Talk:Accelerating expansion of the universe

message: I'm not in favor of any one theory as there is no reason, or evidence, yet to believe any one of them is better in a lot of cases. The article in its current form is not very encompassing of the topic and could use significantly more work to add to it. It could even be there is no mysterious acceleration happening since that is based on an axiom that there is no special place or time in the universe (which is believed with no evidence whatsoever that it is actually true). This could already be argued against for a few reasons such as the time we live in is special since we are able to observe enough space to see other galaxies. In the future most intelligent civilizations may only be able to see a few local galaxies and therefore come to a very different conclusion on what happened in the timeline of the universe, perhaps not even being able to form a timeline of the universe since they won't be able to see the expansion occurring. Anyway there are a lot more theories and information should be added based on the Copernicus test of no special place existing and the idea that there is no reason we could not exist in a special place. I admit that it could be a very small chance but perhaps the universe is infinite and a special place is necessary for advanced life to form so it wouldn't matter how unlikely it is because it would happen an infinite amount of times. Or, for reasons unknown, the highly improbable happened regardless of how poor the probability is. Science becomes limited when we hold something to be true only because we want it tone true.  — Preceding unsigned comment added by 2601:B:A3C0:7:A819:A15:7CD:529 (talk) 17:37, 3 September 2013 (UTC)
thread_title:  More theories for the accelerating expansion  

message: I've temporarily semi-protected this page to cut off an edit war that has already exceeded the three revert rule.  I agree that some of the material that 89.110.* has been adding is problematic in that it espouses a minority viewpoint on interpreting the evolution of the universe that doesn't deserve the prominence he is giving it (WP:WEIGHT).  However, some of his edits, including grammatical changes and additional background info (e.g. mentioning the Nobel prize in the intro) are probably reasonable.  I would encourage the parties to review the edits, restore any of 89.110.* content that is reasonable, and discuss the points of disagreement.  Dragons flight (talk) 21:08, 24 February 2015 (UTC)
replies: text: Thanks. I have restored much of the IP warrior's lead and edited it for neutrality etc., but I am on a bleepy thing so cannot easily do this for the body of the article. — Cheers, Steelpillow (Talk) 21:32, 24 February 2015 (UTC)
thread_title:  Protection 

message: Evidence for acceleration - 
Supernova observation - 
"In an accelerating universe, the universe was expanding more slowly in the past than it is today, which means it took a longer time to expand from 2/3 to 1.0 times its present size compared to a non-accelerating universe."
Should this not be "it took a shorter time", since expansion is accelerating?
Also, the use of the word "accelerating" to describe an increased rate of expansion is confusing, since in physics a decreasing rate of expansion would be just as accurately described as an acceleration. It seems imprecise to express it this way, with the implicit assumption that acceleration would necessarily mean an increased rate.  — Preceding unsigned comment added by 70.59.95.151 (talk) 16:52, 15 July 2018 (UTC)
thread_title:  longer time? 

