thermodynamics? — Preceding unsigned comment added by 72.35.120.22 (talk) 08:08, 17 January 2016 (UTC)

Because the second law doesn't say the total amount of dark energy can't increase. It says the total amount of entropy can't decrease. Those are simply two different things. Perhaps you meant to ask about the first law instead? --Amble (talk) 08:20, 17 January 2016 (UTC)

Yes, I would like to know whether this claimed property of dark energy violates the law of conservation of mass and energy. 72.35.111.51 (talk) 08:05, 29 January 2016 (UTC)

Even before introducing dark energy, general relativity already violates the classical notions of conservation of mass, energy, and momentum. Instead, general relativity allows for a related but more complicated combined relationship, the stress-energy tensor to be locally conserved. See here. I believe the stress-energy tensor is also locally conserved in a universe with dark energy. However, most models of the universe, including those with a global inflationary cosmology, will not globally conserve energy. As you guess, a constant dark energy plus an expanding universe implies a violation of total energy conservation; however, general relativity already suggests that expecting global energy conservation may not have been the right idea to begin with. Dragons flight (talk) 08:23, 29 January 2016 (UTC)

Conservation of energy is the first law of thermodynamics, not the second law. As Dragons flight says, it becomes more difficult to define global conservation of energy and momentum in general relativity. There is still a local conservation law, but there's no longer a unique definition for something like the "total energy of the universe." You could find that the total energy is conserved or not depending on how you choose to calculate it. There are perfectly sensible ways to define the total energy of a dark energy dominated universe that do conserve the total energy. See for more discussion [6]. --Amble (talk) 15:39, 29 January 2016 (UTC)

Citations

Article 2016-03-29 states 'A paper published in 2016 proposed that dark energy may distort gravitational waves.[15]'. This is a reference to a blog post, which refers in turn to an arxiv paper. It is hard to see how this meets the test for inclusion. Recommend deletion. John Pons (talk) 08:09, 29 March 2016 (UTC)

Agreed. I removed it. --Amble (talk) 13:34, 30 March 2016 (UTC)

Supernovae

Unsatisfactory treatment. There is no mention of what the particular findings were or explanation of those (very important) findings. Asgrrr (talk) 02:29, 6 June 2016 (UTC)

Planck (Spacecraft): 69% dark energy, 26% dark matter, 5% ordinary matter

I tweaked... "the best current measurements indicate that dark energy contributes 69% of the total energy in the present-day observable universe. The mass–energy of dark matter and ordinary (baryonic) matter contribute 26% and 5%, respectively, and other components such as neutrinos and photons contribute a very small amount." 73.85.207.51 (talk) 12:08, 5 July 2016 (UTC)

Boring bullshit and darkness

puny (not puny in large scales) quantum decoherence that will grow larger in the future ubiquitously Dark energy is partial quantum decoherence among wavefunctions inside bigger ones. Entropy increases with time and we have amplification of the phenomenon (accelerative spatial expansion) until the next Big Bang. Why to render something boring difficult? Find a hobby! — Preceding unsigned comment added by 85.73.219.77 (talk) 11:57, 29 July 2016 (UTC)

the Universe is what it is

The Universe is particles and virtual particles (or quantum fields above and below the actuality threshold), nothing less - nothing more. Particles are "trying to communicate" immediately, but "quantum noise" becomes an intermediary, and that medium quasi-particles and particles, blur the initial dimensions of space, so that intermediary "noise space", statistically becomes actual. The rate of "noise space" actualization is not constant because baryonic matter, radiation and universal quantum noise proportionality spread out and their relative ratios change through the lifespan of the Universe. Dark Energy is quantum decoherence. Pseudo-wise unrealistic ideas are moronic. — Preceding unsigned comment added by 2A02:587:4103:9700:5040:8F69:E3E2:4F13 (talk) 08:47, 20 September 2016 (UTC)

The energy density of the dark energy claimed indifferent to a factor of 7?

Ok, under "Nature of dark energy" it says the density is "10^−27 kg/m^3" but at the top of the page, it says "the density of dark energy (~ 7 × 10^−30 g/cm^3) is very low". Ok, now 7 × 10^−30 g/cm3 is 7 × 10^−27 kg/m^3 (it's a million times less since it's cm^3 instead of m^3, but a thousand times more since it's g instead of kg so in total the number goes down by 1000). I could understand rounding off 7 x 10^-28 to "10^-27", but not 7 x 10^-27, that's dropping a factor of 7. So which is it, 7 x 10^-27 or 10^-27 kg/m^3?

