Talk:Cosmic microwave background

Template:Vital article

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)

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.

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
• protos + photons = first thermal radiation

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

[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.