Talk:Accelerating expansion of the universe

More theories for the accelerating expansion

In the section "alternative theories" the sentence "Räsänen does not consider the model likely" is not backed up by the reference added to that sentence. In the New Scientist article referred to Räsänen in stead is quoted as thinking that his theory is a plausible explanation for the accelerated expansion. His theory is just in its initial stages and the toy models he considers have some flaws vis à vis the modelling of the real universe.

More theories for the accelerating expansion

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)

So I would at the very least suggest a disclaimer be placed stating that the article for this subject needs a lot more work to be anywhere near completion. I would also just like to say I don't support theories that are not provable or falsifiable. They do have to be logically put together and have predictions that canbe tested in some way. So the theory that the universe is only a year old, presumably by quantum fluctuations since including religious dogma would just start to muddle the science behind physics, for example but everything just appeared into existence in a way to make us believe its older. — Preceding unsigned comment added by 2601:B:A3C0:7:A819:A15:7CD:529 (talk) 17:49, 3 September 2013 (UTC)

An alternative theory: I recently submitted to the university of utah astrophysics group my theory entitled "An Engineered Universe: The Origin and Structure of the Universe". What I attempted to do is imagine the state of affairs before the big bang and postulate what was there and how structure was derived from it with the goal of reproducing the properties of our universe. My background is physics, engineering and I worked for 35.5 years in structural analysis with my interest focused on constitutive modeling. Constitutive modeling related the stress-strain response back to the material's internal constitutive structures. What seemed apparent to me is that our space is a composite structure. So I postulated the properties of the elementary constituent and proceeded developing structure. The approach continually surprized me as I slowly realized how different features/properties of our universe emerged. The randomness of quantum behavior, quantum foam, quantum entanglement, elements of the uncertainty principle, distance/separation, the exponential growth of space, a quantum theory of gravity, the big bang, separation of matter and anti-matter, charge balance, some dark matter, a potential route to gravity force neutralization, a possible approach to travel without inertia, and I ended on the accelerating universe with the slowing of time as contributing to the apparent acceleration. In this theory, an embryonic universe builds for ~2 trillion year (1.88T which was calculated from the physical constants and the generally accepted properties of our universe) and then is forced to split (big bang) into two 3D branes in the bulk - using string theory nomenclature. (It has features somewhat similar to the Ekpyrotic Universe model.) The structure of these two spaces have inherent differences leading to slight asymmetric decay nature of some particles. The randomness of the CMB occurs naturally. The theory does not permit worm holes and a singularity never occurs during the bang. There results two time metrics, one for growth of space and one for our electromagnetic existence. The interaction of the two leads to increased acceleration of space. ----spacemaker@comcast.net — Preceding unsigned comment added by 71.195.249.185 (talk) 18:05, 8 February 2014 (UTC)

GA Review

The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

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This review is transcluded from Talk:Accelerating expansion of the universe/GA1. The edit link for this section can be used to add comments to the review.

Reviewer: Spinningspark (talk · contribs) 12:39, 7 November 2014 (UTC)

The nominator of this article does not appear to be currently active (she allowed another recent GA nomination to fail after it got to a point where it was on the point of being passed with one relatively minor fixable issue) so I will restrict my initial comments to a few general remarks on the lead. If someone wants to do the work on the article, then please make yourself known and I will do a full review. Otherwise I will fail it in a few days time.

The lead is deficient in that it does not fully reflect the content of the article. The first section is mostly about the Hubble parameter which is not mentioned. A lot of space is given in the body to models other than dark energy, but these are not even mentioned in the lead. The lead makes the claim that dark energy is the most widely accepted explanation, but this claim is does not appear in the body and is not cited anywhere. The section "Theories for the consequences to the universe" does not appear to be covered in the lead at all. SpinningSpark 12:39, 7 November 2014 (UTC)

@Spinningspark:, I'd be willing to take over as a de facto nominator, but I'll be pretty busy for most of the next month. If you can give me until Thanksgiving, I may be able to do some substantial work to address any problems you bring up during the review. StringTheory11 (t • c) 00:43, 14 November 2014 (UTC)

No problem, I'll wait until you have improved the lead before continuing with the review and then we can take it from there. Not sure exactly when thanksgiving is (we don't do it in my country) but there is no rush. As long as things are moving forward I am happy to keep the review open. SpinningSpark 01:46, 14 November 2014 (UTC)

Thanksgiving is Thursday the 27th; I should have been more clear on that. StringTheory11 (t • c) 19:58, 14 November 2014 (UTC)

Ok @Spinningspark:, I have some free time today, so did a cursory read of the article. I agree that it is nowhere near GA-class at the moment, and probably isn't even a B-class article as it stands. Thus, I think that the article should certainly be failed now, as taking this to GA would take a lot of effort, more than can be put in in a GA review. StringTheory11 (t • c) 20:49, 23 November 2014 (UTC)

Sorry to hear that, but as the original proposer still is not taking an interest, I agree it is best to close this and submit it again at a later date. SpinningSpark 23:29, 23 November 2014 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Protection

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)

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)

longer time?

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)

Error in Acceleration time?

