Talk:Cosmic microwave background/Archive 1

Dark Matter
If our galaxy is shrouded in a cloud of dark matter (which influences the path of photons as seen in gravitational lensing), should it influence the perceived wavelengths of CMB, its black body properties or even its anisotropy? For instance, if we suppose that dark matter forms a thin, uniform "shell" around our galaxy, and since we are not located at the center of the galaxy, should light coming from different directions be affected in subtly different ways by the dark matter it crosses? One last question: Could the CMB be caused by this dark matter acting like a black body? How could we tell?

I moved here the contents of CBR because the term is more general that the CMBR, that this article describes. --AN

I'm starting some discussion on Talk:Sunyaev-Zeldovich effect which relates to recent changes and reversions of Cosmic microwave background radiation as well. If anyone watching here has anything to say on the relevance of the Dirac sea to the SZ effect please take a look. --EddEdmondson 09:45, 25 Mar 2004 (UTC)

Move
I moved here the contents of CBR because the term is more general that the CMBR, that this article describes. --AN

I'm starting some discussion on Talk:Sunyaev-Zeldovich effect which relates to recent changes and reversions of Cosmic microwave background radiation as well. If anyone watching here has anything to say on the relevance of the Dirac sea to the SZ effect please take a look. --EddEdmondson 09:45, 25 Mar 2004 (UTC)

Compton/Thomson Scattering
The article describes the radiation in the pre-recombination era as interacting with the plasma through Compton scattering, and a link is given. I thought that this should be Thomson scattering, but wasn't sure as I'm a lowly undergraduate. Perhaps I misunderstand the usage here? Or am I just mistaken?


 * same thing. I think technically, Thomson scattering is classical while Compton is quantum.  However in terms of terminology, ive heard physicist use both.  --Blckavnger 23:19, 17 November 2006 (UTC)

Reionization Period?
I'd like to see discussion either here or at reionization about how the reionization period related to the CMB. --zandperl 03:56, 9 Jul 2004 (UTC)

-

No it doesn't.... -

Yes it does.

The CMB photons are rescattered from free charges such as electrons, which have been liberated from neutral atoms by ionizing (ultraviolet) radiation. The intergalactic medium (IGM) is known to be ionized today, but is at sufficiently low density in most of the volume of the Universe that it does not significantly affect the CMB. If the IGM was ionized at very early times, when the universe was still denser, then there are two main effects: 1) small scale anisotropies are erased (just like if you are looking through fog, objects appear fuzzy) and 2) the details of how photons scatter off of free electrons (Thomson scattering) induces polarization anisotropies on large angular scales. This large angle polarization is correlated with the large angle temperature perturbation.

Both effects have been observed by the WMAP satellite, which has led the WMAP team (and others after it) to conclude that the universe must have been ionized at very early times. The detailed provenance of this early ionizing radiation is still a matter of scientific debate. It may have included the radiation given off by the supernovae caused by the very first population of stars (population III stars) or the ionizing radiation produced by the accretion disks of massive black holes.

--BenWandelt 18:49, 11 September 2005 (UTC)

WMAP data reviewed (early 2004), casts doubt on anisotropy
See here for a recent reappriasal of the WMAP data by Professor Tom Shanks of the University of Durham that casts some doubt on some of the anisotropic evidence.

$$\ell C_\ell$$

Confusing
The line: "During the mid-1990s, the lack of detection of anisotropies in the CMB led to some interest in nonstandard cosmologies (such as plasma cosmology) mostly as a backup in case detectors failed to find anisotropy in the CMB. The discovery of these anisotropies combined with a large amount of new data coming in has greatly reduced interest in these alternative theories"

....does not make sense. During the mid 90's? Didn't we know about anisotropy since COBE's results in early 1992?--Deglr6328 04:59, 27 Dec 2004 (UTC)

Also, I've read the line "we've been scooped" as being attributed to Gamow, speaking about Alpher's original thesis topic before he changed it to the dynamic and evolving universe. -66.229.50.199 17:08, 13 June 2006 (UTC)

CMB prediction
I thought the CMB was predicted long before George Gamow, Ralph Alpher, and Robert Hermann in the 1940s, as follows:


 * 1926: Sir Arthur Eddington estimates the thermal background radiation temperature as 3.2K.
 * 1930s: Cosmologist Ernst Regener calculates that intergalactic space has a background temperature of 2.8K
 * 1938: Nobel Prize winner (1920) Walther Nernst estimates 0.75K
 * 1946: Robert Dicke predicts an MBR (microwave background radiation) temperature of 20K (ref: Helge Kragh)
 * 1946: Robert Dicke predicts an MBR temperature of "less that 20K" but later revised to 45K (ref: Stephen G. Brush)
 * 1946: Gamow estimates a temperature of 50K
 * 1948: Ralph Alpher and Robert Herman re-estimate Gamow's estimate at 5K.
 * 1949: Ralph Alpher and Robert Herman re-re-estimate Gamow's estimate at 28K.
 * 1960s: Robert Dicke re-estimates a MBR (microwave background radiation) temperature of 40K (ref: Helge Kragh)


 * These are estimates of a non-thermal temperature such as average starlight. Gamow's paper was the first to predict blackbody radiation as a remnant of the formation of the universe. --72.165.205.81 06:54, 20 December 2006 (UTC)

"Large-scale structure of the cosmos" category
Should this article be placed in the "Large-scale structure of the cosmos" category? &mdash;Vespristiano 02:50, 8 Jan 2005 (UTC)


 * the CMB does reveal data about large-scale structure but also reveals data about the early universe. so while the data from CMB is used in conjugation with galaxy surveys such as SDSS and 2dfgrs, it reveals more data about cosmology than any current observation.  However, data from all observations like sne Ia and light element abdance are needed together to have any solid interpretation of cosmology.  If we use data from WMAP by itself, has quite a few best fits such as open universe with almost all matter iirc.  --Blckavnger 23:25, 17 November 2006 (UTC)

Style, coordination
As a lot of other cosmology related articles, this article has a very large "See also" list. I'd to propose trimming this down: What's the opinion of the other contributors?
 * Don't link to articles which are already linked in the prose.
 * Don't link to articles, which are not centrally related. They can be reached via the category.

