Talk:Inflation (cosmology)/Archive 4

BICEP2 measurement supports inflation, not BBM
I've seen people on the web confused about the meaning of the news about the BICEP2 measurement. I believe a lot of it stems from confusion about the difference between the standard Big Bang model and the theory of inflation. The former is a model of an expansionary universe that goes back to recombination, nucleosynthesis, and baryogenesis, back to 10^-3 seconds or so, while it had a decelerating expansion rate. The latter is a theory during an earlier epoch, at somewhere like 10^-33 seconds, so well before the known parts of the standard Big Bang model, during which the expansion rate was growing exponentially.

I am not a physicist, but as I understand the news, it was an observation supporting inflation. It doesn't seem right to me to say this result supports the big bang theory. If they had not measured any B-Modes, the BBM would not be any less well satisfied today. The results are interpreted in terms of the BBM: they had to subtract off the E-modes and B-modes predicted by big bang, in order to isolate the gravitational wave signal. If the big bang model were wrong, they entire computation would be meaningless, so in no sense can the measurement be said to "support big bang".

Finally, I will note that the NYTimes changed the title of their article from "Detection of Waves in Space Buttresses Landmark Theory of Big Bang" to "Space Ripples Reveal Big Bang’s Smoking Gun" . Perhaps someone made the same complaint to the NYTimes that I am making here: this measurement is not about big bang, and conflating them is at best misleading, but more likely just wrong.

So I have removed the phrase "and for the Big Bang." from the sentence which read "BICEP2 collaboration announced the detection of inflationary gravitational waves in the B-mode power spectrum, apparently providing strong evidence for Guth's theory of inflation, and for the Big Bang". I have also updated the title of the NYTimes article. -lethe talk [ +] 03:45, 23 March 2014 (UTC)

Reverts
Hello IP editor. Science20.com is not a reliable source. Next time you try to add that back, I will report you for edit warring and your account could get blocked. If the fact is notable you should be able to find evidence of it in a reliable source. Jehochman Talk 12:46, 27 March 2014 (UTC)


 * Edit warring continues under various IP addresses. Maybe this page should be semi-protected ? Gandalf61 (talk) 10:58, 28 March 2014 (UTC)


 * Submitted request for protection. Aldebaran66 (talk) 16:00, 28 March 2014 (UTC)


 * Who needs "protection" ? Objective information needs protection, instead of suppressing any "disturbing" contribution. Of course, one can understand that nowadays universities and institutions need money and make a lot of propaganda. But Wikipedia should not follow any scientific "party line".

I semiprotected the article in response to the request. Please check the article and see if the current version is OK. --Orlady (talk) 04:34, 29 March 2014 (UTC)

timeline of the discovery
I just looked at Alan Guth's original PRD paper and found that it was published on January 198*1*, though it was received on Aug 1980. Both the published/received dates of all the early contributions should be checked. — Preceding unsigned comment added by 60.43.120.31 (talk) 22:56, 29 March 2014 (UTC)

Lede - needs edit
The following appears in the lede: "As a direct consequence of inflation, the Universe appears to be the same in all directions (isotropic) and the cosmic microwave background radiation is distributed evenly." This is exactly wrong. (The Theory of ) Inflation is a consequence of our observations, NOT the other way around. It is NEVER correct to claim a theory results in observations.173.189.77.96 (talk) 20:43, 13 April 2014 (UTC)
 * The problem results only from your insertion of the words "theory of". The physical phenomenon "inflation" certainly can lede to observations. "The theory of" inflation as you would put it, simply is the hypothesis that inflation happend in the early universe. And you are correct that one of the reasons to posit this hypothesis is that it explains why we observe the universe to be isotropic at large scales.
 * Your last assertion is manifestly wrong. E.g. It is quite correct to assert that: "the theory of spontaneous symmetry breaking has led to observation of the Higgs boson." (i.e. theoretical predictions are often a reason to look for certain things).TR 08:43, 14 April 2014 (UTC)
 * I disagree with your claim that inflation is a physical phenomenon. Inflation is, by your claim, real and hence irrefutable, correct?  Please cite a single peer reviewed source that has made this amazing (theological) claim.
 * The article should state that IF inflation happened then it would result (as we now understand it) in a Universe with an appearance similar to ours. As far as your assertion that theory leads to observation, you're just logic-chopping; but you may be right that for the average reader such a narrative device is useful. Were both WWII and Yang-Mills "significant" in "leading" to the LHC? What historical fact did not "lead" to it?  I also note that inflation is not well constrained enough to qualify as Theory of Physics (in the formal sense, and as (well) described in the lede). I maintain my STRONG objection to any statement that ANY facts are consequences of ANY theory.216.96.79.20 (talk) 16:05, 21 April 2014 (UTC)
 * lol.TR 21:36, 21 April 2014 (UTC)

Inflation theory was devised by Alan Guth AND Andrei Linde.
The ingredients for inflation theory were laid by Andrei Linde, afterwards Alan Guth proposed his theory (which was wrong in a way) and months later Andrei Linde developed THE Inflation Theory as we know it today.

So I think the second paragraph of the article should be modified. — Preceding unsigned comment added by 189.128.157.149 (talk) 08:41, 11 May 2014 (UTC)

Lede - "strong" evidence - BICEP2
I have made 3 changes to lede: 1. I moved the BICEP2 results to the end, it doesn't belong where it was, I think, simply because the dust hasn't settled yet. Its important but the study as of June 1, 2014 is still not even complete. (The part of the paper on systematics have been (supposedly) "submitted" but not yet 'accepted' by an 'undisclosed' journal.) 2. I removed 'apparently', since I think this qualification is unnecessary here. If the BICEP2 results turn out to be wrong, the discussion of them will (most likely) be removed from the lede completely, we don't need to couch it this way. (But I have no strong objection to a revert to add it back if it is believed to somehow aid in understanding). and 3. Please see the talk page of Inflationary Epoch, where I made the same change. Briefly, as of June, '14 the evidence is NOT looking "strong". So I changed "strong evidence" to "the first clear experimental" evidence. I also added a reference to one blog which has consolidated a lot of more robust sources (both for the criticism and of responses to it). Add to that the problems with foreground (and possibly lensing) then it is clear that it is not, YET, strong evidence. note: I am not committed to using "clear" rather than "direct", but it seems to me that power spectrum of b-mode polarization effects of g-waves is less than direct evidence.Abitslow (talk) 21:49, 1 June 2014 (UTC)
 * Weakening the text for now like you've done sounds reasonable, since there do seem to be minor but notable reports of caution, for example and . Not wild about using Woit's blog as the go-to source for further information; let's avoid making a habit of it in the future. Rolf H Nelson (talk) 03:33, 2 June 2014 (UTC)

