Talk:Cosmic microwave background

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Former good article Cosmic microwave background was one of the Natural sciences good articles, but it has been removed from the list. There are suggestions below for improving the article to meet the good article criteria. Once these issues have been addressed, the article can be renominated. Editors may also seek a reassessment of the decision if they believe there was a mistake.
Article milestones
Date Process Result
January 29, 2006 Good article nominee Listed
July 13, 2009 Good article reassessment Delisted
Current status: Delisted good article
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Pictures showing the removed foreground elements, as well as highlighting the anomalies?[edit]

I think pictures like that would help improve the article, not to mention the readers' understanding of what is being described. --TiagoTiago (talk) 05:01, 27 September 2014 (UTC)

Lede needs edit.[edit]

The lede states: "(Alternatively if spectral radiance is defined as dEλ/dλ then...". This is just wrong. That is, dE/dλ is NOT spectral radiance. The implied claim is also made that dE/dv can be called 'spectral radiance', which if I understand the terminology correctly is also wrong. It is technically correct, I think, to state "spectral radiance dE/dv peaks at ..." but dE/dv qualifies (clarifies) the term 'spectral radiance' - since it could be, for instance, photon count rather than energy which is 'peaking'. This is just slightly sloppy. Why not make it correct by describing the spectral radiance function which peaks? Alternatively, you could speak about the differential (or incremental) change in energy with frequency or wavelength having a maximum.Abitslow (talk) 18:41, 30 December 2014 (UTC)

Flux[edit]

I would like to see a sentence on the flux in photons per second per area, and watts per square meter. 10 trillion photons per second per squared centimeter is stated at [1] but figure is rough. But most of what I look at so far are problems for students to solve and not a reliable source. Also is energy density more like 4.178×10-14?[2] Graeme Bartlett (talk) 22:46, 18 January 2015 (UTC)

1964 discovery? APS says 1963; Wilson says 1965...?[edit]

The American Physical Society says: June 1963: Discovery of the Cosmic Microwave Background, at http://www.aps.org/publications/apsnews/200207/history.cfm I assume the main article is correct. There are also claims that the discovery was made in 1965. It's obvious that there's widespread confusion about the date that the big bang theory was proposed (not on WP, but all over the web on "authoritative" sites), and when was, and by whom was, the expanding universe proposed: http://scitation.aip.org/content/aip/magazine/physicstoday/article/64/8/10.1063/PT.3.1194 But seems like the date of the discovery of the CMB should be more clear. In Wilson's Nobel lecture at http://www.nobelprize.org/nobel_prizes/physics/laureates/1978/wilson-lecture.pdf he gives dates of 1963 and 1965, and for 1964 only references the work of Doroshkevich and Novikov. So, is there a correct year of the discovery of the CMB? Bob Enyart, Denver KGOV radio host (talk) 05:03, 26 February 2015 (UTC)

Just found this in Penzias' lecture http://www.nobelprize.org/nobel_prizes/physics/laureates/1978/penzias-lecture.pdf "The year 1964 also marked a reawakened interest in the "Gamow Theory” by Hoyle and Taylor (1964) as well as the first unambiguous detection of the relict radiation." So, "unambiguous". That seems to settle it in favor of the main article's date. Bob Enyart, Denver KGOV radio host (talk) 05:14, 26 February 2015 (UTC)
They started working on the project in 1963, detected the signal in 1964, took data 1964-65, and understood the nature of the signal and published in 1965. It comes down (as often happens) to the question of whether you have to know what you've discovered before you can say you've discovered it. [3] --Amble (talk) 06:03, 26 February 2015 (UTC)

Misleading Introduction[edit]

The first line of this article:

The cosmic microwave background (CMB) is the thermal radiation left over from the "Big Bang" of cosmology.

I think it's misleading. CMB is from the time of recombination, 300,000 years after the Big Bang, not from the Big Bang itself. How about changing it to "...thermal radiation left over from the time of recombination." 220.244.178.10 (talk) 11:56, 6 April 2015 (UTC)

Frequency on Graph should be labeled Wavenumber[edit]

The graph of cosmic microwave background spectrum measured by the FIRAS instrument on the COBE labels the x-axis to be in terms of frequency, but it should be labeled in terms of wavenumber, since the units are 1/cm.

Dust and not dust[edit]

These two edits by Wdanwatts [4], [5] suggest that galactic dust emission is responsible for large-scale features in the CMB. The second edit does have a more suitable source than the first edit did. However, the basic problem is that the article text and the sources are talking about two different things. The article is talking about the CMB temperature anisotropies, which have been measured to very high signal-to-noise on a wide range of angular scales and at many frequencies. The foreground (such as dust) contributions here are small away from the galactic plane, and are well understood. The temperature anisotropies are generated by primordial scalar density perturbations which evolve in a simple way to create the "acoustic peaks" in the CMB power spectrum. Where galactic dust becomes relevant is in looking for a different, much fainter signal in the CMB polarization. The pure-curl or "B-mode" component of the polarization is used to search for a possible signal of inflationary gravitational waves or "tensor perturbations". The very faint B-mode polarization signal has only recently been detected at all, and is now beginning to be measured with high signal to noise at multiple frequencies. It appears that dust does contribute most or all of the detected B-mode polarization signal, so there is no clear evidence for a detection of IGW. However, this simply isn't relevant to this section of the article, which is describing the much larger and very precisely measured temperature anisotropy signal. --Amble (talk) 01:57, 13 May 2015 (UTC)

That said, the reference to BICEP (actually BICEP1, not BICEP2 which detected the B-mode signal) also seems to be a bit out of place. A very large number of experiments have measured large-scale CMB anisotropies. Perhaps BICEP1 is mentioned for its measurement of E-mode polarization (which is well measured apart from dust), but I'm not really sure. It would perhaps be better not to single out any particular experiments here. --Amble (talk) 02:02, 13 May 2015 (UTC)

Subjective Worldview Claim[edit]

The next-to-last paragraph of the lede begins with this: "Precise measurements of the CMB are critical to cosmology, since any proposed model of the universe must explain this radiation."