Also, I'd like to ask, whether it would make sense and find interest contributors, to set up a "cosmological coordination", a WikiProject to have an eye on consistency, missing and duplicated articles.

Pjacobi 19:22, 2005 Jan 29 (UTC)

Features Question
Could someone describe how the 700 km/s velocity, described as the basis for the dipole shift in the CMB, was measured/inferred? Is it the inferred velocity of the Local Group that would cause the observed dipole shift? Does this dipole pattern induce a "preferred coordinate system" for the universe? Dan Watts 19:00, 26 Apr 2005 (UTC)

It is actually a dipole due to the motion of the Earth wrt the CMB -- that's all components including the motion of the sun through the galaxy and the motion of the galaxy toward the great attractor. It introduces a preferred Galilean reference frame which jives fine with GR since GR just requires Lorentz invariance. The feature looks like a giant hotspot and a giant coldspot on the sky due to the velocity-related redshift. See this picture of it.Joshuaschroeder 06:27, 15 May 2005 (UTC)


 * Therefore, shouldn't the CMBR section state that it is consistent with such motion instead of being worded such that it appears to be an independent statement of the galactic motion?  Instead of "It is mostly due to the motion of the observer against the CMB, which is some 700 km/s ..." shouldn't it be a more accurate statement such as "This feature is consistent with the observer moving at some 700 km/s relative to the CMB." ? Dan Watts 14:41, 15 May 2005 (UTC)

APOD
Congratulations are in order. This article is linked to NASA's Astronomy Picture of the Day feature for May 8th. http://antwrp.gsfc.nasa.gov/apod/ap050508.html Fire Star 05:35, 8 May 2005 (UTC)

Experiments
What is "high /" ? This is seen in: "Its detectors got a trial run at the Antarctic Viper telescope as ACBAR (Arcminute Cosmology Bolometer Array Receiver) experiment, which gave the currently most precise measurements at high /, and at the Archeops balloon telescope." Dan Watts 21:58, 27 September 2005 (UTC)


 * Jargon. It means small angular scales. The l comes from spherical harmonics. –Joke137 22:43, 27 September 2005 (UTC)

rewriting...
I thought this page could use some improvement, so I'm being bold. I am slowly trying to rewrite the thing, and I have moved a lot of content to the cosmic microwave background experiments page. I've also been added a lot of primary and secondary references. Other changes: I think this could be a featured article some day. Probably I will do some more work on it tomorrow. –Joke 03:50, 8 December 2005 (UTC)
 * 1) I culled almost all of the links. In my opinion, the links to Wayne Hu's webpage and the LAMBDA are so useful, they are probably the only external links that are necessary.
 * 2) I intend to update the "CMB and the Big Bang" section to be a sort of semi-pedagogical discussion of CMB physics, with sections about temperature, anisotropy, the meaning of the peaks (i.e. acoustic oscillations and diffusion damping), polarization, secondary anisotropy (Sachs-Wolfe effect, Sunyaev-Zel'dovich effect), current issues etc...
 * 3) The "see also" section had so many links so as to be useless. Why did it, for example, link to black dwarf? Either links should be in the main text, or not be in the article at all (unless we make a big collection of CMB articles, like the CMB experiments link).

By the way, if we must have it, can someone at least carefully reference the timeline? Oh, and most of the references in footnotes I added are online through ADS, the arXiv or the journals. If someone would like to add links, that would be great. Otherwise, I may do it one day. –Joke 04:10, 8 December 2005 (UTC)


 * Do you think that if you redirect the Cosmic Background Radiation page to this page, then you should explain (a) some more about the CBR, and how the CMR is an important component (b) credit the earlier scientists for their successful prediction of the CBR temperature, rather than criticising them for not predicting the CMR which everyone seems to agree is different. It's like criticising Newton for not knowing about Einstein's relativity. --Iantresman 08:30, 8 December 2005 (UTC)

Well, I'm honestly not sure what the other components are. The CMB is the background because it his at a higher redshift than anything else in the universe. There was a sentence in the cosmic background radiation page that read "There is also background radiation in the infrared, x-rays, etc., with different causes; most of these are ultimately attributable to unresolved individual sources." That, as best as I can tell, means they are actually foregrounds. I guess there is the cosmic infrared background, which is due to distant starlight. Someone should certainly make a page about that. I don't object to having a cosmic background radiation page, I just think that the present incarnation wasn't very useful. –Joke 14:38, 8 December 2005 (UTC)


 * But "Cosmic Background Radiation" is used quite frequently, and was successfully predicted by a bunch of scientists, which deserves credit. --Iantresman 18:05, 8 December 2005 (UTC)

Cosmic background radiation
I'm concerned that since the "Cosmic background radiation" page now redirects to this Cosmic microwave background radiation article:
 * 1) There is now no mention of "Cosmic background radiation" (although an acronym is provided)
 * 2) Except for the "Timeline", credit is not provided for Guillaume, Eddington, Regener and Nernst, for correctly predicting its temperature

Either: --Iantresman 14:37, 9 December 2005 (UTC)
 * 1) CMB is synonymous with CBR, in which case, Guillaume et al correctly predicted its temperature first
 * 2) CMB is different to CBR, in which case, (a) it requires an explanation, and (b) details that Guillaume et al correctly predicted its temperature.

