Talk:Cosmic microwave background

cmb has not proven to be evidence of a big bang... its hypothesized... and very far from proven. in fact its unlikely it is evidence of a big bang. in fact its unlikely the universe was ever created... it simply is. no beginning no end — Preceding unsigned comment added by Majorheadrush (talk • contribs) 13:37, 30 August 2019 (UTC)

Pictures showing the removed foreground elements, as well as highlighting the anomalies?

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.

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

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...?

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

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)

flaws? this article is one of best Ive seen on wiki, describes what subject is understandable. quantities might need clarification. Juror1 (talk) 09:58, 7 December 2017 (UTC)

Frequency on Graph should be labeled Wavenumber

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.

I edited the Image to reflect the changes as this also bothers me. In general I think it would be better to have a plot with the frequency but I don't have the data. I just have one question, how do I upload / reference correctly the changed image?

Dust and not dust

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

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

Etymology

• 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 (talk • contribs)

[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 (talk • contribs)

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

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)

My edits

Someone has undone my edits twice today without adequately explaining why. Regarding the quote that they restored to the introduction, there were several problems with it. Firstly, it was not made clear that it was text taken from an external source. Second, that source is a non-free source. Third, it did not say anything that was not better expressed elsewhere in the introduction. Fourth, it did not fit in at all with the text surrounding it. Thus, it added nothing to the article, but was a copyright violation. This is supposed to be a free encyclopaedia, so using non-free text can only be done in certain situations. One key justification is that a free alternative is not available. That's clearly not the case here.

As for the other two edits the user objected to, they haven't yet indicated why. Perhaps they would do so here. 128.40.9.164 (talk) 21:05, 29 November 2016 (UTC)

I think that we can certainly do without that multiline quote. There seems to be no reason to have it. Its not as if it is something irreplaceable such as the first words spoken after the CMB was found. Graeme Bartlett (talk) 21:20, 29 November 2016 (UTC)

Thank you for your input. It is disappointing that the user who was undoing the edits never bothered to justify his actions. 128.40.9.164 (talk) 16:18, 6 December 2016 (UTC)

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Source for value of photon energy of CMB photons

The article currently states in the third paragraph of the introduction

"The photon energy of CMB photons is about 6.626534 × 10⁻⁴ eV."

Where does this value come from? I searched via both Google and Google Scholar but was unable to locate a source for this claim. -- Toshio Yamaguchi 10:13, 27 August 2017 (UTC)

This comes from computing the energy of a photon at the stated frequency. Back of the envelope computation: Energy is given by $E=hf$, where $h$ is Planck's constant and $f$ the frequency of light. The article states that the peak frequency is at 160.23 GHz. Then, computing $E$ yieds 1.0616952 × 10^-22 J. Convert from Joules to electron Volts and you get that answer. — Preceding unsigned comment added by 142.197.11.70 (talk) 21:03, 31 December 2017 (UTC)

A Commons file used on this page has been nominated for speedy deletion

The following Wikimedia Commons file used on this page has been nominated for speedy deletion:

• ESA Planck CMB.jpg

You can see the reason for deletion at the file description page linked above. —Community Tech bot (talk) 03:51, 7 August 2018 (UTC)

Should mention water vapour blocks the microwaves

In the Cosmic microwave background#Microwave background observations this article mentions that the radiation is observed from satellites and telescopes in the Atacama desert in Chile and at the South Pole. However it does not explain to the reader why this is.

I think the section should have an intro paragraph briefly summarizing the reasons. I'm quoting here from the South Pole Telescope article - this text could be edited and trimmed down a little as an introductory motivational paragraph

"The South Pole is the premier observing site in the world for millimeter-wavelength observations. The Pole's high altitude (2.8 km/1.7 mi above sea level) means the atmosphere is thin, and the extreme cold keeps the amount of water vapor in the air low. This is particularly important for observing at millimeter wavelengths, where incoming signals can be absorbed by water vapor, and where water vapor emits radiation that can be confused with astronomical signals. Because the sun does not rise and set daily, the atmosphere at the pole is particularly stable. Further, there is no interference from the sun in the millimeter range during the months of polar night."