184.100.150.71 (talk) 04:33, 25 October 2016 (UTC)

Its not as bad as you make out, 7 x 10^-27 is just a bit under 10^-27 kg/m^3. Graeme Bartlett (talk) 11:17, 25 October 2016 (UTC)

Only marginal evidence of accelerating expansion ~3 sigma

"Marginal evidence for cosmic acceleration from Type Ia supernovae", J. T. Nielsen, A. Guffanti & S. Sarkar - estimated evidence for accelerating expansion of the universe (and so existence of dark energy) with only ~3 sigma, which is insufficient. Article in under CC-BY 4.0: http://www.nature.com/articles/srep35596 OverQuantum (talk) 10:38, 24 October 2016 (UTC)

A) You're ignoring the fact that Type Ia supernovae are not the only evidence for dark energy. The studies of the cosmic microwave background for example constrain the cosmological parameter space in a complementary way and together these observations (and others) strongly exclude a universe with no dark energy. B) Even if Type Ia supernova were the only line of evidence, the concept of sufficient evidence favors greatly by field of study. A 3-sigma effect (~1 chance in 370 of being accidental) would be taken as strong evidence in many disciplines, even if particle physicists would be reluctant to rely to declare a discovery below the 5-sigma level. The standards of a field often reflect how wary one is of the multiple comparisons problem. Particle physicists look at many billions of collisions and hope to find a few that are interesting, so the risk of chance occurrences is high. Cosmologists, on the other hand, have exactly one universe to look at. Hence, they have reduced concern about accidental variations appearing as significant. Dragons flight (talk) 12:34, 24 October 2016 (UTC)

They make almost no mention of CMB, BAO, clusters, or lensing, each of which lends its own evidence. You can't claim to have a model that fits "as well" without showing that it matches those measurements as well. It will be interesting to see how the community responds to this, but it's far too soon to include it on wikipedia. - Parejkoj (talk) 16:15, 24 October 2016 (UTC)

Someone has again added this - [[User:Parejkoj|Parejkoj] you said in your edit summary that this had been debunked by the community, could you add any sources saying this? Absolutelypuremilk (talk) 20:39, 25 December 2016 (UTC)

Here's two: Rubin & Hayden, Ringermacher & Mead. The final sentence of Rubin & Hayden reads, "We conclude that the analysis in N16 is both incorrect in its method and unreasonable in its assumptions, leading the authors to question a result that is quite secure when addressed properly." This also comes from conversations with colleagues and the Astronomers Facebook group, and my own reading of the work (mentioned above). - Parejkoj (talk) 22:55, 25 December 2016 (UTC)

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should this be included

It might be early but looks interesting and would certainly change a few things. It basically states that there is no dark energy or need for it, the acceleration is due to instability in space time; and is consistant with general relativity. [7] TVGarfield (talk) 01:17, 15 December 2017 (UTC)

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should this be included

It might be early but looks interesting and would certainly change a few things. It basically states that there is no dark energy or need for it, the acceleration is due to instability in space time; and is consistant with general relativity. [8] TVGarfield (talk) 01:17, 15 December 2017 (UTC)

A Different Look at Dark Energy

Astronomers have made measurements that show the most distant galaxies are moving away at accelerating velocities. This seems to contradict logic, which previously believed that the galaxies were slowing down due to the internal gravity of the universe. In order to explain the apparent expansion with all galaxies accelerating away from each other, scientists have simply created a concept called “dark energy”. This mysterious force, which has never been detected, measured, or explained, is believed to counteract gravity, producing “inflation” of the entire universe. The most distant galaxies appear to be accelerating away at the greatest speeds. This will eventually result in the end of the universe. It is speculated that all galaxies and stars will eventually disintegrate and disappear, and even atoms will evaporate (many billions of years in the future). This may be a misinterpretation of the measurements.

There was a similar misconception long ago when everyone believed the earth was the center of everything, with the sun and planets revolving around the earth. But astronomers were puzzled by the observed “retrograde motion” of some planets (like Mars and Jupiter) which at times appeared to actually move backwards. Ptolemy and Aristotle tried to explain these phenomena by creating the concept of “epicycles” or backward loops that were part of the planets’ orbits around the earth. This idea was accepted for hundreds of years as scientific fact that explained the retrograde motions of the planets. When Copernicus and Galileo showed that the planets actually revolve around the Sun, the retrograde motion loop theory was easily debunked as an optical illusion resulting from the relative positions and motions of the earth and other planets. The point here is that accurate astronomical measurements do not necessarily lead to valid conclusions.