I may be wrong but I believe that the term "Cosmic Background Radiation" includes the Cosmic Neutrino Background as well as the Cosmic Microwave Background. Thus it is a more general term. Spebudmak 04:27, 20 April 2006 (UTC)

Cosmic background radiation censorship
It's suggested that "cosmic microwave background radiation" (CMBR) is sometimes abbreviated as CBR (Cosmic background radiation), which technically includes microwave and non-microwave background radiation; there use to be a small article on the CBR, but it was deleted and redirected to this article.

The timeline of the cosmic microwave background radiation, used to show estimates for tbe CBR, which predates the CMBR. These have now been removed by user:ScienceApologist claiming that they are irrelevant. :


 * 1896 	Charles Edouard Guillaume estimates the "radiation of the stars" to be 5.6K.
 * 1926 	Sir Arthur Eddington estimates the non-thermal radiation of starlight in the galaxy has an effective temperature of 3.2K.
 * 1930s	Cosmologist Ernst Regener calculates that the non-thermal spectrum of cosmic rays in the galaxy has an effective temperature of 2.8K

You would think that an article would at least explain the difference between the "cosmic microwave background radiation" (CMBR) and the "cosmic background radiation" (CBR), and why one is more significant than the other.

And likewise, include the contributions from Guillaume, Eddington and Regener, and explain their significance, and difference to the estimate from the CMBR. --Iantresman 13:11, 16 January 2006 (UTC)


 * If you want to report on predictions from the cosmic ray background, report it on the cosmic ray page. If you want to report on Eddington's integrated starlight ideas, report it on the Eddington page but leave it off this page. --ScienceApologist 00:51, 17 January 2006 (UTC)


 * The page defines the "cosmic microwave background radiation" by (a) referring directly to the "CBR" in the introduction (b) by redirecting the old "cosmic background radiation" page here. That makes it relevant. To suggest that the CBR predictions are mentioned on the cosmic ray page, is a bit like suggesting that the "cosmic microwave background radiation" predictions are placed in the microwave page. --Iantresman 08:06, 17 January 2006 (UTC)


 * In the historical literature people referred to the CBR instead of the CMB, but meant them to be synonymous. That's why they are considered the same. There is no background radiation proposed with Eddington's proposal because intergalactic space is transparent as a plasma. Cosmic rays are not considered "background". --ScienceApologist 00:14, 18 January 2006 (UTC)


 * All very interesting, and personally, I think it should be part of the article. As far as us laymen are concerned, Guillaume and Eddington were measuring temperatures, as did Dicke and Gamow. The article IGNORES all this, rather than EXPLAINING it. --Iantresman 08:37, 18 January 2006 (UTC)


 * Well, Guillaume and Eddington didn't measure anything, they asked a question regarding the physical relationships of phenomena. The article as it currently stands ignores points that are unrelated to the phenomena itself (are only connected by nonstandard cosmology proponents, for example). Since there is nearly no one left who supports steady state or static universe cosmologies, there is no reason to go into detail explaining their convoluted machinations on the subject. --ScienceApologist 17:12, 22 January 2006 (UTC)
 * No Jesuit could have done a better job defending the faith. Twang (talk) 08:59, 26 November 2009 (UTC)

ga
This looks to be a pretty good, well-referenced article. I'd say it's at least 75 percent to being a FA. Deckiller 00:28, 29 January 2006 (UTC)

Poor wording in Features

 * At this point, the photons did not scatter off of the now neutral atoms and begin to travel freely through space.

This ought to either be an affirmative statement, that is "the photons remained..." or somesuch, or it ought to at least mention why it is that it might be expected that the photons would scatter off and why they did not. - Centrx 16:45, 19 February 2006 (UTC)
 * Or it could very well have been vandalized, down in Relationship to the Big Bang under Temperature, it states that this time is generally known as the "time of last scattering", that is that the decoupling or recombination was a scattering. Anyhow, it is unclear and ought to be changed. - Centrx 16:47, 19 February 2006 (UTC)

Backlink to Noise
Why is this here, in this form? This article is not only linked from Noise - see. Please could someone explain the necessity or I will remove the link. QmunkE 15:38, 10 March 2006 (UTC)

This originally made sense but I agree it should not now be here. I discovered Noise in a mess, and re-worked it in a way that made sense, including many sections on different types of noise. The original pr it into a disambiguation page, copying sections of my text to a dozen pages. It was clear to me that they no longer made sense, and that disambiguation was often being used in this way, fragmenting pages, and taking away the common struction and introduction. So I devised the Root page concept, and implemented it on Noise to try it out. One page was called Noise (big bang), but someone decided to turn that into a redirect to here. I would have simple left Noise (big bang) as part of the set, with a link pointing here. Since then there has been much discussion on Root page, and there is no doubt that whether to group or not group is a hard question. The backlink idea was adopted at the suggestion of somone else, but has now been dropped, in favour of a 'branchlist' template which just a special form of navigation template (see this at Electronics. I like this, but there is no doubt this is a controvertial topic. I still think there is a problem, which was demonstrated by Noise. Some people were writing pages as if this were just an acoustic term, others as if it were just an electronic phonomenon, and there was much duplication under different names, eg noise nuisance, environmental noise. The same is happening on many other pages, but without more support for my idea to create a degree of centralised editing I can do no more.