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)]

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)

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)

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)

@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)

In any case - Enjoy! :) Drbogdan (talk) 13:50, 2 April 2016 (UTC)

References

Hope the discussion copied above helps in some way - in any case - Enjoy! :) Drbogdan (talk) 16:16, 2 April 2016 (UTC)

Mechanism

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)

The second part is a restatement of the first. 91.122.8.180 (talk) 11:24, 17 April 2016 (UTC)

Only marginal evidence ~3 sigma

"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)

Agree saomeone should add this. that theory alwSergey Woropaew (talk) 10:29, 25 February 2018 (UTC)ays looke waek

It's already in the article (ref #42). Banedon (talk) 20:48, 25 February 2018 (UTC)

Criticism of supernova observational data

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)

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)

Supernova observation and Accelerated Expansion

Article says:

"So a supernova with a measured redshift z = 0.5 implies the universe was 1/(1 + 0.5) = 0.67 of its present size when the supernova exploded. 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 two thirds its present size to its present size, compared to a non-accelerating universe with the same present-day value of the Hubble constant."

This seems problematic to me. This would be true of a decelerating universe. This age of universe is: 0.67 *13.8= 9.2 billion years at constant expansion rate and it will take it 4.6 billion years to reach current size. A decelerating universe will take more time to reach current size, while accelerating one will be bigger; which is other way to say that it took more than 9.2 billion years to reach 0.67 and less than 4.6 to to reach 1.0.

This question was posted before by somebody else but was not answered. The editor who added this section is no more active. If no explanation comes in next few days, I will change it to: which means it took a shorter time to expand from two thirds its present size to its present size, compared to a non-accelerating universe. Shorter time, bigger size, fainter nova--AhmadLX (talk) 03:43, 20 May 2018 (UTC)

@Waleswatcher: , @Banedon: could you guys please shed some light on this? Thank you--AhmadLX (talk) 18:51, 21 May 2018 (UTC)

@AhmadLX: The current text is correct. The key is "with the same present-day value of the Hubble constant". That is equivalent to saying "with the same rate of expansion today". A decelerating universe was expanding faster in the past than it is now. An accelerating universe is the opposite. So a decelerating universe covers the "distance" from z=.5 to z=0 faster than an accelerating one. Waleswatcher (talk) 19:31, 21 May 2018 (UTC)

Hi, thanks for your response. But you are assuming acceleration started very recently. And that way, the two versions of the universe (decelerating and accelerating) won't converge at z=0, which they must (they would differ in size). Also, acceleration started around 4 billion years ago.AhmadLX (talk) 20:05, 21 May 2018 (UTC)

"you are assuming acceleration started very recently" - no, I'm not assuming that. Maybe an analogy will help. Suppose I tell you a car is going 60mph (one mile per minute) right now. If the car neither accelerated nor decelerated over the last minute, then it took it one minute to travel the last mile before now. If it decelerated over the last minute, then it took less than a minute to travel that last mile. If it accelerated (over a sufficiently long time), then it took it more than a minute to travel that last mile. If it accelerated for a while and then decelerated, then it depends. Right?

"And that way, the two versions of the universe (decelerating and accelerating) won't converge at z=0, which they must (they would differ in size)." Not so. Set a = a_0 today. Set \dot a/a = H_0 today. Now with those same a and H today, consider two different pasts, one that is accelerating and one decelerating. (By the way before I wrote my first response I did this exercise and worked out the math, just to be sure.)

"Also, acceleration started around 4 billion years ago." That is true and makes it more complicated, but it would only matter if the universe was decelerating faster prior to 4 billion years ago then in the decelerating always scenario (think about the car). Waleswatcher (talk) 20:57, 21 May 2018 (UTC)

"If it decelerated over the last minute, then it took less than a minute to travel that last mile.". If it decelerated it will take more time to cover the last mile, I guess :) But I figured out the mistake that I was making. I was constraining decelerating universe to have same age as accelerating one . Thanks anyway. Maybe you can add a note on this in the article? AhmadLX (talk) 22:41, 21 May 2018 (UTC)

No, it will take less! Remember, we are comparing two "trajectories" with the same final speed and same final location, and asking how long it took to cover the last mile before reaching that final location. If you decelerated, it means you were going faster before, so less time.

You mean a note explaining this in more detail? I'm a little leery of that, we should probably have a reliable source to summarize rather than adding our own explanations. Waleswatcher (talk) 00:13, 22 May 2018 (UTC)

Yeah but it is confusing as it stands. A note doesn't necessarily require ref I think. Current description is unsourced anyway; risk of getting cn tagged will be reduced if there is note explaining apparent confusion. thanks. AhmadLX (talk) 02:16, 25 May 2018 (UTC)

"Accelerating expansion" is incorrect.