FTL expansion?
The first sentence of the introduction describes inflation as a period of faster-than-light expansion. I find this at best misleading. Metric expansion does not involve the FTL movement of objects in the sense of propagation (e.g. of waves) in the space. If we mean the increase in distance between hypothetical far-apart objects over time, then any metric expansion could be dubbed superluminal if we pick two objects which are far enough apart, since apparent relative velocity is basically

velocity = Hubble * distance

Did the original author want to allude to the fact that for this kind of exponential expansion, the comoving horizon becomes smaller? But that's not the same thing as FTL movement.

My main worry is that due to the choice of words "faster than light" in such a prominent location, it lets inflation appear to be in conflict with relativity to the casual reader, while it really isn't. Aknochel (talk) 09:59, 13 May 2014 (UTC)

Ok, since noone had any comments, I've deleted the statement about faster than light and put a more general "rapid" Aknochel (talk) 22:02, 30 May 2014 (UTC)


 * Sounds good to me. Technically the current universe is still expanding faster than light anyway, although there's an obvious difference between the current universe where only regions of billions of light-years are expanding faster than light, and the inflationary universe where much smaller regions are expanding faster than light. Rolf H Nelson (talk) 03:23, 2 June 2014 (UTC)

I do agree with Rolf Nelson but the word rapid is vague. Rapid is used for different things for a car or someone running. i don't see how the word rapid is better than faster than light, beside book written by Tegmark, Guth, Brian Greene, Alex Vilenkin, Michio Kaku and Joao Magueijo use "Superluminal or faster than the speed of light expansion" for inflation and they are expert in their field. Rod 02.06.2014 — Preceding unsigned comment added by 151.230.92.188 (talk) 10:13, 2 June 2014 (UTC)
 * Do you have a particular reference in mind? NASA states "The Inflation Theory proposes a period of extremely rapid (exponential) expansion of the universe during its first few moments" and Tegmark summarizes it as "The repeated doubling in size of an explosive subatomic speck of inflating material", so I'm fine with leaving the "faster than light" until after the lede. Rolf H Nelson (talk) 05:09, 4 June 2014 (UTC)

Max Tegmark in his book "Our Mathematical Universe" mentioned a " Large speed of many billion ligth-years per day" to describe inflation. Magueijo (faster than the speed of light book) and John Moffat (Reinventing gravity) talk of superluminal expansion. Michael turner talk of superluminal expansion in most of his academic papers. Michio Kaku (parallel worlds) use faster than light expansion.the list isn't exhausive. Rod
 * Any attempt to characterize inflation by a speed is misguided and completely misses the point. The reason that inflation does what it does, is due to acceleration of the expansion. This has been fixed in the lede, can we stop this discussion now?TR 08:17, 4 June 2014 (UTC)

How can inflation smooth out initial inhomogeneities?
Can someone explain why an exponential expansion shouldn’t just enlarge the scale of initial inhomogeneities –instead of smoothing them out as the inflation is designed to do?Antonquery (talk) 03:28, 28 April 2014 (UTC)
 * Don't understand the question. Unless it's a fractal (which some critics like Penrose say it could be), enlarging a scale generally smooths it out. Rolf H Nelson (talk) 03:51, 29 April 2014 (UTC)
 * Would you please explain why enlarging a scale smooths out inhomogeneities? Antonquery (talk) 07:41, 9 May 2014 (UTC)
 * Simply put, unless its fractal, inhomogeneities have a minimum length scale. Given enough e-foldings of inflation this length scale becomes larger than the observable universe. The result an observable universe that has no inhomogeneities. tadaTR 11:55, 9 May 2014 (UTC)
 * I still don’t get it and the e-folding page also isn't much help. If and when e-folding actually does smooth out inhomogeneities, then does this mean that the reverse process creates inhomogeneities? Antonquery (talk) 01:24, 10 May 2014 (UTC)
 * Unless the universe is fractal, There are a finite number of inhomogeneities in a given unit volume. Therefore the universe post-inflation has fewer inhomogeneities per unit volume than before inflation, and is therefore smoother. The reverse process doesn't create inhomogeneities, but rather clusters them together. Rolf H Nelson (talk) 23:49, 24 May 2014 (UTC)

The idea is not that inflation evened out the universe, but that initially sides of pockets which were in thermals equilibrium before inflation are first exponentially stretched during inflation and then allowed to expand in the currently expanding semi-linear way. This explains why the universe is so homogeneous, except for quantum fluctuations. — Preceding unsigned comment added by 2001:470:D076:0:D13B:9478:F114:A430 (talk) 17:13, 1 June 2014 (UTC)
 * Do you mean that the present observable universe originates from a small area which before inflation already was quite homogeneous, an area surrounded by regions with a quite different energy density or temperature which due to inflation were pushed out of view?
 * So if the expansion of the universe wouldn’t accelerate but decelerate, these regions with a different temperature/density eventually would become observable –so at scales much larger than the observable universe, it still would be inhomogeneous? Antonquery (talk) 01:05, 2 June 2014 (UTC)
 * That is the basic idea, yes. Rolf H Nelson (talk) 03:16, 2 June 2014 (UTC)

Wow: so if the pre-inflation area which presently is our observable universe bordered on an area with a quite different density, then an observer at the rim of our observable universe (who sits at the rim of our observable universe) would observe a universe which at one side looks totally different from the other –so his observable universe would be quite inhomogeneous, which makes me wonder what cosmology he might develop. I really can’t believe that we are the lucky sods who find themselves in a homogeneous universe –especially as this would contradict the cosmological principle. Antonquery (talk) 12:51, 3 June 2014 (UTC)
 * Not quite; the current inflationary theories postulate an inflationary regime over a volume many orders of magnitude larger than what became the observable universe. Further, most published scenarios leave us causally disconnected from the bulk of the universe. Shmuel (Seymour J.) Metz Username:Chatul (talk) 20:16, 3 June 2014 (UTC)