message: FWIW - following discussion seems particularly relevant to the "Accelerating expansion of the universe" article (see copy below):
Copied from Talk:Timeline of the formation of the Universe#Error in Acceleration time?
"Error in Acceleration time?"
You have an error in the acceleration time. That acceleration started 6.2 billion years ago, that is, 7.6 billion years after the Big Bang. [Note: Preceding unsigned comment added by 190.215.80.188 (talk) 12:32, 5 October 2015 (UTC)
replies: text: FWIW - the above comment about the time the universe expansion began accelerating seems supported by astrophysicist Ethan Siegel "... about 7.8 billion years old, or about 6 billion years ago, some 1.5 billion years before our Solar System formed." - however, a note by astronomer Joshua Frieman at CalTech notes => "the Universe began accelerating at redshift z ~ 0.4 and age t ~ 10 Gyr." [Note: "9.4" Gyr? determined using a cosmological calculator.] - estimated time that expanding universe began accelerating may need clarification - comments from others welcome of course - in any case - Enjoy! :) Drbogdan (talk) 16:17, 1 April 2016 (UTC)
replies: text: BRIEF Followup: The "7.8 billion years old" age of the accelerating expanding universe seems to be supported by comments made on the following talk page => "User talk:I9Q79oL78KiL0QTFHgyc#HELP: Clarify Time Expanding Universe Accelerated?" - see copy below:
Copied from "User talk:I9Q79oL78KiL0QTFHgyc#HELP: Clarify Time Expanding Universe Accelerated?":
"HELP: Clarify Time Expanding Universe Accelerated?"
Hello Josh:
IF POSSIBLE => may need help to clarify the best known Time the expanding universe began accelerating - this refers to several Wikipedia pages including "Accelerating expansion of the universe", "Timeline of the formation of the Universe" and "Talk:Timeline of the formation of the Universe#Error in Acceleration time?" - Times presented on these pages (and related ones) seem to vary and include "7.8 billion years old"/astrophysicist ESiegel; "10 Gyr" (z ~ 0.4)/astronomer JAFrieman; "9.4 Gyr" (determined from z = 0.4 per Fermilab calculator); perhaps other values as well - any help to clarify the Time the expanding universe began accelerating would be appreciated - in any case - Enjoy! :) Drbogdan (talk) 12:44, 2 April 2016 (UTC)

text: 10 Gyrs is approximately right. It is going to occur at a redshift that solves the equation \Omega_\Lambda = \Omega_m (1 + z)^3 Roughly, \Omega_\Lambda = 0.7 and \Omega_m = 0.3, so it's actually closer to z=0.3 which I think puts it closer to the 7.8 billion year estimate. jps (talk) 13:15, 2 April 2016 (UTC)
replies: text: @jps - Thank you *very much* for your comments - and clarifications - they're *greatly* appreciated - Thanks again - and - Enjoy! :) Drbogdan (talk) 13:21, 2 April 2016 (UTC)

text: In any case - Enjoy! :) Drbogdan (talk) 13:50, 2 April 2016 (UTC)
thread_title:  Error in [[Accelerating expansion of the universe|Acceleration time]]? 

message: I have removed a section added by ‎91.122.8.180 called "Mechanism" that looks to be original research.  The first part talking about gravitational collapse is referenced, but the subsequent parts do not appear to have support from any reference. The addition can be seen in https://en.wikipedia.org/w/index.php?title=Accelerating_expansion_of_the_universe&oldid=715685352 , so do people here agree that this section should not be in the article? Graeme Bartlett (talk) 11:18, 17 April 2016 (UTC)
replies: text: The second part is a restatement of the first. 91.122.8.180 (talk) 11:24, 17 April 2016 (UTC)
thread_title: Mechanism

message: "Marginal evidence for cosmic acceleration from Type Ia supernovae", J. T. Nielsen, A. Guffanti & S. Sarkar - estimated evidence for accelerating expansion with only ~3 sigma, which is insufficient. Article in under CC-BY 4.0: http://www.nature.com/articles/srep35596 OverQuantum (talk) 10:36, 24 October 2016 (UTC)
replies: text: Agree saomeone should add this. that theory alwSergey Woropaew (talk) 10:29, 25 February 2018 (UTC)
replies: text: It's already in the article (ref #42). Banedon (talk) 20:48, 25 February 2018 (UTC)
thread_title:  Only marginal evidence ~3 sigma 