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)

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)

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)

The proper noun used as the name of our universe is Universe

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)

Lead sentence

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)

"laymans section"

I think this page, and pages like it, need a section,or links to pages that simplify some of these things. For instance, a 10 year old kid coming here to read this for whatever reason, probably won't understand half of it. An example is this sentence 'an accelerated expansion can be accounted for by a positive value of the cosmological constant Λ,' see that funny symbol, im guessing it's Greek, i aint got a clue, but even if it is, knowing that still doesn't add meaning to it to me in the context of this sentence, and a kid trading this is just gonna see a weird symbol. A lot of wikipedia pages about things like this or quantum mechanics or, scientific equations for ex,seen to be written under the using that the reader knows what they are looking at. But they won't. I love reading new stuff, and live for learning new things about absolutely anything on here, but i constantly find myself, especially in regards to scientific and mathematical explanations, not understanding half of the symbols used, or how to actually put something in reading into words. Take that symbol from earlier. How do you word that symbol in your head when reading it when you dont know what it means? And i think it would be greatly beneficial, for thickos like myself lol, and especially for younger readers of wikipedia pages, if there was a so called laymans section, or simplified section /explanation of the subject. Would also love to know what that upside down v is and how you pronounce it.lol D0S81 (talk) 02:01, 4 March 2020 (UTC)

The trouble, is seems to me, is that scientists, or science enthusiasts, don't take science seriously. If they did, they would understand that there is no "ego" as it is ordinarily conceived. Darwin was right, humans are animals. Or to put it differently, they are both flesh and blood. If you take the imaginary "soul" out of the picture, what's left? The self doesn't have any continuous existence in time. As humans, we certainly don't have the "virtue" and "honesty" that we ascribe to ourselves. Arguably, the human mind is a self-serving lying machine, capable of adding two-plus-two or engineering a rocket with a mission to Pluto and beyond, but untrustworthy when it comes to emotionally-charged issues.

Wikipedia should be an information source for everyone, including, as you say, 10-year-olds trying to understand the universe. But it is monopolized by pedantic types who are showing off to each other. It's as if the questioner (in this case the person searching the internet for answers to a question) is ignored while the "experts" huddle together in a circle competing against each other.

Some articles, such as this one, should be written in two versions: one for lay people, and another for advanced readers. The layperson's verson should appear first, and at the top of the page there could be a link to the "advanced" version.

James 2600:8801:BE31:D300:A8E7:F7D4:F07D:1027 (talk) 17:04, 17 April 2022 (UTC)

Doubt about the acceleration

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.

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)

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)

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)

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)

81.156.186.152 (talk) 23:04, 2 January 2022 (UTC) I think, for a more complete article, it would be appropriate to add whatever well considered doubts there may be over the cosmic acceleration, as well as the strong reason that favours a cosmic acceleration; that, prior to the apparent discovery of the acceleration, the calculable age of the visible universe was too young to fit with its apparent state of evolution. An acceleration made the visible universe older and seemed to answer that mystery. (MarkJamesBridger)

81.156.186.139 (talk) 10:00, 3 January 2022 (UTC)The article should mention the original simple reason why a cosmic acceleration was not expected prior to its discovery (and the reason why there may still be doubts about it). It was naturally assumed that the expansion would be slowing down due to the effect of gravity. An acceleration against gravity, for whatever reason, agent or dark energy is used to ’explain’ that, means something that is doing work continuously, and therefore adding energy to the whole system, breaking the conservation of energy principle. The only way to escape this breach of the laws of physics is consider the cause of the acceleration not to be something that works against gravity but an effect of gravity itself. This was Einstein’s idea when he first used the Cosmological constant to hold what he believed was a steady state universe. In framing the cosmological constant within general relativity, one is saying it is an effect of gravity, rather than some force working against gravity. General relativity may describe the curvature of space-time but not the direction in which gravity may go, i.e. whether it is a push or a pull. That leaves the option open for the cosmological constant to be adjusted to fit whatever is believed or observed. This however is a somewhat arbitrary explanation and a deeper explanation of gravity may require that it has one direction, that it is always a pull or an attraction. In that case a model of the universe is required where the accelerating expansion is not gravity repelling things on the grand scale but gravity falling towards things on a grand scale. This is possible in a multiverse where there is no expansion between the neighbouring cosmoses/universes (thus a constant overall density), so that when they individually expand they will be falling towards each other and eventually overlapping. At some stage in the evolution of our own ‘universe’ we may see increasing evidence for this, given improving telescopes, to overturn the assumption that our universe is heading for a cold dark death of ever diminishing density. (Mark James Bridger) 81.156.186.139 (talk) 10:00, 3 January 2022 (UTC)

The article should also note, as a historical fact, that the theory that the cosmic acceleration is an effect of gravity (in this constant density model of a multiverse) is the only theory that was predictive, i.e. it was proposed in advance of the 1998 observations. To be specific it was recorded as a text in an oil on wood panel painting titled The Eternal and Infinite Universe, which was publicly exhibited in a gallery named The Jelly Leg'd Chicken gallery in Reading, Bershire, UK in January 1995 in a group exhibition. I am the artist of the painting and have witnesses to affirm this. The fact/ possibility that the cosmic acceleration was only predicted by an artist seems to agree with yet another of Einstein's expressed thoughts; that 'the greatest scientists are artists as well'!. (Mark James Bridger) 81.156.186.139 (talk) 11:37, 3 January 2022 (UTC)

References

Science

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)

Black holes could be the source of dark energy causing the accelerating expansion of the universe.

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)

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)