Well, never mind how many orders of magnitude; if there are areas adjoining each other of different densities, then there must be many observers who find themselves in such border regions and observe their universe to be inhomogeneous. Antonquery (talk) 02:37, 4 June 2014 (UTC)


 * As, I have told you many times before this is not a place to discuss physic. For the record, the statement you make only works if there were a perfectly sharp transition between the two regions, which is unphysical. In reality, there would always be a gradient. And the slope of that gradient would be flattened out by inflation to the extend that even an observer in the gradient region could not distinguish it from flat (and homogeneous). Now, if you want to discuss this any further I suggest you go somewhere else.TR 08:24, 4 June 2014 (UTC)

"a number of predictions that have been confirmed by observation (7)" - this statement is contradicted by the very paper cited
Tsujikawa's 2003 review states "we are living in an exciting era where the early universe models can be strongly constrained from the upcoming observational data." and nowhere mentions predictions confirmed. In other words, it not only does not support the statement "the basic picture makes a number of predictions that have been confirmed by observation" but contradicts it, and offers a different opinion.

How about changing that statement to something like 'Researchers hope that future observational data will shed more light on the evolution of the early universe'? -(unsigned comment by 88.91.220.46)


 * It certainly doesn't "contradict the paper cited". Here's a quote: "Thus perturbations imprinted during inﬂation can be the origin of large-scale structure in the universe. In fact temperature anisotropies observed by the COBE satellite in 1992 exhibit nearly scale-invariant spectra as predicted by the inﬂationary paradigm. Recent observations of WMAP also show strong evidence for inﬂation [11]."  Waleswatcher  ( talk ) 00:08, 8 June 2014 (UTC)

Photon number density at the end of inflation
I am quoting from the textbook of Barbara Ryden "Introduction To Cosmology", page 206:

"Not only is inflation very effective at driving down the number density of magnetic monopoles, it is also effective at driving down the number density of every other type of particle, including photons."

According to the textbook, at the end of inflation, photon number density becomes negligible. It is only after reheating, the photon number density grows back up. Do you have any source for your counter remark that photon aren't negligible at the end of inflation? Thanks for your information.--老陳 (talk) 06:00, 12 June 2014 (UTC)
 * You are correct, I didn't consider that reheating is logically a different phase, after inflation. Rolf H Nelson (talk) 01:05, 15 June 2014 (UTC)

Was inflation faster then light or was light slower then ?.
Just to be sure, inflation refers to a time area in the history of the universe. In which it expanded faster then light. Do we mean here as compared to: The theoretical max speed of light in empty space. Or to the theoretical max speed of light in a medium (dense space / plasma). A recent article posted everywhere on the web now also point out that light itself doesnt travel at its max speed due to quantum effects photons convert to electrons and back again. So despite such factors and the time area when space wasn't empty.Would inflation still have been faster as the C lightspeed. Or if light traveled slower would it simply mean that our universe is older (and thus inflation has not happened). — Preceding unsigned comment added by 84.107.183.36 (talk) 11:04, 25 June 2014 (UTC)


 * We mean the fundamental constant c, the speed of light in a vacuum. More precisely, we mean the fundamental constant c in General relativity relating units of length to units of time, which conventionally is assumed to be equal to the propagation speed derived from Maxwell's equations. Shmuel (Seymour J.) Metz Username:Chatul (talk) 20:54, 25 June 2014 (UTC)

Expansion speed of the universe and light speed
Due is universally accepted that the light speed (the electromagnetic radiation for to be more precise) is a universe constant that can´t surpase in the vacumm a value of 299.792.458 m/s according the latest measures.

Also regarding that all the information that we have shows that the universe at great scale is homogeneus and isotropic there are two concepts that at simple sight collide in an evident way:

1) The universe is expanding in an acelerated way, what means that galaxies separated each other from very wide distances are moving away each from the other at a speed faster than the light speed.

2) The speed of the light is a constant of the universe.

3) Considering the observations, it is logic to supose that the matter and energy that compose the universe is homogeneous.

There are in this article many theories and counter-theories that explain how the universe is or could be, avoiding to explain or deal with this huge contradiction that don´t require to be a genius in mathematics or physics for to see it. — Preceding unsigned comment added by 190.177.211.129 (talk) 20:35, 25 July 2014


 * You've found that an expanding universe can't happen within special relativity. That's perfectly true.  Special relativity is a subset of general relativity.  General relativity describes many things that can't happen in special relativity -- for example, gravitational redshift, which can be verified in laboratory experiments.  Another thing that can't happen in special relativity is an expanding universe, which implies a Hubble volume.  There's no question of objects moving faster than the speed of light, but instead, space itself expands.  It is a perfectly straightforward possibility in general relativity.  --Amble (talk) 21:53, 25 July 2014 (UTC)

--

I understand the problem of redshift, Doppler effect and gravitational lens, but we known that exist visible and very far galaxies that is probably that in a certain future will not more be visible for us due they will fall out of the "horizont of events" due they are moving away from us at a higher speed than the light, the problem is the following.

The geodesic that separate us from the far galaxy has in some way changed his length due this object can not be seen more, but the disappearance of the object is not due to a decrease in the size that becomes it invisible but due it is falling out of the horizon of events.

Only objects moving away from us at a speed higher than the light can fall out of the horizon events. But in what place of the space-time has happen a discontinuity of the physical laws for to say that this object, the far galaxy, is not part of our local system? — Preceding unsigned comment added by 190.177.211.129 (talk) 23:17, 25 July 2014


 * Please sign your posts. (It makes it easier for others to follow the conversation, and unlike some other online systems it doesn't happen automatically.)  You can do this by typing this at the end of your message: --~ .  It gets automatically converted to a signature like this: --Amble (talk) 23:24, 25 July 2014 (UTC)


 * What you need to understand is metric expansion of space. Without this you're trying to describe the horizon essentially in terms of special relativity, which is not adequate.  You need general relativity.  The metric expansion involves no motion of objects, no discontinuity, no geodesic connecting us to a galaxy sufficiently far away. --Amble (talk) 23:30, 25 July 2014 (UTC)

Amble, in the future i will post with user:pef890 (newly opened my account yesterday) I have read carefully the article about the "metric expansion of the space" and also have re-read the Einstein´s general relativity theory, that in general I understand (or I think so, regarding my limits in knowledges of topology).