Sorry to have troubled you. --Lindosland 12:45, 27 March 2006 (UTC)

Airport
When initiating a search using 'CMB', I came upon this page instead of the airport based in Colombo, Sri Lanka, which I was looking for. I have added this as a disambiguation. 69.138.62.148 04:05, 30 June 2006 (UTC)
 * I've changed CMB into a disambiguation page, so the abbreviation isn't needed here. SWAdair 04:09, 30 June 2006 (UTC)

Is this really sensible? I imagine the vast majority of people are looking for the cosmic microwave background – instead, why not leave the disambiguation at the top of the page for people who are looking for it? –Joke 20:32, 30 June 2006 (UTC)
 * I added the disambiguation to the top, and moved CMB to CMB (disambiguation). CMB now redirects here. Please discuss if you don't agree. –Joke 01:37, 1 October 2006 (UTC)

Shadow (and other) problems
Where should a comment on the CMB 'Shadow problem' be put? (see http://www.physorg.com/news76314500.html ) Or on the lack of gravitational lensing? ( http://universe.nasa.gov/press/2005/050802a.html ) Dan Watts 16:19, 7 September 2006 (UTC)

Source for Penzias/Wilson geographic claims?
Is there a source for the claim that Penzias and Wilson did their work in Holmdel? In 1986 I worked in Holmdel and spent a little time around Murray Hill as well. In Murray Hill I saw what I was told was the antenna they had used. It had obviously (?) not been moved there from Holmdel. I always believed Penzias and Wilson had worked in Murray Hill. —The preceding unsigned comment was added by RobertKennedy (talk • contribs).


 * I think you must be mistaken. The antenna is still there near the top of the hill in Holmdel (it is on the national register of historic places, or whatever). You can check Peebles' book (The Principles of Physical Cosmology), Penzias and Wilson's paper, or pretty much anywhere on the web to confirm. You can see a picture of the antenna here . I know they built other instruments after that – perhaps one of them was in Murray Hill? –Joke 01:31, 4 October 2006 (UTC)

The source of my confusion, now resolved, is this: Crawford Hill, where Penzias and Wilson did their work, was a separate location from the Holmdel location of Bell Labs, although both were in Holmdel township. I remembered the "Hill" part of the location's name, and my brain garbled the rest. It seems like it would be clearer if the article used the Crawford Hill name for the location rather than suggesting that the work was done at the Holmdel facility. For example, page 189 of "Three Degrees Above Zero," by Jeremy Bernstein, makes very clear that Crawford Hill was a separate facility, distinct from the Holmdel facility.

"Histrory" needs fix
The second paragraph of the current History section begins with the sentence, "The results of Gamow were not widely discussed." But Gamow is not mentioned previously in the text. I'm not sure what the correct fix should be, but either Gamow should be mentioned earlier or this sentence should be dropped.

JCNSmith 10:52, 8 October 2006 (UTC)

Wien's Law doesn't apply?
So Wien's displacement law gives the relationship between a black body and the peak wavelength it produces:
 * $$T \lambda_\mathrm{max} = 2.898... \times 10^{-3} \ \mathrm{m \ K}. \,$$

If we plug in the value given in the introduction, $$\lambda_{max} = 1.9 \ \mathrm{mm} \,$$, this equation tells us the temperature of the black body is:
 * $$\frac{2.898 \times 10^{-3} \ \mathrm{m \ K} }{1.9 \times 10^{-3} \ \mathrm{m}} = 1.5 \ \mathrm{K} \,$$

which doesn't agree with the '2.7 K' temperature given. Why the disagreement? JabberWok 02:27, 11 March 2007 (UTC) ---

You need to use the frequency form of the law, not the wavelength form. The 2.7 K peak is at 160 GHz when considering the peak of intensity per unit frequency as opposed to per unit wavelength.212.16.102.77 11:13, 15 March 2007 (UTC) ---

I was confused about this, too. Perhaps we could clarify to something like: "The peak emission occurs at 160.4 GHz using the frequency formulation of Planck's Law, which corresponds to a wavelength of 1.9 mm, or at 1.06 mm using the wavelength formulation, which corresponds to a frequency of 283 GHz." with some appropriate links Kerouacesque (talk) 05:54, 18 June 2009 (UTC)


 * OK, I added a footnote (it did not seem important enough to go in the intro itself) with links.  LouScheffer (talk) 11:38, 18 June 2009 (UTC)

Theory recently disputed - earthly origin for microwave background rad.
This should be of high interrest.

I recieved a broadcasted mail from a Ph.D. from Ohio State University containing a link, to this paper that he had authored and which have been published on the 19th march in Progress in Physics, commenting "It demonstrates that the CMB cannot have a cosmic origin."
 * EDIT: I realized that the Pierre-Marie Robitaille that sent the mail is same as the author of the mentioned article, and is not directly connected to my study in Århus. MigB 13:35, 22 March 2007 (UTC)

The conclusion of the article is: "This constitutes further evidence that the microwave background [4] is of Earthly origin [6–8]. We will never know the temperature of the Universe."

Since I am only a student at the moment, I will leave it to the community to discuss the validity of the paper. —The preceding unsigned comment was added by MigB (talk • contribs) 16:28, 20 March 2007 (UTC).