message: The essential query I would like to make is "Are the supernova observations data beyond the critical threshold that would lend credence to the idea of the universe's accelerating expansion?".  The below site seems to suggest that such a 'reasonable doubt' criteria is not met, at least in regards to the Supernova data.  I think the article should state this.   
According to : 
http://www.ox.ac.uk/news/science-blog/universe-expanding-accelerating-rate-%E2%80%93-or-it
"We analysed the latest catalogue of 740 Type Ia supernovae – over ten times bigger than the original samples on which the discovery claim was based – and found that the evidence for accelerated expansion is, at most, what physicists call "3 sigma". This is far short of the 5 sigma standard required to claim a discovery of fundamental significance."
Of course, it is possible that the Universe is expanding at an accelerating rate (especially given the other observations), but, according to this website, the issue is not resolved beyond a reasonable doubt in relation to the Supernova data.  This may influence the class of viable theories for the accelerating rate of expansion of the universe.  
ASavantDude (talk) 20:28, 23 March 2018 (UTC)
replies: text: Already in article - "Yet other possibilities are that the accelerated expansion of the universe is an illusion caused by the relative motion of us to the rest of the universe, or that the supernovae sample size used wasn't large enough (emphasis mine)." I'll add that Prof. Sarkar's work isn't widely accepted. Banedon (talk) 03:00, 24 March 2018 (UTC)
thread_title: Criticism of supernova observational data

message: This article repeats one of the most common misconceptions about the accelerated expansion of the universe.  It's unfortunate because it's a misconception which is repeated in a great many sources which talk about the expansion.
To elucidate what is wrong about this description, a little bit of math helps.  In simplified form, the first Friedmann equation can be written as:
: \frac{\dot{a}^2}{a^2} = H^2 = \frac{8 \pi G \rho + \Lambda c^2}{3} 
Here, H is the rate of expansion, a is the scale factor, Λ is the cosmological constant, ρ is the matter/energy density of the contents of the universe, G is the gravitational constant, and c is the speed of light (note that I'm ignoring curvature here, as it's not relevant to the discussion).
As the universe expands, the density ρ decreases (except in the hypothetical Big Rip cosmology which is typically considered highly unlikely).  Since Λ is a constant, and ρ only decreases, it is impossible for the rate of expansion H to increase.
What is referred to as the accelerated expansion, then, refers not at all to the rate of expansion H, but instead to the fact that distances between objects are increasing at an accelerated rate.  This can be represented mathematically as \ddot{a} > 0.
I propose the following changes to this article:
:1) Rename it to "Accelerated Expansion of the Universe", redirect the old page to the new one.
:2) Clean up the wording to eliminate all reference to the rate of expansion increasing.  Some of the math could also be made more clear.
:3) Add a section which explains and refers to this misconception (or, at a minimum, a sentence stating the misconception with a citation that goes into detail).  I don't currently have a good citation which refers to this misconception, but I could hunt for one.
Kbdick24 (talk) 23:31, 10 November 2018 (UTC)
replies: text: It's just a matter of how one defines "rate of expansion". I would say that if \ddot{a} > 0, the rate of expansion is accelerating. Eric Kvaalen (talk) 07:48, 20 April 2021 (UTC)

text: Using "accelerated" will be factually incorrect - as long as the second derivative of the scale factor is positive "accelerating" is true. The explanation that the objects accelerate but the first derivative at a fixed distance is (most probably) dropping should suffice.  Kerguelen Rogue Avon (talk) 19:00, 29 September 2022 (UTC)
thread_title:  "Accelerating expansion" is incorrect. 

message: For other universes we write universe. (How does that sound different?)
Our Universe is pronounced in a conceited way.  — Preceding unsigned comment added by 2A02:587:410E:FF00:B1B0:8DDB:B80B:7431 (talk) 07:46, 8 March 2019 (UTC)
thread_title:  The proper noun used as the name of our universe is Universe 

message: Current lead sentence is dreadful.
Better just to say that H will never drop below a certain value.  cheers, Michael C. Price talk 18:09, 27 March 2019 (UTC)
thread_title:  Lead sentence 