Looking to the "Talk" section of the article, not only myself found severe doubts about the consistence of this theory (metric expansion of the space) but many other on different aspects that I myself didn´t have considered.

But I want to center my objections in two points that look established as true at the same time but have intrinsec contradictions each with the other.

1) The universe has not center. 2) The universe is or looks actually flat and is expanding (acelerated expansion) in all directions at the same time.

Try to imagine an expansion of particles that happen at the same time from only two expansion center (for example two explosions). You will find that´s unavoidable, past a certain time, that particles from one expansion center will approximate or possibly collide with the particles of the other expansion center.

To say that the universe has no center and at the same time that it is expanding equally in all directions, is like to say that there are infinite infinitesimal expansion centers.

Please tell me how the particles will run away far one of each other without approximating or colliding mutually in high proportions.

Another objection, considering that the metric expansion of the universe is related with the elasticity of the time dimension, is that this phenomena is not observable our local system (considered as all the galaxies that can mutually interact with their gravity field).

If we discard the "magic" objection to the invisible, untouchable, unreacheable and unfindable "concept" called "dark energy", that´s supposed that fills all the vaccum space but that nobody has found traces up today.

There should be a trancisional part of the space where the gravitational action of the galaxies cedes influence to dark energy, but oh! problem: the space is homogeneous and isotropic, so it does no matter how far we go, we will find, at galaxy scales, a mutual continuous influence of gravity of the galaxies.

So, where is the part of the space in where dark energy takes the command and expands the universe at a higher than light speed? — Preceding unsigned comment added by Pef890 (talk • contribs) 01:53, 28 July 2014 (UTC)

Dear Pef890, Thanks for creating an account. I hope you'll enjoy editing a variety of articles. You ask: Please tell me how the particles will run away far one of each other without approximating or colliding mutually in high proportions. The answer is again that what's happening is a metric expansion of space, and not a motion of particles within static space. All of the distances between all of the particles increase proportionally. It immediately follows that there is no reason for any such collision. You also ask: So, where is the part of the space in where dark energy takes the command and expands the universe at a higher than light speed? As far as we are able to determine, dark energy acts uniformly at all points in the universe, not only in one part or another. However, it is typically rather negligible within bound systems such as galaxies, where the mutual gravitation among the bound bodies easily overcomes the effect of dark energy. Such bound systems therefore do not expand appreciably as a result of the accelerating expansion of the universe. In a Big Rip scenario this would no longer be the case, and clusters, then galaxies, then solar systems, then eventually atoms would be torn apart. --Amble (talk) 21:55, 31 July 2014 (UTC)

BICEP2 Results
In theoretical status under Andrei Linde section there's a sentence related to BICEP2 results that currently states: The BICEP2 experiment detected evidence for primordial gravitational waves consistent with Linde's model. Given the current uncertainty of BICEP2 results, a statement that evidence of gravitational waves have been detected by BICEP2 seems wrong or at best too early to tell. Some of the other references to BICEP2 results in this page seem at least slightly questionable if not as clearly premature as the sentence quoted above. Have not (cannot) made edits since the page is protected. Tunkki-1970 (talk) 12:17, 18 October 2014 (UTC)
 * ✅ - Thank you for your comments - *entirely* agree with you - rm your noted sentence - welcome further suggestions - in any case - Thanks again - and - Enjoy! :) Drbogdan (talk) 12:51, 18 October 2014 (UTC)

Contradicts other articles!
This article states (I quote):

"In the standard hot big bang model, without inflation, the cosmological horizon moves out, bringing new regions into view." (And I would guess that this is supposed to happen also WITH inflation!)

But in the Big Bang article instead we can read: "Modern observations of accelerating expansion imply that more and more of the currently visible universe will pass beyond our event horizon and out of contact with us."

I sense an act in bad need of cleaning up! This article could e.g. refer to a Hot big bang article that would support its statement, and clarify the issue .... Hilmer B (talk) 18:16, 25 October 2014 (UTC)


 * I suggest changing the statement here to read "...without inflation (nor any acceleration of the expansion prior to our current era), the cosmological horizon would have moved out..." This would explain away the seeming contradiction, but perhaps that would make the overview the overview too wordy?50.174.178.168 (talk) 16:00, 14 June 2015 (UTC)

Description of Einstein Universe is misleading
The Einstein Universe is the first thing described in the subsection on precursors to inflation (under History). It is described there as a "three-dimensional sphere with a uniform density of matter." A 3-sphere is meant; but, for the overwhelming majority of readers, the existing language will conjure up an image of a 3-dimensional ball of material suspended within empty 3-dimensional space, whereas Einstein's model actually distributed matter throughout a 3-dimensional "surface" bounding a 4-dimensional hypersphere. As such, space in Einstein's model had no centre and no edge, in accordance with all modern cosmological models. I suggest changing "three-dimensional sphere" to "three-dimensional "surface" of a four-dimensional hypersphere" with the word hypersphere linking to the article describing what a 3-sphere is. (Wikipedia has a separate article defining a hypersphere more generally, but that article currently looks very confusing to non-experts, and I feel it would be much better to link to the specific 3-sphere example that Einstein used in his model.)50.174.178.168 (talk) 16:38, 14 June 2015 (UTC)