 * Sadly the author of this "paper" does not understand that spacecraft are outside the Earth's atmosphere, and says that the thermal radiation from the air is spoiling the view for the CMB spacecraft. The paper has not been published in Progress in Physics. Rnt20 21:17, 20 March 2007 (UTC)


 * It has been published in PiP, volume 3, 2007, under the name "On the Earth Microwave Background: Absorption and Scattering by the Atmosphere", and is available online at their website: | Ptep-online, available issues. I have invited the author of the paper to join this discussion, and hope he will accept the invitation MigB 13:35, 22 March 2007 (UTC)


 * This is unbelievably sad. This guy is in biomedical engineering / radiology and he's writing a paper on physics and cosmology. I don't mean to use an ad hominem against him, but he doesn't seem to understand that satellites orbit the earth and view space indepedently of this phantom ocean radiation that he's so fond of. Even spacecraft such as Voyager 1 and 2 out past the asteroid belt saw the 2.7 K. Did Earth's oceans somehow affect their measurements too? 129.162.1.41 21:49, 5 June 2007 (UTC)

adiabatic cooling vs. cosmological redshift
I just removed the parenthetical statement (diff) in the sentence:


 * As the universe expanded, adiabatic cooling (of which the cosmological redshift is an on-going symptom) caused the plasma to cool until it became favourable for electrons to combine with protons and form hydrogen atoms.

The sentence made it sound as if light from distant galaxies is redshifted because of some kind of "adiabatic cooling" process along the way, but this is misleading.

The plasma cooled because the "container" (if you will) holding it expanded slowly and without any heat transfer to an outside system (this being the universe). While the cosmological redshift is also due to the expansion of the universe, there's no thermodynamics involved, it's just GR. Wesino 13:22, 5 May 2007 (UTC)

Where is the CBR?
Where does the CBR manifest itself? Are there 2.7K photons coming out from all observable space? If there is empty space (no particle whatsoever which is next to impossible, I know), would there still be 2.7K photons being emitted from it? In other words, does the CBR require matter to be present? Are there photons coming from the space behind my monitor that to some extent have higher energies due to the 2.7K background radiation? Please help me! 129.162.1.41 21:36, 5 June 2007 (UTC)


 * As with all light, the photons don't need matter to travel though - in fact, they travel better without it. The photons aren't being emitted from empty space now (or anything now); they were all created in the early universe, and have been travelling through space since the epoch of decoupling, about 13.7 billion years ago (see the article...) Mike Peel 00:08, 6 June 2007 (UTC)


 * So there's an electromagnetic field of 2.7K photons throughout the universe? I understand there's some clumpiness at the micro-Kelvin level (so called anisotropies), but for the most part, would 1 cubic-centimeter of space in my apartment have the same number of photons attributable to CMB as a cubic-centimeter in the Andromeda galaxy? 129.162.1.41 16:25, 19 June 2007 (UTC)


 * As long as the time from Big Bang is identical, the answer is yes (plus minus a statistical error - I'm not sure if a cubic has enough photons for good statistics). --Friendly Neighbour 16:30, 19 June 2007 (UTC)
 * I found it here: there are 412 (plus minus 1) CMB photons per cubic cm. You will have the same density in Andromeda Galaxy (unless you reach it in a billion years or so which may dilute the radiation a little). --Friendly Neighbour 16:52, 19 June 2007 (UTC)

Introduction
I think the sentence "(most often abbreviated CMB but occasionally CMBR, CBR or MBR, also referred as relic radiation)" should be downgraded to a footnote, because it breaks the flow of the prose in the introduction. Any opinions? 212.16.104.4 22:29, 19 June 2007 (UTC) 168.187.119.27 05:28, 29 July 2007 (UTC)

Cosmology for dummies
This article seems to be written by cosmologists for cosmologists. Is that fair to the general readership of wikipedia? It seems reasonable to expect some kind of plain overview in an encyclopedic article like this, if only in the introduction. The first paragraph alone of the features section has so many unexplained terms and assumes so much background knowledge that it took me half an hour of hyperlink chasing to get a clue to what it means. Come on guys - you're the ones who understand all this stuff - explain it!


 * yes i agree its a little too much jargon for the first paragraph.(and i study the CMB for a living!). unfortunately im not a good enough writer to make it more accessible yet keep it encyclopedic.  hopefully someone will come along and fix it.  --Blckavnger (talk) 08:17, 30 January 2008 (UTC)


 * OK, I took a stab at this. Please improve/correct if you can, LouScheffer (talk) 18:04, 5 November 2008 (UTC)

Speed of earth relative to CMB
Shouldn't this article mention the speed of the Earth relative to the background radiation (approx. 370 km/s), and the anisotropy this causes, which is corrected for in the images here? Amaurea 12:40, 12 September 2007 (UTC)


 * Excellent suggestion. Just want to endorse this good idea. I really hope someone does it; if not I may get around to having a crack at it sometime. &mdash;Duae Quartunciae (talk · cont)  12:44, 12 September 2007 (UTC)


 * I add myself to this wish list, if someone has the competence to fix this properly, please do.Agge1000 10:15, 13 October 2007 (UTC)

"Axis of Evil"?
As a non-cosmologist I'd taken idle pleasure in imagining geometric patterns in CMB maps, but was stunned to find an article actually reporting some such pattern in the article in the political "Axis of evil" entry. Could someone elaborate on this phenomenon in this article? Thanks. 70.15.116.59 16:28, 1 December 2007 (UTC)