When the astronomers measure that a galaxy 10 billion light years from us is moving away at a tremendous accelerating rate, they are not thinking in 4 dimensions. We must consider TIME. We can never see the universe or obtain measurements of how it “is”; we can only see how it WAS many years ago. We cannot even see our Sun as it is .. only as it was 8 minutes ago. When a galaxy 10 billion light years away is measured to be receding at a tremendous speed, we must remember that this is how it was moving 10 billion years ago, not long after the Big Bang explosion. It is entirely possible that it has since slowed down dramatically, and could now even be moving back toward us (or may not even exist today). Similarly the galaxies closer to us appear to be moving away at much lower speeds because we are seeing them as they were moving more recently, perhaps only a few million light years in the past. Indeed, Andromeda, 2.5 million light years away from us, is moving TOWARD us on a collision course! The results of that train-wreck will then crash into other galaxies in our local group. Does this sound like “run-away inflation” where all the galaxies are flying apart at incredible speeds as they are accelerating away from each other?

Perhaps the truth is that, early in the life of the universe, the galaxies were indeed flying apart at very high speeds. But in the billions of years since then they have slowed down, due to gravity of the universe, as we observe in those galaxies closer to us. If that is happening, it would spell the demise of “dark energy” and “inflation”. The run-away inflation of the universe may be only an illusion, the same as “retrograde motion” of the planets was centuries ago. The difficulty is that we have no way to know what distant galaxies are doing NOW because it is impossible to view or measure them as they actually are in our present time.

Perhaps astronomers should create a graph of galactic speeds vs. their distances. They might discover that the rapidly receding galaxies only appear that way because they are looking back so far in time. We need some modern Galileos, Hubbles, or Einsteins to figure out how our universe actually works (recalling that Einstein once believed the universe was static and unchanging). Is Dark Energy only an illusion … the same as we once believed in epicycles and backward motion of the planets?

© 2016 Gerald Brooks, Santa Clarita CA — Preceding unsigned comment added by GRBrooks (talk • contribs) 08:23, 31 May 2017 (UTC)

Wikipedia is Not a Forum. If you have specific changes to make to the page, with references to reliable sources, you can suggest those here. The above text has no such suggestions. - Parejkoj (talk) 16:51, 31 May 2017 (UTC)

Gerald Brooks's commentary does at least draw attention to an interesting (and important?) point - in this sentence of his: "The difficulty is that we have no way to know what distant galaxies are doing NOW because it is impossible to view or measure them as they actually are in our present time"....

Incidentally [> a "suggestion from me !"] it would be good to have more clarification as to how exactly cosmologists deduced that the universe is expanding more rapidly now, than it was a few billion years ago.

Great point. Even though we do not measure what exactly a galaxy is doing today, we are measuring what happened to it 10 million years ago when the light left all of those stars. It is true that those stars today will have evolved, turned into a supernovae (if they are massive enough) or remained dimly shining (if it is less massive). The thing is the light we recieve is a message that tells us what was happening in our universe in that era. The large-scale modeling of the universe takes that into account when evaluating the what the universe is comprised of. To help answer your question about 'how exactly' to measure the acceleration through supernovae measurements is the comparison of distance to the object to the velocity. If things were moving at a constant velocity, i.e. the universe is expanding at a constant rate, then this relationship would be a straight-line. However, when measurements were made of the universe for the furthest away objects, they found that this relationship was not a straight-line rather it had a curved. The amount that it curved is consistent with an acceleration. To explain that acceleration, there needs to be something else beyond our standard understanding of the fundamental things in the universe. Dark Energy was coined by Prof. Mike Turner as a term to describe this other energy. There are other cosmological measurements beyond supernovae measurements, i.e. the cosmic microwave background, baryon acoustic oscillations, etc. that are consistent with this amount of dark energy existing in the universe. Active areas of research are trying to explain what this entity actually is. Cosmojellyfish (talk) 02:01, 22 January 2020 (UTC)

Gerald also writes: "When a galaxy 10 billion light years away is measured to be receding at a tremendous speed, we must remember that this is how it was moving 10 billion years ago"' - which is presumably his way of focussing on the manner in which Dark Energy is acting; i.e., if we suppose that 10 billion years ago the galaxy was receding at tremendous speed, then [under the influence of Dark Energy] it should surely be receding even more rapidly now? --DLMcN (talk) 16:27, 21 May 2018 (UTC)

Dark Energy 69%, Dark Matter 26%, Ordinary Matter 5%

The Planck spacecraft gives us the reading of Dark Energy 69%, Dark Matter 26%, Ordinary Matter 5%. 73.85.202.208 (talk) 14:47, 3 March 2021 (UTC)