Eternal Inflation before Big Bang
I don't think the broad opening statement should place inflation after the Big Bang. I don't know precisely which versions place it before or after, but I've hear Max Tegmark say the theory doesn't work if you put it after the Big Bang, and Alan Guth describing inflation as a theory of what banged and how it banged. I thus, understood all inlation models to be an attempt to explain the Big Bang, so I am greatfull to this page for the detailed census of various inflation models. Inflation after the Big Bang doesn't get rid of the singularity/energy conservation problem as in Guth's "ultimate free lunch" I understand inflation prior to the Big Bang along with quantum fluctuations (claimed to be imprinted in the CMB) necessarily implies eternal inflation After further reading, I suggest a re write opening statement that allows or presumes "Big Bang" theory refers to be FLRW solution to Einstein's equations that runs the universe backwards toward a singularity. Going backwards, before you reach singularity Big Bang theory breaks down and enters realm of the quantum. Inflation is a theory of the early universe in the quantum realm when the Big Bang "discription" does not apply. I think we can still use the term Big Bang as a broad term for the universe's narrative, but in this sense also, it does not to make sense to place inflation after the BB. BB should not be about the beginning as there was no bang and it wasn't big. NOW huge galaxies moving apart with respect to each other faster than light, Big Bang seems a better definition of the universe we now live in. Before inflation Max Tegmark described the approx size of the universe as much less than a proton, and mass of a few grams, a substance, an energy, of invariant density such that it's mass/energy increases in step with volume increase. But definitely no singularity. — Preceding unsigned comment added by Andrewboychurch (talk • contribs) 03:48, 29 June 2015 (UTC)

Andrew Church (talk) 23:54, 28 June 2015 (UTC)

Pet theory
"Inflation and generalized uncertainty principle" appears to be a pet theory and not established in the standard theory. (Moreover it links to a personal webpage which seems inappropriate.) This section detracts from the article and should be remove. — Preceding unsigned comment added by 107.1.169.29 (talk) 21:39, 27 September 2015 (UTC)

Predictions?
In the introduction it says "the basic picture makes a number of predictions that have been confirmed by observation.[3]". Nevertheless, in the source no such prediction is mentioned. — Preceding unsigned comment added by Ryanexler (talk • contribs) 13:58, 29 September 2015 (UTC)
 * It does mention a couple of predictions in the text that is also quoted in the footnote. However, it is a rather old source and not the best one to support this particular sentence. --Amble (talk) 20:49, 29 September 2015 (UTC)

Inflationary theory introduction
Given the audience of Wikipedia, it is probably worth mentioning in the introductory paragraph that an inflationary epoch is theoretical. Richardbrucebaxter (talk) 22:07, 30 September 2015 (UTC)

Geometric Algebra
The mathematics of space-time are described fairly accurately by geometric algebra (GA). One interesting feature of using GA for describing a 4-dimensional space-time is that all characteristics of an object's state or of an interaction between two object are use the same basic math. That math implies that when a photon impacts an object there are two consequences. the first is that the object gains some momentum. The other is that the amount of space-time increases. If that is true then while there was a large number of light-matter interactions in the begining of the universe, the volume of space-time should have increased in proportion to the number of interactions. When the matter became nutral and the light interaction diminished, the increase in the volume of space-time should have slowed considerably. When stars formed and re-ionization started, the increase in the volume of space-time should started increasing again.

Does anyone have details to this that can add it to this article? 198.203.213.6 (talk) 14:39, 5 October 2015 (UTC)

Semi-protected edit request on 6 November 2015
I'd change

"These models propose that while the Universe, on the largest scales, expands exponentially it was, is and always will be, spatially infinite and has existed, and will exist, forever."

to

"These models propose that, while the Universe, on the largest scales, expands exponentially, it was, is, and always will be spatially infinite and has existed, and will exist, forever."

because abusing commas is sad. =( this is a rather complicated sentence. It contains an independent clause with two interrupters stuck inside it inceptions style, a list, and a dependent clause added to the end that also has it's own interrupter. It's no wonder they had trouble writing it out. I guess the sentence could be reduced to something less complex, but it's corrected version is completely legit grammar-wise, and i kind-of like it that way; it makes me laugh. though clarity may call for the first interrupter to be rewritten as

"..., while the Universe expands exponentially on the largest scales, ..."

Note: Some people don't put the serial comma before the 'and' in a list, but i think it's both harmless and potentially useful, especially in a case like this where the writer is attempting to communicate a specific flow. Then again, this may require a more formal version, but I'll leave that to the editor.

Wulframm (talk) 02:55, 6 November 2015 (UTC)
 * Padlock-silver-open.svg Not done: According to the page's protection level you should be able to edit the page yourself. If you seem to be unable to, please reopen the request with further details. Mdann52 (talk) 19:32, 28 November 2015 (UTC)

Inflation before or after Big Bang??
I'm just a reader, but I'm reading 13.8 by John Gribbin, and I'm puzzled why this article says that the Inflation period occurs after the Big Bang, but he is clear and pointed that it occurred prior to the Big Bang. A quick search to verify I'm not reading a typo in his book confirms as much.

If there is debate on the topic, this article should touch on it. I'm left to assume this is an error within the Wiki article.

Also: http://scienceblogs.com/startswithabang/2010/01/12/q-a-did-inflation-happen-befor/

Tonic5 (talk) 03:50, 3 October 2016 (UTC)


 * This is mostly a terminology issue. There is no clear consensus on what is meant with "the Big Bang". Possibilities, among other things include the initial singularity (if it exists at all) and the reheated phase right after inflation, depending on what definition you use can can happen before or after inflation. (I think you can probably make a case for calling inflation "the big bang".) To make things worse this ambiguity is not usually discussed explicitly in the literature, making it difficult to write a section on Wikipedia about it based on reliable secondary sources. I agree it would be a good thing for such a section to exist, and if you have found good sources discussing it, have at it, be bold.TR 13:33, 3 October 2016 (UTC)

Thanks Timothy. I have no problems being bold, but as I'm just trying to understand the topic for myself I feel I hardly have a place explaining it to others. I take your point about calling inflation part of "the Big Bang" but it seems there's actual dispute about the actual sequencing, and moreover it seems that some consider the distinction significant.

Gribbin says: "Guth realized that a process called symmetry breaking ... could have poured out energy in the first split second of time, pushing the Universe through a phase of rapid expansion, which he called inflation, and ending up with the Big Bang.  (People often make the mistake of using the term Big Bang to include inflation, but the crucial point is that inflation came before the Big Bang" (italics Gribbin's)

All that I have is a book by this guy, and a link to an article written by a man whose claims to credibility include owning a "nationally renowned beard" and having been courted by the circus (and also a PhD in theoretical astrophysics.) Tonic5 (talk) 22:35, 3 October 2016 (UTC)


 * Andrei Linde uses the "big bang" to mean the singularity: . Guth 1981 just calls it the initial singularity. If there's confusion, I've clarified it to mean singularity. Rolf H Nelson (talk) 03:29, 4 October 2016 (UTC)

Remove adjective "supercooled" from reheating section, or clarify?
I think the term "supercooled" may only apply to "old inflation", not to new inflation (aka slow roll inflation).