It is easily adapted to include the reasons for observing in the dry Atacama desert and from above the atmosphere in satellites. If you have any thoughts do say - otherwise if there is no response after a few days, I will be WP:BOLD and add the para myself. Robert Walker (talk) 16:09, 16 August 2018 (UTC)

References

Not too technical

The section --2600:1700:BFC2:A3E0:9DED:3F05:1D3E:333E (talk) 15:37, 12 August 2019 (UTC)Relationship to the Big Bang has a sidebar that says it is ( or may be ) too technical for the average reader; It is nothing of the sort and I find it lacking some features of what may be correct only for an entire volume of work yet me — with no formal training in the subject — only what I can find on the internet — see only significant prior work by the reader is to be expected before it is an easy read; This subject is rapidly developing due to machines which have never here-to-fore existed yet archaic convention continues to rule and dominate efforts 2600:1700:BFC2:A3E0:9DED:3F05:1D3E:333E (talk) 15:37, 12 August 2019 (UTC) there is nothing complex that needs to be kept from view as the work is not such that just anybody with no prior work raises their hand while professionals are working

nicholas_jordan456 ••• I am not familiar with how to do wikki; I believe I am on a talk page and not making any edits

I agree, I have removed the tag. Tags such as this should (unless it is really obvious) always say what exactly is too technical in the reason parameter or make a comment on the talk page. Bellowhead678 (talk) 19:13, 12 August 2019 (UTC)

Can there be a clear statement: for the CMB, z = ____?

The article already has this: "Since decoupling, the temperature of the background radiation has dropped by a factor of roughly 1100[52] due to the expansion of the universe. As the universe expands, the CMB photons are redshifted, causing them to decrease in energy. The temperature of this radiation stays inversely proportional to a parameter that describes the relative expansion of the universe over time, known as the scale length. The temperature Tr of the CMB as a function of redshift, z, can be shown to be proportional to the temperature of the CMB as observed in the present day (2.725 K or 0.2348 meV):[53] Tr = 2.725 ⋅ (1 + z) For details about the reasoning that the radiation is evidence for the Big Bang, see Cosmic background radiation of the Big Bang." So might it be helpful to add to the article a succinct statement, something to the effect of: "The cosmic microwave background has a redshift of z = 1089", or something like that? Thanks for your consideration! Bob Enyart, Denver KGOV radio host (talk) 02:34, 27 December 2019 (UTC)

Thanks!

In my humble opinion, this is a very well written article. Chapeau! — Preceding unsigned comment added by Koitus~nlwiki (talk • contribs) 13:10, 15 February 2020 (UTC)

CMB Peak Frequencies

I came to the article attempting to find the peak frequencies of the cosmic microwave background but have been unable to locate that information. I know that the peak frequency is 160.4 but do not know what the other three peak frequencies are. Does anyone here know?

CWatchman (talk) 17:48, 16 September 2020 (UTC)

The main peak has a thermal 2.725 kelvin black body spectrum which peaks in the microwave range at a frequency of 160.4 GHz, corresponding to a wavelength of 1.9 mm.

CWatchman (talk) 17:50, 16 September 2020 (UTC)

Nagging Shortfall

If the observer is close to the edge of the Universe, the CMB from that side should be blue shifted vs the CMB from the far side.

The graph of CMB we have puts the observer smack dab in the center of the Universe. It is more likely that all points in the Universe observe the same CMB. That means that CMB does not delineate the beginning of the Universe.GuildCompounder (talk) 20:18, 31 October 2020 (UTC)

Your comment suggests you think the Universe is finite in extent. The Copernican principle would suggest that we do not occupy a special position at the "center", but instead just see the view shared by all other locations. That would suggest there is no center and no edge, or at least none within the observable Universe. Praemonitus (talk) 16:54, 12 April 2021 (UTC)

Proposed merge of "Timeline of prediction, discovery and interpretation" into "Timeline of cosmological theories"

The article section titled "Timeline of prediction, discovery and interpretation" would seem to be somewhat redundant with the "History" section. I'm proposing that we merge it into the related Timeline of cosmological theories article where it likely would be more useful and relevant. Do you concur? Praemonitus (talk) 16:49, 12 April 2021 (UTC)