I would like to humbly point out that this is a subjective worldview claim. There's no such thing as a model which adequately "explains" every observed phenomenon; each model has its strengths and weaknesses. So the author is showing favoritism toward CMB and any model which explains it (at the expense of explaining certain other phenomena).

Admittedly this favoritism may reflect the Scientific Consensus on the subject, which is surely Wikipedia's intent. But at least we need not be dishonest that it's favoritism. The Scientific Consensus can be selective about which phenomena it says "must" be explained and which it does not.

QuartzMMN (talk) 04:11, 29 June 2015 (UTC)

Any proposed model needs to explain it because if it doesn't, the model is clearly wrong. That's hardly 'subjective'. Headbomb {talk / contribs / physics / books} 22:19, 29 June 2015 (UTC)
Apologies ... you seem not to have understood my comment. By your reasoning, every model ever conceived should be "clearly wrong," because none of them are perfect.
E.g., one might consider life on earth a more conspicuous phenomenon than the CMB - and more deserving of an explanation. Yet decades of research has brought the Scientific Consensus no closer to explaining it than "reasonable conjecture".
Intelligent people must live with speculation when faced with no alternative. Our choice of model is not whether to speculate, but on what to speculate.
In light of this, I hope you see how ridiculous it is to stake a claim on one observed phenomenon and say it "must be explained" above more obvious phenomena. It merely reflects a preference about what sort of speculation one can live with.
QuartzMMN (talk) 16:47, 11 August 2015 (UTC)

Cosmic microwave background or paleophotons or protophotons[edit]

Etymology[edit]

  • paleos + photons = old thermal radiation [旧光子 paleophoton]
  • protos + photons = first thermal radiation
  • archo- /archaeo- + photons [introduced by experimental physicist Giorgos Grammatikakis] = first thermal radiation — Preceding unsigned comment added by 2.84.220.197 (talk) 17:11, 26 September 2015 (UTC)

rare term but used among students

proto-photons has a second meaning - it is a theoretical not yet discovered particle supposedly contributing to gravity - this is a totally separate - not connected meaning— Preceding unsigned comment added by 2.84.220.197 (talkcontribs)

[ask for more]

  • Students may have made this up, but we need to see this used in reliable writings. I did a Google scholar search and found nothing at all. Graeme Bartlett (talk) 00:12, 24 September 2015 (UTC)
  • I totally agree! Cosmic microwave background is easier to pronounce than protophotons or paleophotons. We must stick to the old name. Students aren't wise enough to be listened.— Preceding unsigned comment added by 2.84.220.197 (talkcontribs)
Students have done all kinds of valuable work on the CMB, including making major contributions to things that are mentioned in the article. They published their work in scientific journals, which are reflected in secondary sources, and Wikipedia uses those. When students try to put things they've made up directly into the article, we welcome them to Wikipedia and invite them to help build the encyclopedia (but remove the made-up stuff). If you'd like to help improve CMB articles, I'd be happy to suggest some tasks that would be really helpful. --Amble (talk) 15:21, 24 September 2015 (UTC)
旧光子 translates to "old photons". But our Chinese article on the topic is called zh:宇宙微波背景辐射, and does not make a mention of 旧光子. This 旧光子 name gives a hint of tired light. Graeme Bartlett (talk) 04:53, 8 October 2015 (UTC)

"tired light" is not lectically [as a word] the same as "tired photon" as you claimed, it would have been in Chinese: 累光子 - tired photon/not tired light. Also "tired" doesn't mean old, but yes Fritz Zwicky claimed that time plays a crucial role. By the way tired light is hypothetical, and the CMB - cosmic microwave background experimental fact.

旧 means old but also paleo-, a prefix in Japanese and Chinese - same character. Paleo- means that the photon was emitted in the past. Tired light means that hypothetically a photon emitted in the past, has been affected by the expansion of space-time. So these terms focus on different issues.

Timeline[edit]

The timeline section appears to have been merged with this article by a single editor without discussion. To me it badly disrupts the flow of the article and should be moved back to the original location. What do you think? Praemonitus (talk) 22:11, 1 April 2016 (UTC)

As a test, I moved the timeline down to the bottom. Is that better? Isambard Kingdom (talk) 22:20, 1 April 2016 (UTC)
Yes, I think that would be an improvement. Praemonitus (talk) 15:20, 2 April 2016 (UTC)
Is the timeline even necessary? Isambard Kingdom (talk) 15:21, 2 April 2016 (UTC)
It may depend on who you ask. Among editors there seems to be an audience for creating timelines, outlines, lists, and the like; possibly because they are easier to build than proper articles. But to me they don't provide a very engaging read. Praemonitus (talk) 17:27, 2 April 2016 (UTC)