The section on Reheating says "Inflation is a period of supercooled expansion, when the temperature drops by a factor of 100,000 or so. […] When inflation ends the temperature returns to the pre-inflationary temperature; this is called reheating or thermalization.”

This makes it sound like all inflation models involve a supercooled state (where there is a metastable state which is forbidden from decaying classically into a more stable state). But slow roll inflation works differently. Seems like either the adjective supercooled should be removed, or some clarification should be added to indicate this is how it works in old inflation but not new inflation. (Although reheating occurs in both cases.)

For more, see: https://www.quora.com/In-what-sense-does-cosmic-inflation-represent-a-supercooled-state/answer/Jeff-L-Jones — Preceding unsigned comment added by Spoonless (talk • contribs) 02:02, 25 October 2016 (UTC)

Add all theories
Dark energy is a fact. Inflation a the future extreme effect of dark energy. Mention all opinions, and focus on actual data. We have actual data ONLY about dark energy. Of course we need inflation, but as an extreme dark energy due to future conditions. We don't mention all theories.


 * No, dark energy is a plausible inference from observed supernovae. Other exploanations are possible, although IMHO they are less likely. Shmuel (Seymour J.) Metz Username:Chatul (talk) 20:21, 1 May 2017 (UTC)


 * It also certainly not a proven fact that the "dark energy" inferred from various measurements has equation of state parameter w=-1. Depending on the exact value of w different future scenarios are possible including deSitter-like phase if w=-1. This would still not be inflation though. "Inflation" refers specifically to a de Sitterlike phase preceding the current matter/energy dominated phase. One if it key properties is that it comes to an end at some point.TR 14:40, 2 May 2017 (UTC)

Horizon is transient
It is not generally true that in an expanding universe regions beyond the cosmological horizon must remain forever unobservable. However, in a Accelerating universe the horizon is a permanent limit, and we appear to live in such a universe. Shmuel (Seymour J.) Metz Username:Chatul (talk) 17:15, 25 May 2017 (UTC)

Semi-protected edit request on 12 July 2017
Please change, in paragraph 3 "The hypothetical field thought to be responsible for inflation is called the inflaton.[7]" to "The hypothetical field thought to be responsible for inflation is called the Higgs Field.[7]

Source: The Inflationary Universe - Alan Guth 94.119.64.8 (talk) 15:03, 12 July 2017 (UTC)
 * Yes check.svg Done jd22292 (Jalen D. Folf) (talk) 15:35, 12 July 2017 (UTC)


 * Please change "The hypothetical field thought to be responsible for inflation is called the Higgs Field.[7]" back to "The hypothetical field thought to be responsible for inflation is called the inflaton.[7]" in paragraph 3. The inflationary hypothesis does not assume that the Inflaton is a Higgs Boson, and current data do not support the idea that the Inflaton is the Higgs Boson. Shmuel (Seymour J.) Metz Username:Chatul (talk) 17:27, 12 July 2017 (UTC)
 * Edit-undo.svg Undone: This request has been undone. Additionally, I'd be in trouble if this turns into an edit war. jd22292 (Jalen D. Folf) (talk) 20:12, 12 July 2017 (UTC)

External links modified
Hello fellow Wikipedians,

I have just modified 2 external links on Inflation (cosmology). Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
 * Added archive https://web.archive.org/web/20120130063002/http://astrophysics.fic.uni.lodz.pl/100yrs/pdf/07/060.pdf to http://astrophysics.fic.uni.lodz.pl/100yrs/pdf/07/060.pdf
 * Added tag to http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+EPRINT+HEP-PH%2F9606387
 * Added tag to http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+EPRINT+HEP-PH%2F9807278
 * Added archive https://web.archive.org/web/20041120175509/http://www2.iap.fr/Conferences/Colloque/col2004/Docs/20040628_liddle.pdf to http://www2.iap.fr/Conferences/Colloque/col2004/Docs/20040628_liddle.pdf
 * Added tag to http://www.symmetrymag.org/cms/?pid=1000037

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

Cheers.— InternetArchiveBot  (Report bug) 19:39, 13 November 2017 (UTC)

Spelling and Punctuation
These may be very minor points in this complicated topic, but "dissention" under "Eternal Inflation" is spelled incorrectly. Also, there should be a period between "1983" and footnote 99 instead of a comma in the next sentence. Finally, the formatting for ellipses in the "Criticisms" section is not consistent between the second and third paragraphs. — Preceding unsigned comment added by 50.1.78.130 (talk • contribs)


 * See WP:BOLD. Headbomb {t · c · p · b} 22:29, 22 May 2018 (UTC)


 * Ah, the page is semi-protected. I've updated the article with your feedback. If you see other things (or if I missed something), let us know! Headbomb {t · c · p · b} 22:31, 22 May 2018 (UTC)

In the second paragraph, it reads "no magnetic monopoles have been observed." "No" and "none" are singular terms so it should read "no magnetic monopole has been observed."

Overview section claims only one scalar field known
To quote, "No physical field has yet been discovered that is responsible for this inflation. However such a field would be scalar and the first scalar field proven to exist was only discovered in 2012 - 2013 and is still being researched." How can this be true? Off the top of my head, I can think of other scalar fields such as the electric potential, gravitational potential, temperature ... Banedon (talk) 06:17, 3 September 2018 (UTC)


 * That depends on what you mean by a "scalar field". When you're dealing with Cosmology or high energy particles, you pretty much have to take Relativity into account, and you must treat the "electric potential" and "magnetic potential" as artifacts of a particular coordinate system rather than fields in their own right; the actual physical entity is the Electromagnetic four-vector potential. Similarly with Gravitation, there is no scalar gravitational potential in General Relativity.


 * As for temperature, it is not a fundamental field, but a statistical aggregate.


