Talk:Cosmic microwave background radiation

From Wikipedia, the free encyclopedia

↓ Skip to table of contents ↓

Cosmic microwave background radiation has been listed as a good article under the good-article criteria. If you can improve it further, please do.
If it no longer meets these criteria, you can delist it, or ask for a review.

Astronomy Portal

This article is within the scope of WikiProject Astronomy, which collaborates on articles related to astronomy, and WikiProject Physics, which collaborates on articles related to physics.

This article has been rated as GA-Class on the assessment scale.

Help with this template

This article has been rated but has no comments. If appropriate, please review the article and leave comments here to identify the strengths and weaknesses of the article and what work it will need.

Physics Portal

This article is within the scope of WikiProject Physics, which collaborates on articles related to physics.

This article has been rated as GA-Class on the assessment scale.

High

This article is on a subject of High importance within physics.

Help with this template

This article has been rated but has no comments. If appropriate, please review the article and leave comments here to identify the strengths and weaknesses of the article and what work it will need.

Cosmic microwave background radiation is included in the 2006 Wikipedia CD Selection, or is a candidate for inclusion in the next version. Please maintain high quality standards and, if possible, stick to GFDL-compatible images.

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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.

$\ell C_\ell$

[edit] 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)

[edit] 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)

[edit] "Large-scale structure of the cosmos" category

Should this article be placed in the "Large-scale structure of the cosmos" category? —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)

[edit] 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:

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.

What's the opinion of the other contributors?

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)

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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 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.
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...
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).

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)

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)

[edit] Cosmic background radiation

I'm concerned that since the "Cosmic background radiation" page now redirects to this Cosmic microwave background radiation article:

There is now no mention of "Cosmic background radiation" (although an acronym is provided)
Except for the "Timeline", credit is not provided for Guillaume, Eddington, Regener and Nernst, for correctly predicting its temperature

Either:

CMB is synonymous with CBR, in which case, Guillaume et al correctly predicted its temperature first
CMB is different to CBR, in which case, (a) it requires an explanation, and (b) details that Guillaume et al correctly predicted its temperature.

--Iantresman 14:37, 9 December 2005 (UTC)

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)

[edit] 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. [1]:

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)

[edit] 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)

[edit] Footnotes

I'd like to attempt to format the footnotes as per timeline of evolution, using the ref-tag. Would anyone object? -- Ec5618 11:28, 2 February 2006 (UTC)

I've changed the footnoting system, but not the style. Ideally, each footnote would contain a reference to the location of the cited material, and a quick quote to prove the relevance, tone and context of the information (again, see timeline of evolution). Unfortunately, this material may not be ideally suited to quick quoting, and most of the references are to books and scientific publications, none of which are linked to through weblinks. I may attempt to locate some useful quotes through Google books and Pubmed, but would appreciate some assistance from more knowledgeable contributors (who may have direct access to the books mentioned).

That is, assuming such a footnoting style would be appreciated. -- Ec5618 14:51, 4 February 2006 (UTC)

Hm, this ref-tag is interesting. I'm not sure about quotes for the reason you mention. Adding links is on my long-term list of things to do. It is possible to access nearly all these articles online, at least if you have the appropriate subscriptions. Anything in Phys. Rev. or Phys. Rev. Lett. may be accessed through the journal web pages at the American Physical Society. I assume that other articles are accessible through Science Direct or the Astrophysical Journal webpages. Finally, select old articles are scanned at the NASA Astrophysics Data System (which also provides journal links) and new stuff at the arXiv. Some are even occasionally accessible at the HEPdoc search (which searches scanned versions at CERN, DESY, SLAC and especially KEK) and JSTOR. –Joke 15:22, 4 February 2006 (UTC)

[edit] 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)

[edit] Backlink to Noise

Why is this here, in this form? This article is not only linked from Noise - see [2]. 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)

[edit] 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)

[edit] 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)

[edit] 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 [3]. 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.

[edit] "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)

[edit] 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)

[edit] 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)

Retrieved from "http://en.wikipedia.org../../../c/o/s/Talk%7ECosmic_microwave_background_radiation_a997.html"