Oppose; the topics are overlapping, but Timeline of cosmological theories is broader; suggest leaving the structure as it is, but adding a see also template in Talk:Cosmic microwave background#Timeline of prediction, discovery and interpretation. Klbrain (talk) 14:03, 22 May 2022 (UTC)

Why have separate History and Timeline sections in this article? Their purposes are redundant. Praemonitus (talk) 16:03, 22 May 2022 (UTC)

It is very common to have a separate timeline (see, for example, the descendants of Category:Historical timelines), primarily because for important topics it is worth having a narrative history covering major events, and more comprehensive listing covering (also) more minor event. Hence, this is a conventional form of WP:SUMMARY. Klbrain (talk) 16:50, 4 June 2022 (UTC)

It is common to have a separate timeline in separate articles, yes. This article is already quite long, so a reasonable compromise would be to do a content fork. "Timeline of cosmic microwave background knowledge", perhaps? Praemonitus (talk) 19:02, 4 June 2022 (UTC)

My view remains that the current structure works for readers, with a history section proving a narrative of key events, the timeline providing a list of events (not all of which are important enough to be covered in the narrative, and the separate Timeline of cosmological theories being a list for a broader topic. I might be misunderstanding the compromise position proposed, but I don't think that we need a new separate page. Klbrain (talk) 07:51, 22 October 2022 (UTC)

Addition of Explanation of the impact the temperature of the CMB's quantum fluctuations has on the Density of matter in the Universe

The article should include an explanation of how high temperatures after the Big Bang due to quantum fluctuations resulted in higher mass densities of localities throughout the Universe. Something explaining that warmer areas are denser and cooler areas are more void-like would be good to include. ScientistBuilder (talk) 19:21, 12 October 2021 (UTC)ScientistBuilderScientistBuilder (talk) 19:21, 12 October 2021 (UTC)

It's actually the other way around! Areas where the CMB temperature is higher are less dense, and areas where the CMB temperature is lower are more dense. [6], [7] --Amble (talk) 19:10, 22 October 2021 (UTC)

This topic is briefly mentioned in the Multipole section but could be expanded upon. Praemonitus (talk) 19:25, 22 October 2021 (UTC)

Decoupling complete

The maximum of the PVF (the time when it is most likely that a given CMB photon last scattered) is known quite precisely. The first-year WMAP results put the time at which P(t) has a maximum as 372,000 years.[58] This is often taken as the "time" at which the CMB formed. However, to figure out how long it took the photons and baryons to decouple, we need a measure of the width of the PVF. The WMAP team finds that the PVF is greater than half of its maximal value (the "full width at half maximum", or FWHM) over an interval of 115,000 years. By this measure, decoupling took place over roughly 115,000 years, and when it was complete, the universe was roughly 487,000 years old.

Perhaps my understanding is faulty, but wouldn't it be (mostly) complete after: 372,000 + (115,000/2) = 429,500 years? Praemonitus (talk) 20:04, 22 October 2021 (UTC)

B-Mode section out of date

We are now at Keck/BICEP3, which is returning r < 0.036. The current section looks 7 years out of date.

Also, r is never defined.

2600:1700:C280:3FD0:F92F:79DA:1665:C1DF (talk) 21:42, 6 December 2021 (UTC)

Missing Responses and Criticism

This article is missing a responses and criticism section 185.107.13.110 (talk) 09:00, 24 April 2022 (UTC)

See wikipedia:Criticism for some reasons not to have a separate section for criticism. The article does have a lot of material on the history and study of the CMB and why people regard it as very important. It’s not obvious what would go in a criticism section (too isotopic? Not polarized enough?). Could you give some specific examples of what you think is missing? —Amble (talk) 16:53, 24 April 2022 (UTC)

Image is gone

The map of the Cosmic Microwave Background from Planck was recently deleted from Commons due to "no permission". Is this image available under CC BY-SA (likely in a paper), or does it need to be uploaded locally as fair use? SevenSpheres (talk) 23:02, 28 October 2022 (UTC)