 * Of course, composite particles like the Pion can be approximated as scalar fields, but that breaks down at high energy. Shmuel (Seymour J.) Metz Username:Chatul (talk) 10:35, 3 September 2018 (UTC)
 * I'd suggest editing that clarification into the article, then. Banedon (talk) 04:32, 4 September 2018 (UTC)

Space expands
This sentence is not lucid:

"This process of falling outward and replacement points closer in are always steadily replacing points further out—an exponential expansion of space–time."

Is the process of falling outward, like the replacement points closer in, replacing points further out? Processes are almost completely unlike points - I'm sure that's not what it means, but that's what it says. The article is hard enough to understand without patent nonsense like this. Can someone who knows what this sentence is supposed to mean please fix it? Otherwise, in the fullness of time I will delete the sentence in accordance with WP:BOLLOCKS.

More broadly (and more ambitiously) it would be massively cool if someone who really understands this subject could provide a layman's explanation, comprehensible to someone who could understand (say) Einstein's thought experiment, is familiar with Hubble's discoveries, and has a layman's knowledge the Standard Model. MrDemeanour (talk) 13:41, 14 October 2018 (UTC)

Space expands (bis)
It says:

"To say that space expands exponentially means that two inertial observers are moving farther apart with accelerating velocity."

That appears to me to be an idiosyncratic use of the term 'exponential', a term that has a precise mathematical definition (and no non-mathematical definition that I am aware of). It doesn't normally mean 'increasing' or 'accelerating', it normally means that the rate of increase is proportional to the instantaneous magnitude. So is the above sentence wrong, or is the term 'exponential' used differently when discussing cosmic inflation from its use in other fields? Or is my understanding of the term 'exponential' incorrect?

This is rather important, because all short definitions and explanations of cosmic inflation make use of the term.

Perhaps we should just add 'in very simple terms' to that sentence, to make it clear that we are not using language precisely; but then I guess we should replace the term 'inertial observer' with something that can fairly be described as a 'very simple term'.

I would try to fix this issue, but (a) I am a layman, not a trained scientist, and (b) I have always had a hard time swallowing this theory, which probably exposes the fact that I don't understand it. MrDemeanour (talk) 13:56, 14 October 2018 (UTC)

Inflation and the need for a Big Bang singularity
At the start of this article it is suggested that an inflationary phase is inserted into the Big Bang cosmology at a very early time, and it may well be that this is how it was originally envisaged. However, these days I understand it is recognised that the existence of inflation obviates the need for a singularity. For example, the "eternal inflation" model certainly does not have a singularity preceding the inflationary phase: rather inflation is the norm and the phase of the Big Bang that emerges from inflation is hypothesised to occur within this unending background.

Of course the reason the singularity at the beginning of the Big Bang was originally identified as a (problematic) feature of the model was that this was the result of the extrapolation of known physics to the extreme. Once inflation is added, this extrapolation does not lead to the same conclusion, so it seems that once inflation is added, it is inappropriate to suggest that we have any motivation to believe in a singularity (or something to replace this singularity) before the inflationary epoch.

So aren't cosmologies with a singularity preceding inflation a historical hang over, rather than being genuinely scientifically motivated? Elroch (talk) 17:41, 22 September 2018 (UTC)
 * I don't think inflation obviates the need for a singularity. One can construct models which doesn't have a singularity of course (see e.g. big bounce) but these models can exist even without inflation, and they're not standard right now. The standard model of cosmology is Lambda-CDM, which keeps the initial singularity. Banedon (talk) 02:07, 24 September 2018 (UTC)
 * Elroch, you wrote "For example, the "eternal inflation" model certainly does not have a singularity preceding the inflationary phase". That is not remotely certain, see for instance https://arxiv.org/abs/gr-qc/9312022 that concludes the contrary.  Waleswatcher  ( talk ) 18:47, 25 September 2018 (UTC)
 * This paper is about the implications of a classical model and discusses in its conclusions the issue of incorporating quantum mechanics (never mind quantum gravity). A more balanced view is to be found summarised in a nice article by Ethan Siegel https://www.forbes.com/sites/startswithabang/2018/07/27/there-was-no-big-bang-singularity/#42e902d17d81 . I understand that most relevant physicists would agree that quantum gravity makes singularities impossible because there is a smallest scale that is meaningful - the Planck scale. Here is a an article summarising the conclusions of more sophisticated reasoning about a similar result: https://www.newscientist.com/article/dn23611-quantum-gravity-takes-singularity-out-of-black-holes/ . String theorists have arrived at the notion of a Fuzzball_(string_theory) which replaces a singularity. It does seem that singularities are the result of extrapolating mathematics too far rather than being physical. Elroch (talk) 11:17, 23 October 2018 (UTC)
 * Siegel's article doesn't say there was no singularity before inflation. It says there might not have been one ("There may have been a singularity at the very beginning of space and time, with inflation arising after that, but there's no guarantee"), and that it's hard to find out.  Our article currently says "The inflationary epoch lasted from 10−36 seconds after the conjectured Big Bang singularity to sometime...", which is consistent ("conjectured") with Siegel's views (not that he's a particularly reliable source on this; some statements he makes there are incorrect).  Anyway, this is not a discussion forum.  Do you have a specific suggestion for how to improve the article?  If not I will bow out of this discussion, respectfully.    Waleswatcher  ( talk ) 14:56, 23 October 2018 (UTC)

Space expands (what follows 'bis'?)
It says:

"This steady-state exponentially expanding spacetime is called a de Sitter space [...]".

The linked article on de Sitter space doesn't mention 'exponential' or 'expanding'. If a de Sitter space is exponentially expanding, that seems to be a significant fact about such spaces; shouldn't the article mention it (before diving into abstruse mathematical formulae)?