Surface of Last Scattering
The estimate of the surface of scattering (13.7 billion light-years) completely ignores the expansion of the universe since decoupling. The fabric of space has expanded considerably since recombination, so shouldn't the estimate include this. As a similar example, if you use an Einstein-de Sitter model of the universe ( a(t) = kt^(2/3) ), then the particle horizon is at 3ct, as opposed to ct as this method of estimation would suggest. Or am I just missing something here? Niel.bowerman (talk) 07:44, 8 January 2008 (UTC)


 * i dont know exactly what u r asking but the estimate to last scattering surface (lss) is based on the model fit to the observed power specturm. im assuming that number is from flat lambdaCDM model of the Friedman eqn so it does take into account expansion after recombination (otherwise i dont know how else they could get a number?  thus i dont really understand the question?).  of course i dont know if that number is quoted right or not. --Blckavnger (talk) 08:33, 30 January 2008 (UTC)


 * CMBR Dipole: Speeding Through the Universe

The map indicates that the Local Group moves at about 600 kilometers per second relative to this primordial radiation. This high speed was initially unexpected and its magnitude is still unexplained. Why are we moving so fast? What is out there?

MY ANSWER:: I believe we are making music. There are five universes - Perpetual (ours), iii, Grappa, Toirai and Tandem. Each has this speed of movement and is being played by oblivion as a sort of musical instrument. There would be a oblivion's threshold where the greatest force would be exerted upon the universes "musical instrument". But this would not be where the greatest reception of sound would be. Each universe would be like a key played of a trumpet, swirling around up and down as oblivion's threshold played them. Annie —Preceding unsigned comment added by 69.85.255.34 (talk) 20:27, 9 March 2008 (UTC)

what is the source for the time of the last scaterring?
This article says the last scattering or decoupling took place 487,000 years after Big Bang. Introduction to Cosmology by Barbara Ryden says it took place 350,000 years after Big Bang. —Preceding unsigned comment added by CosmologyProfessor (talk • contribs) 06:25, 6 March 2008 (UTC)

Linked from NASA's Astronomy Picture of the Day
All of you who work on this page, nice job: this was linked from NASA's Astronomy Picture of the Day for March 9, 2008. Ante  lan  talk  00:32, 10 March 2008 (UTC)

Introduction / diagram inconsistency
In introduction (and later) it appears that the wavelenght of CMB is 1.9 mm but the subsequent diagram (in Features) shows the peak at 5 cm. Aren't they supposed to be the same thing?

Also in a previous discussion "Wien's law doesn't apply" it seems like the temperature is wrong as well (for 1.9 mm). There is a reply claiming that the frequency form of the law should be applied without saying what that form is (frequency and wavelenght should be tied in my opinion, so I could not see why they should lead to different results).

Am I missing something here?

Adsp (talk) 21:08, 7 May 2008 (UTC)


 * Yes. The axis of the diagram is "waves / centimeter" = "waves per centimeter" (i.e. wavenumber in the technical jargon), not "wavelength / centimetre" = "wavelength in centimeters". If the wavelength is just under 0.2 cm there are just over 5 waves per centimeter. 140.105.79.118 (talk) 15:40, 23 May 2008 (UTC)

If CMB is isotropic then stealth technology is useless, because we can watch stealth aircraft as a shadow on CMB. W.z.c. —Preceding unsigned comment added by W.z.c. (talk • contribs) 15:21, 3 June 2008 (UTC)


 * It's a lot more difficult to detect something by a decrement than it is to illuminate something and see that it is present by its reflections (i.e. by radar). In order to pick out a decrement in the CMB, even if the aircraft is fairly large (say an arcminute across) then you'd need lots of radiometer chains and telescopes to cover the whole sky simultaneously (and those aren't cheap). You'd have to worry about lots of interfering effects: the atmosphere, satellites, nearby mobile phones, etc. Plus you would need a lot of computing power, and plenty of highly skilled manpower to make sense of all of the data. Astronomers only look at small sections of the sky at once when observing the CMB, and take their time about covering the whole sky.
 * It's not impossible, but I'm sure that there's better methods that could be used, a few of which are mentioned in the Stealth technology article. Mike Peel (talk) 21:49, 3 June 2008 (UTC)

Why did the photons "cool" ( z value?)
Please excuse this ignorant question, I am just a chemist. But why did the photons "cool" after being emitted? If they were emitted by matter at 3,000 kelvins, why do they now look as if they were emitted by matter at 2.7 kelvins? Again, I am not a physicist, but it was my understanding that photons do not spontaneously decrease in energy. Is this red shifting?66.92.68.214 (talk) 07:25, 3 July 2008 (UTC)


 * Yes, it is redshift. I reworded that statement to eliminate the "cooling" idea. Makuabob (talk) 13:11, 28 November 2008 (UTC)

So the CMB is redshifted light. Why no mention of it's z value?

local mini bang and CMB
Is it not true that if a localized bang occurred in otherwise empty space that the CMB map would look exactly the same? That is, if the universe turned out to be a trillion times larger than expected and it had a large empty space - much larger than the area of space we can currently detect, and a "bang" event occurred within it, the CMB would look the same as what we would expect if the entire universe had been create from a bang event? What reasons could there possibly be, if this is true, to jump from a more modest hypothesis regarding local space to a grander one involving the whole universe? —Preceding unsigned comment added by 66.94.176.22 (talk) 03:23, 21 September 2008 (UTC)

Big Bang Referrences
(moved these comments, made by 66.94.176.22, to the end here, and combined them with comments from the article itself LouScheffer (talk) 02:13, 26 September 2008 (UTC))

Doesn't this sort of thing belong in the Big Bang article and not here? How many times does this need to be stated in this article?