message: I have added the following paragraph:
:In 2019 a paper was published claiming that the conclusion in favor of an accelerating expansion is unfounded. The authors anayzed the Joint Light-curve Analysis catalog of Type Ia supernovas, containing ten times as many supernovas as were used in the 1998 analyses, and found that there was a large dipole in the relationship between luminosity distance and redshift, falling off exponentially with distance (decreasing by a factor of e over 100 megaparsecs). When including this dipole into the fit, there was little evidence for a "monopole", that is, for an isotropic acceleration in all directions. The dipole is roughly aligned with our motion with respect to the cosmic microwave background, but not exactly, with the supernovas being dimmer at a given redshift in the direction of Hydra.Wolchover, Natalie (27 September 2011) 'Accelerating universe' could be just an illusion, NBC News
Last night my edit was quickly reverted with the comment "This sort of claim needs additional citations." I have added four more references, but I object to the idea that we should exclude a paragraph like this just because the conclusion has not been widely accepted. The analysis is good. The authors are not lying. The paper was peer reviewed. We should not exclude such information just because it goes against some Nobel prizes. We are Wikipedia, not the Nobel committee. Note that I did not dare to write "the acceleration is wrong", I just reported that a new analysis has been done, and the results call into question the whole idea of the acceleration. I don't believe that Wikipedia has a policy of excluding the mention of any research that goes against the received wisdom. It is certainly important if the conclusions are true. Eric Kvaalen (talk) 07:48, 20 April 2021 (UTC)
replies: text: I object to including this. The relevant policy is WP:FRINGE. To quote, "a Wikipedia article should not make a fringe theory appear more notable or more widely accepted than it is". It's certainly important if the conclusions are true, but since few cosmologists are taking the conclusions seriously, they don't deserve to be included. I am going to revert. Banedon (talk) 07:59, 20 April 2021 (UTC)
replies: text: I object to your reversion. I asked that my edit not be reverted until consensus be reached, and you ignored that. I did not make the theory appear more widely accepted than it is, and it is certainly notable. We should not be taking sides with the "establishment" in ignoring facts that go against their long-standing idées fixes. Our readers should be told that the evidence for a global acceleration is weak when one analyzes a larger set of data and when one allows for a dipole. Why should Wikipedia deprive its "poor readers" of such facts? Eric Kvaalen (talk) 06:04, 21 April 2021 (UTC)
replies: text: Relevant policy here is WP:BRD - I do not need to wait for consensus that the material should be removed before reverting. As for why it should be removed, we deprive our "poor readers" of such facts for the same reason we do not include claims such as how the Michelson-Morley experiment detected the aether back in the early 20th century. There are lots of fringe theories; if we include one then there's an argument to include all of them and the article will become very bloated. The article should cover only the mainstream. If you agree that the theory is not widely accepted, then please give an explanation why WP:FRINGE does not apply. Banedon (talk) 03:00, 26 April 2021 (UTC)
thread_title: Doubt about the acceleration

message: Lemaître law,[1] is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving away from Earth. The velocity of the galaxies has been determined by their redshift, a shift of the light they emit toward the red end of the visible spectrum. 120.29.104.58 (talk) 13:41, 6 September 2022 (UTC)
thread_title:  Science 

message: This should be added to the article - the whole article needs a facelift. It is 9 years old and a lot has changed or has become part of the consensus of our understanding. In the last few days (February 15, 2023) scientists have published an article sumarized and explained here:
https://earthsky.org/space/black-holes-as-the-source-of-dark-energy/?utm_source=EarthSky+News&utm_campaign=aca33d4354-EMAIL_CAMPAIGN_2018_02_02_COPY_01&utm_medium=email&utm_term=0_c643945d79-aca33d4354-395634733&mc_cid=aca33d4354&mc_eid=429423be84 2600:4040:2C32:B400:E065:8E67:E2FC:22D1 (talk) 16:01, 18 February 2023 (UTC)
replies: text: As I wrote in the Dark Energy article, I think this is too soon. The research is new, and there are a lot of people skeptical about it, not least because they don't understand it. It's not clear for example how black holes can drive accelerating expansion, or if some/any of the evidence for accelerating expansion is being challenged. For example, does this new paper actually argue that the universe's expansion isn't accelerating? It does seem like the new paper only purports to explain accelerating expansion, in which case this article is still up-to-date. Banedon (talk) 07:39, 20 February 2023 (UTC)
thread_title:  Black holes could be the source of dark energy causing the accelerating expansion of the universe.