MrDemeanour (talk) 14:02, 14 October 2018 (UTC)


 * MrDemeanour, I tried to improve the wording a little. I do understand the material well, but I don't have time now for a more thorough re-write or to find more/better sources.  Hope this helps at least a little (and thanks for pointing out how much it needs TLC).   Waleswatcher  ( talk ) 17:00, 24 October 2018 (UTC)


 * Thanks User:Waleswatcher. That helped some. It still links exponential expansion to De Sitter Space; that article still doesn't mention 'exponential' or 'expansion'. Perhaps the exponential expansion bit is buried in terms such as 'Λ' and 'vacuum energy', that I can't unpack; but it does also say that a 4-dimensional De Sitter Space is a model for our universe. If that's the case, and if a De Sitter Space involves exponential expansion, then I would have thought that cosmological inflation would be directly implied by adopting that model, and not just an attempt to resolve some unexplained physical observations. Oh well. MrDemeanour (talk) 09:00, 25 October 2018 (UTC)
 * De Sitter certainly involves exponential expansion, so that's a shortcoming of the dS article. This is why you should never use wiki articles as sources for wiki articles.  FYI you can see the exponential in the "flat slicing" metric, and less clearly in some of the others.  Waleswatcher  ( talk ) 12:28, 25 October 2018 (UTC)
 * As for it being a model of our universe, that's because it seems the universe today is expanding (quasi)exponentially. But this article focuses on the hypothetical period in the early universe when it did the same, but at a much higher rate.   Waleswatcher  ( talk ) 13:25, 25 October 2018 (UTC)


 * Thanks again.
 * I haven't edited based on using WP as a source; I came here to ask anyone who does understand this stuff (and can interpret appropriate secondary sources) to help clear this up. It's clear that I'm way out of my depth here; I kinda hoped to use WP as a beginners guide to cosmic inflation. That seems to be a lost cause!
 * It's a shame that the article on De Sitter Spaces doesn't support the claims in this article. Perhaps, in the fullness of time, someone will come along and fix that article. MrDemeanour (talk) 16:29, 25 October 2018 (UTC)
 * Yeah, I've added the dS article to me "to do" list. Unfortunately many physics articles are in pretty bad shape - there just aren't enough active knowledgable editors.   Waleswatcher  ( talk ) 18:35, 25 October 2018 (UTC)

When My Lord, oh when? (kidding)
The Big Bang Theory came from a priest: George Lemaître !!!

That's why there are still 2 religious addings in that theory: - our big bang system has to come from nothing - our big bang system has to be the whole universe

For all we know now for sure, is that ALL WE CAN OBSERVE FOR NOW, is coming from one "Bang". But those religious addings are causing lotta trouble: - Einstein's calculations revealed a flaw, causing the need to add a ridiculous theory about Dark Energy - Our big bang system couldn't come from such tiny volume, which lead to the ridiculous adding of the theory of Cosmological Inflation.

Just know when you're wrong, instead of grabbing band aid to keep a religious theory alive! — Preceding unsigned comment added by 2A02:1812:C69:F800:6006:C817:37E1:EA26 (talk) 13:51, 12 March 2019 (UTC)


 * You're not even wrong. Lemaitre was a serious astronomer and physicist. His theory was based on Hubble and General Relativity, not on Catholic theology.


 * Einstein's calculations did not reveal a flaw. Rather, he believed that the Universe was static and added a term to make it come out that way; a term that he regarded as his "biggest blunder" after Hubble's observations. This was long before the observations that led to the term dark energy.


 * Asserting that something could not happen is not a measurement, simply a prejudice. Now, if you can demonstrate that the current theory predicts that it is impossible, or can come up with data to challenge the current theory, it might be possible to take your claim seriously.


 * Of course, there isn't one Big Bang theory, there are many. Not all of them require an initial singularity, and some of them have a past prior to the Big Bang, e.g., Eternal inflation. The cosmologists have an intense interest in collecting more data in order to estimate which, if any, of the competing Big Bang Theories is correct. Meanwhile, CMB data from, e.g., COBE, WMAP, are hard to argue away. Shmuel (Seymour J.) Metz Username:Chatul (talk) 17:11, 12 March 2019 (UTC)

Semi-protected edit request on 17 May 2019
– Þjarkur (talk) 15:23, 17 May 2019 (UTC)

Pltype (talk) 01:57, 17 May 2019 (UTC)


 * Hello Pltype, this seemed to be a copy paste of the entire article. Could you word your request on the form "please change X to Y"? Thank you. – Þjarkur (talk) 15:23, 17 May 2019 (UTC)

Semi-protected edit request on 10 August 2019
The link for "vacuum energy" direct to wikipedia's page for "dark energy". I believe this is true for all instances on the page, Please fix. 2601:989:4200:8D6:0:0:0:CC6F (talk) 21:00, 10 August 2019 (UTC)
 * Red information icon with gradient background.svg Not done: It seems like you're suggesting that we change the vacuum energy links to vacuum energy . This should not be done per the manual of style. --Trialpears (talk) 10:01, 14 August 2019 (UTC)

Semi-protected edit request on 21 September 2019
under opening title: inflation(cosmology) -> first paragraph -> last sentence: "... the universe continues to expand, but at a less rapid rate", change to: '... the universe continues to expand, but at a more or less constant rate'. (it is not the rate that becomes less rapid, it is the growing of the rate that becomes less rapid) 176.12.216.205 (talk) 13:27, 21 September 2019 (UTC)


 * . Changed tense and wording a bit differently to emphasize that this was immediately following inflation.  –Deacon Vorbis (carbon &bull; videos) 14:47, 21 September 2019 (UTC)

Inflation: a theory of exponential expansion of space in the first decillionth of a second after the BIG Bang-Bit Bang
Inflation: a theory of exponential expansion of space in the first decillionth of a second after the Big Bang-Bit Bang. Inflation is followed by expansion. 192.88.124.40 (talk) 16:51, 3 March 2020 (UTC)

You confuse the visible horizon with the subliminally receding particle horizon
You wrote: The observable universe is one causal patch...

What we see now isn't how particles move now.

The causal horizon from an arbitrary central point, forms a sphere with all the subliminally receding particles, which can causally interact. — Preceding unsigned comment added by 2A02:587:4100:AD70:786B:A998:B71:F7E7 (talk) 01:07, 7 June 2020 (UTC)
 * The section could use clarification, I feel the section currently is neither rigorous, nor would be clear to new readers. Rolf H Nelson (talk) 23:18, 7 June 2020 (UTC)

Phoenix universe of Georges Lemaître
From the article: ‘Phoenix universe of Georges Lemaître’

I don't think Lemaître invented the Phoenix universe, he didn't seem to favour it, and he didn't even coin the term, although he might have inspired it. In any case, this needs rephrasing. — Preceding unsigned comment added by 77.61.180.106 (talk) 06:00, 15 January 2021 (UTC)