"The big bang theory suggests that the cosmic microwave background fills all of observable space, and that most of the radiation energy in the universe is in the cosmic microwave background, which makes up a fraction of roughly 5×10-5 of the total density of the universe.[5]"

BTW, the article seems to me to have been improved. Thank you.

Now, regarding adiabatic cooling. Is this really the best way to state it. Considering that entropy means the loss of ability to do work with transference to heat energy, should this be stated differently?


 * I think that the rewording of the 'photons cooling' remark clarifies the way in which the photons 'cooled.' Color temperature specifically relates to black-body radiation. As mentioned below, photons are massless and do no 'work' so they can't cool adiabatically. Redshift (in whichever form) is the only way to reduce their temperature without interactions. Makuabob (talk) 12:42, 28 November 2008 (UTC)

Confusing Comparison
"FIRAS compared the CMB with a reference black body and no difference could be seen in their spectra."

Shouldn't this read: "FIRAS compared the CMB with a reference black body and no differences were noted between their spectra." Makuabob (talk) 01:10, 1 November 2008 (UTC)

In the Features section of the article, the black body comparison phrase: FIRAS compared the CMB with a reference black body and no difference could be seen in their spectra. Yet, near the end of that same section, it is stated: ...prediction of its almost perfect black body spectrum... So,... is it perfect or isn't it? FIRAS said it is,... who says otherwise? Is there a reference to support "almost perfect"? BTW, did the FIRAS experiment compare the CMBR to a reference black body that was at the same temperature as the CMBR? If it did not, then there was a difference in temperature and the phrase "no difference could be seen in their spectra" is incorrect. Neither of these points is what I'd call 'nit-picking.' Is the CMB a perfect black body curve (re: FIRAS) or not? First, the article says 'perfect' then it says "nearly perfect." Also, was there a difference between the reference black body source and the CMB, or not? Wikipedia is not supposed to be like going to Tolkein's elves for advice, who would say both "Yes" and "No." (belated signature -->)Makuabob (talk) 11:53, 23 November 2008 (UTC)


 * I would expect that the "reference black body" would actually be a mathematical function describing a perfect black body with the best-fit temperature (the standard 2.725), being as the CMB has the best black body spectrum that we know to exist. In science, nothing is ever perfect - the best it gets is always nearly perfect, as the measurement will have errors on it due to the instrument etc. In this case, it agrees extremely well with a perfect black body, to within the error bars. Mike Peel (talk) 08:23, 23 November 2008 (UTC)


 * Looked up FIRAS results. They did compare to an internal black body, and the spectra agreed to experimental precision.  So it's a perfect match as far as the experiment goes (if they were *exactly* the same, you'd get the same measurements they got), but there could still be small differences, too small for the experiment to see.  I added an explanation of this to the article.   LouScheffer (talk) 15:26, 23 November 2008 (UTC)


 * I agree, LouScheffer. I went to the COBE article and saw that FIRAS had an onboard black body reference. The re-wording is clear; well done. I also found a paper explaining the process used with the FIRAS data. The uncertainty in the 'perfection' of the CMBR black body form is primarily due to uncertainty about how our galaxy's influence was to be removed from the FIRAS data. Makuabob (talk) 00:25, 24 November 2008 (UTC)

Intro needs to be rewritten
The intro needs to conform better with WP:OBVIOUS. It took me several readings to get a picture of CMB and I still don't quite understand exactly what it is. IMHO we get into too much technical detail right in the very first paragraph when we should be using more general statements to say exactly what it is and why it is important.  howcheng  {chat} 18:39, 3 November 2008 (UTC)


 * OK, I wrote a not-as-technical first paragraph. Please improve/correct if you can, LouScheffer (talk) 18:04, 5 November 2008 (UTC)

How does the observer's position in the Universe affect the CMB?
If a civilisation in a distant galaxy made these observations would they get the same pattern in their sky as we do. Does its precise shape depend on where in the Universe you are. i.e. Is the pattern a unique universal object common to the whole Universe or does it vary depending on the observers location? Lumos3 (talk) 13:10, 5 November 2008 (UTC)


 * A damn good question, but one that will not get answered anytime soon. IF the pattern looked different from "a galaxy far, far away," that might mean a parallax effect, which might mean some established cosmologists are wrong. Gasp! How will we get to another galaxy to make the comparison? Or do we ask E.T. to fax home? Makuabob (talk) 12:31, 28 November 2008 (UTC)


 * Theoretically, they would see a different pattern in the sky but that pattern would be determined by the same spectrum as we measure, just with different phases. So if you looked at the map, it would look different, but e.g. most of the power in it would still be on the degree scale. Mike Peel (talk) 20:56, 12 December 2008 (UTC)

"The photons have continued cooling..." Features section
Photons don't "cool." They are the force carrier of the electromagnetic force. They are massless. Other than redshift, how would photons "cool?" Can we call a spade, a spade here? The temperature of the CMBR looks "cooler" due to redshift. The article should relay that fact to its reader. Anybody interested in reading about the CMBR will understand "redshift." Makuabob (talk) 12:07, 24 November 2008 (UTC) There are "° K" notations in Features section although correct notation would be "K", for example 2.725 K (the unit is Kelvin, not degrees Kelvin). IlkkaP (talk) 20:35, 13 December 2008 (UTC)


 * Ah, ha! I see now that the degree symbol is not used. Thanks for bringing that up. Makuabob (talk) 12:10, 14 December 2008 (UTC)

Remarks

 * The following visually identical images are being displayed in the article: File:WMAP TT power spectrum.png & File:PowerSpectrumExt.svg. Is there any reason to retain the PNG version? If not, is it prefereable to place the image under "Primary anisotropy" or "Data analysis"? Thanks.&mdash;RJH (talk) 20:21, 12 December 2008 (UTC)
 * No, and I'd have it under the "Primary anisotropy" section. Mike Peel (talk) 20:52, 12 December 2008 (UTC)
 * Thank you.&mdash;RJH (talk) 21:28, 12 December 2008 (UTC)
 * To me at least, the following sentence in the lead doesn't seem to exclude sources such as the intergalactic medium: "Instead there is a very faint glow, almost exactly the same in all directions, not coming from any star or galaxy." Some of the wording is also redundant with the previous sentence. Would it make sense to say, "Instead there is a very faint glow, almost exactly the same in all directions, that is not coming from any localized source"?&mdash;RJH (talk)
 * Some of the wording in the lead (and possibly elsewhere; I haven't checked yet) may come under Words to avoid. What stands out for me are statements like "In simple terms", "Technically" and Crucially". There are also some editorial remarks in the references that seem unsubstantiated by citations. See note #9: Andrew (1941), for example.&mdash;RJH (talk)
 * Hi! I re-wrote the lead a few weeks ago since the version before was very technical, to the point that a non-scientific user would have trouble figuring out exactly what it is.  The 'in simple terms' is there to contrast with the 'technically', which is there to re-assure the non-technical reader that they do not need to read that sentence.  The 'crucially' is there since lots of theories can give a black body spectrum, but the ripples accounted for by inflation represent the best evidence for the big bang.  As far as the ISM, I like your idea but I'd probably say 'associated with a specific source' since the ISM is not very localized.
 * However, these are just my opinions about what makes a good lead and a non-technical introduction. Feel free to go ahead and improve it!  LouScheffer (talk) 23:14, 12 December 2008 (UTC)
 * Thank you for the detailed feedback. I'll go ahead and make a few tweaks but try to maintain the flavor.&mdash;RJH (talk) 23:20, 12 December 2008 (UTC)


 * It looks like there are big chunks of this article that are missing references. In particular, large chunks of the "Relationship to the Big Bang" and "Data analysis" sections, and the entire "Microwave background observations" section lack citations. Kinda surprised it passed GA. =) I'll try to add more over the next few weeks, if I can figure out the appropriate refs. In the process I might have to tag it with Fact templates though.&mdash;RJH (talk) 23:37, 15 December 2008 (UTC)
 * Hello again. Does anybody happen to know where the following statement came from? "...the CMB spectrum the most precisely measured black body spectrum in nature." It seems like something that would be difficult to prove, so I'd like to find a reference to show that this is not OR. However, I haven't had much success. It may need to be removed if no citation is available. Thanks.&mdash;RJH (talk) 18:47, 17 December 2008 (UTC)
 * There is the statement The FIRAS measurement remains the most precise measurement of a thermal Planck spectrum ever made, while the DMR observations revealed the temperature of the cmb to be isotropic to a few parts in 10^5 from the thesis: Jones' thesis which in turn cites two other papers for that statement. This appears to mean most precisely measured as opposed to closest to a pure blackbody, but combining most closely measured and appears to be a blackbody implies the statement in the article (but I don't have easy access to the cited references).  LouScheffer (talk) 20:20, 17 December 2008 (UTC)
 * Thank you for your help. From your lead I was able to track down a pdf reference.&mdash;RJH (talk) 20:47, 18 December 2008 (UTC)


 * This statement seems a little puzzling: "In the theory, the early universe was made up of a hot plasma of photons, electrons and baryons." Is this meant to explain the isotropy? It sounds like a time point following the lepton/anti-lepton annihilation (or the Quark-Hadron Transition?), but this is not clarified. I thought the isotropy was caused by inflation, which happened "much" earlier (in the logarithmic sense).&mdash;RJH (talk) 21:56, 19 December 2008 (UTC)
 * Fixed.&mdash;RJH (talk) 21:59, 22 December 2008 (UTC)

Radiation energy density?
I have a question about the statement that, "the radiation energy in the universe ... makes up a fraction of roughly 5 × 10-5 of the total density of the universe." Sources give a current radiation energy density of:
 * &rho;re = 0.26 eV/cm3.

For example:

If we are at the critical density, Turner (1992) gives:
 * &rho;crit = 1.05 × 104 eV/cm3.

Thus I get a ratio of 2.5$$ rather than 5$$. So... would anybody happen to have a reference for the latter value? I haven't had much luck.&mdash;RJH (talk) 19:42, 29 December 2008 (UTC)
 * Found a ref.&mdash;RJH (talk) 16:51, 2 January 2009 (UTC)

Summary; You can still detect radiation from the big bang explosion. The space between the stars and galixies is pitch black but with a radio telescope there is a faint background glow, almost exatally the same in all directions. This glow is strongest in the microwave region of the radio specrum. —Preceding unsigned comment added by 86.170.143.164 (talk) 15:42, 17 January 2009 (UTC)
 * A concern with your description is that the term "big bang" is not explained before you use it. At present, the big bang is described in the second paragraph, as the discovery of the CMB led to the big bang theory, rather than vice versa.&mdash;RJH (talk) 23:33, 19 January 2009 (UTC)

Assessment comment
Substituted at 20:21, 2 May 2016 (UTC)